What needs to be considered in the VREF pin when using an ADC?

[a_ziliu]

For all NuMicro? series, the VREF pin must be connected with an external capacitor, and its capacitance value needs to limit power supply ripple to be less than one LSB of ADC to avoid power noise to interfere with ADC accuracy. For example, if the 12-bit ADC and VREF voltage is 3.3V, the size of the ripple should be less than 3.3/(2^12) = 0.8mV.