Matthias

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  • Temperature Sensor using MCP9700 Thermistor and a Standard NTC Thermistor

  • Created: Oct 12, 2017

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Summary

One of the most commonly measured parameters in electronic systems is the temperature. Temperature sensors are devices that measure the amount of energy generated by the system. It allows detecting any physical change to the temperature producing either an analog or digital output. On the other hand, thermistors are the most commonly used temperature sensor among others. This reference design contains analog circuitry to measure temperature. It uses both standard thermistor and MCP9700 linear active thermistor from Microchip. It also uses NTCLE203E3103FB0 NTC thermistor to convert temperature to resistance. In addition, this design includes the MCP9700 linear active thermistor that outputs voltage proportional to temperature. This sensor provides a 10mV per degree Celsius temperature coefficient and it measures temperature from -40°C to +125°C.


In this design, the thermistor is placed in a voltage divider network. It is biased using a resistive stack, which can be adjusted using the user settable DIP switches. The voltage across the thermistor is proportional to change in temperature. The output voltage from the voltage divider is filtered and is connected to the CH0 input of the MCP6S22 programmable gain amplifier CH0 input. The PIC18F2550 is used to measure the voltage output of the MCP9700 and the MCP6S22 using an integrated 10-bit Analog to Digital Converter (ADC). It communicates to a PC via mini-USB interface.


This design explores the capability of the MCP9700 linear active thermistor as compared to a standard NTC thermistor. Unlike resistive sensors, e.g., thermistors, the linear active thermistor IC does not require an additional signal-conditioning circuit. Therefore, the biasing circuit development overhead for thermistor solutions can be avoided by implementing a sensor from these low-cost devices. Typical applications of this sensor include general purpose temperature monitoring in entertainment systems, home appliances, battery packs, and portable equipment.