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  1. #1
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    Slef powered USB device

    Hi
    I designed the usb device as slef powered without VBUS from USB Connector.
    1) If My board is connected to USB Hub or PC USB Port, USB HUB or PC USB Port is damaged. It isn't operated again.
    : Board is using cicular connector(=12pin) in stead of the standard USB Connector
    : Board CPU is always connected Internal 5V of board as soon as Circular cable connection
    What is a root cause?
    --> connected PC USB or HUB USB
    Circular cable connection --> Board Power On --> HUB/PC usb was broken after the repeat testing


    2) So, I added USB Switch in my board.
    ---> Connected PC USB or HUB USB
    Circular connection --> Board Power On --> 1[S] Delay in put to USB Enable pin --> USB Switch D+/D- connection enable --> USB Detection OK --> No Problem

    Could you advise in detail?

    Thanks

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  2. #2
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    Re: Slef powered USB device

    What's the voltage on the USB signaling lines? 3.3V or 5V? Is the ground of the USB connector (reference potential) connected to your self powered circuit?

    A block diagram of your circuit, or a few pics could be helpful to get a better view on the problem.


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  3. #3
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    Re: Self powered USB device

    Doesn't explain USB interface damage, but USB specification require a self-powered device to monitor the VBUS line and not to drive to bus lines before a voltage has been detected.


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  4. #4
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    Re: Slef powered USB device

    Dear FvM
    Yes, your comment is correct.
    USB Specification is required as your comments.
    But , If USB requirement isn't applied, it happen to the similar failure or problem as HUS dead or damage.
    There isn't an explaination in detailed.
    for example) If CPU VBUS Pin is always applied to 5V regardless USB Cable connection, What is a electrical problem/timing sequence as soon as USB cable connection?
    CPU always recognize USB Cable connection because CPU VBUS Pin(USB Connection VBUS Pin is No connected) is always applied to 5V.
    the root cause is in-rush(?) current on D+/D- ?
    I want to know the detailed information why USB HUB /PC USB was broken. I can't find out USB Specification.
    I added the solution using USB Switch with enable delay time(~1S) without the exact understanding.
    1[S] is a long time. Generally, How long time is drive D+/D- after VBUS is connected (or detected) when VBUS from pc/HUB is delivered.
    Thanks



  5. #5
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    Re: Self powered USB device

    USB specification requires short circuit strength of USB receivers, any USB data or power line against each other. In so far the hub shouldn't be damaged even if the device is controlled incorrectly.

    I think the most likely explanation is this: Your 12 pin connector misses the feature of power/ground connecting first but has been hot-plugged though.


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  6. #6
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    Re: Slef powered USB device

    How long time is the interval between 5V and D+ Pull for safety operation?
    Where is explained in USB Specification?
    If the requirement isn't applied, What is a problem as electrical side?

    Hi FvM
    Please explain in detailed.
    Your 12 pin connector misses the feature of power/ground connecting first but has been hot-plugged though.
    If the device is controlled incorrectly, what is a electrical problem ?

    Hi ArticCynda

    Attached the some picture.
    Added USB Switch : After internal 5V is delivered to CPU USB Pin, D+/D- is connected after 1[S] .

    Thanks



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  7. #7
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    Re: Slef powered USB device

    Hi
    If I don't use VBUS detection when board is connected to HUB Or PC USB ,
    (no connector VBUS of hub )
    What is a problem ? Maybe, it is flyback voltage from board to hub or PC ..
    I found out the improvement soultion but don't find out the root cause when hub or PC USB was brokend.
    Could you inform the expected root cause?
    Thanks



  8. #8
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    Re: Self powered USB device

    VBUS detection is a requirement for compliant operation, not particularly marked as a protection means. As I already mentioned, the infinite short circuit endurance of USB transceivers should prevent damage. Of course I don't know if the specification is kept by your equipment.

    It's guaranteed with USB connectors that ground and VUSB connect before and disconnect after signal lines during attachment and detachment (hot plug). If your connector doesn't have this feature, it must not be hot-plugged. Or at least solid overvoltage protection beyond the USB standard must be provided.


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