Electronic – Is it safe to apply higher voltage to the output of a MIC2920A voltage regulator

voltage-regulator

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.

EDIT

The regulator's input is a regulated 5V, so I wouldn't be going over that.

EDIT 2

It works!

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!

Best Answer

Surmises only - hard to be sure for a specific part with no hard data.

Connecting one as stated and measuring current flow into regulator would tell you something.

A look at the block diagram at the bottom of page 5 of the datasheet suggests you will be trying to reverse bias junctions in Q24 & Q26 (top right of page).I'd expect the 4.5-3.3= 1.2V overvoltage to be low enough to have a good chance of being safe.

Is power applied to the regulator during programming? If not you may breakdown internal intrinsic body diodes (which we may not have got). After which anything can happen.

You mention a reverse protection diode. It's not obvious where you were going to put that. It's usual to place a diode from regulator output to regulator input - Schottky probably a good idea.

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