We made two boards for AD7682/AD7689. One of them work perfectly, one of them does not. The voltage reference for it is unstable from time to time. The reference does not export 4.096V any more, but randomly move from 0V to 4.9V.
We use the internal reference of AD7682 as a voltage reference for a DAC. The reference at REF pin is followed by AD4841-2 as a voltage follower. However, the voltage reference is unstable. When we solder out the AD4841, the adc reference works again.
And when we solder the AD4841 back, it continues to work. However, on one day it suddenly does not work again....And the cycle repeats twice in these two weeks...
Is it because the capacitive input for AD4841 is too large?(10uF) Or what could be the reason? What should I check?
The schematic is like following: