7025L55PFG - INTEGRATED DEVICE TECHNOLOGY

LM95241

April 4, 2011

Dual Remote Diode Temperature Sensor with SMBus

Interface and TruTherm™ Technology (65nm/90nm)

General Description

The LM95241 is a precision dual remote diode temperature

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

The 2-wire serial interface of the LM95241 is compatible with

SMBus 2.0. The LM95241 can sense three temperature

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

as two diode connected transistors. The LM95241 includes

digital filtering and an advanced input stage that includes

analog filtering and TruTherm technology that reduces pro-

cessor-to-processor non-ideality spread. The diode connect-

ed 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 such as 90nm and 65nm. The LM95241 supports

user selectable thermal diode non-ideality of either Intel pro-

cessor on 90nm or 65nm process or 2N3904.

The LM95241 resolution format for remote temperature read-

ings can be programmed to be 11-bits signed or unsigned with

the digital filtering disabled. When the filtering is enabled the

resolution increases to 13-bits signed or unsigned. In the un-

signed mode the LM95241 remote diode readings can re-

solve temperatures above 127°C. Local temperature read-

ings have a resolution of 9-bits plus sign.

Features

■Accurately senses die temperature of remote ICs or diode

junctions

■Uses TruTherm technology for precision “thermal diode”

temperature measurement

■Thermal diode input stage with analog filtering

■Thermal diode digital filtering

■Intel processor on 65nm or 90nm process or 2N3904 non-

ideality selection

■Remote diode fault detection

■On-board local temperature sensing

■Remote 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

■Remote 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

■Local temperature readings:

—0.25 °C

—9-bits plus sign

■Status register support

■Programmable conversion rate allows user optimization of

power consumption

■Shutdown mode one-shot conversion control

■SMBus 2.0 compatible interface, supports TIMEOUT

■8-pin MSOP package

Key Specifications

■ Remote Diode Temperature Accuracy

TA=20°C to 40°C, TD=45°C to 85°C ±1.25 °C (max)

TA=0°C to 85°C, TD=25°C to 140°C ±2.5 °C (max)

■ Local Temperature Accuracy

TA=0°C to 85°C ±3.0 °C (max)

■ Supply Voltage 3.0 V to 3.6 V

■ Average Supply Current 471 µA (typ)

Applications

■Processor/Computer System Thermal Management

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

■Electronic Test Equipment

■Office Electronics

Connection Diagram

MSOP-8

20199702

TOP VIEW

I2C® is a registered trademark of Phillips Corporation.

LM95241 Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm

Technology (65nm/90nm)

Ordering Information

Part Number Package

Marking

NS Package

Number

Transport

Media

SMBus Device

Address

LM95241CIMM T28C MUA08A (MSOP-8) 1000 Units on Tape and Reel 010 1011

LM95241CIMMX T28C MUA08A (MSOP-8) 3500 Units on Tape and Reel 010 1011

LM95241CIMM-1 T29C MUA08A (MSOP-8) 1000 Units on Tape and Reel 001 1001

LM95241CIMMX-1 T29C MUA08A (MSOP-8) 3500 Units on Tape and Reel 001 1001

LM95241CIMM-2 T30C MUA08A (MSOP-8) 1000 Units on Tape and Reel 010 1010

LM95241CIMMX-2 T30C MUA08A (MSOP-8) 3500 Units on Tape and Reel 010 1010

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.

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

VDD 6 Positive Supply Voltage Input DC Voltage from 3.0 V to 3.6 V. VDD 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

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LM95241

Simplified Block Diagram

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Typical Application

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LM95241

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 (VDD + 0.3 V)

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

Package Input Current (Note 2) 30 mA

SMBDAT Output Sink Current 10 mA

Junction Temperature

(Note 3)

+125°C

Storage Temperature −65°C to +150°C

ESD Susceptibility (Note 4)

Human Body Model 2000 V

Machine Model 200 V

Charged Device Model Model 1000 V

For soldering specifications,

see product folder at www.national.com and

www.national.com/ms/MS/MS-SOLDERING.pdf

Operating Ratings

(Note 1, Note 3)

Operating Temperature Range 0°C to +125°C

Electrical Characteristics

Temperature Range TMIN≤TA≤TMAX

LM95241CIMM 0°C≤TA≤+85°C

Supply Voltage Range (VDD)+3.0V to +3.6V

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for VDD=+3.0Vdc to 3.6Vdc. Boldface limits apply for TA = TJ =

TMIN≤TA≤TMAX; all other limits TA= TJ=+25°C, unless otherwise noted. TJ is the junction temperature of the LM95241. TD is the

junction temperature of the remote thermal diode.

Parameter Conditions Typical Limits Units

(Note 6) (Note 7)(Limit)

Accuracy Using Local Diode TA = 0°C to +85°C, (Note 8) ±1 ±3 °C (max)

Accuracy Using Remote Diode, see (Note 9) for

Thermal Diode Processor Type.

TA = +20°C to +40°

TD = +45°C

to +85°C

±1.25 °C (max)

TA = +0°C to +85°C TD = +25°C

to +140°C

±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 for All

Remote Channels

76.5 86.1 ms (max)

TruTherm Mode Enabled for All

Remote Channels

79.1 88.9 ms (max)

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

rate

471 640 µA (max)

Shutdown 356 µA

D− Source Voltage 0.4 V

Diode Source Current Ratio 16

Diode Source Current (VD+ − VD−)=+ 0.65V; high-level 172 230 µA (max)

100 µA (min)

Low-level 11 µA

Power-On Reset Threshold Measure on VDD input, falling edge 2.7

1.6

V (max)

V (min)

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LM95241

Logic Electrical Characteristics

Digital DC Characteristics

Unless otherwise noted, these specifications apply for VDD=+3.0 to 3.6 Vdc. Boldface limits apply for TA = TJ = TMIN to TMAX;

all other limits TA= TJ=+25°C, unless otherwise noted.

Symbol Parameter Conditions Typical Limits Units

(Note 6) (Note 7)(Limit)

SMBDAT, SMBCLK INPUTS

VIN(1) Logical “1” Input Voltage 2.1 V (min)

VIN(0) Logical “0”Input Voltage 0.8 V (max)

VIN(HYST) SMBDAT and SMBCLK Digital Input

Hysteresis

400 mV

IIN(1) Logical “1” Input Current VIN = VDD 0.005 ±10 µA (max)

IIN(0) Logical “0” Input Current VIN = 0 V −0.005 ±10 µA (max)

CIN Input Capacitance 5 pF

SMBDAT OUTPUT

IOH High Level Output Current VOH = VDD 10 µA (max)

VOL SMBus Low Level Output Voltage IOL = 4mA

IOL = 6mA

0.4

0.6

V (max)

SMBus Digital Switching Characteristics

Unless otherwise noted, these specifications apply for VDD=+3.0 Vdc to +3.6 Vdc, CL (load capacitance) on output lines = 80 pF.

Boldface limits apply for TA = TJ = TMIN to TMAX; all other limits TA = TJ = +25°C, unless otherwise noted.

The switching characteristics of the LM95241 fully meet or exceed the published specifications of the SMBus version 2.0. The

following parameters are the timing relationships between SMBCLK and SMBDAT signals related to the LM95241. They adhere

to but are not necessarily the SMBus bus specifications.

Symbol Parameter Conditions Typical Limits Units

(Note 6) (Note 7)(Limit)

fSMB SMBus Clock Frequency 100

kHz (max)

kHz (min)

tLOW SMBus Clock Low Time from VIN(0)max to VIN(0)max 4.7

µs (min)

ms (max)

tHIGH SMBus Clock High Time from VIN(1)min to VIN(1)min 4.0 µs (min)

tR,SMB SMBus Rise Time (Note 12) 1 µs (max)

tF,SMB SMBus Fall Time (Note 13) 0.3 µs (max)

tOF Output Fall Time CL = 400pF,

IO = 3mA, (Note 13)

250 ns (max)

tTIMEOUT SMBDAT and SMBCLK Time Low for Reset of

Serial Interface (Note 14)

ms (min)

ms (max)

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

tHD;DAT Data Out Stable after SMBCLK Low 300

1075

ns (min)

ns (max)

tHD;STA Start Condition SMBDAT Low to SMBCLK Low

(Start condition hold before the first clock falling

edge)

100 ns (min)

tSU;STO Stop Condition SMBCLK High to SMBDAT Low

(Stop Condition Setup)

100 ns (min)

tSU;STA SMBus Repeated Start-Condition Setup Time,

SMBCLK High to SMBDAT Low

0.6 µs (min)

tBUF SMBus Free Time Between Stop and Start

Conditions

1.3 µs (min)

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LM95241

SMBus Communication

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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 conditions 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 LM95241'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.

Pin # Label Circui

All Input ESD Protection Structure Circuits

1 D1+ A

2 D1− A

3 D2+ A

4 D2− A

5 GND B

6 VDD 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 air flow:

– MSOP-8 = 210°C/W

Note 4: Human body model (HBM), 100pF discharged through a 1.5kΩ resistor. Machine model (MM), 200pF discharged directly into each pin. Charged Device

Model (CDM) simulates a pin slowly acquiring charge (such as from a device sliding down the feeder in an automated assembler) then rapidly being discharged.

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

Note 6: Typical figures are at TA = 25°C and represent most likely parametric norms at the 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 LM95241 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 LM95241CIMM is guaranteed when using a typical thermal diode of an Intel processor on a 65 nm process or an MMBT3904 diode-

connected transistor, as selected in the Remote Diode Model Select register. See typical performance curve for performance with Intel processor on a 90nm

process.

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 LM95241 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 LM95241's SMBus state machine, therefore setting

SMBDAT and SMBCLK pins to a high impedance state.

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LM95241

Typical Performance Characteristics

Intel Processor on 65nm Process or 90nm Process Thermal

Diode Performance Comparison

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Thermal Diode Capacitor or PCB Leakage Current Effect

Remote Diode Temperature Reading

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Remote Temperature Reading Sensitivity to Thermal Diode

Filter Capacitance

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Conversion Rate Effect on Average Power Supply Current

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LM95241

1.0 Functional Description

The LM95241 is a digital sensor that can sense the temper-

ature 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

ΔVbe temperature sensing method. The LM95241 can sup-

port two external transistor types, a Intel processor on 65nm

or 90mn process thermal diode or a 2N3904 diode connected

transistor. The transistor type is register programmable and

does not require software intervention after initialization. The

LM95241 has an advanced input stage using National

Semiconductor's TruTherm technology that reduces the

spread in non-ideality found in Intel processors on 65nm or

90nm process. Internal analog filtering has been included in

the thermal 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 LM95241, 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 LM95241

to the system requirements. The LM95241 can be placed in

shutdown to minimize power consumption when temperature

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

mode allows system control of the conversion rate for ultimate

flexibility.

The remote diode temperature resolution is variable and de-

pends on whether the digital filter is activated. When the

digital filter is active the resolution is thirteen bits and is pro-

grammable 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 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 LM95241 remote diode temperature accuracy is trimmed

for the typical thermal diode of a Intel processor on 65nm or

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

is guaranteed only when using either of these diodes when

selected appropriately. TruTherm mode should be enabled

when measuring a Intel processor on 65nm or 90nm process

and disabled when measuring a 3904 transistor.

Diode fault detection circuitry in the LM95241 can detect the

presence of a remote diode.

The LM95241 register set has an 8-bit data structure and in-

cludes:

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

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

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 LM95241 typically takes

77.8 ms to convert the Local Temperature, Remote Temper-

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

the conversion process is the busy bit (D7) in the Status reg-

ister (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 Configuration Register

(03h). When the conversion rate is modified a delay is insert-

ed between conversions, the actual maximum conversion

time remains at 88.9 ms. Different conversion rates will cause

the LM95241 to draw different amounts of supply current as

shown in Figure 1.

20199706

FIGURE 1. Conversion Rate Effect on Power Supply

Current

1.2 POWER-ON-DEFAULT STATES

LM95241 always powers up to these known default states.

The LM95241 remains in these states until after the first con-

version.

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 Intel processor on 65nm

or 90nm process with TruTherm Mode enabled. Remote

Diode 2 model is set to 2N3904/MMBT3904 with

TruTherm mode disabled.

6. Status Register depends on state of thermal diode inputs

7. Configuration register set to 00h; continuous conversion

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LM95241

1.3 SMBus INTERFACE

The LM95241 operates as a slave on the SMBus, so the

SMBCLK line is an input and the SMBDAT line is bidirectional.

The LM95241 never drives the SMBCLK line and it does not

support clock stretching. According to SMBus specifications,

the LM95241 has a 7-bit slave address. All bits A6 through

A0 are internally programmed and cannot be changed by

software or hardware. The SMBus slave address is depen-

dent on the LM95241 part number ordered:

Version A6 A5 A4 A3 A2 A1 A0

LM95241CIMM 0 1 0 1 0 1 1

LM95241CIMM-1 0 0 1 1 0 0 1

LM95241CIMM-2 0 1 0 1 0 1 0

1.4 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and Re-

mote 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 available 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 avail-

able 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 0111 FFF7h

−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 available

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

temperature readings greater than +127.75°C are clamped to

+127.75°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 tem-

perature reading errors due to internal heating of the

LM95241. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95241 specification for High

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

82kΩ(5%) or 88.7kΩ(1%).

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LM95241

1.6 DIODE FAULT DETECTION

The LM95241 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−,

VDD or D+ is floating, the Remote Temperature reading is –

128.000 °C if signed format is selected and +255.875 if un-

signed format is selected. In addition, the appropriate status

1.7 COMMUNICATING WITH THE LM95241

The data registers in the LM95241 are selected by the Com-

mand Register. At power-up the Command Register is set to

“00”, the location for the Read Local Temperature Register.

The Command Register latches the last location it was set to.

Each data register in the LM95241 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

A Write to the LM95241 will always include the address byte

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

data byte.

Reading the LM95241 can take place either of two ways:

1. If the location latched in the Command Register is correct

(most of the time it is expected that the Command

Registers because that will be the data most frequently

read from the LM95241), 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 LM95241 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 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.

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(a) Serial Bus Write to the Internal Command Register

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

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LM95241

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20199714

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

FIGURE 2. SMBus Timing Diagrams for Access of Data

1.8 SERIAL INTERFACE RESET

In the event that the SMBus Master is RESET while the

LM95241 is transmitting on the SMBDAT line, the LM95241

must be returned to a known state in the communication pro-

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

1. When SMBDAT is LOW, the LM95241 SMBus state

machine resets to the SMBus idle state if either SMBDAT

or SMBCLK are held low for more than 35ms (tTIMEOUT).

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 LM95241 will respond properly to an

SMBus start condition at any point during the

communication. After the start the LM95241 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.

11 www.national.com

LM95241

2.0 LM95241 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 Intel

processor on 65nm or 90nm

process thermal diode model

Remote Diode TruTherm Mode

Control

07h 01h 6 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

LM95241.

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 A4h RO

www.national.com 12

LM95241

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.

3Remote 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. This bit will be set even if the diode

is desconnected.

2Remote 1 TruTherm Mode Enabled

(R1TME)

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. This bit will be set even if the diode

is disconnected.

1 Remote Diode 2 Missing (RD2M) When set to "1" Remote Diode 2 is missing. (See Section 1.6 for further

details.) 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 3904 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. (See Section 1.6 for further

details.) 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 3904 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 76.5 ms, 13.1 Hz (typ), when TruTherm Mode is

disabled (Diode Equation) for both remote channels; 77.8 ms, 12.9 Hz

(typ), when TruTherm Mode is enabled (Transistor Equation) 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)

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 +127.75 °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 +127.75 °C)

0 Reserved Reports "0" when read.

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

13 www.national.com

LM95241

2.3 REMOTE DIODE FILTER CONTROL REGISTER

(Read/write Address 06h):

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 0 0 R2FE 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 1Filter 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

0 0 0 0 0 R2MS 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: Intel processor on 65nm or 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: Intel processor on 65nm or 90nm process model (make sure TruTherm

mode is enabled)

Power up default is 1.

Power up default is 01h.

www.national.com 14

LM95241

2.5 REMOTE DIODE 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.

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 0 0 0 0 0 0

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

15 www.national.com

LM95241

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 0 0 0 0 0

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.

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 A4h. This register will increment by 1 every time there is a revision to the die by National

Semiconductor.

www.national.com 16

LM95241

3.0 Applications Hints

The LM95241 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 because the

path of best thermal conductivity is between the die and the

pins, its temperature will effectively be that of the printed cir-

cuit board lands and traces soldered to the LM95241's pins.

This presumes that the ambient air temperature 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 temperature of the LM95241 die will

be at an intermediate temperature between the surface and

air temperatures. Again, the primary thermal conduction path

is through the leads, so the circuit board temperature will con-

tribute to the die temperature much more strongly than will the

air temperature.

To measure temperature external to the LM95241'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, in-

dependent of the LM95241'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 a 2N3904 transistor

base emitter junction be used with the collector tied to the

base.

The LM95241's TruTherm technology allows accurate sens-

ing of integrated thermal diodes, such as those found on sub-

micron geometry processors. With TruTherm technology

turned off, the LM95241 can measure a diode connected

transistor such as the 2N3904 or MMBT3904.

The LM95241 has been optimized to measure the remote

thermal diode integrated in a Intel processor on 65nm or 90nm

process or an MMBT3904 transistor. Using the Remote Diode

Model Select register either pair of remote inputs can be as-

signed to measure either a Intel processor on 65nm or 90nm

process or an MMBT3904 transistor.

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 re-

lationship holds for variables VBE, T and IF:

(1)

where:

•q = 1.6×10−19 Coulombs (the electron charge),

•T = Absolute Temperature in Kelvin

•k = 1.38×10−23joules/K (Boltzmann's constant),

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

manufactured on,

•IS = Saturation Current and is process dependent,

•If= Forward Current through the base emitter junction

•VBE = Base Emitter Voltage drop

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

inated, yielding the following equation

(2)

In Equation 2, η and IS are dependant upon the process that

was used in the fabrication of the particular diode. By forcing

two currents with a very controlled ratio(IF2/IF1) and measuring

the resulting voltage difference, it is possible to eliminate the

IS term. Solving for the forward voltage difference 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 ap-

plied to an integrated diode such as a processor transistor

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)

20199743

FIGURE 3. Thermal Diode Current Paths

17 www.national.com

LM95241

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 topology.

3.1.2 Calculating Total System Accuracy

The voltage seen by the LM95241 also includes the IFRS volt-

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

is the only other parameter not accounted for and depends

on the diode that is used for measurement. Since ΔVBE is

proportional to both η and T, the variations in η cannot be

distinguished from variations in temperature. Since the non-

ideality factor is not controlled by the temperature sensor, it

will directly add to the inaccuracy of the sensor. For the Pen-

tium D processor on 65nm process, Intel specifies a +4.06%/

−0.89% variation in η from part to part when the processor

diode is measured by a circuit that assumes diode equation,

Equation 4, as true. As an example, assume a temperature

sensor has an accuracy specification of ±1.25°C at a temper-

ature of 65 °C (338 Kelvin) and the processor diode has a

non-ideality variation of +4.06%/−0.89%. The resulting sys-

tem accuracy of the processor temperature being sensed will

be:

TACC = + 1.25°C + (+4.06% of 338 K) = +14.97 °C

and

TACC = - 1.25°C + (−0.89% of 338 K) = −4.26 °C

TrueTherm technology uses the transistor equation, Equation

5, resulting in a non-ideality spread that truly reflects the pro-

cess variation which is very small. The transistor equation

non-ideality spread is ±0.4% for the Pentium D processor on

65nm process. The resulting accuracy when using TruTherm

technology improves to:

TACC = ±1.25°C + (±0.4% of 338 K) = ± 2.60 °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 D processor on

65 nm process, this is specified at 4.52Ω typical. The

LM95241 accommodates the typical series resistance of the

Pentium D processor on 65nm process. The error that is not

accounted for is the spread of the Pentium's series resistance,

that is 2.79Ω to 6.24Ω or ±1.73Ω. The equation to calculate

the temperature error due to series resistance (TER) for the

LM95241 is simply:

(6)

Solving Equation 6 for RPCB equal to ±1.73Ω results in the

additional error due to the spread in the series resistance of

±1.07°C. The spread in error cannot be canceled out, as it

would require measuring each individual thermal diode de-

vice. 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 can-

celled out by subtracting it from the output readings of the

LM95241.

Processor Family Transistor Equation

nD, non-ideality

Series

min typ max

Intel processor on 65nm

process

0.997 1.001 1.005 4.52 Ω

Processor Family Diode Equation ηD,

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 on 65 nm

porcess

1.000 1.009 1.050 4.52 Ω

Pentium M Processor

(Centrino)

1.0015

1.0022

1.0028

3.06 Ω

MMBT3904 1.003

AMD Athlon MP model 6 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 1.0026

0.93 Ω

3.1.3 Compensating for Different Non-Ideality

In order to compensate for the errors introduced by non-ide-

ality, 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 LM95241 is calibrated

for two non-ideality factors and series resistance values thus

supporting the MMBT3904 transistor and the Intel processor

on 65nm or 90nm process without the requirement for addi-

tional trims. For most accurate measurements TruTherm

mode should be turned on when measuring the Intel proces-

sor on the 65nm or 90nm process to minimize the error

introduced by the false non-ideality spread (see 3.1.1 Diode

Non-Ideality Factor Effect on Accuracy). When a temperature

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 (TCF) required to

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

ported by the LM95241.

TCF = [(ηS−ηProcessor) ÷ ηS] × (TCR+ 273 K) (7)

where

•ηS = LM95241 non-ideality for accuracy specification

•ηT = target thermal diode typical non-ideality

•TCR = 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 LM95233. For

example when using the LM95241, with the 3904 mode se-

www.national.com 18

LM95241

lected, 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:

TCF=[(1.003−1.008)÷1.003]×(80+273) =−1.75°C

Therefore, 1.75°C should be subtracted from the temperature

readings of the LM95241 to compensate for the differing typ-

ical non-ideality target.

3.2 PCB LAYOUT FOR MINIMIZING NOISE

20199717

FIGURE 4. Ideal Diode Trace Layout

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 sensor

and the LM95241 can cause temperature conversion errors.

Keep in mind that the signal level the LM95241 is trying to

measure is in microvolts. The following guidelines should be

followed:

1. VDD should be bypassed with a 0.1µF capacitor in parallel

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 LM95241.

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 LM95241 pins.

3. Ideally, the LM95241 should be placed within 10cm of the

Processor diode pins with the traces being as straight,

short and identical as possible. Trace resistance of 1Ω

can 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 LM95241's GND pin is as

close as possible to the Processor's GND that is

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 LM95241. 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 LM95241's SMBCLK input. Additional resistance can be

added in series with the SMBDAT and SMBCLK lines to fur-

ther 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.

19 www.national.com

LM95241

Physical Dimensions inches (millimeters) unless otherwise noted

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

JEDEC Registration Number MO-187

Order Number LM95241CIMM or LM95241CIMMX

NS Package Number MUA08A

www.national.com 20

LM95241

Notes

21 www.national.com

LM95241

Notes

LM95241 Dual Remote Diode Temperature Sensor with SMBus Interface and TruTherm

Technology (65nm/90nm)

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