LM94022BIMGNOPB - NATIONAL SEMICONDUCTOR

LM92

LM92 +/-0.33C Accurate, 12-Bit + Sign Temperature Sensor and Thermal

Window Comparatorwith Two-Wire Interface

Literature Number: SNIS110C

LM92

November 2, 2010

±0.33°C Accurate, 12-Bit + Sign Temperature Sensor and

Thermal Window Comparator with Two-Wire Interface

General Description

The LM92 is a digital temperature sensor and thermal window

comparator with an I2C™ Serial Bus interface and an accu-

racy of ±0.33°C. The window-comparator architecture of the

LM92 eases the design of temperature control systems. The

open-drain Interrupt (INT) output becomes active whenever

temperature goes outside a programmable window, while a

separate Critical Temperature Alarm (T_CRIT_A) output be-

comes active when the temperature exceeds a pro-

grammable critical limit. The INT output can operate in either

a comparator or event mode, while the T_CRIT_A output op-

erates in comparator mode only.

The host can program both the upper and lower limits of the

window as well as the critical temperature limit. Pro-

grammable hysterisis as well as a fault queue are available

to minimize false tripping. Two pins (A0, A1) are available for

address selection. The sensor powers up with default thresh-

olds of 2°C THYST, 10°C TLOW, 64°C THIGH, and 80°C T_CRIT.

The LM92's 2.7V to 5.5V supply voltage range, Serial Bus

interface, 12-bit + sign output, and full-scale range of over

128°C make it ideal for a wide range of applications. These

include thermal management and protection applications in

personal computers, electronic test equipment, office elec-

tronics, automotive, medical and HVAC applications.

Features

■Window comparison simplifies design of ACPI compatible

temperature monitoring and control.

■Serial Bus interface

■Separate open-drain outputs for Interrupt and Critical

Temperature shutdown

■Shutdown mode to minimize power consumption

■Up to 4 LM92s can be connected to a single bus

■12-bit + sign output

■Operation up to 150°C

Key Specifications

■ Supply Voltage 2.7V to 5.5V

■ Supply Current operating 350 µA (typ)

625 µA (max)

shutdown 5 µA (typ)

■ Temperature 30°C ±0.33°C (max)

Accuracy 10°C to 50°C ±0.50°C (max)

−10°C to 85°C ±1.0°C (max)

125°C ±1.25°C (max)

−25°C to 150°C ±1.5°C (max)

■ Linearity ±0.5°C (max)

■ Resolution 0.0625°C

Applications

■HVAC

■Medical Electronics

■Electronic Test Equipment

■System Thermal Management

■Personal Computers

■Office Electronics

■Automotive

I2C® is a registered trademark of Philips Corporation.

LM92 ±0.33°C Accurate, 12-Bit + Sign Temperature Sensor and Thermal Window Comparator

with Two-Wire Interface

Simplified Block Diagram

10105101

Connection Diagram

SO-8

10105102

LM92

See NS Package Number M08A

Ordering Information

Order Number Supply Voltage Supplied As

LM92CIM 2.7V to 5.5V

LM92CIMX 2.7V to 5.5V 2500 Units on Tape and Reel

Pin Descriptions

Label Pin # Function Typical Connection

SDA 1 Serial Bi-Directional Data Line. Open Drain Output From Controller

SCL 2 Serial Bus Clock Input From Controller

T_CRIT_A 3 Critical Temperature Alarm Open Drain Output Pull Up Resistor, Controller Interrupt Line or

System Hardware Shutdown

GND 4 Power Supply Ground Ground

INT 5 Interrupt Open Drain Output Pull Up Resistor, Controller Interrupt Line

+V S 8 Positive Supply Voltage Input DC Voltage from 2.7V to 5.5V

A0–A1 7,6 User-Set Address Inputs Ground (Low, “0”) or +VS (High, “1”)

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LM92

Typical Application

10105103

FIGURE 1.

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LM92

Absolute Maximum Ratings (Note 1)

Supply Voltage −0.3 V to 6.5V

Voltage at any Pin −0.3 V

to (+VS + 0.3V)

Input Current at any Pin 5 mA

Package Input Current (Note 2) 20 mA

T_CRIT_A and INT Output Sink

Current 10 mA

T_CRIT_A and INT Output Voltage 6.5V

Storage Temperature −65°C to +125°C

ESD Susceptibility (Note 4)

Human Body Model 2500V

Machine Model 250V

Operating Ratings (Note 1, Note 5)

Specified Temperature Range TMIN to TMAX

(Note 6) −55°C to +150°C

Supply Voltage Range (+VS)+2.7V to +5.5V

Soldering process must comply with National

Semiconductor's Reflow Temperature Profile specifications.

Refer to www.national.com/packaging. (Note 3)

Electrical Characteristics

Temperature-to-Digital Converter Characteristics

Unless otherwise noted, these specifications apply for +VS= +2.7V to +5.5V for LM92CIM . Boldface limits apply for TA = TJ =

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

Parameter Conditions Typical

(Note 7)

Limits

(Note 8)

Units

(Limit)

Accuracy (This is a summary. For more

detailed information please see (Note

9))

T A = +30°C, +VS = 3.3V to 4.0V ±0.33

°C (max)

T A = 10°C or +50°C, +VS = 3.3V to

4.0V

±0.50

T A = −10 °C or +85°C, +VS = 3.3V

to 4.0V

±1.00

T A = +125°C, +VS = 4.0V ±1.25

T A = −25°C to 150°C, +VS = 4.0V ±1.50

Resolution (Note 10) 13

0.0625

Bits

°C

Linearity (Note 11) ±0.5 °C (max)

Offset Error of Transfer Function (Note

12)

+VS = 4.0V °C (max)

Offset Error of Transfer Function Supply

Sensitivity

2.7V ≤ +VS< 3.6V °C/V (max)

3.6V ≤ +VS≤ 5.5V °C/V (max)

Temperature Conversion Time (Note 13) 500 1000 ms

Quiescent Current I2C Inactive 0.35 mA

I2C Active 0.35 0.625 mA (max)

Shutdown Mode 5 µA

T HYST Default Temperature (Note 15, Note 16) 2 °C

T LOW Default Temperature (Note 16) 10 °C

T HIGH Default Temperature (Note 16) 64 °C

T C Default Temperature (Note 16) 80 °C

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LM92

Digital DC Characteristics

Unless otherwise noted, these specifications apply for +VS= +2.7V to +5.5V for LM92CIM . Boldface limits apply for TA = TJ =

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

Symbol Parameter Conditions Typical

(Note 7)

Limits

(Note 8)

Units

(Limit)

V IN(1) SDA and SCL Logical “1” Input

Voltage

+VS × 0.7 V (min)

+VS+0.3 V (max)

V IN(0) SDA and SCL Logical “0” Input

Voltage

−0.3 V (min)

+VS × 0.3 V (max)

VIN(HYST) SDA and SCL Digital Input Hysteresis 500 250 mV (min)

V IN(1) A0 and A1 Logical “1” Input Voltage 2.0 V (min)

+VS+0.3 V (max)

V IN(0) A0 and A1 Logical “0” Input Voltage −0.3 V (min)

0.7 V (max)

I IN(1) Logical “1” Input Current V IN = + VS0.005 1.0 µA (max)

I IN(0) Logical “0” Input Current V IN = 0 V −0.005 −1.0 µA (max)

C IN Capacitance of All Digital Inputs 20 pF

I OH High Level Output Current V OH = + VS 10 µA (max)

V OL Low Level Output Voltage I OL = 3 mA 0.4 V (max)

T_CRIT_A Output Saturation Voltage I OUT = 4.0 mA

(Note 14)

0.8 V (max)

T_CRIT_A Delay 1Conversions

(max)

t OF Output Fall Time C L = 400 pF 250 ns (max)

I O = 3 mA

Serial Bus Digital Switching Characteristics

Unless otherwise noted, these specifications apply for +VS= +2.7V to +5.5V for LM92CIM . Boldface limits apply for TA = TJ =

TMIN to TMAX; all other limits TA= TJ= +25 °C, unless otherwise noted. CL (load capacitance) on output lines = 80 pF unless

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

Symbol Parameter Conditions

Typical

(Note 7)

Limits

(Note 8,

Note 18)

Units

(Limit)

t 1 SCL (Clock) Period 2.5 µs(min)

1ms(max)

t 2 Data in Set-Up Time to SCL High 100 ns(min)

t 3 Data Out Stable after SCL Low 0ns(min)

t 4 SDA Low Set-Up Time to SCL Low (Start Condition) 100 ns(min)

t 5 SDA High Hold Time after SCL High (Stop Condition) 100 ns(min)

tTIMEOUT SDA and SCL Time Low for Reset of Serial Interface (Note 17) 75

300

ms (min)

ms (max)

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LM92

Serial Bus Communication

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

the device beyond its rated operating conditions.

Note 2: When the input voltage (VI) at any pin exceeds the power supplies (VI < GND or VI > +VS) the current at that pin should be limited to 5 mA. The 20 mA

maximum package input current rating limits the number of pins that can safely exceed the power supplies with an input current of 5 mA to four.

Note 3: Reflow temperature profiles are different for lead-free and non-lead-free packages.

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

Note 5: LM92 θJA (thermal resistance, junction-to-ambient) when attached to a printed circuit board with 2 oz. foil is 200 °C/W.

Note 6: While the LM92 has a full-scale-range in excess of 128 °C, prolonged operation at temperatures above 125 °C is not recommended.

Note 7: Typicals are at TA = 25 °C and represent most likely parametric norm.

Note 8: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).

Note 9: The limits found in the following table supersede the limits shown in the Electrical Characteristics Table. The Accuracy specification includes errors due

to linearity, offset and gain. The accuracy specification includes effects of self heating with negligible digital output loading. Pull-up resistors should be maximized

(10k typical recommended), so that self heating due to digital output loading is negligible.

Temperature Accuracy Parameter Limits Units

Conditions +VS=2.7V +VS=3.3V +VS=4V +VS=5V +VS=5.5V

T A = −25°C −1.35/+1.50 −1.25/+1.50 −1.25/+1.50 −1.05/+1.70 −1.05/+1.80 °C (max)

T A = −10°C ±1.00 −0.90/+1.00 −0.90/+1.00 −0.70/+1.20 −0.70/+1.30 °C (max)

T A = 0°C −0.80/+0.75 −0.70/+0.75 −0.70/+0.75 −0.50/+0.95 −0.50/+1.05 °C (max)

T A = 10°C −0.60/+0.50 ±0.50 ±0.50 −0.30/+0.70 −0.30/+0.80 °C (max)

T A = 30°C −0.43/+0.33 ±0.33 ±0.33 −0.13/+0.53 −0.13/+0.63 °C (max)

T A = 50°C −0.60/+0.50 ±0.50 ±0.50 −0.30/+0.70 −0.30/+0.80 °C (max)

T A = 85°C −1.10/+0.85 −1.00/+0.85 −1.00/+0.85 −0.80/+1.05 −0.80/+1.15 °C (max)

T A = 125°C −1.60/+1.25 −1.50/+1.25 ±1.25 −1.05/+1.45 −1.05/+1.55 °C (max)

T A = 150°C ±1.90 −1.75/+1.50 ±1.50 −1.30/+1.70 −1.30/+1.80 °C (max)

Limits at intermediate temperatures can be calculated using a straight line interpolation as shown in the following graphs:

Accuracy vs Temperature with +Vs = 5V

10105120

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LM92

Accuracy vs Temperature with +Vs = 3.3V

10105121

Note 10: 12 bits + sign, two's complement

Note 11: Linearity Error is defined as the worse case difference of an actual reading to that of a calculated reading derived from the straight line whose endpoints

are measured at 30°C and 125°C for the range of 30°C to 125°C or whose endpoints are measured at 30°C and −25°C for the range of 30°C to −25°.

Note 12: Offset Error calibration should be done at 30°C. The residual error of the transfer function is then equivalent to the Accuracy Limit minus the Offset Limit.

This does not take into account the power supply sensitivity of the offset error. Nor, does it take into account the error introduced by the calibration system used.

Note 13: This specification is provided only to indicate how often temperature data is updated. The LM92 can be read at any time without regard to conversion

state (and will yield last conversion result). If a conversion is in process it will be interrupted and restarted after the end of the read.

Note 14: For best accuracy, minimize output loading. 10k pull-ups resistors should be sufficient. Higher sink currents can affect sensor accuracy with internal

heating. This can cause an error of 0.64 °C at full rated sink current and saturation voltage based on junction-to-ambient thermal resistance.

Note 15: Hysteresis value adds to the TLOW setpoint value (e.g.: if TLOW setpoint = 10 °C, and hysteresis = 2 °C, then actual hysteresis point is 10+2 = 12 °C);

and subtracts from the THIGH and T_CRIT setpoints (e.g.: if THIGH setpoint = 64 °C, and hysteresis = 2 °C, then actual hysteresis point is 64−2 = 62 °C). For a

detailed discussion of the function of hysteresis refer to Section 1.1, TEMPERATURE COMPARISON, and Figure 3.

Note 16: Default values set at power up.

Note 17: Holding the SDA and/or SCL lines Low for a time interval greater than tTIMEOUT will cause the LM92 to reset SCL and SDA to the IDLE state of the serial

bus communication (SDA and SCL set High).

Note 18: Timing specifications are tested at the bus input logic levels (Vin(0)=0.3xVA for a falling edge and Vin(1)=0.7xVA for a rising edge) when the SCL and

SDA edge rates are similar.

10105105

FIGURE 2. Temperature-to-Digital Transfer Function (Non-linear scale for clarity)

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LM92

1.0 Functional Description

The LM92 temperature sensor incorporates a band-gap type

temperature sensor, 13-bit ADC, and a digital comparator

with user-programmable upper and lower limit values. The

comparator activates either the INT line for temperatures out-

side the TLOW and THIGH window, or the T_CRIT_A line for

temperatures which exceed T_CRIT. The lines are pro-

grammable for mode and polarity.

1.1 TEMPERATURE COMPARISON

LM92 provides a window comparison against a lower (TLOW)

and upper (THIGH) trip point. A second upper trip point

(T_CRIT) functions as a critical alarm shutdown. Figure 3 de-

picts the comparison function as well as the modes of oper-

ation.

1.1.1 Status Bits

The internal Status bits operate as follows:

“True”: Temperature above a THIGH or T_CRIT is “true” for

those respective bits. A “true” for TLOW is temperature below

TLOW.

“False”: Assuming temperature has previously crossed

above THIGH or T_CRIT, then the temperature must drop be-

low the points corresponding THYST (THIGH − THYST or

T_CRIT − THYST) in order for the condition to be false. For

TLOW, assuming temperature has previously crossed below

TLOW, a “false” occurs when temperature goes above TLOW +

THYST.

The Status bits are not affected by reads or any other actions,

and always represent the state of temperature vs. setpoints.

1.1.2 Hardwire Outputs

The T_CRIT_A hardwire output mirrors the T_CRIT_A flag,

when the flag is true, the T_CRIT_A output is asserted at all

times regardless of mode. Reading the LM92 has no effect

on the T_CRIT_A output, although the internal conversion is

restarted.

The behavior of the INT hardwire output is as follows:

Comparator Interrupt Mode (Default): User reading part

resets output until next measurement completes. If condition

is still true, output is set again at end of next conversion cycle.

For example, if a user never reads the part, and temperature

goes below TLOW then INT becomes active. It would stay that

way until temperature goes above TLOW + THYST. However if

the user reads the part, the output would be reset. At the end

of the next conversion cycle, if the condition is true, it is set

again. If not, it remains reset.

Event Interrupt Mode: User reading part resets output until

next condition "event" occurs (in other words, output is only

set once for a true condition, if reset by a read, it remains reset

until the next triggering threshold has been crossed). Con-

versely, if a user never read the part, the output would stay

set indefinitely after the first event that set the output. An

“event” for Event Interrupt Mode is defined as:

1. Transitioning upward across a setpoint, or

2. Transitioning downward across a setpoint's

corresponding hysteresis (after having exceeded that

setpoint).

For example, if a user never read the part, and temperature

went below TLOW then INT would become active. It would stay

that way forever if a user never read the part.

However if the user read the part, the output would be reset.

Even if the condition is true, it will remain reset. The temper-

ature must cross above TLOW + THYST to set the output again.

In either mode, reading any register in the LM92 restarts the

conversion. This allows a designer to know exactly when the

LM92 begins a comparison. This prevents unnecessary In-

terrupts just after reprogramming setpoints. Typically, system

Interrupt inputs are masked prior to reprogramming trip

points. By doing a read just after resetting trip points, but prior

to unmasking, unexpected Interrupts are prevented.

Avoid programming setpoints so close that their hysteresis

values overlap. An example would be that with a THYST value

of 2 °C then setting THIGH and TLOW to within 4 °C of each

other will violate this restriction. To be more specific, with

THYST set to 2 °C assume THIGH set to 64 °C. If TLOW is set

equal to, or higher than 60 °C this restriction is violated.

1.2 DEFAULT SETTINGS

The LM92 always powers up in a known state. LM92 power

up default conditions are:

1. Comparator Interrupt Mode

2. TLOW set to 10 °C

3. THIGH set to 64 °C

4. T_CRIT set to 80 °C

5. THYST set to 2 °C

6. INT and T_CRIT_A active low

7. Pointer set to “00”; Temperature Register

The LM92 registers will always reset to these default values

when the power supply voltage is brought up from zero volts

as the supply crosses the voltage level plotted in the following

curve. The LM92 registers will reset again when the power

supply drops below the voltage plotted in this curve.

Average Power on Reset Voltage

vs Temperature

10105118

1.3 SERIAL BUS INTERFACE

The LM92 operates as a slave on the Serial Bus, so the SCL

line is an input (no clock is generated by the LM92) and the

SDA line is a bi-directional serial data line. According to Serial

Bus specifications, the LM92 has a 7-bit slave address. The

five most significant bits of the slave address are hard wired

inside the LM92 and are “10010”. The two least significant bits

of the address are assigned to pins A1–A0, and are set by

connecting these pins to ground for a low, (0); or to +VS for a

high, (1).

Therefore, the complete slave address is:

1 0 0 1 0 A1 A0

MSB LSB

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LM92

10105106

Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn't read, the outputs would go low and stay that way until the LM92 is read.

Comparator Interrupt Mode is drawn as if the user never reads the part. If the user does read, the outputs will go high once read instruction is executed and, if

the fault condition still exists, go low at the end of the next conversion.

FIGURE 3. Temperature Response Diagram

1.4 TEMPERATURE DATA FORMAT

Temperature data can be read from the Temperature and Set

Point registers; and written to the Set Point registers. Tem-

perature data can be read at any time, although reading faster

than the conversion time of the LM92 will prevent data from

being updated. Temperature data is represented by a 13-bit,

two's complement word with an LSB (Least Significant Bit)

equal to 0.0625 °C:

Temperature Digital Output

Binary Hex

+130°C 0 1000 0 010 0000 08 20h

+125 °C 0 0111 1101 0000 07 D0h

+80 °C 0 0101 0000 0000 05 00h

+64 °C 0 0100 0000 0000 04 00h

+25 °C 0 0001 1001 0000 01 90h

+10 °C 0 0000 1010 0000 00 A0h

+2 °C 0 0000 0010 0000 00 20h

+0.0625 °C 0 0000 0000 0001 00 01h

0 °C 00 0000 0000 00 00h

−0.0625 °C 1 1111 1111 1111 1F FFh

−25 °C 1 1110 0111 0000 1E 70h

−55 °C 1 1100 1001 0000 1C 90h

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LM92

1.5 SHUTDOWN MODE

Shutdown mode is enabled by setting the shutdown bit in the

Configuration register via the Serial Bus. Shutdown mode re-

duces power supply current to 5 μA typical. T_CRIT_A is reset

if previously set. Since conversions are stoped during shut-

down, T_CRIT_A and INT will not be operational. The Serial

Bus interface remains active. Activity on the clock and data

lines of the Serial Bus may slightly increase shutdown mode

quiescent current. Registers can be read from and written to

in shutdown mode. The LM92 takes miliseconds to respond

to the shutdown command.

1.6 INT AND T_CRIT_A OUTPUT

The INT and T_CRIT_A outputs are open-drain outputs and

do not have internal pull-ups. A "high" level will not be ob-

served on these pins until pull-up current is provided from

some external source, typically a pull-up resistor. Choice of

resistor value depends on many system factors but, in gen-

eral, the pull-up resistor should be as large as possible. This

will minimize any errors due to internal heating of the LM92.

The maximum resistance of the pull up, based on LM92 spec-

ification for High Level Output Current, to provide a 2 volt high

level, is 30K ohms.

1.7 FAULT QUEUE

A fault queue of 4 faults is provided to prevent false tripping

when the LM92 is used in noisy environments. The 4 faults

must occur consecutively to set flags as well as INT and

T_CRIT_A outputs. The fault queue is enabled by setting bit

4 of the Configuration Register high (see Section 1.11).

1.8 INTERNAL REGISTER STRUCTURE

10105107

There are four data registers in the LM92, selected by the

Pointer register. At power-up the Pointer is set to “00”; the

location for the Temperature Register. The Pointer register

latches the last location it was set to. In Interrupt Mode, a read

from the LM92 resets the INT output. Placing the device in

Shutdown mode resets the INT and T_CRIT_A outputs. All

registers are read and write, except the Temperature register

which is read only.

A write to the LM92 will always include the address byte and

the Pointer byte. A write to the Configuration register requires

one data byte, while the TLOW, THIGH, and T_CRIT registers

require two data bytes.

Reading the LM92 can take place either of two ways: If the

location latched in the Pointer is correct (most of the time it is

expected that the Pointer will point to the Temperature regis-

ter because it will be the data most frequently read from the

LM92), then the read can simply consist of an address byte,

followed by retrieving the corresponding number of data

bytes. If the Pointer needs to be set, then an address byte,

pointer byte, repeat start, and another address byte plus re-

quired number of data bytes will accomplish a read.

The first data byte is the most significant byte with most sig-

nificant bit first, permitting only as much data as necessary to

be read to determine the temperature condition. For instance,

if the first four bits of the temperature data indicates a critical

condition, the host processor could immediately take action

to remedy the excessive temperature. At the end of a read,

the LM92 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).

An inadvertent 8-bit read from a 16-bit register, with the D7

bit low, can cause the LM92 to stop in a state where the SDA

line is held low as shown in Figure 4. This can prevent any

further bus communication until at least 9 additional clock cy-

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LM92

cles have occurred. Alternatively, the master can issue clock

cycles until SDA goes high, at which time issuing a “Stop”

condition will reset the LM92.

10105108

FIGURE 4. Inadvertent 8-Bit Read from 16-Bit Register where D7 is Zero (“0”)

1.9 POINTER REGISTER

(Selects which registers will be read from or written to):

P7 P6 P5 P4 P3 P2 P1 P0

0 0 0 0 0 Register Select

P0–P2: Register Select:

P2 P1 P0 Register

000Temperature (Read only) (Power-up default)

0 0 1 Configuration (Read/Write)

0 1 0 THYST (Read/Write)

0 1 1 T_CRIT (Read/Write)

1 0 0 TLOW (Read/Write)

1 0 1 THIGH (Read/Write)

1 1 1 Manufacturer's ID

P3–P7: Must be kept zero.

1.10 TEMPERATURE REGISTER

(Read Only):

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Sign MSB Bit 10 Bit 9 Bit 8 Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 CRIT HIGH LOW

Status Bits

D0–D2: Status Bits

D3–D15: Temperature Data. One LSB = 0.0625°C. Two's complement format.

1.11 CONFIGURATION REGISTER

(Read/Write):

D7 D6 D5 D4 D3 D2 D1 D0

0 0 0 Fault Queue INT Polarity T_CRIT_A

Polarity

INT Mode Shutdown

D0: Shutdown - When set to 1 the LM92 goes to low power shutdown mode. Power up default of “0”.

D1: Interrupt mode - 0 is Comparator Interrupt mode, 1 is Event Interrupt mode. Power up default of “0”.

D2, D3: T_CRIT_A and INT Polarity - 0 is active low, 1 is active high. Outputs are open-drain. Power up default of “0”

D4: Fault Queue - When set to 1 the Fault Queu is enabled, see Section 1.7. Power up default of “0”.

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LM92

D5–D7: These bits are used for production testing and must be kept zero for normal operation.

1.12 THYST, TLOW, THIGH AND T_CRIT_A REGISTERS

(Read/Write):

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

Sign MSB Bit 10 Bit 9 Bit 8 Bit7 Bit6 Bit5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 X X X

D0–D2: Undefined

D3–D15: THYST, TLOW, THIGH or T_CRIT Trip Temperature Data. Power up default is TLOW = 10°C, THIGH = 64°C, T_CRIT = 80°C,

THYST = 2°C.

THYST is subtracted from THIGH, and T_CRIT, and added to TLOW.

Avoid programming setpoints so close that their hysteresis values overlap. See Section 1.1.

1.13 Manufacturer's Identification Register

(Read only):

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

1000000000000001

D0–D15: Manufactures ID.

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LM92

2.0 I2C Timing Diagrams

10105109

Typical 2-Byte Read From Preset Pointer Location Such as Temp or Comparison Registers

10105110

Typical Pointer Set Followed by Immediate Read for 2-Byte Register such as Temp or Comparison Registers

10105111

Typical 1-Byte Read from Configuration Register with Preset Pointer

FIGURE 5.

10105112

Typical Pointer Set Followed by Immediate Read from Configuration Register

10105113

Configuration Register Write

10105114

Comparison Register Write

FIGURE 6. Timing Diagrams

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LM92

3.0 Application Hints

The temperature response graph in Figure 7 depicts a typical

application designed to meet ACPI requirements. In this type

of application, the temperature scale is given an arbitrary val-

ue of "granularity", or the window within which temperature

notification events should occur. The LM92 can be pro-

grammed to the window size chosen by the designer, and will

issue interrupts to the processor whenever the window limits

have been crossed. The internal flags permit quick determi-

nation of whether the temperature is rising or falling.

The T_CRIT limit would typically use its separate output to

activate hardware shutdown circuitry separate from the pro-

cessor. This is done because it is expected that if temperature

has gotten this high that the processor may not be respond-

ing. The separate circuitry can then shut down the system,

usually by shutting down the power supply.

Note that the INT and T_CRIT_A outputs are separate, but

can be wire-or'd together. Alternatively the T_CRIT_A can be

diode or'd to the INT line in such a way that a T_CRIT_A event

activates the INT line, but an INT event does not activate the

T_CRIT_A line. This may be useful in the event that it is de-

sirable to notify both the processor and separate T_CRIT_A

shutdown circuitry of a critical temperature alarm at the same

time (maybe the processor is still working and can coordinate

a graceful shutdown with the separate shutdown circuit).

To implement ACPI compatible sensing it is necessary to

sense whenever the temperature goes outside the window,

issue an interrupt, service the interrupt, and reprogram the

window according to the desired granularity of the tempera-

ture scale. The reprogrammed window will now have the

current temperature inside it, ready to issue an interrupt

whenever the temperature deviates from the current window.

To understand this graph, assume that at the left hand side

the system is at some nominal temperature. For the 1st event

temperature rises above the upper window limit, THIGH, caus-

ing INT to go active. The system responds to the interrupt by

querying the LM92's status bits and determines that THIGH

was exceeded, indicating that temperature is rising. The sys-

tem then reprograms the temperature limits to a value higher

by an amount equal to the desired granularity. Note that in

Event Interrupt Mode, reprogramming the limits has caused

a second, known, interrupt to be issued since temperature

has been returned within the window. In Comparator Interrupt

Mode, the LM92 simply stops issuing interrupts.

The 2nd event is another identical rise in temperature. The

3rd event is typical of a drop in temperature. This is one of the

conditions that demonstrates the power of the LM92, as the

user receives notification that a lower limit is exceeded in such

a way that temperature is dropping.

The Critical Alarm Event activates the separate T_CRIT_A

output. Typically, this would feed circuitry separate from the

processor on the assumption that if the system reached this

temperature, the processor might not be responding.

10105115

Note: Event Interrupt mode is drawn as if the user is reading the part. If the user doesn't read, the outputs would go low and stay that way until the LM92 is read.

FIGURE 7. Temperature Response Diagram for ACPI Implementation

www.national.com 14

LM92

4.0 Typical Applications

10105116

FIGURE 8. Typical Application

10105117

FIGURE 9. Remote HVAC temperature sensor communicates via 3 wires, including thermostat signals.

15 www.national.com

LM92

10105119

FIGURE 10. ACPI Compatible Terminal Alarm Shutdown. By powering the LM92 from auxilary output of the power supply,

a non-functioning overheated computer can be powered down to preserve as much of the system as possible.

www.national.com 16

LM92

Physical Dimensions inches (millimeters) unless otherwise noted

8-Lead (0.150″ Wide) Molded Small Outline Package (SOP), JEDEC

Order Number LM92CIM or LM92CIMX

NS Package Number M08A

17 www.national.com

LM92

Notes

LM92 ±0.33°C Accurate, 12-Bit + Sign Temperature Sensor and Thermal Window Comparator

with Two-Wire Interface

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