Is PB5 really not 5V tolerant?

kk6gm · ‎2011-09-29

Posted on September 29, 2011 at 18:35

The data sheet I have says it isn't, and yet it's not an ADC input as all the other non 5V tolerant pins seem to be. Of course I'll believe the datasheet if there's no positive information that it's wrong, but it seems suspicious enough (and datasheets have been known to be wrong!) that I thought I'd ask if anybody has better info.

donald2 · ‎2011-09-29

Posted on September 29, 2011 at 21:04

Grrrr, the board software discarded my first response.

Short answer (because I'm not willing to recreate the previous long message): PB5 is buggy. It's bitten me twice. It's likely that this pin was intended to be 5V tolerant, but the same bugs that broke MOSI and TIM3 output also broke the protection structure.

kk6gm · ‎2011-09-29

Posted on September 29, 2011 at 21:41

OK, thanks for clearing up that mystery.

donald2 · ‎2011-09-29

Posted on September 29, 2011 at 23:19

Also, to be safe, assume PB5 still has the restriction of 5V-tolerant pins and cannot accept injected current. (Regular pins allow 5 mA, which means you can sense higher voltage with just a high value resistor. 5V pins must be protected with both a resistor and a Schottky diode to Vdd.)

kk6gm · ‎2011-09-29

Posted on September 29, 2011 at 23:38

Ah, I didn't know about that ability. Thanks for pointing it out.