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TUSB4020BI: USB_VBUS connection for USB Power Delivery application

K.Yaita
Guru 29720 points

Part Number: TUSB4020BI
Other Parts Discussed in Thread: TPS65987D

Hi Team,

My customer considers using TUSB4020BI with TPS65987D for HUB application that supports USB Power Delivery.
Is there a recommendation where to connect USB_VBUS pin in this case?

The background of the question is it is possible VBUS is applied up to 20V with USB Power Delivery.
If 20V is applied to VBUS, it exceeds abs maximum rating of USB_VBUS (~1.4V) even if the following resister dividers are set.


Best Regards,
Yaita

  • +1
    TI__Guru 60870 points

    Hi Yaita,

    Depending on the application, it may be possible to use the LDO_3V3 from the TPS65987D to drive USB_VBUS.  The resistors in the divider network can be adjusted since the voltage is 3.3V instead of 5V.  The USB-VBUS pin should be around 500 mV when power is on.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Guru 29720 points

    Hi JMMN-san,

    I apologize for the lack of information on the HUB application.
    It is like a self-powered HUB so VIN_3V3 is always supplied and LDO_3V3 outputs 3.3V regardless of Type-C cable is attached/disconnected.
    Is there a recommendation where to connect USB_VBUS pin in this case?

    I also found the following TPS65987D GPIO events.
    Is it reasonable to apply the following "Port 0 Plug Event" and connect the GPIO to USB_VBUS?



    Best Regards,
    Yaita

  • 0 in reply to K.Yaita
    TI__Guru 60870 points

    Hi Yaita,

    Sorry I hit "resolved" by mistake.

    That GPIO looks like it would be a good fit to drive VBUS, I can move this thread to the PD team forum to confirm it.

    Is VBUS a set voltage in the system or can it vary from 5V to 20V?  The other option is to possibly use a comparator or a FET to drive USB_VBUS to the hub.

    Regards,

    JMMN

  • 0 in reply to JMMN
    Guru 29720 points

    Hi JMMN-san,

    VBUS can vary from 5V to 20V depending on USB PD negotiation.
    Could you move this thread to the PD team forum to confirm?
    I appreciate your kind support.

    Best Regards,
    Yaita

  • +1 in reply to K.Yaita
    TI__Genius 9210 points

    Hello Yaita, JMMN,

    Plug event will get asserted whenever there is a connection on the Type C port. I believe this can meet your requirement. 

    Hello JMMN,

    Could you describe the functionality of USB_VBUS signal? I believe its to monitor upstream vbus and propagate connect/disconnect to downstream ports and also to enable/disable US2 PHY. If yes, its not a good idea to connect USB_VBUS to Vbus of a PD capable upstream. Vbus line can be at 0V potential during power role swap and this will disconnect USB2 signal.   

    Thanks

    Prajith

  • +1 in reply to Prajith Cheerakkoda
    TI__Guru 60870 points

    Hi Prajith,

    Yes, the USB_VBUS is a detection input to the hub that lets the hub know when an active host is connected.  If USB_VBUS is low, the hub will not connect, but if USB_VBUS is tied high in the system when the host is not present it can lead the interoperability issues where the host and the hub get out of sync.  Also, the USB_VBUS is not designed to handle a wide variation in VBUS input voltages.  It sounds like the GPIO from the PD controller will work well here.

    Thanks,

    JMMN

  • 0 in reply to JMMN
    TI__Genius 9210 points

    Hello JMMN,

    Thanks for clarification, GPIO plug event should suffice. 

    Thanks

    Prajith