The Analog-to-Digital Converter (ADC) on the ispPAC-POWR devices has no internal averaging circuit or filtering circuitry. When used in an electrically quiet system, the ADC will typically have less than one LSB of uncertainty, which corresponds to either 2mV or 6mV depending on the attenuation range. The converter has an acquisition time of approximately 16us, so it will be sensitive to any noise or fluctuations in the VMON voltage up to at least several hundred kHz. If there are fixed-frequency ripple or noise components present on the VMON input, and the ADC is operated at a constant sampling rate, Nyquist sampling effects could alias the high-frequency noise and make it appear as a lower-frequency ripple in the digitized sample stream.
While many ispPAC-POWR applications using the ADC will operate adequately with no input filtering hardware, those in which significant noise is expected can often benefit from the addition of an external filter added to the ADC inputs. In many cases a simple single-pole RC lowpass filter may be sufficient.