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STM32 USB DFU circuit

Associate II

I would like to program an STM32F446RET MCU with USB DFU bootloader. I did the following connections:
- board VCC to USB cable and VBUS_FS
- board GND to USB cable
- UDB_DP to USB cable
- USB_DN to USB cable
When reset BOOT0=3.3V and BOOT1=GND

The MCU seems to enter in the bootloader (the main program does not start) but STM32Programmer is not able to connect to the USB device

Am I missing something?

EDIT 1: This is a circuit that is very close to the one I used




I discovered the source of the problem, but not the solution. Here's more details. There is a USB A receptacle on the board and:

  • if I use a USB-A to USB-A cable to connect the board to the PC everything works.
  • if I use a USB-A to USB-C cable to connect the board to the PC it does not work.
  • if I use two cable adapters: USB-A to USB-A (male) and USB-A (female) to USB C, it works

It seems like that when USB C is used we need an additional circuit (the same that it is inside the cable adapter). Which circuit? I'm not able to find anything on the internet


Is this a custom board? If so, is a schematic available?

Can you program it using the SWD connections?

> board VCC to USB cable and VBUS_FS

I'm hoping you're converting the 5V to 3.3V with an LDO before connecting it to board VCC, right?

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Associate II

Thanks for the help!

Yes, this is a custom board. And I am able to program it with SWD.

I edited the question to add a simplified schematic of the whole circuit.

The board is not powered through USB but has another power source which provide both 5V (which is connected to USB and VBUS_FS) and 3.3 V (to power the MCU).

The reply is below, sorry for the confusion. I'm new to the STM forum