5 Volt Tolerant Pins

In the following document:


It says:

[1] FT = 5.0V tolerant pins. All pins except A3 and DAC are 5V tolerant (when not in analog mode). If used as a 5V input the pull-up/pull-down resistor must be disabled.

How does one disable the pull-up/pull-down resistor? I want to avoid destroying the digital pins.

Using pinMode INPUT_PULLUP or INPUT_PULLDOWN enables the pull-up or pull-down, which limits the pin to 3.3V.

Using just INPUT allows 5V inputs on all pins except A3 and A6 (DAC) when used with digitalRead. This also includes the other A pins, and pins like RX and TX.

Using analogRead on any analog input (A pin or the additional ones on the Electron) only allows 3.3V maximum.


Just fried a Photon, trying to narrow down why. I was doing analogRead on A6 and A7 (DAC and WKP i think) using a I2C breakout available on a PhoBot shield. Didn’t occur to me that the breakout was for I2C @ 5v. I was also supplying 13+ volts (12v lead-acid battery on solar, using a charge controller output) to the shield when the spec said max 12 (though the PhoBot states 12v max in, the onboard CJ1117 looks like recommended is under 15v). It won’t turn on anymore, and smells funny / gets hot when powered by USB.

Is it more likely that I friend the regulator with the ~13v+ or could I do more than just kill a pin by supplying over 3.3v input on an analogRead.


Edit: Added links to product and hardware schematics for PhoBot shield and CJ1117 regulator.

A6 (and A3) is under no circumstances 5V tolerant so that’s most likely a gonner.
For A7 you probably frazzled the ADC stage but that can have adverse side effects on the entire GPIO too.
Any damage to one GPIO can also have effects on neighbouring circuitry.

That sounds serious, but you may be lucky (rather unlikely tho’) and may not have damaged the controller itself. You could try that with a reliable 3.3V (min. ~150mA) source feeding into 3v3 and see what happens.
But I’d be prepared for a fare-well

1 Like

I’ll have a small ceremony for it.

Thanks for the comments.