ADT7490ARQZ - ON Semiconductor - Datasheet.Directory

 Semiconductor Components Industries, LLC, 2012

July, 2012 − Rev. 5

1Publication Order Number:

ADT7490/D

ADT7490

Remote Thermal Monitor

and Fan Controller with

PECI Interface

The ADT7490 is a thermal monitor and multiple PWM fan

controller for noise-sensitive or power-sensitive applications requiring

active system cooling. The ADT7490 includes a local temperature

sensor, two remote temperature sensors including series resistance

cancellation, and monitors CPU temperature with a PECI interface.

The ADT7490 can drive a fan using either a low or high frequency

drive signal, and measure and control the speed of up to four fans so

they operate at the lowest possible speed for minimum acoustic noise.

The automatic fan speed control loop optimizes fan speed

for a given temperature using the PECI, remote, or local temperature

information. The effectiveness of the system’s thermal solution can be

monitored using the THERM input. The ADT7490 also provides

critical thermal protection to the system using the bidirectional

THERM/SMBALERT pin as an output to prevent system or

component overheating.

Features

Temperature Measurement

1 Local On-Chip Temperature Sensor

2 Remote Temperature Sensors

3 Current External Temperature Sensors with Series Resistance

Cancellation (SRC)

PECI Interface for CPU Thermal Information and Support of Up

to 4 PECI Inputs on 1 Pin

Fan Drive and Fan Speed Control

3 High Frequency or Low Frequency PWM Outputs for Use with

3-wire or 4-wire Fans

4 TACH Inputs to Measure Fan Speed

OS Independent Automatic Fan Speed Control Based on Thermal

Information

Dynamic TMIN Control Mode to Optimize System Acoustics

Default Startup at 100% PWM for All Fans for Robust Operation

Bidirectional THERM/SMBALERT Pin to Flag Out-of-Limit and

Overtemperature Conditions

GPIO Functionality to Support Extra Features

Can be Used for Loadline Setting for Voltage Regulation, LED

Control, or Other Functions

IMON Monitoring for CPU Current and Power Information

Footprint and Register Compatible with ADT7473/ADT7475/

ADT7476/ADT7476A Family of Fan Controllers

SMBus Interface with Addressing Capability for Up to 3 Devices

Applications

Personal Computers

Servers

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PIN ASSIGNMENT

QSOP−24 NB

CASE 492B

# = Pb-Free Package

See detailed ordering and shipping information in the package

dimensions section on page 74 of this data sheet.

ORDERING INFORMATION

MARKING DIAGRAMS

ADT7490

ARQZ

#DateCode

TOP MARKING

Assembly Lot

BOTTOM MARKING

+2.5VIN/THERM

PWM1/XTO

VCCP

+12VIN

+5VIN

D1+

*TACH4/THERM/SMBALERT/ADDR SELECT

IMON

SDA

SCL

GND

VCC

GPIO1

GPIO2

PECI

PWM2/

SMBALERT

ADT7490

VTT

TACH3

TACH1

TACH2

D1−

D2+

D2−

PWM3/ADDREN

ADT7490

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ADT7490

PWM REGISTERS

AND CONTROLLERS

(HF AND LF)

ACOUSTIC

ENHANCEMENT

FAN SPEED

COUNTER

PERFORMANCE

MONITORING

THERMAL

PROTECTION

INPUT

SIGNAL

CONDITIONING

AND

ANALOG

MULTIPLEXER

BAND GAP

TEMP. SENSOR

10-BIT

ADC

BAND GAP

REFERENCE

SMBus

ADDRESS

SELECTION

SERIAL BUS

INTERFACE

ADDRESS

POINTER

PWM

CONFIGURATION

REGISTERS

INTERRUPT

MASKING

INTERRUPT

STATUS

REGISTERS

VALUE AND

LIMIT

REGISTERS

LIMIT

COMPARATORS

GND

ADDR SELECT SCL SDA

PWM1

PWM2

PWM3

TACH1

TACH2

TACH3

TACH4

THERM/

SMBALERT

VTT

D1+

D1−

D2+

D2−

VCC

GPIO

VCCP

+12VIN

+5VIN

GPIO2

GPIO1

ACOUSTIC

ENHANCEMENT

CONTROL

Figure 1. Functional Block Diagram

+2.5VIN

IMON

AUTOMATIC

FAN SPEED

CONTROL

DYNAMIC TMIN

CONTROL

PECI

INTERFACE

PECI

ADT7490

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Table 1. ABSOLUTE MAXIMUM RATINGS

Parameter Rating Unit

Positive Supply Voltage (VCC) 3.6 V

Maximum Voltage on +12 VIN Pin 16 V

Maximum Voltage on +5 VIN Pin 6.25 V

Maximum Voltage on All Open-drain Outputs (excluding PWM pins) 3.6 V

Maximum Voltage on TACHx/PWMx Pins +5.5 V

Voltage on Remaining Input or Output Pins −0.3 to +4.2 V

Input Current at Any Pin 5 mA

Package Input Current 20 mA

Maximum Junction Temperature (TJ MAX) 150 C

Storage Temperature Range −65 to +150 C

Lead Temperature, Soldering

IR Reflow Peak Temperature

Pb-Free Peak Temperature

Lead Temperature (Soldering, 10 sec)

220

260

300

C

ESD Rating

HBM

FICDM

0.5

Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the

Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect

device reliability.

NOTE: This device is ESD sensitive. Use standard ESD precautions when handling.

Table 2. THERMAL CHARACTERISTICS (Note 1)

Package Type qJA qJC Unit

24-lead QSOP 122 31.25 C/W

1. qJA is specified for the worst-case conditions, that is, a device soldered in a circuit board for surface-mount packages.

Table 3. ELECTRICAL CHARACTERISTICS

(TA=T

MIN to TMAX, VCC =V

MIN to VMAX, unless otherwise noted) (Note 1)

Parameter Conditions Min Typ Max Unit

Power Supply

Supply Voltage 3.0 3.3 3.6 V

Supply Current, ICC Interface Inactive, ADC Active −1.5 5.0 mA

Temperature-to-Digital Converter

Local Sensor Accuracy

Resolution

0CTA85C

−40CTA+125C

−

0.5

−

0.25

1.5

2.5

−

C

Remote Diode Sensor Accuracy 0CTA85C

−40CTA+125C

−

0.5

−

0.25

1.5

2.5

−

C

Remote Sensor Source Current Mid Level

Low Level

High Level

−

192

−

Series Resistance Cancellation

(Note 2)

The ADT7490 Cancels Up to 2 kW in

Series with the Remote Thermal Sensor

− − 1.5 kW

ADT7490

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Table 3. ELECTRICAL CHARACTERISTICS (continued)

(TA=T

MIN to TMAX, VCC =V

MIN to VMAX, unless otherwise noted) (Note 1)

Parameter UnitMaxTypMinConditions

Analog-to-Digital Converter (Including MUX and Attentuators)

Total Unadjusted Error (TUE) For All Channels: −40CTA+125C

For All Other Channels Except +12 VIN:

0CTA+125C

−

2

1.5

Differential Non-linearity (DNL) 8 Bits − − 1 LSB

Power Supply Sensitivity −0.1 −%/V

Conversion Times (Note 2)

Voltage Inputs

VTT Voltage Input (Note 3)

Local Temperature

Remote Temperature

Averaging Enabled, All Channels

Excluding VTT (Note 3)

Averaging Enabled

−

Total Monitoring Cycle Time

Averaging disabled

−

169

193

−

Input Resistance For +12 VIN Channel

For All Other Channels

150

200

100

−

Fan RPM-to-Digital Converter

Accuracy 0CTA85C

−40CTA+125C

−

10

14

Full-scale Count − − 65,535

Nominal Input RPM Fan Count = 0xBFFF

Fan Count = 0x3FFF

Fan Count = 0x0438

Fan Count = 0x021C

−

109

329

5,000

10,000

−

RPM

Open-Drain Digital Outputs, PWM1 TO PWM3, XTO

Current Sink, IOL − − 8.0 mA

Output Low Voltage, VOL IOUT = −8.0 mA − − 0.4 V

High Level Output Current, IOH VOUT = VCC −0.1 20 mA

Open-Drain Serial Data Bus Output (SDA)

Output Low Voltage, VOL IOUT = −4.0 mA − − 0.4 V

High Level Output Current, IOH VOUT = VCC −0.1 1.0 mA

SMBus Digital Inputs (SCL, SDA)

Input High Voltage, VIH 2.0 − − V

Input Low Voltage, VIL − − 0.8 V

Hysteresis −500 −mV

Digital I/O (PECI Pin) (Note 2)

VTT

, Supply Voltage 0.95 −1.26 V

Input High Voltage, VIH 0.55 VTT

(Note 3)

− − V

Input Low Voltage, VIL − − 0.5 VTT

(Note 3)

Hysteresis (Note 2) Hysteresis between Input Switching

Levels

0.1 VTT

(Note 3)

− − mV

High Level Output Source Current,

ISOURCE

VOH = 0.75 VTT − − 6.0 mA

Low Level Output Sink Current, ISINK VOL = 0.25 VTT 0.5 −1.0 mA

Signal Noise Immunity, VNOISE Noise Glitches from 10 MHz to

100 MHz, Width Up to 50 ns

300 − − mV

p-p

ADT7490

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Table 3. ELECTRICAL CHARACTERISTICS (continued)

(TA=T

MIN to TMAX, VCC =V

MIN to VMAX, unless otherwise noted) (Note 1)

Parameter UnitMaxTypMinConditions

Digital Input Logic Levels (TACH1 to TACH3)

Input High Voltage, VIH Maximum Input Voltage

2.0

−

5.5

Input Low Voltage, VIL Minimum Input Voltage

−

−0.3

−

0.8

−

Hysteresis −0.5 −V p-p

Digital Input Logic Levels (THERM)

Input High Voltage, VIH 0.75 VCCP − − V

Input Low Voltage, VIL − − 0.4 V

Digital Input Current

Input High Current, IIH VIN = VCC −1−mA

Input Low Current, IIL VIN = 0 −1−mA

Input Capacitance, CIN −5.0 −pF

Serial Bus Timing (Note 2) (See Figure 2)

Clock Frequency, fSCLK 10 −400 kHz

Glitch Immunity, tSW − − 50 ns

Bus Free Time, tBUF 4.7 − − ms

SCL Low Time, tLOW 4.7 − − ms

SCL High Time, tHIGH 4.0 −50 ms

SCL, SDA Rise Time, tr− − 1,000 ns

SCL, SDA Fall Time, tf− − 300 ms

Data Setup Time, tSU;DAT 250 − − ns

Detect Clock Low Timeout, tTIMEOUT Can be Optionally Disabled 15 −35 ms

1. All voltages are measured with respect to GND, unless otherwise specified. Typical voltages are TA=25C and represent a parametric norm.

Logic inputs accept input high voltages up to VMAX, even when the device is operating down to VMIN. Timing specifications are tested at logic

levels of VIL = 0.8 V for a falling edge, and VIH = 2.0 V for a rising edge.

2. Guaranteed by design, not production tested.

3. VTT is the voltage input on Pin 8. The VTT voltage is determined by the processor installed on the system.

Figure 2. Serial Bus Timing Diagram

tSU; DAT

tHIGH

tHD; DAT

tLOW

tSU; STO

SCL

SDA

tBUF

tHD; STA

tSU; STA

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Table 4. PIN ASSIGNMENT

Pin No. Mnemonic Type Description

1 SDA Digital I/O SMBus Bidirectional Serial Data. Open drain, requires SMBus pullup.

2 SCL Digital Input SMBus Serial Clock Input. Open drain, requires SMBus pullup.

3 GND Ground Ground Pin.

4 VCC Power Supply 3.3 V 10%.

5 GPIO1 Digital Input/Output General-purpose Open-drain Digital Input/Output. Frequently used for

switching load line resistors into VR load line circuitry or for switching LEDs

using external FETs.

6 GPIO2 Digital Input/Output General-purpose Open-drain Digital Input/Output. Frequently used for

switching load line resistors into VR load line circuitry or for switching LEDs

using external FETs.

7 PECI Digital Input/Output PECI Input to Report CPU Thermal Information. PECI voltage level is

referenced on the VTT input.

8 VTT Analog Input Voltage Reference for PECI. This is the supply voltage for the PECI interface

and must be present to measure temperature over the PECI interface. This

voltage is also monitored and presented in Register 0x1E.

9 TACH3 Digital Input Fan Tachometer Input to Measure Speed of Fan 3 (Open-drain Digital Input).

10 PWM2/SMBALERT Digital Output Pulse-width Modulated Output to Control Fan 2 Speed. Open drain requires

10 kW typical pullup. Digital Output (Open Drain). This pin can be

reconfigured as an SMBALERT interrupt output to signal out-of-limit

conditions.

11 TACH1 Digital Input Fan Tachometer Input to Measure Speed Of Fan 1 (Open-drain Digital Input).

12 TACH2 Digital Input Fan Tachometer Input To Measure Speed Of Fan 2 (Open-drain Digital Input).

13 PWM3/

ADDREN

Digital Output Pulse-width Modulated Output to Control Fan 3 Speed. Open drain requires

10 kW typical pullup. If pulled low on powerup, the ADT7490 enters address

select mode, and the state of Pin 14 (ADDR SELECT) determines the

ADT7490 slave address.

14 TACH4/THERM/

SMBALERT/

ADDR SELECT

Digital Input/Output Fan Tachometer Input to Measure Speed of Fan 4 (Open-drain Digital Input).

May be reconfigured as a bidirectional THERM pin. Can be connected to the

PROCHOT output of the processor, to time and monitor PROCHOT assertions.

Can be used as an output to signal overtemperature conditions or for clock

modulation purposes. Active Low Digital Output. The SMBALERT pin is used to

signal out-of-limit comparisons of temperature, voltage, and fan speed. This is

compatible with SMBus alert. Can also be used at device powerup to assign

SMBus address.

15 D2−Analog Input Negative Connection for Remote Temperature Sensor 2.

16 D2+ Analog Input Positive Connection to Remote Temperature Sensor 2.

17 D1−Analog Input Negative Connection for Remote Temperature Sensor 1.

18 D1+ Analog Input Positive Connection to Remote Temperature Sensor 1.

19 IMON Analog Input Monitors Current Output of Analog Devices ADP319x family of VRD10/VRD11

controllers.

20 +5 VIN Analog Input Monitors 5.0 V Supply Using Internal Resistor Dividers.

21 +12 VIN Analog Input Monitors 12 V Supply Using Internal Resistor Dividers.

22 +2.5 VIN/THERM Analog Input Monitors 2.5 V Supply Using Internal Resistor Dividers. Alternatively, this pin

can be reconfigured as a bidirectional THERM pin. Can be connected to the

PROCHOT output of the processor to time and monitor PROCHOT assertions.

Can be used as an output to signal overtemperature conditions or for clock

modulation purposes.

23 VCCP Analog Input Monitors CPU VCC Voltage (to maximum of 3.0 V). All voltage inputs can

have their resistor dividers removed allowing for full-scale input of 2.25 V of

the ADC channel.

24 PWM1/XTO Digital Output Pulse-width Modulated Output to Control Fan 1 Speed. Open drain requires

10 kW typical pullup. Also functions as the output for the XNOR tree test

enable mode.

ADT7490

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Table 5. COMPARISON OF ADT7490 AND ADT7476A CONFIGURATIONS

Pin No. ADT7490 ADT7476A

1 SDA SDA

2 SCL SCL

3 GND GND

4 VCC VCC

5 GPIO1 VID0/GPIO0

6 GPIO2 VID1/GPIO1

7 PECI VID2/GPIO2

8 VTT VID3/GPIO3

9 TACH3 TACH3

10 PWM2/SMBALERT PWM2/SMBALERT

11 TACH1 TACH1

12 TACH2 TACH2

13 PWM3/ADDREN PWM3/ADDREN

14 TACH4/THERM/SMBALERT/ADDR SELECT TACH4/THERM/SMBALERT/GPIO6/ADDR SELECT

15 D2−D2−

16 D2+ D2+

17 D1−D1−

18 D1+ D1+

19 IMON VID4/GPIO4

20 +5 VIN +5 VIN

21 +12 VIN +12 VIN/VID5

22 +2.5 VIN/ THERM +2.5 VIN/ THERM

23 VCCP VCCP

24 PWM1/XTO PWM1/XTO

TYPICAL PERFORMANCE CHARACTERISTICS

Figure 3. Supply Current vs. Supply Voltage

VDD (V)

3.0

NORMAL IDD (mA)

3.5

3.1 3.2 3.3 3.4 3.5 3.6

3.7

3.9

4.1

4.3

4.5

4.7

DEV 1

DEV 3

DEV 2

Figure 4. Supply Current vs. Temperature

TEMPERATURE (C)

−40

NORMAL IDD (mA)

4.12

DEV 3

−20 0 20 40 60 80 100 120

DEV 1

DEV 2

4.14

4.16

4.18

4.20

4.22

4.24

ADT7490

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TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)

Figure 5. Local Temperature Sensor Error Figure 6. Remote 1 Temperature Sensor Error

Figure 7. Remote 2 Temperature Sensor Error Figure 8. ADT7490 Response to Thermal Shock

Figure 9. Temperature Error vs. Series Resistance Figure 10. Local Temperature Error vs. Power

Supply Noise Frequency

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

DEV 8

DEV 9

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

DEV 15

DEV 16

DEV 17

DEV 18

DEV 19

DEV 20

DEV 21

DEV 22

DEV 23

DEV 24

DEV 25

DEV 26

DEV 27

DEV 28

DEV 29

DEV 30

DEV 31

DEV 32

MEAN

LOW SPEC

HIGH SPEC

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

DEV 8

DEV 9

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

DEV 15

DEV 16

DEV 17

DEV 18

DEV 19

DEV 20

DEV 21

DEV 22

DEV 23

DEV 24

DEV 25

DEV 26

DEV 27

DEV 28

DEV 29

DEV 30

DEV 31

DEV 32

MEAN

LOW SPEC

HIGH SPEC

TEMPERATURE (C)

−40

TEMPERATURE ERROR (C)

−1.5

−20 0 25 40 60 70 85 100 125

−1.0

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

TEMPERATURE (C)

−40

TEMPERATURE ERROR (C)

−1.5

−20 0 25 40 60 70 85 100 125

−1.0

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

−2.0

TEMPERATURE (C)

−40

TEMPERATURE ERROR (C)

−1.5

−20 0 25 40 60 70 85 100 125

−1.0

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

−2.0

DEV 1

DEV 2

DEV 3

DEV 4

DEV 5

DEV 6

DEV 7

DEV 8

DEV 9

DEV 10

DEV 11

DEV 12

DEV 13

DEV 14

DEV 15

DEV 16

DEV 17

DEV 18

DEV 19

DEV 20

DEV 21

DEV 22

DEV 23

DEV 24

DEV 25

DEV 26

DEV 27

DEV 28

DEV 29

DEV 30

DEV 31

DEV 32

MEAN

LOW SPEC

HIGH SPEC

TIME (s)

MEASURED TEMPERATURE (C)

LOCAL

10 20 30 40 50 60

100

120

140

EXTERNAL 1

EXTERNAL 2

SERIES RESISTANCE (W)

TEMPERATURE ERROR (C)

−8

DEV 3

DEV 1

DEV 2

200 400 600 800 1000 1200 1400 1600

−6

−4

−2

POWER SUPPLY NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

−1.0

100 mV

100 200 300 400 500 600

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

250 mV

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TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)

Figure 11. Remote Temperature Error vs. Power

Supply Noise Frequency

Figure 12. Temperature Error vs. Common-Mode

Noise Frequency

Figure 13. Temperature Error vs. Differential Mode

Noise Frequency

Figure 14. Temperature Error vs. Capacitance

Between D+ and D−

Figure 15. TACH Accuracy vs. Supply Voltage Figure 16. TACH Accuracy vs. Temperature

POWER SUPPLY NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

−1.2

100 mV

100 200 300 400 500 600

−1.0

−0.8

−0.6

−0.4

−0.2

0.2

0.4

0.6

250 mV

COMMON-MODE NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

−10

100 mV

100 200 300 400 500 600

−5

60 mV

40 mV

DIFFERENTIAL MODE NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

−20

100 mV

100 200 300 400 500 600

60 mV

40 mV

100

120

140

160

CAPACITANCE (nF)

TEMPERATURE ERROR (C)

−35

DEV 3

2 4 6 8 10 12 14 16 18 20 22

−30

−25

−20

−15

−10

−5

DEV 2

DEV 1

VDD (V)

3.0

ACCURACY (%)

−2.0

DEV 3

DEV 2

DEV 1

3.1 3.2 3.3 3.4 3.5 3.6

−1.5

−1.0

−0.5

0.5

1.0

1.5

TEMPERATURE (C)

−40

ACCURACY (%)

−8

DEV 3

DEV 2

DEV 1

−20 0 20 40 60 80 100 120

−6

−4

−2

ADT7490

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Theory of Operation

The ADT7490 is a complete thermal monitor and multiple

fan controller for any system requiring thermal monitoring

and cooling. The device communicates with the system via

a serial system management bus. The serial bus controller

has a serial data line for reading and writing addresses and

data (Pin 1), and an input line for the serial clock (Pin 2). All

control and programming functions for the ADT7490 are

performed over the serial bus. In addition, Pin 14 can be

reconfigured as an SMBALERT output to signal

out-of-limit conditions.

Feature Comparisons Between the ADT7490 and

ADT7476A

The ADT7490 is pin and register map compatible with the

ADT7476A. The new or additional features are detailed in

the following sections.

PECI Input

CPU thermal information is provided through the PECI

input. The ADT7490 has PECI master capabilities and can

read the CPU thermal information through the PECI

interface. Each CPU address can have up to two PECI

domains. The ADT7490 has the ability to record four PECI

temperature readings corresponding to the four PECI

addresses of 0x30 to 0x33. The hotter of the two domains at

any given address is stored in the PECI value registers. A

PECI reading is a negative value, in degrees Celsius, which

represents the offset from the thermal control circuit (TCC)

activation temperature. PECI information is not converted

to absolute temperature reading. PECI information is in a

16-bit twos complement value; however, the ADT7490

records the sign bit as well as the bits from 12:6 in the 16-bit

PECI payload. See the Platform Environment Control

Interface (PECI) Specification from Intel for more details

on the PECI data format. The PECI format is represented in

Table 6.

Table 6. PECI DATA FORMAT

MSB Upper Nibble MSB Lower Nibble

S x x x x x x x

Sign Bit Integer Value (0C to 127C)

There are associated high and low limits for each PECI

reading that can be programmed. The limit values take the

same format as the PECI reading. Therefore, the

programmed limits are not absolute temperatures but a

relative offset in degrees Celsius from the TCC activation

temperature. An out-of-limit event is recorded as follows:

High Limit > Comparison Performed

Low Limit  Comparison Performed

An out-of-limit event is recorded in the associated status

Temperature Data REPLACE Mode

The REPLACE mode is configured by setting Bit 4 of

Remote 1 registers are replaced by PECI0 data and vice

versa. This is a legacy mode that allows the thermal data

from CPU1 to be stored in the same registers as in the

ADT7476A. This reduces the software changes in systems

transitioning from CPUs with thermal diodes to CPUs with

a PECI interface. See the PECI Temperature Measurement

section for more details.

Fan Control Using PECI Information

The CPU thermal information from PECI can be used in the

existing automatic fan control algorithms. This temperature

reading remains relative to TCC activation temperature and

the associated AFC control parameters are programmed in

relative temperatures as opposed to absolute temperatures,

and are in the same format as detailed in Table 6. PECIMIN,

TRANGE, and TCONTROL are user defined.

Figure 17. Overview of Automatic Fan Speed Control

Using PECI Thermal Information

TRANGE

PWMMAX

PWMMIN

PWM = 0%

PWM = 100%

(TMIN)

PECIMIN (TMAX)

TCONTROL

TCC

PECI = 0

Dynamic TMIN Fan Control Mode

The automatic fan speed control incorporates a feature

called dynamic TMIN control. This intelligent fan control

feature reduces the design effort required to program the

automatic fan speed control loop and improves the system

acoustics.

VTT Input

The VTT voltage is monitored on Pin 8. This voltage is

also used as the reference voltage for the PECI interface. The

VTT voltage must be connected to the ADT7490 in order for

the PECI interface to be operational.

IMON Monitoring

The IMON input on Pin 19 can be used to monitor the IMON

output of ON Semiconductor’s VR10/VR11.1 controllers.

IMON is a voltage representation of the CPU current. Using

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the IMON value and the measured VCCP value on Pin 23, the

CPU power consumption can be calculated. See the

appropriate Analog Devices flex mode data sheet for

calculations. The IMON information can be considered as an

early indication of an increase in CPU temperature.

Startup Operation

At startup, the ADT7490 turns the fans on to 100% PWM.

This allows the most robust operation at turn-on.

Serial Bus Interface

Control of the ADT7490 is carried out using the serial

system management bus (SMBus). The ADT7490 is

connected to this bus as a slave device, under the control of

a master controller. The ADT7490 has a 7-bit serial bus

address. When the device is powered up with Pin 13

(PWM3/ADDREN) high, the ADT7490 has a default

SMBus address of 0101110 or 0x2E. The read/write bit must

be added to obtain the 8-bit address. If more than one

ADT7490 is to be used in a system, each ADT7490 is placed

in address select mode by strapping Pin 13 low on powerup.

The logic state of Pin 14 then determines the device’s

SMBus address. The logic of these pins is sampled on

powerup.

The device address is monitored from powerup but not

latched until the first valid SMBus transaction, more

precisely on the low-to-high transition at the beginning of

the eighth SCL pulse, when the serial bus address byte

matches the selected slave address. The selected slave

address is chosen using the ADDREN/ADDR SELECT

pins. Any attempted changes in the address have no effect

after this.

Table 7. HARD-WIRING THE ADT7490 SMBus

DEVICE ADDRESS

Pin 13 State Pin 14 State Address

0Low (10 kW to GND) 0101100 (0x2C)

0High (10 kW Pullup) 0101101 (0x2D)

1Don’t Care 0101110 (0x2E)

Data is sent over the serial bus in sequences of nine clock

pulses: eight bits of data followed by an acknowledge bit

from the slave device. Transitions on the data line must

occur during the low period of the clock signal and remain

stable during the high period, because a low-to-high

transition when the clock is high may be interpreted as a stop

signal. The number of data bytes that can be transmitted over

the serial bus in a single read or write operation is limited

only by what the master and slave devices can handle.

When all data bytes have been read or written, stop

conditions are established. In write mode, the master pulls

the data line high during the 10th clock pulse to assert a stop

condition. In read mode, the master device overrides the

acknowledge bit by pulling the data line high during the low

period before the ninth clock pulse; this is known as no

acknowledge. The master takes the data line low during the

low period before the 10th clock pulse, and then high during

the 10th clock pulse to assert a stop condition.

Any number of bytes of data can be transferred over the

serial bus in one operation, but it is not possible to mix read

and write in one operation because the type of operation is

determined at the beginning and cannot subsequently be

changed without starting a new operation.

In the ADT7490, write operations contain either one or

two bytes, and read operations contain one byte. To write

data to one of the device data registers or read data from it,

the address pointer register must be set so that the correct

data register is addressed. Then data can be written into that

always contains an address that is stored in the address

pointer register. If data is to be written to the device, the write

operation must contain a second data byte that is written to

the register selected by the address pointer register.

This write operation is shown in Figure 18. The device

address is sent over the bus, and then R/W is set to 0. This

is followed by two data bytes. The first data byte is the

address of the internal data register to be written to, which

is stored in the address pointer register. The second data byte

is the data to be written to the internal data register.

When reading data from a register, there are two

possibilities:

1. If the ADT7490 address pointer register value is

unknown or not the desired value, it must first be

set to the correct value before data can be read

from the desired data register. This is done by

performing a write to the ADT7490 as before, but

only the data byte containing the register address

is sent because no data is written to the register.

This is shown in Figure 19.

A read operation is then performed consisting of

the serial bus address, R/W bit set to 1, followed

by the data byte read from the data register. This is

shown in Figure 20.

2. If the address pointer register is known to be

already at the desired address, data can be read

from the corresponding data register without first

writing to the address pointer register, as shown in

Figure 20.

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Figure 18. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

SCL

SDA 10 1110D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7490

START BY

MASTER

ACK. BY

ADT7490

D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7490 STOP BY

MASTER

SCL (CONTINUED)

SDA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

R/W

Figure 19. Writing to the Address Pointer Register Only

SCL

SDA 101110D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7490

STOP BY

MASTER

START BY

MASTER FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

119

ACK. BY

ADT7490

R/W

Figure 20. Reading Data from a Previously Selected Register

SCL

SDA 101110D7 D6 D5 D4 D3 D2 D1 D0

NO ACK. BY

MASTER STOP BY

MASTER

START BY

MASTER FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

DATA BYTE FROM ADT7490

119

ACK. BY

ADT7490

R/W

It is possible to read a data byte from a data register

without first writing to the address pointer register if the

address pointer register is already at the correct value.

However, it is not possible to write data to a register without

writing to the address pointer register because the first data

byte of a write is always written to the address pointer

In addition to supporting the send byte and receive byte

protocols, the ADT7490 also supports the read byte protocol

(see System Management Bus Specifications Rev. 2 for

more information; this document is available from the

SMBus organization).

If several read or write operations must be performed in

succession, the master can send a repeat start condition

instead of a stop condition to begin a new operation.

Write Operations

The SMBus specification defines several protocols for

different types of read and write operations. The ones used

in the ADT7490 are discussed here. The following

abbreviations are used in the diagrams:

S: Start

P: Stop

R: Read

W: Write

A: Acknowledge

A: No acknowledge

The ADT7490 uses the following SMBus write protocols.

Send Byte

In this operation, the master device sends a single

command byte to a slave device, as follows:

1. The master device asserts a start condition on

SDA.

2. The master sends the 7-bit slave address followed

by the write bit (low).

3. The addressed slave device asserts ACK on SDA.

4. The master sends a command code.

5. The slave asserts ACK on SDA.

6. The master asserts a stop condition on SDA and

the transaction ends.

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For the ADT7490, the send byte protocol is used to write

a register address to RAM for a subsequent single-byte read

from the same address. This operation is illustrated in

Figure 21.

Figure 21. Setting a Register Address for

Subsequent Read

SLAVE

ADDRESS WASAP

ADDRESS

231564

If the master is required to read data from the register

immediately after setting up the address, it can assert a repeat

start condition immediately after the final ACK and carry

out a single-byte read without asserting an intermediate stop

condition.

Write Byte

In this operation, the master device sends a command byte

and one data byte to the slave device, as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address followed

by the write bit (low).

3. The addressed slave device asserts ACK on SDA.

4. The master sends a command code.

5. The slave asserts ACK on SDA.

6. The master sends a data byte.

7. The slave asserts ACK on SDA.

8. The master asserts a stop condition on SDA, and

the transaction ends.

The byte write operation is illustrated in Figure 22.

Figure 22. Single-byte Write to a Register

SLAVE

ADDRESS W A DATASAAP

ADDRESS

23156784

Read Operations

The ADT7490 uses the following SMBus read protocols.

Receive Byte

This operation is useful when repeatedly reading a single

this operation, the master device receives a single byte from

a slave device, as follows:

1. The master device asserts a start condition on SDA.

2. The master sends the 7-bit slave address followed

by the read bit (high).

3. The addressed slave device asserts ACK on SDA.

4. The master receives a data byte.

5. The master asserts NO ACK on SDA.

6. The master asserts a stop condition on SDA, and

the transaction ends.

In the ADT7490, the receive byte protocol is used to read

a single byte of data from a register whose address has

previously been set by a send byte or write byte operation.

This operation is illustrated in Figure 23.

Figure 23. Single-byte Read from a Register

SLAVE

ADDRESS DATAARSAP

243156

Alert Response Address

Alert response address (ARA) is a feature of SMBus

devices that allows an interrupting device to identify itself

to the host when multiple devices exist on the same bus.

The SMBALERT output can be used as either an interrupt

output or an SMBALERT. One or more outputs can be

connected to a common SMBALERT line connected to the

master. If a device’s SMBALERT line goes low, the

following events occur:

1. SMBALERT is pulled low.

2. The master initiates a read operation and sends the

alert response address (ARA = 0001 100). This is

a general call address that must not be used as a

specific device address.

3. The device whose SMBALERT output is low

responds to the alert response address, and the

master reads its device address. The address of the

device is now known and can be interrogated in

the usual way.

4. If more than one device’s SMBALERT output is

low, the one with the lowest device address has

priority in accordance with normal SMBus

arbitration.

5. Once the ADT7490 has responded to the alert

response address, the master must read the status

registers, and the SMBALERT is cleared only if

the error condition is gone.

SMBus Timeout

The ADT7490 includes an SMBus timeout feature. If

there is no SMBus activity for 35 ms, the ADT7490 assumes

the bus is locked and releases the bus. This prevents the

device from locking or holding the SMBus expecting data.

Some SMBus controllers cannot work with the SMBus

timeout feature, so it can be disabled.

Configuration Register 7 (Register 0x11)

Bit 4 (TODIS) = 0, SMBus Timeout Enabled (Default)

Bit 4 (TODIS) = 1, SMBus Timeout Disabled

Voltage Measurement Input

The ADT7490 has six external voltage measurement

channels. It can also measure its own supply voltage, VCC.

Pin 20 to Pin 23 can measure 5.0 V, 12 V, and 2.5 V

supplies, and the processor core voltage VCCP (0 V to 3.0 V

input). The 2.5 V input can be used to monitor a chipset

supply voltage in computer systems. The VCC supply

voltage measurement is carried out through the VCC pin

(Pin 4). Pin 8 measures the VTT voltage of the processor and

is the dedicated reference voltage for the PECI circuitry. The

IMON input on Pin 19 can be used to monitor the IMON

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output of ON Semiconductor’s VR11.1 controllers. IMON is

a voltage representation of the CPU current.

Analog-to-Digital Converter

All analog inputs are multiplexed into the on-chip,

successive approximation, analog-to-digital converter. This

ADC has a resolution of 10 bits. The basic input range is 0 V

to 2.25 V, but the inputs have built-in attenuators to allow

measurement of 2.5 V, 3.3 V, 5.0 V, 12 V, and the processor

core voltage VCCP without any external components. To

allow the tolerance of these supply voltages, the ADC

produces an output of 3/4 full scale (768 decimal or

0x300 hexadecimal) for the nominal input voltage, and

therefore, has adequate headroom to cope with

overvoltages.

Input Circuitry

The internal structure for the analog inputs is shown in

Figure 24 . The input circuit consists of an input protection

diode, an attenuator, plus a capacitor to form a first-order

low-pass filter that gives input immunity to high frequency

noise.

Figure 24. Analog Inputs Structure

17.5 kW

52.5 kW

VCCP

35 pF

45 kW

94 kW

+2.5VIN

30 pF

68 kW

71 kW

VCC

30 pF

93 kW

47 kW

+5VIN

30 pF

120 kW

20 kW

+12VIN

30 pF

MUX

45 kW

94 kW

IMON

30 pF

45 kW

VTT

30 pF

Table 8. VOLTAGE MEASUREMENT REGISTERS

0x1D IMON Reading 0x00

0x1E VTT Reading 0x00

0x20 +2.5 VIN Reading 0x00

0x21 VCCP Reading 0x00

0x22 VCC Reading 0x00

0x23 +5 VIN Reading 0x00

0x24 +12 VIN Reading 0x00

Voltage Limit Registers

Associated with each voltage measurement channel is a

high and low limit register. Exceeding the programmed high

or low limit causes the appropriate status bit to be set.

Exceeding either limit can also generate SMBALERT

interrupts.

Table 9. VOLTAGE LIMIT REGISTERS

0x85 IMON Low Limit 0x00

0x87 IMON High Limit 0xFF

0x84 VTT Low Limit 0x00

0x86 VTT High Limit 0xFF

0x44 +2.5 VIN Low Limit 0x00

0x45 +2.5 VIN High Limit 0xFF

0x46 VCCP Low Limit 0x00

0x47 VCCP High Limit 0xFF

0x48 VCC Low Limit 0x00

0x49 VCC High Limit 0xFF

0x4A +5.0 VIN Low Limit 0x00

0x4B +5.0 VIN High Limit 0xFF

0x4C +12 VIN Low Limit 0x00

0x4D +12 VIN High Limit 0xFF

When the ADC is running, it samples and converts a

voltage input in 0.7 ms and averages 16 conversions to

reduce noise; a measurement takes nominally 11 ms.

Extended Resolution Registers

Voltage measurements can be made with higher accuracy

using the extended resolution registers (0x1F, 0x76, and

0x77). Whenever the extended resolution registers are read,

the corresponding data in the voltage measurement registers

(0x1D, 0x1E, and 0x20 to 0x24) is locked until their data is

read. That is, if extended resolution is required, the extended

resolution register must be read first, immediately followed

by the appropriate voltage measurement register.

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Additional ADC Functions for Voltage Measurements

A number of other functions are available on the

ADT7490 to offer the system designer increased flexibility.

The functions described in the following sections are

enabled by setting the appropriate bit in Configuration

Configuration Register 2 (Register 0x73)

Bit 4 (AVG) = 1, Averaging Off.

Bit 5 (ATTN) = 1, Bypass Input Attenuators.

Bit 6 (CONV) = 1, Single-channel Convert Mode.

Turn-off Averaging

For each voltage/temperature measurement read from a

value register, 16 readings have actually been made

internally and the results averaged before being placed into

the value register. When faster conversions are needed,

setting Bit 4 (AVG) of Configuration Register 2 (0x73)

turns averaging off. This effectively gives a reading that is

16 times faster, but the reading can be noisier. The default

round-robin cycle time takes 146.5 ms.

Table 10. CONVERSION TIME WITH AVERAGING

DISABLED

Channel Measurement Time (ms)

Voltage Channels 0.7

Remote Temperature 1 7

Remote Temperature 2 7

Local Temperature 1.3

When Bit 7 (ExtraSlow) of Configuration Register 6

(0x10) is set, the default round-robin cycle time increases to

240 ms.

Bypass All Voltage Input Attenuators

Setting Bit 5 of Configuration Register 2 (0x73) removes

the attenuation circuitry from the 2.5 VIN, VCCP

, VCC,

IN, and 12 VIN inputs. This allows the user to directly

connect external sensors or rescale the analog voltage

measurement inputs for other applications. The input range

of the ADC without the attenuators is 0 V to 2.25 V.

Bypass Individual Voltage Input Attenuators

Bits [7:4] of Configuration Register 4 (0x7D) can be used

to bypass individual voltage channel attenuators.

Table 11. BYPASSING INDIVIDUAL VOLTAGE INPUT

ATTENUATORS

Configuration Register 4 (0x7D)

Bit No. Channel Attenuated

[4] Bypass +2.5 VIN Attenuator

[5] Bypass VCCP Attenuator

[6] Bypass +5 VIN Attenuator

[7] Bypass +12 VIN Attenuator

Single-channel ADC Conversion

While single-channel mode is intended as a test mode that

can be used to increase sampling times for a specific

channel, therefore helping to analyze that channel’s

performance in greater detail, it can also have other

applications.

Setting Bit 6 of Configuration Register 2 (0x73) places

the ADT7490 into single-channel ADC conversion mode. In

this mode, the ADT7490 can read a single voltage channel

only. The selected voltage input is read every 0.7 ms. The

appropriate ADC channel is selected by writing to Bits [7:4]

of the TACH1 minimum high byte register (0x55).

Table 12. PROGRAMMING SINGLE-CHANNEL ADC

MODE

Bits [7:4], Register 0x55 Channel Selected (Note 1)

0000 +2.5 VIN

0001 VCCP

0010 VCC

0011 +5 VIN

0100 +12 VIN

0101 Remote 1 Temperature

0110 Local Temperature

0111 Remote 2 Temperature

1000 VTT

1001 IMON

1. In the process of configuring single-channel ADC conversion

mode, the TACH1 minimum high byte is also changed, possibly

trading off TACH1 minimum high byte functionality with

single-channel mode functionality.

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Table 13. 10-BIT ADC OUTPUT CODE VS. VIN

Input Voltage ADC Output

+12 VIN +5 VIN VCC (3.3 VIN)+2.5 VIN VCCP VTT/IMON Decimal Binary (10 Bits)

<0.0156 <0.0065 <0.0042 <0.0032 <0.00293 <0.00220 0 00000000 00

0.0156 to

0.0312

0.0065 to

0.0130

0.0042 to

0.0085

0.0032 to

0.0065

0.0293 to

0.0058

0.00220 to

0.00440

100000000 01

0.0312 to

0.0469

0.0130 to

0.0195

0.0085 to

0.0128

0.0065 to

0.0097

0.0058 to

0.0087

0.00440 to

0,00660

200000000 10

0.0469 to

0.0625

0.0195 to

0.0260

0.0128 to

0.0171

0.0097 to

0.0130

0.0087 to

0.0117

0,00660 to

0.00881

300000000 11

0.0625 to

0.0781

0.0260 to

0.0325

0.0171 to

0.0214

0.0130 to

0.0162

0.0117 to

0.0146

0.00881 to

0.01100

400000001 00

0.0781 to

0.0937

0.0325 to

0.0390

0.0214 to

0.0257

0.0162 to

0.0195

0.0146 to

0.0175

0.01100 to

0.01320

500000001 01

0.0937 to

0.1093

0.0390 to

0.0455

0.0257 to

0.0300

0.0195 to

0.0227

0.0175 to

0.0205

0.01320 to

0.01541

600000001 10

0.1093 to

0.1250

0.0455 to

0.0521

0.0300 to

0.0343

0.0227 to

0.0260

0.0205 to

0.0234

0.01541 to

0.01761

700000001 11

0.1250 to

0.14060

0.0521 to

0.0586

0.0343 to

0.0386

0.0260 to

0.0292

0.0234 to

0.0263

0.01761 to

0.01981

800000010 00

− − − − − − − −

4.0000 to

4.0156

1.6675 to

1.6740

1.1000 to

1.1042

0.8325 to

0.8357

0.7500 to

0.7529

0.5636 to

0.5658

256

(1/4 scale)

01000000 00

− − − − − − − −

8.0000 to

8.0156

3.3300 to

3.3415

2.2000–2.204

1.6650 to

1.6682

1.5000 to

1.5029

1.1272 to

1.1294

512

(1/2 scale)

10000000 00

− − − − − − − −

12.0000 to

12.0156

5.0025 to

5.0090

3.3000 to

3.3042

2.4975 to

2.5007

2.2500 to

2.2529

1.6809 to

1.6930

768

(3/4 scale)

11000000 00

− − − − − − − −

15.8281 to

15.8437

6.5983 to

6.6048

4.3527 to

4.3570

3.2942 to

3.2974

2.9677 to

2.9707

2.2301 to

2.2323

1013 11111101 01

15.8437 to

15.8593

6.6048 to

6.6113

4.3570 to

4.3613

3.2974 to

3.3007

2.9707 to

2.9736

2.2323 to

2.2346

1014 11111101 10

15.8593 to

15.8750

6.6113 to

6.6178

4.3613 to

4.3656

3.3007 to

3.3039

2.9736 to

2.9765

2.2346 to

2.2368

1015 11111101 11

15.8750 to

15.8906

6.6178 to

6.6244

4.3656 to

4.3699

3.3039 to

3.3072

2.9765 to

2.9794

2.2368 to

2.23899

1016 11111110 00

15.8906 to

15.9062

6.6244 to

6.6309

4.3699 to

4.3742

3.3072 to

3.3104

2.9794 to

2.9824

2,23899 to

2.2412

1017 11111110 01

15.9062 to

15.9218

6.6309 to

6.6374

4.3742 to

4.3785

3.3104 to

3.3137

2.9824 to

2.9853

2.2412 to

2.2434

1018 11111110 10

15.9218 to

15.9375

6.6374 to

6.4390

4.3785 to

4.3828

3.3137 to

3.3169

2.9853 to

2.9882

2.2434 to

2.2456

1019 11111110 11

15.9375 to

15.9531

6.6439 to

6.6504

4.3828 to

4.3871

3.3169 to

3.3202

2.9882 to

2.9912

2.2456 to

2.2478

1020 11111111 00

15.9531 to

15.9687

6.6504 to

6.6569

4.3871 to

4.3914

3.3202 to

3.3234

2.9912 to

2.9941

2.2478 to

2.25

1021 11111111 01

15.9687 to

15.9843

6.6569 to

6.6634

4.3914 to

4.3957

3.3234 to

3.3267

2.9941 to

2.9970

2.25 to

2.2522

1022 11111111 10

>15.9843 >6.6634 >4.3957 >3.3267 >2.9970 >2.2522 1023 1111111111 1

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Temperature Measurement

The ADT7490 has four temperature measurement

channels: one local, two remote thermal diodes, and a PECI.

The local and thermal diode readings are analog temperature

measurements, whereas PECI is a digital temperature

reading.

PECI Temperature Measurement

The PECI interface is a dedicated thermal interface. The

CPU temperature measurement is carried out internally in

the CPU. This information is digitized and transferred to the

ADT7490 via the PECI interface. The ADT7490 is a PECI

host device and therefore, polls the CPU for thermal

information.

The PECI measurement differs from traditional thermal

diode temperature measurements in that the measurement is

a relative value instead of an absolute value. The PECI

reading is a negative value that indicates how close the CPU

temperature is from the thermal throttling or TCC point of the

CPU.

The ADT7490 records and uses the PECI measurement

for fan control in its relative format. Therefore, care must be

taken in programming the relevant limits and fan control

parameters in the PECI format. Refer to the PECI Input

section and Table 6 for further PECI information.

PECI monitoring is enabled on the ADT7490 by setting

the PECI monitoring bit in Configuration Register 1

(Register 0x40, Bit 4). The ADT7490 can measure the

temperature of up to four dual-core CPUs. The number of

CPUs in the system that provide PECI information is set in

Bits [7:6] of Register 0x88. Each CPU is distinguished by

the PECI address. The number of domains, or domain count,

per CPU address must also be programmed into the

ADT7490. The ADT7490 reads the temperature of both

domains per CPU, however, only the PECI value of the

hottest domain is recorded in the PECI value register.

PECI0 domains: Register 0x36, Bit 3

PECI1 domains: Register 0x88, Bit 5

PECI2 domains: Register 0x88, Bit 4

PECI3 domains: Register 0x88, Bit 3

PECI Reading Registers

PECI Limit Registers

Each PECI measurement shares the same high and low

limits.

PECI Offset Registers

Each PECI reading has a dedicated offset register to

calibrate the PECI measurement and account for errors in

the temperature reading. The LSBs add a 1C offset to the

temperature reading so that the 8-bit register effectively

allows temperature offsets of up to 128C with a resolution

of 1C.

PECI Data Smoothing

The PECI smoothing interval is programmed in PECI

Configuration Register 1 (0x36). Bits [2:0] of Register 0x36

set the duration over which the PECI data being read by the

ADT7490 is averaged. These bits set the duration over

which smoothing is carried out on the PECI data read. The

refresh rate in the PECI value registers is the same as the

smoothing interval programmed.

The smoothing interval is calculated using the following

formula:

(eq. 1)

Smoothing Interval +#reads ǒtBIT 67 #CPU )tIDLEǓ

where:

#reads is the number of readings defined in Register 0x36,

Bits [2:0]

tBIT is the negotiated bit rate.

67 is the number of bits in each PECI reading.

#CPU is the number of CPUs providing PECI data

(1 to 4).

tIDLE = 14 ms, the delay between consecutive reads.

For example,

#reads = 4096

tBIT = 1 ms (1 MHz speed)

#CPU = 1

Smoothing Interval = 331 ms = PECI reading refresh rate

PECI Error Codes

There are two different error conditions for PECI data,

PECI data errors, and PECI bus communications errors.

Table 14 describes the two different error conditions. If the

ADT7490 reads an error code (0x8000 to 0x8003) from the

CPU over the PECI interface, Bit 1 is set in Interrupt

Status 3 register (0x43), indicating a data error. The value of

the error code is not included in the PECI value averaging

sum. This means that a value of 0x00 is added to the PECI

sum when an error code is recorded. The error code is not

reported in the appropriate PECI value register. If an invalid

FCS is recorded by the ADT7490, Bit 2 is set in the Interrupt

Status 3 register (0x43), indicating a communications error.

An alert is generated on the SMBALERT pin when either or

both of these status bits are asserted.

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Table 14. PECI ERROR INDICATORS

PECI

Data Description Action

0x8000 to

0x8003

PECI Data Error Bit 1 of Register

0x43 is set to 1

Invalid

FCS

PECI Communications Error Bit 2 of Register

0x43 is set to 1

Each PECI channel also has an associated status bit to

indicate if the PECI high or low limits have been exceeded.

An alert is generated on the SMBALERT pin when these

status bits are asserted.

Table 15. PECI STATUS BITS

Channel Register Bit

PECI0 0x43 0

PECI1 0x81 3

PECI2 0x81 4

PECI3 0x81 5

Temperature Data REPLACE Mode

The REPLACE mode is configured by setting Bit 4 of

Remote 1 registers are replaced by PECI0 data. This is a

legacy mode that allows the thermal data from CPU1 to be

stored in the same registers as in the ADT7476A. This

reduces the software changes in systems transitioning from

CPUs with thermal diodes to CPUs with a PECI interface.

However, note that even though the associated registers are

swapped, the correct data format (PECI vs. absolute

temperature, see Table 6) must be written to and interpreted

from these registers.

Notes

In Table 16, registers listed under the Remote 1 Default

column are in absolute temperature format by default and

are in PECI format in REPLACE mode. Registers listed

under the PECI0 Default column are in PECI format by

default and in absolute temperature format in REPLACE

mode.

Table 16. REPLACE MODE TEMPERATURE

REGISTERS

Remote 1

Default PECI0 Default

Value Register Reg. 0x25 Reg. 0x33

Low Limit Reg. 0x4E Reg. 0x34

High Limit Reg. 0x4F Reg. 0x35

TMIN Reg. 0x67 Reg. 0x3B

TRANGE Reg. 0x5F,

Bits [7:4]

Reg. 0x3C,

Bits [7:4]

Enhanced Acoustics Reg. 0x62,

Bits [2:0]

Reg. 0x3C,

Bits [2:0]

Enhanced Acoustics

Enable

Reg. 0x62, Bit 3 Reg. 0x3C, Bit 3

THERM TCONTROL Reg. 0x6A Reg. 0x3D

TMIN Hysteresis Reg. 0x6D,

Bits [7:4]

Reg. 0x6D,

Bits [3:0]

(Note 1)

Reg. 0x6E,

Bits [3:0]

Reg. 0x6E,

Bits [7:4]

(Note 1)

Temperature offset Reg. 0x70 Reg. 0x94

Operating Point for

Dynamic TMIN

Reg. 0x8B Reg. 0x8A

1. In REPLACE mode, the Remote 2 and local temperature

hysteresis values are swapped.

In REPLACE mode, the temperature zone controlling the

relevant PWM output are also swapped from Remote 1 to

PECI0. The swap of control only occurs if the default

behavior setting for Register 0x5C Bits [7:5],

Local Temperature Measurement

The ADT7490 contains an on-chip band gap temperature

sensor whose output is digitized by the on-chip 10-bit ADC.

The 8-bit MSB temperature data is stored in the local

temperature register (Address 0x26). Because both positive

and negative temperatures can be measured, the temperature

data is stored in Offset 64 format or twos complement

format, as shown in Table 17 and Table 18. Theoretically,

the temperature sensor and ADC can measure temperatures

from −128C to +127C (or −64C to +191C in the

extended temperature range) with a resolution of 0.25C.

However, this exceeds the operating temperature range of

the device, so local temperature measurements outside the

ADT7490 operating temperature range are not possible.

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Table 17. TWOS COMPLEMENT TEMPERATURE DATA

FORMAT

Temperature Digital Output (10-bit) (Note 1)

–128C1000 0000 00 (Diode Fault)

–63C1100 0001 00

–50C1100 1110 00

–25C1110 0111 00

–10C1111 0110 00

0C0000 0000 00

10.25C0000 1010 01

25.5C0001 1001 10

50.75C0011 0010 11

75C0100 1011 00

100C0110 0100 00

125C0111 1101 00

127C0111 1111 00

1. Bold numbers denote 2 LSBs of measurement in the Extended

Resolution 2 register (Register 0x77) with 0.25C resolution.

Table 18. OFFSET 64 DATA FORMAT

Temperature Digital Output (10-bit) (Note 1)

–64C0000 0000 00 (Diode Fault)

–63C0000 0001 00

–1C0011 1111 00

0C0100 0000 00

1C0100 0001 00

10C0100 1010 00

25C0101 1001 00

50C0111 0010 00

75C1000 1001 00

100C1010 0100 00

125C1011 1101 00

191C1111 1111 00

1. Bold numbers denote 2 LSBs of measurement in the Extended

Resolution 2 register (Register 0x77) with 0.25C resolution.

Thermal Diode Temperature Measurement Method

A simple method of measuring temperature is to exploit

the negative temperature coefficient of a diode, measuring

the base-emitter voltage (VBE) of a transistor operated at

constant current. Unfortunately, this technique requires

calibration to null out the effect of the absolute value of VBE,

which varies from device to device.

The technique used in the ADT7490 is to measure the

change in VBE when the device is operated at three different

currents. Previous devices have used only two operating

currents, but the use of a third current allows automatic

cancellation of resistances in series with the external

temperature sensor.

Figure 28 shows the input signal conditioning used to

measure the output of an external temperature sensor. This

figure shows the external sensor as a substrate transistor, but

it could equally be a discrete transistor, such as a

2N3904/2N3906.

If a discrete transistor is used, the collector is not grounded

and should be linked to the base. If a PNP transistor is used,

the base is connected to the D– input and the emitter to the

D+ input. If an NPN transistor is used, the emitter is

connected to the D– input and the base to the D+ input.

Figure 25 and Figure 26 show how to connect the ADT7490

to an NPN or PNP transistor for temperature measurement.

Figure 25. Measuring Temperature by Using

an NPN Transistor

ADT7490

D+

D−

2N3904

NPN

Figure 26. Measuring Temperature by Using

a PNP Transistor

ADT7490

D+

D−

2N3906

PNP

To prevent ground noise from interfering with the

measurement, the more negative terminal of the sensor is not

referenced to ground, but is biased above ground by an

internal diode at the D− input. C1 can optionally be added as

a noise filter (recommended maximum value of 1,000 pF).

However, a better option in noisy environments is to add a

filter, as described in the section.

Remote Temperature Measurement

The ADT7490 can measure the temperature of two remote

diode sensors or diode-connected transistors connected to

Pin 10 and Pin 11, or Pin 12 and Pin 13.

The forward voltage of a diode or diode-connected

transistor operated at a constant current exhibits a negative

temperature coefficient of about −2 mV/C. Unfortunately,

the absolute value of VBE varies from device to device, and

individual calibration is required to null this out. Therefore,

the technique is unsuitable for mass production. The

technique used in the ADT7490 is to measure the change in

VBE when the device is operated at three different currents.

This is given by:

(eq. 2)

DVBE +kT

q In(N)

where:

k is the Boltzmann constant.

q is the charge on the carrier.

T is the absolute temperature in Kelvin.

N is the ratio of the two currents.

To measure DVBE, the operating current through the

sensor is switched among three related currents. N1 I and

N2 I are different multiples of the current I, as shown in

Figure 27. The currents through the temperature diode are

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switched between I and N1 I, giving DVBE1, and then

between I and N2 I, giving DVBE2. The temperature can

then be calculated using the two DVBE measurements. This

method can also cancel the effect of any series resistance on

the temperature measurement.

The resulting DVBE waveforms are passed through a

65 kHz low-pass filter to remove noise and then to a

chopper-stabilized amplifier. This amplifies and rectifies the

waveform to produce a dc voltage proportional to DVBE.

The ADC digitizes this voltage, and a temperature

measurement is produced. To reduce the effects of noise,

digital filtering is performed by averaging the results of 16

measurement cycles.

The results of remote temperature measurements are

stored in 10-bit, twos complement format, as listed in

Table 17. The extra resolution for the temperature

measurements is held in the Extended Resolution Register 2

(0x77). This gives temperature readings with a resolution of

0.25C.

Figure 27. Signal Conditioning for Remote Diode Temperature Sensors

LOW-PASS FILTER

fC = 65 kHz

REMOTE

SENSING

TRANSISTOR

D+

D−

VCC

IBIAS

I N1  I

VOUT+

VOUT−

To ADC

N2  I

Series Resistance Cancellation

Parasitic resistance to the ADT7490 D+ and D− inputs

(seen in series with the remote diode) is caused by a variety

of factors, including PCB track resistance and track length.

This series resistance appears as a temperature offset in the

remote sensor’s temperature measurement. This error

typically causes a 0.5C offset per ohm of parasitic

resistance in series with the remote diode.

The ADT7490 automatically cancels out the effect of this

series resistance on the temperature reading, giving a more

accurate result without the need for user characterization of

this resistance. The ADT7490 is designed to automatically

cancel, typically up to 1.5 kW of resistance. By using an

advanced temperature measurement method, this is

transparent to the user. This feature allows resistances to be

added to the sensor path to produce a filter, allowing the part

to be used in noisy environments.

Noise Filtering

For temperature sensors operating in noisy environments,

previous practice was to place a capacitor across the D+ pin

and the D− pin to help combat the effects of noise. However,

large capacitance affect the accuracy of the temperature

measurement, leading to a recommended maximum

capacitor value of 1,000 pF. This capacitor reduces the

noise, but does not eliminate it, which makes using the

sensor difficult in a very noisy environment.

The ADT7490 has a major advantage over other devices

for eliminating the effects of noise on the external sensor.

Using the series resistance cancellation feature, a filter can

be constructed between the external temperature sensor and

the part. The effect of any filter resistance seen in series with

the remote sensor is automatically canceled from the

temperature result.

The construction of a filter allows the ADT7490 and the

remote temperature sensor to operate in noisy environments.

Figure 28 shows a low-pass RC filter with the following

values:

R+100 W,C+1nF (eq. 3)

This filtering reduces both common-mode noise and

differential noise.

Figure 28. Filter between Remote Sensor and ADT7490

100 W

100 W1 nF

D+

D−

REMOTE

TEMPERATURE

SENSOR

Factors Affecting Diode Accuracy

Remote Sensing Diode

The ADT7490 is designed to work with either substrate

transistors built into processors or discrete transistors.

Substrate transistors are generally PNP types with the

collector connected to the substrate. Discrete types can be

either PNP or NPN transistors connected as a diode

(base-shorted to the collector). To reduce the error due to

variations in both substrate and discrete transistors, a

number of factors should be taken into consideration:

The ideality factor, nf, of the transistor is a measure of

the deviation of the thermal diode from ideal behavior.

The ADT7490 is trimmed for an nf value of 1.008. Use

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the following equation to calculate the error introduced

at a temperature T (C) when using a transistor whose

nf does not equal 1.008. Refer to the data sheet for the

related CPU to obtain the nf values.

DT+(nf *1.008)ń1.008 ǒ273.15 K )TǓ(eq. 4)

To factor this in, the user can write the DT value to the

offset register. The ADT7490 automatically adds it to

or subtracts it from the temperature measurement.

Some CPU manufacturers specify the high and low

current levels of the substrate transistors. The high

current level of the ADT7490, IHIGH, is 192 mA and the

low level current, ILOW, is 12 mA. If the ADT7490

current levels do not match the current levels specified

by the CPU manufacturer, it may be necessary to

remove an offset. The CPU’s data sheet advises

whether this offset needs to be removed and how to

calculate it. This offset can be programmed to the offset

offset must be considered, the algebraic sum of these

offsets must be programmed to the offset register.

If a discrete transistor is used with the ADT7490, the best

accuracy is obtained by choosing devices according to the

following criteria:

Base-emitter voltage greater than 0.25 V at 12 mA at the

highest operating temperature.

Base-emitter voltage less than 0.95 V at 192 mA at the

lowest operating temperature.

Base resistance less than 100 W.

Small variation in hFE (such as 50 to 150) that indicates

tight control of VBE characteristics.

Transistors, such as 2N3904, 2N3906, or equivalents in

SOT−23 packages, are suitable devices to use.

Reading Temperature from the ADT7490

It is important to note that temperature can be read from

the ADT7490 as an 8-bit value (with 1C resolution) or as

a 10-bit value (with 0.25C resolution). If only 1C

resolution is required, the temperature readings can be read

back at any time and in no particular order.

If the 10-bit measurement is required, it involves a

2-register read for each measurement. The Extended

Resolution 2 register (0x77) should be read first. This causes

all temperature reading registers to be frozen until all

temperature reading registers have been read from. This

prevents an MSB reading from being updated while its two

LSBs are being read and vice versa.

Nulling Out Temperature Errors

As CPUs run faster, it becomes more difficult to avoid

high frequency clocks when routing the D+/D− traces

around a system board. Even when recommended layout

guidelines are followed, some temperature errors may still

be attributable to noise coupled onto the D+/D− lines.

Constant high frequency noise usually attenuates or

increases temperature measurements by a linear, constant

value.

The ADT7490 has temperature offset registers at

Address 0x70, Address 0x71, and Address 0x72 for the

Remote 1, local, and Remote 2 temperature channels,

respectively. By performing a one-time calibration of the

system, the user can determine the offset caused by system

board noise and null it out using the offset registers. The

offset registers automatically add a twos complement 8-bit

reading to every temperature measurement.

The temperature offset range and resolution is selected by

setting Bit 1 of Register 0x7C. This ensures that the readings

in the temperature measurement registers are as accurate as

possible. Setting this bit to 0 means the LSBs add 0.5C

offset to the temperature reading, so the 8-bit register

effectively allows temperature offsets from −63C to +64C

with a resolution of 0.5C. Setting this bit to 1 means the

LSBs add 1C offset to the temperature reading, so the 8-bit

−63C to +127C with a resolution of 1C. For the PECI

offset registers, the resolution is always 1C.

Table 19. TEMPERATURE OFFSET REGISTERS

0x70 Remote 1 Temperature Offset 0x00 (0C)

0x71 Local Temperature Offset 0x00 (0C)

0x72 Remote 2 Temperature Offset 0x00 (0C)

0x94 PECI0 Temperature Offset 0x00 (0C)

0x95 PECI1 Temperature Offset 0x00 (0C)

0x96 PECI2 Temperature Offset 0x00 (0C)

0x97 PECI3 Temperature Offset 0x00 (0C)

Temperature Measurement Limit Registers

Associated with each temperature measurement channel

are high and low limit registers. Exceeding the programmed

high or low limit causes the appropriate status bit to be set.

Exceeding either limit can also generate SMBALERT

interrupts (depending on the way the interrupt mask register

is programmed and assuming that SMBALERT is set as an

output on the appropriate pin).

Additional ADC Functions for Temperature

Measurement

A number of other functions are available on the

ADT7490 to offer the system designer increased flexibility.

Turn-off Averaging

For each temperature measurement read from a value

the results averaged, before being placed into the value

measurement. Setting Bit 4 of Configuration Register 2

(0x73) turns averaging off. The default round-robin cycle

time with averaging off is a maximum of 23 ms.

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Table 20. CONVERSION TIME WITH AVERAGING

DISABLED

Channel Measurement Time (ms)

Voltage Channels 0.7

Remote Temperature 1 7

Remote Temperature 2 7

Local Temperature 1.3

When Bit 7 of Configuration Register 6 (0x10) is set, the

default round-robin cycle time increases to a maximum of

193 ms.

Table 21. CONVERSION TIME WITH AVERAGING

ENABLED

Channel Measurement Time (ms)

Voltage Channels 11

Remote Temperature 39

Local Temperature 12

Single-channel ADC Conversions

Setting Bit 6 of Configuration Register 2 (Register 0x73)

places the ADT7490 into single-channel ADC conversion

mode. In this mode, the ADT7490 can be made to read a

single temperature channel only. The appropriate ADC

channel is selected by writing to Bits [7:4] of the TACH1

Minimum High Byte register (0x55).

Table 22. PROGRAMMING SINGLE-CHANNEL ADC

MODE FOR TEMPERATURES

Bits [7:4], Register 0x55 Channel Selected

Remote 1 Temperature 0101

Local Temperature 0110

Remote 2 Temperature 0111

Configuration Register 2 (Register 0x73)

Bit 4 (AVG) = 1, Averaging Off.

Bit 6 (CONV) = 1, Single-channel Convert Mode.

Overtemperature Events

Overtemperature events on any of the temperature

channels can be detected and dealt with automatically in

automatic fan speed control mode. Register 0x6A to

local and remote diode temperature channels. The

equivalent PECI limit is TCONTROL in Register 0x3D. When

a temperature exceeds its THERM temperature limit, all

PWM outputs run at 100% duty cycle (default). This can be

changed to maximum PWM duty cycle as programmed in

Bit 3 of Register 0x7D.

The fans run at this speed until the temperature drops

below THERM minus hysteresis. This can be disabled by

setting the BOOST bit in Configuration Register 3, Bit 2

(0x78). The hysteresis value for the THERM temperature

limit is the value programmed into the hysteresis registers

(0x6D and 0x6E). The default hysteresis value is 4C.

Figure 29. THERM Temperature Limit Operation

THERM LIMIT

TEMPERATURE

FANS 100%

HYSTERESIS (C)

THERM can be disabled by setting Bit 2 of Configuration

In Offset 64 mode, writing −64C to the appropriate

THERM temperature limit.

In twos complement mode, writing −128C to the

appropriate THERM temperature limit.

Limits, Status Registers, and Interrupts

Limit Values

Associated with each measurement channel on the

ADT7490 are high and low limits. These can form the basis of

system status monitoring; a status bit can be set for any

out-of-limit condition and is detected by polling the device.

Alternatively, SMBALERT interrupts can be generated to flag

out-of-limit conditions to a processor or micro-controller.

8-bit Limits

The following is a list of 8-bit limits on the ADT7490:

Table 23. VOLTAGE LIMIT REGISTERS

0x44 +2.5 VIN Low Limit 0x00

0x45 +2.5 VIN High Limit 0xFF

0x46 VCCP Low Limit 0x00

0x47 VCCP High Limit 0xFF

0x48 VCC Low Limit 0x00

0x49 VCC High Limit 0xFF

0x4A +5 VIN Low Limit 0x00

0x4B +5 VIN High Limit 0xFF

0x4C +12 VIN Low Limit 0x00

0x4D +12 VIN High Limit 0xFF

0x84 VTT Low Limit 0x00

0x86 VTT High Limit 0xFF

0x85 IMON Low Limit 0x00

0x87 IMON High Limit 0xFF

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Table 24. TEMPERATURE LIMIT REGISTERS

0x4E Remote 1 Temperature Low Limit 0x81

0x4F Remote 1 Temperature High Limit 0x7F

0x6A Remote 1 THERM Temp. Limit 0x64

0x50 Local Temperature Low Limit 0x81

0x51 Local Temperature High Limit 0x7F

0x6B Local THERM Temperature Limit 0x64

0x52 Remote 2 Temperature Low Limit 0x81

0x53 Remote 2 Temperature High Limit 0x7F

0x6C Remote 2 THERM Temp. Limit 0x64

0x34 PECI Low Limit 0x81

0x35 PECI High Limit 0x00

0x3D PECI TCONTROL Limit 0x00

Table 25. THERM TIMER LIMIT REGISTER

0x7A THERM Timer Limit 0x00

16-bit Limits

The fan TACH measurements are 16-bit results. The fan

TACH limits are also 16 bits, consisting of a high byte and

low byte. Only high limits exist for fan TACHs because fans

running under speed or stalled are normally the only

conditions of interest. Because the fan TACH period is

actually being measured, exceeding the limit indicates a

slow or stalled fan.

Table 26. FAN LIMIT REGISTERS

0x54 TACH1 Minimum Low Byte 0xFF

0x55 TACH1 Minimum High Byte 0xFF

0x56 TACH2 Minimum Low Byte 0xFF

0x57 TACH2 Minimum High Byte 0xFF

0x58 TACH3 Minimum Low Byte 0xFF

0x59 TACH3 Minimum High Byte 0xFF

0x5A TACH4 Minimum Low Byte 0xFF

0x5B TACH4 Minimum High Byte 0xFF

Out-of-Limit Comparisons

Once all limits have been programmed, the ADT7490 can

be enabled for monitoring. The ADT7490 measures all

voltage and temperature measurements in round-robin

format and sets the appropriate status bit to indicate

out-of-limit conditions. TACH measurements are not part of

this round-robin cycle. Comparisons are done differently

depending on whether the measured value is being

compared to a high or low limit.

High Limit > Comparison Performed

Low Limit  Comparison Performed

Voltage and temperature channels use a window

comparator for error detecting and, therefore, have high and

low limits. Fan speed measurements use only a low limit.

Analog Monitoring Cycle Time

The analog monitoring cycle begins when a 1 is written to

the start bit (Bit 0) of Configuration Register 1 (0x40). The

ADC measures each analog input in turn and, as each

measurement is completed, the result is automatically stored

in the appropriate value register. This round-robin

monitoring cycle continues unless disabled by writing a 0 to

Bit 0 of Configuration Register 1.

As the ADC is normally left to free-run in this manner, the

time taken to monitor all the analog inputs is normally not

of interest, because the most recently measured value of any

input can be read out at any time. For applications where the

monitoring cycle time is important, it can easily be

calculated.

The total number of channels measured consists of

Six Dedicated Supply Voltage Inputs

Supply Voltage (VCC Pin)

Local Temperature

Two Remote Temperatures

As mentioned previously, the ADC performs round-robin

conversions and takes 11 ms for each voltage measurement,

12 ms for a local temperature reading, and 39 ms for each

remote temperature reading. The total monitoring cycle time

for averaged voltage and temperature monitoring is,

therefore, nominally

(7 11))12 )(2 39)+167 ms (eq. 5)

Fan TACH measurements and PECI thermal measurements

are made in parallel and are not synchronized with the analog

measurements in any way.

Interrupt Status Registers

The results of limit comparisons are stored in Interrupt

Status Register 1 to Interrupt Status Register 4. The status

measurement and limit comparison on that channel. If a

measurement is within limits, the corresponding interrupt

status register bit is cleared to 0. If the measurement is out of

limit, the corresponding interrupt status register bit is set to 1.

The state of the various measurement channels can be

polled by reading the interrupt status registers over the serial

bus. In Bit 7 (OOL) of Interrupt Status Register 1 (0x41), a

Logic 1 indicates an out-of-limit event has been flagged in

Interrupt Status Register 2. This means the user also needs to

read Interrupt Status Register 2. There is a similar OOL bit in

Interrupt Status Register 2 and Interrupt Status Register 3,

indicating an out-of-limit event in the next status register.

Alternatively, Pin 10 or Pin 14 can be configured as an

SMBALERT output. This hard interrupt automatically

notifies the system supervisor of an out-of-limit condition.

Reading the interrupt status registers clears the appropriate

status bit as long as the error condition that caused the

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interrupt has cleared. Interrupt status register bits are sticky.

Whenever an interrupt status bit is set, indicating an

out-of-limit condition, it remains set even if the event that

caused it has gone away (until read).

The only way to clear the interrupt status bit is to read the

interrupt status register after the event has gone away.

Interrupt status mask registers allow individual interrupt

sources to be masked from causing an SMBALERT on the

dedicated alert pin. However, if one of these masked

interrupt sources goes out of limit, its associated interrupt

status bit is set in the interrupt status registers.

Full details of the Interrupt Status and Interrupt Mask

registers associated with each measurement channels are

detailed in the Table 27 and in the full register map in the

Table 27. INTERRUPT STATUS AND INTERRUPT MASK REGISTER ADDRESS AND BIT ASSIGNMENTS

Interrupt

Status

Interrupt

Mask

0x41 0x74 OOL R2T LT R1T +5 VIN VCC VCCP +2.5 VIN/THERM

0x42 0x75 D2 FAULT D1 FAULT FAN4/THERM FAN3 FAN2 FAN1 OOL +12 VIN

0x43 0x82 OOL RES RES RES OVT COM

DATA PECI0

0x81 0x83 VTT IMON PECI3 PECI2 PECI1 RES RES RES

SMBALERT Interrupt Behavior

The ADT7490 can be polled for status, or an SMBALERT

interrupt can be generated for out-of-limit conditions. It is

important to note how the SMBALERT output and status

bits behave when writing interrupt handler software.

Figure 30. SMBALERT and Status Bit Behavior

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

CLEARED ON READ

(TEMP BELOW LIMIT)

TEMP BACK IN LIMIT

(STATUS BIT STAYS SET)

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

Figure 30 shows how the SMBALERT output and sticky

status bits behave. Once a limit is exceeded, the

corresponding status bit is set to 1. The status bit remains set

until the error condition subsides and the status register is

read. The status bits are referred to as sticky, because they

remain set until read by software. This ensures that an

out-of-limit event cannot be missed if software is polling the

device periodically.

Note that the SMBALERT output remains low for the

entire duration that a reading is out of limit and until the

status register has been read. This has implications on how

software handles the interrupt.

Handling SMBALERT Interrupts

To prevent the system from being tied up servicing

interrupts, it is recommend to handle the SMBALERT

interrupt as follows:

1. Detect the SMBALERT assertion.

2. Enter the interrupt handler.

3. Read the status registers to identify the interrupt

source.

4. Mask the interrupt source by setting the

appropriate mask bit in the interrupt mask registers

(0x74, 0x75, 0x82, and 0x83).

5. Take the appropriate action for a given interrupt

source.

6. Exit the interrupt handler.

7. Periodically poll the status registers. If the

interrupt status bit has cleared, reset the

corresponding interrupt mask bit to 0. This causes

the SMBALERT output and status bits to behave

as shown in Figure 31.

Masking Interrupt Sources

The interrupt mask registers allow individual interrupt

sources to be masked out to prevent SMBALERT interrupts.

Note that masking an interrupt source prevents only the

SMBALERT output from being asserted; the appropriate

status bit is set normally (see Figure 31). Full details of the

status and mask registers associated with each measurement

channel are detailed in Table 27 and Table 44.

Figure 31. How Masking the Interrupt Source Affects

SMBALERT Output

HIGH LIMIT

TEMPERATURE

“STICKY”

STATUS BIT

SMBALERT

CLEARED ON READ

(TEMP BELOW LIMIT)

TEMP BACK IN LIMIT

(STATUS BIT STAYS SET)

INTERRUPT

MASK BIT SET INTERRUPT MASK BIT

CLEARED

(SMBALERT RE-ARMED)

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Enabling the SMBALERT Interrupt Output

The SMBALERT interrupt function is disabled by

default. Pin 10 or Pin 14 can be reconfigured as an

SMBALERT output to signal out-of-limit conditions.

Table 28. CONFIGURING PIN 10 AS SMBALERT

OUTPUT

Configuration Register 3

(Register 0x78), Bit 0

[1] Pin 10 = SMBALERT

[0] Pin 10 = PWM2 (Default)

Assigning THERM Functionality to a Pin

Pin 14 on the ADT7490 has three possible functions:

SMBALERT, THERM, and TACH4. The user chooses the

required functionality by setting Bit 0 and Bit 1 of

Configuration Register 4 at Address 0x7D.

If THERM is enabled (Bit 1, Configuration Register 3

at Address 0x78),

Pin 22 becomes THERM.

If Pin 14 is configured as THERM (Bit 0 and Bit 1 of

Configuration Register 4 at Address 0x7D), THERM is

enabled on this pin.

If THERM is not enabled,

Pin 22 becomes a 2.5 VIN measurement input.

If Pin 14 is configured as THERM, THERM is disabled

on this pin.

Table 29. CONFIGURING PIN 14 IN REGISTER 0x7D

Bit 1 Bit 0 Function

0 0 TACH4

0 1 THERM

1 0 SMBALERT

1 1 Reserved

THERM as an Input

When THERM is configured as an input, the user can time

assertions on the THERM pin. This can be useful for

connecting to the PROCHOT output of a CPU to gauge

system performance.

The user can also set up the ADT7490 so that the fans run

at 100% when the THERM pin is driven low externally. The

fans run at 100% for the duration of the time that the THERM

pin is pulled low. This is done by setting the BOOST bit

(Bit 2) in Configuration Register 3 (Address 0x78) to 1. This

works only if the fan is already running, for example, in

manual mode when the current duty cycle is above 0x00, or

in automatic mode when the temperature is above TMIN.

If the temperature is below TMIN or if the duty cycle in

manual mode is set to 0x00, pulling the THERM low

externally has no effect. See Figure 32 for more information.

Figure 32. Asserting THERM Low as an Input in

Automatic Fan Speed Control Mode

THERM ASSERTED TO LOW AS

AN INPUT: FANS DO NOT GO

TO 100% BECAUSE TEMPERATURE

IS BELOW TMIN

THERM ASSERTED TO LOW AS

AN INPUT: FANS GO TO 100%

BECAUSE TEMPERATURE IS

ABOVE TMIN AND FANS ARE

ALREADY RUNNING.

TMIN

THERM

THERM Timer

The ADT7490 has an internal timer to measure THERM

assertion time. For example, the THERM input can be

connected to the PROCHOT output of a CPU to measure

system performance. The THERM input can also

be connected to the output of a trip point temperature sensor.

The timer is started on the assertion of the ADT7490

THERM input and stopped when THERM is deasserted.

The timer counts THERM times cumulatively, that is, the

timer resumes counting on the next THERM assertion. The

THERM timer continues to accumulate THERM assertion

times until the timer is read (it is cleared on read), or until it

reaches full scale. If the counter reaches full scale, it stops

at that reading until cleared.

The 8-bit THERM timer status register (0x79) is designed

so that Bit 0 is set to 1 on the first THERM assertion. Once

the cumulative THERM assertion time has exceeded

45.52 ms, Bit 1 of the THERM timer is set and Bit 0 now

becomes the LSB of the timer with a resolution of 22.76 ms

(see Figure 33).

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Figure 33. Understanding the THERM Timer

THERM ASSERTED

22.76 ms

THERM ASSERTED

45.52 ms

THERM ASSERTED

113.8 ms

(91.04 ms + 22.76 ms)

THERM

TIMER

(REG. 0x79)

THERM

TIMER

(REG. 0x79)

THERM

TIMER

(REG. 0x79)

ACCUMULATE THERM LOW

ASSERTION TIMES

ACCUMULATE THERM LOW

ASSERTION TIMES

10000000

01234567

01000000

01234567

10100000

01234567

When using the THERM timer, be aware of the following:

After a THERM timer read (Register 0x79):

The contents of the timer are cleared on read.

Bit 5 of Interrupt Status 2 register (0x42) needs to be

cleared (assuming that the THERM timer limit has

been exceeded).

If the THERM timer is read during a THERM assertion,

the following happens:

The contents of the timer are cleared.

Bit 0 of the THERM timer is set to 1, because a

THERM assertion is occurring.

The THERM timer increments from zero.

If the THERM timer limit (Register 0x7A) = 0x00, the

F4P bit is set.

Generating SMBALERT Interrupts from THERM Timer

Events

The ADT7490 can generate SMBALERTs when a

programmable THERM timer limit has been exceeded. This

allows the system designer to ignore brief, infrequent

THERM assertions while capturing longer THERM timer

events. Register 0x7A is the THERM timer limit register.

This 8-bit register allows a limit from 0 sec (first THERM

assertion) to 5.825 sec to be set before an SMBALERT is

generated. The THERM timer value is compared with the

contents of the THERM timer limit register. If the THERM

timer value exceeds the THERM timer limit value, the

FAN4 bit (Bit 5) of Status Register 2 is set and an

SMBALERT is generated.

Note that depending on which pins are configured as a

THERM timer, setting the FAN4/THERM bit (Bit 5) of the

Interrupt Mask Register 2 (0x75), or bit 0 of the Interrupt

Mask Register 1 (0x74), masks out SMBALERT; although

the FAN4 bit of Interrupt Status Register 2 is still set if the

THERM timer limit is exceeded.

Figure 34 is a functional block diagram of the THERM

timer, THERM limit, and its associated circuitry. Writing a

value of 0x00 to the THERM Timer Limit register (0x7A)

causes an SMBALERT to be generated on the first THERM

assertion. A THERM timer limit value of 0x01 generates an

SMBALERT once cumulative THERM assertions exceed

45.52 ms.

Configuring the Relevant THERM Behavior

1. Configure the desired pin as the THERM timer

input. Setting Bit 1 (THERM timer enable) of

Configuration Register 3 (Register 0x78) enables

the THERM timer monitoring functionality. This is

disabled on Pin 14 and Pin 22 by default.

Setting Bit 0 and Bit 1 (Pin 14 Func) of

Configuration Register 4 (Register 0x7D) enables

THERM timer output functionality on Pin 22 (Bit 1

of Configuration Register 3, THERM, must also be

set). Pin 14 can also be used as TACH4.

2. Select the desired fan behavior for THERM timer

events. Assuming the fans are running, setting Bit 2

(BOOST bit) of Configuration Register 3

(Register 0x78) causes all fans to run at 100% duty

cycle whenever THERM is asserted.

This allows fail-safe system cooling. If this bit = 0,

the fans run at their current settings and are not

affected by THERM events. If the fans are not

already running when THERM is asserted, the fans

do not run to full speed.

3. Select whether THERM timer events should

generate SMBALERT interrupts.

Bit 5 of Interrupt Mask Register 2 (0x75) or Bit 0

of Interrupt Mask Register 1 (0x74), depending on

which pins are configured as a THERM timer,

when set, masks out SMBALERTs when the

THERM timer limit value is exceeded. This bit

should be cleared if SMBALERTs based on

THERM events are required.

4. Select a suitable THERM limit value.

This value determines whether an SMBALERT is

generated on the first THERM assertion, or only if

a cumulative THERM assertion time limit is

exceeded. A value of 0x00 causes an SMBALERT

to be generated on the first THERM assertion.

5. Select a THERM monitoring time.

This value specifies how often OS- or BIOS-level

software checks the THERM timer. For example,

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BIOS can read the THERM timer once an hour to

determine the cumulative THERM assertion time.

If, for example, the total THERM assertion time is

<22.76 ms in Hour 1, >182.08 ms in Hour 2, and

>2.914 sec in Hour 3, this indicates that system

performance is degrading significantly because

THERM is asserting more frequently on an hourly

basis.

Figure 34. Functional Block Diagram of THERM Monitoring Circuitry

COMPARATOR

THERM

2.914 s

1.457 s

728.32 ms

364.16 ms

91.04 ms

45.52 ms

22.76 ms

182.08 ms

THERM TIMER LIMIT

(REG. 0x7A)

2.914 s

1.457 s

728.32 ms

364.16 ms

91.04 ms

45.52 ms

22.76 ms

182.08 ms

THERM TIMER STATUS

(REG. 0x79)

THERM TIMER CLEARED ON READ

SMBALERT

FAN4 BIT (BIT 5)

INTERRUPT MASK REGISTER 2

(REG. 0x75)

CLEARED

ON READ

FAN4 BIT (BIT 5)

INTERRUPT STATUS 2

OUTIN

RESET

LATCH

1 = MASK

01234567 01234567

Alternatively, OS- or BIOS-level software can time-stamp

when the system is powered on. If an SMBALERT is

generated due to the THERM timer limit being exceeded,

another time-stamp can be taken. The difference in time can

be calculated for a fixed THERM timer limit time.

For example, if it takes one week for a THERM timer limit

of 2.914 sec to be exceeded, and the next time it takes only

1 hour, this is an indication of a serious degradation in system

performance.

Configuring the THERM Pin as an Output

In addition to monitoring THERM as an input, the

ADT7490 can optionally drive THERM low as an output.

When PROCHOT is bidirectional, THERM can be used to

throttle the processor by asserting PROCHOT. The user can

preprogram system-critical thermal limits. If the

temperature exceeds a thermal limit by 0.25C, THERM

asserts low. If the temperature is still above the thermal limit

on the next monitoring cycle, THERM stays low. THERM

remains asserted low until the temperature is equal to or

below the thermal limit. Because the temperature for that

channel is measured only once for every monitoring cycle,

after THERM asserts, it is guaranteed to remain low for at

least one monitoring cycle.

The THERM pin can be configured to assert low if the

Remote 1 THERM, local THERM, Remote 2 THERM or

PECI temperature limits are exceeded by 0.25C. The

THERM temperature limit registers are at Register 0x6A,

Bits [5:7] of Configuration Register 5 (0x7C) enables the

THERM output feature for the Remote 1, local, and

Remote 2 temperature channels, respectively. Figure 35

shows how the THERM pin asserts low as an output in the

event of a critical overtemperature.

Figure 35. Asserting THERM as an Output, Based on

Tripping THERM Limits

THERM LIMIT

MONITORING

CYCLE

TEMP

THERM

0.255C

THERM LIMIT

An alternative method of disabling THERM is to program

the THERM temperature limit to –63C or less in Offset 64

mode, or −128C or less in twos complement mode; that is,

for THERM temperature limit values less than –63C or

–128C, respectively, THERM is disabled.

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Enabling and Disabling THERM on Individual

Channels.

The THERM pin can be enabled/disabled for individual

or combinations of temperature channels using Bits [7:5] of

Configuration Register 5 (0x7C).

THERM Hysteresis

Setting Bit 0 of Configuration Register 7 (0x11) disables

THERM hysteresis.

If THERM hysteresis is enabled and THERM is disabled

(Bit 2 of Configuration Register 4, 0x7D), the THERM

event is not reflected in the status register and the fans do not

go to full speed. If THERM hysteresis is disabled and

THERM is disabled (Bit 2 of Configuration Register 4,

0x7D) and assuming the appropriate pin is configured as

THERM, the THERM pin asserts low when a THERM event

occurs.

If THERM and THERM hysteresis are both enabled, the

THERM output asserts as expected.

THERM Operation in Manual Mode

In manual mode, THERM events do not cause fans to go

to full speed, unless Bit 5 of Configuration Register 1

(0x40) is set to 1.

Additionally, Bit 3 of Configuration Register 4 (0x7D)

can be used to select PWM speed on THERM event (100%

or maximum PWM).

Bit 2 in Configuration Register 4 (0x7D) can be set to

disable THERM events from affecting the fans.

Fan Drive Using PWM Control

The ADT7490 uses pulse-width modulation (PWM) to

control fan speed. This relies on varying the duty cycle (or

on/off ratio) of a square wave applied to the fan to vary the

fan speed. The external circuitry required to drive a fan using

PWM control is extremely simple. For 4-wire fans, the

PWM drive may need only a pullup resistor. In many cases,

the 4-wire fan PWM input has a built-in, pullup resistor.

The ADT7490 PWM frequency can be set to a selection

of low frequencies or a single high PWM frequency. The

low frequency options are used for 3-wire fans, while the

high frequency option is usually used with 4-wire fans.

For 3-wire fans, a single N-channel MOSFET is the only

drive device required. The specifications of the MOSFET

depend on the maximum current required by the fan being

driven and the input capacitance of the FET. Because a

10 kW (or greater) resistor must be used as a PWM pullup,

an FET with large input capacitance can cause the PWM

output to become distorted and adversely affect the fan

control range. This is a requirement only when using high

frequency PWM mode.

Typical notebook fans draw a nominal 170 mA, therefore,

SOT devices can be used where board space is a concern. In

desktops, fans typically draw 250 mA to 300 mA each. If

several fans are driven in parallel from a single PWM output

or drive larger server fans, the MOSFET must handle the

higher current requirements. The only other stipulation is

that the MOSFET should have a gate voltage drive,

VGS < 3.3 V, for direct interfacing to the PWM output pin.

The MOSFET should also have a low on resistance to ensure

that there is not a significant voltage drop across the FET,

which would reduce the voltage applied across the fan and,

therefore, the maximum operating speed of the fan.

Figure 36 shows how to drive a 3-wire fan using PWM

control.

Figure 36. Driving a 3-wire Fan Using an N-channel

MOSFET

ADT7490

TACH

PWM Q1

NDT3055L

12 V

FAN

3.3 V

12 V12 V

10 kW

4.7 kW

10 kW

1N4148

TACH

Figure 36 uses a 10 kW pullup resistor for the TACH

signal. This assumes that the TACH signal is an

open-collector from the fan. In all cases, the TACH signal

from the fan must be kept below 3.6 V maximum to prevent

damaging the ADT7490.

Figure 37 shows a fan drive circuit using an NPN

transistor such as a general-purpose MMBT2222. While

these devices are inexpensive, they tend to have much lower

current handling capabilities and higher on resistance than

MOSFETs. When choosing a transistor, care should be taken

to ensure that it meets the fan’s current requirements. Ensure

that the base resistor is chosen so that the transistor is

saturated when the fan is powered on.

Figure 37. Driving a 3-wire Fan Using

an NPN Transistor

ADT7490

TACH

PWM Q1

MMBT2222

12 V

FAN

3.3 V

12 V12 V

10 kW

4.7 kW

470 W

10 kW

1N4148

TACH

Because the fan drive circuitry in 4-wire fans is not

switched on or off, as with previous PWM driven/powered

fans, the internal drive circuit is always on and uses the

PWM input as a signal instead of a power supply. This

enables the internal fan drive circuit to perform better than

3-wire fans, especially for high frequency applications.

Figure 38 shows a typical drive circuit for 4-wire fans.

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Figure 38. Driving a 4-wire Fan

ADT7490

TACH

PWM

12 V, 4-WIRE FAN

12 V12 V

10 kW

4.7 kW

10 kW

TACH

VCC

TACH

PWM

3.3 V

2 kW

Driving Two Fans from PWM3

The ADT7490 has four TACH inputs available for fan

speed measurement, but only three PWM drive outputs. If a

fourth fan is being used in the system, it should be driven

from the PWM3 output in parallel with the third fan.

Figure 39 shows how to drive two fans in parallel using

low cost NPN transistors. Figure 40 shows the equivalent

circuit using a MOSFET.

Because the MOSFET can handle up to 3.5 A, it is simply

a matter of connecting another fan directly in parallel with

the first. Care should be taken in designing drive circuits

with transistors and FETs to ensure the PWM outputs are not

required to source current, and that they sink less than the

5 mA maximum current specified in the data sheet.

Driving up to Three Fans from PWM3

TACH measurements for fans are synchronized to

particular PWM channels; for example, TACH1 is

synchronized to PWM1. TACH3 and TACH4 are both

synchronized to PWM3, so PWM3 can drive two fans.

Alternatively, PWM3 can be programmed to synchronize

TACH2, TACH3, and TACH4 to the PWM3 output. This

allows PWM3 to drive two or three fans. In this case, the

drive circuitry looks the same, as shown in Figure 39 and

Figure 40. The SYNC bit in Register 0x62 enables this

function.

Synchronization is not required in high frequency mode

when used with 4-wire fans.

SYNC, Enhanced Acoustics Register 1 (Register 0x62)

Bit 4 (SYNC) = 1, synchronizes TACH2, TACH3, and

TACH4 to PWM3.

Figure 39. Interfacing Two Fans in Parallel to the

PWM3 Output Using Low Cost NPN Transistors

ADT7490

PWM3 Q1

MMBT3904

3.3 V

1 kW

TACH4

2.2 kW

3.3 V TACH3

10 kW

12 V

MMBT2222

1N4148

MMBT2222

3.3 V 3.3 V

Figure 40. Interfacing Two Fans in Parallel to the

PWM3 Output Using a Single N-channel MOSFET

ADT7490

TACH4

NDT3055L

3.3 V

10 kW

TYP

TACH3

PWM3

3.3 V

10 kW

TYP

10 kW

TYP

+V +V

5 V

12 V

FAN

TACH

1N4148

5 V

12 V

FAN

TACH

3.3 V

Laying Out 3-wire Fans

Figure 41 shows how to lay out a common circuit

arrangement for 3-wire fans.

Figure 41. Planning for 3-wire Fans on a PCB

MMBT2222

TACH

12 V or 5 V

1N4148

PWM

3.3 V or 5 V

TACH Inputs

Pin 9, Pin 11, Pin 12, and Pin 14 (when configured as

TACH inputs) are high impedance inputs intended for fan

speed measurement.

Signal conditioning in the ADT7490 accommodates the

slow rise and fall times typical of fan tachometer outputs. The

maximum input signal range is 0 V to 3.6 V, even though VCC

is 3.3 V. In the event that these inputs are supplied from fan

outputs that exceed 0 V to 3.6 V, either resistive attenuation

of the fan signal or diode clamping must be included to keep

inputs within an acceptable range.

Figure 42 to Figure 45 show circuits for the most common

fan TACH outputs.

If the fan TACH output has a resistive pullup to VCC, it can

be connected directly to the fan input, as shown in Figure 42.

Figure 42. Fan with TACH Pullup to VCC

12 V VCC

FAN SPEED

COUNTER

TACH

OUTPUT

TACH

PULLUP

4.7 kW

TYP

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If the fan output has a resistive pullup to 12 V, or other

voltage greater than 3.6 V, the fan output can be clamped

with a Zener diode, as shown in Figure 43. The Zener diode

voltage should be chosen so that it is greater than VIH of the

TACH input but less than 3.6 V, allowing for the voltage

tolerance of the Zener. A value of between 3.0 V and 3.6 V

is suitable.

Figure 43. Fan with Strong TACH Pullup to > 3.6 V,

(for Example, 12 V) Clamped with Zener Diode

12 V VCC

FAN SPEED

COUNTER

TACH

OUTPUT TACH

PULLUP

4.7 kW

TYP

ADT7490

ZD1*

*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8  VCC

If the fan has a strong pullup (less than 1 kW) to 12 V or

a totem-pole output, a series resistor can be added to limit the

Zener current, as shown in Figure 44.

Figure 44. Fan with Strong TACH. Pullup to > VCC

or Totem-Pole Output, Clamped with

Zener Diode and Resistor

5 V or12 V VCC

FAN SPEED

COUNTER

TACH

ADT7490

*CHOOSE ZD1 VOLTAGE APPROXIMATELY 0.8  VCC

PULLUP

TYP < 1 kW

OR TOTEM-POLE

ZD1*

ZENER

TACH

OUTPUT

FAN

10 kW

Alternatively, a resistive attenuator can be used, as shown

in Figure 45. R1 and R2 should be chosen such that

(eq. 6)

2VtVPULLUP R2ń

RPULLUP )R1 )R2

t3.6 V

The fan inputs have an input resistance of nominally

160 kW to ground, which should be taken into account when

calculating resistor values.

With a pullup voltage of 12 V and pullup resistor less than

1 kW, suitable values for R1 and R2 are 100 kW and 40 kW,

respectively. This gives a high input voltage of 3.42 V.

Figure 45. Fan with Strong TACH. Pullup to > VCC or

Totem-Pole Output, Attenuated with R1/R2

12 V VCC

FAN SPEED

COUNTER

TACH

ADT7490

< 1 kWR1

100 kW

40 kW

TACH

OUTPUT

The fan counter does not count the fan TACH output

pulses directly because the fan speed could be less than

1,000 RPM, and it takes several seconds to accumulate a

reasonably large and accurate count. Instead, the period of

the fan revolution is measured by gating an on-chip 90 kHz

oscillator into the input of a 16-bit counter for N periods of

the fan TACH output (see Figure 46), so the accumulated

count is actually proportional to the fan tachometer period

and inversely proportional to the fan speed.

N, the number of pulses counted, is determined by the

settings of the TACH pulses per revolution register (0x7B).

This register contains two bits for each fan, allowing one,

two (default), three, or four TACH pulses to be counted.

Figure 46. Fan Speed Measurement

CLOCK

PWM

TACH

Fan Speed Measurement Registers

The fan tachometer registers are 16-bit values consisting

of a 2-byte read from the ADT7490.

Table 30. FAN TACHOMETER REGISTERS

0x28 TACH1 Low Byte 0x00

0x29 TACH1 High Byte 0x00

0x2A TACH2 Low Byte 0x00

0x2B TACH2 High Byte 0x00

0x2C TACH3 Low Byte 0x00

0x2D TACH3 High Byte 0x00

0x2E TACH4 Low Byte 0x00

0x2F TACH4 High Byte 0x00

Reading Fan Speed from the ADT7490

The measurement of fan speeds involves a 2-register read

for each measurement. The low byte should be read first.

This causes the high byte to be frozen until both high and

low byte registers have been read, preventing erroneous

TACH readings. The fan tachometer reading registers report

back the number of 11.11 ms period clocks (90 kHz

oscillator) gated to the fan speed counter, from the rising

edge of the first fan TACH pulse to the rising edge of the

third fan TACH pulse (assuming two pulses per revolution

are being counted).

Because the device is essentially measuring the fan TACH

period, the higher the count value, the slower the fan is

actually running. A 16-bit fan tachometer reading of

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0xFFFF indicates that either the fan has stalled or is running

very slowly (<100 RPM).

High Limit > Comparison Performed

Because the actual fan TACH period is being measured,

falling below a fan TACH limit by 1 sets the appropriate

status bit and can be used to generate an SMBALERT.

Fan TACH Limit Registers

The fan TACH limit registers are 16-bit values consisting

of two bytes.

Table 31. FAN TACH LIMIT REGISTERS

0x54 TACH1 Minimum Low Byte 0xFF

0x55 TACH1 Minimum High Byte 0xFF

0x56 TACH2 Minimum Low Byte 0xFF

0x57 TACH2 Minimum High Byte 0xFF

0x58 TACH3 Minimum Low Byte 0xFF

0x59 TACH3 Minimum High Byte 0xFF

0x5A TACH4 Minimum Low Byte 0xFF

0x5B TACH4 Minimum High Byte 0xFF

Fan Speed Measurement Rate

The fan TACH readings are normally updated once

every second.

When set, the FAST bit (Bit 3) of Configuration Register 3

(0x78), updates the fan TACH readings every 250 ms.

DC Bits

If any of the fans are not being driven by a PWM channel

but are powered directly from 5.0 V or 12 V, their associated

dc bit in Configuration Register 3 should be set. This allows

TACH readings to be taken on a continuous basis for fans

connected directly to a dc source. For 4-wire fans, once high

frequency mode is enabled, the dc bits do not need to be set

because this is automatically done internally.

Calculating Fan Speed

Assuming a fan with a two pulses per revolution, and with

the ADT7490 programmed to measure two pulses per

revolution, fan speed is calculated by

Fan Speed (RPM) = (90,000 60)/Fan TACH Reading

where Fan TACH Reading is the 16-bit fan tachometer

reading.

Example

TACH1 High Byte (Register 0x29) = 0x17

TACH1 Low Byte (Register 0x28) = 0xFF

What is Fan 1 speed in RPM?

Fan 1 TACH Reading = 0x17FF = 6143 (decimal)

RPM = (f 60)/Fan 1 TACH Reading

RPM = (90,000 60)/6143

Fan Speed = 879 RPM

Fan Pulses per Revolution

Different fan models can output either one, two, three, or

four TACH pulses per revolution. Once the number of fan

TACH pulses has been determined, it can be programmed

into the TACH pulses per revolution register (0x7B) for each

fan. Alternatively, this register can be used to determine the

number or pulses per revolution output by a given fan. By

plotting fan speed measurements at 100% speed with

different pulses per revolution setting, the smoothest graph

with the lowest ripple determines the correct pulses per

revolution value.

TACH Pulses per Revolution Register

Bits [1:0], FAN1 default = 2 pulses per revolution

Bits [3:2], FAN2 default = 2 pulses per revolution

Bits [5:4], FAN3 default = 2 pulses per revolution

Bits [7:6], FAN4 default = 2 pulses per revolution

00 = 1 pulse per revolution

01 = 2 pulses per revolution

10 = 3 pulses per revolution

11 = 4 pulses per revolution

Fan Spin-up

The ADT7490 has a unique fan spin-up function. It spins

the fan at 100% PWM duty cycle until two TACH pulses are

detected on the TACH input. When two TACH pulses have

been detected, the PWM duty cycle goes to the expected

running value, for example, 33%. The advantage of this is

that fans have different spin-up characteristics and take

different times to overcome inertia. The ADT7490 runs the

fans just fast enough to overcome inertia and is quieter on

spin-up than fans programmed to spin up for a given spin-up

time.

Fan Startup Timeout

To prevent the generation of false interrupts as a fan spins

up, because the fan is below running speed, the ADT7490

includes a fan startup timeout function. During this time, the

ADT7490 looks for two TACH pulses. If two TACH pulses

are not detected, an interrupt is generated.

Fan startup timeout can be disabled by setting Bit 3

(FSPDIS) of Configuration Register 7 (0x11).

Table 32. PWM1, PWM2, PWM3 CONFIGURATION

(REG. 0x5C, REG. 0x5D, REG. 0x5E)

Bit Mnemonic Description

[2:0] SPIN These Bits Control the Startup

Timeout for PWM1 (0x5C),

PWM2 (0x5D), PWM3 (0x5E).

000 = No Startup Timeout

001 = 100 ms

010 = 250 ms (Default)

011 = 400 ms

100 = 667 ms

101 = 1 s

110 = 2 s

111 = 4 s

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Disabling Fan Startup Timeout

Although a fan startup makes fan spin-ups much quieter

than fixed-time spin-ups, the option exists to use fixed

spin-up times. Setting Bit 3 (FSPDIS) to 1 in Configuration

TACH pulses. Instead, the fan spins up for the fixed time as

selected in Register 0x5C to Register 0x5E.

PWM Logic State

The PWM outputs can be programmed high for 100%

duty cycle (non-inverted) or low for 100% duty cycle

(inverted).

Table 33. PWM1 CONFIGURATION (REG. 0x5C)

Bit Mnemonic Description

[4] INV 0 = Logic High for 100% PWM Duty

Cycle (Non-inverted)

1 = Logic Low for 100% PWM Duty

Cycle (Inverted)

Table 34. PWM2 CONFIGURATION (REG. 0x5D)

Bit Mnemonic Description

[4] INV 0 = Logic High for 100% PWM Duty

Cycle

1 = Logic Low for 100% PWM Duty

Cycle

Table 35. PWM3 CONFIGURATION (REG. 0x5E)

Bit Mnemonic Description

[4] INV 0 = Logic High for 100% PWM Duty

Cycle (Non-inverted)

1 = Logic Low for 100% PWM Duty

Cycle (Inverted)

Low Frequency Mode PWM Drive Frequency

The PWM drive frequency can be adjusted for the

application. Register 0x5F to Register 0x61 configure the

PWM frequency for PWM1 to PWM3, respectively.

Table 36. PWM1, PWM2, PWM3 FREQUENCY

REGISTERS (REG. 0x5F TO 0x61)

Bit Mnemonic Description

[2:0] FREQ 000 = 11.0 Hz

001 = 14.7 Hz

010 = 22.1 Hz

011 = 29.4 Hz

100 = 35.3 Hz (Default)

101 = 44.1 Hz

110 = 58.8 Hz

111 = 88.2 Hz

High Frequency Mode PWM Drive

Setting Bit 3 of Register 0x5F, Register 0x60, and

Fan 2, and Fan 3, respectively.

In high frequency mode, the PWM drive frequency is

always 22.5 kHz. When high frequency mode is enabled, the

dc bits are automatically asserted internally and do not need

to be changed.

Fan Speed Control

The ADT7490 controls fan speed using automatic and

manual modes.

In automatic fan speed control mode, fan speed is

automatically varied with temperature and without CPU

intervention, once initial parameters are set up. The

advantage is that, if the system hangs, the user is guaranteed

that the system is protected from overheating.

In manual fan speed control mode, the ADT7490 allows

the duty cycle of any PWM output to be manually adjusted.

This can be useful if the user wants to change fan speed in

software or adjust PWM duty cycle output for test purposes.

Bits [7:5] of Register 0x5C to Register 0x5E (PWM

Configuration) control the behavior of each PWM output.

Table 37. PWM CONFIGURATION REGISTERS

(REG. 0x5C TO REG. 0x5E)

Bit Mnemonic Description

[7:5] BHVR 111 = Manual Mode

Once under manual control, each PWM output can be

manually updated by writing to Register 0x30 to

Programming the PWM Current Duty Cycle Registers

The PWM current duty cycle registers are 8-bit registers

that allow the PWM duty cycle for each output to be set

anywhere from 0% to 100% in steps of 0.39%. The value to

be programmed into the PWMMIN register is given by

Value (decimal) = PWMMIN/0.39%

Example 1

For a PWM duty cycle of 50%,

Value (decimal) = 50%/0.39% = 128 (decimal)

Value = 128 (decimal) or 0x80 (hexadecimal)

Example 2

For a PWM duty cycle of 33%,

Value (decimal) = 33%/0.39% = 85 (decimal)

Value = 85 (decimal) or 0x54 (hexadecimal)

Table 38. PWM DUTY CYCLE REGISTERS

0x30 PWM1 Current Duty Cycle 0xFF (100%)

0x31 PWM2 Current Duty Cycle 0xFF (100%)

0x32 PWM3 Current Duty Cycle 0xFF (100%)

By reading the PWMx current duty cycle registers, the

user can keep track of the current duty cycle on each PWM

output, even when the fans are running in automatic fan

speed control mode or acoustic enhancement mode.

Programming TRANGE

TRANGE defines the distance between TMIN and 100%

PWM. For the ADT7467, ADT7468, and ADT7473,

TRANGE is effectively a slope. For the ADT7475, ADT7476,

and ADT7490, TRANGE is no longer a slope but defines the

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temperature region where the PWM output linearly ramps

from PWMMIN to 100% PWM.

Figure 47. TRANGE

TMIN

PWM = 100%

PWM = 0%

PWMMIN

PWMMAX

TRANGE

Programming the Automatic Fan Speed Control Loop

To more efficiently understand the automatic fan speed

control loop, using the ADT7490 evaluation board and

software while reading this section is recommended.

This section provides the system designer with an

understanding of the automatic fan control loop, and

provides step-by-step guidance on effectively evaluating

and selecting critical system parameters. To optimize the

system characteristics, the designer needs to give some

thought to system configuration, including the number of

fans, where they are located, and what temperatures are

being measured in the particular system.

The mechanical or thermal engineer who is tasked with

the system thermal characterization should also be involved

at the beginning of the system development process.

Manual Fan Control Overview

In unusual circumstances, it can be necessary to manually

control the speed of the fans. Because the ADT7490 has an

SMBus interface, a system can read back all necessary

voltage, fan speed, and temperature information, and use

this information to control the speed of the fans by writing

to the current PWM duty cycle register (0x30, 0x31, and

0x32) of the appropriate fan. Bits [7:5] of the PWMx

configuration registers (0x5C, 0x5D, and 0x5E) are used to

set fans up for manual control.

THERM Operation in Manual Mode

In manual mode, if the temperature increases above the

programmed THERM temperature limit, the fans

automatically speed up to maximum PWM or 100% PWM,

whichever way the appropriate fan channel is configured.

Automatic Fan Control Overview

The ADT7490 can automatically control the speed of fans

based on the measured temperature. This is done

independently of CPU intervention once the initial

parameters are set up.

The ADT7490 has a local temperature sensor and two

remote temperature channels that can be connected to a CPU

on-chip thermal diode (available on IntelPentium class

and other CPUs). These three temperature channels can be

used as the basis for automatic fan speed control to drive fans

using pulse-width modulation (PWM).

Automatic fan speed control reduces acoustic noise by

optimizing fan speed according to accurately measured

temperature. Reducing fan speed can also decrease system

current consumption. The automatic fan speed control mode

is very flexible due to the number of programmable

parameters, including TMIN and TRANGE. The TMIN and

TRANGE values for a temperature channel and, therefore, for

a given fan are critical, because they define the thermal

characteristics of the system. The thermal validation of the

system is one of the most important steps in the design

process, so these values should be selected carefully.

Figure 48 gives a top-level overview of the automatic fan

control circuitry on the ADT7490. From a systems-level

perspective, up to three system temperatures can be

monitored and used to control three PWM outputs. The three

PWM outputs can be used to control up to four fans. The

ADT7490 allows the speed of four fans to be monitored.

Each temperature channel has a thermal calibration block,

allowing the designer to individually configure the thermal

characteristics of each temperature channel. For example,

users can decide to run the CPU fan when CPU temperature

increases above 60C and a chassis fan when the local

temperature increases above 45C.

At this stage, the designer has not assigned these thermal

calibration settings to a particular fan drive (PWM) channel.

The right side of Figure 48 shows controls that are

fan-specific. The designer has individual control over

parameters such as minimum PWM duty cycle, fan speed

failure thresholds, and even ramp control of the PWM

outputs. Automatic fan control ultimately allows graceful

fan speed changes that are less perceptible to the system user.

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Figure 48. Automatic Fan Control Block Diagram

THERMAL CALIBRATION

REMOTE1 =

AMBIENT

TEMP

100%

TMIN TRANGE

THERMAL CALIBRATION

100%

TMIN TRANGE

THERMAL CALIBRATION

100%

TMIN TRANGE

LOCAL =

VRM TEMP

REMOTE2 =

GPU TEMP

PWM

MIN

PWM

MIN

PWM

MIN

MUX

PWM

CONFIG

PWM

GENERATOR

PWM1

PWM2

PWM3

TACH1

TACH2

TACH3

TACHOMETER 1

MEASUREMENT

TACHOMETER 2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER 3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

CONFIG

PWM

GENERATOR

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

THERMAL CALIBRATION

100%

TMIN TRANGE

PECI =

CPU TEMP

Step 1: Hardware Configuration

During system design, the motherboard sensing and

control capabilities should be addressed early in the design

stages. Decisions about how these capabilities are used

should involve the system thermal/mechanical engineer.

Ask the following questions:

What ADT7490 functionality is used?

PWM2 or SMBALERT?

TACH4 fan speed measurement or overtemperature

THERM function?

2.5 VIN voltage monitoring or overtemperature

THERM function?

The ADT7490 offers multifunctional pins that can be

reconfigured to suit different system requirements and

physical layouts. These multifunction pins are software

programmable.

How many fans are supported in the system, three or

four? This influences the choice of whether to use the

TACH4 pin or to reconfigure it for the THERM

function.

Is the CPU fan to be controlled using the ADT7490, or

will the CPU fan run at full speed 100% of the time?

If run at 100%, it frees up a PWM output, but the system

is louder.

Where is the ADT7490 going to be physically located

in the system?

This influences the assignment of the temperature

measurement channels to particular system thermal zones.

For example, locating the ADT7490 close to the VRM

controller circuitry allows the VRM temperature to be

monitored using the local temperature channel.

Step 2: Configuring the Muxtiplexer

After the system hardware configuration is determined,

the fans can be assigned to particular temperature channels.

Not only can fans be assigned to individual channels, but the

behavior of the fans is also configurable. For example, fans

can be run under automatic fan control, can be run manually

(under software control), or can be run at the fastest speed

calculated by multiple temperature channels. The mux is the

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bridge between temperature measurement channels and the

three PWM outputs.

Bits [7:5] (BHVR) of Register 0x5C, Register 0x5D, and

behavior of the fans connected to the PWM1, PWM2, and

PWM3 outputs, respectively. The values selected for these

bits determine how the multiplexer connects a temperature

measurement channel to a PWM output.

Automatic Fan Control Multiplexer Options

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

000 = Remote 1 temperature controls PWMx

001 = Local temperature controls PWMx

010 = Remote 2 temperature controls PWMx

101 = Fastest speed calculated by local and Remote 2

temperature controls PWMx

110 = Fastest speed calculated by all three temperature

channels controls PWMx

The fastest speed calculated options pertain to controlling

one PWM output based on multiple temperature channels.

The thermal characteristics of the three temperature zones

can be set to drive a single fan. An example is the fan turning

on when the Remote 1 temperature exceeds 60C or if

the local temperature exceeds 45C.

Setting the ALT bit in Register 0x5C, Register 0x5D, and

Bits [7:5] of the PWM configuration registers.

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

000 = PECI0 reading controls PWMx

001 = PECI1 reading controls PWMx

010 = PECI2 reading controls PWMx

011 = PECI3 reading controls PWMx

101 = Fastest speed calculated by all four PECI

readings controls PWMx

111 = Fastest speed calculated by all thermal zones

(Local, Rem1, Rem2 and PECI) controls PWMx

Other Mux Options

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

011 = PWMx runs full speed

100 = PWMx disabled (default)

111 = Manual mode. PWMx is running under software

control. In this mode, PWM duty cycle registers

(Register 0x30 to Register 0x32) are writable and

control the PWM outputs.

Bits [7:5] (BHVR), Register 0x5C, Register 0x5D, and

100 = PWMx runs at 100% duty cycle

110 = PWMx runs at 100% duty cycle

Step 3: TMIN Settings for Thermal Calibration Channels

TMIN is the temperature at which the fans start to turn on

under automatic fan control. The speed at which the fan runs

at TMIN is programmed later. The TMIN values chosen are

temperature channel specific, for example, 25C for

ambient channel, 30C for VRM temperature, and 40C for

processor temperature.

TMIN is an 8-bit value, either twos complement or Offset

64, that can be programmed in 1C increments. A TMIN

channel: Remote 1, local, Remote 2 and PECI temperature.

When the TMIN value is exceeded, the fan turns on and runs

at the minimum PWM duty cycle. The fan turns off once the

temperature has dropped below TMIN −THYST.

To overcome fan inertia, the fan is spun up until two valid

TACH rising edges are counted. See the Fan Startup

Timeout section for more details. In some cases, primarily

for psycho-acoustic reasons, it is desirable that the fan never

switch off below TMIN. When set, Bits [7:5] of Enhanced

Acoustics Register 1 (0x62) keep the fans running at the

PWM minimum duty cycle if the temperature should fall

below TMIN.

Table 39. TMIN REGISTERS

0x67 Remote 1 Temperature TMIN 0x5A (90C)

0x68 Local Temperature TMIN 0x5A (90C)

0x69 Remote 2 Temperature TMIN 0x5A (90C)

0x3B PECI TMIN 0xE0 (−32C)

Enhanced Acoustics Register 1 (Register 0x62)

Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when

the temperature is below TMIN –T

HYST.

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty

cycle below TMIN –T

HYST.

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

the temperature is below TMIN –T

HYST.

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty

cycle below TMIN –T

HYST.

Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

the temperature is below TMIN –T

HYST.

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty

cycle below TMIN –T

HYST.

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Figure 49. Understanding the TMIN Parameter

THERMAL CALIBRATION

REMOTE1 =

AMBIENT TEMP

100%

TMIN TRANGE

PWM

MIN

MUX

TACHOMETER1

MEASUREMENT

PWM

MIN

PWM

MIN

THERMAL CALIBRATION

100%

TMIN TRANGE

THERMAL CALIBRATION

100%

TMIN TRANGE

LOCAL =

VRM TEMP

REMOTE2 =

CPU TEMP

TACHOMETER2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM1

PWM2

PWM3

TACH3

TACH2

TACH1

CPU FAN SINK

FRONT CHASSIS

REAR CHASSIS

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

TMIN

100%

PWM DUTY CYCLE

Step 4: PWMMIN for Each PWM (Fan) Output

PWMMIN is the minimum PWM duty cycle at which each

fan in the system runs. It is also the start speed for each fan

under automatic fan control once the temperature rises

above TMIN. For maximum system acoustic benefit,

PWMMIN should be as low as possible. Depending on the

fan used, the PWMMIN setting is usually in the 20% to 33%

duty cycle range. This value can be found through fan

validation.

Figure 50. PWMMIN Determines Minimum

PWM Duty Cycle

TMIN

100%

PWM DUTY CYCLE

TEMPERATURE

PWMMIN

More than one PWM output can be controlled from a

single temperature measurement channel. For example,

Remote 1 temperature can control PWM1 and PWM2

outputs. If two different fans are used on PWM1 and PWM2,

the fan characteristics can be set up differently. As a result,

Fan 1 driven by PWM1 can have a different PWMMIN value

than that of Fan 2 connected to PWM2. Figure 51 illustrates

this as PWM1MIN (front fan) turned on at a minimum duty

cycle of 20%, while PWM2MIN (rear fan) is turned on at a

minimum of 40% duty cycle. Note that both fans turn on at

exactly the same temperature, defined by TMIN.

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Figure 51. Operating Two Different Fans from

a Single Temperature Channel

TMIN

100%

TEMPERATURE

PWM1MIN

PWM2MIN PWM1

PWM2

PWM DUTY CYCLE

Programming the PWMMIN Registers

The PWMMIN registers are 8-bit registers that allow the

minimum PWM duty cycle for each output to be configured

anywhere from 0% to 100%. This allows the minimum

PWM duty cycle to be set in steps of 0.39%.

The value to be programmed into the PWMMIN register is

given by:

Value (decimal) = PWMMIN/0.39%

Example 1

For a minimum PWM duty cycle of 50%,

Value (decimal) = 50%/0.39% = 128 (decimal)

Value = 128 (decimal) or 0x80 (hexadecimal)

Example 2

For a minimum PWM duty cycle of 33%,

Value (decimal) = 33%/0.39% = 85 (decimal)

Value = 85 (decimal) or 0x54 (hexadecimal)

Table 40. PWMMIN REGISTERS

0x64 PWM1 Minimum Duty Cycle 0x80 (50%)

0x65 PWM2 Minimum Duty Cycle 0x80 (50%)

0x66 PWM3 Minimum Duty Cycle 0x80 (50%)

Note on Fan Speed and PWM Duty Cycle

The PWM duty cycle does not directly correlate to fan

speed in RPM. Running a fan at 33% PWM duty cycle does

not equate to running the fan at 33% speed. Driving a fan at

33% PWM duty cycle actually runs the fan at closer to 50%

of its full speed. This is because fan speed in %RPM

generally relates to the square root of PWM duty cycle.

Given a PWM square wave as the drive signal, fan speed in

RPM approximates to

% fanspeed +PWM Duty Cycle 10

Ǹ(eq. 7)

Step 5: PWMMAX for PWM (Fan) Outputs

PWMMAX is the maximum duty cycle that each fan in the

system runs at under the automatic fan speed control loop.

For maximum system acoustic benefit, PWMMAX should be

as low as possible, but should be capable of maintaining the

processor temperature limit at an acceptable level. If the

THERM temperature limit is exceeded, the fans are still

boosted to 100% for fail-safe cooling.

There is a PWMMAX limit for each fan channel. The

default value of this register is 0xFF and has no effect unless

it is programmed.

Figure 52. PWMMAX Determines Maximum PWM Duty

Cycle Below the THERM Temperature Limit

TMIN

100%

TEMPERATURE

PWMMIN

PWMMAX

PWM DUTY CYCLE

Programming the PWMMAX Registers

The PWMMAX registers are 8-bit registers that allow the

maximum PWM duty cycle for each output to be configured

anywhere from 0% to 100%. This allows the maximum

PWM duty cycle to be set in steps of 0.39%.

The value to be programmed into the PWMMAX register

is given by:

Value (decimal) = PWMMAX/0.39%

Example 1

For a maximum PWM duty cycle of 50%,

Value (decimal) – 50%/0.39% = 128 (decimal)

Value = 128 (decimal) or 0x80 (hexadecimal)

Example 2

For a minimum PWM duty cycle of 75%,

Value (decimal) = 75%/0.39% = 85 (decimal)

Value = 192 (decimal) or 0xC0 (hexadecimal)

Table 41. PWMMAX REGISTERS

0x38 PWM1 Maximum Duty Cycle 0xFF (100%)

0x39 PWM2 Maximum Duty Cycle 0xFF (100%)

0x3A PWM3 Maximum Duty Cycle 0xFF (100%)

Step 6: TRANGE for Temperature Channels

TRANGE is the range of temperature over which automatic

fan control occurs once the programmed TMIN temperature

has been exceeded. TRANGE is the temperature range between

PWMMIN and 100% PWM where the fan speed changes

linearly. Otherwise stated, it is the line drawn between the

TMIN/PWMMIN and the (TMIN +T

RANGE)/100% PWM

intersection points.

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Figure 53. TRANGE Parameter Affects Cooling Slope

TMIN

100%

TEMPERATURE

PWMMIN

PWM DUTY CYCLE

TRANGE

The TRANGE is determined by the following procedure:

1. Determine the maximum operating temperature for

that channel (for example, 70C).

2. Determine experimentally the fan speed (PWM

duty cycle value) that does not exceed the

temperature at the worst-case operating points. For

example, 70C is reached when the fans are

running at 50% PWM duty cycle.

3. Determine the slope of the required control loop to

meet these requirements.

4. Using the ADT7490 evaluation software,

graphically program and visualize this

functionality. Ask a local Analog Devices

representative for details.

As PWMMIN is changed, the automatic fan control slope

changes.

Figure 54. Adjusting PWMMIN Changes the Automatic

Fan Control Slope

TMIN

100%

30C

PWM DUTY CYCLE

33%

50%

As TRANGE is changed, the slope changes. As TRANGE

gets smaller, the fans reach 100% speed with a smaller

temperature change.

Figure 55. Increasing TRANGE Changes the AFC Slope

TMIN

100%

30C

PWM DUTY CYCLE

10%

40C

45C

54C

TMIN−HYST

Figure 56. Changing PWMMAX Does Not Change the

AFC Slope

TRANGE

100%

PWM DUTY CYCLE

10%

TMIN−HYST

MAX

PWM

Selecting TRANGE

The TRANGE value can be selected for each temperature

channel: Remote 1, local, Remote 2, and PECI temperature.

Bits [7:4] (TRANGE) of Register 0x5F to Register 0x61 and

temperature channel.

Table 42. SELECTING A TRANGE VALUE

Bits [7:4] (Note 1) TRANGE (5C)

0000 2

0001 2.5

0010 3.33

0011 4

0100 5

0101 6.67

0110 8

0111 10

1000 13.33

1001 16

1010 20

1011 26.67

1100 32 (default)

1101 40

1110 53.33

1111 80

1. Register 0x5F configures Remote 1 TRANGE; Register 0x60

configures local TRANGE; Register 0x61 configures Remote 2

TRANGE, Register 0x3C configures PECI TRANGE.

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Actual Changes in PWM Output

(Advanced Acoustics Settings)

While the automatic fan control algorithm describes the

general response of the PWM output, it is also necessary to

note that the enhanced acoustics registers (0x62, 0x63, and

0x3C) can be used to set/clamp the maximum rate of change

of PWM output for a given temperature zone. This means that

if TRANGE is programmed with an AFC slope that is quite

steep, a relatively small change in temperature could cause a

large change in PWM output and possibly an audible change

in fan speed, which can be noticeable/annoying to end users.

Decreasing the speed of the PWM output changes by

programming the smoothing on the appropriate temperature

channels (Register 0x62 and Register 0x63) changes how

fast the fan speed increases/decreases in the event of a

temperature spike. Slowly the PWM duty cycle increases

until the PWM duty cycle reaches the appropriate duty cycle

as defined by the AFC curve.

Figure 57 shows PWM duty cycle vs. temperature for

each TRANGE setting. Figure 57B shows how each TRANGE

setting affects fan speed vs. temperature. As can be seen

from the graph, the effect on fan speed is nonlinear.

Figure 57. TRANGE vs. Actual Fan Speed

(Not PWM Drive) Profile

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

TEMPERATURE ABOVE TMIN

PWM DUTY CYCLE (%)

020 40 60 80 100 120

100

TEMPERATURE ABOVE TMIN

FAN SPEED (% OF MAX)

020 40 60 80 100 120

100

(A)

(B)

The graphs in Figure 57 assume the fan starts from 0%

PWM duty cycle. Clearly, the minimum PWM duty cycle,

PWMMIN, needs to be factored in to see how the loop

actually performs in the system. Figure 58 shows how

TRANGE is affected when the PWMMIN value is set to 20%.

It can be seen that the fan actually runs at about 45% fan

speed when the temperature exceeds TMIN.

Figure 58. TRANGE and % Fan Speed Slopes with

PWMMIN = 20%

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

25C

805C

53.35C

405C

325C

26.65C

205C

165C

13.35C

105C

85C

6.675C

55C

45C

3.335C

2.55C

TEMPERATURE ABOVE TMIN

PWM DUTY CYCLE (%)

020 40 60 80 100 120

100

TEMPERATURE ABOVE TMIN

FAN SPEED (% OF MAX)

020 40 60 80 100 120

100

(A)

(B)

Step 7: TTHERM for Temperature Channels

TTHERM is the absolute maximum temperature allowed

on a temperature channel. For PECI temperature channels,

the equivalent parameter is TCONTROL. Above this

temperature, a component such as the CPU or VRM may be

operating beyond its safe operating limit. When the

temperature measured exceeds TTHERM, all fans are driven

at 100% PWM duty cycle (full speed) to provide critical

system cooling.

The fans remain running at 100% until the temperature

drops below TTHERM minus hysteresis, where hysteresis is

the number programmed into the hysteresis registers (0x6D

and 0x6E). The default hysteresis value is 4C.

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The TTHERM limit should be considered the maximum

worst-case operating temperature of the system. Because

exceeding any TTHERM limit runs all fans at 100%, it has

very negative acoustic effects. Ultimately, this limit should

be set up as a fail-safe, and one should ensure that it is not

exceeded under normal system operating conditions.

Note that TTHERM limits are non-maskable and affect the

fan speed no matter how automatic fan control settings are

configured. This allows some flexibility, because a TRANGE

value can be selected based on its slope, while a hard limit

(such as 70C), can be programmed as TMAX (the

temperature at which the fan reaches full speed) by setting

TTHERM to that limit (for example, 70C).

Table 43. THERM REGISTERS

0x6A Remote 1 THERM Limit 0x64 (100C)

0x6B Local THERM Limit 0x64 (100C)

0x6C Remote 2 THERM Limit 0x64 (100C)

0x3D PECI TCONTROL Limit 0x00 (0C)

THERM Hysteresis

THERM hysteresis on a particular channel is configured

via the hysteresis settings in the following section (0x6D and

0x6E). For example, setting hysteresis on the Remote 1

channel also sets the hysteresis on Remote 1 THERM.

Hysteresis Registers

Bits [7:4], Remote 1 Temperature Hysteresis (4C default)

Bits [3:0], Local Temperature Hysteresis (4C default)

Bits [7:4], Remote 2 Temperature Hysteresis (4C default)

Bits [3:0], PECI Temperature Hysteresis (4C default)

Because each hysteresis setting is four bits, hysteresis

values are programmable from 1C to 15C. It is not

recommended that hysteresis values ever be programmed to

0C, because this disables hysteresis. In effect, this causes

the fans to cycle (during a THERM event) between normal

speed and 100% speed, or, while operating close to TMIN,

between normal speed and off, creating unsettling acoustic

noise.

Figure 59. How TTHERM Relates to Automatic Fan Control

THERMAL CALIBRATION

REMOTE1 =

AMBIENT TEMP

100%

TMIN TRANGE

PWM

MIN

MUX

TACHOMETER1

MEASUREMENT

PWM

MIN

PWM

MIN

THERMAL CALIBRATION

100%

TMIN TRANGE

THERMAL CALIBRATION

100%

TMIN TRANGE

LOCAL =

VRM TEMP

REMOTE2 =

CPU TEMP

TACHOMETER2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM1

PWM2

PWM3

TACH3

TACH2

TACH1

CPU FAN SINK

FRONT CHASSIS

REAR CHASSIS

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

TMIN

100%

PWM DUTY CYCLE

TTHERM

TRANGE

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Step 8: THYST for Temperature Channels

THYST is the amount of extra cooling a fan provides after

the temperature measured has dropped back below TMIN

before the fan turns off. The premise for temperature

hysteresis (THYST) is that, without it, the fan would merely

chatter, or cycle on and off regularly, whenever the

temperature is hovering at about the TMIN setting.

The THYST value chosen determines the amount of time

needed for the system to cool down or heat up as the fan is

turning on and off. Values of hysteresis are programmable in

the range of 1C to 15C. Larger values of THYST prevent the

fans from chattering on and off. The THYST default value is

set at 4C.

The THYST setting applies not only to the temperature

hysteresis for fan on/off, but the same setting is used for the

TTHERM hysteresis value, described in the Step 7: TTHERM

for Temperature Channels section. Therefore, programming

both fan on/off and the THERM function.

In some applications, it is required that fans not turn off

below TMIN, but remain running at PWMMIN. Bits [7:5] of

Enhanced Acoustics Register 1 (0x62) allow the fans to be

turned off or to be kept spinning below TMIN. If the fans are

always on, the THYST value has no effect on the fan when the

temperature drops below TMIN.

Figure 60. The THYST Value Applies to Fan On/Off Hysteresis and THERM Hysteresis

THERMAL CALIBRATION

REMOTE1 =

AMBIENT TEMP

100%

TMIN TRANGE

PWM

MIN

MUX

TACHOMETER1

MEASUREMENT

PWM

MIN

PWM

MIN

THERMAL CALIBRATION

100%

TMIN TRANGE

THERMAL CALIBRATION

100%

TMIN TRANGE

LOCAL =

VRM TEMP

REMOTE2 =

CPU TEMP

TACHOMETER2

MEASUREMENT

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

TACHOMETER3

AND 4

MEASUREMENT

PWM

CONFIG

PWM

GENERATOR

PWM1

PWM2

PWM3

TACH3

TACH2

TACH1

CPU FAN SINK

FRONT CHASSIS

REAR CHASSIS

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

RAMP

CONTROL

(ACOUSTIC

ENHANCEMENT)

PWM

CONFIG

PWM

GENERATOR

PWM

CONFIG

PWM

GENERATOR

TMIN

100%

PWM DUTY CYCLE

TTHERM

TRANGE

THERM Hysteresis

Any hysteresis programmed via Register 0x6D and

THERM channel.

Enhanced Acoustics Register 1 (Register 0x62)

Bit 7 (MIN3) = 0, PWM3 is off (0% PWM duty cycle) when

temperature is below TMIN −THYST.

Bit 7 (MIN3) = 1, PWM3 runs at PWM3 minimum duty

cycle below TMIN −THYST.

Bit 6 (MIN2) = 0, PWM2 is off (0% PWM duty cycle) when

the temperature is below TMIN −THYST.

Bit 6 (MIN2) = 1, PWM2 runs at PWM2 minimum duty

cycle below TMIN −THYST.

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Bit 5 (MIN1) = 0, PWM1 is off (0% PWM duty cycle) when

the temperature is below TMIN −THYST.

Bit 5 (MIN1) = 1, PWM1 runs at PWM1 minimum duty

cycle below TMIN −THYST.

Configuration Register 6 (Register 0x10)

Bit 0 (SLOW) = 1, slows the ramp rate for PWM changes

associated with the Remote 1 temperature channel by 4.

Bit 1 (SLOW) = 1, slows the ramp rate for PWM changes

associated with the local temperature channel by 4.

Bit 2 (SLOW) = 1, slows the ramp rate for PWM changes

associated with the Remote 2 temperature channel by 4.

Bit 7 (ExtraSlow) = 1, slows the ramp rate for all fans by a

factor of 39.2%.

The following sections list the ramp-up times when the

SLOW bit is set for each temperature monitoring channel.

Enhanced Acoustics Register 1 (Register 0x62)

Bits [2:0] ACOU, selects the ramp rate for PWM outputs

associated with the Remote Temperature 1 input.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

Enhanced Acoustics Register 2 (Register 0x63)

Bits [2:0] ACOU3, selects the ramp rate for PWM outputs

associated with the local temperature channel.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

[6:4] ACOU2, selects the ramp rate for PWM outputs

associated with the Remote Temperature 2 input.

000 = 37.5 sec

001 = 18.8 sec

010 = 12.5 sec

011 = 7.5 sec

100 = 4.7 sec

101 = 3.1 sec

110 = 1.6 sec

111 = 0.8 sec

When Bit 7 of Configuration Register 6 (0x10) = 1, the

preceding ramp rates change to

000 = 52.2 sec

001 = 26.1 sec

010 = 17.4 sec

011 = 10.4 sec

100 = 6.5 sec

101 = 4.4 sec

110 = 2.2 sec

111 = 1.1 sec

Setting the appropriate SLOW Bit 2, Bit 1, or Bit 0 of

Configuration Register 6 (0x10) slows the ramp rate further

by a factor of 4.

Programming the GPIOs

The ADT7490 has two dedicated GPIOs (Pin 5 and

Pin 6).The direction (input or output) and polarity (active

high or active low) of the GPIOs is set in the GPIO

Configuration Register (0x80). Bit 2 and Bit 3 of

configured as inputs and assert the GPIO pins when

configured as outputs.

XNOR Tree Test Mode

The ADT7490 includes an XNOR tree test mode. This

mode is useful for in-circuit test equipment at board-level

testing. By applying stimulus to the pins included in the

XNOR tree, it is possible to detect opens, or shorts, on the

system board.

The XNOR tree test is invoked by setting Bit 0 (XEN) of

the XNOR Tree Test Enable register (Register 0x6F).

Figure 61 shows the signals that are exercised in the

XNOR tree test mode.

Figure 61. XNOR Tree Test

PWM2

TACH1

TACH2

TACH3

TACH4 PWM1/XTO

PWM3

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Table 44. ADT7490 REGISTERS

Addr R/W Desc Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0

De-

fault

Lock-

able

0x10 R/W Config.

Reg. 6

Extra

Slow

VCCP

Low

Res Res Res SLOW

Remote

SLOW

Local

SLOW

Remote

0x00 Yes

0x11 R/W Config.

Reg. 7

RES RES RES TODIS FSPDIS Vx1 FSPD THERM

Hys

0x00 Yes

0x12 RExtended

Revision

RES RES RES RES RES RES RES − − −

0x1A RPECI1 7 6 5 4 3 2 1 0 0x80 −

0x1B RPECI2 7 6 5 4 3 2 1 0 0x80 −

0x1C RPECI3 7 6 5 4 3 2 1 0 0x80 −

0x1D R IMON

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x1E R VTT

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x1F RExtended

Resolution

IMON IMON VTT VTT RES RES RES RES 0x00 −

0x20 R+2.5VIN

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x21 R VCCP

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x22 R VCC

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x23 R+5VIN

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x24 R+12VIN

Meas.

9 8 7 6 5 4 3 2 0x00 −

0x25 RRemote 1

Temp .

9 8 7 6 5 4 3 2 0x80 −

0x26 RLocal

Temp .

9 8 7 6 5 4 3 2 0x80 −

0x27 RRemote 2

Temp .

9 8 7 6 5 4 3 2 0x80 −

0x28 RTACH1

Low Byte

7 6 5 4 3 2 1 0 0x00 −

0x29 RTACH1

High Byte

15 14 13 12 11 10 9 8 0x00 −

0x2A RTACH2

Low Byte

7 6 5 4 3 2 1 0 0x00 −

0x2B RTACH2

High Byte

15 14 13 12 11 10 9 8 0x00 −

0x2C RTACH3

Low Byte

7 6 5 4 3 2 1 0 0x00 −

0x2D RTACH3

High Byte

15 14 13 12 11 10 9 8 0x00 −

0x2E RTACH4

Low Byte

7 6 5 4 3 2 1 0 0x00 −

0x2F RTACH4

High Byte

15 14 13 12 11 10 9 8 0x00 −

0x30 R/W PWM1

Current

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF −

0x31 R/W PWM2

Current

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF −

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Table 44. ADT7490 REGISTERS (continued)

Addr

Lock-

able

De-

fault

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 7DescR/W

0x32 R/W PWM3

Current

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF −

0x33 RPECI0 7 6 5 4 3 2 1 0 0x80 −

0x34 R/W PECI Low

Limit

7 6 5 4 3 2 1 0 0x81 −

0x35 R/W PECI

High Limit

7 6 5 4 3 2 1 0 0x00 −

0x36 R/W PECI

Config.

RES RES RES RE−

PLACE

DOM0 AVG2 AVG1 AVG0 0x00 Yes

0x38 R/W Max

PWM1

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF Yes

0x39 R/W Max

PWM2

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF Yes

0x3A R/W Max

PWM3

Duty

Cycle

7 6 5 4 3 2 1 0 0xFF Yes

0x3B R/W PECI

TMIN

7 6 5 4 3 2 1 0 0xE0 Yes

0x3C R/W PECI

TRANGE/

Enhanced

Acoustics

RANGE RANGE RANGE RANGE ENP ACOU ACOU ACOU 0xC0 Yes

0x3D R/W PECI

TCONTROL

Limit

7 6 5 4 3 2 1 0 0x00 Yes

0x3E RCompany

ID No.

7 6 5 4 3 2 1 0 0x41 −

0x3F RVersion VER3 VER2 VER1 VER0 4−Wire PECI REV1 REV0 0x06X −

0x40 R/W Config.

RES RES THERM

Manual

PECI

Monitor

Fan

Boost

RDY LOCK STRT 0x04 Yes

0x41 RInterrupt

Status 1

OOL R2T LT R1T +5VIN VCC VCCP +2.5VIN/

THERM

0x00 −

0x42 RInterrupt

Status 2

FAULT

FAN4/

THERM

FAN3 FAN2 FAN1 OOL +12VIN 0x00 −

0x43 RInterrupt

Status 3

OOL RES RES RES OVT

(THERM

Temp

Limit)

COMM DATA PECI0 0x00 −

0x44 R/W +2.5VIN

Low Limit

7 6 5 4 3 2 1 0 0x00 −

0x45 R/W +2.5VIN

High Limit

7 6 5 4 3 2 1 0 0xFF −

0x46 R/W VCCP

Low Limit

7 6 5 4 3 2 1 0 0x00 −

0x47 R/W VCCP

High Limit

7 6 5 4 3 2 1 0 0xFF −

0x48 R/W VCC

Low Limit

7 6 5 4 3 2 1 0 0x00 −

0x49 R/W VCC

High Limit

7 6 5 4 3 2 1 0 0xFF −

0x4A R/W +5VIN

Low Limit

7 6 5 4 3 2 1 0 0x00 −

0x4B R/W +5VIN

High Limit

7 6 5 4 3 2 1 0 0xFF −

ADT7490

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Table 44. ADT7490 REGISTERS (continued)

Addr

Lock-

able

De-

fault

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 7DescR/W

0x4C R/W +12VIN

Low Limit

7 6 5 4 3 2 1 0 0x00 −

0x4D R/W +12VIN

High Limit

7 6 5 4 3 2 1 0 0xFF −

0x4E R/W Remote 1

Temp Lo w

Limit

7 6 5 4 3 2 1 0 0x81 −

0x4F R/W Remote 1

Temp

High Limit

7 6 5 4 3 2 1 0 0x7F −

0x50 R/W Local

Temp Lo w

Limit

7 6 5 4 3 2 1 0 0x81 −

0x51 R/W Local

Temp

High Limit

7 6 5 4 3 2 1 0 0x7F −

0x52 R/W Remote 2

Temp Lo w

Limit

7 6 5 4 3 2 1 0 0x81 −

0x53 R/W Remote 2

Temp

High Limit

7 6 5 4 3 2 1 0 0x7F −

0x54 R/W TACH1

Min Low

Byte

7 6 5 4 3 2 1 0 0xFF −

0x55 R/W TACH1

Min High

Byte

15 14 13 12 11 10 9 8 0xFF −

0x56 R/W TACH2

Min Low

Byte

7 6 5 4 3 2 1 0 0xFF −

0x57 R/W TACH2

Min High

Byte

15 14 13 12 11 10 9 8 0xFF −

0x58 R/W TACH3

Min Low

Byte

7 6 5 4 3 2 1 0 0xFF −

0x59 R/W TACH3

Min High

Byte

15 14 13 12 11 10 9 8 0xFF −

0x5A R/W TACH4

Min Low

Byte

7 6 5 4 3 2 1 0 0xFF −

0x5B R/W TACH4

Min High

Byte

15 14 13 12 11 10 9 8 0xFF −

0x5C R/W PWM1

Config.

BHVR BHVR BHVR INV ALT SPIN SPIN SPIN 0x62 Yes

0x5D R/W PWM2

Config.

BHVR BHVR BHVR INV ALT SPIN SPIN SPIN 0x62 Yes

0x5E R/W PWM3

Config.

BHVR BHVR BHVR INV ALT SPIN SPIN SPIN 0x62 Yes

0x5F R/W Remote 1

TRANGE/

PWM1

Frequency

RANGE RANGE RANGE RANGE HF/LF FREQ FREQ FREQ 0xC4 Yes

0x60 R/W Local

TRANGE/P

WM2

Frequency

RANGE RANGE RANGE RANGE HF/LF FREQ FREQ FREQ 0xC4 Yes

0x61 R/W Remote 2

TRANGE/P

WM3

Frequency

RANGE RANGE RANGE RANGE HF/LF FREQ FREQ FREQ 0xC4 Yes

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Table 44. ADT7490 REGISTERS (continued)

Addr

Lock-

able

De-

fault

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 7DescR/W

0x62 R/W Enhanced

Acoustics

Reg. 1

MIN3 MIN2 MIN1 SYNC EN1 ACOU ACOU ACOU 0x00 Yes

0x63 R/W Enhanced

Acoustics

Reg. 2

EN2 ACOU2 ACOU2 ACOU2 EN3 ACOU3 ACOU3 ACOU3 0x00 Yes

0x64 R/W PWM1

Min Duty

Cycle

7 6 5 4 3 2 1 0 0x80 Yes

0x65 R/W PWM2

Min Duty

Cycle

7 6 5 4 3 2 1 0 0x80 Yes

0x66 R/W PWM3

Min Duty

Cycle

7 6 5 4 3 2 1 0 0x80 Yes

0x67 R/W Remote 1

Temp .

TMIN

7 6 5 4 3 2 1 0 0x5A Yes

0x68 R/W Local

Temp .

TMIN

7 6 5 4 3 2 1 0 0x5A Yes

0x69 R/W Remote 2

Temp .

TMIN

7 6 5 4 3 2 1 0 0x5A Yes

0x6A R/W Remote 1

THERM

Temp .

Limit

7 6 5 4 3 2 1 0 0x64 Yes

0x6B R/W Local

THERM

Temp .

Limit

7 6 5 4 3 2 1 0 0x64 Yes

0x6C R/W Remote 2

THERM

Temp .

Limit

7 6 5 4 3 2 1 0 0x64 Yes

0x6D R/W Remote 1

and Local

Temp . /

TMIN

Hysteresis

HYSR1 HYSR1 HYSR1 HYSR1 HYSL HYSL HYSL HYSL 0x44 Yes

0x6E R/W Remote 2

and PECI

Temp . /

TMIN

Hysteresis

HYSR2 HYSR2 HYSR2 HYSR2 HYSP HYSP HYSP HYSP 0x44 Yes

0x6F R/W XNOR

Tree Test

Enable

RES RES RES RES RES RES RES XEN 0x00 Yes

0x70 R/W Remote 1

Temp

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x71 R/W Local

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x72 R/W Remote 2

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x73 R/W Config.

Reg. 2

Shutdo

CONV ATTN AVG Fan3

Detect

Fan2

Detect

Fan1

Detect

Fan

PresDT

0x00 Yes

0x74 R/W Interrupt

Mask

Reg. 1

OOL R2T LT R1T +5VIN VCC VCCP +2.5VIN/

THERM

0x00 −

0x75 R/W Interrupt

Mask

Reg. 2

FAULT

FAN4/

THERM

FAN3 FAN2 FAN1 OOL +12VIN/

0x00 −

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Table 44. ADT7490 REGISTERS (continued)

Addr

Lock-

able

De-

fault

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 7DescR/W

0x76 RExtended

Resolution

+5VIN +5VIN VCC VCC VCCP VCCP +2.5VIN +2.5VIN 0x00 −

0x77 RExtended

Resolution

TDM2 TDM2 LTMP LTMP TDM1 TDM1 +12VIN +12VIN 0x00 −

0x78 R/W Config.

Reg. 3

DC4 DC3 DC2 DC1 FAST BOOST THERM/

+2.5VIN

ALERT

Enable

0x00 Yes

0x79 RTHERM

Timer

Status

TMR TMR TMR TMR TMR TMR TMR ASRT/

TMR0

0x00 −

0x7A R/W THERM

Timer

Limit

LIMT LIMT LIMT LIMT LIMT LIMT LIMT LIMT 0x00 −

0x7B R/W TACH

Pulses per

Revolution

FAN4 FAN4 FAN3 FAN3 FAN2 FAN2 FAN1 FAN1 0x55 −

0x7C R/W Config.

THERM

Output

Only

Local

THERM

Output

Only

THERM

Output

Only

PECI

THERM

Output

Only

RES RES Te m p

Offset

TWOS

COMPL

0x01 Yes

0x7D R/W Config.

BpAtt

+12VIN

BpAtt

+5VIN

BpAtt

VCCP

BpAtt

+2.5VIN

Max/Full

THERM

Disable

Pin 14

Func

Pin 14

Func

0x00 Yes

0x7E RTes t 1 DO NOT WRITE TO THIS REGISTER 0x00 Yes

0x7F RTes t 2 DO NOT WRITE TO THIS REGISTER 0x00 Yes

0x80 R/W GPIO

Config.

GPIO1

DIR

GPIO2

DIR

GPIO1

POL

GPIO2

POL

GPIO1 GPIO2 RES RES 0x00 −

0x81 RInterrupt

Status 4

VTT IMON PECI3 PECI2 PECI1 RES RES RES 0x00 −

0x82 R/W Interrupt

Mask 3

OOL RES RES RES OVT COMM DATA PECI0 0x00 −

0x83 R/W Interrupt

Mask 4

VTT IMON PECI3 PECI2 PECI1 RES RES RES 0x00 −

0x84 R/W VTT Low

Limit

7 6 5 4 3 2 1 0 0x00 Yes

0x85 R/W IMON Low

Limit

7 6 5 4 3 2 1 0 0x00 Yes

0x86 R/W VTT High

Limit

7 6 5 4 3 2 1 0 0xFF Yes

0x87 R/W IMON High

Limit

7 6 5 4 3 2 1 0 0xFF Yes

0x88 R/W PECI

Config. 2

#CPU #CPU DOM1 DOM2 DOM3 RES RES RES 0x00 Yes

0x89 RTEST 3 DO NOT WRITE TO THIS REGISTER 0x00 Yes

0x8A R/W PECI

Operating

Point

7 6 5 4 3 2 1 0 0xFB Yes

0x8B R/W Remote 1

Operating

Point

7 6 5 4 3 2 1 0 0x64 Yes

0x8C R/W Local

Temp .

Operating

Point

7 6 5 4 3 2 1 0 0x64 Yes

0x8D R/W Remote 2

Operating

Point

7 6 5 4 3 2 1 0 0x64 Yes

0x8E R/W Dynamic

TMIN

Control

Reg. 1

R2T LT R1T PHTR2 PHTL PHTR1 VCCPLO CYR2 0x00 Yes

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Table 44. ADT7490 REGISTERS (continued)

Addr

Lock-

able

De-

fault

Bit 0Bit 1Bit 2Bit 3Bit 4Bit 5Bit 6Bit 7DescR/W

0x8F R/W Dynamic

TMIN

Control

Reg. 2

CYR2 CYR2 CYL CYL CYL CYR1 CYR1 CYR1 0x00 Yes

0x90 R/W Dynamic

TMIN

Control

Reg. 3

PECI PHTP CYP CYP CYP RES RES RES 0x00 Yes

0x94 R/W PECI0

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x95 R/W PECI1

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x96 R/W PECI2

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

0x97 R/W PECI3

Temp .

Offset

7 6 5 4 3 2 1 0 0x00 Yes

−0x41 − − 0x74 OOL R2T LT R1T +5VIN VCC VCCP +2.5VIN/

THERM

Table 45. REGISTER 0x10 − CONFIGURATION REGISTER 6 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[0] SLOW

Remote 1

R/W When this bit is set, fan smoothing times are multiplied x4 for Remote 1 temperature channel

(as defined in Register 0x62).

[1] SLOW

Local

R/W When this bit is set, fan smoothing times are multiplied x4 for local temperature channel

(as defined in Register 0x63).

[2] SLOW

Remote 2

R/W When this bit is set, fan smoothing times are multiplied x4 for Remote 2 temperature channel

(as defined in Register 0x63).

[3] Res N/A Reserved

[4] Res N/A Reserved

[5] Res N/A Reserved

[6] VCCP Low R/W VCCP Low = 1. When the power is supplied from 3.3 V STANDBY and the core voltage

(VCCP) drops below its VCCP low limit value (Register 0x46), the following occurs:

Status Bit 1 in Status Register 1 is set.

SMBALERT is generated, if enabled.

PROCHOT monitoring is disabled.

Everything is re-enabled once VCCP increases above the VCCP low limit.

When VCCP increases above the low limit:

PROCHOT monitoring is enabled.

Fans return to their programmed state after a spin-up cycle.

[7] ExtraSlow R/W When this bit is set, all fan smoothing times are increased by a further 39.2%

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

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Table 46. REGISTER 0x11 − CONFIGURATION REGISTER 7 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[0] THERMHys R/W THERM hysteresis is enabled by default. Setting this bit to 1 disables THERM hysteresis.

[1] FSPD R/W When set to 1, this bit runs all fans at maximum speed as programmed in the maximum PWM

duty cycle registers (0x38 to 0x3A). Power-on default = 0. This bit is not locked at any time.

[2] Vx1 R/W BIOS should set this bit to 1 when the ADT7490 is configured to measure current from an

Analog Devices ADOPT VRM controller and to measure the CPU core voltage. This bit

allows monitoring software to display CPU watts usage. (Lockable.)

[3] FSPDIS R/W Logic 1 disables fan spin-up for two TACH pulses. Instead, the PWM outputs go high for the

entire fan spin-up timeout selected.

[4] TODIS R/W When this bit is set to 1, the SMBus timeout feature is disabled. In this state, if at any point

during an SMBus transaction involving the ADT7490 activity ceases for more than 35 ms, the

ADT7490 assumes the bus is locked and releases the bus. This allows the ADT7490 to be

used with SMBus controllers that cannot handle SMBus timeouts. (Lockable.)

[7:5] RES N/A Reserved. Do not write to these bits.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

Table 47. PECI READING REGISTERS (POWER-ON DEFAULT = 0x80)

0x33 Read-only PECI0: This Register Reads the Eight Bits Representative of PECI Client Address 0x30

0x1A Read-only PECI1: This Register Reads the Eight Bits Representative of PECI Client Address 0x31

0x1B Read-only PECI2: This Register Reads the Eight Bits Representative of PECI Client Address 0x32

0x1C Read-only PECI3: This Register Reads the Eight Bits Representative of PECI Client Address 0x33

Table 48. IMON/VTT READING REGISTERS (POWER-ON DEFAULT = 0x00)

0x1D Read-only Reflects the voltage measurement at the IMON input on Pin 19 (8 MSBs of reading). Input

range of 0 V to 2.25 V.

0x1E Read-only Reflects the voltage measurement at the VTT input on Pin 8 (8 MSBs of reading). Input range

of 0 V to 2.25 V.

Table 49. REGISTER 0x1F − EXTENDED RESOLUTION 3 (POWER-ON DEFAULT = 0x00)

Bit No. R/W Description

[3:0] Read-only Reserved

[5:4] Read-only Hold the Two LSBs of the 10-bit VTT Measurement

[7:6] Read-only Hold the Two LSBs of the 10-bit IMON Measurement

Table 50. VOLTAGE READING REGISTERS (POWER-ON DEFAULT = 0x00) (Note 1)

0x20 Read-only Reflects the Voltage Measurement at the 2.5 VIN Input on Pin 22 (8 MSBs of Reading)

0x21 Read-only Reflects the Voltage Measurement (Note 2) at the VCCP Input on Pin 23 (8 MSBs of Reading)

0x22 Read-only Reflects the Voltage Measurement (Note 3) at the VCC Input on Pin 4 (8 MSBs of Reading)

0x23 Read-only Reflects the Voltage Measurement at the 5 VIN Input on Pin 20 (8 MSBs of Reading)

0x24 Read-only Reflects the Voltage Measurement at the 12 VIN Input on Pin 21 (8 MSBs of Reading)

1. If the extended resolution bits of these readings are also being read, the extended resolution registers (Register 0x76, Register 0x77) must

be read first. Once the extended resolution registers have been read, the associated MSB reading registers are frozen until read. Both the

extended resolution registers and the MSB registers are frozen.

2. If VCCP Low (Bit 6 of 0x10) is set, VCCP can control the sleep state of the ADT7490.

3. VCC (Pin 4) is the supply voltage for the ADT7490.

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Table 51. TEMPERATURE READING REGISTERS (POWER-ON DEFAULT = 0x80) (Note 1 and 2)

0x25 Read-only Remote 1 Temperature Reading (Note 3 and 4) (8 MSBs of Reading)

0x26 Read-only Local Temperature Reading (8 MSBs of Reading)

0x27 Read-only Remote 2 Temperature Reading (Note 3 and 4) (8 MSBs of Reading)

1. If the extended resolution bits of these readings are also being read, the extended resolution registers (Register 0x76, Register 0x77) must

be read first. Once the extended resolution registers have been read, all associated MSB reading registers are frozen until read. Both the

extended resolution registers and the MSB registers are frozen.

2. These temperature readings can be in twos complement or Offset 64 format; this interpretation is determined by Bit 0 of Configuration

3. In twos complement mode, a temperature reading of −128C (0x80) indicates a diode fault (open or short) on that channel.

4. In Offset 64 mode, a temperature reading of −64C (0x00) indicates a diode fault (open or short) on that channel.

Table 52. FAN TACHOMETER READING REGISTERS (POWER-ON DEFAULT = 0x00) (Note 1)

0x28 Read-only TACH1 Low Byte

0x29 Read-only TACH1 High Byte

0x2A Read-only TACH2 Low Byte

0x2B Read-only TACH2 High Byte

0x2C Read-only TACH3 Low Byte

0x2D Read-only TACH3 High Byte

0x2E Read-only TACH4 Low Byte

0x2F Read-only TACH4 High Byte

1. These registers count the number of 11.11Ăms periods (based on an internal 90ĂkHz clock) that occur between a number of consecutive fan TACH

pulses (defaultĂ=Ă2). The number of TACH pulses used to count can be changed using the TACH Pulses per Revolution register (RegisterĂ0x7B).

This allows the fan speed to be accurately measured. Because a valid fan tachometer reading requires that two bytes be read, the low byte must

be read first. Both the low and high bytes are then frozen until read. At power-on, these registers contain 0x0000 until the first valid fan TACH

measurement is read into these registers. This prevents false interrupts from occurring while the fans are spinning up. A count of 0xFFFF

indicates that a fan is one of the following: stalled or blocked (object jamming the fan), failed (internal circuitry destroyed), or not populated. (The

ADT7490 expects to see a fan connected to each TACH. If a fan is not connected to that TACH, its TACH minimum high and low bytes should

be set to 0xFFFF.) An alternate function, for example, is TACH4 reconfigured as the THERM pin.

Table 53. CURRENT PWM DUTY CYCLE REGISTERS (POWER-ON DEFAULT = 0xFF) (Note 1)

0x30 R/W PWM1 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)

0x31 R/W PWM2 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)

0x32 R/W PWM3 Current Duty Cycle (0% to 100% Duty Cycle = 0x00 to 0xFF)

1. These registers reflect the PWM duty cycle driving each fan at any given time. When in automatic fan speed control mode, the ADT7490

reports the PWM duty cycles back through these registers. The PWM duty cycle values vary according to temperature in automatic fan speed

control mode. During fan startup, these registers report back 0x00. In manual mode, the PWM duty cycle outputs can be set to any duty cycle

value by writing to these registers.

Table 54. REGISTER 0x33 − PECI0 READING REGISTER (POWER-ON DEFAULT = 0x80)

0x33 Read-only PECI0: This Register Reads the Eight Bits Representative of PECI Client Address 0x30

Table 55. PECI LIMIT REGISTERS

0x34 R/W PECI Low Limit 0x81

0x35 R/W PECI High Limit 0x00

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Table 56. REGISTER 0x36 − PECI CONFIGURATION REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] AVG[2:0] R/W PECI Smoothing Interval. These bits set the duration over which smoothing is carried out on

the PECI data read. Note that the PECI smoothing interval is equal to the PECI register

update interval. The smoothing interval is calculated using the following formula:

Smooth Interval = #reads  (tBIT  67  #CPU + tIDLE)

where:

#reads is the number of readings defined below.

tBIT is the negotiated bit rate.

67 is the number of bits in each PECI reading.

#CPU is the number of CPUs providing PECI data (1 to 4).

tIDLE = 14 ms, the delay between consecutive reads.

Bit Code Number of PECI Readings

000 16

001 2048

010 4096

011 8192

100 16384

101 32768

110 65536

111 Reserved

[3] DOM0 R/W CPU Domain Count information. Set to 0 indicates that CPU 1 associated with the PECI0

reading has a single domain (default). Set to 1 indicates that the system CPU 1 contains two

domains.

[4] REPLACE R/W If this bit is set to 0, it indicates that the ADT7490 is operating in standard mode. If this bit is

set to 1, the Remote 1 Temperature register (Register 0x25) is overwritten by PECI0

information (Register 0x33) and vice versa. Note that in this mode, all associated user

programmable limit and fan control registers are also swapped and should be programmed in

the appropriate PECI or absolute temperature format.

[7:5] RES R Reserved

1. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to these

registers fail.

Table 57. MAXIMUM PWM DUTY CYCLE (POWER-ON DEFAULT = 0xFF) (Note 1)

0x38 R/W Maximum Duty Cycle for PWM1 Output, Default = 100% (0xFF)

0x39 R/W Maximum Duty Cycle for PWM2 Output, Default = 100% (0xFF)

0x3A R/W Maximum Duty Cycle for PWM3 Output, Default = 100% (0xFF)

1. These registers set the maximum PWM duty cycle of the PWM output.

2. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to these

registers fail.

Table 58. PECI TMIN REGISTER (POWER-ON DEFAULT = 0xE0, VALUE = −32)

0x3B R/W PECI TMIN. When the PECI measurement exceeds PECI TMIN, the appropriate fans run at

PWMMIN and increase according to the automatic fan speed control slope.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set. Any further attempts to write to this register have

no effect.

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Table 59. REGISTER 0x3C − PECI TRANGE/ENHANCED ACOUSTICS REGISTER (POWER-ON DEFAULT = 0xC0)

Bit No. Mnemonic

R/W

(Note 1) Description

[2:0] ACOU R/W Assuming that PWMx is associated with the PECI channel, these bits define the maximum

rate of change of the PWMx output for PECI temperature-related changes. Instead of the fan

speed jumping instantaneously to its newly determined speed, it ramps gracefully at the rate

determined by these bits. This feature ultimately enhances the acoustics of the fan. The

smoothing times below are based on a refresh rate of the round robin cycle. The PECI data,

for 0% to 100%, must be multiplied each time by:

PECI Refresh Rate

Round Robin Cycle

where the PECI refresh rate is defined in Register 0x36 and the round robin cycle is typically

165 ms.

When Bit 7 of Configuration Register 6 (0x10) is 0

Bit Code Time for 0% to 100%

000 = 1 37.5 sec

001 = 2 18.8 sec

010 = 3 12.5 sec

011 = 4 7.5 sec

100 = 8 4.7 sec

101 = 12 3.1 sec

110 = 24 1.6 sec

111 = 48 0.8 sec

When Bit 7 of Configuration Register 6 (0x10) is 1

Bit Code Time for 0% to 100%

000 = 1 52.2 sec

001 = 2 26.1 sec

010 = 3 17.4 sec

011 = 4 10.4 sec

100 = 8 6.5 sec

101 = 12 4.4 sec

110 = 24 2.2 sec

111 = 48 1.1 sec

[3] ENP R/W When this bit is set to 1, smoothing is enabled on the PECI channel allowing enhanced

acoustics on the associated PWM output.

[7:4] RANGE R/W These bits determine the PWM duty cycle vs. the temperature range for automatic fan

control.

Bit Code Temperature

0000 2C

0001 2.5C

0010 3.33C

0011 4C

0100 5C

0101 6.67C

0110 8C

0111 10C

1000 13.33C

1001 16C

1010 20C

1011 26.67C

1100 32C (Default)

1101 40C

1110 53.33C

1111 80C

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

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Table 60. TCONTROL LIMIT REGISTER (POWER-ON DEFAULT = 0x00) (Note 1)

0x3D R/W PECI TCONTROL Limit

1. If any PECI reading exceeds the TCONTROL limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism

incorporated to cool the system in the event of a critical overtemperature. It also ensures some level of cooling in the event that software

or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below

TCONTROL limit −hysteresis.

2. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 61. REGISTER 0x3F − VERSION REGISTER

Bit No. Mnemonic R/W Description

[1:0] REV[1:0] Read-only These two bits indicate the ADT7490 silicon revision number. 0x00 indicates Revision 0,

0x01 indicates Revision 1, and so on. 0x11 indicates that further revision information can be

found in the “Extended Revision” register (0x12). The revision number is then found by

adding 0x11 to the contents of the extended revision register.

[2] PECI Read-only This bit is set to 1 indicating that the ADT7490 supports the PECI interface.

[3] 4-wire Read-only This bit is set to 1 indicating that the ADT7490 may be configured to drive 4-wire fans using

high frequency PWM.

[7:4] VER[3:0] Read-only These bits indicate the version number of the device. This is set to 6, indicating that the

ADT7490 is part of the Heceta 6 ASIC family.

Table 62. REGISTER 0x40 − CONFIGURATION REGISTER 1 (POWER-ON DEFAULT = 0x04)

Bit No. Mnemonic R/W (Note 1) Description

[0] STRT

(Notes 2, 3)

R/W Logic 1 enables monitoring and PWM control outputs based on the limit settings

programmed. Logic 0 disables monitoring and PWM control is based on the default powerup

limit settings. Note that the limit values programmed are preserved even if a Logic 0 is written

to this bit and the default settings are enabled. This bit does not become locked once Bit 1

(Lock bit) is set.

[1] LOCK Write once Logic 1 locks all limit values to their current settings. Once this bit is set, all lockable registers

become read-only and cannot be modified until the ADT7490 is powered down and powered

up again. This prevents rogue programs such as viruses from modifying critical system limit

settings. (Lockable.)

[2] RDY Read-only This bit is set to 1 by the ADT7490 to indicate that the device is fully powered up and ready

to begin system monitoring.

[3] Fan Boost R/W When this bit is set to Logic 1, all PWM outputs go to 100% regardless of other fan speed

configurations and automatic fan speed control settings. When this bit is set to 0, the fan

speed control returns to the fan speed setting calculated by the preprogrammed fan speed

control settings. This bit remains writable after the Lock bit is set.

[4] PECI

Monitor

R/W Set this bit to Logic 1 to enable CPU thermal monitoring via PECI interface. This bit becomes

read-only when the Lock bit is set.

[5] THERM in

Manual

R/W When this bit is set to Logic 1, THERM is enabled so that the fans go to 100% duty cycle on a

THERM or TCONTROL assertion overriding any other fan setting, even when the PWMs are

configured for manual mode, or disabled. This bit becomes read-only when the Lock bit is set.

[7:6] RES Read-only Reserved.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

2. Bit 0 (STRT) of Configuration Register 1 (0x40) remains writable after the Lock bit is set.

3. When monitoring (STRT) is disabled, PWM outputs always go to 100% for thermal protection.

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Table 63. REGISTER 0x41 − INTERRUPT STATUS REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] +2.5 VIN/

THERM

Read-only +2.5 VIN = 1 indicates that the 2.5 VIN high or low limit has been exceeded. This bit is cleared

on a read of the status register only if the error condition has subsided. If Pin 22 is configured

as THERM, this bit is asserted when the timer limit has been exceeded.

[1] VCCP Read-only VCCP = 1 indicates that the VCCP high or low limit has been exceeded. This bit is cleared on

a read of the status register only if the error condition has subsided.

[2] VCC Read-only VCC = 1 indicates that the VCC high or low limit has been exceeded. This bit is cleared on a

read of the status register only if the error condition has subsided.

[3] +5 VIN Read-only +5 VIN = 1 indicates that the 5 VIN high or low limit has been exceeded. This bit is cleared on

a read of the status register only if the error condition has subsided.

[4] R1T Read-only R1T = 1 indicates that the Remote 1 low or high temperature has been exceeded. This bit is

cleared on a read of the status register only if the error condition has subsided.

[5] LT Read-only LT = 1 indicates that the local low or high temperature has been exceeded. This bit is cleared

on a read of the status register only if the error condition has subsided.

[6] R2T Read-only R2T = 1 indicates that the Remote 2 low or high temperature has been exceeded. This bit is

cleared on a read of the status register only if the error condition has subsided.

[7] OOL Read-only OOL = 1 indicates that an out-of-limit event has been latched in Interrupt Status Register 2

(0x42). This bit is a logical OR of all status bits in Interrupt Status Register 2. Software can

test this bit in isolation to determine whether any of the voltage, temperature, or fan speed

readings represented by Interrupt Status Register 2 are out-of-limit, which eliminates the

need to read Interrupt Status Register 2 during every interrupt or polling cycle.

Table 64. REGISTER 0x42 − INTERRUPT STATUS REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] +12 VIN Read-only +12 VIN = 1 indicates that the 12 VIN high or low limit has been exceeded. This bit is cleared

on a read of the status register only if the error condition has subsided.

[1] OOL Read-only OOL = 1 indicates that an out-of-limit event has been latched in Interrupt Status Register 3

(0x43). This bit is a logical OR of all status bits in Interrupt Status Register 3. Software can

test this bit in isolation to determine whether any of the voltage, temperature, or fan speed

readings represented by Interrupt Status Register 3 are out-of-limit, which eliminates the

need to read Interrupt Status Register 3 during every interrupt or polling cycle.

[2] FAN1 Read-only FAN1 = 1 indicates that Fan 1 has dropped below minimum speed or has stalled. This bit is

not set when the PWM1 output is off.

[3] FAN2 Read-only FAN2 = 1 indicates that Fan 2 has dropped below minimum speed or has stalled. This bit is

not set when the PWM2 output is off.

[4] FAN3 Read-only FAN3 = 1 indicates that Fan 3 has dropped below minimum speed or has stalled. This bit is

not set when the PWM3 output is off.

[5] FAN4/

THERM

Read-only When Pin 14 is programmed as a TACH4 input, FAN4 = 1 indicates that Fan 4 has dropped

below minimum speed or has stalled. This bit is not set when the PWM3 output is off.

If Pin 14 is configured as the THERM timer input for THERM monitoring, this bit is set when

the THERM assertion time exceeds the limit programmed in the THERM timer limit register

(Register 0x7A).

[6] D1 FAULT Read-only D1 FAULT = 1 indicates either an open or short circuit on the Thermal Diode 1 inputs.

[7] D2 FAULT Read-only D2 FAULT = 1 indicates either an open or short circuit on the Thermal Diode 2 inputs.

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Table 65. REGISTER 0x43 − INTERRUPT STATUS REGISTER 3 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] PECI0 Read-only A Logic 1 indicates that the PECI high or low limit has been exceeded by the PECI value

from PECI Client Address 0x30. This bit is cleared on a read of the status register only if the

error condition has subsided.

[1] DATA Read-only A Logic 1 indicates that valid PECI data cannot be obtained for the processor and a specified

error code has been recorded.

[2] COMM Read-only A Logic 1 indicates that there is a communications error (for example, invalid FCS) on the

PECI interface.

[3] OVT

(THERM

Temp Limit)

Read-only OVT = 1 indicates that one of the THERM overtemperature limits has been exceeded. This bit

is cleared on a read of the status register when the temperature drops below THERM −THYST

[6:4] RES Read-only Reserved

[7] OOL Read-only OOL = 1 indicates that an out-of-limit event has been latched in Interrupt Status Register 4

(0x81). This bit is a logical OR of all status bits in Interrupt Status Register 4. Software can

test this bit in isolation to determine whether any of the voltage, temperature, or fan speed

readings represented by Interrupt Status Register 4 are out-of-limit, which eliminates the need

to read Interrupt Status Register 4 during every interrupt or polling cycle.

Table 66. VOLTAGE LIMIT REGISTERS (Note 1)

0x44 R/W +2.5 VIN Low Limit 0x00

0x45 R/W +2.5 VIN High Limit 0xFF

0x46 R/W VCCP Low Limit 0x00

0x47 R/W VCCP High Limit 0xFF

0x48 R/W VCC Low Limit 0x00

0x49 R/W VCC High Limit 0xFF

0x4A R/W +5 VIN Low Limit 0x00

0x4B R/W +5 VIN High Limit 0xFF

0x4C R/W +12 VIN Low Limit 0x00

0x4D R/W +12 VIN High Limit 0xFF

1. Setting the Configuration Register 1 (0x40) Lock bit has no effect on these registers.

2. High limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low limits: An interrupt is generated when a value

is equal to or below its low limit (comparison).

Table 67. TEMPERATURE LIMIT REGISTERS (Note 1)

0x4E R/W Remote 1 Temperature Low Limit 0x81

0x4F R/W Remote 1 Temperature High Limit 0x7F

0x50 R/W Local Temperature Low Limit 0x81

0x51 R/W Local Temperature High Limit 0x7F

0x52 R/W Remote 2 Temperature Low Limit 0x81

0x53 R/W Remote 2 Temperature High Limit 0x7F

1. Exceeding any of these temperature limits by 1C causes the appropriate status bit to be set in the interrupt status register. Setting the

Configuration Register 1 (0x40) Lock bit has no effect on these registers.

2. High limits: An interrupt is generated when a value exceeds its high limit (> comparison). Low limits: An interrupt is generated when a value

is equal to or below its low limit (comparison).

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Table 68. FAN TACHOMETER LIMIT REGISTERS (Note 1)

0x34 R/W PECI Low Limit 0x81

0x54 R/W TACH1 Minimum Low Byte 0xFF

0x55 R/W TACH1 Minimum High Byte/Single-channel ADC Channel Select 0xFF

0x56 R/W TACH2 Minimum Low Byte 0xFF

0x57 R/W TACH2 Minimum High Byte 0xFF

0x58 R/W TACH3 Minimum Low Byte 0xFF

0x59 R/W TACH3 Minimum High Byte 0xFF

0x5A R/W TACH4 Minimum Low Byte 0xFF

0x5B R/W TACH4 Minimum High Byte 0xFF

1. Exceeding any of the TACH limit registers by 1 indicates that the fan is running too slowly or has stalled. The appropriate status bit is set

in Interrupt Status Register 2 (0x42) to indicate fan failure. Setting the Configuration Register 1 (0x40) Lock bit has no effect on these

registers.

Table 69. REGISTER 0x55 − TACH1 MINIMUM HIGH BYTE (POWER-ON DEFAULT = 0xFF)

Bit No. Mnemonic R/W Description

[3:0] Reserved Read-only When Bit 6 of Configuration 2 Register (0x73) is set (single-channel ADC mode), these bits

are reserved. Otherwise, these bits represent Bits [3:0] of the TACH1 minimum high byte.

[7:4] SCADC R/W When Bit 6 of Configuration 2 Register (0x73) is set (single-channel ADC mode), these bits

are used to select the only channel from which the ADC will take measurements. Otherwise,

these bits represent Bits [7:4] of the TACH1 minimum high byte.

Bit Code Single-channel Select

0000 +2.5 VIN

0001 VCCP

0010 VCC

0011 +5 VIN

0100 +12 VIN

0101 Remote 1 Temperature

0110 Local Temperature

0111 Remote 2 Temperature

1000 VTT

1001 IMON

Table 70. PWM CONFIGURATION REGISTERS

0x34 R/W PECI Low Limit 0x81

0x5C R/W PWM1 Configuration 0x62

0x5D R/W PWM2 Configuration 0x62

0x5E R/W PWM3 Configuration 0x62

1. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to these

registers fail.

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Table 71. REGISTER 0x5C, REGISTER 0x5D, AND REGISTER 0x5E − PWM1, PWM2, AND PWM3 CONFIGURATION

REGISTERS (POWER-ON DEFAULT = 0x62)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] SPIN R/W These bits control the startup timeout for PWMx. The PWM output stays high until two valid

TACH rising edges are seen from the fan. If there is not a valid TACH signal during the fan

TACH measurement directly after the fan startup timeout period, the TACH measurement reads

0xFFFF and Interrupt Status Register 2 reflects the fan fault. If the TACH minimum high and

low bytes contain 0xFFFF or 0x0000, then the Interrupt Status Register 2 bit is not set, even if

the fan has not started.

Bit Code Startup Time

000 No Startup Timeout

001 100 ms

010 250 ms (Default)

011 400 ms

100 667 ms

101 1 sec

110 2 sec

111 4 sec

[3] ALT R/W Use alternative behavior setting options in Bits [7:5] below for PWMx by setting this bit to 1.

Default = 0.

[4] INV R/W This bit inverts the PWM output. The default is 0, which corresponds to a logic high output for

100% duty cycle. Setting this bit to 1 inverts the PWM output, so a 100% duty cycle

corresponds to a logic low output.

[7:5] BHVR

(Note 2)

R/W These bits assign each fan to a particular temperature sensor for localized cooling. Setting Bit 3

to Logic 1 in this register chooses whether the default of alternative behavior option is selected.

Default Behavior Bits Alternative Behavior Bits (Note 2)

000 = Remote 1 temperature controls

PWMx (automatic fan control mode).

000 = PECI0 reading controls PWMx

(automatic fan control mode).

001 = Local temperature controls PWMx

(automatic fan control mode).

001 = PECI1 reading controls PWMx

(automatic fan control mode).

010 = Remote 2 temperature controls

PWMx (automatic fan control mode).

010 = PECI2 reading controls PWMx

(automatic fan control mode).

011 = PWMx runs full speed (default). 011 = PECI3 reading controls PWMx

(automatic fan control mode).

100 = PWMx disabled. 100 = Reserved. If selected, fans run at 100%

duty cycle.

101 = Fastest speed calculated by local

and Remote 2 temperature controls PWMx.

101 = Fastest of all four PECI channels. Fastest

speed calculated by all four PECI readings.

110 = Fastest speed calculated by all three

temperature channel controls PWMx.

110 = Reserved. If selected, fans run at 100%

duty cycle.

111 = Manual mode. PWM duty cycle

registers (Register 0x30 to Register 0x32)

become writable.

111 = Fastest speed calculated by all of the

thermal zones (Local, Remote 1, Remote 2,

and PECI temperatures).

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

2. When REPLACE mode is selected, (Register 0x36, Bit 4 set to 1) PWM1 is automatically configured for the alternative behavior setting.

Table 72. TEMPERATURE TRANGE/PWM FREQUENCY REGISTERS

0x5F R/W Remote 1 TRANGE/PWM1 Frequency 0xC4

0x60 R/W Local TRANGE/PWM2 Frequency 0xC4

0x61 R/W Remote 2 TRANGE/PWM3 Frequency 0xC4

1. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set. Any further attempts to write to these registers

have no effect.

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Table 73. REGISTER 0x5F, REGISTER 0x60, AND REGISTER 0x61 − REMOTE 1 TRANGE/PWM1 FREQUENCY,

LOCAL TRANGE/PWM2 FREQUENCY, AND REMOTE 2 TRANGE/PWM3 FREQUENCY (POWER-ON DEFAULT = 0xC4)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] FREQ R/W These bits control the PWMx frequency (only apply when PWM channel is in low frequency

mode).

Bit Code Frequency

000 11.0 Hz

001 14.7 Hz

010 22.1 Hz

011 29.4 Hz

100 35.3 Hz (Default)

101 44.1 Hz

110 58.8 Hz

111 88.2 Hz

[3] HF/LF R/W HF/LF = 1, high frequency PWM mode is enabled for PWMx.

HF/LF = 0, low frequency PWM mode is enabled for PWMx.

[7:4] RANGE R/W These bits determine the PWM duty cycle vs. the temperature range for automatic fan

control.

Bit Code Temperature

0000 2C

0001 2.5C

0010 3.33C

0011 4C

0100 5C

0101 6.67C

0110 8C

0111 10C

1000 13.33C

1001 16C

1010 20C

1011 26.67C

1100 32C (Default)

1101 40C

1110 53.33C

1111 80C

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set. Any further attempts to write to this register have

no effect.

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Table 74. REGISTER 0x62 − ENHANCED ACOUSTICS REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic

R/W

(Note 1) Description

[2:0] ACOU

(Note 2)

R/W Assuming that PWMx is associated with the Remote 1 temperature channel, these bits define

the maximum rate of change of the PWMx output for Remote 1 temperature-related changes.

Instead of the fan speed jumping instantaneously to its newly determined speed, it ramps

gracefully at the rate determined by these bits. This feature ultimately enhances the acoustics

of the fan.

When Bit 7 of Configuration Register 6 (0x10) is 0

Bit Code Time for 0% to 100%

000 = 1 37.5 sec

001 = 2 18.8 sec

010 = 3 12.5 sec

011 = 4 7.5 sec

100 = 8 4.7 sec

101 = 12 3.1 sec

110 = 24 1.6 sec

111 = 48 0.8 sec

When Bit 7 of Configuration Register 6 (0x10) is 1

Bit Code Time for 0% to 100%

000 = 1 52.2 sec

001 = 2 26.1 sec

010 = 3 17.4 sec

011 = 4 10.4 sec

100 = 8 6.5 sec

101 = 12 4.4 sec

110 = 24 2.2 sec

111 = 48 1.1 sec

[3] EN1 R/W When this bit is 1, smoothing is enabled on Remote 1 temperature channel.

[4] SYNC R/W SYNC = 1 synchronizes fan speed measurements on TACH2, TACH3, and TACH4 to PWM3.

This allows up to three fans to be driven from PWM3 output and their speeds to be measured.

SYNC = 0 synchronizes only TACH3 and TACH4 to PWM3 output.

[5] MIN1 R/W When the ADT7490 is in automatic fan control mode, this bit defines whether PWM1 is off

(0% duty cycle) or at PWM1 minimum duty cycle when the controlling temperature is below

its TMIN −hysteresis value.

0 = 0% duty cycle below TMIN – hysteresis.

1 = PWM1 minimum duty cycle below TMIN – hysteresis.

[6] MIN2 R/W When the ADT7490 is in automatic fan speed control mode, this bit defines whether PWM2 is

off (0% duty cycle) or at PWM2 minimum duty cycle when the controlling temperature is

below its TMIN −hysteresis value.

0 = 0% duty cycle below TMIN – hysteresis.

1 = PWM2 minimum duty cycle below TMIN – hysteresis.

[7] MIN3 R/W When the ADT7490 is in automatic fan speed control mode, this bit defines whether PWM3 is

off (0% duty cycle) or at PWM3 minimum duty cycle when the controlling temperature is

below its TMIN – hysteresis value.

0 = 0% duty cycle below TMIN – hysteresis.

1 = PWM3 minimum duty cycle below TMIN – hysteresis.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

2. Setting the relevant bit of Configuration Register 6 (0x10, Bits [2:0]) further decreases these ramp rates by a factor of 4.

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Table 75. REGISTER 0x63 − ENHANCED ACOUSTICS REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] ACOU2 R/W Assuming that PWMx is associated with the local temperature channel, these bits define the

maximum rate of change of the PWMx output for local temperature-related changes. Instead of

the fan speed jumping instantaneously to its newly determined speed, it ramps gracefully at the

rate determined by these bits. This feature ultimately enhances the acoustics of the fan.

When Bit 7 of Configuration Register 6 (0x10) is 0

Bit Code Time for 0% to 100%

000 = 1 37.5 sec

001 = 2 18.8 sec

010 = 3 12.5 sec

011 = 4 7.5 sec

100 = 8 4.7 sec

101 = 12 3.1 sec

110 = 24 1.6 sec

111 = 48 0.8 sec

When Bit 7 of Configuration Register 6 (0x10) is 1

Bit Code Time for 0% to 100%

000 = 1 52.2 sec

001 = 2 26.1 sec

010 = 3 17.4 sec

011 = 4 10.4 sec

100 = 8 6.5 sec

101 = 12 4.4 sec

110 = 24 2.2 sec

111 = 48 1.1 sec

[3] EN2 R/W When this bit is 1, smoothing is enabled on the local temperature channel.

[6:4] ACOU3 R/W Assuming that PWMx is associated with the Remote 2 temperature channel, these bits define

the maximum rate of change of the PWMx output for Remote 2 Temperature related

changes. Instead of the fan speed jumping instantaneously to its newly determined speed, it

ramps gracefully at the rate determined by these bits. This feature ultimately enhances the

acoustics of the fan.

[7] EN3 R/W When this bit is 1, smoothing is enabled on the Remote 2 temperature channel.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 76. PWM MINIMUM DUTY CYCLE REGISTERS

0x64 R/W PWM1 Minimum Duty Cycle 0x80 (50% Duty Cycle)

0x65 R/W PWM2 Minimum Duty Cycle 0x80 (50% Duty Cycle)

0x66 R/W PWM3 Minimum Duty Cycle 0x80 (50% Duty Cycle)

1. These registers become read-only when the ADT7490 is in automatic fan control mode.

Table 77. REGISTER 0x64, REGISTER 0x65, AND REGISTER 0x66 − PWM1, PWM2, AND PWM3 MIN DUTY CYCLES

(POWER-ON DEFAULT = 0x80)

[7:0] R/W These bits define the PWMMIN duty cycle for PWMx.

0x00 = 0% Duty Cycle (Fan Off)

0x40 = 25% Duty Cycle

0x80 = 50% Duty Cycle

0xFF = 100% Duty Cycle (Fan Full Speed)

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

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Table 78. TMIN REGISTERS (Note 1)

0x67 R/W Remote 1 Temperature TMIN 0x5A (90C)

0x68 R/W Local Temperature TMIN 0x5A (90C)

0x69 R/W Remote 2 Temperature TMIN 0x5A (90C)

1. These are the TMIN registers for each temperature channel. When the temperature measured exceeds TMIN, the appropriate fan runs at

minimum speed and increases with temperature according to TRANGE.

2. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set. Any further attempts to write to these registers

have no effect.

Table 79. THERM LIMIT REGISTERS (Note 1)

0x6A R/W Remote 1 THERM Temperature Limit 0x64 (100C)

0x6B R/W Local THERM Temperature Limit 0x64 (100C)

0x6C R/W Remote 2 THERM Temperature Limit 0x64 (100C)

1. If any temperature measured exceeds its THERM limit, all PWM outputs drive their fans at 100% duty cycle. This is a fail-safe mechanism

incorporated to cool the system in the event of a critical over temperature. It also ensures some level of cooling in the event that software

or hardware locks up. If set to 0x80, this feature is disabled. The PWM output remains at 100% until the temperature drops below

THERM limit −hysteresis. If the THERM pin is programmed as an output, exceeding these limits by 0.25C can cause the THERM pin to

assert low as an output.

2. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to these

registers have no effect.

Table 80. TEMPERATURE/TMIN HYSTERESIS REGISTERS

0x6D R/W Remote 1 and Local Temperature/TMIN Hysteresis 0x44

0x6E R/W PECI and Remote 2 Temperature/TMIN Hysteresis 0x44

1. These registers become read-only when the Configuration Register 1(0x40) Lock bit is set to 1. Any further attempts to write to these registers

have no effect.

Table 81. REGISTER 0x6D − REMOTE 1 AND LOCAL TEMPERATURE/TMIN HYSTERESIS

(POWER-ON DEFAULT = 0x44)

Bit No.

(Note 1) Mnemonic

R/W

(Note 2) Description

[3:0] HYSL R/W Local temperature hysteresis. 0C to 15C of hysteresis can be applied to the Local

temperature AFC control loops.

[7:4] HYSR1 R/W Remote 1 temperature hysteresis. 0C to 15C of hysteresis can be applied to the Remote 1

Temperature AFC control loops.

1. Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that

channel falls below its TMIN value, the fan remains running at PWMMIN duty cycle until the temperature = TMIN −hysteresis. Up to 15C of

hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel if its THERM

limit is exceeded. The PWM output being controlled goes to 100%, if the THERM limit is exceeded and remains at 100% until the temperature

drops below THERM −hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4C. Setting

the hysteresis value lower than 4C causes the fan to switch on and off regularly when the temperature is close to TMIN.

2. These registers become read-only when the Configuration Register 1 Lock bit is set to 1. Any further attempts to write to these registers have

no effect.

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Table 82. REGISTER 0x6E − REMOTE 2 AND PECI TEMPERATURE/TMIN HYSTERESIS

(POWER-ON DEFAULT = 0x44)

Bit No.

(Note 1) Mnemonic

R/W

(Note 2) Description

[3:0] HYSP R/W PECI temperature hysteresis. 0C to 15C of hysteresis can be applied to the PECI AFC

control loops.

[7:4] HYSR2 R/W Remote 2 temperature hysteresis. 0C to 15C of hysteresis can be applied to the local

temperature AFC control loops.

1. Each 4-bit value controls the amount of temperature hysteresis applied to a particular temperature channel. Once the temperature for that

channel falls below its TMIN value, the fan remains running at PWMMIN duty cycle until the temperature = TMIN −hysteresis. Up to 15C of

hysteresis can be assigned to any temperature channel. The hysteresis value chosen also applies to that temperature channel, if its THERM

limit is exceeded. The PWM output being controlled goes to 100%, if the THERM limit is exceeded and remains at 100% until the temperature

drops below THERM −hysteresis. For acoustic reasons, it is recommended that the hysteresis value not be programmed less than 4C. Setting

the hysteresis value lower than 4C causes the fan to switch on and off regularly when the temperature is close to TMIN.

2. These registers become read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to these

registers have no effect.

Table 83. REGISTER 0x6F − XNOR TREE TEST ENABLE (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[0] XEN R/W If the XEN bit is set to 1, the device enters the XNOR tree test mode. Clearing the bit

removes the device from the XNOR tree test mode.

[7:1] RES R/W Unused/reserved. Do not write to these bits.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 84. REGISTER 0x70 − REMOTE 1 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the Remote 1 temperature channel measurement.

Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 85. REGISTER 0x71 − LOCAL TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the local temperature measurement. Bit 1 of

Configuration Register 5 (0x7C) determines the range and resolution of this register.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 86. REGISTER 0x72 − REMOTE 2 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the Remote 2 temperature channel measurement.

Bit 1 of Configuration Register 5 (0x7C) determines the range and resolution of this register.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

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Table 87. REGISTER 0x73 − CONFIGURATION REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

0 FanPresDT R/W When FanPresDT = 1, the state of Bits [3:1] of this register reflects the presence of a 4-wire

fan on the appropriate TACH channel.

1 Fan1Detect Read-only Fan1Detect = 1 indicates that a 4-wire fan is connected to the PWM1 input.

2 Fan2Detect Read-only Fan2Detect = 1 indicates that a 4-wire fan is connected to the PWM2 input.

3 Fan3Detect Read-only Fan3Detect = 1 indicates that a 4-wire fan is connected to the PWM3 input.

4AVG R/W AVG = 1 indicates that averaging on the temperature and voltage measurements is turned

off. This allows measurements on each channel to be made much faster (x16).

5 ATTN R/W ATTN = 1 indicates that the ADT7490 removes the attenuators from the +2.5 VIN, VCCP

+5 VIN, and +12 VIN inputs. These inputs can be used for other functions such as connecting

up external sensors. It is also possible to remove attenuators from individual channels using

Bits [7:4] of Configuration Register 4 (0x7D).

6 CONV R/W CONV = 1 indicates that the ADT7490 is put into a single-channel ADC conversion mode. In

this mode, the ADT7490 can be made to read continuously from one input only, for example,

Remote 1 temperature. The appropriate ADC channel is selected by writing to Bits [7:4] of

TACH1 minimum high byte register (0x55).

When CONV = 1, Bits [7:4], Register 0x55

Bit Code ADC Channel Selected

0000 +2.5 VIN

0001 VCCP

0010 VCC

0011 +5 VIN

0100 +12 VIN

0101 Remote 1 Temperature

0110 Local Temperature

0111 Remote 2 Temperature

1000 VTT

1001 IMON

7 Shutdown R/W When the shutdown bit is set to 1, the ADT7490 goes into shutdown mode.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 88. REGISTER 0x74 − INTERRUPT MASK REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] +2.5 VIN/

THERM

R/W +2.5 VIN/THERM = 1 masks SMBALERT for out-of-limit conditions on the +2.5 VIN/THERM

timer channel.

[1] VCCP R/W VCCP = 1 masks SMBALERT for out-of-limit conditions on the VCCP channel.

[2] VCC R/W VCC = 1 masks SMBALERT for out-of-limit conditions on the VCC channel.

[3] +5 VIN R/W +5 VIN = 1 masks SMBALERT for out-of-limit conditions on the +5 VIN channel.

[4] R1T R/W R1T = 1 masks SMBALERT for out-of-limit conditions on the Remote 1 temperature channel.

[5] LT R/W LT = 1 masks SMBALERT for out-of-limit conditions on the local temperature channel.

[6] R2T R/W R2T = 1 masks SMBALERT for out-of-limit conditions on the Remote 2 temperature channel.

[7] OOL R/W OOL = 1 masks SMBALERT assertions when the OOL status bit is set.

Note that the OOL mask bit is independent of the individual mask bits associated with

Interrupt Status Register 2. Therefore, if the intention is to mask SMBALERT assertions for

any of the Interrupt Status Register 2 bits, OOL must also be masked.

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Table 89. REGISTER 0x75 − INTERRUPT MASK REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] +12 VIN R/W When Pin 21 is configured as a +12 VIN input, +12 VIN = 1 masks SMBALERT for out-of-limit

conditions on the +12 VIN channel.

[1] OOL R/W OOL = 1 masks SMBALERT assertions when the OOL status bit is set.

Note that the OOL mask bit is independent of the individual mask bits in Interrupt Mask

Interrupt Status Register 4 bits, OOL must also be masked.

[2] FAN1 R/W FAN1 = 1 masks SMBALERT for a Fan 1 fault.

[3] FAN2 R/W FAN2 = 1 masks SMBALERT for a Fan 2 fault.

[4] FAN3 R/W FAN3 = 1 masks SMBALERT for a Fan 3 fault.

[5] Fan4/

THERM

R/W If Pin 14 is configured as TACH4, Fan4/THERM = 1 masks SMBALERT for a Fan 4 fault. If

Pin 14 is configured as THERM, Fan4/THERM = 1 masks SMBALERT for an exceeded

THERM timer limit.

[6] D1 FAULT R/W D1 = 1 masks SMBALERT for a diode open or short on a Remote 1 channel.

[7] D2 FAULT R/W D2 = 1 masks SMBALERT for a diode open or short on a Remote 2 channel.

Table 90. REGISTER 0x76 − EXTENDED RESOLUTION REGISTER 1 (POWER-ON DEFAULT = 0x00) (Note 1)

Bit No. Mnemonic R/W Description

[1:0] +2.5 VIN Read-only +2.5 VIN LSBs. Holds the 2 LSBs of the 10-bit +2.5 VIN Measurement

[3:2] VCCP Read-only VCCP LSBs. Holds the 2 LSBs of the 10-bit VCCP Measurement

[5:4] VCC Read-only VCC LSBs. Holds the 2 LSBs of the 10-bit VCC Measurement

[7:6] +5 VIN Read-only +5 VIN LSBs. Holds the 2 LSBs of the 10-bit +5 VIN Measurement

1. If this register is read, this register and the registers holding the MSB of each reading are frozen until read.

Table 91. REGISTER 0x77 − EXTENDED RESOLUTION REGISTER 2 (POWER-ON DEFAULT = 0x00) (Note 1)

Bit No. Mnemonic R/W Description

[1:0] +12 VIN Read-only +12 VIN LSBs. Holds the 2 LSBs of the 10-bit +12 VIN Measurement

[3:2] TDM1 Read-only Remote 1 Temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 1 Temperature

Measurement

[5:4] LTMP Read-only Local Temperature LSBs. Holds the 2 LSBs of the 10-bit Local Temperature Measurement

[7:6] TDM2 Read-only Remote 2 Temperature LSBs. Holds the 2 LSBs of the 10-bit Remote 2 Temperature

Measurement

1. If this register is read, this register and the registers holding the MSB of each reading are frozen until read.

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Table 92. REGISTER 0x78 − CONFIGURATION REGISTER 3 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[0] ALERT

Enable

R/W ALERT = 1, Pin 10 (PWM2/SMBALERT) is configured as an SMBALERT interrupt output to

indicate out-of-limit error conditions.

ALERT = 0, Pin 10 (PWM2/SMBALERT) is configured as the PWM2 output.

[1] THERM/

+2.5VIN

R/W THERM = 1 enables THERM functionality on Pin 22 and Pin 14, if Pin 14 is configured as

THERM, determined by Bit 0 and Bit 1 (Pin 14 Func) of Configuration Register 4 (0x7D).

When THERM is asserted, if the fans are running and the BOOST bit is set, then the fans run

at full speed. Alternatively, THERM can be programmed so that a timer is triggered to time

how long THERM has been asserted.

THERM = 0 enables +2.5VIN measurement on Pin 22 and disables THERM. If Bits [5:7] of

Configuration Register 5 (0x7C) are set, THERM is bidirectional. If they are 0, THERM is a

timer input only.

Pin 14 Func (0x7D) THERM/+2.5 VIN (0x78) Pin 22 Pin 14

+2.5 VIN

THERM

+2.5 VIN

THERM

TACH4

SMBALERT

N/A

TACH4

THERM

SMBALERT

N/A

[2] BOOST R/W When THERM is an input and BOOST = 1, assertion of THERM causes all fans to run at the

maximum programmed duty cycle for fail−safe cooling.

[3] FAST R/W FAST = 1 enables fast TACH measurements on all channels. This increases the TACH

measurement rate from once per second to once every 250 ms (4x).

[4] DC1 R/W DC1 = 1 enables TACH measurements to be continuously made on TACH1. Fans must be

driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven

motors.

[5] DC2 R/W DC2 = 1 enables TACH measurements to be continuously made on TACH2. Fans must be

driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven

motors.

[6] DC3 R/W DC3 = 1 enables TACH measurements to be continuously made on TACH3. Fans must be

driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven

motors.

[7] DC4 R/W DC4 = 1 enables TACH measurements to be continuously made on TACH4. Fans must be

driven by dc. Setting this bit prevents pulse stretching because it is not required for dc-driven

motors.

1. Bits [3:0] of this register become read-only when the Configuration Register 1 Lock (0x40) bit is set to 1. Any further attempts to write to

Bits [3:0] have no effect.

Table 93. REGISTER 0x79 − THERM TIMER STATUS REGISTER (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[0] ASRT/

TMR0

RThis bit is set high on the assertion of the THERM input and is cleared on read. If the THERM

assertion time exceeds 45.52 ms, this bit is set and becomes the LSB of the 8-bit TMR

reading. This allows THERM assertion times from 45.52 ms to 5.82 sec to be reported back

with a resolution of 22.76 ms.

[7:1] TMR R Times how long THERM input is asserted. These seven bits read 0 until the THERM

assertion time exceeds 45.52 ms.

Table 94. REGISTER 0x7A − THERM TIMER LIMIT REGISTER (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[7:0] LIMT R/W Sets maximum THERM assertion length allowed before an interrupt is generated. This is an

8-bit limit with a resolution of 22.76 ms allowing THERM assertion limits of 45.52 ms to 5.82 sec

to be programmed. If the THERM assertion time exceeds this limit, Bit 5 (FAN4/THERM) of

Interrupt Status Register 2 (0x42) is set. If the limit value is 0x00, an interrupt is generated

immediately on the assertion of the THERM input. If THERM is configured as an output, the

THERM timer limit should be set to 0xFF to avoid unwanted alerts from being generated.

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Table 95. REGISTER 0x7B − TACH PULSES PER REVOLUTION REGISTER (POWER-ON DEFAULT = 0x55)

Bit No. Mnemonic R/W Description

[1:0] FAN1 R/W Sets number of pulses to be counted when measuring Fan 1 speed. Can be used to

determine fan pulses per revolution for unknown fan type.

Bit Code Pulses Counted

00 1

01 2 (Default)

10 3

11 4

[3:2] FAN2 R/W Sets number of pulses to be counted when measuring Fan 2 speed. Can be used to

determine fan pulses per revolution for unknown fan type.

Bit Code Pulses Counted

00 1

01 2 (Default)

10 3

11 4

[5:4] FAN3 R/W Sets number of pulses to be counted when measuring Fan 3 speed. Can be used to

determine fan pulses per revolution for unknown fan type.

Bit Code Pulses Counted

00 1

01 2 (Default)

10 3

11 4

[7:6] FAN4 R/W Sets number of pulses to be counted when measuring Fan 4 speed. Can be used to

determine fan pulses per revolution for unknown fan type.

Bit Code Pulses Counted

00 1

01 2 (Default)

10 3

11 4

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Table 96. REGISTER 0x7C − CONFIGURATION REGISTER 5 (POWER-ON DEFAULT = 0x01)

Bit No. Mnemonic R/W (Note 1) Description

[0] TWOS

COMPL

R/W TWOS COMPL = 1 sets the temperature range to the twos complement temperature range.

TWOS COMPL = 0 changes the temperature range to the Offset 64 temperature range.

When this bit is changed, the ADT7490 interprets all relevant temperature register values as

defined by this bit.

[1] Temp Offset R/W Temp Offset = 0 sets offset range to −63C to +64C with 0.5C resolution.

Temp Offset = 1 sets offset range to −63C to +127C with 1C resolution.

These settings apply to Register 0x70, Register 0x71, and Register 0x72 (Remote 1, Internal,

and Remote 2 Temperature offset registers. Note that PECI offset is always 1C resolution).

[3:2] RES R/W Reserved.

[4] PECI R1

THERM

Output Only

R/W PECI R1 = 1 enables THERM assertions when the PECI temperature read is higher than the

PECI TCONTROL limit and the THERM pin is bidirectional. If THERM is configured as an

output, the THERM timer limit register (0x7A) should be set to 0xFF to avoid unwanted alerts

from being generated.

PECI R1 = 0 indicates that the THERM pin is configured as a timer input only. Can also be

disabled by writing one of the following values to the PECI TCONTROL limit register (0x3D):

Writing −64C in Offset 64 mode.

Writing −128C in twos complement mode.

[5] R1 THERM

Output Only

R/W R1 = 1 enables THERM assertions when the Remote 1 temperature read is higher than the

Remote 1 THERM limit and the THERM pin is bidirectional. If THERM is configured as an

output, the THERM timer limit (Register 0x7A) should be set to 0xFF to avoid unwanted

alerts from being generated.

R1 = 0 indicates that the THERM pin is configured as a timer input only. Can also be disabled

by writing one of the following values to the Remote 1 THERM Temp Limit register (0x6A):

Writing −64C in Offset 64 mode.

Writing −128C in twos complement mode.

[6] Local

THERM

Output Only

R/W R1 = 1 enables THERM assertions when the Local temperature read is higher than the Local

THERM limit and the THERM pin is bidirectional. If THERM is configured as an output, the

THERM timer limit (Register 0x7A) should be set to 0xFF to avoid unwanted alerts from

being generated.

R1 = 0 indicates that the THERM pin is configured as a timer input only. Can also be disabled

by writing one of the below values to the local THERM limit register (0x6B):

Writing −64C in Offset 64 mode.

Writing −128C in twos complement mode.

[7] R2 THERM

Output Only

R/W R1 = 1 enables THERM assertions when the Remote 2 temperature read is higher than the

Remote 2 THERM limit and the THERM pin is bidirectional. If THERM is configured as an

output, the THERM timer limit (Register 0x7A) should be set to 0xFF to avoid unwanted

alerts from being generated.

R1 = 0 indicates that the THERM pin is configured as a timer input only. C an also be

disabled by writing one of the below values to the Remote 2 THERM temperature limit

Writing −64C in Offset 64 mode.

Writing −128C in twos complement mode.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

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Table 97. REGISTER 0x7D − CONFIGURATION REGISTER 4 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[1:0] Pin 14 Func R/W These bits set the functionality of Pin 14.

00 = TACH4 (Default)

01 = THERM

10 = SMBALERT

11 = Reserved

[2] THERM

Disable

R/W THERM Disable = 0 enables THERM overtemperature output assuming THERM is correctly

configured (0x78, 0x7C, and 0x7D).

THERM Disable = 1 disables THERM overtemperature output on all channels. THERM can

also be disabled on any channel by:

Writing −64C to the appropriate THERM temperature limit in Offset 64 mode.

Writing −128C to the appropriate THERM temperature limit in twos complement mode.

[3] Max/Full on

THERM

R/W Max/Full on THERM = 0 indicates that fans go to 100% when THERM temperature limit is

exceeded.

Max/Full on THERM = 1 indicates that fans go to maximum speed (0x38, 0x39, 0x3A) when

THERM temperature limit is exceeded.

[4] BpAtt

+2.5 VIN

R/W Bypass +2.5VIN attenuator. When set, the measurement scale for this channel changes from

0 V (0x00) to 2.25 V (0xFF).

[5] BpAtt VCCP R/W Bypass VCCP attenuator. When set, the measurement scale for this channel changes from

0 V (0x00) to 2.25 V (0xFF).

[6] BpAtt

+5 VIN

R/W Bypass +5 VIN attenuator. When set, the measurement scale for this channel changes from

0 V (0x00) to 2.25 V (0xFF).

[7] BpAtt

+12 VIN

R/W Bypass +12 VIN attenuator. When set, the measurement scale for this channel changes from

0 V (0x00) to 2.25 V (0xFF).

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 98. REGISTER 0x7E − MANUFACTURER’S TEST REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[7:0] Reserved Read-only Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and

should not be written to under normal operation.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 99. REGISTER 0x7F − MANUFACTURER’S TEST REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[7:0] Reserved Read-only Manufacturer’s test register. These bits are reserved for manufacturer’s test purposes and

should not be written to under normal operation.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 100. REGISTER 0x80 − GPIO CONFIGURATION REGISTER (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[1:0] RES Reserved Reserved

[2] GPIO2 R/W If GPIO2 is set to input, this register reflects the state of the pin. If GPIO2 is configured as an

output, writing to this register asserts the output high or low depending on the polarity.

[3] GPIO1 R/W If GPIO1 is set to input, this register reflects the state of the pin. If GPIO1 is configured as an

output, writing to this register asserts the output high or low depending on the polarity.

[4] GPIO2 POL R/W GPIO2 polarity bit. Set to 0 for active low. Set to 1 for active high.

[5] GPIO1 POL R/W GPIO1 polarity bit. Set to 0 for active low. Set to 1 for active high.

[6] GPIO2 DIR R/W GPIO2 direction bit. Set to 1 for GPIO1 to act as an input, set to 0 for GPIO2 to act as an output.

[7] GPIO1 DIR R/W GPIO1 direction bit. Set to 1 for GPIO1 to act as an input, set to 0 for GPIO1 to act as an output.

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Table 101. REGISTER 0x81 − INTERRUPT STATUS REGISTER 4 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W Description

[2:0] RES Read-only Reserved

[3] PECI1 Read-only A Logic 1 indicates that the PECI high or low limit has been exceeded by the PECI value

from PECI Client Address 0x31. This bit is cleared on a read of the status register only if the

error condition has subsided.

[4] PECI2 Read-only A Logic 1 indicates that the PECI high or low limit has been exceeded by the PECI value

from PECI Client Address 0x32. This bit is cleared on a read of the status register only if the

error condition has subsided.

[5] PECI3 Read-only A Logic 1 indicates that the PECI high or low limit has been exceeded by the PECI value

from PECI Client Address 0x33. This bit is cleared on a read of the status register only if the

error condition has subsided.

[6] IMON Read-only A Logic 1 indicates that the IMON high or low limit has been exceeded. This bit is cleared on a

read of the status register only if the error condition has subsided.

[7] VTT Read-only A Logic 1 indicates that the VTT high or low limit has been exceeded. This bit is cleared on a

read of the status register only if the error condition has subsided.

Table 102. REGISTER 0x82 − INTERRUPT MASK REGISTER 3 (POWER-ON DEFAULT = 0x00) (Note 1)

Bit No. Mnemonic R/W Description

[0] PECI0 R/W A Logic 1 masks SMBALERT assertions for out-of-limit conditions on PECI0.

[1] DATA R/W A Logic 1 masks SMBALERT assertions for PECI data errors.

[2] COMM R/W A Logic 1 masks SMBALERT assertions for PECI communications errors.

[3] OVT R/W OVT = 1 masks SMBALERT for overtemperature THERM conditions.

[6:4] RES R/W Reserved

[7] OOL R/W OOL = 1 masks SMBALERT assertions when the OOL status bit is set.

Note that the OOL mask bit is independent of the individual mask bits of Interrupt Mask

Interrupt Status Register 4 bits, OOL must also be masked.

1. If the mask bits in Register 0x82 are set, it is also necessary to set the OOL mask bit in Register 0x75 to ensure the SMBALERT output is

not asserted.

Table 103. REGISTER 0x83 − INTERRUPT MASK REGISTER 4 (POWER-ON DEFAULT = 0x00) (Note 1)

Bit No. Mnemonic R/W Description

[2:0] RES R/W Reserved

[3] PECI1 R/W A Logic 1 masks ALERT assertions for out-of-limit conditions on PECI1.

[4] PECI2 R/W A Logic 1 masks ALERT assertions for out-of-limit conditions on PECI2.

[5] PECI3 R/W A Logic 1 masks ALERT assertions for out-of-limit conditions on PECI3.

[6] IMON R/W A Logic 1 masks ALERT assertions for out-of-limit conditions on IMON.

[7] VTT R/W A Logic 1 masks ALERT assertions for out-of-limit conditions on VTT

1. If the mask bits in Register 0x83 are set, it is also necessary to set the OOL mask bit in Register 0x82 to ensure the SMBALERT output is

not asserted.

Table 104. VTT

, IMON LIMIT REGISTERS

0x84 R/W VTT Low Limit 0x00

0x85 R/W IMON Low Limit 0x00

0x86 R/W VTT High Limit 0xFF

0x87 R/W IMON High Limit 0xFF

1. These registers becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to these

registers fail.

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Table 105. REGISTER 0x88 − PECI CONFIGURATION REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] RES R/W Reserved

[3] DOM3 R/W CPU domain count information. Set to 0 indicates that CPU 4 associated with the PECI3

reading has a single domain (default). Set to 1 indicates that the system CPU4 contains two

domains.

[4] DOM2 R/W CPU domain count information. Set to 0 indicates that CPU 3 associated with the PECI2

reading has a single domain (default). Set to 1 indicates that the system CPU3 contains two

domains.

[5] DOM1 R/W CPU domain count information. Set to 0 indicates that CPU 2 associated with the PECI1

reading has a single domain (default). Set to 1 indicates that the system CPU2 contains two

domains.

[7:6] #CPU R/W CPU count. These bits indicate the number of CPUs in the system, which provide PECI

thermal information to the ADT7490.

00 = 1 CPU (default); indicates that PECI0 data is available from CPU 1 at Address 0x30.

01 = 2 CPUs; indicates that PECI0 data is available from CPU1 at Address 0x30 and PECI1

data is available from CPU 2 at Address 0x31.

10 = 3 CPUs; indicates that PECI0 data is available from CPU1 at Address 0x30, PECI1 data

is available from CPU 2 at Address 0x31 and PECI2 data is available from CPU 3 at

Address 0x32.

11 = 4 CPUs; indicates that PECI0 data is available from CPU1 at Address 0x30, PECI1 data

is available from CPU 2 at Address 0x31, PECI2 data is available from CPU 3 at

Address 0x32 and PECI3 data is available from CPU 4 at Address 0x33.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

Table 106. OPERATING POINT REGISTERS (Note 1 and 2)

0x8A R/W PECI Operating Point Register 0xFB

0x8B R/W Remote 1 Operating Point Register (Default = 100C) 0x64

0x8C R/W Local Temperature Operating Point Register (Default = 100C) 0x64

0x8D R/W Remote 2 Operating Point Register (Default = 100C) 0x64

1. These registers set the target operating point for each temperature channel when the dynamic TMIN control feature is enabled.

2. The fans being controlled are adjusted to maintain temperature about an operating point.

3. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

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Table 107. REGISTER 0x8E − DYNAMIC TMIN CONTROL REGISTER 1 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[0] CYR2 R/W MSB of 3-bit Remote 2 Cycle Value. The other two bits of the code reside in Dynamic TMIN

Control Register 2 (0x8F). These three bits define the delay time between making

subsequent TMIN adjustments in the control loop in terms of the number of monitoring cycles.

The system has associated thermal time constants that need to be found to optimize the

response of fans and the control loop.

[1] VCCPLO R/W VCCPLO = 1. When the power is supplied from 3.3 V STANDBY and the core voltage (VCCP)

drops below its VCCP low limit value (0x46), the following occurs:

Status Bit 1 in Status Register 1 is set.

SMBALERT is generated, if enabled.

PROCHOT monitoring is disabled.

Dynamic TMIN control is disabled.

The device is prevented from entering shutdown.

Everything is re-enabled once VCCP increases above the VCCP low limit.

[2] PHTR1 R/W PHTR1 = 1 copies the Remote 1 current temperature to the Remote 1 operating point

THERM is asserted, allowing the system to run as quietly as possible without affecting

system performance.

PHTR1 = 0 ignores any THERM assertions on the THERM pin. The Remote 1 operating

point register reflects its programmed value.

[3] PHTL R/W PHTL = 1 copies the local channel’s current temperature to the local operating point register

if THERM is asserted. The operating point contains the temperature at which THERM is

asserted. This allows the system to run as quietly as possible without affecting system

performance.

PHTL = 0 ignores any THERM assertions on the THERM pin. The local temperature

operating point register reflects its programmed value.

[4] PHTR2 R/W PHTR2 = 1 copies the Remote 2 current temperature to the Remote 2 operating point

THERM is asserted, allowing the system to run as quietly as possible without affecting

system performance.

PHTR2 = 0 ignores any THERM assertions on the THERM pin. The Remote 2 operating

point register reflects its programmed value.

[5] R1T R/W R1T = 1 enables dynamic TMIN control on the Remote 1 temperature channel. The chosen

TMIN value is dynamically adjusted based on the current temperature, operating point, and

high and low limits for this zone.

R1T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the

channel behaves as described in the section.

[6] LT R/W LT = 1 enables dynamic TMIN control on the local temperature channel. The chosen TMIN

value is dynamically adjusted based on the current temperature, operating point, and high

and low limits for this zone.

LT = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the

channel behaves as described in the Automatic Fan Control Overview section.

[7] R2T R/W R2T = 1 enables dynamic TMIN control on the Remote 2 temperature channel. The chosen

TMIN value is dynamically adjusted based on the current temperature, operating point, and

high and low limits for this zone.

R2T = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted, and the

channel behaves as described in the Automatic Fan Control Overview section.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

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Table 108. REGISTER 0x8F − DYNAMIC TMIN CONTROL REGISTER 2 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] CYR1 R/W 3-bit Remote 1 Cycle Value. These three bits define the delay time between making

subsequent TMIN adjustments in the control loop for the Remote 1 channel in terms of

number of monitoring cycles. The system has associated thermal time constants that need to

be found to optimize the response of fans and the control loop.

Bit Code Decrease Cycle Increase Cycle

000

001

010

011

100

101

110

111

8 cycles (1 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

2048 cycles (256 sec)

[5:3] CYL R/W 3-bit Local Temperature Cycle Value. These three bits define the delay time between making

subsequent TMIN adjustments in the control loop for the local temperature channel in terms of

number of monitoring cycles. The system has associated thermal time constants that need to

be found to optimize the response of fans and the control loop.

Bit Code Decrease Cycle Increase Cycle

000

001

010

011

100

101

110

111

8 cycles (1 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

2048 cycles (256 sec)

[7:6] CYR2 R/W 2 LSBs of 3-bit Remote 2 Cycle Value. The MSB of the 3-bit code resides in the Dynamic

TMIN Control Register 1 (Register 0x8E). These three bits define the delay time between

making subsequent TMIN adjustments in the control loop for the Remote 2 channel in terms

of number of monitoring cycles. The system has associated thermal time constants that need

to be found to optimize the response of fans and the control loop.

Bit Code Decrease Cycle Increase Cycle

000

001

010

011

100

101

110

111

8 cycles (1 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

2048 cycles (256 sec)

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

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Table 109. REGISTER 0x90 − DYNAMIC TMIN CONTROL REGISTER 3 (POWER-ON DEFAULT = 0x00)

Bit No. Mnemonic R/W (Note 1) Description

[2:0] RES Reserved Reserved

[5:3] CYP R/W 3-bit PECI Temperature Cycle Value. These three bits define the delay time between making

subsequent TMIN adjustments in the control loop for the PECI temperature channels in terms

of number of monitoring cycles. The system has associated thermal time constants that need

to be found to optimize the response of fans and the control loop.

Bit Code Decrease Cycle Increase Cycle

000

001

010

011

100

101

110

111

8 cycles (1 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

16 cycles (2 sec)

32 cycles (4 sec)

64 cycles (8 sec)

128 cycles (16 sec)

256 cycles (32 sec)

512 cycles (64 sec)

1024 cycles (128 sec)

2048 cycles (256 sec)

[6] PHTP R/W PHTR1 = 1 copies the PECI0 current reading to the PECI operating point register if THERM

is asserted. The operating point contains the temperature at which THERM is asserted,

allowing the system to run as quietly as possible without affecting system performance.

PHTR1 = 0 ignores any THERM assertions on the THERM pin. The PECI operating point

[7] PECI R/W PECI = 1 enables dynamic TMIN control on the PECI temperature channel. The chosen TMIN

value is dynamically adjusted based on the current temperature, operating point, and high

and low limits for this zone.

PECI = 0 disables dynamic TMIN control. The TMIN value chosen is not adjusted and the

channel behaves as described in the Automatic Fan Control Overview section.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any subsequent attempts to write to this

Table 110. REGISTER 0x94 − PECI0 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the PECI0 channel measurements. The

programmable offset range is from −63C to +127C with 1C resolution.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 111. REGISTER 0x95 − PECI1 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the PECI1 channel measurements. The

programmable offset range is from −63C to +127C with 1C resolution.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 112. REGISTER 0x96 − PECI2 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the PECI2 channel measurements. The

programmable offset range is from −63C to +127C with 1C resolution.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

Table 113. REGISTER 0x97 − PECI3 TEMPERATURE OFFSET (POWER-ON DEFAULT = 0x00)

Bit No. R/W (Note 1) Description

[7:0] R/W Allows a temperature offset to be automatically applied to the PECI3 channel measurements. The

programmable offset range is from −63C to +127C with 1C resolution.

1. This register becomes read-only when the Configuration Register 1 (0x40) Lock bit is set to 1. Any further attempts to write to this register

have no effect.

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Table 114. ORDERING INFORMATION

Device Order Number* Package Type Package Option Shipping†

ADT7490ARQZ−REEL 24-lead QSOP RQ−24 2,500 Tape & Reel

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging

Specifications Brochure, BRD8011/D.

*This is a Pb-Free package.

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PACKAGE DIMENSIONS

QSOP24 NB

CASE 492B−01

ISSUE A

*For additional information on our Pb-Free strategy and soldering

details, please download the ON Semiconductor Soldering and

Mounting Techniques Reference Manual, SOLDERRM/D.

SOLDERING FOOTPRINT*

0.25 C

DETAIL A

h x 45 _

DIM MAXMIN

MILLIMETERS

A1.35 1.75

b0.20 0.30

L0.40 1.27

e0.635 BSC

h0.22 0.50

C0.19 0.25

A1 0.10 0.25

M0 8

NOTES:

1. DIMENSIONING AND TOLERANCING PER ASME

Y14.5M, 1994.

2. CONTROLLING DIMENSION: MILLIMETERS.

3. DIMENSION b DOES NOT INCLUDE DAMBAR

PROTRUSION.

4. DIMENSION D DOES NOT INCLUDE MOLD FLASH,

PROTRUSIONS, OR GATE BURRS. MOLD FLASH,

PROTRUSIONS, OR GATE BURRS SHALL NOT

EXCEED 0.15 PER SIDE. DIMENSION E1 DOES NOT

INCLUDE INTERLEAD FLASH OR PROTRUSION.

INTERLEAD FLASH OR PROTRUSION SHALL NOT

EXCEED 0.15 PER SIDE. D AND E1 ARE

DETERMINED AT DATUM H.

5. DATUMS A AND B ARE DETERMINED AT DATUM H.

24X

SEATING

PLANE

0.10 C

A-B D

0.20 C

112

24 13

24X CM

D8.65 BSC

E6.00 BSC

E1 3.90 BSC

L2 0.25 BSC

0.25 C D

0.20 C D

2X 12 TIPS

0.10 C H

GAUGE

PLANE

6.40

24X

0.42 24X

1.12

0.635

DIMENSIONS: MILLIMETERS

PITCH

112

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ADT7490/D

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