D24V6F3 Shutdown Pin left floating- consequences =?


I was rereading the pageon the D24V6F3 board, and it says about the shutdown-pin “You should not leave this pin disconnected.”

Sadly, I did exactly that on all my board revisions, and I’m pretty much done with adjusting what were my many mistakes :p. I can short Vout to Shutdown on the pololu board itself for now, but I was wondering how realistic that warning is. I ran the board for at least a few dozen hours without noticing a problem with leaving shutdown pin floating. What is the specific danger of keeping it disconnected?


Hi, Tomek.

There is a very weak pull-up inside the regulator IC that in some setups could be enough to keep the regulator enabled. However, we have found that that pull-up very is easy to overcome, so in some setups it might be hard to turn on the regulator or keep it from shutting off, especially if the board is exposed and people might be touching it. I do not think leaving that pin floating should be dangerous for the board itself, so if it is working for you without being pulled high and nothing else in your system would be damaged if your 3.3V source cut out, it might be fine. I would recommend connecting it to VIN to be safe though.


Thanks! It was a miss on my part to not see that recommendation clearly noted on the page. It seems I’ve been lucky with the weak pullup and my board is hidden from view or touch. Hopefully that’ll all work OK, though I guess I’ll also short the shutdown pin to high for the couple boards I have lying around.

Edit: Oh! The product page I can connect it directly to Vin, that is, for me, 30V. Is that correct? Not just Vout? I.e, the shutdown pin is 42V tolerant? That’ll be 10x easier since they’re next to each other :).

Sidenote: Pololu is killing it with these voltage regulators they’ve recently come out with. It seems someone or multiple people are doing awesome work on compact affordable regulators.

For reference I have tied the shutdown pin to Vin of 20V, and have not had a problem. So it looks like the page (not too surprisingly) is correct, and it’s safe to tie to Vin. Great board!

It looks like you already verified this, but just to clarify, the SHDN pin can tolerate voltages up to the voltage applied to the VIN pin, but not voltages over VIN. So, for your case where VIN is 30V, you could apply up to 30V to SHDN, but not 40V, however, if you were supplying 42V to VIN, you could apply 42V to SHDN.