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FireBeetle ESP32-E: unexpected battery voltage

Unread postPosted:Thu Oct 28, 2021 1:27 pm
by semeraro.stefano
Dear everyone,
I bought a FireBeetle ESP32-E board (NOT THE ESP32 ONE!) ... KU_DFR0654.


This board integrates a voltage divider connected to PIN A2 of the ESP32-E chip, with two 1Mohm resistors:

I have a fully charged lipo cell with measures 4.2v. But if I measure the voltage at the A2 pin of the board i read 1.4v instead of 2.1v as expected from the voltage divider.

I checked the schematic of the board and I don't see anything suspicious. These are my 2 thoughts:
- Maybe the leakage current of the esp32 pin is affecting the voltage divider. But from the esp32 datasheet the maximum leakege current of every pin should be 50na so it shouldn't affect this much to the divider
- The copper traces on the PCB may affect the voltage divider, but their resistance should be negligible

So I don't know why I'm reading this value, can you help me please?