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usb otg voltage level shifter

MMARI.1
Senior

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  ???

MMARI1_0-1713601726547.png

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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 ??? 

MMARI1_1-1713602790786.png

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

MMARI1_2-1713603479534.png

 

 

 

1 ACCEPTED SOLUTION

Accepted Solutions
AScha.3
Chief

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 .

If you feel a post has answered your question, please click "Accept as Solution".

View solution in original post

2 REPLIES 2
AScha.3
Chief

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 .

If you feel a post has answered your question, please click "Accept as Solution".

hi, good morning ... since main controller chip operating voltage is 3.3v  and  External USB Peripheral Device (like Mouse , Keyboard..Etc) working on 5V  from this i am started to understand in detailed way .  My concern is USB Peripheral should not damage the MCU in Long RUN  . All your Technical explanation will improve my confidence and will improve further   .