STM32H750 and USB3300-EZK has stopped working

sophie · ‎2026-01-25

I designed a board that uses a STM32H750 with a USB3300-EZK that has stopped communicating over USB. It's been having intermittent issues for the last day or so (sometimes I'd need to power cycle the board before it would show up, but then it would work flawlessly). Earlier today, I plugged it into a Raspberry Pi, and then it died fully. I've plugged it into that Pi before without issue.

Despite probably hundreds of cycles at this point, I haven't gotten the USB to work again. The PHY is generating a stable 60MHz clock, and DIR is low. I haven't observed any communication on the D0..8 lines. That leads me to believe the problem is with the STM32.

I am using pc2_c and pc3_c, which are supposed to work with USB, although I've heard they're more susceptible to (static?) damage.

I do have a second board that I can switch to, although I don't have a third prototype, and it really would be good to figure out what happened here so I can prevent it from happening again.

sophie · ‎2026-01-26

I unfortunately don't have a spare USB3300 (or a spare STM32H7) but I may have to pick one up.

The reason why I think it's a problem with the STM32H7, and not the USB3300, is because DIR and NXT are both low, which should imply that the mcu is good to put data on the data bus, but that never happens. I did write a little program to check the value of pc2 and pc3 and they both came back low though, even when I enable the internal pull-up resistor. So it seems like the analog switch might be okay.

I don't have any ESD protection but supposedly the USB3300 has it built-in. The only other I/O is a VGA output which is connected to the STM32H7 through a resistor DAC. Unfortunately it has no ESD protection, although the dead board seems uncorrelated with plugging/unplugging from the VGA.