Ran into a bit of a strange issue with a voltage divider. I take the voltage of a single cell li-ion and divide it down to a 0 - 3V range so it can be read by an ESP32, I then multiply this voltage by a fixed constant to know what the battery voltage is.

This same circuit has been built on 50+ PCB's but I'm only seeing the issue on 2 specific boards. There is a parallel capacitor for some filtering, but on these 2 specific boards, with this capacitor fitted the voltage reported by the ESP32 is incorrect. Not by a huge amount, in the region of ~200mV.

If I remove the capacitor the voltage is reported correctly.

What I'm struggling to understand is how a parallel capacitor which should in theory be open circuit at DC, is affecting the voltage divider circuit.

Is anyone able to shed any light on why this is happening?

Ran into a bit of a strange issue with a voltage divider. I take the voltage of a single cell li-ion and divide it down to a 0 - 3V range so it can be read by an ESP32, I then multiply this voltage by a fixed constant to know what the battery voltage is.

This same circuit has been built on 50+ PCB's but I'm only seeing the issue on 2 specific boards. There is a parallel capacitor for some filtering, but on these 2 specific boards, with this capacitor fitted the voltage reported by the ESP32 is incorrect. Not by a huge amount, in the region of ~200mV.

If I remove the capacitor the voltage is reported correctly.

What I'm struggling to understand is how a parallel capacitor which should in theory be open circuit at DC, is affecting the voltage divider circuit.

Is anyone able to shed any light on why this is happening?

EDIT: Capacitor used is an 0402 X5R 10uF 6.3V MLCC - Kemet C0402C106M9PACTU (Datasheet) (Spec sheet)