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AM3352: Using DRVBUS and D+/D- independent on same Interface

Sebastian Graf
Prodigy 100 points

Part Number: AM3352

Is it possible to use an embedded partner device without supply just over USB0_D+ and D- line, and controlling an external 5V charging connector via USB0_DRVBUS pin independent. So 5V can be switched either on and off while the interface to D+ and D- are always active?

 

USB_DRVBUS_DP_DM.jpg

  • 0
    TI__Genius 11610 points

    Hello Sebastian,

    Thank you for reaching out to our Sitara MPU Hardware Applications support team !

    The AM335x USB topic owner is getting back from his holiday tomorrow.

    Please expect his response by end of this week.

    Your  patience is appreciated !

    Best Regards,

    Anastas Yordanov 

  • 0
    TI__Mastermind 25050 points

    Hi Sebastian,

    An USB device, even being self-powered, may need to "see" the VBUS ramping up on it's own VBUS-sense pin. This is part of Session Start and Session End protocols described in USB 2.0 standard. 

    It is roughly happening like that:

    Host port must have VBUS active (via hardware-controlled DRVVBUS signal and a power switch);

    VBUS propagates to device;

    device sees the VBUS and pulls up 1.5 k ohms on one of D+/D- wires;

    host sees this connection, and after a 100 ms delay asserts USB RESET signaling (SE0 etc.).

    Best Regards,

    Stan

  • 0
    Prodigy 100 points

    Thanks Stan for the quick answer.

    I understand your answer and your explanation of the USB standard. I am aware, that my idea is not totally what the interface has been designed for: Host and Device have some reuirements to the VBUS line. In my situation I have to deal economizing with GPIOs and I already use both USB interfaces for an embedded communication. Now I need an additional switchable 5V-output (based on or similar to USB). So there is the idea, to use the power control line of one USB interface for external power while the data lines are used for the (totally independent from power out) embedded communication. Even if not USB conform this would only work if the internal interface does not relate both functions to each other (e.g. Data line can only be active while power line is enabled). 

    The intension of my question is to understand this relation inside the interface.

  • 0 in reply to Sebastian Graf
    TI__Mastermind 25050 points

    Hi Sebastian,

    You can use off course DRVVBUS to control external power switch and use it for another purpose. See the excerpt from TRM and make sure DRVVBUS behavior is fine for you. Note that DRVVBUS is controlled solely by hardware.

    What I'm saying is that if your USB device has a VBUS-sense pin, you may need to use it to sense the switchable VBUS from SoC's USB controller via the power switch. 

    Regards,

    Stan