LM95235DIMM_技术文档

August 15, 2008

LM95235/LM95235Q

Precision Remote Diode Temperature Sensor with SMBus

Interface and TruTherm™ Technology

Diode Model Selection Bit - MMBT3904 or 65/90 nm

processor diodes

Two Formats: −128°C to 127.875°C and

■

General Description

The LM95235 is an 11-bit digital temperature sensor with a

■

2-wire System Management Bus (SMBus) interface and

0°C to 255.875°C

TruTherm technology that can monitor the temperature of a

remote diode as well as its own temperature. The LM95235

Digital filter for remote channel

■

Programmable TCRIT and OS thresholds

■

can be used to very accurately monitor the temperature of

external devices such as microprocessors, graphics proces-

sors, or a diode-connected MMBT3904 transistor. For auto-

motive applications the LM95235Q is available that is AEC-

Q100 Grade3 compliant and is manufactured on an

Automotive Grade Flow. TruTherm BJT (transistor) beta com-

pensation technology allows the LM95235 to precisely mon-

itor thermal diodes found in 90 nm and smaller geometry

processes. LM95235 reports temperature in two different for-

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

The LM95235 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.

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 LM86/LM89

8-pin MSOP package

Key Specifications

3.0 V to 3.6 V

350 µA (typ)

■ꢀSupply Voltage

The remote temperature channel of the LM95235 has a pro-

grammable digital filter. The LM95235 contains a diode model

selection bit to select between a typical Intel® processor on

a 65 nm or 90 nm process or MMBT3904, as well as an offset

register for maximum flexibility and best accuracy.

■ꢀSupply Current, Conv. Rate = 1 Hz

■ꢀRemote Diode Temperature Accuracy

ꢀT_A= 25°C to 85°C; T_D= 60°C to 100°C

ꢀT_A= 25°C to 85°C; T_D= 40°C to 125°C

■ꢀLocal Temperature Accuracy

ꢀT_A= 25°C to 100°C

±0.75°C (max)

±1.5°C (max)

The LM95235 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 LM95235 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.

±2.0°C (max)

16 to 0.4 Hz

■ꢀConversion Rate, Both Channels

Applications

Processor/Computer System Thermal Management

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

Features

■

Remote and Local temperature channels

■

Electronic Test Equipment and Office Electronics

■

TruTherm BJT beta compensation technology

LM95235Q is AEC-Q100 Grade 3 compliant and is

manufactured on an Automotive Grade Flow

Connection Diagram

MSOP-8

20174902

TOP VIEW

TruTherm™ is a trademark of National Semiconductor Corporation.

Intel® is a registered trademark of Intel Corporation.

Pentium® is a registered trademark of Intel Corporation.

201749

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Ordering Information

Packag

e

Markin

g

NS Package

Number

Order Code

Transport Media

Features

T36C

T36D

T36E

36QE

MUA08A

(MSOP-8)

1000 Units on Tape and Reel

3500 Units on Tape and Reel

1000 Units on Tape and Reel

3500 Units on Tape and Reel

1000 Units on Tape and Reel

3500 Units on Tape and Reel

1000 Units on Tape and Reel

3500 Units on Tape and Reel

T_A= 25°C to 85°C

LM95235CIMM

LM95235CIMMX

LM95235DIMM

LM95235DIMMX

LM95235EIMM

LM95235EIMMX

LM95235QEIMM

LM95235QEIMMX

MUA08A

(MSOP-8)

MUA08A

(MSOP-8)

T_A= -40°C to 85°C,

T_D= -40°C to 125°C

MUA08A

(MSOP-8)

MUA08A

(MSOP-8)

T_A= -40°C to 85°C,

T_D= -40°C to 125°C, 3904 only

MUA08A

(MSOP-8)

MUA08A

(MSOP-8)

T_A= -40°C to 85°C,

T_D= -40°C to 125°C, 3904 only

AEC-Q100 Grade 3 Compiant with

Automotive Grade Flow

MUA08A

(MSOP-8)

Simplified Block Diagram

20174901

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2

Pin Descriptions

Number

Name

Type

Function and Connection

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.

V_DD

1

Power

2

3

D+

D-

Analog Input/Output Positive input from the thermal diode.

Analog Input/Output Negative input from the thermal diode.

Critical temperature output. Open-drain output requires pull-up resistor.

Active “LOW”.

Device ground.

4

5

T_CRIT

GND

Digital Output

Ground

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 V_DD, GND, or to the middle of a resistor divider

connected between V_DDand GND. When programmed as an OS comparator

output it is active “Low” and open drain.

6

OS/A0

Digital Input/Output

7

8

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

SMBCLK Digital Input SMBus interface clock pin.

Typical Application

20174903

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Absolute Maximum Ratings (Note 1)

Operating Ratings

(Note 1)

Supply Voltage, V_DD

−0.3V to 6.0V

−0.5V to 6.0V

Operating Temperature Range

-40°C to +125°C

Voltage at SMBDAT, SMBCLK,

Electrical Characteristics

Temperature Range

ꢁT_CRIT, OS/A0 Pins

Voltage at Other Pins

T_MIN≤ T_A≤ T_MAX

0°C ≤ T_A≤ +85°C

-40°C ≤ T_A≤ +85°C

+3.0V to +3.6V

(V_DD+0.3V)

±1 mA

LM95235CIMM

Input Current at D− Pin (Note 4)

Input Current at All Other Pins

(Note 4)

Output Sink Current

SMBDAT, T_Crit, OS Pins

Package Input Current (Note 4)

ESD Susceptibility (Note 3)

Human Body Model

Machine Model

LM95235DIMM

±5 mA

LM95235EIMM, LM95235QEIMM

Supply Voltage (V_DD

)

10 mA

30 mA

Soldering process

must

comply

with

National

Semiconductor's Reflow Temperature Profile specifications.

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

ꢁ

2500V

250V

Charged Device Model

1000V

Junction Temperature (Note 2)

Storage Temperature

+125°C

−65°C to +150°C

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for V_DD= +3.0 Vdc to 3.6 Vdc. Boldface limits apply for T_A= T_J=

T_MIN≤ T_A≤ T_MAX; all other limits T_A= T_J= +25°C, unless otherwise noted. T_Jis the junction temperature of the LM95235. T_Ais

the ambient temperature of the LM95235. T_Dis the junction temperature of the remote thermal diode.

Parameter

Conditions

Typical LM95235

LM95235

DIMM/

Limits

LM95235

EIMM

LM95235

QEIMM

Limits

Units

CIMM

Limits

(Note 7)

(Note 6)

(Note 7)

Temperature Accuracy

Using Local Diode (Note 8)

T_A= 25°C to +100°C

±1

±2

°C (max)

T_A= -40°C to +25°C

±6.0

Temperature Accuracy

Using Remote Diode

(Note 9)

T_A= +25°C to +85°C;

T_D= +60°C to +100°C

65nm Intel

Processor

±0.5

±0.75

±1.0

±0.75

±1.0

±0.75

±1.0

°C (max)

T_A= +25°C to +85°C;

T_D= +60°C to +100°C

MMBT3904

MMBT3904 or

65nm Intel

Processor

T_A= +25°C to +85°C;

T_D= +40°C to +120°C

±0.75

±1.5

±3.0

±1.5

°C (max)

MMBT3904 or

65nm Intel

Processor

T_A= -40°C to +25°C;

T_D= +25°C to +125°C

T_A= -40°C to +25°C;

T_D= +25°C to +125°C

MMBT3904

±3.0

±5.0

°C (max)

T_A= -40°C to +25°C;

T_D= -40°C to +25°C

±5.0

11

0.125

13

Bits

°C

Digital Filter Off

Digital Filter On

Remote Diode

Measurement Resolution

Bits

0.03125

11

°C

Local Diode Measurement

Resolution

Bits

0.125

63

°C

Conversion Time, Fastest Local and Remote Channels

72

ms (max)

ms

Setting (Note 10)

Local or Remote Channels

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Parameter

Conditions

Typical LM95235

LM95235

DIMM/

Limits

LM95235

EIMM

LM95235

QEIMM

Limits

Units

CIMM

Limits

(Note 7)

(Note 6)

(Note 7)

SMBus Inactive, 1 Hz conversion rate

(Note 11)

350

650

225

650

225

650

µA (max)

Quiescent Current

D− Source Voltage

Standby Mode

300

400

172

10.75

16

µA

mV

High-level

Low-level

225

µA (max)

µA

External Diode Current

Source

Diode Source Current Ratio

2.8

1.6

2.8

1.6

2.8

1.6

V (max)

V (min)

°C

Power-On Reset Voltage

T_CRIT Pin Temperature Default

Threshold

+110

+85

OS Pin Temperature

Threshold

Default

°C

Logic Electrical Characteristics

Digital DC Characteristics

Unless otherwise noted, these specifications apply for V_DD= +3.0 Vdc to 3.6 Vdc. Boldface limits apply for T_A= T_J= T_MINto

T_MAX; all other limits T_A= T_J= +25°C, unless otherwise noted.

Symbol

Parameter

Conditions

Typical

Limits

Units

(Limit)

(Note 6)

(Note 7)

SMBDAT, SMBCLK INPUTS

V_IN(1)

Logical “1” Input Voltage

Logical “0” Input Voltage

2.1

0.8

V (min)

V (max)

mV

V_IN(0)

V_IN(HYST)

SMBDAT and SMBCLK Digital Input Hysteresis

Logical “1” Input Current

400

−0.005

0.005

5

I_IN(1)

V_IN= V_DD

V_IN= 0 V

−10

+10

µA (max)

pF

I_IN(0)

Logical “0” Input Current

C_IN

Input Capacitance

A0 DIGITAL INPUT

V_IH

0.90 × V_DD

0.57 × V_DD

0.43 × V_DD

0.10 × V_DD

−10

Input High Voltage

V (min)

V (max)

V (min)

V (max)

µA (max)

pF

V_IM

Input Middle Voltage

V_IL

Input Low Voltage

I_IN(1)

I_IN(0)

C_IN

Logical “1” Input Current

Logical “0” Input Current

Input Capacitance

V_IN= V_DD

V_IN= 0 V

−0.005

0.005

5

+10

SMBDAT, T_CRIT, OS DIGITAL OUTPUTS

I_OH

High Level Output Leakage Current

V_OUT= V_DD

I_OL= 6 mA

10

µA (max)

V (max)

V_{OL(T_CRIT, OS)}

T_CRIT, OS Low Level Output Voltage

SMBDAT Low Level Output Voltage

Digital Output Capacitance

0.4

I_OL= 4 mA

I_OL= 6 mA

0.4

0.6

V (max)

V_OL(SMBDAT)

C_OUT

5

pF

5

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SMBus Digital Switching Characteristics

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

Boldface limits apply for T_A= T_J= T_MINto T_MAX; all other limits T_A= T_J= +25°C, unless otherwise noted.

The switching characteristics of the LM95235 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 LM95235. They adhere

to, but are not necessarily, the SMBus specifications.

Symbol

Parameter

Conditions

Typical Limits

Units

(Limit)

(Note 6) (Note 7)

100

10

kHz

(max)

f_SMB

SMBus Clock Frequency

kHz (min)

4.7

25

µs (min)

ms (max)

t_LOW

from V_IN(0)max to V_IN(0)max

SMBus Clock Low Time

t_HIGH

from V_IN(1)min to V_IN(1)min

(Note 12)

SMBus Clock High Time

SMBus Rise Time

4.0

µs (min)

µs (max)

t_R,SMB

t_F,SMB

1

SMBus Fall Time

(Note 13)

0.3

C_L= 400 pF,

t_OF

Output Fall Time

250

ns (max)

I_O= 3 mA, (Note 13)

SMBDAT and SMBCLK Time Low for Reset of Serial

Interface (Note 14)

25

35

ms (min)

ms (max)

t_TIMEOUT

t_SU;DAT

t_HD;DAT

Data In Setup Time to SMBCLK High

250

ns (min)

300

1075

ns (min)

ns (max)

Data Out Stable after SMBCLK Low

Start Condition SMBDAT Low to SMBCLK Low (Start

condition hold before the first clock falling edge)

t_HD;STA

t_SU;STO

t_SU;STA

t_BUF

100

ns (min)

Stop Condition SMBCLK High to SMBDAT Low (Stop

Condition Setup)

SMBus Repeated Start-Condition Setup Time,

SMBCLK High to SMBDAT Low

0.6

1.3

µs (min)

SMBus Free Time Between Stop and Start Conditions

SMBus Communication

20174909

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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:

ꢀꢀθ_JAfor MSOP-8 package = 210°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 (V_I) at any pin exceeds the power supplies (V_I< GND or V_I> V_DD), 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 LM95235'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

V_DD

Circuit

Pin ESD Protection Structure Circuits

1

2

3

4

5

6

7

8

A

B

A

B

D+

D−

T_CRIT

GND

OS/A0

SMBDAT

SMBCLK

ꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁCircuit B

ꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁꢁCircuit A

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

Note 6: Typical figures are at T_A= 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 LM95235 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 LM95235 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: This specification is provided only to indicate how often temperature data is updated. The LM95235 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 (V_IN(0)max - 0.15V) to (V_IN(1)min + 0.15V).

Note 13: The output fall time is measured from (V_IN(1)min + 0.15V) to (V_IN(0)max - 0.15V).

Note 14: Holding the SMBDAT and/or SMBCLK lines Low for a time interval greater than t_TIMEOUTwill reset the LM95235's SMBus state machine, therefore setting

SMBDAT and SMBCLK pins to a high impedance state.

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Typical Performance Characteristics

Thermal Diode Capacitor or PCB Leakage Current Effect Remote Temperature Reading Sensitivity to Thermal Diode

Remote Diode Temperature Reading

Filter Capacitance, TruTherm Enabled

20174905

20174907

Conversion Rate Effect on Average Power Supply Current

Intel Processor on 65nm Process or 90nm Process

Thermal Diode Performance Comparison

20174906

20174950

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LM95235 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.

1.0 Functional Description

The LM95235 is a temperature sensor that measures Local

and Remote temperature zones. The LM95235 uses a ΔV_be

temperature sensing method. A differential voltage, repre-

senting temperature, is digitized using a Sigma-Delta analog

to digital converter. TruTherm Technology allows the

LM95235 to accurately sense the temperature of a thermal

diode found on die fabricated using a sub-micron process. For

more information on TruTherm Technology see Section 3.0

Application Hints. The LM95235 is compatible with the serial

SMBus version 2.0 two-wire serial interface.

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

Register is 7 bits for limits between 0°C and 127°C. The Re-

mote Temperature TCRIT and OS Limit Registers are 8 bits

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

The LM95235 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:

1.1 CONVERSION SEQUENCE

In the power-up default state the LM95235 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 LM95235 to draw different amounts of supply cur-

rent as shown in Figure 1.

Output Pin

T_CRIT

OS

Remote, °C

Local, °C

110

85

The following table describes the limit register mapping to the

T_CRIT and/or OS pins:

Output Pin

T_CRIT

Remote

Local

Remote

TCRIT Limit

Local Shared OS/TCRIT

Limit

Remote OS Local Shared OS/TCRIT

Limit Limit

OS

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 LM95235 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 LM95235’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.

20174906

FIGURE 1. Conversion Rate Effect on Power Supply

Current

1.2 POWER-ON-DEFAULT STATES

LM95235 always powers up to these known default states.

The LM95235 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

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

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

LM95235 as follows:

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

and an impulse input.

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

LM95235 as follows:

A. Remote Diode digital filter defaults on.

B. The Remote Diode mode defaults to a typical Intel

processor on 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).

a) Seventeen and fifty degree step²⁰r¹e⁷⁴s⁹p²⁵onse

1.3 SMBus INTERFACE

The LM95235 operates as a slave on the SMBus, so the

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

The LM95235 never drives the SMBCLK line and it does not

support clock stretching. According to SMBus specifications,

the LM95235 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 the possible selections.

SMBus Device Address

State of the A0 Pin

HEX

18

Binary

Low

Mid-Supply

High

001 1000

010 1001

100 1100

29

4C

b) Impulse response with input transien²t⁰s¹⁷l⁴e⁹²s⁶s than 4°C

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 LM95235 will immediately detect the state

of this pin to determine its SMBus slave address. The

LM95235 does not latch the state of the A0 pin when it is

functioning as an input.

1.4 DIGITAL FILTER

In order to suppress erroneous remote temperature readings

due to noise, the LM95235 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

0

FE0

0

Filter Setting

Filter Off

20174928

c) Impuse response with input transients greater than 4°

0

1

Reserved

Filter On

C

1

0

FIGURE 2. Filter Impulse and Step Response Curves

1

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

a 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.

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13-bit, 2's complement (12-bit plus sign)

Temperature Digital Output

Binary

Hex

+125°C

+25°C

0111 1101 0000 0000

0001 1001 0000 0000

0000 0001 0000 0000

0000 0000 0000 1000

0000 0000 0000 0000

1111 1111 1111 1000

1111 1111 0000 0000

1110 0111 0000 0000

1100 1001 0000 0000

7D00h

1900h

0100h

0008h

0000h

FFF8h

FF00h

E700h

C900h

+1°C

+0.03125°C

0°C

−0.03125°C

−1°C

−25°C

−55°C

20174927

13-bit, unsigned binary

FIGURE 3. Digital Filter Response in a typical Intel

processor on a 65 nm or 90 nm process. The filter curves

were purposely offset for clarity.

Temperature

Digital Output

Binary

Hex

1.5 TEMPERATURE DATA FORMAT

+255.875°C

+255°C

+201°C

+125°C

+25°C

1111 1111 1110 0000

1111 1111 0000 0000

1100 1001 0000 0000

0111 1101 0000 0000

0001 1001 0000 0000

0000 0001 0000 0000

0000 0000 0000 1000

0000 0000 0000 0000

FFE0h

FF00h

C900h

7D00h

1900h

0100h

0008h

0000h

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".

+1°C

+0.03125°C

0°C

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".

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.

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

Temperature

Digital Output

Binary

Hex

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

+125°C

+25°C

+1°C

0111 1101 0000 0000

0001 1001 0000 0000

0000 0001 0000 0000

0000 0000 0010 0000

0000 0000 0000 0000

1111 1111 1110 0000

1111 1111 0000 0000

1110 0111 0000 0000

1100 1001 0000 0000

7D00h

1900h

0100h

0020h

0000h

FFE0h

FF00h

E700h

C900h

Temperature

Digital Output

Binary

Hex

+125°C

+25°C

+1°C

0111 1101 0000 0000

0001 1001 0000 0000

0000 0001 0000 0000

0000 0000 0010 0000

0000 0000 0000 0000

1111 1111 1110 0000

1111 1111 0000 0000

1110 0111 0000 0000

1100 1001 0000 0000

7D00h

1900h

0100h

0020h

0000h

FFE0h

FF00h

E700h

C900h

+0.125°C

0°C

−0.125°C

−1°C

+0.125°C

0°C

−25°C

−55°C

−0.125°C

−1°C

11-bit, unsigned binary

−25°C

−55°C

Temperature

Digital Output

Binary

Hex

1.6 SMBDAT OPEN-DRAIN OUTPUT

+255.875°C

+255°C

+201°C

+125°C

+25°C

1111 1111 1110 0000

1111 1111 0000 0000

1100 1001 0000 0000

0111 1101 0000 0000

0001 1001 0000 0000

0000 0001 0000 0000

0000 0000 0010 0000

0000 0000 0000 0000

FFE0h

FF00h

C900h

7D00h

1900h

0100h

0020h

0000h

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

LM95235. The maximum resistance of the pull-up to provide

a 2.1V high level, based on LM95235 specification for High

+1°C

+0.125°C

0°C

11

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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 LM95235'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

20174915

FIGURE 5. OS Temperature Response Diagram

1.9 DIODE FAULT DETECTION

The LM95235 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−,

V_DDor 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.

1.10 COMMUNICATING with the LM95235

The data registers in the LM95235 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 LM95235 falls into one of four types

of user accessibility:

1. Read only

20174913

2. Write only

3. Write/Read same address

4. Write/Read different address

FIGURE 4. T_CRIT Comparator Temperature Response

Diagram

A Write to the LM95235 will always include the address byte

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

data byte.

1.8 OS OUTPUT AND OS LIMIT

The LM95235'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

Register. The OS output and the Status Register flags are

updated after every Local and Remote temperature conver-

sion. See Figure 5.

Reading the LM95235 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

Register will point to one of the Read Temperature

Registers because that will be the data most frequently

read from the LM95235), 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 LM95235 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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12

20174911

(a) Serial Bus Write to the Internal Command Register

20174910

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

20174912

(c) Serial Bus byte Read from a Register with the internal Command Register preset to desired value.

20174914

(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

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1.11 SERIAL INTERFACE RESET

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

SMBus start. The LM95235 will respond properly to an

SMBus start condition at any point during the

communication. After the start the LM95235 will expect

an SMBus Address address byte.

In the event that the SMBus Master is RESET while the

LM95235 is transmitting on the SMBDAT line, the LM95235

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 LM95235 SMBus state

machine resets to the SMBus idle state if either SMBDAT

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

Note that according to SMBus specification 2.0 all

devices are to timeout when either the SMBCLK or

SMBDAT lines are held low for 25 - 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.

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

register and it is the write operation that causes the one-shot

conversion. The data written to this address is irrelevant and

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

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14

2.0 LM95235 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

Register Summary

Read

Write

No.

of

bits

POR

Default

(Hex)

Read/

Write

Register Name

Address Address

(Hex) (Hex)

TEMPERATURE SIGNED VALUE REGISTERS

Description

Local Temp MSB

Local Temp LSB

Supports SMBus byte

0x00

0x30

NA

8

3

RO

−

All unused bits are reported as "0".

Remote Temp MSB –

Signed

0x01

0x10

NA

8

RO Supports SMBus byte

−

Remote Temp LSB –

Signed

5/3

RO All unused bits are reported as "0".

TEMPERATURE UNSIGNED VALUE REGISTERS

Remote Temp MSB –

Unsigned

0x31

0x32

NA

8

RO Supports SMBus byte reads

−

Remote Temp LSB –

Unsigned

5/3

RO All unused bits are reported as "0".

DIODE CONFIGURATION REGISTERS

Filter Enable, Diode Model Select, Diode

R/W

Configuration Register 2

0xBF

0x11

0x12

0xBF

0x11

0x12

5

8

3

0x1F

0x00

Fault Mask; Pin 6 OS/A0 function select

Remote Offset

High Byte

R/W 2's Complement

Remote Offset

Low Byte

2's Complement

R/W

All unused bits are reported as "0".

GENERAL CONFIGURATION REGISTERS

STOP/RUN , Remote TCRIT mask,

R/W Remote OS mask, Local TCRIT mask,

Local OS mask

0x03/

0x09

0x09/

0x03

Configuration Register 1

5

0x00

0x04/0x0 0x04/0x0

Conversion Rate

One-Shot

2

0x02

R/W Continuous or specific settings

A

A write to this register activates one

WO

NA

0x0F

−

conversion if STOP/RUN bit = 1.

STATUS REGISTERS

Status Register 1

0x02

0x33

NA

5

2

RO Busy bit, and status bits

−

Status Register 2

RO Not Ready bit, Diode detect bit

LIMIT REGISTERS

0x07/

0x0D

0x0D/

0x07

Unsigned 0 to 255 °C

R/W

Remote OS Limit

8

7

0x55

Default 85 °C

Local Shared OS and

T_Crit Limit

Unsigned 0 to 127 °C

R/W

0x20

Default 85 °C

Unsigned 0 to 255 °C

R/W

Remote T_Crit Limit

Common Hysteresis

0x19

0x21

0x19

0x21

8

5

0x6E

0x0A

Default 110 °C

R/W up to 31°C

15

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Read

Address Address

(Hex) (Hex)

IDENTIFICATION REGISTERS

Write

No.

of

bits

POR

Default

(Hex)

Read/

Write

Register Name

Description

Manufacturer ID

Revision ID

0xFE

0xFF

0x01

0xB1

RO Always returns 0x01

RO Returns revision number.

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16

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

Temperature Data: LSb = 0.125°C.

(Read Only Address 01h)

Signed Remote Temperature MSB

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.

(Read Only Address 10h)

Signed Remote Temperature LSB, Filter On

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

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

Temperature Data: LSb = 0.125°C filter off or 0.03125°C filter on.

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.

(Read Only Address 32h)

Unsigned Remote Temperature LSB, Filter On

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

17

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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

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

T_CRIT

Mask

0

OS/A0 Function Select

OS Fault Mask

TruTherm Select

RFE1

RFE0

1

Bits

Name

Description

Reports "0" when read.

0: Address (A0) function is enabled

7

Reserved

6

OS/A0 Function Select

1: Over-temperature Shutdown (OS) is enabled

0: Off

1: On

5

4

Diode Fault Mask for OS

Diode Fault Mask for T_CRIT

0: Off

1: On

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

disabled.

1: Selects Diode Model 1, A typical Intel Processor, with 65 nm or 90

nm technology, and TruTherm technology enabled.

Remote Diode TruTherm

Mode Select

3

00: Filter Disable

01: Reserved

10: Reserved

2-1

0

Remote Filter Enable

Reserved

11: Filter Enable

Reports "1" when read.

Power up default is 1Fh.

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

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

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18

2.3 GENERAL CONFIGURATION REGISTERS

Configuration Register 1

D3

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

D7

D6

D5

D4

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.

0: Active / Converting

1: Standby

6

5

4

STOP/RUN

Reserved

Reports "0" when read.

0: Off

1: On

Remote T_CRIT Mask

0: Off

1: On

3

2

Remote OS Mask

0: Off

1: On

Local T_CRIT Mask

0: Off

1: On

1

0

Local OS Mask

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

MSb

LSb

Bits

Name

Description

Reports "0" when read.

7:2

Reserved

00: Continuous (33 ms typical when remote

diode is missing or fault or 63 ms typical with

remote diode connected)

01: 0.364 seconds

1:0

Conversion Rate

10: 1 second

11: 2.5 seconds

Power up default is 02h (1 second).

(Write Only Address 0Fh):

One Shot Register

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

19

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2.4 STATUS REGISTERS

Status Register 1

(Read Only Address 02h):

D7

D6

D5

D4

D3

D2

D1

D0

Busy

0

ROS

0

Diode Fault

RTCRIT

LOC

Bits

Name

Description

7

6-5

4

Busy

When set to "1" the part is converting.

Report "0" when read.

Reserved

ROS

Status Bit for Remote OS

Reports "0" when read.

3

Reserved

2

Status bit for missing diode (Either D+ is shorted to GND, and/or V_DD, and/or D-; or

D+ is floating.)

Diode Fault

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

report −128.000°C.

1

0

RTCRIT

LOC

Status bit for Remote TCRIT.

Status bit for the shared Local OS and TCRIT .

Status Register 2

(Read Only Address 33h):

D7

D6

TruTherm 3904 Detect

D5

D4

D3

D2

D1

D0

Not Ready

0

Bits

Name

Description

7

Not Ready

Waiting for 30 ms power-up sequence to end.

1: MMBT3904 is connected and TruTherm technology is enabled.

0: MMBT3904 is connected and TruTherm technology is disabled.

6

TruTherm 3904 Detect

Reserved

5-0

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).

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).

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20

Common Hysteresis Register

(Read/Write Address 21h):

D7

D6

D5

D4

D3

D2

D1

D0

0

16

8

4

2

1

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

0

1

Revision ID Register

(Read Only Address FFh): Default is B1h. This register will increment by 1 every time there is a revision to the die by National

Semiconductor. The initial revision bits for B1h are shown below.

D7

D6

D5

D4

D3

D2

D1

D0

1

0

1

0

1

21

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3.0 Applications Hints

The LM95235 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 LM95235'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 LM95235 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.

•

q = 1.6×10⁻¹⁹Coulombs (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,

I_S= Saturation Current and is process dependent,

I_f= Forward Current through the base-emitter junction

V_BE= Base-Emitter Voltage drop

•

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

inated, yielding the following equation

To measure temperature external to the LM95235'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 LM95235'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.

(2)

In Equation 2, η and I_Sare dependant upon the process that

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

two currents with a very controlled ratio(I_F2/ I_F1) and measur-

ing the resulting voltage difference, it is possible to eliminate

the I_Sterm. Solving for the forward voltage difference yields

the relationship:

(3)

The LM95235's TruTherm technology allows accurate sens-

ing of integrated thermal diodes, such as those found on most

processors. With TruTherm technology turned off, the

LM95235 can measure a diode-connected transistor such as

the MMBT3904 or the thermal diode found in an AMD pro-

cessor.

Solving Equation 3 for temperature yields:

The LM95235 has been optimized to measure the remote

thermal diode integrated in a typical Intel processor on

65 nm or 90 nm process or an MMBT3904 transistor. Using

the Remote Diode Model Select register either pair of remote

inputs can be assigned to be either a typical Intel processor

on 65 nm or 90 nm process or an MMBT3904.

(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 7 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.

3.1 DIODE NON-IDEALITY

3.1.1 Diode Non-Ideality Factor Effect on Accuracy

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.

When a transistor is connected as a diode, the following re-

lationship holds for variables V_BE, T and I_F:

(5)

(1)

where:

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22

20174943

FIGURE 7. Thermal Diode Current Paths

TruTherm should only be enabled when measuring the tem-

perature of a transistor integrated as shown in the processor

of Figure 7, because Equation 5 only applies to this topology.

(6)

Solving Equation 6 for R_PCBequal 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.

3.1.2 Calculating Total System Accuracy

The voltage seen by the LM95235 also includes the I_FR_Svolt-

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 ΔV_BEis

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 +1.19%/−0.27%. The resulting system

accuracy of the processor temperature being sensed will be:

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

LM95235.

Processor Family

Series

Transistor Equation η_T,

R,Ω

non-ideality

min

typ

max

Intel Processor on

65 nm process

0.997

1.001

1.005

4.52

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

and

Processor Family

Series

Diode Equation η_D, non-

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

R,Ω

ideality

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 ±0.39% for the Pentium 4 processor on

90 nm process. The resulting accuracy when using TruTherm

technology improves to:

min

typ

max

Pentium III CPUID

67h

1

1.0065

1.0125

Pentium III CPUID

68h/

PGA370Socket/

Celeron

1.0057

1.008

1.0125

T_ACC= ±0.75°C + (±0.39% of 353 K) = ± 2.16 °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 65 nm

process, this is specified at 4.52Ω typical. The LM95235 ac-

commodates the typical series resistance of Intel Processor

on 65 nm process. The error that is not accounted for is the

spread of the processor's series resistance, that is 2.79Ω to

6.24Ω or ±1.73Ω. The equation to calculate the temperature

error due to series resistance (T_ER) for the LM95235 is simply:

Pentium 4, 423 pin 0.9933

Pentium 4, 478 pin 0.9933

1.0045

1.0368

Pentium 4 on 0.13

micron process, 2 - 1.0011

3.06 GHz

1.0021

1.0030 3.64

Pentium 4 on 90 nm

1.0083

1.011

1.009

1.023

1.050

3.33

4.52

process

Intel Processor on

1.000

65 nm process

23

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3.2 PCB LAYOUT FOR MINIMIZING NOISE

Pentium M

(Centrino)

1.00151 1.00220 1.00289 3.06

1.003

MMBT3904

AMD Athlon MP

model 6

1.002

1.008

1.016

AMD Athlon 64

AMD Opteron

AMD Sempron

1.008

1.096

1.00261

0.93

3.1.3 Compensating for Different Non-Ideality

20174917

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 LM95235 is calibrated

for two non-ideality factors and series resistance values thus

supporting the MMBT3904 transistor and Intel processors on

65nm process without the requirement for additional trims.

For most accurate measurements TruTherm mode should be

turned on when measuring the Intel processor on 65nm pro-

cess to minimize the error introduced by the false non-ideality

spread (see 3.1.1 Diode Non-Ideality Factor Effect on Accu-

racy). When a temperature sensor calibrated for a particular

processor type is used with a different processor type, addi-

tional errors are introduced.

FIGURE 8. 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 LM95235 can cause temperature conversion errors.

Keep in mind that the signal level the LM95235 is trying to

measure is in microvolts. The following guidelines should be

followed:

1. V_DDshould 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 LM95235.

Temperature errors associated with non-ideality of different

processor types may be reduced in a specific temperature

range of concern through use of software calibration. Typical

Non-ideality specification differences cause a gain variation

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

ture range of interest should be the target temperature for

calibration purposes. The following equation can be used to

calculate the temperature correction factor (T_CF) required to

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

ported by the LM95235.

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

high frequency noise but may not be necessary. Make

sure the traces to the 100 pF capacitor are matched.

Place the filter capacitors close to the LM95235 pins.

3. Ideally, the LM95235 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.

(7)

where

•

η_S= LM95235 non-ideality for accuracy specification

_PROCESSOR= Processor thermal diode typical non-ideality

T_CR= center of the temperature range of interest in °C

η

5. Avoid routing diode traces in close proximity to power

supply switching or filtering inductors.

The correction factor should be directly added to the temper-

ature reading produced by the LM95235. For example when

using the LM95235, with the 3904 mode selected, to measure

a AMD Athlon processor, with a typical non-ideality of 1.008,

for a temperature range of 60 °C to 100 °C the correction fac-

tor would calculate to:

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.

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 LM95235's GND pin is as

close as possible to the Processors GND associated with

the sense diode.

(8)

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.

Therefore, 1.75°C should be subtracted from the temperature

readings of the LM95235 to compensate for the differing typ-

ical non-ideality target.

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 LM95235. SMBus no acknowledge is the most common

symptom, causing unnecessary traffic on the bus. Although

www.national.com

24

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 LM95235'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.

25

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Physical Dimensions inches (millimeters) unless otherwise noted

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

JEDEC Registration Number MO-187

Order Number LM95235CIMM, LM95235DIMM, LM95235EIMM, LM95235QEIMM, LM95235CIMMX, LM95235DIMMX,

LM95235EIMMX, and LM95235QEIMMX,

NS Package Number MUA08A

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26

Notes

27

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Notes

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型号：	LM95235DIMM
厂家：	National Semiconductor
描述：	Precision Remote Diode Temperature Sensor with SMBus Interface and TruTherm? Technology 精密远程二极管温度传感器，具有SMBus接口和TruTherm ？技术二极管传感器温度传感器
文件：	总28页 (文件大小：553K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LM95235DIMM [NSC]

相关型号：

LM95235DIMM/NOPB

LM95235DIMMX

LM95235DIMMX/NOPB

LM95235EIMM

LM95235EIMM/NOPB

LM95235EIMMX

LM95235EIMMX/NOPB

LM95235Q

LM95235QEIMM

LM95235QEIMM

LM95235QEIMM/NOPB

LM95235QEIMMX