Programmable temperature switch type analog temperature sensor based on LM57

The LM57 is a high precision, dual output, integrated, analog temperature sensor temperature switch. By using two external 1% resistors, the trip temperature (TTRIP) is programmable and can be any 256 trip temperature and takes up very little board space.

TI's LM57 is a high precision, dual output, integrated, analog temperature sensor temperature switch. The trip temperature (TTRIP) is programmable by using two external 1% resistors. The LM57 uses a very small package of resistors (0.5mm & TImes; 1mm) that can be programmed to any 256 trip temperature and takes up very little board space. The VTEMP output can provide an analog output voltage with a negative temperature coefficient (NTC) that is proportional to the measured temperature.

The built-in temperature hysteresis (THYST) of the LM57 device keeps the output stable (in a thermally oscillating environment). When the die temperature exceeds TTRIP, the digital temperature switch output will be activated and when the temperature is below TTRIP minus THYST, the digital temperature switch output will be released. One of the digital outputs, TOVER, is a highly active push-pull structure. For other digital outputs, TOVER is a low active open-drain configuration.

Figure 1 LM57 internal block diagram

If the TRIP-TEST input is high, the digital output will be active. A processor can read the logic levels of the temperature switch outputs to confirm that they are active. This allows for on-site verification, and the comparator and output circuits function properly after system assembly. When the TRIP-TEST pin is high, the trip level reference voltage appears on the VTEMP pin. The system can then use this voltage to more closely calibrate the accuracy of the sensor. Connecting TOVER to TRIP-TEST latches the output after the output is disconnected. It can be removed by forcibly depressing TRIP-TEST or by setting the LM57 to power down.

Table 1 List of LM57 program materials

Since the maximum current consumes only 28μA, the device has very low self-heating, about 0.02 ° C in still air.

Main features of LM57

●The breaking temperature is set by an external resistor

●External resistance contributes to zero error

●Push-pull and open-drain temperature switch output

● Wide operating temperature, trip temperature range -50 ° C ~ 150 ° C

● Fully linear analog VTEMP temperature sensor output

● Short circuit protection analog and digital output

●TRIP-TEST pin allows testing in the system

● Digital output blocking function

● Ultra-small 2.5mm & TImes; 2.5mm 8-pin WSON package

Figure 2 Schematic diagram of the LM57 scheme

Figure 3 PCB component layout

LM57 application

●Mobile phone

●Wireless transceiver

●Digital camera

●Personal Digital Assistant (PDA)

●Battery management

●Car

●Disk drive

●game

●Electric

Conclusion

The LM57EVM Evaluation Module (EVM) helps designers evaluate the operation and performance of the LM57. The LM57 is a high precision, dual output analog temperature sensor with integrated temperature switch. The user can set the open circuit temperature (TTRIP) through a programmable resistor. The LM57 can be programmed to any 256 trip temperature. In addition, the EVM includes an LM57 resistor programmable temperature switch and an analog temperature sensor. It is pre-assembled with the LLP-8-10 LM57BISD and has a 10°C hysteresis with the LM57. Its head connector allows the user to expose all package leads for viewing and testing.

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