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Thread: Issues powering back up after using super cap

  1. #1
    Junior Member
    Join Date
    Nov 2022

    Issues powering back up after using super cap


    I've had a look around and can't see anything definitive, so any help is appreciated.

    I have set up a 1.5F super cap which keeps the teensy running for a short time after power is removed.
    If you wait for the cap to discharge then reconnect the power, the teensy starts up fine.

    However, if you remove the power, wait a few seconds for the teensy to drop out, then reconnect while the cap still has maybe 2 volts left, the teensy will not fire back up.
    The voltage will be back to up to 4.8-5v so it should be running really.
    It would be equivalent to powering up a teensy with 2 volts on a bench supply then ramping the PSU up to 5v quite quickly.

    Is this brown-out protection or similar?
    Any ideas about how to work around it?

  2. #2
    Senior Member+ defragster's Avatar
    Join Date
    Feb 2015
    It might be triggering something in the power up sequence: See

    @Paul made a good post about the process - maybe that would be good linked to that section? It involved having 3.3V on vBat IIRC to make sure the MCU powers up right?

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