51.6.2.5 Reference Configuration
The ADC has various sources for its reference voltage VREF. The Reference Voltage Selection bit field in the Reference Control register (REFCTRL.REFSEL) determines which reference is selected. By default, the internal voltage reference (VREF) is selected. Based on customer application requirements, the external or internal reference can be selected. Refer to REFCTRL.REFSEL for further details on available selections.
Note: If the internal bandgap voltage reference
is selected (REFCTRL.REFSEL = 0x0), the On Demand operation mode (CTRLA.ONDEMAND= 0) is not
supported and a delay of minimum 40µs must be respected between the enable of the ADC
(CTRLA.ENABLE) and the start of the first conversion. In case an ADC conversion is
triggered by an input event, the delay must be introduced between the enable of the ADC and
the enable of the ADC EVSYS channel.