Issues powering back up after using super cap

[jamesportman]

Hi,

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?

[defragster]

It might be triggering something in the power up sequence: See pjrc.com/store/ic_mkl02_t4.html

@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?