RE: NRF52840: accidental back-powering by applying voltage to GPIO pin when power is off

hmolesworth — Thu, 24 Apr 2025 19:51:57 GMT

Best test is to repeatedly remove and replace the battery with various delays and see if there are are any hangup issues.

Best fix might be to switch to a flying-capacitor sample where no potential divider is required; suggest 10nF fixed and 10nF fly from same supplier, nc connects C1 to C2 and port pin discharges both then switch pin to saadc mode, switch on then switch off: vin to saadc is then Vbatt/2. Only static drain is minuscule analogue switch supply, use break-before-make type.

I wrote some code here:

flying-capacitor battery measurement

RE: NRF52840: accidental back-powering by applying voltage to GPIO pin when power is off

Turbo J — Tue, 22 Apr 2025 06:50:20 GMT

Terrible idea to use a voltage divider without a cutoff transistor or similar circuitry. You are not supposed to load a discharged Li-ion battery at all - that could set it on fire AFAIK.

The voltage into the Nordic chip is the least of your problems.

Expect fun stuff like randomly erased flash pages in the field due to brownouts. The diode from the pin to VDD rail is not intended for this kind of abuse, but it probably won't blow up.