The ADC incorporates an integrated temperature sensor. The temperature sensor is comprised of two internal diodes with one diode having 16 times the current density of the other, as shown in Figure 9-4. The difference in current density of the diodes yields a differential output voltage that is proportional to absolute temperature. Measure the temperature sensor voltage with either ADC1 or ADC2. For ADC1 measurement, set the INPMUX register (address 06h) to BBh. For ADC2 measurement, set the ADC2MUX register (address 16h) to BBh. Equation 9 shows how to convert the temperature sensor reading to degrees Celcius (°C):
Before temperature sensor measurement, enable the PGA, set gain = 1, disable chop mode, and make sure the internal voltage reference is powered on. As a result of the low package-to-PCB thermal resistance, the internal device temperature closely tracks the PCB temperature. Note that ADC self-heating results in an increase of 0.7°C relative to the temperature of the surrounding PCB.