USB renumeration in NUCLEO-F446RE

[Ellu1213]

I am designing a board using STM32F446RE (with embedded ST link) with NUCLEO-F446RE as a reference. While going through the NUCLEO-F446RE schematic, I am not clear regarding the USB renumeration process and hardware connection. Could you please explain the working of transistor and the whole circuit in the schematic attached and about USB enumeration. Why USB RENUMn is Would you recommend using this in my design?

 

[waclawek.jan]

You are looking at the Nucleo on-bard STLink's STM32F103 schematics.  The target STM32F446 is different, it has a different USB and has the DP pullup built in, including the switch.

I don't know of a good schematics reference for STM32F446, but you may want to have a look at the 'F407 DISCO for inspiration, its USB is identical to that of 'F446.

JW

[Ellu1213]

Thank you very much for your prompt response. In my design, I am using both MCU, like NUCLEO-F446RE. One as main MCU(STM32F446RE) and other as programmer (STM32F103CBT6) for embedded ST link. I have question regarding the USB enumeration of STM32F103CBT6 as per the above schematics. Please explain me the following: 1) Could you please explain the working of transistor and the whole circuit in the schematic attached?

2) Why USB Renumn pin connected to GPIO?

3)Would you recommend using this in my design?

Thanks in advance

[waclawek.jan]

The 1k5 pullup on PD indicates to host/hub that a FullSpeed device is connected. The transistor provides a means to remove the pullup, imitating disconnect/reconnect.

JW

https://community.st.com/t5/stm32-mcu-products/custom-board-design-using-stm32f446re-and-stm32f103cbt6/td-p/571039