Hello everyone,
I’m working on a PCB that includes an STM32F303. This is my first board using USB, although it’s not my first time working with USB code; I’ve previously developed various USB applications on demo boards.
During development, I powered the board with an external lab DC power supply from GW Instek, providing 15V to the board. I developed my software (STM32 side) working with USB, and everything was working fine. The board controls high-power LEDs/COBs, and from the Python code on the PC side, I could adjust the light intensity of the LED/COB as intended. Everything was going great.
Then, I replaced the lab DC power supply with a commercial power supply (XP Power VCB60US15) that fits my box. Before connecting it to the PCB, I verified that the 15V was correct. After connecting both the power supply and the USB to the development USB hub, one of the LEDs/COBs started lighting up (which was unexpected, as this wasn't the behavior when powered by the GW Instek supply). I then ran the lsusb command on a Linux terminal to detect the board, but it didn’t show up. I checked the boards functionnalities through a hardware interface (an incremental encoder managed by the STM32 that allows to manage the COBs/LEDs), and I could still control the power of the COB as usual. The board perfectly works when driven from the incremental coder, but not anymore from USB. I also checked the various bias voltages of the board, everything works as usual. Strange.
Next, I powered the PCB again using again the GW Instek power supply, but lsusb still didn't detect the board, even though everything was functioning normally through the user interface, as previously.
It seems the USB interface might be damaged, but I don't understand why. Here’s how I’ve wired the interface. In this schematic, VDD refers to the 3.3V that powers the STM32 itself.
I’m unable to pinpoint the issue or make a diagnosis about what happened. Please note that I did not connect the ground of the XP power supply to the PCB ground (my box is made of plastic, so grounding isn't required), and I believe this is also the case for the GW Instek power supply. But even if both were connected I would not really understand the problem.
Do you think the internal USB hardware of the STM32 chip is likely damaged? Does anyone have an idea of what might have caused this issue? Should I consider adding extra protection to the USB connection on the PCB?
Best regards,
Mikhaël
