Hi Arttu, I'm not familiar with the SBOA437 app note so I don't have any first hand knowledge of how well the internal reference of the ADS8689 will perform in this case. That being said, we generally don't recomend using the internal reference of any ADC to drive external circuits without first buffering it to minimize loading which will impact the ADC performance. Adding a buffer to the REFIO pin and applying that as 'Vp' above would be my suggestion.
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