32.3.3.8 Temperature Measurement

An on-chip temperature sensor is available. To do a temperature measurement, follow these steps:

1. Configure the voltage reference to internal 2.048V by writing to the Reference Selection (REFSEL) bit field the ADCn.CTRLC register.
2. Select the temperature sensor as input in the Positive Input Multiplexer (ADCn.MUXPOS) register.
3. Configure the ADC Sample Duration by writing a value ≥ $35\mathrm{\mu s}\times f_{\text{CLK\_ADC}}$ to the Sample Duration (SAMPDUR) bit field in the Control E (ADCn.CTRLE) register.
4. Acquire the temperature sensor output voltage by running a 10-bit Single-Ended conversion.
5. Process the measurement result, as described below.

The measured voltage has an almost linear relationship with the temperature. Due to process variations, the temperature sensor output voltage varies between individual devices at the same temperature. The individual compensation factors determined during production test are stored in the Signature Row. These compensations factors are generated for the internal 2.048V reference.

• SIGROW.TEMPSENSE0 contains the slope of the temperature sensor characteristics
• SIGROW.TEMPSENSE1 contains the offset of the temperature sensor characteristics

In order to achieve more accurate results, the result of the temperature sensor measurement must be processed in the application software using compensation values from device production or user calibration.

The temperature (in kelvin) is calculated by the following equation:

$T=\frac{(\text{Offset}-\text{ADC Result})\times \text{Slope}}{1024}$

It is recommended to follow these steps in the application code when using the compensation values from the Signature Row:

#define SCALING_FACTOR 1024 // Used to get a whole number in the signature row

uint16_t sigrow_offset = SIGROW.TEMPSENSE1; // Read unsigned offset from signature row
uint16_t sigrow_slope = SIGROW.TEMPSENSE0;  // Read unsigned gain/slope from signature row
uint16_t adc_reading = ADC0.RESULT;         // ADC0 conversion result

uint32_t temp = sigrow_offset - adc_reading;
temp *= sigrow_slope;   // Result will overflow 16-bit variable
temp += SCALING_FACTOR / 2;         // Ensure correct rounding on division below
temp /= SCALING_FACTOR;            // Round off to nearest degree in kelvin
uint16_t temperature_in_K = temp;
int16_t temperature_in_C = temp - 273;

If another reference (V_ADCREF) than 2.048V is required, the offset and slope values need to be adjusted according to the following equations:

$\text{Slope}=\text{TEMPSENSE0}\times \frac{{\text{V}}_{\text{ADCREF}}}{2.048\text{V}}$

$\text{Offset}=\text{TEMPSENSE1}\times \frac{2.048\text{V}}{{\text{V}}_{\text{ADCREF}}}$