Temperature Sensor ICs Simplif

文章摘要：Abstract: When you set out to select a temperature sensor, you are no longer limited to either an analog output or a digital output device. There is now a broad selection of sensor types, one of which should match your system's needs. This application note surveys the wide variety of temperature

Temperature Sensor ICs Simplif,标签：计算机控制技术,工厂电气控制技术,http://www.88dzw.com
Abstract: When you set out to select a temperature sensor, you are no longer limited to either an analog output or a digital output device. There is now a broad selection of sensor types, one of which should match your system's needs. This application note surveys the wide variety of temperature sensor ICs available to help the designer make the best choice for a particular design.

When you set out to select a temperature sensor, you are no longer limited to either an analog-output or a digital-output device. There is now a broad selection of sensor types, one of which should match your system's needs.

When asked what I do for a living, I tell people I'm an analog electronics engineer. When next asked, "What does 'analog' mean?" I often use temperature sensors to explain the concept. I tell them that we engineers sometimes use sensors that give an analog of temperature in the form of voltage or current. To further define the analog world, I contrast it with the digital realm by saying that the voltage or current signals are usually converted to 1s and 0s so that computers can use the information. Sometimes this explanation suffices; sometimes it doesn't.

What this explanation does do is suggest the basic migration of temperature sensors. Until recently, all the temperature sensors on the market provided analog outputs. Thermistors, RTDs, and thermocouples were followed by another analog-output device, the silicon temperature sensor. In most applications, unfortunately, these analog-output devices require a comparator, an ADC, or an amplifier at their output to make them useful.

Thus, when higher levels of integration became feasible, temperature sensors with digital interfaces became available. These ICs are sold in a variety of forms, from simple devices that signal when a specific temperature has been exceeded to those that report both remote and local temperatures while providing warnings at programmed temperature settings. The choice now isn't simply between analog-output and digital-output sensors; there is a broad range of sensor types from which to choose.

Classes of Temperature Sensors

Four temperature-sensor types are illustrated in Figure 1. An ideal analog sensor provides an output voltage that is a perfectly linear function of temperature (A). In the digital I/O class of sensor (B), temperature data in the form of multiple 1s and 0s are passed to the microcontroller, often via a serial bus. Along the same bus, data are sent to the temperature sensor from the microcontroller, usually to set the temperature limit at which the alert pin's digital output will trip. Alert interrupts the microcontroller when the temperature limit has been exceeded. This type of device can also provide fan control.


Figure 1. Sensor and IC manufacturers currently offer four classes of temperature sensors.

"Analog-plus" sensors (C) are available with various types of digital outputs. The VOUT versus temperature curve is for an IC whose digital output switches when a specific temperature has been exceeded. In this case, the "plus" added to the analog temperature sensor is nothing more than a comparator and a voltage reference. Other types of "plus" parts ship temperature data in the form of the delay time after the part has been strobed, or in the form of the frequency or the period of a square wave, which will be discussed later.

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