I'm using AD7764, it working fine with some of my board, but there is one board it did not work for some reason. I cannot figure out the issue with it. I would like had some suggestions only what to checking for figure out the issue on the board. The board using AD7764 have 5V supply for Analog, and 2.5V for Digital. 4V Reference bias. I had replace the IC, check all the supply voltage pins, Vref pin. The build-in diff-opamp seem to work but did not center at 2V on the output. The Rbias pin always stay at 0V (where it should be 4V as the working board).