nRF52 not booting properly without reset

[Dajgoro Labinac]

Hi

I did a bunch of boards for a product, and in the latest version I used a BQ25121 PMIC which also has a reset output which I tied to the nRF52 input. On the previous boards the reset signal was tied directly to a button and it worked. But now when the nRF52 is powered, BLE does not work for some reason, and some other bits of code don't work either. But when I reset it manually it all works fine. The reset reason(RESETREAS) after powerup on the new board is 0, while on the old boards or after it was reset via switch its 1. When its 1 it all works fine, but not when its 0. I tried detecting the reset reason being 0 and then issue a reset via firmware, but that does not help. All the BQ25121 has is a open drain output, so it should behave much like a physical switch, but something is affecting the nRF52 and making it not boot properly.

[Nguyen Hoan Hoang]

Try adding a pullup resistor. I believe open drain requires external pullup

[Dajgoro Labinac]

I tried a 20k pullup, then I also tried a 6.8nF cap which is just enough to straight out the bouncing, but keep the timing, and it did not help. Then I cut the trace to the PMIC chip, and the issue is still there, there is probably more to this. Now I'm trying to disable the reset input, but removing "CONFIG_GPIO_AS_PINRESET" does not seem to help.

When checking the signals again with the pmic trace cut, the signals look identical to the old version of the board, but the issue still persists.