We are using multiple AD7949 devices on one of our boards. The devices are set to use internal reference of 4.096V. Packs have been in the field and functional for some time and we are now seeing RMAs that are being traced to the ADC. Of the 4 devices on the board ... 3 of them are showing Ref = 4.09v, and Ref_In = 2.31v ... the 4th ADC is showing Ref = 3.78v and Ref_In = 2.13v.
Given that the units were functional when they left the factory, is there anything that could cause this shift in the internally generated reference?