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Two port implementation for a USB application consuming more than 2.5W

Discussion in 'Embedded' started by Kieran O' Leary, Aug 11, 2008.

  1. Hello,



    I am currently working on a USB 2.0 bus powered application that I expect to
    consume more than 2.5W.



    As such, I wish to use two USB ports to power the application in a similar
    manner to that used on some USB bus powered external hard drives.



    Has anybody had any success in implementing such a scheme and remaining USB
    2.0 compliant? In particular, I wish to "politely" request 500mA from the
    USB host for the second (power-only) port rather than assuming that 500mA
    will be automatically available.



    Does anybody know of any circuit implementations available on the web that
    will implement the two port scheme - fully compliant or otherwise?



    Any recommendations on how to do it?



    Any advice on any gotchas, etc. to watch out for?



    Any help would be greatly appreciated.



    Many thanks,

    Kieran
     
    Kieran O' Leary, Aug 11, 2008
    #1
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  2. Kieran O' Leary

    sky465nm Guest

    I am currently working on a USB 2.0 bus powered application that I expect to
    Ask port1 for 500 mA, and only then ask port2 for another 500mA.
    And report to the enduser what happends. Like led1 red->green, led2 red->green.
    If the device doesn't get it's way powerwise let it still be present. But leave
    powerhungry parts offline.
    IF the potentials of the usb ports doesn't match. Not that I think any usb
    device does this..
    However a user might plug the connectors to two different devices ;)
    (gotcha!)
     
    sky465nm, Aug 12, 2008
    #2
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  3. Hi Brendan,

    This is a reasonable point. As it happens, any indicators that I will use
    will be software based.

    Excuse my ignorance but do you know if people with colour blindness have
    difficulty distingushing colours (red/green) on computer monitors in the
    same way as with LEDs, etc.?

    Thanks,
    Kieran
     
    Kieran O' Leary, Aug 12, 2008
    #3
  4. Hi,

    Thanks ... I think that this is the avenue that I will go down alright
    although the idea of using a second USB peripheral IC just to enumerate
    correctly to get the 500mA doesn't seem very cost effective to me.

    I may try to implement part of the second USB interface in some spare
    capacity I may have available on an FPGA.

    A possible potential difference between the two 5V voltage sources is
    something that will require some thought alright but I have some ideas for
    this.

    Thanks again.

    Cheers,
    Kieran
     
    Kieran O' Leary, Aug 12, 2008
    #4
  5. Kieran O' Leary

    CBFalconer Guest

    There are all sorts of colour blindness'. I have one, and rarely
    notice it. Some weird text colour schemes, including green type on
    some sort of background, are very hard for me to see.
     
    CBFalconer, Aug 12, 2008
    #5
  6. Kieran O' Leary

    CBFalconer Guest

    Just ensure that you load the two supplies separately. I.e. don't
    parallel the two supplies. Since their output voltages will not be
    equal, the result would be that one supplied all the current.
     
    CBFalconer, Aug 12, 2008
    #6
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