The target of this circuit is to measure a local temperature range of –55 to 105°C at an accuracy of 0.25%. There is a default NTC thermistor, but there is an option to externally connect a different thermistor. The thermistor network is powered by the voltage reference utilized by the corresponding ADC (5 V for external ADC, 2.5 V for internal ADC). This results in the design being ratiometric and thus the measurement accuracy does not depend on the accuracy of the reference voltage. A buffer op amp is utilized to provide high input impedance on the sensor size and a low-impedance to the ADC to ensure a fast settling time.

Figure 2-7 Thermistor Temperature Sensing