Other Parts Discussed in Thread: OPA387,
I have an ADS1114 receiving an input signal between 0V - 4V, the signal goes through an OPA387 set up as a buffer, just before the A0 input of the ADC i have a low pass filter for 80hz made from a 200ohm resistor and a 10uF ceramic SMD capacitor. Sometimes the setup works great and other times i have this weird issue where the voltage drops and varies wildly from the actual input signal voltage, i can measure this voltage drop just after the 80hz filter resistor, one end of the resistor has the actual voltage and the other end has a dropped voltage that keeps jumping around, always lower than the actual signal voltage though. The ADC is making correct measurements of said varying voltage. I have no idea where this could be coming from. I have tried to remove the 80hz filter capacitor and now there is just a 200ohm resistor in line with the buffer, nothing has changed though. The ADC does this in both single ended & differential modes. The input signal does not vary at all when the issue appears and keeps steady. Again this system has worked on occasions and there is no significant voltage drop from the 200ohm resistor when this system works as designed. Following is the schematic.
