ADT7482ARMZ-REEL7 - ON Semiconductor

 Semiconductor Components Industries, LLC, 2012

July, 2012 − Rev. 4

1Publication Order Number:

ADT7482/D

ADT7482

Dual Channel Temperature

Sensor and Overtemperature

Alarm

The ADT7482 is a three-channel digital thermometer and

under/overtemperature alarm for PCs and thermal management

systems. It can measure the temperature in two remote locations, such

as in the remote thermal diode in a CPU or GPU, or using a discrete

diode connected transistor. This device also measures its own ambient

temperature.

One feature of the ADT7482 is series resistance cancellation where

up to 1.5 kW (typical) of resistance in series with each of the

temperature monitoring diodes can be automatically cancelled from

the temperature result, allowing noise filtering. The temperature of the

remote thermal diodes and ambient temperature can be measured

accurate to 1C. The temperature measurement range, which defaults

to 0C to 127C, can be switched to a wider measurement range of

from −55C to +150C.

The ADT7482 communicates over a 2-wire serial interface

compatible with System Management Bus (SMBus) standards. The

default address of the ADT7482 is 0x4C. An ALERT output signals

when the on-chip or remote temperature is outside the programmed

limits. The THERM output is a comparator output that allows on/off

control of a cooling fan. The ALERT output can be reconfigured as a

second THERM output if required.

Features

1 Local and 2 Remote Temperature Sensors

0.25C Resolution/1C Accuracy on Remote Channels

1C Resolution/1C Accuracy on Local Channel

Automatically Cancels Up to 1.5 kW (Typ) of Resistance in Series

with the Remote Sensors

Extended, Switchable Temperature Measurement Range

0C to +127C (Default) or −55C to +150C

2-wire SMBus Serial Interface with SMBus Alert Support

Programmable Over/Undertemperature Limits

Offset Registers for System Calibration

Up to 2 Overtemperature Fail-Safe THERM Outputs

Small, 10-lead MSOP Package

240ĂmA Operating Current, 5ĂmA Standby Current

This Device is Pb-Free, Halogen Free and is RoHS Compliant

Applications

Desktop and Notebook Computers

Industrial Controllers

Smart Batteries

Automotive

Embedded Systems

Burn-in Applications

Instrumentation

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See detailed ordering and shipping information in the package

dimensions section on page 19 of this data sheet.

ORDERING INFORMATION

MSOP−10

CASE 846AC

T0A

AYWG

PIN ASSIGNMENT

T0A = Device Code

A = Assembly Location

Y = Year

W = Work Week

G= Pb-Free Package

(Note: Microdot may be in either location)

ALERT/THERM2

SCLK

SDATA

D2+

D2−

VDD

D1+

D1−

THERM

GND

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Figure 1. Functional Block Diagram

ON-CHIP

TEMPERATURE

SENSOR

ANALOG

MUX BUSY

11-BIT ADC

LOCAL TEMPERATURE

VALUE REGISTER

REMOTE 1 AND 2 TEMP

OFFSET REGISTER

RUN/STANDBY

EXTERNAL DIODE OPEN-CIRCUIT

STATUS REGISTERS

SMBus INTERFACE

LIMIT COMPARATOR

DIGITAL MUX

INTERRUPT

MASKING

SDATA SCLK

109

ONE-SHOT

CONVERSION RATE

LOCAL TEMPERATURE

THERM LIMIT REGISTER

LOCAL TEMPERATURE

LOW LIMIT REGISTER

LOCAL TEMPERATURE

HIGH LIMIT REGISTER

REMOTE 1 & 2 TEMP.

THERM LIMIT REG.

REMOTE 1 & 2 TEMP.

LOW LIMIT REGISTERS

REMOTE 1 & 2 TEMP.

HIGH LIMIT REGISTERS

CONFIGURATION

GND

VDD

ADT7482

D1+

ALERT/THERM2THERM

D1−3

D2+ 7

D2−6

REMOTE 1 AND 2 TEMP

VALUE REGISTER

ADDRESS POINTER

SRC

Table 1. ABSOLUTE MAXIMUM RATINGS

Parameter Rating Unit

Positive Supply Voltage (VDD) to GND −0.3 to +3.6 V

D+ −0.3 to VDD + 0.3 V

D− to GND −0.3 to +0.6 V

SCLK, SDATA, ALERT, THERM −0.3 to +3.6 V

Input Current, SDATA, THERM −1 to +50 mA

Input Current, D−1 mA

ESD Rating, All Pins (Human Body Model) 2,000 V

Maximum Junction Temperature (TJ MAX) 150 C

Storage Temperature Range −65 to +150 C

IR Reflow Peak Temperature 220 C

IR Reflow Peak Temperature for Pb-Free 260 C

Lead Temperature, Soldering (10 sec) 300 C

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

10-lead MSOP 142 43.7 C/W

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

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Table 3. PIN ASSIGNMENT

Pin No. Mnemonic Description

1 VDD Positive Supply, 3.0 V to 3.6 V.

2 D1+ Positive Connection to the First Remote (Remote 1) Temperature Sensor.

3 D1−Negative Connection to the First Remote (Remote 1) Temperature Sensor.

4 THERM Open-Drain Output. This pin can be used to turn a fan on/off or throttle a CPU clock in the event of an

overtemperature condition. Requires pullup resistor.

5 GND Supply Ground Connection.

6 D2−Negative Connection to the Second Remote (Remote 2) Temperature Sensor.

7 D2+ Positive Connection to the Second Remote (Remote 2) Temperature Sensor.

8 ALERT/THERM2 Open-Drain Logic Output. This pin is used as interrupt or SMBus alert. May also be configured as a

second THERM output. Requires pullup resistor.

9 SDATA Logic Input/Output, SMBus Serial Data. Open-Drain Output. Requires pullup resistor.

10 SCLK Logic Input, SMBus Serial Clock. Requires pullup resistor.

Table 4. TIMING SPECIFICATIONS (Note 1)

Parameter Limit at TMIN and TMAX Unit Description

fSCLK 400 kHz max

tLOW 1.3 ms min Clock Low Period, between 10% Points

tHIGH 0.6 ms min Clock High Period, between 90% Points

tR300 ms max Clock/Data Rise Time

tF300 ns max Clock/Data Fall Time

tSU; STA 600 ms min Start Condition Setup Time

tHD; STA

(Note 2)

600 ms min Start Condition Hold Time

tSU; DAT

(Note 3)

100 ns min Data Setup Time

tSU; STO

(Note 4)

600 ms min Stop Condition Setup Time

tBUF 1.3 ms min Bus Free Time between Stop and Start Conditions

1. Guaranteed by design, not production tested.

2. Time from 10% of SDATA to 90% of SCLK.

3. Time for 10% or 90% of SDATA to 10% of SCLK.

4. Time for 90% of SCLK to 10% of SDATA.

Figure 2. Serial Bus Timing

STOPSTART

tSU; DAT

tHIGH

tHD; DAT

tLOW

tSU; STO

STOP START

SCLK

SDATA

tBUF

tHD; STA

tSU; STA

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Table 5. ELECTRICAL CHARACTERISTICS (TA=−40C to +120C, VDD = 3.0 V to 3.6 V, unless otherwise noted.)

Parameter Test Conditions Min Typ Max Unit

Power Supply

Supply Voltage, VDD 3.0 3.30 3.6 V

Average Operating Supply Current, IDD 0.0625 Conversions/Sec Rate (Note 1) −240 350 mA

Standby Mode −5.0 30 mA

Undervoltage Lockout Threshold VDD Input, Disables ADC, Rising Edge −2.55 −V

Power-On Reset Threshold 1.0 −2.5 V

Temperature-to-Digital Converter

Local Sensor Accuracy 0C  TA  +70C

0C  TA  +85C

−40C  TA  +100C

−

1.0

1.5

2.5

C

Resolution −1.0 −C

Remote Diode Sensor Accuracy (Note 2) 0C  TA  +70C, −55C  TD  +150C

0C  TA  +85C, −55C  TD  +150C

−40C  TA  +100C, −55C  TD  +150C

−

1.0

1.5

2.5

C

Resolution −0.25 −C

Remote Sensor Source Current High Level (Note 3)

Mid Level (Note 3)

Low Level (Note 2)

−

220

13.5

−

Maximum Series Resistance Cancelled Resistance Split Evenly on D+ and D− Lines −1.5 −kW

Conversion Time From Stop Bit to Conversion Complete

(All Channels) One-shot Mode with

Averaging Switched On

−71 93 ms

One-shot Mode with Averaging Off

(Conversion Rate = 16, 32, or 64

Conversions per Second)

−11.5 15 ms

Open-Drain Digital Outputs (THERM, ALERT / THERM2)

Output Low Voltage, VOL IOUT = −6.0 mA − − 0.4 V

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

SMBus Interface (Note 3 and 4)

Logic Input High Voltage, VIH SCLK, SDATA 2.1 − − V

Logic Input Low Voltage, VIL SCLK, SDATA − − 0.8 V

Hysteresis −500 −mV

SDA Output Low Voltage, VOL IOUT = −6.0 mA − − 0.4 V

Logic Input Current, IIH, IIL −1.0 −+1.0 mA

SMBus Input Capacitance, SCLK, SDATA −5.0 −pF

SMBus Clock Frequency − − 400 kHz

SMBus Timeout (Note 5) User Programmable −25 64 ms

SCLK Falling Edge to SDATA Valid Time Master Clocking in Data − − 1.0 ms

1. See Table 11 for conversion rates.

2. Guaranteed by characterization, but not production tested.

3. Guaranteed by design, but not production tested.

4. See the Timing Specifications section for more information.

5. Disabled by default. For details on enabling the SMBus, see the Serial Bus Interface section.

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TYPICAL PERFORMANCE CHARACTERISTICS

Figure 3. Local Temperature Error vs. Temperature Figure 4. Remote 1 Temperature Error

vs. Temperature

Figure 5. Remote 2 Temperature Error

vs. Temperature

Figure 6. Temperature Error vs. D+/D− Leakage

Resistance

Figure 7. Temperature Error vs. D+/D− Capacitance Figure 8. Operating Supply Current

vs. Conversion Rate

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

MEAN

HIGH 4S

LOW 4S

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

HIGH 4S

LOW 4S

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

MEAN

HIGH 4S

LOW 4S

TEMPERATURE (C)

−50

TEMPERATURE ERROR (C)

−1.0

0 50 100 150

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

TEMPERATURE (C)

−50

TEMPERATURE ERROR (C)

−1.0

0 50 100 150

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

TEMPERATURE (C)

−50

TEMPERATURE ERROR (C)

−1.0

0 50 100 150

−0.5

0.5

1.0

1.5

2.0

2.5

3.0

3.5

LEAKAGE RESISTANCE (MW)

TEMPERATURE ERROR (C)

−25

D+ To VCC

D+ To GND

10 100

−20

−15

−10

−5

CAPACITANCE (nF)

TEMPERATURE ERROR (C)

−18

5 10152025

−16

−14

−12

−10

−8

−6

−4

−2

DEV 2

DEV 4

DEV 3

CONVERTION RATE (Hz)

0.01

IDD (mA)

0.1 1 10 100

100

200

300

400

500

600

700

1000

900

800

DEV 4BC

DEV 3BC

DEV 2BC

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TYPICAL PERFORMANCE CHARACTERISTICS (Cont’d)

Figure 9. Operating Supply Current vs. Voltage Figure 10. Standby Supply Current vs. Voltage

Figure 11. Standby Supply Current vs. SCLK

Frequency

Figure 12. Temperature Error vs. Common-Mode

Noise Frequency

Figure 13. Temperature Error vs. Differential Mode

Noise Frequency

VDD (V)

3.0

408

IDD (mA)

3.1 3.2 3.3 3.4 3.5 3.6

410

412

414

416

418

420

422

DEV 4BC

DEV 3BC

DEV 2BC

VDD (V)

3.0

IDD (mA)

DEV 3

DEV 4

DEV 2

3.1 3.2 3.3 3.4 3.5 3.6

3.2

3.4

3.6

3.8

4.0

4.2

4.4

ISTBY (mA)

DEV 2BC

DEV 3BC

DEV 4BC

10 100 1000

FSCL (kHz) NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

100 200 300 400 500 600

50 mV

20 mV

100 mV

NOISE FREQUENCY (MHz)

TEMPERATURE ERROR (C)

−10 100 200 300 400 500 600

50 mV

20 mV

100 mV

Figure 14. Temperature Error vs. Series Resistance

TOTAL SERIES RESISTANCE ON D+/D− LINES (W)

TEMPERATURE ERROR (C)

500 1000 1500 2000 2500

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Theory of Operation

The ADT7482 is a local and 2 remote temperature sensor

and overtemperature/undertemperature alarm. When the

ADT7482 is operating normally, the on-board ADC operates

in a free-running mode. The analog input multiplexer

alternately selects either the on-chip temperature sensor to

measure its local temperature or either of the remote

temperature sensors. The ADC digitizes these signals and the

results are stored in the local, Remote 1, and Remote 2

temperature value registers.

The local and remote measurement results are compared

with the corresponding high, low, and THERM temperature

limits, stored in on-chip registers. Out-of-limit comparisons

generate flags that are stored in the status register. A result that

exceeds the high temperature limit, the low temperature limit,

or a remote diode open circuit causes the ALERT output to

assert low. Exceeding THERM temperature limits causes the

THERM output to assert low. The ALERT output can be

reprogrammed as a second THERM output.

The limit registers can be programmed, and the device

controlled and configured, via the serial SMBus. The

contents of any register can also be read back via the SMBus.

Control and configuration functions consist of switching

the device between normal operation and standby mode,

selecting the temperature measurement scale, masking or

enabling the ALERT output, switching Pin 8 between

ALERT and THERM2, and selecting the conversion rate.

Series Resistance Cancellation

Parasitic resistance to the D+ and D− inputs to the

ADT7482, 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 temperature measurement. This error

typically causes a 0.5C offset per ohm of parasitic resistance

in series with the remote diode.

The ADT7482 automatically cancels out the effect of this

series resistance on the temperature reading, providing a more

accurate result, without the need for user characterization of

this resistance. The ADT7482 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. See the Noise Filtering

section for more details.

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. However, 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 ADT7482 is to measure the

change in VBE when the device is operated at three different

currents. Previous devices have used only two operating

currents. The use of a third current allows automatic

cancellation of resistances in series with the external

temperature sensor.

Figure 15 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. If a discrete

transistor is used, the collector is not grounded and should

be linked to the base. 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.

Capacitor C1 can be added as a noise filter (a recommended

maximum value of 1,000 pF). However, a better option in

noisy environments is to add a filter, as described in the

Noise Filtering section. See the Layout Considerations

section for more information.

To measure DVBE, the operating current through the

sensor is switched among three related currents. Shown in

Figure 15, N1 I and N2 I are different multiples of the

current, I. The currents through the temperature diode are

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 be shown to 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

for low conversion rates. At rates of 16, 32, and

64 conversions/second, no digital averaging takes place.

Signal conditioning and measurement of the internal

temperature sensor are performed in the same manner.

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Figure 15. Input Signal Conditioning

LOW-PASS FILTER

fC = 65 kHz

REMOTE

SENSING

TRANSISTOR BIAS

DIODE

D+

D−

VDD

IBIAS

I N1  I

VOUT+

VOUT−

To ADC

N2  I

C1*

*CAPACITOR C1 IS OPTIONAL.

IT SHOULD ONLY BE USED IN

NOISY ENVIRONMENTS.

Temperature Measurement Results

The results of the local and remote temperature

measurements are stored in the local and remote temperature

value registers and are compared with limits programmed

into the local and remote high and low limit registers.

The local temperature measurement is an 8-bit measurement

with 1C resolution. The remote temperature measurements

are 10-bit measurements, with the 8 MSBs stored in one

list of the temperature measurement registers.

Table 6. REGISTER ADDRESS FOR THE

TEMPERATURE VALUES

Temperature

Channel

MSBs

LSBs

Local 0x00 N/A

Remote 1 0x01 0x10 (2 MSBs)

Remote 2 0x30 0x33 (2 MSBs)

Set Bit 3 of the Configuration 1 register to 1, to read the

Remote 2 temperature values from the following register

addresses:

Remote 2, MSBs = 0x01

Remote 2, LSBs = 0x10

The above is true only when Bit 3 of the Configuration 1

this bit back to 0.

Only the two MSBs in the remote temperature low byte

are used. This gives the remote temperature measurement a

resolution of 0.25C. Table 7 shows the data format for the

remote temperature low byte.

Table 7. EXTENDED TEMPERATURE RESOLUTION

(REMOTE TEMPERATURE LOW BYTE)

Extended Resolution

Remote Temperature

Low Byte

0.00C0 000 0000

0.25C0 100 0000

0.50C1 000 0000

0.75C1 100 0000

When reading the full remote temperature value, both the

high and low byte, the two registers should be read LSB first

and then MSB. Reading the LSB causes the MSB to be

locked until it is read. This guarantees that the two values are

read as a result of the same temperature measurement.

Temperature Measurement Range

The temperature measurement range for both local and

remote measurements is, by default, 0C to +127C.

However, the ADT7482 can be operated using an extended

temperature range. It can measure the full temperature range

of a remote thermal diode, from −55C to +150C. Switch

between these two temperature ranges by setting or clearing

Bit 2 in the Configuration 1 register. A valid result is

available in the next measurement cycle after changing the

temperature range.

In extended temperature mode, the upper and lower

temperature measured by the ADT7482 is limited by the

remote diode selection. The temperature registers

themselves can have values from −64C to +191C.

However, most temperature-sensing diodes have a

maximum temperature range of −55C to +150C.

Note that while both local and remote temperature

measurements can be made while the part is in extended

temperature mode, the ADT7482 itself should not be

exposed to temperatures greater than those specified in the

Absolute Maximum Ratings section. Further, the device is

only guaranteed to operate as specified at ambient

temperatures from −40C to +120C.

Temperature Data Format

When the measurement range is in extended mode, an

offset binary data format is used for both local and remote

results. Temperature values in the offset binary data format

are offset by +64. Examples of temperatures in both data

formats are shown in Table 8.

Switching between measurement ranges can be done at

any time. Switching the range also switches the data format.

The next temperature result following the switching is

reported back to the register in the new format. However, the

contents of the limit registers do not change. Ensure that

when the data format changes, the limit registers are

reprogrammed as necessary. For more information, refer to

the Limit Registers section.

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The ADT7482 has two temperature data formats. When

the temperature measurement range is from 0C to 127C

(default), the temperature data format for both local and

remote temperature results is binary.

Table 8. TEMPERATURE DATA FORMAT

(LOCAL AND REMOTE TEMPERATURE HIGH BYTE)

Temperature Binary

Offset Binary

(Note 1)

−55C0 000 0000

(Note 2)

0 000 1001

0C0 000 0000 0 100 0000

+1C0 000 0001 0 100 0001

+10C0 000 1010 0 100 1010

+25C0 001 1001 0 101 1001

+50C0 011 0010 0 111 0010

+75C0 100 1011 1 000 1011

+100C0 110 0100 1 010 0100

+125C0 111 1101 1 011 1101

+127C0 111 1111 1 011 1111

+150C0 111 1111

(Note 3)

1 101 0110

1. Offset binary scale temperature values are offset by +64.

2. Binary scale temperature measurement returns 0 for all

temperatures < 0C.

3. Binary scale temperature measurement returns 127 for all

temperatures > 127C.

Registers

The registers in the ADT7482 are 8-bits wide. These

registers are used to store the results of remote and local

temperature measurements and high and low temperature

limits and to configure and control the device. A description

of these registers follows.

Address Pointer Register

The address pointer register itself does not have, or

require, an address, as the first byte of every write operation

is automatically written to this register. The data in this first

byte always contains the address of another register on the

ADT7482, which is stored in the address pointer register. It

is to this register address that the second byte of a write

operation is written to or to which a subsequent read

operation is performed.

The power-on default value of the address pointer register

is 0x00. Therefore, if a read operation is performed

immediately after power-on, without first writing to the

address pointer, the value of the local temperature is

returned, since its register address is 0x00.

Configuration Registers

There are two configuration registers used to control the

operation of the ADT7482. Configuration 1 register is at

Address 0x03 for reads and Address 0x09 for writes. See

Table 9 for details regarding the operation of this register.

Configuration 2 Register is at Address 0x24 for both reads

and writes. Setting Bit 7 of this register locks all lockable

registers. The affected registers can only be modified if the

ADT7482 is powered down and powered up again. See

Table 16 for a list of the registers affected by the lock bit.

Temperature Value Registers

The ADT7482 has five registers to store the results of

local and remote temperature measurements. These

registers can only be written to by the ADC and can be read

over the SMBus.

The local temperature value register is at Address 0x00.

The Remote 1 temperature value high byte register is at

Address 0x01; the Remote 1 low byte register is at

Address 0x10.

The Remote 2 temperature value high byte register is at

Address 0x30; the Remote 2 low byte register is at

Address 0x33.

The Remote 2 temperature values can be read from

Addresses 0x01 for the high byte and Address 0x10 for

the low byte if Bit 3 of Configuration Register 1 is set

to 1.

To read the Remote 1 temperature values, set Bit 3 of

Configuration Register 1 to 0.

The power-on default for all five registers is 0x00.

Table 9. CONFIGURATION 1 REGISTER (READ ADDRESS 0x03, WRITE ADDRESS 0x09)

Bit Mnemonic Function

7Mask Setting this bit to 1 masks all ALERTs on the ALERT pin. Default = 0 = ALERT enabled. This applies only if Pin 8 is

configured as ALERT, otherwise it has no effect.

6Mon/STBY Setting this bit to 1 places the ADT7482 in standby mode, that is, it suspends all temperature measurements

(ADC). The SMBus remains active and values can be written to, and read from, the registers. THERM and ALERT

are also active in standby mode. Changes made to the limit registers in standby mode that effect the THERM or

ALERT outputs cause these signals to be updated. Default = 0 = temperature monitoring enabled.

5AL/TH This bit selects the function of Pin 8. Default = 0 = ALERT. Setting this bit to 1 configures Pin 8 as the THERM2 pin.

4Reserved Reserved for future use.

3Remote 1

/Remote2

Setting this bit to 1 enables the user to read the Remote 2 values from the Remote 1 registers. When default = 0,

Remote 1 temperature values and limits are read from these registers.

2Tem p

Range

Setting this bit to 1 enables the extended temperature measurement range of −50C to +150C.

Default = 0 = 0C to +127C.

1Mask R1 Setting this bit to 1 masks ALERTs due to the Remote 1 temperature exceeding a programmed limit. Default = 0.

0Mask R2 Setting this bit to 1 masks ALERTs due to the Remote 2 temperature exceeding a programmed limit. Default = 0.

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Table 10. CONFIGURATION 2 REGISTER (ADDRESS 0x24)

Bit Mnemonic Function

7Lock Bit Setting this bit to 1 locks all lockable registers to their current values. This prevents tampering with settings

until the device is powered down. Default = 0.

<6:0> Res Reserved for future use.

Conversion Rate Register

The conversion rate register is at Address 0x04 for reads

and Address 0x0A for writes. The four LSBs of this register

are used to program the conversion times from 15.5 ms

(Code 0x0A) to 16 seconds (Code 0x00). To program the

ADT7482 to perform continuous measurements, set the

conversion rate register to 0x0B. For example, a conversion

rate of 8 conversions/second means that, beginning at

125 ms intervals, the device performs a conversion on the

local and the remote temperature channels. The four MSBs

of this register are reserved and should not be written to.

This register can be written to and read back over the

SMBus. The default value of this register is 0x07, giving a

rate of 8 conversions per second. Use of slower conversion

times greatly reduces the device power consumption.

Limit Registers

The ADT7482 has three limits for each temperature

channel: high, low, and THERM temperature limits for

local, Remote 1, and Remote 2 temperature measurements.

The remote temperature high and low limits span two

registers each, to contain an upper and lower byte for each

limit. There is also a THERM hysteresis register. All limit

registers can be written to and read back over the SMBus.

See Table 16 for limit register addresses and power-on

default values.

When Pin 8 is configured as an ALERT output, the high

limit registers perform a > comparison while the low limit

registers perform a  comparison. For example, if the high

limit register is programmed with 80C, then measuring

81C results in an out-of-limit condition, setting a flag in the

status register. If the low limit register is programmed with

0C, measuring 0C or lower results in an out-of-limit

condition.

Exceeding either the local or remote THERM limit asserts

THERM low. When Pin 8 is configured as THERM2,

exceeding either the local or remote high limit asserts

THERM2 low. A default hysteresis value of 10C is

provided that applies to both THERM channels. This

hysteresis value can be reprogrammed.

It is important to remember that the temperature limits

data format is the same as the temperature measurement data

format. If the temperature measurement uses the default

binary scale, then the temperature limits also use the binary

scale. If the temperature measurement scale is switched,

however, the temperature limits do not switch automatically.

The limit registers must be reprogrammed to the desired

value in the correct data format. For example, if the remote

low limit is set at 10C and the default binary scale is used,

the limit register value should be 0000 1010b. If the scale is

switched to offset binary, the value in the low temperature

limit register should be reprogrammed to be 0100 1010b.

Table 11. CONVERSION RATE/CHANNEL SELECTOR REGISTER (READ ADDRESS 0x04, WRITE ADDRESS 0x0A)

Bit Mnemonic Function

7 Reserved Reserved for Future Use. Do Not Write to this Bit.

6 Reserved Reserved for Future Use. Do Not Write to this Bit.

5 Reserved Reserved for Future Use. Do Not Write to this Bit.

4 Reserved Reserved for Future Use. Do Not Write to this Bit.

<3:0> Conversion Rates These Bits Set how often the ADT7482 Measures each Temperature Channel.

Conversions/sec Time (seconds)

0000 = 0.0625 16

0001 = 0.125 8

0010 = 0.25 4

0011 = 0.5 2

0100 = 1 1

0101 = 2 500 m

0110 = 4 250 m

0111 = 8 = Default 125 m

1000 = 16 62.5 m

1001 = 32 31.25 m

1010 = 64 15.5 m

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Status Registers

The status registers are read-only registers at

Addresses 0x02 (Status Register 1) and Address 0x23

(Status Register 2). They contain status information for the

ADT7482.

Table 12. STATUS REGISTER 1 BIT ASSIGNMENTS

Bit Mnemonic Function ALERT

7 BUSY 1 when ADC Converting No

6LHIGH

(Note 1)

1 when Local High

Temperature Limit Tripped

Yes

5LLOW

(Note 1)

1 when Local Low

Temperature Limit Tripped

Yes

4R1HIGH

(Note 1)

1 when Remote 1 High

Temperature Limit Tripped

Yes

3R1LOW

(Note 1)

1 when Remote 1 Low

Temperature Limit Tripped

Yes

2D1 OPEN

(Note 1)

1 when Remote 1 Sensor

Open Circuit

Yes

1 R1THRM1 1 when Remote 1 THERM

Limit Tripped

0 LTHRM1 1 when Local THERM Limit

Tripped

1. These flags stay high until the status register is read, or they are

reset by POR.

Table 13. STATUS REGISTER 2 BIT ASSIGNMENTS

Bit Mnemonic Function ALERT

7 Res Reserved for Future Use No

6 Res Reserved for Future Use No

5 Res Reserved for Future Use No

4R2HIGH

(Note 1)

1 when Remote 2 High

Temperature Limit Tripped

Yes

3R2LOW

(Note 1)

1 when Remote 2 Low

Temperature Limit Tripped

Yes

2D2 OPEN

(Note 1)

1 when Remote 2 Sensor

Open Circuit

Yes

1 R2THRM1 1 when Remote 2 THERM

Limit Tripped

0 ALERT 1 when ALERT Condition

Exists

1. These flags stay high until the status register is read, or they are

reset by POR.

The eight flags that can generate an ALERT are NOR’d

together. When any flags are high, the ALERT interrupt

latch is set and the ALERT output goes low (provided they

are not masked out).

Reading the Status 1 register clears the 5 flags, (Bit 6

through Bit 2) in Status Register 1, provided the error

conditions that caused the flags to be set have gone away.

Reading the Status 2 Register clears the three flags, (Bit 4

through Bit 2) in Status Register 2, provided the error

conditions that caused the flags to be set have gone away. A

flag bit can only be reset if the corresponding value register

contains an in-limit measurement or if the sensor is good.

The ALERT interrupt latch is not reset by reading the

status register. It is reset when the ALERT output has been

serviced by the master reading the device address, provided

the error condition has gone away and the status register flag

bits have been reset.

When Flag 1 and/or Flag 0 of Status Register 1 or Flag 1

of Status Register 2 are set, the THERM output goes low to

indicate that the temperature measurements are outside the

programmed limits. The THERM output does not need to be

reset, unlike the ALERT output. Once the measurements are

within the limits, the corresponding status register bits are

reset automatically, and the THERM output goes high. To

add hysteresis, program Register 0x21. The THERM output

is reset only when the temperature falls below the THERM

limit minus hysteresis.

When Pin 8 is configured as THERM2, only the high

temperature limits are relevant. If Flag 6 or Flag 4 of Status

THERM2 output goes low to indicate that the temperature

measurements are outside the programmed limits. Flag 5

and Flag 3 of Status Register 1 and Flag 3 of Status

THERM2 is otherwise the same as THERM.

Bit 0 of the Status Register 2 is set whenever the

ADT7482 ALERT output is asserted low. Read Status

the ALERT. This bit is reset when the ALERT output is reset.

If the ALERT output is masked, then this bit is not set.

Offset Register

Offset errors can be introduced into the remote

temperature measurement by clock noise or by the thermal

diode being located away from the hot spot. To achieve the

specified accuracy on this channel, these offsets must be

removed.

The offset values are stored as 10-bit, twos complement

values.

The Remote 1 Offset MSBs are stored in Register 0x11

and the LSBs are stored in Register 0x12 (low byte, left

justified). The Remote 2 Offset MSBs are stored in

(low byte, left justified).

The Remote 2 Offset can be written to or read from the

Remote 1 Offset Registers if Bit 3 of the

Configuration 1 register is set to 1. This bit should be

set to 0 (default) to read the Remote 1 offset values.

Only the upper 2 bits of the LSB registers are used. The

MSB of MSB offset registers is the sign bit. The minimum

offset that can be programmed is −128C, and the maximum

is +127.75C. The value in the offset register is added or

subtracted to the measured value of the remote temperature.

The offset register powers up with a default value of 0C

and has no effect unless a different value is written to it.

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Table 14. SAMPLE OFFSET REGISTER CODES

Offset Value 0x11/0x34 0x12/0x35

−128C1000 0000 00 00 0000

−4C1111 1100 00 00 0000

−1C1111 1111 00 000000

−0.25C1111 1111 10 00 0000

0C0000 0000 00 00 0000

+0.25C0000 0000 01 00 0000

+1C0000 0001 00 00 0000

+4C0000 0100 00 00 0000

+127.75C0111 1111 11 00 0000

One-shot Register

The one-shot register initiates a conversion and

comparison cycle when the ADT7482 is in standby mode,

after which the device returns to standby. Writing to the

one-shot register address (0x0F) causes the ADT7482 to

perform a conversion and comparison on both the local and

the remote temperature channels. This is not a data register

as such, and it is the write operation to Address 0x0F that

causes the one-shot conversion. The data written to this

address is irrelevant and is not stored.

Consecutive ALERT Register

The value written to this register determines how many

out-of-limit measurements must occur before an ALERT is

generated. The default value is that one out-of-limit

measurement generates an ALERT. The maximum value

that can be chosen is 4. This register allows some filtering

of the output. This is particularly useful at the fastest three

conversion rates, where no averaging takes place. This

Table 15.

Table 15. CONSECUTIVE ALERT REGISTER BIT

Amount of Out-of-Limit

Measurements Required

yza 000x 1

yza 001x 2

yza 011x 3

yza 111x 4

NOTES: y = SMBus SCL timeout bit. Default = 0. See the Serial

Bus Interface section for more information.

z = SMBus SDA timeout bit. Default = 0. See the Serial

Bus Interface section for more information.

a = Mask Internal ALERTs.

x = Don’t care bit.

Table 16. LIST OF REGISTERS

Read

Address

(Hex)

Write

Address

(Hex) Mnemonic Power-On Default Comment Lock

N/A N/A Address Pointer Undefined No

00 N/A Local Temperature Value 0000 0000 (0x00) No

01 N/A Remote 1 Temperature Value High Byte 0000 0000 (0x00) Bit 3 Conf. Reg. = 0 No

01 N/A Remote 2 Temperature Value High Byte 0000 0000 (0x00) Bit 3 Conf. Reg. = 1 No

02 N/A Status Register 1 Undefined No

03 09 Configuration Register 1 0000 0000 (0x00) Yes

04 0A Conversion Rate 0000 0111 (0x07) Yes

05 0B Local Temperature High Limit 0101 0101 (0x55) (85C) Yes

06 0C Local Temperature Low Limit 0000 0000 (0x00) (0C) Yes

07 0D Remote 1 Temperature High Limit High Byte 0101 0101 (0x55) (85C) Bit 3 Conf. Reg. = 0 Yes

07 0D Remote 2 Temperature High Limit High Byte 0101 0101 (0x55) (85C) Bit 3 Conf. Reg. = 1 Yes

08 0E Remote 1 Temperature Low Limit High Byte 0000 0000 (0x00) (0C) Bit 3 Conf. Reg. = 0 Yes

08 0E Remote 2 Temperature Low Limit High Byte 0000 0000 (0x00) (0C) Bit 3 Conf. Reg. = 1 Yes

N/A 0F

(Note 1)

One Shot N/A

10 N/A Remote 1 Temperature Value Low Byte 0000 0000 Bit 3 Conf. Reg. = 0 No

10 N/A Remote 2 Temperature Value Low Byte 0000 0000 Bit 3 Conf. Reg. = 1 No

11 11 Remote 1 Temperature Offset High Byte 0000 0000 Bit 3 Conf. Reg. = 0 Yes

11 11 Remote 2 Temperature Offset High Byte 0000 0000 Bit 3 Conf. Reg. = 1 Yes

12 12 Remote 1 Temperature Offset Low Byte 0000 0000 Bit 3 Conf. Reg. = 0 Yes

12 12 Remote 2 Temperature Offset Low Byte 0000 0000 Bit 3 Conf. Reg. = 1 Yes

13 13 Remote 1 Temperature High Limit Low Byte 0000 0000 Bit 3 Conf. Reg. = 0 Yes

13 13 Remote 2 Temperature High Limit Low Byte 0000 0000 Bit 3 Conf. Reg. = 1 Yes

14 14 Remote 1 Temperature Low Limit Low Byte 0000 0000 Bit 3 Conf. Reg. = 0 Ye s

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Table 16. LIST OF REGISTERS (continued)

Read

Address

(Hex) LockCommentPower-On DefaultMnemonic

Write

Address

(Hex)

14 14 Remote 2 Temperature Low Limit Low Byte 0000 0000 Bit 3 Conf. Reg. = 1 Ye s

19 19 Remote 1 THERM Limit 0101 0101 (0x55) (85C) Bit 3 Conf. Reg. = 0 Yes

19 19 Remote 2 THERM Limit 0101 0101 (0x55) (85C) Bit 3 Conf. Reg. = 1 Yes

20 20 Local THERM Limit 0101 0101 (0x55) (85C) Yes

21 21 THERM Hysteresis 0000 1010 (0x0A) (10C) Yes

22 22 Consecutive ALERT 0000 0001 (0x01) Yes

23 N/A Status Register 2 0000 0000 (0x00) No

24 24 Configuration 2 Register 0000 0000 (0x00) Yes

30 N/A Remote 2 Temperature Value High Byte 0000 0000 (0x00) No

31 31 Remote 2 Temperature High Limit High Byte 0101 0101 (0x55) (85C) Yes

32 32 Remote 2 Temperature Low Limit High Byte 0000 0000 (0x00) (0C) Yes

33 N/A Remote 2 Temperature Value Low Byte 0000 0000 (0x00) No

34 34 Remote 2 Temperature Offset High Byte 0000 0000 (0x00) Yes

35 35 Remote 2 Temperature Offset Low Byte 0000 0000 (0x00) Ye s

36 36 Remote 2 Temperature High Limit Low Byte 0000 0000 (0x00) (0C) Yes

37 37 Remote 2 Temperature Low Limit Low Byte 0000 0000 (0x00) (0C) Yes

39 39 Remote 2 THERM Limit 0101 0101 (0x55) (85C) Yes

FE N/A Manufacturer ID 0100 0001 (0x41) N/A

FF N/A Die Revision Code 0110 0101 (0x65) N/A

1. Writing to address 0F causes the ADT7482 to perform a single measurement. It is not a data register as such and it does not matter what

data is written to it.

Serial Bus Interface

Control of the ADT7482 is achieved via the serial bus.

The ADT7482 is connected to this bus as a slave device,

under the control of a master device.

The ADT7482 has an SMBus timeout feature. When this is

enabled, the SMBus times out after typically 25 ms of no

activity. However, this feature is not enabled by default. Set

Bit 7 (SCL Timeout Bit) of the consecutive alert register

(Address = 0x22) to enable the SCL Timeout. Set Bit 6 (SDA

Timeout Bit) of the consecutive alert register (Address = 0x22)

to enable the SDA Timeout.

Consult the SMBus 1.1 Specification for more information

(www.smbus.org).

Addressing the Device

In general, every SMBus device has a 7-bit device

address, except for some devices that have extended, 10-bit

addresses. When the master device sends a device address

over the bus, the slave device with that address responds.

The ADT7482 is available with one device address, 0x4C

(1001 100b). The address mentioned in this data sheet is a

7-bit address. The R/W bit needs to be added to arrive at an

8-bit address.

Serial Bus Protocol Operation

The master initiates data transfer by establishing a start

condition, defined as a high-to-low transition on the serial

data line SDATA while the serial clock line SCLK remains

high. This indicates that an address/data stream follows.

All slave peripherals connected to the serial bus respond

to the start condition and shift in the next eight bits,

consisting of a 7-bit address (MSB first) plus an R/W bit,

which determines the direction of the data transfer, that is,

whether data is to be written to or read from the slave device.

The peripheral whose address corresponds to the transmitted

address responds by pulling the data line low during the low

period before the ninth clock pulse, known as the

acknowledge bit. All other devices on the bus now remain

idle while the selected device waits for data to be read from

or written to it. If the R/W bit is a 0, the master writes to the

slave device. If the R/W bit is a 1, the master reads from the

slave device.

Data is sent over the serial bus in a sequence 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, since a low-to-high transition

when the clock is high can 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 tenth 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

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acknowledge. The master then takes the data line low during

the low period before the tenth clock pulse, then high during

the tenth 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 case of the

ADT7482, write operations contain either one or two bytes,

while read operations contain one byte.

To write data to one of the device data registers or to read

data from it, the address pointer register must be set so that

the correct data register is addressed. The first byte of a write

operation always contains a valid address that is stored in the

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

the write operation contains a second data byte that is written

to the register selected by the address pointer register.

This procedure is illustrated in Figure 16. The device

address is sent over the bus followed by R/W 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.

Figure 16. Writing a Register Address to the Address Pointer Register, then Writing Data to the Selected Register

SCLK

SDATA 00 1100D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7482

START BY

MASTER

ACK. BY

ADT7482

D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7482 STOP BY

MASTER

SCLK (CONTINUED)

SDATA (CONTINUED)

FRAME 1

SERIAL BUS ADDRESS BYTE FRAME 2

ADDRESS POINTER REGISTER BYTE

FRAME 3

DATA BYTE

R/W

Figure 17. Writing to the Address Pointer Register Only

SCLK

SDATA 00

1100D7 D6 D5 D4 D3 D2 D1 D0

ACK. BY

ADT7482

STOP BY

MASTER

START BY

MASTER FRAME 1

SERIAL BUS ADDRESS BYTE

FRAME 2

ADDRESS POINTER REGISTER BYTE

119

ACK. BY

ADT7482

R/W

Figure 18. Reading Data from a Previously Selected Register

SCLK

SDATA 001100D7 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 ADT7482

119

ACK. BY

ADT7482

R/W

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Reading Data from a Register

When reading data from a register there are two

possibilities:

1. If the ADT7482 address pointer register value is

unknown or not the desired value, it is first

necessary to set it to the correct value before data

can be read from the desired data register. This is

done by performing a write to the ADT7482 as

before, but only the data byte containing the

written to the register. This is shown in Figure 17.

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 18.

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 and the bus

transaction shown in Figure 17 can be omitted.

When reading data from a register, it is important to note

the following points:

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

without first writing to the address pointer register.

However, if the address pointer register is already at the

correct value, it is not possible to write data to a register

without writing to the address pointer register. This is

because the first data byte of a write is always written

to the address pointer register.

Remember that some of the ADT7482 registers have

different addresses for read and write operations. The

write address of a register must be written to the

address pointer if data is to be written to that register,

but it may not be possible to read data from that

address. The read address of a register must be written

to the address pointer before data can be read from that

ALERT Output

Pin 8 can be configured as an ALERT output. The ALERT

output goes low whenever an out-of-limit measurement is

detected, or if the remote temperature sensor is an open

circuit. It is an open-drain output and requires a pullup to

VDD. Several ALERT outputs can be wire-OR’ed together,

so that the common line goes low if one or more of the

ALERT outputs goes low.

The ALERT output can be used as an interrupt signal to a

processor, or it can be used as a SMBALERT. Slave devices

on the SMBus cannot normally signal to the bus master that

they want to talk, but the SMBALERT function allows them

to do so.

One or more ALERT outputs can be connected to a

common SMBALERT line connected to the master. When

the SMBALERT line is pulled low by one of the devices, the

following procedure occurs as illustrated in Figure 19.

Figure 19. Use of SMBALERT

ALERT RESPONSE

ADDRESS

MASTER SENDS

ARA AND READ

COMMAND DEVICE SENDS

ITS ADDRESS

RDSTART ACK DEVICE

ADDRESS

ACK STOP

MASTER

RECEIVES

SMBALERT

1. SMBALERT is pulled low.

2. Master initiates a read operation and sends the

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

a general call address that should not be used as a

specific device address.

3. The device whose ALERT output is low responds

to the alert response address and the master reads

its device address. As the device address is seven

bits, an LSB of 1 is added. The address of the

device is now known and it can be interrogated in

the usual way.

4. If more than one device has a low ALERT, the one

with the lowest device address has priority, in

accordance with normal SMBus arbitration.

5. Once the ADT7482 has responded to the alert

response address, it resets its ALERT output,

provided that the error condition that caused the

ALERT no longer exists. If the SMBALERT line

remains low, the master sends the ARA again, and

so on until all devices with low ALERT outputs

respond.

Low Power Standby Mode

The ADT7482 can be put into low power standby mode

by setting Bit 6 (Mon/STBY bit) of the Configuration 1

When Bit 6 is 0, the ADT7482 operates normally. When

Bit 6 is 1, the ADC is inhibited, and any conversion in

progress is terminated without writing the result to the

corresponding value register.

The SMBus is still enabled in low power standby mode.

Power consumption in this standby mode is reduced to a

typical of 5 mA if there is no SMBus activity or up to 30 mA

if there are clock and data signals on the bus.

When the device is in standby mode, it is still possible to

initiate a one-shot conversion of all channels by writing to

the one-shot register (Address 0x0F), after which the device

returns to standby. It does not matter what is written to the

one-shot register as all data written to it is ignored. It is also

possible to write new values to the limit register while in

standby mode. If the values stored in the temperature value

registers are now outside the new limits, an ALERT is

generated, even though the ADT7482 is still in standby

mode.

Sensor Fault Detection

The ADT7482 has sensor fault detection circuitry

internally at its D+ inputs. This circuit can detect situations

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where a remote diode is not connected, or is incorrectly

connected, to the ADT7482. A simple voltage comparator

trips if the voltage at D+ exceeds VDD −1 V (typical),

signifying an open circuit between D+ and D−. The output

of this comparator is checked when a conversion is initiated.

Bit 2 (D1 OPEN flag) of the Status Register 1

(Address 0x02) is set if a fault is detected on the Remote 1

channel. Bit 2 (D2 OPEN flag) of the Status Register 2

(Address 0x23) is set if a fault is detected on the Remote 2

channel. If the ALERT pin is enabled, setting this flag causes

ALERT to assert low.

If a remote sensor is not used with the ADT7482, then the

D+ and D− inputs of the ADT7482 need to be tied together

to prevent the OPEN flag from being set continuously.

Most temperature sensing diodes have an operating

temperature range of −55C to +150C. Above 150C, they

lose their semiconductor characteristics and approximate

conductors instead. This results in a diode short, setting the

open flag. The remote diode in this case no longer gives an

accurate temperature measurement. A read of the

temperature result register gives the last good temperature

measurement. Be aware that while the diode fault is

triggered, the temperature measurement on the remote

channels may not be accurate.

Interrupt System

The ADT7482 has two interrupt outputs, ALERT and

THERM. Both have different functions and behavior.

ALERT is maskable and responds to violations of software

programmed temperature limits or an open-circuit fault on

the remote diode. THERM is intended as a fail-safe interrupt

output that cannot be masked.

If the Remote 1, Remote 2, or local temperature exceeds

the programmed high temperature limits, or equals or

exceeds the low temperature limits, the ALERT output is

asserted low. An open-circuit fault on the remote diode also

causes ALERT to assert. ALERT is reset when serviced by

a master reading its device address, provided the error

condition has gone away, and the status register has been

reset.

The THERM output asserts low if the Remote 1,

Remote 2, or local temperature exceeds the programmed

THERM limits. The THERM temperature limits should

normally be equal to or greater than the high temperature

limits. THERM is reset automatically when the temperature

falls back within the (THERM −hysteresis) limit. The local

and remote THERM limits are set by default to 85C. A

hysteresis value can be programmed, in which case,

THERM resets when the temperature falls to the limit value

minus the hysteresis value. This applies to both local and

remote measurement channels. The power-on hysteresis

default value is 10C, but this can be reprogrammed to any

value after powerup.

The hysteresis loop on the THERM outputs is useful when

THERM is used for on/off control of a fan. The system can

be set up so that when THERM asserts, a fan can be switched

on to cool the system. When THERM goes high again, the

fan can be switched off. Programming a hysteresis value

protects from fan jitter, where the temperature hovers

around the THERM limit, and the fan is constantly being

switched on and off.

Table 17. THERM HYSTERESIS

THERM Hysteresis Binary Representation

0C0 000 0000

1C0 000 0001

10C0 000 1010

If the ADT7482 is in the default temperature range (0C

to 127C), then THERM hysteresis must be less than the

THERM limit.

Figure 20 shows how the THERM and ALERT outputs

operate. If desired, use the ALERT output as a SMBALERT

to signal to the host via the SMBus that the temperature has

risen. Use the THERM output to turn on a fan to cool the

system, if the temperature continues to increase. This

method ensures that there is a fail-safe mechanism to cool

the system, without the need for host intervention.

Figure 20. Operation of the ALERT and THERM

Interrupts

1005C

THERM LIMIT

905C

805C

705C

605C

505C

405C

THERM LIMIT − HYSTERESIS

HIGH TEMP LIMIT

RESET BY MASTER

TEMPERATURE

ALERT

THERM

1. If the measured temperature exceeds the high

temperature limit, the ALERT output asserts low.

2. If the temperature continues to increase and

exceeds the THERM limit, the THERM output

asserts low. This can be used to throttle the CPU

clock or switch on a fan.

3. The THERM output de-asserts (goes high) when

the temperature falls to THERM limit minus

hysteresis. In Figure 20, the default hysteresis

value of 10C is shown.

4. The ALERT output de-asserts only when the

temperature has fallen below the high temperature

limit, and the master has read the device address

and cleared the status register.

Pin 8 on the ADT7482 can be configured as either an

ALERT output or as an additional THERM output.

THERM2 asserts low when the temperature exceeds the

programmed local and/or remote high temperature limits. It

is reset in the same manner as THERM, and it is not

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maskable. The programmed hysteresis value applies to

THERM2 also.

Figure 21 shows how THERM and THERM2 might

operate together to implement two methods of cooling the

system. In this example, the THERM2 limits are set lower

than the THERM limits. The THERM2 output could be used

to turn on a fan. If the temperature continues to rise and

exceeds the THERM limits, the THERM output could

provide additional cooling by throttling the CPU.

Figure 21. Operation of the THERM and THERM2

Interrupts

THERM2 LIMIT

905C

805C

705C

605C

505C

405C

TEMPERATURE

THERM

305C

THERM LIMIT

THERM2

1. When the THERM2 limit is exceeded, the

THERM2 signal asserts low.

2. If the temperature continues to increase and

exceeds the THERM limit, the THERM output

asserts low.

3. The THERM output de-asserts (goes high) when

the temperature falls to THERM limit minus

hysteresis. In Figure 21, there is no hysteresis

value shown.

4. As the system cools further, and the temperature

falls below the THERM2 limit, the THERM2

signal resets. Again, no hysteresis value is shown

for THERM2.

The temperature measurement could be either the local or

the remote temperature measurement.

Applications Information

Noise Filtering

For temperature sensors operating in noisy environments,

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

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

However, large capacitance’s affect the accuracy of the

temperature measurement, leading to a recommended

maximum capacitor value of 1,000 pF. While this capacitor

reduces the noise, it does not eliminate it, making it difficult

to use the sensor in a very noisy environment.

The ADT7482 has a major advantage over other devices

for eliminating the effects of noise on the external sensor.

The series resistance cancellation feature allows a filter to 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 cancelled from the

temperature result.

The construction of a filter allows the ADT7482 and the

remote temperature sensor to operate in noisy environments.

Figure 22 shows a low-pass R-C-R filter, with the following

values:

R = 100 W and C = 1 nF

This filtering reduces both common-mode noise and

differential noise.

Figure 22. Filter Between Remote Sensor

and ADT7482

100 W

100 W1 nF

D+

D−

REMOTE

TEMPERATURE

SENSOR

Factors Affecting Diode Accuracy

Remote Sensing Diode

The ADT7482 is designed to work with substrate

transistors built into processors or with 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 collector). If an NPN transistor is used, the

collector and base are connected to D+ and the emitter to D−.

If a PNP transistor is used, the collector and base are

connected to D− and the emitter to D+.

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 ADT7482 is trimmed for an nf value of 1.008. The

following equation can be used to calculate the error

introduced at a temperature T (C), when using a

transistor whose nf does not equal 1.008. Consult the

processor data sheet for the nf values.

(eq. 1)

DT+ǒnf*1.008Ǔń1.008 ǒ273.15 Kelvin )TǓ

To factor this in, write the DT value to the offset register.

It is then automatically added to or subtracted from the

temperature measurement by the ADT7482.

Some CPU manufacturers specify the high and low

current levels of the substrate transistors. The high

current level of the ADT7482, IHIGH, is 220 mA and the

low level current, ILOW, is 13.5 mA. If the ADT7482

current levels do not match the current levels specified

by the CPU manufacturer, it may be necessary to

remove an offset. The CPU data sheet advises whether

this offset needs to be removed and how to calculate it.

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This offset can be programmed to the offset register. It

is important to note that if more than one offset must be

considered, the algebraic sum of these offsets must be

programmed to the offset register.

If a discrete transistor is being used with the ADT7482,

the best accuracy is obtained by choosing devices according

to the following criteria:

Base-emitter voltage greater than 0.25 V at 6 mA, at the

highest operating temperature.

Base-emitter voltage less than 0.95 V at 100 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.

Thermal Inertia and Self-heating

Accuracy depends on the temperature of the remote

sensing diode and/or the local temperature sensor being at

the same temperature as that being measured. A number of

factors can affect this. Ideally, the sensor should be in good

thermal contact with the part of the system being measured.

If it is not, the thermal inertia caused by the sensor’s mass

causes a lag in the response of the sensor to a temperature

change. In the case of the remote sensor, this should not be

a problem, since it is either a substrate transistor in the

processor or a small package device, such as SOT−23,

placed in close proximity to it.

The on-chip sensor, however, is often remote from the

processor and only monitors the general ambient

temperature around the package. In practice, the ADT7482

package is in electrical, and hence thermal, contact with a

PCB and may also be in a forced airflow. How accurately the

temperature of the board and/or the forced airflow reflects

the temperature to be measured also affects the accuracy.

Self-heating due to the power dissipated in the ADT7482 or

the remote sensor causes the chip temperature of the device

or remote sensor to rise above ambient. However, the current

forced through the remote sensor is so small that self-heating

is negligible. In the case of the ADT7482, the worst-case

condition occurs when the device is converting at

64 conversions per second while sinking the maximum

current of 1 mA at the ALERT and THERM output. In this

case, the total power dissipation in the device is about

4.5 mW. The thermal resistance, qJA, of the MSOP−10

package is about 142C/W.

Layout Considerations

Digital boards can be electrically noisy environments, and

the ADT7482 is measuring very small voltages from the

remote sensor, so care must be taken to minimize noise

induced at the sensor inputs. Take the following precautions:

1. Place the ADT7482 as close as possible to the

remote sensing diode. Provided that the worst

noise sources, that is, clock generators,

data/address buses, and CRTs, are avoided, this

distance can be 4 inches to 8 inches.

2. Route the D+ and D– tracks close together, in

parallel, with grounded guard tracks on each side.

To minimize inductance and reduce noise pickup,

a 5 mil track width and spacing is recommended.

Provide a ground plane under the tracks, if

possible.

Figure 23. Typical Arrangement of Signal Tracks

5 MIL

GND

D−

D+

GND

3. Try to minimize the number of copper/solder

joints that can cause thermocouple effects. Where

copper/solder joints are used, make sure that they

are in both the D+ and D− path and at the same

temperature.

Thermocouple effects should not be a major

problem as 1C corresponds to about 200 mV, and

thermocouple voltages are about 3 mV/C of

temperature difference. Unless there are two

thermocouples with a big temperature differential

between them, thermocouple voltages should be

much less than 200 mV.

4. Place a 0.1 mF bypass capacitor close to the VDD

pin. In extremely noisy environments, an input

filter capacitor can be placed across D+ and D−,

close to the ADT7482. This capacitance can effect

the temperature measurement, so care must be

taken to ensure that any capacitance seen at D+

and D− is a maximum of 1000 pF. This maximum

value includes the filter capacitance, plus any

cable or stray capacitance between the pins and the

sensor diode.

5. If the distance to the remote sensor is more than

8 inches, the use of twisted pair cable is

recommended. A total of 6 feet to 12 feet is

needed.

For long distances (up to 100 feet), use shielded

twisted pair, such as Belden No. 8451 microphone

cable. Connect the twisted pair to D+ and D− and

the shield to GND close to the ADT7482. Leave

the remote end of the shield unconnected to avoid

ground loops.

Because the measurement technique uses switched

current sources, excessive cable or filter capacitance can

affect the measurement. When using long cables, the filter

capacitance can be reduced or removed.

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Application Circuit

Figure 24 shows a typical application circuit for the

ADT7482, using discrete sensor transistors. The pullups on

SCLK, SDATA, and ALERT are required only if they are not

already provided elsewhere in the system.

The SCLK pin and the SDATA pin of the ADT7482 can

be interfaced directly to the SMBus of an I/O controller, such

as the Intel820 chipset.

Figure 24. Typical Application Circuit

FAN

ENABLE

VDD

TYP 10 kW

FAN

CONTROL

CIRCUIT

SMBus

CONTROLLER

5.0 V or 12 V

3.0 V to 3.6 V

TYP 10 kW

0.1 mF

GND

2N3904/06

CPU THERMAL

DIODE

ADT7482

SCLK

SDATA

ALERT

THERM

VDD

D1−

D1+

D2−

D2+

Table 18. ORDERING INFORMATION

Device Order Number* Temperature Range Package Type Shipping†SMBus Address

ADT7482ARMZ−REEL −40C to +125C10-lead MSOP 3,000 Tape & Reel 4C

†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.

*The “Z’’ suffix indicates Pb-Free package available.

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PACKAGE DIMENSIONS

MSOP10

CASE 846AC−01

ISSUE O

0.08 (0.003) A S

DIM MIN MAX MIN MAX

INCHESMILLIMETERS

A2.90 3.10 0.114 0.122

B2.90 3.10 0.114 0.122

C0.95 1.10 0.037 0.043

D0.20 0.30 0.008 0.012

G0.50 BSC 0.020 BSC

H0.05 0.15 0.002 0.006

J0.10 0.21 0.004 0.008

K4.75 5.05 0.187 0.199

L0.40 0.70 0.016 0.028

NOTES:

1. DIMENSIONING AND TOLERANCING PER

ANSI Y14.5M, 1982.

2. CONTROLLING DIMENSION: MILLIMETER.

3. DIMENSION “A” DOES NOT INCLUDE MOLD

FLASH, PROTRUSIONS OR GATE BURRS.

MOLD FLASH, PROTRUSIONS OR GATE

BURRS SHALL NOT EXCEED 0.15 (0.006)

PER SIDE.

4. DIMENSION “B” DOES NOT INCLUDE

INTERLEAD FLASH OR PROTRUSION.

INTERLEAD FLASH OR PROTRUSION

SHALL NOT EXCEED 0.25 (0.010) PER SIDE.

5. 846B−01 OBSOLETE. NEW STANDARD

846B−02

−B−

−A−

PIN 1 ID 8 PL

0.038 (0.0015)

−T−SEATING

PLANE

HJL

ǒmm

inchesǓ

SCALE 8:1

10X 10X

1.04

0.041

0.32

0.0126

5.28

0.208

4.24

0.167

3.20

0.126

0.50

0.0196

*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*

ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC owns the rights to a number of patents, trademarks,

copyrights, trade secrets, and other intellectual property. A listing of SCILLC’s product/patent coverage may be accessed at www.onsemi.com/site/pdf/Patent−Marking.pdf. SCILLC

reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any

particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without

limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications

and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC

does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for

surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where

personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and

its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly,

any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture

of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner.

PUBLICATION ORDERING INFORMATION

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USA/Canada

Europe, Middle East and Africa Technical Support:

Phone: 421 33 790 2910

Japan Customer Focus Center

Phone: 81−3−5817−1050

ADT7482/D

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Phone: 303−675−2175 or 800−344−3860 Toll Free USA/Canada

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