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STM32F407 USB FS (Device Mode) not recognized. "Unknown USB Device (Device Descriptor Request Failed)" Error!

Associate II

I've seen many topics similar to my problem and went through their solutions but they didn't work for me so I'm asking here with details related to my problem. I've made a PCB and implemented USB 2 FS on it using STM32F407 PHY in device mode. here is the schematic:

0693W00000NskvSQAR.pngI've removed two 22 ohm resistors according to this video from ST official channel (around 4:30):

the DM and DP lines are routed differentially and are about 15.4 mm long and Impedance (Zdiff) is about 105.32 (from Altium Designer calculations). there is no specific code yet. I just want PC to be able to recognize it (for now win 10). Device is self powered and VBUS sensing is activated (I've checked without it also and yet no result). Class for FS IP is virtual port com (setting initial values using CubeMX). There is an 8 MHz Crystal on the board and here is the Clock Configuration:


Minimum Heap and Stack sizes are increased to 0x2000 and 0x4000 respectively. MCU is not stucked since it works fine for some check codes. for example making an LED blink. Also checking USB initializations in debug mode, all checks are passed. I've uploaded the same settings into discovery board and it works fine and USB is recognized on PC. So there are 2 possibilities I can see. Either there is a HW problem which I cannot see or the MCU is fake.

Any help is much appreciated.


Associate II

Hi, thank you very much 🙂 . I will check them. And about drivers. For win 10 I think windows inbox drivers are ok although I'm not sure!

Associate II

Make sure you have USB interrupts enabled