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TUSB2046B: understanding USB device states

Roland
Prodigy 20 points
Part Number: TUSB2046B
Other Parts Discussed in Thread: TPS2042

Dear Forum

 

The sole purpose of my application for TUSB2046 is to make a connected USB-device boot-up by emulating a USB-host. There will be NO DATA COMMUNICATION.

The USB-device is externally powered.

This kind of behavior was previously confirmed with random off the shelf USB-hubs that were powered without connecting them to a USB-host PC.

Assuming that this behavior would be reproducible with ANY USB-hub, I designed the following circuit based on TUSB2046B.

The behavior that I now observe is somehow unexpected. In a few words - the USB-device only starts booting-up when the hub is or was connected to a USB-host.

I have tried to depict the sequence and behavior for a clear understanding.

The circled numbers indicate the sequence of connecting/disconnecting the respective wire

 It remains unclear, why the device would not boot-up when the hub is not connected to the USB-host?

If this cannot be answered - how can I emulate a USB-host to the hub (the application will have no access/connection to a PC)

I hope that I was able to describe the issue that I am facing in a clear and consistent manner and that someone out there comes up with a hint or even a solution.

  • 0
    TI__Guru* 93650 points

    Hi Roland,

    We are looking into this and will have feedback tomorrow.

    Regards,, Nasser

  • 0
    TI__Guru 60865 points

    Hi Roland,

    USB hubs are "dumb" devices, so they have no capability to emulate DP/DM signaling from a USB host while unconnected.  What kind of behavior does the device require to boot up?  Is it just looking for VBUS to go high?  Hubs can either permanently enable downstream port power (VBUS) on their ports or implement power switching so that the host sends commands to the hub to enable / disable port power.  Your application implements downstream port power switching with the TPS2042 device, but it sounds like it would be better to permanently enable VBUS on the downstream port.  Can you try tying the power switch enable to active and see if it resolves the issue?

    Regards,

    JMMN

  • 0 in reply to JMMN
    Prodigy 20 points

    Hi

    Thanks for your quick reply. It's ok for the hub to be "dumb" because I'm not asking a lot of it ;-)
    I tried what you suggested. Unfortunately, it did not change the device's behavior.

    So the question still remains - what makes the hub behave like it does.

    I mean, for it to behave like want it to (to boot-up my device), it works if it get's connected to a USB-host and then disconnected again. But once I power-down the hub, it goes back to the other state, where it does not boot-up my device.

    Is there a way to make the hub "think" it is connected to a host by using some passives?

    Thanks
    Roland

  • 0 in reply to Roland
    TI__Guru 60865 points

    HI Roland,

    What is your device looking for on the DP/DM/VBUS lines to boot up?  If I had some idea what states where needed I might be able to point you in the right direction.  The TUSB2046B has external pulldowns on DP/DM lines whether the hub is connected to the host or not.  

    Regards,

    JMMN