The devices have two separate power supplies: RVDD and DVDD. The internal reference buffer and the internal LDO operate on RVDD. The ADC core operates on the LDO output (available on the DECAP pins). DVDD is used for the interface circuits. RVDD and DVDD can be independently set to any value within their permissible ranges.
The RVDD supply voltage value defines the permissible range for the external reference voltage VREF on REFIN pin as:
In other words, to use the external reference voltage of VREF, set RVDD so that:
Place a 10-µF decoupling capacitor between the RVDD and GND pins, and between the DVDD and GND pins, as shown in Figure 120. Use a minimum 1-µF decoupling capacitor between the DECAP pins and the GND pin.