Reference

SAADC can use different reference voltages (VREF), controlled in the REFSEL field of the register CH[n].CONFIG.

The accepted VREF voltages are the following:

Internal reference, VREF=0.9 V
External reference, VREF provided by the EXTREF pin

Note: The external reference voltage should be close (±5%) to the internal reference voltage VREF. Using a lower reference voltage will lead to increased leakage and can lead to undefined behavior.

ADC is preceded by a gain stage which has a programmable gain. The voltage range seen at the input of the gain stage is the following:

VRangeDifferential=±VREF/GAIN

VRangeSingleEnded=±0.5*VREF/GAIN

The AIN[0..7] inputs cannot exceed VDD, or be lower than VSS. The input ranges are also limited by the REFERENCE and GAIN used.

The following condition must always hold true for valid measurements, otherwise the ADC will saturate and report the max value determined by the RESOLUTION.

 [V(P) - V(N) ] * GAIN/REFERENCE ≤ 1