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Airflow and Temperature Sensor

FUNCTIONAL BLOCK DIAGRAM

HYSTERESIS

CURRENT

CURRENT

MIRROR

TMP12

WINDOW

COMPARATOR

HYSTERESIS

VOLTAGE

1k

100

VOLTAGE

REFERENCE

AND

SENSOR

SET

HIGH

SET

LOW

GND

V+

OVER

UNDER

HEATER

PIN CONNECTION

8-Lead SOIC

TOP VIEW

(Not to Scale)

8

7

6

5

1

2

3

4

V+

TMP12

SET HIGH

OVER

SET LOW

UNDER

GND

HEATER

FEATURES

Temperature Sensor Includes 100

Heater

Heater Provides Power IC Emulation

Accuracy

3 Typ from –40 C to +100 C

Operation to 150 C

5 mV/ C Internal Scale Factor

Resistor Programmable Temperature Setpoints

20 mA Open-Collector Setpoint Outputs

Programmable Thermal Hysteresis

Internal 2.5 V Reference

Single 5 V Operation

400

A Quiescent Current (Heater Off)

Minimal External Components

APPLICATIONS

System Airflow Sensor

Equipment Overtemperature Sensor

Overtemperature Protection

Power Supply Thermal Sensor

Low Cost Fan Controller

TMP12

GENERAL DESCRIPTION

The TMP12 is a silicon-based airflow and temperature sensor

designed to be placed in the same airstream as heat generating

components that require cooling. Fan cooling may be required

continuously or during peak power demands. For example, if

the cooling systems of a power supply fails, system reliability

and/or safety may be impaired. By monitoring temperature

while emulating a power IC, the TMP12 can provide a warning

of cooling system failure.

The TMP12 generates an internal voltage that is linearly propor-

tional to Celsius (Centigrade) temperature, nominally 5 mV/

°C.

The linearized output is compared with voltages from an exter-

nal resistive divider connected to the TMP12’s 2.5 V precision

reference. The divider sets up one or two reference voltages, as

required by the user, providing one or two temperature setpoints.

Comparator outputs are open-collector transistors able to sink

over 20 mA. There is an on-board hysteresis generator provided

to speed up the temperature-setpoint output transitions; this

also reduces erratic output transitions in noisy environments.

Hysteresis is programmed by the external resistor chain and

is determined by the total current drawn from the 2.5 V reference.

The TMP12 airflow sensor also incorporates a precision, low

temperature coefficient 100

Ω heater resistor that may be con-

nected directly to an external 5 V supply. When the heater is

activated, it raises the die temperature approximately 20

°C

above ambient (in still air). The purpose of the heater in the

CPU, which has a high internal dissipation.

When subjected to a fast airflow, the package and die tempera-

tures of the power device and the TMP12 (if located in the

same airstream) will be reduced by an amount proportional to

the rate of airflow. The internal temperature rise of the TMP12

may be reduced by placing a resistor in series with the heater, or

by reducing the heater voltage.

The TMP12 is intended for single 5 V supply operation, but will

operate on a 12 V supply. The heater is designed to operate from

5 V only. Specified temperature range is from –40

°C to +125°C,

and operation extends to 150

°C at 5 V with reduced accuracy.

The TMP12 is available in 8-lead SOIC packages.