Issues with power on reset in nRF52840 - the chip hangs

RE: Issues with power on reset in nRF52840 - the chip hangs

david4255334 — Fri, 25 Aug 2023 08:42:54 GMT

Thanks for your replies. As I expected, the best way to avoid the issue is to make sure the power supply rise times are within the specs.

RE: Issues with power on reset in nRF52840 - the chip hangs

Kenneth — Thu, 24 Aug 2023 08:16:49 GMT

Hello,

Using ADC to measure battery voltage, and take appropriate step to enter sleep until battery is replaced/recharged seems to be the way to go here yes.

I think you already understand what the problem is, but just to confirm your assumption: The last power sequence on I see on your screenshot is outside the recommended operating conditions of max 100ms rise time on VDDH:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/recommended_op_conditions.html

Kenneth

RE: Issues with power on reset in nRF52840 - the chip hangs

hmolesworth — Tue, 22 Aug 2023 19:19:59 GMT

When anticipating startup operation from a battery almost completely drained without knowing whether a high-current charging source is connected to the battery it is normal practice to prevent operation of the peripherals, cpu core and external hardware circuits until sufficient battery capacity is available to run these items without a resultant voltage dip forcing a reset. How to know when this is the case? Typically use a vanishingly short bare-metal ADC channel or comparator channel to sample the supply voltage and turn on a known drain (the cpu core as default or even maybe something like 500uA or 1mA peripheral) and monitor the supply for a short interval to see the voltage decay rate. If significantly fast immediately shut down the cpu core (sleep) before further fall in voltage and eventual reset.

Safer designs would use an external device to do this, but the cpu itself works fine as long as the awake time is very short - ie no initialisation of other stuff such as bootloaders or BLE..