TMP35GT9 查看數據表（PDF） - Analog Devices

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TMP35GT9

Low Voltage Temperature Sensors

Analog Devices 

TMP35/TMP36/TMP37

MICROPROCESSOR INTERRUPT GENERATOR

These inexpensive temperature sensors can be used with a

voltage reference and an analog comparator to configure an

interrupt generator for microprocessor applications. With the

popularity of fast microprocessors, the need to indicate a

microprocessor overtemperature condition has grown

tremendously. The circuit in Figure 30 demonstrates one way to

generate an interrupt using a TMP35, a CMP402 analog

comparator, and a REF191, a 2 V precision voltage reference.

The circuit is designed to produce a logic high interrupt signal

if the microprocessor temperature exceeds 80°C. This 80°C trip

point was arbitrarily chosen (final value set by the microprocessor

thermal reference design) and is set using an R3 to R4 voltage

divider of the REF191 output voltage. Because the output of the

TMP35 is scaled by 10 mV/°C, the voltage at the inverting

terminal of the CMP402 is set to 0.8 V.

3.3V

Because temperature is a slowly moving quantity, the possibility

for comparator chatter exists. To avoid this condition, hysteresis

is used around the comparator. In this application, a hysteresis

of 5°C about the trip point was arbitrarily chosen; the ultimate

value for hysteresis should be determined by the end application.

The output logic voltage swing of the comparator with R1 and

R2 determines the amount of comparator hysteresis. Using a

3.3 V supply, the output logic voltage swing of the CMP402 is

2.6 V; therefore, for a hysteresis of 5°C (50 mV @ 10 mV/°C),

R1 is set to 20 kΩ, and R2 is set to 1 MΩ. An expression for the

hysteresis of this circuit is given by

( ) VHYS

=

⎜⎝⎛

R1

R2

⎟⎠⎞

VLOGIC

SWING, CMP402

Because this circuit is probably used in close proximity to high

speed digital circuits, R1 is split into equal values and a 1000 pF

capacitor is used to form a low-pass filter on the output of the

TMP35. Furthermore, to prevent high frequency noise from

contaminating the comparator trip point, a 0.1 μF capacitor is

used across R4.

R2

1MΩ

0.1µF

+VS

VOUT

TMP35

R1A

10kΩ

GND

R5

100kΩ

0.1µF

2

R1B

10kΩ

CL

1000pF

6

REF191

3

4

R3

16kΩ

+

1µF

R4

10kΩ

0.1µF

3

6–

4

CMP402 2

5

14

+

13

VREF

<80°C

0.1µF

INTERRUPT

>80°C

C1 =

1

4

CMP402

Figure 30. Microprocessor Overtemperature Interrupt Generator

Rev. F | Page 13 of 20

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