Temperature switch
National Semiconductor
thermostat comprised of an internal reference, DAC, temperature
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 LM27 has one
digital output (OS/OS/US/US), one digital input (HYST) and
one analog output (VTEMP). The digital output stage can be
preset as either open-drain or push-pull. In addition, it can be
factory programmed to be active HIGH or LOW. The digital
output can be factory programmed to indicate an over temperature
shutdown event (OS or OS) or an under temperature
shutdown event (US or US). When preset as an overtemperature
shutdown (OS) it will go LOW to indicate that
the die temperature is over the internally preset TOS and go
HIGH when the temperature goes below (TOS-THYST). Similarly,
when preprogrammed as an undertemperature shutdown
(US) it will go HIGH to indicate that the temperature is
below TUS and go LOW 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. A
VTEMP analog output provides a voltage that is proportional
to temperature and has a −10.7mV/°C output slope.
Currently, there are several standard parts available, see
ordering information for details. For other part options, contact
a National Semiconductor Distributor or Sales Representative
for information on minimum order qualification. The
LM27 is currently available in a 5-lead SOT-23 package.
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