STM32U5-DK2: USB MSC not enumerating when VBUS sensing is enabled (without UCPD)

[ArunJohn]

Hi ST team,

I'm working with the STM32U5-DK2 board and implementing USB Device MSC class using USBX and external flash (via OSPI) as storage. Everything works fine when VBUS sensing is disabled in STM32CubeIDE — the host detects the device correctly as a USB MSC device.

However, when I enable VBUS sensing in CubeIDE (i.e., "Device Only" mode), the USB device is not detected at all by the host (no enumeration).

Questions:

1. Why does enabling VBUS sensing prevent the device from being enumerated as a USB MSC device?

2. What are the minimum required CubeMX configurations to support VBUS-based detection (using PA9), but without using UCPD or USB PD features?

3. Is there any internal pull-up or alternate pin setting that needs to be done for PA9 in this context?

4. Is there any known erratum or additional hardware jumper/settings specific to the DK2 that could affect VBUS sensing?

Any guidance to make VBUS-based detection + USBX MSC work reliably (without relying on UCPD/PD) would be greatly appreciated.

Thanks!

[FBL]

Dear @ArunJohn 

You can refer to MB1918 schematics.

As you can see, USBC_Detect is connected to PA1 on this board.