For measuring temperature, the current source and the ADC12 module in CC1312R are used. The CC1312's 12-bit ADC has two references: a scaled input for a scaled reference of 4.3V or relative reference, which is nominally the VDDS supply voltage of CC1312R. Note that with LiMnO2 batteries this voltage drops over time and often the battery end-of-life voltage is set at around 2 or 2.1V.

In this TI Design, the sensor controller periodically enables the integrated programmable current source with maximum current of 20uA, implementing a current biasing scheme for both TMP63 devices. The current, driving the room and the radiator sensors must be the same value, routed to a different analog pin, to maintain a ratio-metric measurement.

The voltage drop generated by each TMP63 device with using exactly the same excitation current from the SCE module is amplified in a single-stage amplifier circuit to increase dynamic range, which is necessary at higher temperatures, as seen by the Radiator sensor. The implemented design achieves close to 4× higher resolution for the range of 20° to 90°C (including additional 1.5ºC are added margin on both upper and lower end of this range).

The amplified signal for each TMP63 sensor is fed into the ADC12 on-chip module and converted by firmware into temperature values.

The main application runs under TI RTOS on CC1312R, as TI RTOS enables exact scheduling of the temperature measurements, the PCB touch detection and all other application code.