I have a board that uses an AD623. See attached schematic
The input voltage is 1.45V, the amplifier gain is 5.65, the output voltage is (1.45-0.97) * 5.65 = ~2.7V. Supply voltage is 5V
The problem I see is that with devices with date code 2022 (Other chip marking 9110) the ADC (U38) converts the input correctly. With devices with date code 2027 (other chip marking 4956784)
The ADC converts to a lower value (~40% lower than the correct value). I have tried replacing the ADC, and the conversion issue remained, but after replacing the amplifier with a 2022 date code part, the issue was resolved. When I measured a removed part's internal resistances (between 1 and 6, and between 5 and 8) the values were 146K (spec is ~150K). Measuring the gain resistor on board yielded the correct value.
The issue was detected on 8 boards, all of them had U34 replaced with a 2022 date code parts, and all of them are working correctly now.
Did I get fake devices from our supplier?