a
FEATURES
Temperature Sensor Includes 100
Ω
Heater
Heater Provides Power IC Emulation
Accuracy 3°C 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
µA
Quiescent Current (Heater OFF)
Minimal External Components
APPLICATIONS
System Airflow Sensor
Equipment Over-Temperature Sensor
Over-Temperature Protection
Power Supply Thermal Sensor
Low-Cost Fan Controller
Airflow and Temperature Sensor
TMP12*
FUNCTIONAL BLOCK DIAGRAM
HYSTERESIS
CURRENT
CURRENT
MIRROR
IHYS
VREF
V+
SET
HIGH
WINDOW
COMPARATOR
-
+
+
-
OVER
SET
LOW
VOLTAGE
REFERENCE
AND
SENSOR
1kΩ
UNDER
HYSTERESIS
VOLTAGE
GND
PINOUTS
DIP And SO
VREF
1
2
3
4
TOP VIEW
(Not to Scale)
GENERAL DESCRIPTION
SET HIGH
SET LOW
GND
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, e.g. for a power
supply, and if the cooling systems fails, system reliability and/or
safety may be impaired. By monitoring temperature while emu-
lating a power IC, the TMP12 can provide a warning of cooling
system failure.
The TMP12 generates an internal voltage that is linearly pro-
portional to Celsius (Centigrade) temperature, nominally
5 mV/°C. The linearized output is compared with voltages
from an external resistive divider connected to the TMP12’s
2.5 V precision reference. The divider sets up one or two refer-
ence 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 hys-
teresis 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 incorpo-
rates a precision, low temperature coefficient 100
Ω
heater
resistor that may be connected directly to an external 5 V sup-
ply. When the heater is activated it raises the die temperature in
*Protected by U.S. Patent No. 5,195,827.
the DIP package approximately 20°C above ambient (in still
air). The purpose of the heater in the TMP12 is to emulate a
power IC, such as a regulator or Pentium 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
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,
operation extends to 150°C at 5 V with reduced accuracy.
The TMP12 is available in 8-pin plastic DIP and SO packages.
REV. 0
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
© Analog Devices, Inc., 1995
One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A.
Tel: 617/329-4700
Fax: 617/326-8703
+
-
HEATER
100Ω
8
7
6
5
V+
OVER
UNDER
HEATER
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