LM95231BIMM-1 - National Semiconductor

LM95231

LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus

Interface and TruTherm™ Technology

Literature Number: SNIS139D

LM95231

Precision Dual Remote Diode Temperature Sensor with

SMBus Interface and TruTherm™Technology

General Description

The LM95231 is a precision dual remote diode temperature

sensor (RDTS) that uses National’s TruTherm technology.

The 2-wire serial interface of the LM95231 is compatible with

SMBus 2.0. The LM95231 can sense three temperature

zones, it can measure the temperature of its own die as well

as two diode connected transistors. The LM95231 includes

digital filtering and an advanced input stage that includes

analog filtering and TruTherm technology that reduces

processor-to-processor non-ideality spread. The diode con-

nected transistors can be a “thermal diode” as found in Intel

and AMD processors or can simply be a diode connected

MMBT3904 transistor. TruTherm technology allows accurate

measurement of “thermal diodes” found on small geometry

processes, 90nm and below. The LM95231 supports user

selectable thermal diode non-ideality of either a Pentium®4

processor on 90nm process or 2N3904.

The LM95231 resolution format for remote temperature

readings can be programmed to be 11-bits signed or un-

signed with the digital filtering disabled. When the filtering is

enabled the resolution increases to 13-bits signed or un-

signed. In the unsigned mode the LM95231 remote diode

readings can resolve temperatures above 127˚C. Local tem-

perature readings have a resolution of 9-bits plus sign.

Features

nAccurately senses die temperature of remote ICs or

diode junctions

nUses TruTherm technology for precision “thermal diode”

temperature measurement

nThermal diode input stage with analog filtering

nThermal diode digital filtering

nIntel Pentium 4 processor on 90nm process or 2N3904

non-ideality selection

nRemote diode fault detection

nOn-board local temperature sensing

nRemote temperature readings without digital filtering:

— 0.125 ˚C LSb

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

— 11-bits resolves temperatures above 127 ˚C

nRemote temperature readings with digital filtering:

— 0.03125 ˚C LSb with filtering

— 12-bits plus sign or 13-bits programmable resolution

— 13-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

jRemote Temperature Accuracy ±0.75˚C (max)

jLocal Temperature Accuracy ±3.0˚C (max)

jSupply Voltage 3.0V to 3.6V

jSupply Current 402µA (typ)

Applications

nProcessor/Computer System Thermal Management

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

nElectronic Test Equipment

nOffice Electronics

Connection Diagram

MSOP-8

20120202

TOP VIEW

TruTherm™is a trademark of National Semiconductor Corporation.

I2C®is a registered trademark of Philips Corporation.

Pentium®is a registered trademark of Intel Corporation.

August 2006

LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm

Technology

Ordering Information

Part Number Package

Marking

NS Package

Number

Transport

Media

SMBus Device

Address

Thermal Diode

Accuracy

LM95231BIMM T23B MUA08A (MSOP-8) 1000 Units on Tape and

Reel

010 1011 ±0.75

LM95231BIMMX T23B MUA08A (MSOP-8) 3500 Units on Tape and

Reel

010 1011 ±0.75

LM95231BIMM-1 T25B MUA08A (MSOP-8) 1000 Units on Tape and

Reel

001 1001 ±0.75

LM95231BIMMX-1 T25B MUA08A (MSOP-8) 3500 Units on Tape and

Reel

001 1001 ±0.75

LM95231BIMM-2 T26B MUA08A (MSOP-8) 1000 Units on Tape and

Reel

010 1010 ±0.75

LM95231BIMMX-2 T26B MUA08A (MSOP-8) 3500 Units on Tape and

Reel

010 1010 ±0.75

LM95231CIMM T23C MUA08A (MSOP-8) 1000 Units on Tape and

Reel

010 1011 ±1.25

LM95231CIMMX T23C MUA08A (MSOP-8) 3500 Units on Tape and

Reel

010 1011 ±1.25

LM95231CIMM-1 T25C MUA08A (MSOP-8) 1000 Units on Tape and

Reel

001 1001 ±1.25

LM95231CIMMX-1 T25C MUA08A (MSOP-8) 3500 Units on Tape and

Reel

001 1001 ±1.25

LM95231CIMM-2 T26C MUA08A (MSOP-8) 1000 Units on Tape and

Reel

010 1010 ±1.25

LM95231CIMMX-2 T26C MUA08A (MSOP-8) 3500 Units on Tape and

Reel

010 1010 ±1.25

Typical Application

20120203

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 capacitor

is not required between D1+ and D1-. A 100 pF

capacitor between D1+ and D1− can be added and

may improve performance in noisy systems.

LM95231

www.national.com 2

Pin Descriptions (Continued)

Label Pin # Function Typical Connection

D1− 2 Diode Return Current Sink To Diode Cathode. A capacitor is not required

between D1+ and D1-. A 100 pF capacitor between

D1+ and D1− can be added and may improve

performance in noisy systems.

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 capacitor

is not required between D2+ and D2-. A 100 pF

capacitor between D2+ and D2− can be added and

may improve performance in noisy systems.

D2− 4 Diode Return Current Sink To Diode Cathode. A capacitor is not required

between D2+ and D2-. A 100 pF capacitor between

D2+ and D2− can be added and may improve

performance in noisy systems.

GND 5 Power Supply Ground System low noise 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.

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

Simplified Block Diagram

20120201

LM95231

www.national.com3

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)

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

Package Input Current (Note 2) 30 mA

SMBDAT Output Sink Current 10 mA

Junction Tempeature (Note 3) 125˚C

Storage Temperature −65˚C to +150˚C

ESD Susceptibility (Note 4)

Human Body Model 2000 V

Machine Model 200 V

Soldering process must comply with National’s reflow

temperature profile specifications. Refer to

http://www.national.com/packaging/. (Note 5)

Operating Ratings

(Notes 1, 3)

Operating Temperature Range 0˚C to +125˚C

Electrical Characteristics

Temperature Range T

MIN

≤T

MAX

LM95231BIMM, LM95231CIMM 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 LM95231. T

is the

junction temperature of the remote thermal diode.

Parameter Conditions Typical LM95231

BIMM

LM95231

CIMM

Units

(Note 6) Limits

(Note 7)

Limits

(Note 7)

(Limit)

Accuracy Using Local Diode T

= 0˚C to +85˚C, (Note 8) ±1±3±3˚C (max)

Accuracy Using Remote Diode, see(Note 9)

for Thermal Diode Processor Type.

= +20˚C to

+40˚C; T

+45˚C to +85˚C

Intel 90nm

Thermal

Diode

±0.75 ˚C (max)

= +20˚C to

+40˚C; T

+45˚C to +85˚C

MMBT3904

Thermal

Diode

±1.25 ˚C (max)

= +20˚C to

+40˚C; T

+45˚C to +85˚C

Intel 90nm

and

MMBT3904

Thermal

Diodes

±1.25 ˚C (max)

= +0˚C to

+85˚C; T

+25˚C to

+140˚C

Intel 90nm

and

MMBT3904

Thermal

Diodes

±2.5 ±2.5 ˚C (max)

Remote Diode Measurement Resolution with

filtering turned off

10+sign/11 Bits

0.125 ˚C

Remote Diode Measurement Resolution with

digital filtering turned on

12+sign/13 Bits

0.03125 ˚C

Local Diode Measurement Resolution 9+sign Bits

0.25 ˚C

Conversion Time of All Temperatures at the

Fastest Setting

(Note 11) TruTherm Mode

Disabled

75.8 83.9 83.9 ms (max)

TruTherm Mode enabled 79.2 87.7 87.7 ms (max)

Average Quiescent Current (Note 10) SMBus Inactive, 1 Hz

conversion rate

402 545 545 µA (max)

Shutdown 272 µA

D− Source Voltage 0.4 V

Diode Source Current Ratio 16

LM95231

www.national.com 4

Temperature-to-Digital Converter Characteristics (Continued)

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 LM95231. T

is the

junction temperature of the remote thermal diode.

Parameter Conditions Typical LM95231

BIMM

LM95231

CIMM

Units

(Note 6) Limits

(Note 7)

Limits

(Note 7)

(Limit)

Diode Source Current (V

D+

−V

D−

) = + 0.65V;

high-level

176 300 300 µA (max)

100 100 µA (min)

Low-level 11 µA

Power-On Reset Threshold Measure on V

input, falling

edge

2.7

1.8

2.7

1.8

V (max)

V (min)

Logic Electrical Characteristics

Digital DC Characteristics

Unless otherwise noted, these specifications apply for V

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

MIN

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 LM95231 fully meet or exceed the published specifications of the SMBus version 2.0. The following pa-

rameters are the timing relationships between SMBCLK and SMBDAT signals related to the LM95231. 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)

LM95231

www.national.com5

Logic Electrical Characteristics (Continued)

SMBus Digital Switching Characteristics (Continued)

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 LM95231 fully meet or exceed the published specifications of the SMBus version 2.0. The following pa-

rameters are the timing relationships between SMBCLK and SMBDAT signals related to the LM95231. They adhere to but are

not necessarily the SMBus bus specifications.

Symbol Parameter Conditions Typical Limits Units

(Note 6) (Note 7) (Limit)

HD;DAT

Data Out Stable after SMBCLK Low 300

1075

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)

SMBus Communication

20120209

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is

guaranteed to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics.

The guaranteed specifications apply only for the test condition listed. Some performance characteristics may degrade when the device is not operated under the

listed test conditions. Operation of the device beyond the Maximum Operating Ratings is not recommended.

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 figures below for the LM95231’s pins. 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.

LM95231

www.national.com 6

Logic Electrical Characteristics (Continued)

Label Circuit Pin ESD Protection Structure Circuits

1 D1+ A

Circuit A

Circuit B

Circuit C

2 D1− A

3 D2+ A

4 D2− A

5 GND B

7 SMBDAT C

8 SMBCLK C

Note 3: Thermal resistance junction-to-ambient when attached to a printed circuit board with 1oz. foil and no airflow:

– MSOP-8 = 210˚C/W

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

Note 5: Reflow temperature profiles are different for packages containing lead (Pb) than for those that do not.

Note 6: Typicals are at TA= 25˚C and represent most likely parametric norm at time of product characterization. The typical specifications are not guaranteed.

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 LM95231 and the thermal resistance. See (Note 3) for the thermal resistance to be used in the self-heating calculation.

Note 9: The accuracy of the LM95231 is guaranteed when using the thermal diode of Pentium 4 processor on 90nm process or an MMBT3904 type transistor, as

selected in the Remote Diode Model Select register.

Note 10: Quiescent current will not increase substantially when the SMBus is active.

Note 11: This specification is provided only to indicate how often temperature data is updated. The LM95231 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 LM95231’s SMBus state machine, therefore setting

SMBDAT and SMBCLK pins to a high impedance state.

LM95231

www.national.com7

Typical Performance Characteristics

Thermal Diode Capacitor or PCB Leakage Current Effect

Remote Diode Temperature Reading

Remote Temperature Reading Sensitivity to Thermal

Diode Filter Capacitance

20120205 20120207

Conversion Rate Effect on Average Power Supply

Current

20120247

1.0 Functional Description

The LM95231 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 external transistor junctions using a ∆V

temperature sensing method. The LM95231 can support two

external transistor types, a Pentium 4 processor on 90nm

process thermal diode or a 2N3904 diode connected tran-

sistor. The transistor type is register programmable and does

not require software intervention after initialization. The

LM95231 has an advanced input stage using National Semi-

conductor’s TruTherm technology that reduces the spread in

non-ideality found in Pentium 4 processors on 90nm pro-

cess. Internal analog filtering has been included in the ther-

mal diode input stage thus minimizing the need for external

thermal diode filter capacitors. In addition a digital filter has

been added. These noise immunity improvements in the

analog input stage along with the digital filtering will allow

longer trace tracks or cabling to the thermal diode than

previous thermal diode sensor devices.

The 2-wire serial interface, of the LM95231, is compatible

with SMBus 2.0 and I2C®. Please see the SMBus 2.0 speci-

fication 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 LM95231

to the system requirements. The LM95231 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 variable and

depends on whether the digital filter is activated. When the

digital filter is active the resolution is thirteen bits and is

programmable to 13-bits unsigned or 12-bits plus sign, with

a least-significant-bit (LSb) weight for both resolutions of

0.03125˚C. When the digital filter is inactive the resolution is

eleven bits and is programmable to 11-bits unsigned or

10-bits plus sign, with a least-significant-bit (LSb) weight for

both resolutions of 0.125˚C. The unsigned resolution allows

LM95231

www.national.com 8

1.0 Functional Description (Continued)

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 LM95231 remote diode temperature accuracy will be

trimmed for the thermal diode of a Pentium 4 processor on

90nm process or a 2N3904 transistor and the accuracy will

be guaranteed only when using either of these diodes when

selected appropriately. TruTherm mode should be enabled

when measuring a Pentium 4 processor on 90nm process

and disabled when measuring a 2N3904 transistor. Enabling

TruTherm mode with a 2N3904 transistor connected may

produce unexpected temperature readings.

Diode fault detection circuitry in the LM95231 can detect the

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

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

The LM95231 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

7. Status Register: busy, diode fault

8. Configuration Register: resolution control, conversion

rate control, standby control

9. Remote Diode Filter Setting

10. Remote Diode Model Select

11. Remote Diode TruTherm Mode Control

12. 1-shot Register

13. Manufacturer ID

14. Revision ID

1.1 CONVERSION SEQUENCE

In the power up default state the LM95231 takes maximum a

77.5 ms to convert the Local Temperature, Remote Tem-

perature 1 and 2, and to update all of its registers. Only

during the conversion process is the busy bit (D7) in the

Status register (02h) high. These conversions are addressed

in a round robin sequence. The conversion rate may be

modified by the Conversion Rate bits found in the Configu-

ration Register (03h). When the conversion rate is modified a

delay is inserted between conversions, the actual maximum

conversion time remains at 87.7 ms. Different conversion

rates will cause the LM95231 to draw different amounts of

supply current as shown in Figure 1.

1.2 POWER-ON-DEFAULT STATES

LM95231 always powers up to these known default states.

The LM95231 remains in these states until after the first

conversion.

1. Command Register set to 00h

2. Local Temperature set to 0˚C until the end of the first

conversion

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

the first conversion

4. Remote Diode digital filters are on.

5. Remote Diode 1 model is set to Pentium 4 processor on

90nm process with TruTherm mode enabled. Remote

Diode 2 model is set to 2N3904 with TruTherm mode

disabled.

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

puts

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

typical time = 85.8 ms when TruTherm Mode is enabled

for Remote 1 only

1.3 SMBus INTERFACE

The LM95231 operates as a slave on the SMBus, so the

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

tional. The LM95231 never drives the SMBCLK line and it

does not support clock stretching. According to SMBus

specifications, the LM95231 has a 7-bit slave address. All

bits A6 through A0 are internally programmed and can not be

changed by software or hardware. The SMBus slave ad-

dress is dependent on the LM95231 part number ordered:

Part Number A6 A5 A4 A3 A2 A1 A0

LM95231BIMM,

LM95231CIMM

0101011

LM95231BIMM-1,

LM95231CIMM-1

0011001

LM95231BIMM-2,

LM95231CIMM-2

0101010

20120247

FIGURE 1. Conversion Rate Effect on Power Supply

Current

LM95231

www.national.com9

1.0 Functional Description (Continued)

1.4 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and

Remote Temperature registers .

Remote temperature data with the digital filter off is repre-

sented 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 avail-

able in two 8-bit registers. Unused 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

Remote temperature data with the digital filter on is repre-

sented by a 13-bit, two’s complement word or unsigned

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

0.03125˚C (1/32˚C). The data format is a left justified 16-bit

word available in two 8-bit registers. Unused bits will always

report "0".

13-bit, 2’s complement (12-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

+0.03125˚C 0000 0000 0000 1000 0008h

0˚C 0000 0000 0000 0000 0000h

−0.03125˚C 1111 1111 1111 1000 FFF8h

−1˚C 1111 1111 0000 0000 FF00h

−25˚C 1110 0111 0000 0000 E700h

−55˚C 1100 1001 0000 0000 C900h

13-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

+0.03125˚C 0000 0000 0000 1000 0008h

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

clamped to +127.875˚C, they will not roll-over to negative

temperature 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

+0.25˚C 0000 0000 0100 0000 0040h

0˚C 0000 0000 0000 0000 0000h

−0.25˚C 1111 1111 1100 0000 FFC0h

−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

LM95231. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95231 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 LM95231 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. When

TruTherm mode is active the condition of diode short of D+

to D− will not be detected. Connecting a 2N3904 transistor

with TruTherm mode active may cause a detection of a diode

fault.

LM95231

www.national.com 10

1.0 Functional Description (Continued)

1.7 COMMUNICATING with the LM95231

The data registers in the LM95231 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 LM95231 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 LM95231 will always include the address byte

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

data byte.

Reading the LM95231 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 LM95231), 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 LM95231 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). When retrieving all 11 bits from a previous remote

diode temperature 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 consecu-

tively, each time the MSB is read, the LSB associated with

that temperature will be locked in and override the previous

LSB value locked-in.

LM95231

www.national.com11

1.0 Functional Description (Continued)

20120211

(a) Serial Bus Write to the Internal Command Register

20120210

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

20120212

20120214

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

FIGURE 2. SMBus Timing Diagrams for Access of Data

LM95231

www.national.com 12

1.0 Functional Description (Continued)

1.8 SERIAL INTERFACE RESET

In the event that the SMBus Master is RESET while the

LM95231 is transmitting on the SMBDAT line, the LM95231

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 LM95231 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 LM95231 will respond properly to an

SMBus start condition at any point during the communi-

cation. After the start the LM95231 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 LM95231 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 5 4 status bits and 1 busy bit

Configuration Register 03h 00h R/W 5 Includes conversion rate

control

Remote Diode Filter Control 06h 05h R/W 2 Controls thermal diode filter

setting

Remote Diode Model Type

Select

30h 01h R/W 2 Selects the 2N3904 or

Pentium 4 processor on 90nm

process thermal diode model

Remote Diode TruTherm

Mode Control

07h 01h 8 Enables or disables TruTherm

technology for Remote Diode

measurements

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 LM95231.

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 3/5 All unused bits will report zero

Remote Temperature 2 LSB 22h - RO 3/5 All unused bits will report zero

Manufacturer ID FEh 01h RO

Revision ID FFh A1h RO

LM95231

www.national.com13

2.0 LM95231 Registers (Continued)

2.1 STATUS REGISTER

(Read Only Address 02h):

D7 D6 D5 D4 D3 D2 D1 D0

Busy Reserved R2TME R1TME RD2M RD1M

000

Bits Name Description

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

6-4 Reserved Reports "0" when read.

3 Remote 2 TruTherm Mode

Enabled (R2TME)

When set to "1" indicates that the TruTherm Mode has been activated

for Remote diode 2. After being enabled TruTherm Mode will take at

most one conversion cycle to be fully active.

2 Remote 1 TruTherm Mode

Enabled (R2TME)

When set to "1" indicates that the TruTherm Mode has been activated

for Remote diode 1. After being enabled TruTherm Mode will take at

most one conversion cycle to be fully active.

1 Remote Diode 2 Missing (RD2M) When set to "1" 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. Note,

connecting a 2N3904 transistor to Remote 2 inputs with TruTherm

mode active may also cause this bit to be set.

0 Remote Diode 1 Missing (RD1M) When set to "1" 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. Note,

connecting a 2N3904 transistor to Remote 1 inputs with TruTherm

mode active may also cause this bit to be set.

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 75.8 ms, 13.2 Hz (typ), when diode mode is

selected for both remote channels; 77.5 ms, 12.9 Hz (typ), when

TruTherm Mode is enabled for one remote channel.

01: converts every 182 ms, 5.5 Hz (typ)

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

11: converts every 2.7 seconds, 0.37 Hz (typ)

Note: typically a remote diode conversion takes 30 ms with diode

mode is selected; when the TruTherm Mode is selected a conversion

takes an additional 1.7 ms; a local conversion takes 15.8 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)

LM95231

www.national.com 14

2.0 LM95231 Registers (Continued)

2.3 REMOTE DIODE FILTER CONTROL REGISTER

(Read/write Address 06h):

D7 D6 D5 D4 D3 D2 D1 D0

00000R2FE 0 R1FE

Bits Name Description

7-3 Reserved Reports "0" when read.

2 Remote 2 Filter Enable (R2FE) 0: Filter Off

1: Noise Filter On

1 Reserved Reports "0" when read.

0 Remote 1 Filter Enable (R1FE) 0: Filter Off

1: Noise Filter On

Power up default is 05h.

2.4 REMOTE DIODE MODEL TYPE SELECT REGISTER

(Read/Write Address 30h):

D7 D6 D5 D4 D3 D2 D1 D0

00000R2MS 0 R1MS

Bits Name Description

7-3 Reserved Reports "0" when read.

2 Remote Diode 2 Model Select

(R2MS)

0: 2N3904 model (make sure TruTherm mode is disabled)

1: Pentium 4 processor on 90nm process model (make sure TruTherm

mode is enabled)

Power up default is 0.

1 Reserved Reports "0" when read.

0 Remote Diode 1 Model Select

(R1MS)

0: 2N3904 model (make sure TruTherm mode is disabled)

1: Pentium 4 processor on 90nm process model (make sure TruTherm

mode is enabled)

Power up default is 1.

Power up default is 01h.

2.5 REMOTE TruTherm MODE CONTROL

(Read/Write Address 07h):

D7 D6 D5 D4 D3 D2 D1 D0

Reserved R2M2 R2M1 R2M0 Reserved R1M2 R1M1 R1M0

Bits Description

7 Reserved Must be left at 0.

6-4 R2M2:R2M0 000: Remote 2 TruTherm Mode disabled; used when measuring

MMBT3904 transistors

001: Remote 2 TruTherm Mode enabled; used when measuring

Processors

111: Remote 2 TruTherm Mode enabled; used when measuring

Processors

Note, all other codes provide unspecified results and should not be

used.

3 Reserved Must be left at 0.

LM95231

www.national.com15

2.0 LM95231 Registers (Continued)

Bits Description

2-0 R1M2:R1M0 000: Remote 1 TruTherm Mode disabled; used when measuring

MMBT3904 transistors

001: Remote 1 TruTherm Mode enabled; used when measuring

Processors

111: Remote 1 TruTherm Mode enabled; used when measuring

Processors

Note, all other codes provide unspecified results and should not be

used.

Power up default is 01h.

2.6 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 with filter off:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0.5 0.25 0.125 00000

Temperature Data: LSb = 0.125˚C or 1/8˚C.

12-bit plus sign or 13-bit unsigned binary formats with filter on:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0.5 0.25 0.125 0.0625 0.03125 0 0 0

Temperature Data: LSb = 0.03125˚C or 1/32˚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.

LM95231

www.national.com 16

2.0 LM95231 Registers (Continued)

2.7 MANUFACTURERS ID REGISTER

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

2.8 DIE REVISION CODE REGISTER

(Read Address FFh) The default value is A1h. This register will increment by 1 every time there is a revision to the die by National

Semiconductor.

3.0 Applications Hints

The LM95231 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

LM95231’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 LM95231 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 LM95231’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 LM95231’s temperature. 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

an MMBT3904 transistor base emitter junction be used with

the collector tied to the base.

The LM95231’s TruTherm technology allows accurate sens-

ing of integrated thermal diodes, such as those found on

processors. With TruTherm technology turned off, the

LM95231 can measure a diode connected transistor such as

the MMBT3904.

The LM95231 has been optimized to measure the remote

thermal diode integrated in a Pentium 4 processor on 90nm

process or an MMBT3904 transistor. Using the Remote Di-

ode Model Select register either pair of remote inputs can be

assigned to be either a Pentium 4 processor on 90nm pro-

cess or an MMBT3904.

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

(1)

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

(2)

In Equation (2),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 (I

) and

measuring the resulting voltage difference, it is possible to

eliminate the I

term. Solving for the forward voltage differ-

ence yields the relationship:

(3)

Solving Equation (3) for temperature yields:

(4)

Equation (4) holds true when a diode connected transistor

such as the MMBT3904 is used. When this “diode” equation

is applied to an integrated diode such as a processor tran-

sistor with its collector tied to GND as shown in Figure 3 it

will yield a wide non-ideality spread. This wide non-ideality

spread is not due to true process variation but due to the fact

that Equation (4) is an approximation.

TruTherm technology uses the transistor equation, Equation

(5), which is a more accurate representation of the topology

of the thermal diode found in an FPGA or processor.

(5)

LM95231

www.national.com17

3.0 Applications Hints (Continued)

TruTherm should only be enabled when measuring the tem-

perature of a transistor integrated as shown in the processor

of Figure 3, because Equation (5) only applies to this topol-

ogy.

3.1.2 Calculating Total System Accuracy

The voltage seen by the LM95231 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 processor on 90nm process, Intel

specifies a +1.19%/−0.27% variation in ηfrom part to part

when the processor diode is measured by a circuit that

assumes diode equation, Equation (4), as true. As an ex-

ample, assume a temperature sensor has an accuracy

specification of ±0.75˚C at a temperature of 65 ˚C (338

Kelvin) and the processor diode has a non-ideality variation

of +1.19%/−0.27%. The resulting system accuracy of the

processor temperature being sensed will be:

ACC

=±0.75˚C + (+1.19% of 338 K) = +4.76 ˚C

and

ACC

=±0.75˚C + (−0.27% of 338 K) = −1.65 ˚C

TrueTherm technology uses the transistor equation, Equa-

tion (5), resulting in a non-ideality spread that truly reflects

the process variation which is very small. The transistor

equation non-ideality spread is ±0.1% for the Pentium 4

processor on 90nm process. The resulting accuracy when

using TruTherm technology improves to:

ACC

=±0.75˚C + (±0.1% of 338 K) = ±1.08 ˚C

The next error term to be discussed is that due to the series

resistance of the thermal diode and printed circuit board

traces. The thermal diode series resistance is specified on

most processor data sheets. For the Pentium 4 processor on

90 nm process, this is specified at 3.33Ωtypical. The

LM95231 accommodates the typical series resistance of the

Pentium 4 processor on 90 nm process. The error that is not

accounted for is the spread of the Pentium’s series resis-

tance, that is 3.242Ωto 3.594Ωor +0.264Ωto −0.088Ω. The

equation to calculate the temperature error due to series

resistance (T

) for the LM95231 is simply:

(6)

Solving Equation (6) for R

PCB

equal to +0.264Ωand

−0.088Ωresults in the additional error due to the spread in

the series resistance of +0.16˚C to −0.05˚C. The spread in

error cannot be canceled out, as it would require measuring

each individual thermal diode device. This is quite difficult

and impractical in a large volume production environment.

Equation (6) can also be used to calculate the additional

error caused by series resistance on the printed circuit

board. Since the variation of the PCB series resistance is

minimal, the bulk of the error term is always positive and can

simply be cancelled out by subtracting it from the output

readings of the LM95231.

Processor Family Diode Equation η

non-ideality

Series

min typ max

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

1.0083 1.011 1.023 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

AMD Athlon 64 1.008 1.008 1.096

AMD Opteron 1.008 1.008 1.096

AMD Sempron 1.00261 0.93 Ω

3.1.3 Compensating for Different 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 and series resis-

tance of a given processor type. The LM95231 is calibrated

for two non-ideality factors and series resistance values thus

20120243

FIGURE 3. Thermal Diode Current Paths

LM95231

www.national.com 18

3.0 Applications Hints (Continued)

supporting the MMBT3904 transistor and the Pentium 4

processor on 90nm process without the requirement for

additional trims. For most accurate measurements TruTherm

mode should be turned on when measuring the Pentium 4

processor on the 90nm process to minimize the error intro-

duced by the false non-ideality spread (see Section 3.1.1

Diode Non-Ideality Factor Effect on Accuracy). When a tem-

perature sensor calibrated for a particular processor type is

used with a different processor type, additional errors are

introduced.

Temperature errors associated with non-ideality of different

processor types may be reduced in a specific temperature

range of concern through use of software calibration. Typical

Non-ideality specification differences cause a gain variation

of the transfer function, therefore the center of the tempera-

ture range of interest should be the target temperature for

calibration purposes. The following equation can be used to

calculate the temperature correction factor (T

) required to

compensate for a target non-ideality differing from that sup-

ported by the LM95231.

=[(η

−η

Processor

)÷η

]x(T

+ 273 K) (7)

where

•η

= LM95231 non-ideality for accuracy specification

•η

= target thermal diode typical non-ideality

•T

= center of the temperature range of interest in ˚C

The correction factor of Equation (7) should be directly

added to the temperature reading produced by the

LM95231. For example when using the LM95231, with the

3904 mode selected, to measure a AMD Athlon processor,

with a typical non-ideality of 1.008, for a temperature range

of 60 ˚C to 100 ˚C the correction factor would calculate to:

=[(1.003−1.008)÷1.003]x(80+273) =−1.75˚C

Therefore, 1.75˚C should be subtracted from the tempera-

ture readings of the LM95231 to compensate for the differing

typical non-ideality target.

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 LM95231 can cause temperature conversion

errors. Keep in mind that the signal level the LM95231 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 LM95231.

2. A 100pF diode bypass capacitor is recommended to

filter high frequency noise but may not be necessary.

Make sure the traces to the 100pF capacitor are

matched. Place the filter capacitors close to the

LM95231 pins.

3. Ideally, the LM95231 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 0.62˚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 LM95231’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 LM95231. 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 LM95231’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.

20120217

FIGURE 4. Ideal Diode Trace Layout

LM95231

www.national.com19

Physical Dimensions inches (millimeters) unless otherwise noted

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

JEDEC Registration Number MO-187

Order Number LM95231BIMM, LM95231BIMMX, LM95231BIMM-1, LM95231BIMMX-1, LM95231BIMM-2,

LM95231BIMMX-2,

LM95231CIMM, LM95231CIMMX, LM95231CIMM-1, LM95231CIMMX-1, LM95231CIMM-2 or LM95231CIMMX-2

NS Package Number MUA08A

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.

For the most current product information visit us at www.national.com.

LIFE SUPPORT POLICY

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 significant injury to the user.

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 the life support device or

system, or to affect its safety or effectiveness.

BANNED SUBSTANCE COMPLIANCE

National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C2) and Banned Substances

and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at:

www.national.com/quality/green.

Lead free products are RoHS compliant.

National Semiconductor

Americas Customer

Support Center

Email: new.feedback@nsc.com

Tel: 1-800-272-9959

National Semiconductor

Europe Customer Support Center

Fax: +49 (0) 180-530 85 86

Email: europe.support@nsc.com

Deutsch Tel: +49 (0) 69 9508 6208

English Tel: +44 (0) 870 24 0 2171

Français Tel: +33 (0) 1 41 91 8790

National Semiconductor

Asia Pacific Customer

Support Center

Email: ap.support@nsc.com

National Semiconductor

Japan Customer Support Center

Fax: 81-3-5639-7507

Email: jpn.feedback@nsc.com

Tel: 81-3-5639-7560

www.national.com

LM95231 Precision Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm

Technology

IMPORTANT NOTICE

Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, modifications, enhancements, improvements,

and other changes to its products and services at any time and to discontinue any product or service without notice. Customers should

obtain the latest relevant information before placing orders and should verify that such information is current and complete. All products are

sold subject to TI’s terms and conditions of sale supplied at the time of order acknowledgment.

TI warrants performance of its hardware products to the specifications applicable at the time of sale in accordance with TI’s standard

warranty. Testing and other quality control techniques are used to the extent TI deems necessary to support this warranty. Except where

mandated by government requirements, testing of all parameters of each product is not necessarily performed.

TI assumes no liability for applications assistance or customer product design. Customers are responsible for their products and

applications using TI components. To minimize the risks associated with customer products and applications, customers should provide

adequate design and operating safeguards.

TI does not warrant or represent that any license, either express or implied, is granted under any TI patent right, copyright, mask work right,

or other TI intellectual property right relating to any combination, machine, or process in which TI products or services are used. Information

published by TI regarding third-party products or services does not constitute a license from TI to use such products or services or a

warranty or endorsement thereof. Use of such information may require a license from a third party under the patents or other intellectual

property of the third party, or a license from TI under the patents or other intellectual property of TI.

Reproduction of TI information in TI data books or data sheets is permissible only if reproduction is without alteration and is accompanied

by all associated warranties, conditions, limitations, and notices. Reproduction of this information with alteration is an unfair and deceptive

business practice. TI is not responsible or liable for such altered documentation. Information of third parties may be subject to additional

restrictions.

Resale of TI products or services with statements different from or beyond the parameters stated by TI for that product or service voids all

express and any implied warranties for the associated TI product or service and is an unfair and deceptive business practice. TI is not

responsible or liable for any such statements.

TI products are not authorized for use in safety-critical applications (such as life support) where a failure of the TI product would reasonably

be expected to cause severe personal injury or death, unless officers of the parties have executed an agreement specifically governing

such use. Buyers represent that they have all necessary expertise in the safety and regulatory ramifications of their applications, and

acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products

and any use of TI products in such safety-critical applications, notwithstanding any applications-related information or support that may be

provided by TI. Further, Buyers must fully indemnify TI and its representatives against any damages arising out of the use of TI products in

such safety-critical applications.

TI products are neither designed nor intended for use in military/aerospace applications or environments unless the TI products are

specifically designated by TI as military-grade or "enhanced plastic."Only products designated by TI as military-grade meet military

specifications. Buyers acknowledge and agree that any such use of TI products which TI has not designated as military-grade is solely at

the Buyer's risk, and that they are solely responsible for compliance with all legal and regulatory requirements in connection with such use.

TI products are neither designed nor intended for use in automotive applications or environments unless the specific TI products are

designated by TI as compliant with ISO/TS 16949 requirements. Buyers acknowledge and agree that, if they use any non-designated

products in automotive applications, TI will not be responsible for any failure to meet such requirements.

Following are URLs where you can obtain information on other Texas Instruments products and application solutions:

Products Applications

Audio www.ti.com/audio Communications and Telecom www.ti.com/communications

Amplifiers amplifier.ti.com Computers and Peripherals www.ti.com/computers

Data Converters dataconverter.ti.com Consumer Electronics www.ti.com/consumer-apps

DLP®Products www.dlp.com Energy and Lighting www.ti.com/energy

DSP dsp.ti.com Industrial www.ti.com/industrial

Clocks and Timers www.ti.com/clocks Medical www.ti.com/medical

Interface interface.ti.com Security www.ti.com/security

Logic logic.ti.com Space, Avionics and Defense www.ti.com/space-avionics-defense

Power Mgmt power.ti.com Transportation and Automotive www.ti.com/automotive

Microcontrollers microcontroller.ti.com Video and Imaging www.ti.com/video

RFID www.ti-rfid.com

OMAP Mobile Processors www.ti.com/omap

Wireless Connectivity www.ti.com/wirelessconnectivity

TI E2E Community Home Page e2e.ti.com

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265