This temperature-sensing circuit uses minimal passive components and a single voltage source resulting in an ultra-small form factor. The circuit design allows for easy customization to accommodate various configurations and output voltage ranges. An operational amplifier (op amp) is used to offset and amplify the input signal as needed to utilize the full ADC range and improve measurement accuracy. The output of the PTC temperature sensor is fed to the non-inverting input of the amplifier, while a resistor network connected to high- and low-voltage sources offset the output as required.

The following figure shows the circuit schematic for the wide temperature PTC sensor.

1. Use the op amp in a linear operating region. Linear output swing is usually specified under the AOL test conditions.

2. Choose R1 based on the temperature range and the value of the PTC.

3. Using high-value resistors can degrade the phase margin of the amplifier and introduce additional noise in the circuit. It is recommended to use resistor values around 10kΩ or less.

4. A capacitor placed in parallel with the feedback resistor will limit bandwidth, improve stability and help reduce noise.

5. Typical resistance values are selected from the PTC resistor resistance characteristics across temperature. Take consideration for the minimum and maximum resistance limits of the PTC resistor, per temperature.

6. For single op-amp supply conditions, the output cannot swing exactly to 0V but can swing to 5V utilizing the 12-V supply. Increase V_outMin to the linear output swing usually specified under the AOL test conditions to improve accuracy.