7025L25PFG - INTEGRATED DEVICE TECHNOLOGY

March 13, 2008

LM95245

Precision Remote Diode Digital Temperature Sensor with

TruTherm® BJT Beta Compensation Technology for 45nm

Process

General Description

The LM95245 is an 11-bit digital temperature sensor with a

2-wire System Management Bus (SMBus) interface and

TruTherm technology that can monitor the temperature of a

remote diode as well as its own temperature. The LM95245

can be used to very accurately monitor the temperature of

external devices such as microprocessors. TruTherm tech-

nology allows the LM95245 to precisely monitor thermal

diodes found in 90 nm and smaller geometry processes. The

LM95245 is specifically targeted for Intel processors on 45nm

process. LM95245 reports temperature in two different for-

mats for +127.875°C/-128°C range and 0°C/255°C range.

The LM95245 T_CRIT and OS outputs are asserted when

either unmasked channel exceeds its programmed limit and

can be used to shutdown the system, to turn on the system

fans, or as a microcontroller interrupt function. The current

status of the T_CRIT and OS pins can be read back from the

status registers via the SMBus interface. All limits have a

shared programmable hysteresis register.

The remote temperature channel of the LM95245 has a pro-

grammable digital filter. The LM95245 is targeted for a typical

Intel® processor on a 45 nm, 65 nm or 90nm process, and

has an offset register for maximum flexibility and best accu-

racy.

The LM95245 has a three-level address pin to connect up to

3 devices to the same SMBus master, that is shared with the

OS output. The LM95245 has a programmable conversion

rate register and a standby mode to save power. One con-

version can be triggered in standby mode by writing to the

one-shot register.

Features

■Remote and Local temperature channels

■Targeted for Intel 45nm processor diodes

■Two Formats: −128°C to +127.875°C and

0°C to 255.875°C

■Digital filter for remote channel

■Programmable TCRIT and OS thresholds

■Programmable shared hysteresis register

■Diode Fault Detection

■Mask, Offset, and Status Registers

■SMBus 2.0 compatible interface, supports TIMEOUT

■Programmable conversion rate for best power

consumption

■Three-level address pin

■Standby mode one-shot conversion control

■Pin-for-pin compatible with the LM95235 and LM86/LM89/

LM99

■8-pin MSOP and SOP packages

Key Specifications

■ Supply Voltage 3.0 V to 3.6 V

■ Supply Current, Conv. Rate = 1 Hz 350 µA (typ)

■ Remote Diode Temperature Accuracy

TA = 25°C to 85°C; TD = 50°C to 105°C ±0.75°C (max)

TA = 25°C to 85°C; TD = 40°C to 125°C ±1.5°C (max)

■ Local Temperature Accuracy

TA = 25°C to 100°C ±2.0°C (max)

■ Conversion Rate, Both Channels 16 to 0.4 Hz

Applications

■Processor/Computer System Thermal Management

(e.g. Laptops, Desktops, Workstations, Servers)

■Electronic Test Equipment

■Office Electronics

Connection Diagram

MSOP-8 and SOP-8

30015102

TOP VIEW

TruTherm® is a registered trademark of National Semiconductor Corporation.

Intel® is a registered trademark of Intel Corporation.

Pentium® is a registered trademark of Intel Corporation.

LM95245 Precision Remote Diode Digital Temperature Sensor with TruTherm BJT Beta

Compensation Technology for 45nm Process

Ordering Information

Order Number Package

Marking NS Package Number Transport Media SMBus Device

Address

LM95245CIM 95245CIM M08A (SOP-8) 95 Units per Rail 18h, 29h, 4Ch

LM95245CIMM T45C MUA08A (MSOP-8) 1000 Units on Tape and Reel 18h, 29h, 4Ch

LM95245CIMM-1 T46C MUA08A (MSOP-8) 1000 Units on Tape and Reel 19h, 29h, 4Dh

LM95245CIMX 95245CIM M08A (SOP-8) 2500 Units on Tape and Reel 18h, 29h, 4Ch

LM95245CIMMX T45C MUA08A (MSOP-8) 3500 Units on Tape and Reel 18h, 29h, 4Ch

LM95245CIMMX-1 T46C MUA08A (MSOP-8) 3500 Units on Tape and Reel 19h, 29h, 4Dh

Simplified Block Diagram

30015101

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LM95245

Pin Descriptions

Number Name Type Function and Connection

1VDD Power Device power supply. Requires bypass capacitor of 10 µF in parallel with 0.1

µF and 100 pF. Place 100 pF closest to device pin.

2 D+ Analog Input/Output Positive input from the thermal diode.

3 D- Analog Input/Output Negative input from the thermal diode.

4 T_CRIT Digital Output Critical temperature output. Open-drain output requires pull-up resistor.

Active “LOW”.

5 GND Ground Device ground.

6 OS/A0 Digital Input/Output

Over-temperature shutdown comparator output or SMBus slave address

input. Defaults as an SMBus slave address input that selects one of three

addresses. Can be tied to VDD, GND, or to the middle of a resistor divider

connected between VDD and GND. When programmed as an OS comparator

output it is active “Low” and open drain.

7 SMBDAT Digital Input/Output SMBus interface data pin. Open-drain output requires pull-up resistor.

8 SMBCLK Digital Input SMBus interface clock pin.

Typical Application

30015103

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LM95245

Absolute Maximum Ratings (Note 1)

Supply Voltage, VDD −0.3V to 6.0V

Voltage at SMBDAT, SMBCLK, −0.5V to 6.0V

T_CRIT, OS/A0 Pins

Voltage at Other Pins (VDD +0.3V)

Input Current at D− Pin (Note 4) ±1 mA

Input Current at All Other Pins

(Note 4) ±5 mA

Output Sink Current

SMBDAT, T_Crit, OS Pins 10 mA

Package Input Current (Note 4) 30 mA

ESD Susceptibility (Note 3)

Human Body Model

Machine Model

Charged Device Model

2500V

250V

1000V

Junction Temperature (Note 2) +125°C

Storage Temperature −65°C to +150°C

Operating Ratings

(Note 1)

Operating Temperature Range -40°C to +125°C

Electrical Characteristics

Temperature Range TMIN ≤ TA ≤ TMAX

LM95245CIMM, LM95245CIM -40°C ≤ TA ≤ +85°C

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

Soldering process must comply with National

Semiconductor's Reflow Temperature Profile specifications.

Refer to www.national.com/packaging. (Note 5)

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for VDD = +3.0 Vdc to 3.6 Vdc. 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 LM95245. TD is

the junction temperature of the remote thermal diode.

Parameter Conditions Typical

(Note 6)

LM95245

CIMM,

LM95245

CIM

Limits

(Note 7)

Units

Temperature Accuracy Using

Local Diode (Note 8)

TA = 25°C to +100°C ±1 ±2 °C (max)

TA = -40°C to +25°C ±6 °C (max)

Temperature Accuracy Using

Remote Diode

(Note 9)

TA = +25°C to +85°C;

TD = +50°C to +105°C 45nm Intel Processor ±0.5 ±0.75 °C (max)

TA = +25°C to +85°C;

TD = +40°C to +120°C 45nm Intel Processor ±0.75 ±1.5 °C (max)

TA = -40°C to +25°C;

TD = +25°C to +125°C 45nm Intel Processor ±3.0 °C (max)

Remote Diode

Measurement Resolution

Digital Filter Off 11 Bits

0.125 °C

Digital Filter On 13 Bits

0.03125 °C

Local Diode Measurement

Resolution

11 Bits

0.125 °C

Conversion Time, Fastest Setting

(Note 10)

Local and Remote Channels 63 72 ms (max)

Local or Remote Channels 33 ms

Quiescent Current

SMBus Inactive, 1 Hz conversion rate

(Note 11) 350 670 µA (max)

Standby Mode 300 µA

D− Source Voltage 400 mV

External Diode Current Source High-level 172 225 µA (max)

Low-level 10.75 µA

Diode Source Current Ratio 16

Power-On Reset Voltage 2.8 V (max)

1.6 V (min)

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LM95245

Parameter Conditions Typical

(Note 6)

LM95245

CIMM,

LM95245

CIM

Limits

(Note 7)

Units

T_CRIT Pin Temperature

Threshold

Default +110 °C

OS Pin Temperature Threshold Default +85 °C

Logic Electrical Characteristics

Digital DC Characteristics

Unless otherwise noted, these specifications apply for VDD= +3.0 Vdc 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

A0 DIGITAL INPUT

VIH Input High Voltage 0.90 × VDD V (min)

VIM Input Middle Voltage 0.57 × VDD V (max)

0.43 × VDD V (min)

VIL Input Low Voltage 0.10 × VDD V (max)

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, T_CRIT, OS DIGITAL OUTPUTS

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

VOL(T_CRIT, OS) T_CRIT, OS Low Level Output Voltage IOL = 6 mA 0.4 V (max)

VOL(SMBDAT) SMBDAT Low Level Output Voltage IOL = 4 mA

IOL = 6 mA

0.4

0.6

V (max)

COUT Digital Output Capacitance 5 pF

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LM95245

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 LM95245 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 LM95245. They adhere

to, but are not necessarily, the SMBus 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 = 400 pF,

IO = 3 mA, (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)

SMBus Communication

30015109

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LM95245

Notes

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

θJA for MSOP-8 package = 210°C/W

θJA for SOP-8 package = 168°C/W

Note 3: Human body model (HBM) is a charged 100 pF capacitor discharged into a 1.5 kΩ resistor. Machine model (MM), is a charged 200 pF capacitor 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 4: 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 LM95245's pins. Care should be taken not to forward bias the parasitic

diodes on pins 2 and 3. Doing so by more than 50 mV may corrupt the temperature measurements. SNP refers to Snap-back device.

Pin # Label Circuit Pin ESD Protection Structure Circuits

1VDD B

Circuit A

Circuit C

Circuit B

2 D+ A

3 D− A

4 T_CRIT C

5 GND B

6 OS/A0 C

7 SMBDAT C

8 SMBCLK C

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 LM95245 and the thermal resistance. See (Note 2) for the thermal resistance to be used in the self-heating calculation.

Note 9: The accuracy of the LM95245 is guaranteed when using a typical thermal diode of an Intel processor on a 45 nm process, as selected in the Remote

Diode Model Select register. See typical performance curve for performance with Intel processor on a 65nm or 90nm process.

Note 10: This specification is provided only to indicate how often temperature data is updated. The LM95245 can be read at any time without regard to conversion

state (and will yield last conversion result).

Note 11: Quiescent current will not increase substantially when the SMBus is active.

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(0)max - 0.15V).

Note 14: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than tTIMEOUT will reset the LM95245's SMBus state machine, therefore setting

SMBDAT and SMBCLK pins to a high impedance state.

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LM95245

Typical Performance Characteristics

Thermal Diode Capacitor or PCB Leakage Current

Effect Remote Diode Temperature Reading

30015105

Remote Temperature Reading Sensitivity to

Thermal Diode Filter Capacitance, TruTherm Enabled

30015151

Conversion Rate Effect on

Average Power Supply Current

30015106

Intel Processor on 45nm,

65nm, or 90 nm Porcess

Thermal Diode Performance Comparison

30015150

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LM95245

1.0 Functional Description

The LM95245 is a temperature sensor that measures Local

and Remote temperature zones. The LM95245 uses a ΔVbe

temperature sensing method. A differential voltage, repre-

senting temperature, is digitized using a Sigma-Delta analog

to digital converter. TruTherm BJT (Transistor) Beta Com-

pensation Technology allows the LM95245 to accurately

sense the temperature of a thermal diode found on die fabri-

cated using a sub-micron process. For more information on

TruTherm Technology see Section 3.0 Application Hints. The

LM95245 is compatible with the serial SMBus version 2.0 two-

wire serial interface.

The LM95245 has OS and TCRIT open-drain digital outputs

that indicate the state of the local and remote temperature

readings when compared to user-programmable limits. If en-

abled, the local temperature is compared to the user-pro-

grammable Local Shared OS and TCRIT Limit Register

(Default Value = 85°C). The comparison result can trigger the

T_CRIT pin and/or the OS pin depending on the settings of

the Local TCRIT Mask and OS Mask bits found in Configu-

ration Register 1. The comparison result can also be read

back from Status Register 1. If enabled, the remote temper-

ature is compared to the user-programmable Remote TCRIT

Limit Register (Default Value = 110°C), and the Remote OS

Limit Register (Default Value = 85°C) values. The comparison

result can trigger the T_CRIT pin and/or the OS pin depending

on the settings of Configuration Register 1. The following ta-

ble describes the default temperature settings for each mea-

sured temperature that triggers T_CRIT and/or OS pins:

Output Pin Remote, °C Local, °C

T_CRIT 110 85

OS 85 85

The following table describes the limit register mapping to the

T_CRIT and/or OS pins:

Output Pin Remote Local

T_CRIT Remote

TCRIT Limit

Local Shared OS/TCRIT

Limit

OS Remote OS

Limit

Local Shared OS/TCRIT

Limit

The T_CRIT and OS outputs are open-drain, active low.

The remote temperature readings support a programmable

digital filter. Based on the settings in Configuration Register

2 a digital filter can be turned on to improve the noise perfor-

mance of the remote temperature as well as to increase the

resolution of the temperature reading. If the filter is enabled

the filtered readings are used for TCRIT and OS comparisons.

The LM95245 may be placed in low power consumption

(Standby) mode by setting the STOP/RUN bit found in Con-

figuration Register 1. In the Standby mode, the LM95245’s

SMBus interface remains active while all circuitry not required

is turned off. In the Standby mode the host can trigger one

round of conversions by writing to the One-Shot Register. The

value written into this register is not kept. Local and Remote

temperatures will be converted once and the T_CRIT and

OS pins will reflect the comparison results based on this set

of conversions results.

All the temperature readings are in 16-bit left-justified word

format. The 10-bit plus sign local temperature reading is con-

tained in two 8-bit registers: Local Temp MSB and Local Temp

LSB Registers. The remote temperature supports both a 13-

bit unsigned and a 12-bit plus sign format. These readings are

available in their corresponding registers as described in the

LM95245 Register table. The lower 2-bits of the remote tem-

perature reading will contain temperature information only if

the digital filter is enabled. If the digital filter is disabled, these

two bits will read back 0.

The signed and unsigned remote temperature readings are

available simultaneously in separate registers, therefore al-

lowing both negative temperatures and temperatures 128°C

and above to be measured.

All Limit Registers support unsigned temperature format with

1°C LSb resolution. The Local Shared TCRIT and OS Limit

mote Temperature TCRIT and OS Limit Registers are 8 bits

each for limits between 0°C and 255°C.

1.1 CONVERSION SEQUENCE

In the power-up default state the LM95245 takes a maximum

of 1 second to convert the Local Temperature, Remote Tem-

perature, and to update all of its registers. Only during the

conversion process is the Busy bit (D7) in Status Register 1

(02h) high. These conversions are addressed in a round-robin

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

version Rate bits found in the Conversion Rate Register (R/

W: 04h/0Ah). When the conversion rate is modified a delay is

inserted between conversions, the actual maximum conver-

sion time remains at 72 ms. Different conversion rates will

cause the LM95245 to draw different amounts of supply cur-

rent as shown in Figure 1.

30015106

FIGURE 1. Conversion Rate Effect on Power Supply

Current

1.2 POWER-ON-DEFAULT STATES

LM95245 always powers up to these known default states.

The LM95245 remains in these states until after the first con-

version.

1. Command Register set to 00h

2. Conversion Rate register defaults to 02h (1 second).

3. Local Temperature set to 0°C until the end of the first

conversion

4. Remote Diode Temperature set to 0°C until the end of

the first conversion

5. Remote OS limit default is 55h (85 °C).

6. Local Shared and TCRIT limit default is 55h (85 °C).

7. Remote TCRIT limit default is 6Eh (110 °C).

8. Remote Offset High and Low bytes default to 00h.

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LM95245

9. Configuration Register 1 defaults to 00h. This sets the

LM95245 as follows:

A. The STOP/RUN defaults to the active/converting

mode.

B. The Local and Remote TCRIT and OS Masks are

reset to 0.

10. Configuration Register 2 defaults to 1Fh. This sets the

LM95245 as follows:

A. Remote Diode digital filter defaults on.

B. The Remote Diode mode defaults to a typical Intel

processor on 45/65/90 nm process.

C. Diode Fault Mask bit for TCRIT defaults to 1.

D. Diode Fault Mask bit for OS defaults to 0.

E. Pin 6 Function defaults to Address Input function

(A0).

1.3 SMBus INTERFACE

The LM95245 operates as a slave on the SMBus, so the

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

The LM95245 never drives the SMBCLK line and it does not

support clock stretching. According to SMBus specifications,

the LM95245 has a 7-bit slave address. Three SMBus ad-

dresses can be selected by connecting pin 6 (A0) to either

Low, Mid-Supply or High voltages. The address selection ta-

ble below shows two sets of possible selections for the

LM95245CIMM and the LM95245CIMM-1.

State of the A0

LM95245CIMM

SMBus Device

Address

LM95245CIMM-1

SMBus Device

Address

HEX Binary HEX Binary

Low 18 001 1000 19 001

1001

Mid-Supply 29 010 1001 29 010

1001

High 4C 100 1100 4D 100

1100

The OS/A0 pin, after power-up, defaults as an address select

input pin (A0). After power-up, the OS/A0 pin can only be

programmed as an OS output when it is in the “High” state.

Therefore, 4Ch is the only valid slave address that can be

used when the OS/A0 pin is programmed to function as an

OS output. When the OS/A0 pin is programmed to function

as an A0 input the LM95245 will immediately detect the state

of this pin to determine its SMBus slave address. The

LM95245 does not latch the state of the A0 pin when it is

functioning as an input. If the OS/A0 pin is not used it must

be externally connected through hardware to some state, as

shown in the table, in order to guarantee that the proper ad-

dress is selected and not in an indeterminate state. The OS/

A0 does not have an internal pull-up.

1.4 DIGITAL FILTER

In order to suppress erroneous remote temperature readings

due to noise, the LM95245 incorporates a digital filter for the

Remote Temperature Channel. The filter is accessed in the

Configuration Register 2, bits D2 (FE1) and D1(FE0). The fil-

ter can be set according to the following table.

FE1 FE0 Filter Setting

0 0 Filter Off

0 1 Reserved

1 0 Reserved

1 1 Filter On

Figure 2 depicts the filter output in response to a step input

and an impulse input.

30015125

a) Seventeen and fifty degree step response

30015126

b) Impulse response with input transients less than 4°C

30015128

c) Impuse response with input transients

greater than 4°C

FIGURE 2. Filter Impulse and Step Response Curves

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LM95245

Figure 3 shows the filter in use in a typical Intel processor on

a 45/65/90 nm process system. Note that the two curves have

been purposely offset for clarity. Inserting the filter does not

induce an offset as shown.

30015127

FIGURE 3. Digital Filter Response in a typical Intel

processor on a 45nm, 65 nm or 90 nm process. The filter

curves were purposely offset for clarity.

1.5 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 10-bit plus sign, two's complement word and 11-

bit 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 report "0".

Remote temperature data with the digital filter on is repre-

sented by a 12-bit plus sign, two's complement word and 13-

bit 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 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

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 plus sign,

two's complement 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". Local temperature readings greater than +127.875°C are

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

temperature readings.

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LM95245

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

1.6 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

LM95245. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95245 specification for High

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

82 kΩ (5%) or 88.7 kΩ (1%).

1.7 T_CRIT OUTPUT AND TCRIT LIMIT

The LM95245's T_CRIT pin is an active-low open-drain out-

put that is triggered when the local and/or the remote tem-

perature conversion is above the limits defined by the Remote

and/or Local Limit registers. The state of the T_CRIT pin will

return to the HIGH state when both the Local and Remote

temperatures are below the values programmed into the Limit

Registers less the value in the Common Hysteresis Register.

Additionally, if the remote temperature exceeds the value in

the Remote TCRIT Limit Register the Status Bit for Remote

TCRIT (RTCRIT), in Status Register 1, is set to 1. In the same

way if the local temperature exceeds the value in the Local

Shared OS and TCRIT Limit Register the Status Bit for the

Shared Local OS and TCRIT (LOC) bit in Status Register 1 is

set to 1.The T_CRIT output and the Status Register flags are

updated after every Local and Remote temperature conver-

sion. See Figure 4

30015113

FIGURE 4. T_CRIT Comparator Temperature Response

Diagram

1.8 OS OUTPUT AND OS LIMIT

The LM95245's OS/A0 pin is selected as an OS digital output

as described in Section 1.3. As an OS pin, it is activated

whenever the local and/or remote temperature conversion is

above the limits defined by the Limit registers. If the remote

temperature exceeds the value in the Remote OS Limit Reg-

ister the Status Bit for Remote OS (ROS) in Status Register

1 is set to 1. In the same way if the local temperature exceeds

the value in the Local Shared OS and TCRIT Limit Register

the Status Bit for the Shared Local OS and TCRIT (LOC) bit

in Status Register 1 is set to 1. The state of the T_CRIT pin

output will return to the HIGH state when both the Local and

Remote temperatures are below the values programmed into

the Limit Registers less the value in the Common Hysteresis

updated after every Local and Remote temperature conver-

sion. See Figure 5.

30015115

FIGURE 5. OS Temperature Response Diagram

1.9 DIODE FAULT DETECTION

The LM95245 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, VDD or

D+ is floating, the Remote Temperature reading is –

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

unsigned format is selected. In addition, the Status Register

1 bit D2 is set.

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LM95245

1.10 COMMUNICATING with the LM95245

30015111

(a) Serial Bus Write to the Internal Command Register

30015110

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

30015112

30015114

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

FIGURE 6. SMBus Timing Diagrams for Access of Data (Default Address of 4Ch is shown)

13 www.national.com

LM95245

The data registers in the LM95245 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 LM95245 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 LM95245 will always include the address byte

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

data byte.

Reading the LM95245 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 LM95245), 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 LM95245 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.

1.11 SERIAL INTERFACE RESET

In the event that the SMBus Master is RESET while the

LM95245 is transmitting on the SMBDAT line, the LM95245

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 LM95245 SMBus state

machine resets to the SMBus idle state if either SMBDAT

or SMBCLK are held low for more than 35 ms (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 - 35 ms. Therefore, to

insure a timeout of all devices on the bus the SMBCLK

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

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

SMBus start. The LM95245 will respond properly to an

SMBus start condition at any point during the

communication. After the start the LM95245 will expect

an SMBus Address address byte.

1.12 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.

www.national.com 14

LM95245

2.0 LM95245 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. POR means Power-On Reset.

P0-P7: Command

P7 P6 P5 P4 P3 P2 P1 P0

Command

Read

Address

(Hex)

Write

Address

(Hex)

No.

bits

POR

Default

(Hex)

Read/

Write Description

TEMPERATURE SIGNED VALUE REGISTERS

Local Temp MSB 0x00 NA 8 −RO Supports SMBus byte

Local Temp LSB 0x30 NA 3 −RO All unused bits are reported as "0".

Remote Temp MSB –

Signed 0x01 NA 8 −RO Supports SMBus byte

Remote Temp LSB –

Signed 0x10 NA 5/3 −RO All unused bits are reported as "0".

TEMPERATURE UNSIGNED VALUE REGISTERS

Remote Temp MSB –

Unsigned 0x31 NA 8 −RO Supports SMBus byte reads

Remote Temp LSB –

Unsigned 0x32 NA 5/3 −RO All unused bits are reported as "0".

DIODE CONFIGURATION REGISTERS

Configuration Register 2 0xBF 0xBF 5 0x1F R/W Filter Enable, Diode Model Select, Diode

Fault Mask; Pin 6 OS/A0 function select

Remote Offset

High Byte 0x11 0x11 8 0x00 R/W 2's Complement

Remote Offset

Low Byte 0x12 0x12 3 0x00 R/W 2's Complement

All unused bits are reported as "0".

GENERAL CONFIGURATION REGISTERS

Configuration Register 1 0x03/

0x09

0x09/

0x03 5 0x00 R/W

STOP/RUN , Remote TCRIT mask,

Remote OS mask, Local TCRIT mask,

Local OS mask

Conversion Rate 0x04/0x0

0x04/0x0

A2 0x02 R/W Continuous or specific settings

One-Shot NA 0x0F − − WO A write to this register activates one

conversion if STOP/RUN bit = 1.

STATUS REGISTERS

Status Register 1 0x02 NA 5 −RO Busy bit, and status bits

Status Register 2 0x33 NA 2 −RO Not Ready bit

LIMIT REGISTERS

Remote OS Limit 0x07/

0x0D

0x0D/

0x07 8 0x55 R/W Unsigned 0 to 255 °C

Default 85 °C

Local Shared OS and

T_Crit Limit 0x20 0x20 7 0x55 R/W Unsigned 0 to 127 °C

Default 85 °C

Remote T_Crit Limit 0x19 0x19 8 0x6E R/W Unsigned 0 to 255 °C

Default 110 °C

Common Hysteresis 0x21 0x21 5 0x0A R/W up to 31°C

15 www.national.com

LM95245

Read

Address

(Hex)

Write

Address

(Hex)

No.

bits

POR

Default

(Hex)

Read/

Write Description

IDENTIFICATION REGISTERS

Manufacturer ID 0xFE 0x01 RO Always returns 0x01

Revision ID 0xFF 0xB3 RO Returns revision number.

2.1 LOCAL and REMOTE MSB and LSB TEMPERATURE REGISTERS

Local Temperature MSB

(Read Only Address 00h)

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.

Local Temperature LSB

(Read Only Address 30h)

10-bit plus sign format:

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.

Signed Remote Temperature MSB

(Read Only Address 01h)

12-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.

Signed Remote Temperature LSB, Filter On

(Read Only Address 10h)

12-bit plus sign 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

Signed Remote Temperature LSB, Filter Off

(Read Only Address 10h)

12-bit plus sign 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 filter off or 0.03125°C filter on.

www.national.com 16

LM95245

Unsigned Remote Temperature MSB

(Read Only Address 31h)

13-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.

Unsigned Remote Temperature LSB, Filter On

(Read Only Address 32h)

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

Unsigned Remote Temperature LSB, Filter Off

(Read Only Address 32h)

13-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 filter off or 0.03125°C filter on.

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.

2.2 DIODE CONFIGURATION REGISTERS

Configuration Register 2

(Read/write Address BFh):

D7 D6 D5 D4 D3 D2 D1 D0

0 OS/A0 Function Select OS Fault Mask T_CRIT

Mask TruTherm Select RFE1 RFE0 1

Bits Name Description

7 Reserved Reports "0" when read.

6 OS/A0 Function Select 0: Address (A0) function is enabled

1: Over-temperature Shutdown (OS) is enabled

5 Diode Fault Mask for OS 0: Off

1: On

4 Diode Fault Mask for T_CRIT 0: Off

1: On

3Remote Diode TruTherm

Mode Select

0: Selects Diode Model 2, MMBT3904, with TruTherm technology

disabled. Note, performance in this mode is not guaranteed.

1: Selects Diode Model 1, A typical Intel Processor, with 45nm, 65 nm

or 90 nm technology, and TruTherm technology enabled.

2-1 Remote Filter Enable

00: Filter Disable

01: Reserved

10: Reserved

11: Filter Enable

0 Reserved Reports "1" when read.

Power up default is 1Fh.

17 www.national.com

LM95245

Remote Offset High Byte (2's Complement)

(R/W Address 11h)

10-bit plus sign format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value SIGN 64 32 16 8 4 2 1

Power up default is 00h.

Remote Offset Low Byte (2's Complement)

(R/W Address 12h)

10-bit plus sign format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0.50 0.25 0.125 0 0 0 0 0

Power up default is 00h. LSb = 0.125 °C.

2.3 GENERAL CONFIGURATION REGISTERS

Configuration Register 1

(Read/write Address 03h/09h or 09h/03h):

D7 D6 D5 D4 D3 D2 D1 D0

0 STOP/RUN 0 Remote T_CRIT Mask Remote OS Mask Local T_CRIT Mask Local OS Mask 0

Bits Name Description

7 Reserved Reports "0" when read.

6 STOP/RUN 0: Active / Converting

1: Standby

5 Reserved Reports "0" when read.

4 Remote T_CRIT Mask 0: Off

1: On

3 Remote OS Mask 0: Off

1: On

2 Local T_CRIT Mask 0: Off

1: On

1 Local OS Mask 0: Off

1: On

0 Reserved Reports "0" when read.

Power up default is 00h.

Conversion Rate Register

(Read/write Address 04h/0Ah or 0Ah/04h):2-bit format:

BIT D7 D6 D5 D4 D3 D2 D1 D0

Value 0 0 0 0 0 0 MSb LSb

Bits Name Description

7:2 Reserved Reports "0" when read.

1:0 Conversion Rate

00: Continuous (33 ms typical when remote

diode is missing or fault or 63 ms typical with

remote diode connected)

01: 0.364 seconds

10: 1 second

11: 2.5 seconds

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LM95245

Power up default is 02h (1 second).

One Shot Register

(Write Only Address 0Fh):

Writing to this register will start one conversion if the device is in standby mode (i.e. STOP/RUN bit = 1).

2.4 STATUS REGISTERS

Status Register 1

(Read Only Address 02h):

D7 D6 D5 D4 D3 D2 D1 D0

Busy 0 0 ROS 0 Diode Fault RTCRIT LOC

Bits Name Description

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

6-5 Reserved Report "0" when read.

4 ROS Status Bit for Remote OS

3 Reserved Reports "0" when read.

Diode Fault

Status bit for missing diode (Either D+ is shorted to GND, or VDD; or D+ is floating.)

Note: The unsigned registers will report 0°C if read; the signed value registers will

report −128.000°C.

1 RTCRIT Status bit for Remote TCRIT.

0 LOC Status bit for the shared Local OS and TCRIT .

Status Register 2

(Read Only Address 33h):

D7 D6 D5 D4 D3 D2 D1 D0

Not Ready Reserved 0 0 0 0 0 0

Bits Name Description

7 Not Ready Waiting for 30 ms power-up sequence to end.

6 Reserved Can report "0" or "1" when read.

5-0 Reserved Reports "0" when read.

2.5 LIMIT REGISTERS

Unsigned Remote OS Limit - 0°C to 255°C

(Read/Write Address 07h/0Dh or 0Dh/07h):

D7 D6 D5 D4 D3 D2 D1 D0

128 64 32 16 8 4 2 1

Power on Reset default is 55h (85°C).

Unsigned Local Shared OS and T_CRIT Limit - 0°C to 127°C

(Read/Write Address 20h):

D7 D6 D5 D4 D3 D2 D1 D0

128 64 32 16 8 4 2 1

Power on Reset default is 55h (85°C).

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LM95245

Unsigned Remote T_CRIT Limit - 0°C to 255°C

(Read/Write Address 19h):

D7 D6 D5 D4 D3 D2 D1 D0

128 64 32 16 8 4 2 1

Power on Reset default is 6Eh (110°C).

Common Hysteresis Register

(Read/Write Address 21h):

D7 D6 D5 D4 D3 D2 D1 D0

000168421

Power on Reset default is 0Ah (10°C).

2.6 IDENTIFICATION REGISTERS

Manufacturers ID Register

(Read Only Address FEh): Always returns 01h.

D7 D6 D5 D4 D3 D2 D1 D0

00000001

Revision ID Register

(Read Only Address FFh): Default is B3h. This register will increment by 1 every time there is a revision to the die by National

Semiconductor. The initial revision bits for B3h are shown below.

D7 D6 D5 D4 D3 D2 D1 D0

10110011

3.0 Applications Hints

The LM95245 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 LM95245'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 LM95245 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 LM95245'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 LM95245'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 tran-

sistor base-emitter junction be used with the collector tied to

the base. Accuracy using the MMBT3904 is not guaranteed.

For applications requiring the use of the MMBT3904 use the

LM95235.

The LM95245's BJT Beta Compensation TruTherm technol-

ogy allows accurate sensing of integrated thermal diodes,

such as those found on most processors.

The LM95245 has been optimized to measure the remote

thermal diode integrated in a typical Intel processor on

45 nm, 65 nm or 90 nm process. Using the Remote Diode

Model Select register the remote inputs must be assigned to

sense a typical Intel processor on 45nm, 65 nm or 90 nm pro-

cess. The typical performance of the LM95245 with these

processors is shown in Figure 7. The Remote Offset register

can be used to compensate for temperature errors further.

30015150

FIGURE 7. LM95245 typical performance with a variety of

Intel processors

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LM95245

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 = 1.38×10−23 joules/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 measur-

ing 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 8 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 (BJT) equation,

Equation 5, which is a more accurate representation of the

topology of the thermal diode found in an FPGA or processor.

(5)

TruTherm should only be enabled when measuring the tem-

perature of a transistor integrated as shown in the processor

of Figure 8, because Equation 5 only applies to this topology.

30015143

FIGURE 8. Thermal Diode Current Paths

21 www.national.com

LM95245

3.1.2 Calculating Total System Accuracy

The voltage seen by the LM95245 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 for

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

−0.897% 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 ±1.0°C at a temper-

ature of 80°C (353 Kelvin) and the processor diode has a non-

ideality variation of +4.06%/−0.89%. The resulting system

accuracy of the processor temperature being sensed will be:

TACC = + 1.0°C + (+4.06% of 353 K) = +15.3 °C

and

TACC = - 1.0°C + (−0.89% of 353 K) = −4.1 °C

TrueTherm technology uses the transistor equation, Equation

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

cess variation which is very small. The transistor equation

non-ideality spread is ±0.39% for the 65nm thermal diode.

The resulting accuracy when using TruTherm technology im-

proves to:

TACC = ±0.75°C + (±0.39% of 353 K) = ± 2.16 °C

Intel does not specify the diode model ideality and series re-

sistance of the thermal diodes on 45nm so a similar compar-

ison cannot be calculated, but lab experiments have shown

similar improvement. For the 45nm processor the ideality

spread as specified by Intel is -0.399% to +0.699%. The re-

sulting spread in accuracy when using TruTherm technology

with the thermal diode on Intel processors with 45nm process

is:

TACC = -0.75°C + (-0.39% of 353 K) = -2.16 °C

TACC = +0.75°C + (+0.799% of 353 K) = +4.32 °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 Intel processors in 45 nm

process, this is specified at 4.5Ω typical with a minimum of

3Ω and a maximum of 7Ω. The LM95245 accommodates the

typical series resistance of Intel Processor on 45 nm process.

The error that is not accounted for is the spread of the

processor's series resistance. The equation used to calculate

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

LM95245 is simply:

(6)

Solving for RPCB equal to -1.5Ω to 2.5Ω results in the addi-

tional error due to the spread in this series resistance of

-0.93°C to +1.55°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 can-

celled out by subtracting it from the output readings of the

LM95245.

Processor Family Transistor Equation ηT,

non-ideality

Series

R,Ω

min typ max

Intel Processor on

45 nm process

0.997 1.001 1.008 4.5

Intel Processor on

65 nm process

0.997 1.001 1.005 4.52

Note: NA= Not Available at publication of this document.

3.2 PCB LAYOUT FOR MINIMIZING NOISE

30015117

FIGURE 9. 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 LM95245 can cause temperature conversion errors.

Keep in mind that the signal level the LM95245 is trying to

measure is in microvolts. The following guidelines should be

followed:

1. 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. A

bulk capacitance of approximately 10 µF needs to be in

the near vicinity of the LM95245.

2. A 100 pF diode bypass capacitor is recommended to filter

high frequency noise but may not be necessary. The

LM95245 can handle capacitance up to 3.3 nF (see

Typical Performance Curve "Remote Temperature

Reading Sensitivity to Thermal Diode Filter

Capacitance"). Place the filter capacitors close to the

LM95245 pins and make sure the traces to this capacitor

are matched.

3. Ideally, the LM95245 should be placed within 10 cm 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 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 2 cm apart from the high speed digital traces.

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LM95245

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 LM95245'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 400 mVp-p

(typical hysteresis) and undershoot less than 500 mV below

GND, may prevent successful SMBus communication with

the LM95245. SMBus no acknowledge is the most common

symptom, causing unnecessary traffic on the bus. Although

the SMBus maximum frequency of communication is rather

low (100 kHz 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 3 dB corner frequency of about 40 MHz is included on

the LM95245'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.

23 www.national.com

LM95245

Physical Dimensions inches (millimeters) unless otherwise noted

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

JEDEC Registration Number MO-187

Order Number LM95245CIMM, LM95245CIMMX, LM95245CIMM-1, LM95245CIMMX-1

NS Package Number MUA08A

8-Lead (0.150" Wide) Molded Narrow-Small-Outline Package (SOP),

JEDEC Registration Number MS-012

Order Number LM95245CIM or LM95245CIMX

NS Package Number M08A

www.national.com 24

LM95245

Notes

25 www.national.com

LM95245

Notes

LM95245 Precision Remote Diode Digital Temperature Sensor with TruTherm BJT Beta

Compensation Technology for 45nm Process

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