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STM32L4 USB Device with VBUS Sensing ON

Question asked by Amila Perera on May 23, 2018

Hi all,

I'm trying to get the CubeMX generated sample CDC application working on STM32l475VG IoT board.

By following the attached document I was able to get the clock configuration right and the CDC application without VBus Sensing works perfectly fine. I used MSE trimmed by LSE as suggested by the document.


However I would like to get the same application with the same clock configuration on the same dev board running with VBus Sensing ON and it doesn't work at all. This time the device is even not seen by the PC at all.

When VBus Sensing is ON even the HAL_PCD_IRQHandler doesn't get triggered upon connection.


I need VBus Sensing since in my real application we're using the uC in a self-powered device.


I am trying out all these experiments under the assumption that HW on dev board readily supports VBus Sensing, since with the datasheets I can't read that HW changes are required.

Is it really safe to assume that sample USB CDC app should work with VBus sensing ON without modifying the dev board HW ?


With the description mentioned int the attached document, I have a feeling that VBus Sensing is Disabled intentionally for a very specific reason. Is it that the clock configurations have to done differently when it is On ?


Can someone please shed some light on this ?