Do I need a reference buffer to drive an ADC?
Most references will need a reference buffer to drive an ADC. The reference buffer provides a low-impedance output that improves load regulation (the change in output voltage with load current). A reference buffer will also assist in medium-frequency transient load demands. High-frequency load transients can generally only be supplied with large external capacitors.
Some reference ICs include an integrated buffer. This buffer is a general-purpose buffer and may not be adequate to drive a specific ADC.
Some ADCs, have internal buffering or features that may allow them to be driven directly by a reference or a reference with an integrated buffer (e.g. AD4134). Usually the ADC datasheet will give recommended connections and suggested components for the reference inputs.
This webinar provides a more comprehensive discussion on driving the precision ADC's reference input.