July 2007
LM27A
±3°C Accurate, 120°C-150°C Factory Preset Thermostat
(LM27 in Die Form)
Standard parts are available, see ordering information for de-
tails. For other part options, contact a National Semiconductor
General Description
This datasheet applies to the LM27A, which is the die form of
the LM27. The LM27 is available in the SOT23-5 package.
Please refer to the LM27 datasheet for detailed specifications
pertaining to the packaged part.
Distributor or Sales Representative for information on mini-
mum-order qualification.
Applications
The LM27A is a precision, single digital-output, low-power
thermostat comprised of an internal reference, DAC, temper-
ature sensor and comparator. Utilizing factory programming,
it can be manufactured with different trip points as well as
different digital output functionality. The trip point (TOS) can
be preset at the factory to any temperature in the range of
+120°C to +150°C in 1°C increments. The LM27A has two
digital output pads, one digital input (HYST) and one analog
output (VTEMP). One digitial output is an active-high, push-pull
output and the other is an active-low, open-drain output. Ei-
ther of the outputs (but not both) are available.
Microprocessor Thermal Management
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Appliances
Portable Battery Powered Systems
Fan Control
Industrial Process Control
HVAC Systems
Electronic System Protection
Features
The LM27A is available in either an overtemperature shut-
down or an undertemperature shutdown option. An LM27A
with overtemperature shutdown is configured so that its ther-
mostat outputs (OS and OS) will go active when a rising
temperature crosses the trip point and the hysteresis will ap-
ply to a falling temperature. The thermostat outputs of an
LM27A with an undertemperature shutdown (US and US) will
trip on a falling temperature and hysteresis will apply on a
rising temperature. For example, when the LM27A is preset
as an overtemperature shutdown, the active-high output (OS)
will go HIGH and the active-low output (OS) will go LOW to
indicate that the die temperature is over the internally preset
TOS . The outputs will reset to their normal states when the
temperature goes below (TOS–THYST). Similarly, when pre-
programmed as an undertemperature shutdown the active-
high output (US) will go HIGH and the active-low output
(US) will go LOW to indicate that the temperature is below
TUS . The outputs will reset when the temperature is above
(TUS+THYST). The typical hysteresis, THYST, can be set to 2°C
or 10°C and is controlled by the state of the HYST pin. The
VTEMP analog output provides a voltage that is proportional to
temperature and has a −10.7mV/°C output slope.
Internal comparator with pin selectable 2°C or 10°C
hysteresis
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No external components required
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Open-drain or push-pull digital output; supports CMOS
logic levels
Internal temperature sensor with VTEMP output pin
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VTEMP output allows after-assembly system testing
Internal voltage reference and DAC for trip-point setting
Excellent power supply noise rejection
AEC-Q100 Qualified
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Key Specifications
■ꢀPower Supply Voltage
■ꢀPower Supply Current
2.7V to 5.5V
40µA(max)
15µA(typ)
■ꢀHysteresis Temperature
■ꢀTemperature Trip Point Accuracy
2°C or 10°C(typ)
±3°C (max)
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