Add USB connector to my stm32L452 - connections

[SLevi.1]

I want to add a usb connector to my stm32L452, it is powered by an external supply (not usb). I then want to use it as a CDC device, so I can plug into my PC, and it appears as a virtual com port and/or mass storage device. I have some questions:

(1) Am I correct to connect VDDUSB to the 3.3v VDD used to supply the stm32?

(2) The only connections to the socket I was planning were USB_DP, USB_DM, & gnd. Is this correct?

(3) Do I need to do anything about the stm32 and USB detection? I have seen PA9 mentioned on the web, but this would conflict with the use of pin PA9 for an I2C bus.

(4) I was going to leave the 5v from the USB cable disconnected.

[Amel NASRI]

Hi @nonesuchevitt​ ,

I invite you to refer to the application note AN4879 USB hardware and PCB guidelines using STM32 MCUs.

It provides hardware guidelines for PCB design, to ensure electrical compliance with the USB standards with all STM32 Products including STM32L4.

-Amel