It is recommended to keep the connections for the analog power pins, even if the ADC is not used. Following is a summary of how the ADC pins should be connected, if the ADC is not used in an application:
When the ADC is not used, be sure that the clock to the ADC module is not turned on to realize power savings.
When the ADC module is used in an application, unused ADC input pins should be connected to analog ground (VSS1AGND/VSS2AGND)
ADC parameters for gain error and offset error are specified only if the ADC calibration routine is executed from the Boot ROM. See Section 220.127.116.11 for more information.