Custom PCB with STM32F411 - USB issue

[Niharika]

Hi everyone,

I’ve designed a custom PCB using the STM32F411CEU6 and a USB-C connector, but my laptop (Device Manager) and STM32CubeProgrammer fail to detect it as a DFU device or CDC. The board powers up (3.3V LDO confirmed working), and basic SWD flashing works, but USB fails. 

• USB-C Schematic:

  • CC1/CC2: 1kΩ pull-downs to GND (per USB 2.0 Type-C specs).

  • D+/D-: Connected to PA11/USB_DM and PA12/USB_DP.

  • VBUS: Filtered through a ferrite bead (BLM21AG121SN1D) and 2.2µF decoupling caps.

• Boot Configuration: BOOT0: Pulled to GND via 10kΩ resistor (tested pulling high during reset).

• Clock: 8MHz crystal with 30pF load capacitors.

• DFU Entry: Tried BOOT0=1 + reset (via button). Get that the "USB device not recognised."
  
  I have attached my schematic and the clock configuration for reference.

  

  
  
  
  

[gbm]

CCx lines pulldowns are usually 5k1. Check the power supply voltage and the operation of HSE oscillator with the oscilloscope. With BOOT0 = 1 the MCU should be detected by CubeProgrammer as DFU.

[FBL]

Hi @Niharika 

• >> CC1/CC2: 1kΩ pull-downs to GND (per USB 2.0 Type-C specs).

Check AN5225 section 10.1 STM32 USB2.0-only device conversion for USB Type-C platforms: 5.1kΩ with a tolerance of ±1% for example MB1814 

[ahsrabrifat]

You said: “CC1/CC2: 1kΩ pull-downs to GND.”

This is incorrect for a USB device (UFP). USB Type-C devices should not use pull-downs. Instead:

The host has pull-downs (Rd = 5.1kΩ).

The device needs a pull-up resistor on D+ (Full-speed device, 1.5kΩ to 3.3V).

Add a 1.5kΩ pull-up on D+ (PA12) to signal full-speed device presence if using bare USB FS stack (not in-built DFU mode). Keep in mind that the STM32 DFU bootloader mode handles pull-up internally, so this only applies if you’re using CDC or custom USB.

You can also see this STM32F4 Black-pill: WiFi shield (WiFiNINA) design for some clues. 

https://www.pcbway.com/project/shareproject/STM32F4_Black_pill_WiFi_shield_WiFiNINA_f50a0d42.html

[Niharika]

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Add a 1.5kΩ pull-up on D+ (PA12) to signal full-speed device presence if using bare USB FS stack (not in-built DFU mode). Keep in mind that the STM32 DFU bootloader mode handles pull-up internally, so this only applies if you’re using CDC or custom USB.

 @ahsrabrifat The DFU isn't getting recognised, so that pull-up on the D+ shouldn't be an issue as we want to use it in the DFU mode.

 

@gbm @FBL We are using the USB-C to USB A 2.0 cables, so the cc lines shouldn't be an issue.

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[FBL]

Hi @Niharika 

To better understand the issue, could you provide a detailed description of the problem? Do you reproduce the issue on a reference board? Is your device self-powered?