The output result of the ADC depends on the settings in the CH[n].CONFIG and RESOLUTION registers as follows:
RESULT = [V(P) – V(N) ] * GAIN/REFERENCE * 2(RESOLUTION - m)where
- V(P)
- is the voltage at input P
- V(N)
- is the voltage at input N
- GAIN
- is the selected gain setting
- m
- is the mode setting. Use m=0 if CONFIG.MODE=SE, or m=1 if CONFIG.MODE=Diff
- REFERENCE
- is the selected reference voltage
The result generated by the ADC will deviate from the expected due to DC errors like offset, gain, differential non-linearity (DNL), and integral non-linearity (INL). See Electrical specification for details on these parameters. The result can also vary due to AC errors like non-linearities in the GAIN block, settling errors due to high source impedance and sampling jitter. For battery measurement, the DC errors are most noticeable.
The ADC has a wide selection of gains controlled in the GAIN field of the CH[n].CONFIG register. If CH[n].CONFIG.REFSEL=0, the input range of the ADC core is nominally ±0.9 V differentially, and the input must be scaled accordingly with proper gain setting.
The ADC has a temperature dependent offset. If the ADC is to operate over a large temperature range, we recommend running CALIBRATEOFFSET at regular intervals. The CALIBRATEDONE event will be generated when the calibration has been completed. Note that the DONE and RESULTDONE events will also be generated.