App note: Temperature measurement using thermistors

in app notes by DP | 2 comments


Another temperature sensitive device, introducing the thermistor. From its name you could guess that its a temperature dependent resistor which varies its resistance as the temperature changes. See Cypress’ application note on using these devices.

A thermistor is a temperature-sensitive resistor in which resistance varies with temperature. There are two types of thermistors: positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors. This application note describes the more commonly used NTC thermistors, in which resistance decreases with increase in temperature. Based on this principle, temperature is calculated by measuring the resistance.

see also: watchdog timer and a diode as an alternative temperature sensors.

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  1. Thomas says:

    I’m confused. Analog multiplexers and programmable gain amplifiers are really nice to have, but they seem superfluous here. Any old microcontroller with an ADC should be able to carry out the same measurement with the positive refernce tied to VDD and the negative reference tied to ground. You can supply the voltage divider current from an IO pin if you care about power consumption and you could even measure the voltage drop across the high side output fet if you need the extra accuracy (although I would probably just use the typical value from the data sheet). What am I missing here?

  2. ee says:

    I think they’re suggesting you’ll get a more granular result over a wider range if you use their method versus a voltage divider and ADC. However they don’t specify how accurate it would be, nor is there any table of measured values versus actual values to see the error across the range.
    I think any scenario that used their method would probably be a scenario where a voltage divider and ADC would possibly be just as acceptable too. Any more critical scenario would use dedicated parts for the temperature measurement. So kind-of a contrived app note.

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