usb otg voltage level shifter

MMARI.1 · ‎2024-04-20

hi ,

i gone through usb pcb guidelines and other forum discussion but i couldn't catch my doubt .

1). Incase of Using USB Virtual Com Port D+ (PA12) & D - (PA11) pin can be directly connect with Computer USB port without level shifter ???

During the communication Device Class selection exactly D+ & D- is open drain or ???

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2.)Incase of using USB_OTG_FS in Host Only Mode PA9 - connected to Vbus - 5V and D+ (PA12) & D - (PA11) pin - Pendrive or Keyboard .

Looks PA9 is 5volt tolerant pin in stm32f722ze nucleo board so it's safe to keep 5v or it can be reduced to 3.3v with separate voltage divider ??? same time keyboard supply voltage will remain as 5v only . if the Vbus sense PA9 turned to 3.3v sensing then it will affect the D+ & D- signal ??? and additionally logic voltage is necessary ???

while we selecting the below D+ & D- will become open drain or ???

AScha.3 · ‎2024-04-20

Hi,

1. > D+ (PA12) & D - (PA11) pin can be directly connect

Yes. ( USB D+ & D- are 3,3V signal level - always)

> During the communication Device Class selection exactly D+ & D- is open drain or ?

What it should be . 🙂 (half duplex symm. push/pull )

2. > Looks PA9 is 5volt tolerant pin

Yes, but i would recommend some 2k --- 3k3 -- gnd voltage divider to keep 3,3v range (just for extra safety).

>while we selecting the below D+ & D- will become open drain or

It switches, to what is needed. The hardware/driver doing this, is not your responsibility .

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AScha.3 · ‎2024-04-20

Hi,