Need to pull-up D+/D- with USB VCP when use STM32 MCUs?

[Kenji1]

Hi Team

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Is it necessary to add a 1.5k pull-up resistor to D+ or D- when using USB VCP at full speed mode with STM32F405 MCU?

The port of the MCU be automatically pulled up when the USB of the MCU is set?

Please let me know if there any document for recommended circuits.

[waclawek.jan]

> Is it necessary to add a 1.5k pull-up resistor to D+ or D- when using USB VCP at full speed mode with STM32F405 MCU?

No.

> The port of the MCU be automatically pulled up when the USB of the MCU is set?

Yes.

> Please let me know if there any document for recommended circuits.

You can perhaps get inspired by the respective Disco or Eval boards' schematics.

JW

[Muhammed Güler]

https://www.st.com/resource/en/application_note/dm00296349-usb-hardware-and-pcb-guidelines-using-stm32-mcus-stmicroelectronics.pdf

Here are the answers to many USB related questions.

USB supporting models of STM32F4 series MCUs have internal pullup resistor.

[Tejal Gadad]

Hello, so does this mean there is no need to perform VBUS sensing for STM32F446 as the D+ pin already has an embedded pull up resistor? Does this mean the USB device (STM32) is constantly detecting the USB host (PC) even when it is not connected? I am a bit confused now.

[Kenji1]

Hi, thank for the information!