We are using the ADS7828-Q1 in single ended mode. All 8 channels are used on our design. We are using the internal reference, and the chip is powered with +3.3V. On the REFIN/REFOUT pin, we have a 0.1uF capacitor. (Schematic snippet attached.) Our I2C bus is configured for 100kHz.
We are testing by inputting a 1.03V signal into the inputs. With the 2.5V reference, the signal is reading correctly at a 1.03V over 2.5V scale, or 41.2%
After many back to back reads, suddenly we are reading 31.1%. It is as though we are reading the same 1.03V voltage over a 3.3V scale.
Converter PD1,PD0 settings have been verified many times. We are leaving the converter on continuously and using the internal Ref left on continuously.
The issue seems difficult to reproduce. As a next step we will attempt to closely monitor the VDD pin and REFIN/REFOUT pin to see what they are doing when the issue occurs.
Is there anything that would cause the chip to suddenly change it's internal reference (or scale) from 2.5V to 3.3V?