19.9 ADC Voltage Reference

The reference voltage for the ADC (V_REF) indicates the conversion range, which in this case is limited to 0V (V_GND) and V_REF = V_cc. Single ended channels that exceed V_REF will result in codes close to 0x3FF.

V_REF can be selected from V_CC or internal reference. The internal voltage reference can be set to 1.1, 2.2, or 4.3V and is generated from the internal bandgap reference (V_BG) through an internal amplifier. The first ADC conversion result after switching reference voltage source may be inaccurate, and the user is advised to discard this result.