原标题：TI LM57 电阻可编程温度开关型模拟温度传感器参考设计方案

　　TI公司的LM57是一款集成模拟传感器的精确双路输出温度开关器件，温度阀值可通过两个外部1%精度电阻进行设置。LM57通过外部电阻设置可以实现256种不同温度阀值设置，同时内嵌等比例负温度系数传感器通过VTEMP引脚输出模拟量。本文首先介绍芯片的简介、特性、内部框图及应用领域，并给出相应设计方案的设计原理图、元器件列表及PCB元件布局图。

　　The LM57 is a precision, dual-output, temperature switch with integrated analog temperature sensor. The trip temperature (TTRIP) 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 VTEMP output delivers an analog output voltage which is proportional with a negative temperature coefficient (NTC) to the measured temperature.

　　Built-in temperature hysteresis (THYST) keeps the output stable in an environment of thermal oscillation. The digital temperature switch outputs will go active when the die temperature exceeds TTRIP and will release when the temperature falls below a temperature equal to TTRIP minus THYST. One of the digital outputs, TOVER, 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 TOVER 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.

　　LM57主要特性：

　　Trip Temperature Set by External Resistors

　　External Resistor Tolerance Contributes Zero Error

　　Push-Pull and Open-Drain Temperature Switch Outputs

　　Wide Operating Temperature and Trip-Temperature Range of −50℃ to 150℃

　　Very Linear Analog VTEMP Temperature Sensor Output

　　Analog and Digital Outputs are Short-Circuit Protected

　　TRIP-TEST Pin Allows In-System Testing

　　Latching Function for the Digital Outputs

　　Very Small 2.5 mm by 2.5 mm 8-Pin WSON Package

　　LM57应用：

　　Cell Phones

　　Wireless Transceivers

　　Digital Cameras

　　Personal Digital Assistants (PDAs)

　　Battery Management

　　Automotive

　　Disk Drives

　　Games

　　Appliances

　　图1. LM57内部方框图

　　LM57方案介绍：

　　The Texas Instruments LM57EVM evaluation module (EVM) helps designers evaluate the operation and

　　performance of the LM57. The LM57 is a precision, dual-output, temperature switch with an integrated

　　analog temperature sensor. The programmable resistors allow user to set the Trip Temperature (TTRIP).

　　The LM57 can be programmed to any of 256 trip temperatures.

　　The EVM contains one LM57 Resistor-Programmable Temperature Switch and Analog Temperature

　　Sensor. It comes pre-assembled with the LLP-8 LM57BISD-10, and has a 10°C hysteresis of LM57. The

　　header connector allows user to bring all package pins out for ease of characterization and testing.

　　LM57方案材料清单：