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c5505 USB VBus Detection

Gerhard48236
Prodigy 185 points

Anybody out there who has a clue about the meaning of the VBUS bits of the Device Control Register (DEVCTL) ?

VBUS 0-3h      These read-only bits encode the current VBus level as follows:

0                      Below Session End.

1h                    Above Session End, below AValid.

2h                    Above AValid, below VBusValid.

3h                    Above VBusValid.

What are the corresponding voltage levels on the Vbus line ?

An additional hardware question: Should the VBUS pin of the DSP directly connect to the VBUS line of USB or is there a series resistor allowed or recommended ?
If so, which maximum value ?

thx a lot
Gerhard

  • 0
    TI__Mastermind 23785 points

    This is the read only of the status of the VBus relative to the various thresholds concerned in session control.

    Session End threshold id required to be between 0.2V and 0.8V.

    Session Valid threshold for an 'A' device required to be between 0.8V and 2V.

    VBus Valid threshold is required to be between 4.4V and 4.75V.

    This is the internal connection between the USB transceiver and controller.

    Regards,

    Steve

     

  • 0 in reply to Steve Tsang
    Prodigy 185 points

    Thanks Steve,

    I have measured the actual thresholds and they are as follows:

    Session end: 0.47 V
    AValid:  1.33V
    VBus Valid: 4.6V

    The problem is, that a USB connect is triggered by the Vbus valid threshold and that we had issues of devices not recognizing that level, just because the measured voltage on the bus is 4.5 V.

    When changing the connect condition from "level 3" to "level 2 OR 3" it works well, but we are not sure about the disadvantages in doing so.

    Any ideas instead ?

    Thx
    Gerhard

  • 0 in reply to Gerhard48236
    TI__Mastermind 23785 points

    What speed are you supporting? Are you also supporting On-the-Go?

    Steve

  • 0 in reply to Steve Tsang
    Prodigy 185 points

    Sorry for late reply, I was out of office till now.

    We support high speed, device only.

    thx
    Gerhard