LM57

The LM57 is a precision, dual-output, temperature switch with integrated analog temperature sensor. The trip temperature (T_TRIP) is programmable by using two external 1% resistors. Using extremely small packaged resistors (0.5 mm x 1 mm), the LM57 can be programmed to any of 256 trip temperatures while consuming very little board space. The V_TEMP output delivers an analog output voltage which is inversely proportional to the measured temperature.

Built-in temperature hysteresis (T_HYST) keeps the output stable in an environment of thermal oscillation. The digital temperature switch outputs will go active when the die temperature exceeds T_TRIP and will release when the temperature falls below a temperature equal to T_TRIP minus T_HYST. One of the digital outputs, T_OVER, is active-high with a push-pull structure. The other digital output, ^TOVER, is active-low with an open-drain structure.

Driving the TRIP-TEST input high will make the digital outputs active. A processor can read the logic level of the temperature switch outputs, confirming that they changed to their active state. This allows for in-situ verification that the comparator and output circuitry are functional after system assembly. When the TRIP-TEST pin is high, the trip-level reference voltage appears at the Vtemp pin. The system could then use this voltage to calibrate the sensor for even tighter accuracy. Tying T_OVER to TRIP-TEST will latch the output after it trips. It can be cleared by forcing TRIP-TEST low or powering off the LM57.

As it draws only 28µA max from its supply, it has very low self-heating, about 0.02°C in still air.