TMP12FP View Datasheet(PDF) - Analog Devices

Part Name

Description

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TMP12FP

Airflow and Temperature Sensor

Analog Devices 

TMP12

40

38

36

34

32

30

28

26

24

22

20

-75

VOL = 1V, V = 5V

-25

25

75

125

175

TEMPERATURE – °C

Figure 13. Open-Collector Output Sink Current vs.

Temperature

700

600

a. LOAD = 10mA

a

b. LOAD = 5mA

500 c. LOAD = 1mA

400

b

300

200

V = 5V

c

100

0

-75

-25

25

75

125

175

TEMPERATURE – °C

Figure 14. Open-Collector Voltage vs. Temperature

APPLICATIONS INFORMATION

A typical application for the TMP12 is shown in Figure 15. The

TMP12 package is placed in the same cooling airflow as a

high-power dissipation IC. The TMP12’s internal resistor pro-

duces a temperature rise which is proportional to air flow, as

shown in Figure 16. Any interruption in the airflow will produce

an additional temperature rise. When the TMP12 chip tempera-

ture exceeds a user-defined setpoint limit, the system controller

can take corrective action, such as: reducing clock frequency,

shutting down unneeded peripherals, turning on additional fan

cooling, or shutting down the system.

PGA

PACKAGE

PGA

SOCKET

POWER I.C.

AIR FLOW

PC BOARD

TMP12

Figure 15. Typical Application

65

a

60

b

55

c

50

d

45

40

35

0

a. TMP12 DIE TEMP NO AIR FLOW

b. HIGH SET POINT

e

c. LOW SET POINT

d. TMP12 DIE TEMP MAX AIR FLOW

e. SYSTEM AMBIENT TEMPERATURE

50

100

150

200

250

TMP12 PD (mW)

Figure 16. Choosing Temperature Setpoints

Temperature Hysteresis

The temperature hysteresis at each setpoint is the number

of degrees beyond the original setpoint temperature that

must be sensed by the TMP12 before the setpoint compar-

ator will be reset and the output disabled. Hysteresis

prevents “chatter” and “motorboating” in feedback control

systems. For monitoring temperature in computer systems,

hysteresis prevents multiple interrupts to the CPU which

can reduce system performance.

Figure 17 shows the TMP12’s hysteresis profile. The hyster-

esis is programmed, by the user, by setting a specific load

current on the reference voltage output VREF. This output

current, IREF, is also called the hysteresis current. IREF is mir-

rored internally by the TMP12, as shown in the functional

block diagram, and fed to a buffer with an analog switch.

HYSTERESIS

LOW

HI

HYSTERESIS

HIGH

OUTPUT

VOLTAGE

OVER, UNDER

HYSTERESIS HIGH =

HYSTERESIS LOW

LO

TSETLOW

TEMPERATURE

TSETHIGH

Figure 17. TMP12 Hysteresis Profile

After a temperature setpoint has been exceeded and a com-

parator tripped, the hysteresis buffer output is enabled. The

result is a current of the appropriate polarity which gener-

ates a hysteresis offset voltage across an internal 1 kΩ

resistor at the comparator input. The comparator output

remains “on” until the voltage at the comparator input,

now equal to the temperature sensor voltage VPTAT

summed with the hysteresis effect, has returned to the pro-

grammed setpoint voltage. The comparator then returns

REV. 0

–7–

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