2.5 Reference Selection

This ADC features multiple internal ADC reference voltage between 0.55V and V_DD and external reference input V_REFA. Different internal reference voltages are 0.55V, 1.1V, 1.5V, 2.5V, and 4.3V.

The reference voltage for the ADC controls the conversion range of the ADC. Input voltages that exceed the selected reference voltage will be converted to the maximum result value of the ADC. For an ideal 10-bit ADC, the maximum result value is 0x3FF. V_REF can be selected by writing the Reference Selection bits (REFSEL) in the Control C register (ADC.CTRLC) as either V_DD, external reference V_REFA, or an internal reference. V_DD is connected to the ADC through a passive switch. The internal reference is generated from an internal bandgap reference through an internal amplifier, controlled by the Voltage Reference (V_REF) peripheral.