• AVR Freaks

Hot!What possible problems could exist if the VBUS pin is permanently connected to 5V?

Author
DominusT
Super Member
  • Total Posts : 1428
  • Reward points : 0
  • Joined: 2005/07/22 08:31:18
  • Status: online
2019/01/21 11:26:08 (permalink)
0

What possible problems could exist if the VBUS pin is permanently connected to 5V?

Hi.
 
I'm designing a circuit with a PIC32MZ and opto-isolated USB communication.


Only lines D + and D- are isolated so I plan to connect the VBUS pin of the MCU to 5V from an internal source of the circuit.


Necessarily the USB module must detect the 5 V on the host side? (Obviously I should use another optocoupler)

Any suggestions or comments are welcome.
#1

4 Replies Related Threads

    crosland
    Super Member
    • Total Posts : 2041
    • Reward points : 0
    • Joined: 2005/05/10 10:55:05
    • Location: Warks, UK
    • Status: offline
    Re: What possible problems could exist if the VBUS pin is permanently connected to 5V? 2019/01/21 12:41:09 (permalink)
    0
    How are you isolating D+ and D-?
    #2
    DominusT
    Super Member
    • Total Posts : 1428
    • Reward points : 0
    • Joined: 2005/07/22 08:31:18
    • Status: online
    Re: What possible problems could exist if the VBUS pin is permanently connected to 5V? 2019/01/21 12:44:49 (permalink)
    0
    crosland
    How are you isolating D+ and D-?


    With an ADuM4160.
    #3
    jtron
    Starting Member
    • Total Posts : 36
    • Reward points : 0
    • Status: offline
    Re: What possible problems could exist if the VBUS pin is permanently connected to 5V? 2020/08/05 11:04:36 (permalink)
    0
    Hi Dom,
     
    I too have an isolated USB design. I discovered that my dsPIC33 will not detect host disconnects when VBUS is hardwired to 5V. When a disconnect occurs, it isn't recognized until the host reconnects (which results in a disconnect event immediately followed by a connect event).
     
    A workaround for this is to use an additional isolator to effectively pass through the USB cable 5V to the PIC's VBUS pin, which the PIC uses to detect host connections. For a relevant discussion, see this post: https://www.microchip.com/forums/m1149215.aspx
    #4
    DominusT
    Super Member
    • Total Posts : 1428
    • Reward points : 0
    • Joined: 2005/07/22 08:31:18
    • Status: online
    Re: What possible problems could exist if the VBUS pin is permanently connected to 5V? 2020/08/05 11:11:30 (permalink)
    4 (1)
    jtron
    Hi Dom,
     
    I too have an isolated USB design. I discovered that my dsPIC33 will not detect host disconnects when VBUS is hardwired to 5V. When a disconnect occurs, it isn't recognized until the host reconnects (which results in a disconnect event immediately followed by a connect event).
     
    A workaround for this is to use an additional isolator to effectively pass through the USB cable 5V to the PIC's VBUS pin, which the PIC uses to detect host connections. For a relevant discussion, see this post: 


    I solved it as in the attached image, but it is already a long time ago. It works very well without problems.



    Attached Image(s)

    #5
    Jump to:
    © 2020 APG vNext Commercial Version 4.5