The external reference source must provide low-drift and very accurate voltage at the REFIN pin of the ADS891xB. The output broadband noise of most references can be in the order of a few hundred μVRMS. Therefore, to prevent any degradation in the noise performance of the ADC, appropriately filter the output of the voltage reference by using a low-pass filter with a cutoff frequency of a few hundred hertz.
The internal reference buffer of the ADS891xB provides the dynamic load posed on the REFBUFOUT pin during the conversion process. Decouple the REFBUFOUT pin with the REFM pin using the recommended CREFBUF and RESR. See the Layout section for layout recommendations.