LM95221CIMMX/NOPB - NATIONAL SEMICONDUCTOR

LM95221

LM95221 Dual Remote Diode Digital Temperature Sensor with SMBus Interface

Literature Number: SNIS134A

LM95221

Dual Remote Diode Digital Temperature Sensor with

SMBus Interface

General Description

The LM95221 is a dual remote diode temperature sensor in

an 8-lead MSOP package. The 2-wire serial interface of the

LM95221 is compatible with SMBus 2.0. The LM95221 can

sense three temperature zones, it can measure the tempera-

ture of its own die as well as two diode connected transis-

tors. The diode connected transistors can be a thermal diode

as found in Pentium and AMD processors or can simply be a

diode connected MMBT3904 transistor. The LM95221 reso-

lution format for remote temperature readings can be pro-

grammed to be 10-bits plus sign or 11-bits unsigned. In the

unsigned mode the LM95221 remote diode readings can

resolve temperatures above 127˚C. Local temperature read-

ings have a resolution of 9-bits plus sign.

The temperature of any ASIC can be accurately determined

using the LM95221 as long as a dedicated diode (semicon-

ductor junction) is available on the target die. The LM95221

remote sensor accuracy of ±1˚C is factory trimmed for a

series resistance of 2.7 ohms and 1.008 non-ideality factor.

Features

nAccurately senses die temperature of remote ICs or

diode junctions

nRemote diode fault detection

nOn-board local temperature sensing

nRemote temperature readings:

— 0.125 ˚C LSb

— 10-bits plus sign or 11-bits programmable resolution

— 11-bits resolves temperatures above 127 ˚C

nLocal temperature readings:

— 0.25 ˚C

— 9-bits plus sign

nStatus register support

nProgrammable conversion rate allows user optimization

of power consumption

nShutdown mode one-shot conversion control

nSMBus 2.0 compatible interface, supports TIMEOUT

n8-pin MSOP package

Key Specifications

jLocal Temperature Accuracy

=0˚C to 85˚C ±3.0 ˚C (max)

jRemote Diode Temperature Accuracy

=30˚C to 50˚C, T

=45˚C to 85˚C ±1.0 ˚C (max)

=0˚C to 85˚C, T

=25˚C to 140˚C ±3.0 ˚C (max)

jSupply Voltage 3.0 V to 3.6 V

jSupply Current 2 mA (typ)

Applications

nProcessor/Computer System Thermal Management

(e.g. Laptop, Desktop, Workstations, Server)

nElectronic Test Equipment

nOffice Electronics

Simplified Block Diagram

20094301

Pentium™is a trademark of Intel Corporation.

May 2004

LM95221 Dual Remote Diode Digital Temperature Sensor with SMBus Interface

Connection Diagram

MSOP-8

20094302

TOP VIEW

Ordering Information

Part Number Package

Marking

NS Package

Number

Transport

Media

SMBus Device

Address

LM95221CIMM LM95221CIMM MUA08A (MSOP-8) 1000 Units on Tape

and Reel

010 1011

LM95221CIMMX LM95221CIMM MUA08A (MSOP-8) 3500 Units on Tape

and Reel

010 1011

Pin Descriptions

Label Pin # Function Typical Connection

D1+ 1 Diode Current Source To Diode Anode. Connected to remote discrete

diode-connected transistor junction or to the

diode-connected transistor junction on a remote IC

whose die temperature is being sensed. A 2.2 nF

diode bypass capacitor is recommended to filter high

frequency noise. Place the 2.2 nF capacitor between

and as close as possible to the LM95221’s D+ and

D− pins. Make sure the traces to the 2.2 nF

capacitor are matched. Ground this pin if this

thermal diode is not used.

D1− 2 Diode Return Current Sink To Diode Cathode. A 2.2 nF capacitor is

recommended between D1+ and D1-. Ground this

pin if this thermal diode is not used.

D2+ 3 Diode Current Source To Diode Anode. Connected to remote discrete

diode-connected transistor junction or to the

diode-connected transistor junction on a remote IC

whose die temperature is being sensed. A 2.2 nF

diode bypass capacitor is recommended to filter high

frequency noise. Place the 2.2 nF capacitor between

and as close as possible to the LM95221’s D+ and

D− pins. Make sure the traces to the 2.2 nF

capacitor are matched. Ground this pin if this

thermal diode is not used.

D2− 4 Diode Return Current Sink To Diode Cathode. A 2.2 nF capacitor is

recommended between D2+ and D2-. Ground this

pin if this thermal diode is not used.

GND 5 Power Supply Ground Ground

6 Positive Supply Voltage

Input

DC Voltage from 3.0 V to 3.6 V. V

should be

bypassed with a 0.1 µF capacitor in parallel with 100

pF. The 100 pF capacitor should be placed as close

as possible to the power supply pin. Noise should

be kept below 200 mVp-p, a 10 µF capacitor may be

required to achieve this.

LM95221

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Pin Descriptions (Continued)

Label Pin # Function Typical Connection

SMBDAT 7 SMBus Bi-Directional Data

Line, Open-Drain Output

From and to Controller; may require an external

pull-up resistor

SMBCLK 8 SMBus Clock Input From Controller; may require an external pull-up

resistor

Typical Application

20094303

LM95221

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Absolute Maximum Ratings (Note 1)

Supply Voltage −0.3 V to 6.0 V

Voltage at SMBDAT, SMBCLK −0.5V to 6.0V

Voltage at Other Pins −0.3 V to (V

+ 0.3 V)

D− Input Current ±1mA

Input Current at All Other Pins (Note 2) ±5mA

Package Input Current (Note 2) 30 mA

SMBDAT Output Sink Current 10 mA

Storage Temperature −65˚C to +150˚C

Soldering Information, Lead Temperature

MSOP-8 Package (Note 3)

Vapor Phase (60 seconds) 215˚C

Infrared (15 seconds) 220˚C

ESD Susceptibility (Note 4)

Human Body Model 2000 V

Machine Model 200 V

Operating Ratings

(Notes 1, 5)

Operating Temperature Range 0˚C to +115˚C

Electrical Characteristics

Temperature Range T

MIN

≤T

MAX

LM95221CIMM 0˚C≤T

≤+85˚C

Supply Voltage Range (V

) +3.0V to +3.6V

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for V

=+3.0Vdc to 3.6Vdc. Boldface limits apply for T

MIN

≤T

MAX

;all other limits T

=+25˚C, unless otherwise noted. T

is the junction temperature of the LM95221. T

is the

junction temperature of the remote thermal diode.

Parameter Conditions Typical Limits Units

(Note 6) (Note 7) (Limit)

Accuracy Using Local Diode T

= 0˚C to +85˚C, (Note 8) ±1±3˚C (max)

Accuracy Using Remote Diode, see (Note 9) for

Thermal Diode Processor Type.

= +30˚C to

+50˚C

= +45˚C

to +85˚C

±1˚C (max)

= +0˚C to

+85˚C

= +25˚C

to +140˚C

±3˚C (max)

Remote Diode Measurement Resolution 11 Bits

0.125 ˚C

Local Diode Measurement Resolution 10 Bits

0.25 ˚C

Conversion Time of All Temperatures at the

Fastest Setting

(Note 11) 66 73 ms (max)

Quiescent Current (Note 10) SMBus Inactive, 15Hz conversion

rate

2.0 2.6 mA (max)

Shutdown 335 µA

D− Source Voltage 0.7 V

Diode Source Current (D+ − D−)=+ 0.65V; high-level 188 315 µA (max)

110 µA (min)

Low-level 11.75 20 µA (max)

7µA (min)

Low-Level Diode Source Current Variation over

Temperature

= +30˚C to +50˚C +0.5 µA

= +30˚C to +85˚C +1.5 µA

Power-On Reset Threshold Measure on V

input, falling

edge

2.4

1.8

V (max)

V (min)

LM95221

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Logic Electrical Characteristics

DIGITAL DC CHARACTERISTICS Unless otherwise noted, these specifications apply for V

=+3.0 to 3.6 Vdc. Boldface lim-

its apply for T

MIN

to T

MAX

;all other limits T

=+25˚C, unless otherwise noted.

Symbol Parameter Conditions Typical Limits Units

(Note 6) (Note 7) (Limit)

SMBDAT, SMBCLK INPUTS

IN(1)

Logical “1” Input Voltage 2.1 V (min)

IN(0)

Logical “0”Input Voltage 0.8 V (max)

IN(HYST)

SMBDAT and SMBCLK Digital Input

Hysteresis

400 mV

IN(1)

Logical “1” Input Current V

0.005 ±10 µA (max)

IN(0)

Logical “0” Input Current V

= 0 V −0.005 ±10 µA (max)

Input Capacitance 5 pF

SMBDAT OUTPUT

High Level Output Current V

10 µA (max)

SMBus Low Level Output Voltage I

= 4mA

= 6mA

0.4

0.6

V (max)

SMBus DIGITAL SWITCHING CHARACTERISTICS Unless otherwise noted, these specifications apply for V

=+3.0 Vdc to

+3.6 Vdc, C

(load capacitance) on output lines = 80 pF. Boldface limits apply for T

MIN

to T

MAX

;all other limits T

= +25˚C, unless otherwise noted. The switching characteristics of the LM95221 fully meet or exceed the published specifi-

cations of the SMBus version 2.0. The following parameters are the timing relationships between SMBCLK and SMBDAT sig-

nals related to the LM95221. They adhere to but are not necessarily the SMBus bus specifications.

Symbol Parameter Conditions Typical Limits Units

(Note 6) (Note 7) (Limit)

SMB

SMBus Clock Frequency 100

kHz (max)

kHz (min)

LOW

SMBus Clock Low Time from V

IN(0)

max to V

IN(0)

max 4.7

µs (min)

ms (max)

HIGH

SMBus Clock High Time from V

IN(1)

min to V

IN(1)

min 4.0 µs (min)

R,SMB

SMBus Rise Time (Note 12) 1 µs (max)

F,SMB

SMBus Fall Time (Note 13) 0.3 µs (max)

Output Fall Time C

= 400pF,

= 3mA, (Note 13)

250 ns (max)

TIMEOUT

SMBDAT and SMBCLK Time Low for Reset of

Serial Interface (Note 14)

ms (min)

ms (max)

SU;DAT

Data In Setup Time to SMBCLK High 250 ns (min)

HD;DAT

Data Out Stable after SMBCLK Low 300

900

ns (min)

ns (max)

HD;STA

Start Condition SMBDAT Low to SMBCLK

Low (Start condition hold before the first clock

falling edge)

100 ns (min)

SU;STO

Stop Condition SMBCLK High to SMBDAT

Low (Stop Condition Setup)

100 ns (min)

SU;STA

SMBus Repeated Start-Condition Setup Time,

SMBCLK High to SMBDAT Low

0.6 µs (min)

BUF

SMBus Free Time Between Stop and Start

Conditions

1.3 µs (min)

LM95221

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SMBus Communication

20094309

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. DC and AC electrical specifications do not apply when operating

the device beyond its rated operating conditions.

Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI<GND or VI>VDD), the current at that pin should be limited to 5 mA.

Parasitic components and or ESD protection circuitry are shown in the figure below for the LM95221’s pins. The nominal breakdown voltage of D4 is 6.5 V. Care

should be taken not to forward bias the parasitic diode, D1, present on pins: D1+, D2+, D1−, D2−. Doing so by more than 50 mV may corrupt the temperature

measurements.

Pin Name PIN # D1 D2 D3 D4 D5 D6 D7 R1 SNP ESD CLAMP

1x x

D1+ 2 x x x x x x x

D1− 3 xx xxxxx x

D2+ 4 x x x x x x x

D2- 6 xx xxxxx x

SMBDAT 7 x x x x x

SMBCLK 8 x x x

Note: An “x” indicates that the component exists for the designated pin. SNP refers to a snap-back device.

Note 3: See the URL ”http://www.national.com/packaging/“ for other recommendations and methods of soldering surface mount devices.

Note 4: Human body model, 100pF discharged through a 1.5kΩresistor. Machine model, 200pF discharged directly into each pin.

Note 5: Thermal resistance junction-to-ambient when attached to a printed circuit board with 2 oz. foil:

– MSOP-8 = 210˚C/W

Note 6: Typicals are at TA= 25˚C and represent most likely parametric norm.

Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).

Note 8: Local temperature accuracy does not include the effects of self-heating. The rise in temperature due to self-heating is the product of the internal power

dissipation of the LM95221 and the thermal resistance. See (Note 5) for the thermal resistance to be used in the self-heating calculation.

Note 9: The accuracy of the LM95221CIMM is guaranteed when using the thermal diode with a non-ideality of 1.008 and series R= 2.7Ω. When using an

MMBT3904 type transistor as the thermal diode the error band will be offset by -3.25˚C

Note 10: Quiescent current will not increase substantially with an SMBus.

Note 11: This specification is provided only to indicate how often temperature data is updated. The LM95221 can be read at any time without regard to conversion

state (and will yield last conversion result).

Note 12: The output rise time is measured from (VIN(0)max + 0.15V) to (VIN(1)min − 0.15V).

Note 13: The output fall time is measured from (VIN(1)min - 0.15V) to (VIN(1)min + 0.15V).

Note 14: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM95221’s SMBus state machine, therefore setting

SMBDAT and SMBCLK pins to a high impedance state.

20094313

FIGURE 1. ESD Protection Input Structure

LM95221

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Typical Performance Characteristics

Thermal Diode Capacitor or PCB Leakage Current Effect

Remote Diode Temperature Reading

Remote Temperature Reading Sensitivity to Thermal

Diode Filter Capacitance

20094305 20094307

Conversion Rate Effect on Average Power Supply

Current

20094306

1.0 Functional Description

The LM95221 is a digital sensor that can sense the tempera-

ture of 3 thermal zones using a sigma-delta analog-to-digital

converter. It can measure its local die temperature and the

temperature of two diode connected MMBT3904 transistors

using a ∆V

temperature sensing method. The 2-wire serial

interface, of the LM95221, is compatible with SMBus 2.0 and

I2C. Please see the SMBus 2.0 specification for a detailed

description of the differences between the I2C bus and

SMBus.

The temperature conversion rate is programmable to allow

the user to optimize the current consumption of the LM95221

to the system requirements. The LM95221 can be placed in

shutdown to minimize power consumption when tempera-

ture data is not required. While in shutdown, a 1-shot con-

version mode allows system control of the conversion rate

for ultimate flexibility.

The remote diode temperature resolution is eleven bits and

is programmable to 11-bits unsigned or 10-bits plus sign.

The least-significant-bit (LSb) weight for both resolutions is

0.125˚C. The unsigned resolution allows the remote diodes

to sense temperatures above 127˚C. Local temperature

resolution is not programmable and is always 9-bits plus sign

and has a 0.25˚C LSb.

The LM95221 remote diode temperature accuracy will be

trimmed for the thermal diode of a Prescott processor and

the accuracy will be guaranteed only when using this diode.

Diode fault detection circuitry in the LM95221 can detect the

presence of a remote diode: whether D+ is shorted to V

D- or ground, or whether D+ is floating.

The LM95221 register set has an 8-bit data structure and

includes:

1. Most-Significant-Byte (MSB) Local Temperature Regis-

ter

2. Least-Significant-Byte (LSB) Local Temperature Regis-

ter

3. MSB Remote Temperature 1 Register

4. LSB Remote Temperature 1 Register

5. MSB Remote Temperature 2 Register

6. LSB Remote Temperature 2 Register

LM95221

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1.0 Functional Description (Continued)

7. Status Register: busy, diode fault

8. Configuration Register: resolution control, conversion

rate control, standby control

9. 1-shot Register

10. Manufacturer ID

11. Revision ID

1.1 CONVERSION SEQUENCE

The LM95221 takes approximately 66 ms to convert the

Local Temperature, Remote Temperature 1 and 2, and to

update all of its registers. Only during the conversion pro-

cess the busy bit (D7) in the Status register (02h) is high.

These conversions are addressed in a round robin se-

quence. The conversion rate may be modified by the Con-

version Rate bits found in the Configuration Register (03h).

When the conversion rate is modified a delay is inserted

between conversions, the actual conversion time remains at

66ms (26 ms for each remote and 14 ms for local). Different

conversion rates will cause the LM95221 to draw different

amounts of supply current as shown in Figure 2.

1.2 POWER-ON-DEFAULT STATES

LM95221 always powers up to these known default states.

The LM95221 remains in these states until after the first

conversion.

1. Command Register set to 00h

2. Local Temperature set to 0˚C

3. Remote Diode Temperature set to 0˚C until the end of

the first conversion

4. Status Register depends on state of thermal diode in-

puts

5. Configuration register set to 00h; continuous conversion,

time = 66ms

1.3 SMBus INTERFACE

The LM95221 operates as a slave on the SMBus, so the

SMBCLK line is an input and the SMBDAT line is bidirec-

tional. The LM95221 never drives the SMBCLK line and it

does not support clock stretching. According to SMBus

specifications, the LM95221 has a 7-bit slave address. All

bits A6 through A0 are internally programmed and can not be

changed by software or hardware. The LM95221 has the

following SMBus slave address:

Version A6 A5 A4 A3 A2 A1 A0

LM95221 0 1 0 1 0 1 1

1.4 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and

Remote Temperature registers .

Remote temperature data is represented by an 11-bit, two’s

complement word or unsigned binary word with an LSb

(Least Significant Bit) equal to 0.125˚C. The data format is a

left justified 16-bit word available in two 8-bit registers. Un-

used bits will always report "0".

11-bit, 2’s complement (10-bit plus sign)

Temperature Digital Output

Binary Hex

+125˚C 0111 1101 0000 0000 7D00h

+25˚C 0001 1001 0000 0000 1900h

+1˚C 0000 0001 0000 0000 0100h

+0.125˚C 0000 0000 0010 0000 0020h

0˚C 0000 0000 0000 0000 0000h

−0.125˚C 1111 1111 1110 0000 FFE0h

−1˚C 1111 1111 0000 0000 FF00h

−25˚C 1110 0111 0000 0000 E700h

−55˚C 1100 1001 0000 0000 C900h

11-bit, unsigned binary

Temperature Digital Output

Binary Hex

+255.875˚C 1111 1111 1110 0000 FFE0h

+255˚C 1111 1111 0000 0000 FF00h

+201˚C 1100 1001 0000 0000 C900h

+125˚C 0111 1101 0000 0000 7D00h

+25˚C 0001 1001 0000 0000 1900h

+1˚C 0000 0001 0000 0000 0100h

+0.125˚C 0000 0000 0010 0000 0020h

0˚C 0000 0000 0000 0000 0000h

Local Temperature data is represented by a 10-bit, two’s

complement word with an LSb (Least Significant Bit) equal to

0.25˚C. The data format is a left justified 16-bit word avail-

able in two 8-bit registers. Unused bits will always report "0".

Local temperature readings greater than +127.875˚C are not

clamped to +127.875˚C, they will roll-over to negative tem-

perature readings.

Temperature Digital Output

Binary Hex

+125˚C 0111 1101 0000 0000 7D00h

+25˚C 0001 1001 0000 0000 1900h

+1˚C 0000 0001 0000 0000 0100h

+0.125˚C 0000 0000 0010 0000 0020h

0˚C 0000 0000 0000 0000 0000h

20094306

FIGURE 2. Conversion Rate Effect on Power Supply

Current

LM95221

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1.0 Functional Description (Continued)

Temperature Digital Output

Binary Hex

−0.25˚C 1111 1111 1100 0000 FFE0h

−1˚C 1111 1111 0000 0000 FF00h

−25˚C 1110 0111 0000 0000 E700h

−55˚C 1100 1001 0000 0000 C900h

1.5 SMBDAT OPEN-DRAIN OUTPUT

The SMBDAT output is an open-drain output and does not

have internal pull-ups. A “high” level will not be observed on

this pin until pull-up current is provided by some external

source, typically a pull-up resistor. Choice of resistor value

depends on many system factors but, in general, the pull-up

resistor should be as large as possible without effecting the

SMBus desired data rate. This will minimize any internal

temperature reading errors due to internal heating of the

LM95221. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95221 specification for High

Level Output Current with the supply voltage at 3.0V, is

82kΩ(5%) or 88.7kΩ(1%).

1.6 DIODE FAULT DETECTION

The LM95221 is equipped with operational circuitry designed

to detect fault conditions concerning the remote diodes. In

the event that the D+ pin is detected as shorted to GND, D−,

or D+ is floating, the Remote Temperature reading is

–128.000 ˚C if signed format is selected and +255.875 if

unsigned format is selected. In addition, the appropriate

status register bits RD1M or RD2M (D1 or D0) are set.

1.7 COMMUNICATING with the LM95221

The data registers in the LM95221 are selected by the

Command Register. At power-up the Command Register is

set to “00”, the location for the Read Local Temperature

was set to. Each data register in the LM95221 falls into one

of four types of user accessibility:

1. Read only

2. Write only

3. Write/Read same address

4. Write/Read different address

AWrite to the LM95221 will always include the address byte

and the command byte. A write to any register requires one

data byte.

Reading the LM95221 can take place either of two ways:

1. If the location latched in the Command Register is cor-

rect (most of the time it is expected that the Command

isters because that will be the data most frequently read

from the LM95221), then the read can simply consist of

an address byte, followed by retrieving the data byte.

2. If the Command Register needs to be set, then an

address byte, command byte, repeat start, and another

address byte will accomplish a read.

The data byte has the most significant bit first. At the end of

a read, the LM95221 can accept either acknowledge or No

Acknowledge from the Master (No Acknowledge is typically

used as a signal for the slave that the Master has read its

last byte). It takes the LM95221 66 ms to measure the

temperature of the remote diodes and internal diode. When

retrieving all 11 bits from a previous remote diode tempera-

ture measurement, the master must insure that all 11 bits are

from the same temperature conversion. This may be

achieved by reading the MSB register first. The LSB will be

locked after the MSB is read. The LSB will be unlocked after

being read. If the user reads MSBs consecutively, each time

the MSB is read, the LSB associated with that temperature

will be locked in and override the previous LSB value

locked-in.

LM95221

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1.0 Functional Description (Continued)

20094310

(a) Serial Bus Write to the internal Command Register followed by a the Data Byte

20094311

(b) Serial Bus Write to the Internal Command Register

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20094314

(d) Serial Bus Write followed by a Repeat Start and Immediate Read

FIGURE 3. SMBus Timing Diagrams

LM95221

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1.0 Functional Description (Continued)

1.8 SERIAL INTERFACE RESET

In the event that the SMBus Master is RESET while the

LM95221 is transmitting on the SMBDAT line, the LM95221

must be returned to a known state in the communication

protocol. This may be done in one of two ways:

1. When SMBDAT is LOW, the LM95221 SMBus state

machine resets to the SMBus idle state if either SMB-

DAT or SMBCLK are held low for more than 35ms

TIMEOUT

). Note that according to SMBus specification

2.0 all devices are to timeout when either the SMBCLK

or SMBDAT lines are held low for 25-35ms. Therefore, to

insure a timeout of all devices on the bus the SMBCLK

or SMBDAT lines must be held low for at least 35ms.

2. When SMBDAT is HIGH, have the master initiate an

SMBus start. The LM95221 will respond properly to an

SMBus start condition at any point during the communi-

cation. After the start the LM95221 will expect an SMBus

Address address byte.

1.9 ONE-SHOT CONVERSION

The One-Shot register is used to initiate a single conversion

and comparison cycle when the device is in standby mode,

after which the device returns to standby. This is not a data

conversion. The data written to this address is irrelevant and

is not stored. A zero will always be read from this register.

2.0 LM95221 Registers

Command register selects which registers will be read from or written to. Data for this register should be transmitted during the

Command Byte of the SMBus write communication.

P7 P6 P5 P4 P3 P2 P1 P0

Command

P0-P7: Command

Name

Command

(Hex)

Power-On

Default Value

(Hex) Read/Write

# of used

bits Comments

Status Register 02h - RO 3 2 status bits and 1 busy bit

Configuration Register 03h 00h R/W 4 Includes conversion rate

control

1-shot 0Fh - WO - Activates one conversion for

all 3 channels if the chip is in

standby mode (i.e.

RUN/STOP bit = 1). Data

transmitted by the host is

ignored by the LM95221.

Local Temperature MSB 10h - RO 8

Remote Temperature 1 MSB 11h - RO 8

Remote Temperature 2 MSB 12h - RO 8

Local Temperature LSB 20h - RO 2 All unused bits will report zero

Remote Temperature 1 LSB 21h - RO 3 All unused bits will report zero

Remote Temperature 2 LSB 22h - RO 3 All unused bits will report zero

Manufacturer ID FEh 01h RO

Revision ID FFh 61h RO

LM95221

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2.0 LM95221 Registers (Continued)

2.1 STATUS REGISTER

(Read Only Address 02h):

D7 D6 D5 D4 D3 D2 D1 D0

Busy Reserved RD2M RD1M

00000

Bits Name Description

7 Busy When set to "1" the part is converting.

6-2 Reserved Reports "0" when read.

1 Remote diode 2 missing (RD2M) Remote Diode 2 is missing. (i.e. D2+ shorted to V

, Ground or D2-,

or D2+ is floating). Temperature Reading is FFE0h which converts to

255.875 ˚C if unsigned format is selected or 8000h which converts to

–128.000 ˚C if signed format is selected.

0 Remote diode 1 missing (RD1M) Remote Diode 1 is missing. (i.e. D1+ shorted to V

, Ground or D1-,

or D1+ is floating). Temperature Reading is FFE0h which converts to

255.875 ˚C if unsigned format is selected or 8000h which converts to

–128.000 ˚C if signed format is selected.

2.2 CONFIGURATION REGISTER

(Read Address 03h /Write Address 03h):

D7 D6 D5 D4 D3 D2 D1 D0

0 RUN/STOP CR1 CR0 0 R2DF R1DF 0

Bits Name Description

7 Reserved Reports "0" when read.

6 RUN/STOP Logic 1 disables the conversion and puts the part in standby mode.

Conversion can be activated by writing to one-shot register.

5-4 Conversion Rate (CR1:CR0) 00: continuous mode 66ms, 15 Hz (typ)

01: converts every 200ms, 5 Hz (typ)

10: converts every 1 second, 1 Hz (typ)

11: converts every 3 seconds,

⁄

Hz (typ)

Note: typically a remote diode conversion takes 26 ms and local

conversion takes 14 ms.

3 Reserved Reports "0" when read.

2 Remote 2 Data Format (R2DF) Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C)

Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C)

1 Remote 1 Data Format (R1DF) Logic 0: unsigned Temperature format (0 ˚C to +255.875 ˚C)

Logic 1: signed Temperature format (-128 ˚C to +127.875 ˚C)

0 Reserved Reports "0" when read.

Power up default is with all bits “0” (zero)

LM95221

www.national.com 12

2.0 LM95221 Registers (Continued)

2.3 LOCAL and REMOTE MSB and LSB TEMPERATURE REGISTERS

Local Temperature MSB

(Read Only Address 10h) 9-bit plus sign format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value SIGN 64 32 16 8 4 2 1

Temperature Data: LSb = 1˚C.

Local Temperature LSB

(Read Only Address 20h) 9-bit plus sign format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0.5 0.25 000000

Temperature Data: LSb = 0.25˚C.

Remote Temperature MSB

(Read Only Address 11h, 12h) 10 bit plus sign format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value SIGN 64 32 16 8 4 2 1

Temperature Data: LSb = 1˚C.

(Read Only Address 11h, 12h) 11-bit unsigned format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 128 64 32 16 8 4 2 1

Temperature Data: LSb = 1˚C.

Remote Temperature LSB

(Read Only Address 21, 22h) 10-bit plus sign or 11-bit unsigned binary

formats:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0.5 0.25 0.125 00000

Temperature Data: LSb = 0.125˚C.

For data synchronization purposes, the MSB register should be read first if the user wants to read both MSB and LSB registers.

The LSB will be locked after the MSB is read. The LSB will be unlocked after being read. If the user reads MSBs consecutively,

each time the MSB is read, the LSB associated with that temperature will be locked in and override the previous LSB value

locked-in.

2.4 MANUFACTURERS ID REGISTER

(Read Address FEh) The default value is 01h.

2.5 DIE REVISION CODE REGISTER

(Read Address FFh) Value to be determined. This register will increment by 1 every time there is a revision to the die by National

Semiconductor.

LM95221

www.national.com13

3.0 Applications Hints

The LM95221 can be applied easily in the same way as

other integrated-circuit temperature sensors, and its remote

diode sensing capability allows it to be used in new ways as

well. It can be soldered to a printed circuit board, and be-

cause the path of best thermal conductivity is between the

die and the pins, its temperature will effectively be that of the

printed circuit board lands and traces soldered to the

LM95221’s pins. This presumes that the ambient air tem-

perature is almost the same as the surface temperature of

the printed circuit board; if the air temperature is much higher

or lower than the surface temperature, the actual tempera-

ture of the LM95221 die will be at an intermediate tempera-

ture between the surface and air temperatures. Again, the

primary thermal conduction path is through the leads, so the

circuit board temperature will contribute to the die tempera-

ture much more strongly than will the air temperature.

To measure temperature external to the LM95221’s die, use

a remote diode. This diode can be located on the die of a

target IC, allowing measurement of the IC’s temperature,

independent of the LM95221’s temperature. The LM95221

has been optimized to measure the remote thermal diode

with a non-ideality of 1.008 and a series resistance of 2.7Ω.

The thermal diode on the Pentium 4 processor on the 90 nm

process has a typical non-ideality of 1.011 and a typical

series resistance of 3.33Ω. Therefore, when measuring this

thermal diode with the LM95221 a typical offset of +1.5˚C will

be observed. This offset can be compensated for easily by

subracting 1.5˚C from the LM95221’s readings. A discrete

diode can also be used to sense the temperature of external

objects or ambient air. Remember that a discrete diode’s

temperature will be affected, and often dominated, by the

temperature of its leads.

Most silicon diodes do not lend themselves well to this

application. It is recommended that a 2N3904 transistor

base emitter junction be used with the collector tied to the

base.

When measuring a diode-connected 2N3904, with an

LM95221, an offset of -3.25˚C will be observed. This offset

can simply be added to the LM95221’s reading: T

2N3904

LM95221

+ 3.25˚C

3.1 DIODE NON-IDEALITY

3.1.1 Diode Non-Ideality Factor Effect on Accuracy

When a transistor is connected as a diode, the following

relationship holds for variables V

, T and I

where:

•q = 1.6x10

−19

Coulombs (the electron charge),

•T = Absolute Temperature in Kelvin

•k = 1.38x10

−23

joules/K (Boltzmann’s constant),

•ηis the non-ideality factor of the process the diode is

manufactured on,

•I

= Saturation Current and is process dependent,

•I

= Forward Current through the base emitter junction

•V

= Base Emitter Voltage drop

In the active region, the -1 term is negligible and may be

eliminated, yielding the following equation

In the above equation, ηand I

are dependant upon the

process that was used in the fabrication of the particular

diode. By forcing two currents with a very controlled ratio (N)

and measuring the resulting voltage difference, it is possible

to eliminate the I

term. Solving for the forward voltage

difference yields the relationship:

The voltage seen by the LM95221 also includes the I

voltage drop of the series resistance. The non-ideality factor,

η, is the only other parameter not accounted for and de-

pends on the diode that is used for measurement. Since

∆V

is proportional to both ηand T, the variations in η

cannot be distinguished from variations in temperature.

Since the non-ideality factor is not controlled by the tempera-

ture sensor, it will directly add to the inaccuracy of the

sensor. For the Pentium 4 and Mobile Pentium Processor-M

Intel specifies a ±0.1% variation in ηfrom part to part. As an

example, assume a temperature sensor has an accuracy

specification of ±1˚C at room temperature of 25 ˚C and the

process used to manufacture the diode has a non-ideality

variation of ±0.1%. The resulting accuracy of the tempera-

ture sensor at room temperature will be:

ACC

=±1˚C+(

±0.1% of 298 ˚K) = ±1.4 ˚C

The additional inaccuracy in the temperature measurement

caused by η, can be eliminated if each temperature sensor is

calibrated with the remote diode that it will be paired with.

Processor Family η, non-ideality Series

min typ max

Pentium II 1 1.0065 1.0173

Pentium III CPUID 67h 1 1.0065 1.0125

Pentium III CPUID

68h/PGA370Socket/Celeron

1.0057 1.008 1.0125

Pentium 4, 423 pin 0.9933 1.0045 1.0368

Pentium 4, 478 pin 0.9933 1.0045 1.0368

Pentium 4 on 0.13

micron process,

2-3.06GHz

1.0011 1.0021 1.0030 3.64 Ω

Pentium 4 on 90 nm

process

1.011 3.33 Ω

Pentium M Processor

(Centrino)

1.00151 1.00220 1.00289 3.06 Ω

MMBT3904 1.003

AMD Athlon MP model

1.002 1.008 1.016

LM95221

www.national.com 14

3.0 Applications Hints (Continued)

3.1.2 Compensating for Diode Non-Ideality

In order to compensate for the errors introduced by non-

ideality, the temperature sensor is calibrated for a particular

processor. National Semiconductor temperature sensors are

always calibrated to the typical non-ideality of a given pro-

cessor type. The LM95221 is calibrated for a non-ideality of

1.008 and a series resistance of 2.7Ω. When a temperature

sensor calibrated for a particular processor type is used with

a different processor type or a given processor type has a

non-ideality that strays from the typical, errors are intro-

duced.

Temperature errors associated with non-ideality may be re-

duced in a specific temperature range of concern through

use of an offset calibration accomplished through software.

Please send an email to hardware.monitor.team@nsc.com

requesting further information on our recommended offset

value for different processor types.

3.2 PCB LAYOUT FOR MINIMIZING NOISE

In a noisy environment, such as a processor mother board,

layout considerations are very critical. Noise induced on

traces running between the remote temperature diode sen-

sor and the LM95221 can cause temperature conversion

errors. Keep in mind that the signal level the LM95221 is

trying to measure is in microvolts. The following guidelines

should be followed:

1. V

should be bypassed with a 0.1µF capacitor in par-

allel with 100pF. The 100pF capacitor should be placed

as close as possible to the power supply pin. A bulk

capacitance of approximately 10µF needs to be in the

near vicinity of the LM95221.

2. A 2.2nF diode bypass capacitor is required to filter high

frequency noise. Place the 2.2nF capacitor as close as

possible to the LM95221’s D+ and D− pins. Make sure

the traces to the 2.2nF capacitor are matched.

3. Ideally, the LM95221 should be placed within 10cm of

the Processor diode pins with the traces being as

straight, short and identical as possible. Trace resis-

tance of 1Ωcan cause as much as 1˚C of error. This

error can be compensated by using simple software

offset compensation.

4. Diode traces should be surrounded by a GND guard ring

to either side, above and below if possible. This GND

guard should not be between the D+ and D− lines. In the

event that noise does couple to the diode lines it would

be ideal if it is coupled common mode. That is equally to

the D+ and D− lines.

5. Avoid routing diode traces in close proximity to power

supply switching or filtering inductors.

6. Avoid running diode traces close to or parallel to high

speed digital and bus lines. Diode traces should be kept

at least 2cm apart from the high speed digital traces.

7. If it is necessary to cross high speed digital traces, the

diode traces and the high speed digital traces should

cross at a 90 degree angle.

8. The ideal place to connect the LM95221’s GND pin is as

close as possible to the Processors GND associated

with the sense diode.

9. Leakage current between D+ and GND and between D+

and D− should be kept to a minimum. Thirteen nano-

amperes of leakage can cause as much as 0.2˚C of

error in the diode temperature reading. Keeping the

printed circuit board as clean as possible will minimize

leakage current.

Noise coupling into the digital lines greater than 400mVp-p

(typical hysteresis) and undershoot less than 500mV below

GND, may prevent successful SMBus communication with

the LM95221. SMBus no acknowledge is the most common

symptom, causing unnecessary traffic on the bus. Although

the SMBus maximum frequency of communication is rather

low (100kHz max), care still needs to be taken to ensure

proper termination within a system with multiple parts on the

bus and long printed circuit board traces. An RC lowpass

filter with a 3db corner frequency of about 40MHz is included

on the LM95221’s SMBCLK input. Additional resistance can

be added in series with the SMBDAT and SMBCLK lines to

further help filter noise and ringing. Minimize noise coupling

by keeping digital traces out of switching power supply areas

as well as ensuring that digital lines containing high speed

data communications cross at right angles to the SMBDAT

and SMBCLK lines.

20094317

FIGURE 4. Ideal Diode Trace Layout

LM95221

www.national.com15

Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead Molded Mini-Small-Outline Package (MSOP),

JEDEC Registration Number MO-187

Order Number LM95221CIMM or LM95221CIMMX

NS Package Number MUA08A

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NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT

DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL

COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein:

1. Life support devices or systems are devices or

systems which, (a) are intended for surgical implant

into the body, or (b) support or sustain life, and

whose failure to perform when properly used in

accordance with instructions for use provided in the

labeling, can be reasonably expected to result in a

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2. A critical component is any component of a life

support device or system whose failure to perform

can be reasonably expected to cause the failure of

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www.national.com

LM95221 Dual Remote Diode Digital Temperature Sensor with SMBus Interface

National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.

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