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nRF52840 power-on reset failure

JordanYates

Under the recommended operating conditions (page 611) in the nRF52840 datasheet, there is a note specifying:

Important: The on-chip power-on reset circuitry may not function properly for rise times longer
than the specified maximum.

Given a device (with SWD access), is there any way to detect whether the POR circuitry has failed?

Is the error condition when this occurs the same as was stated for the nRF52832 here? (stay in reset state with no code running) 
https://devzone.nordicsemi.com/f/nordic-q-a/47531/power-on-reset-on-nrf52832

We have several devices that we suspect to be in this mode, but wish to validate.
The behavior we can observe is:

  • The standard software is not running (it contains a watchdog)
  • SoC is being supplied 3.3V
  • Pin 18 is configured as nRESET (implying an internal pull-up resistor), but the nRESET pin is low
  • Physically pulling nRESET high does not result in code executing
  • We are unable to connect to the device using JLinkExe tools
  • Physically disconnecting the battery and reinserting it resolves the issue (code starts executing)
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    Okay, I think this would be the POR failing, but I can't confirm it just from your description, but I think it's safe to say that what's causing this is the long rise times. Our expert on the matter is out of office today, but I'll ask him first thing on Monday whether he can provide some more details on whether there's some way to pin point whether it's the POR or something else failing.

    For future HW revisions of your device I would suggest adding some kind of threshold between the solar panels and VDD on the nRF52 so that the nRF won't be provided power until there is enough to make the device run to prevent these extended rise times.

    Best regards,

    Simon

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  • 0

    Okay, I think this would be the POR failing, but I can't confirm it just from your description, but I think it's safe to say that what's causing this is the long rise times. Our expert on the matter is out of office today, but I'll ask him first thing on Monday whether he can provide some more details on whether there's some way to pin point whether it's the POR or something else failing.

    For future HW revisions of your device I would suggest adding some kind of threshold between the solar panels and VDD on the nRF52 so that the nRF won't be provided power until there is enough to make the device run to prevent these extended rise times.

    Best regards,

    Simon

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