Will it have any adverse affect on this voltage regulator if I have 3.3V on the Vout pin (coming from another source) without have any voltage on it’s Vin pin (normally expecting 4 to 6 V). This regulator is mounted on an ItsyBitsyNRF52480 board that is usually powered by a lipo battery, but my only option for power is a stable 3.3V supply, that I can tie directly to the board’s 3v pin. but this will ‘backfeed’ the AP2112K regulator. I’m hoping it won’t be a problem?
I do believe this would be a problem and what one would normally do in this case is tie the battery to the VIN pin of the voltage regulator through a diode to prevent backfeeding from your VBUS (usually USB voltage input).
Here is an schematic example of an Adafruit Feather 32u4 board power section:
The draw back is you lose the voltage drop to the Schottky diode which would make your battery die 700mV or so earlier.
What if I never have Vbus or Vbat connected?
(I can program the ItsyBitsy, with the USB port, and then install it in my project, connecting 3.3V to the 3V pin, and will never need to connect USB/5V again.)
or, I have a hotair reflow, could I just remove the regulator?
thanks. I would prefer either of these options, if they would work, over the battery loss…
You could either remove the voltage regulator or bypass the regulator with a diode going from Input to Output with Anode on the Output
Great! removing it will be grand!
Cheers.
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Once I remove the regulator, if I ever did need to reprogram the itsybitsy, I would have to have it hooked up to a separate 3.3v power source, correct?
Not quite sure how that would work outside of soldering the regulator back in since you’d have the VBUS of the USB for power. This would be the appeal of using the bypass diode.