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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.
a
Low Voltage, Resistor Programmable
Thermostatic Switch
AD22105
© Analog Devices, Inc., 1996
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 617/329-4700 Fax: 617/326-8703
FEATURES
User-Programmable Temperature Setpoint
2.08C Setpoint Accuracy
4.08C Preset Hysteresis
Wide Supply Range (+2.7 V dc to +7.0 V dc)
Wide Temperature Range (–408C to +1508C)
Low Power Dissipation (230 mW @ 3.3 V)
APPLICATIONS
Industrial Process Control
Thermal Control Systems
CPU Monitoring (i.e., Pentium)
Computer Thermal Management Circuits
Fan Control
Handheld/Portable Electronic Equipment
The AD22105 is designed to operate on a single power supply
voltage from +2.7 V to +7.0 V facilitating operation in battery
powered applications as well as in industrial control systems.
Because of low power dissipation (230 µW @ 3.3 V), self-
heating errors are minimized and battery life is maximized.
An optional internal 200 kΩ pull-up resistor is included to
facilitate driving light loads such as CMOS inputs.
Alternatively, a low power LED indicator may be driven directly.
GENERAL DESCRIPTION
The AD22105 is a solid state thermostatic switch. Requiring
only one external programming resistor, the AD22105 can be set
to switch accurately at any temperature in the wide operating
range of –40°C to +150°C. Using a novel circuit architecture,
the AD22105 asserts an open collector output when the ambient
temperature exceeds the user-programmed setpoint temperature.
The AD22105 has approximately 4°C of hysteresis which prevents
rapid thermal on/off cycling.
FUNCTIONAL BLOCK DIAGRAM
1
2
3
4
8
7
6
5
NC
V
S
R
SET
NC
R
PULL–UP
OUT
GND
NC
TEMPERATURE
SENSOR
200kΩ
SET–
POINT
AD22105
12
3
4
8
7
65
OUT
+2.7V TO +7.0V
R
SET
AD22105
TOP VIEW
Figure 1. Typical Application Circuit
