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( File format: PDF, 586 Kbytes )
SOT-23, 3C Accurate, 120C-150C Factory Preset Thermostat from the PowerWise? Family
National Semiconductor

Description
The LM27 is a precision, single digital-output, low-power 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 +120C to +150C in 1C 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 2C or 10C 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.
Features

???Internal comparator with pin selectable 2C or 10C hysteresis
???No external components required
???Open-drain or push-pull digital output; supports CMOS logic levels
???Internal temperature sensor with VTEMP output pin
???VTEMP output allows after-assembly system testing
???Internal voltage reference and DAC for trip-point setting
???Currently available in 5-pin SOT-23 plastic package
???Excellent power supply noise rejection




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