Different behavior reading GPIO SIO02 and SIO28

[Nathan O.]

Hi,

I am working on a product development that uses an nRF52832 (through a LAIRD BL-652 module).

We have a voltage point (named 5V), that is connected to SIO_28 GPIO through a voltage divider. This voltage divider should give us 3V at the GPIO.

Unfortunately the GPIO always read 0. When measuring with a multimeter, we get 0.6V instead of 3V.

If we cut the trace between the divider and SIO_28, we do get 3V at the voltage divider's output.

If we connect the voltage divider to SIO_02 instead of SIO_28, the GPIO reads correctly and we do get 3V (2.95V actually).

Here is our schematics :

Do you have any idea ?

[haakonsh]

My first guess is a blown ESD fuse. If you exeeded the GPIO input voltage spec and ESD diode would short the excess voltage to GND. If enough voltage or current is applied to the pin the ESD diode will blow and the failure mode is a permanent short to GND. 

Can you replicate your symptoms on another board?