I made a mistake on a board recently when adding an optional PIC12F615 processor to supervise my ARM processor.
I didn't realize the PIC needed >4.5V to erase.
So, I've got this MIC2920A 3.3V regulator feeding the PIC (and only the PIC) and I need to let the programmer pod apply 4.5V to it.
Will it work? I don't see anything in the regulator datasheet that says it will or won't. The datasheet discusses how "bulletproof" this thing is, capable of handling -20 to 60V on the input pin. I don't see anything about high voltage on the output pin.
I've got 100 fairly expensive PCBs like this (20 stuffed). I can modify one board for development with a diode or reverse-power-protecting mosfet, but I'd like to be able to easily reprogram these boards later on. I'd planned on simply leaving the PIC off entirely if it didn't work... but it almost works.
The regulator's input is a regulated 5V, so I wouldn't be going over that.
I hooked up a bench supply, set it to 4.5V with a 30mA current limit, and then tried connecting it to the VDD pin of the ISP header (which is wired to the regulator's output pin). I didn't see any measurable current.
I was unable to force the programming pod (PICkit3) to supply 4.5V when there was already 3.3V present, though. The regulator had to be unpowered to program the PIC.
However, this regulator seems fine with it... the GND and VIN pins are 0V, and it draws no current or at least no measurable current.
I was able to erase and reprogram the PIC. Thanks!