The chip has an 8-bit ADC with offset calibration that is used for measuring internal parameters. It can be used in the following measurement modes:

  • Single-shot
  • Timed
  • Averaged

Measurements

  • VBAT voltage measurement
  • VOUT voltage measurement
  • Die temperature measurement (can be used to estimate battery temperature)
  • Offset measurement

An interrupt can be configured to trigger once a measurement is complete. ADC status is available in a register ADC.STATUS. One measurement at a time can be done. New conversion can only be started once status indicates that ADC is ready. Separate result registers are available for each mode and for the averaged result.

By default, ADC uses factory offset calibration stored in register ADC.OFFSETFACTORY. ADC offset can be re-calibrated on demand by selecting mode Offset in register ADC.CONFIG followed by a common conversion task in ADC.TASKS_ADC. The new offset value is stored in ADC.OFFSETMEASURED and can be taken into use instead of the factory calibration using register ADC.OFFSETCFG.

Single-shot measurements

Single-shot measurements are triggered by selecting the mode in register ADC.CONFIG followed by a common conversion task in ADC.TASKS_ADC.

Timed measurements

Timed measurements for battery voltage (VBAT) are enabled in registers ADC.CONFIG and ADC.DELAY, and triggered by ADC.TASKS_ADC.

Software can abort a timed VBAT measurement in register ADC.TASKS_ADC to free up ADC for another measurement. Interrupt and conversion results are available for the aborted measurement.

Averaged measurements

Averaged measurements are enabled in registers ADC.CONFIG and triggered by ADC.TASKS_ADC and the results are available in ADC.AVERAGE. Averaging is available for all modes except offset measurement.

Events and interrupts

An event register and interrupt are available for each measurement and are issued once the measurement has been completed. See registers MAIN.EVENTS_ADC_SET, MAIN.EVENTS_ADC_CLR, MAIN.INTEN_ADC_SET and MAIN.INTEN_ADC_CLR.

Measurement results

Results from the ADC are stored in registers according to the following table.
Table 1. ADC measurements
Value Register
Battery voltage ADC.READVBAT
VOUT voltage ADC.READVOUT
Die temperature ADC.READTEMP
Averaged battery voltage, VOUT, or die temperature ADC.AVERAGE

VBAT

The equation for (instant and delayed) VBAT is given by the following:

In case averaged measurement mode has been used, ADC.READVBAT needs to be replaced with ADC.AVERAGE in the above equation.

VOUT

The equation for VOUT is given by the following:

In case averaged measurement mode has been used, ADC.READVOUT needs to be replaced with ADC.AVERAGE in the above equation.

Die temperature

The die temperature, T (in °C), is given by the following equation:

In case averaged measurement mode has been used, ADC.READTEMP needs to be replaced with ADC.AVERAGE in the above equation.

Die temperature can be used to estimate battery temperature. The self-heating of nPM2100 is negligible in typical Bluetooth® Low Energy applications, making die temperature a good approximation of battery temperature.