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how much power usb-otg devices need.

amit sinha
Prodigy 30 points

When I am connecting USB1.0 hub (it is bus powered as well as self powered.), I am unable to communicate with the device attached to the other side of the hub if the hub is in bus powered mode but when i supply 5V power supply to the hub, communication happens properly.

I am suspecting hub is not driving enough current for the down-stream devices.

Pls let me know how much is the power needed in case of OTG.

  • 0
    Guru 316640 points

    OTG devices supply as much power as they want to. I guess your hub isn't in the device's TPL.

  • 0 in reply to Clemens Ladisch
    Prodigy 30 points

    No. If that would not have been in TPL , it would not have even worked when i supplied 5V (making it self powered.). But, it works when i supply 5V externally to the hub. So there must be some difference coming when the hub is bus-powered and when it is self-powered (and in turn not sufficient for the down stream devices).

    Let me know if there is some difference in power supply limit between OTG and USB standard. That might help me in concluding.

  • 0 in reply to amit sinha
    Guru 316640 points

    The OTG standard does not require any minimum power; the designer is responsible for supplying enough for any device in the TPL.

    It's possible that your OTG device was not designed for bus-powered hubs, or that it does not enforce its TPL.