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USB non-buspowered GND - what to do

Discussion in 'Embedded' started by Tobias Alte, Jul 22, 2004.

  1. Tobias Alte

    Tobias Alte Guest

    Hi,

    I'm currently working on a selfpowered USB device and have just a quick
    question.
    Maybe I overlooked/missed some info on the datasheets etc. but I am
    questioning
    myself what to do with the GND coming from the USB host. My device has its
    own
    supply so I don't need the USB supply.

    Should I connect the USB bus GND to the GND at the board for EMV purposes
    ( and leave USB +5V unconnected ) or must I connect none of the USB supply
    pins
    with the device if I use a external supply ?

    Thx for advice.
     
    Tobias Alte, Jul 22, 2004
    #1
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  2. Of course you must connect the GND. At least you need it as a potentail
    reference for the USB signals.
     
    Reinardt Behm, Jul 22, 2004
    #2
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  3. Tobias Alte

    Tobias Alte Guest

    Reinardt Behm wrote
    Thanks.
     
    Tobias Alte, Jul 23, 2004
    #3
  4. If you are new to electrical engineering, I'd suggest reading up on
    Kirchoff's
    Current Law and Kirchoff's Voltage Law.

    If you are NOT new to electrical engineering, I'd suggest reading up on
    Kirchoff's
    Current Law and Kirchoff's Voltage Law.

    :)
    --Keith Brafford
    Embedded Excellence, Inc.
     
    Keith Brafford, Jul 24, 2004
    #4
  5. Tobias Alte

    steven Guest

    You do? With differential signals?
     
    steven, Jul 25, 2004
    #5
  6. Yes, in practice you do. Unless one gavanicaly isolate one side, one
    need to keep the grounds of the different systems with 30V (On RS-485
    anyway). I am not sure what the common mode range for USB is.

    Regards
    Anton Erasmus
     
    Anton Erasmus, Jul 25, 2004
    #6
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