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TUSB8020B: VBUS Power Switch Implementation

Pang
Expert 2415 points
Part Number: TUSB8020B

Hi Ti,

I have a question on the USB3.0 hub that i want to implement in the design for for extra ports.

We are using Marvell CPU and that interface would come to TUSB3020B and then the down stream ports i am connecting to the LTE modules for the USB interface, which only needs the USB3.0 interface. Not power switching is required as we are not using USB connectors. Separate power management is done for the LTE modules.

For this kind of application do i need to have the power switch and the GNAGED and FULLPWRMANGEMNT pin to be grounded or left open, please see below.

  • 0
    TI__Guru 60870 points
    No, if the ports are permanently connected you do not need to use the PWRCTLx outputs or the OVERCURx inputs. The setting of GANGED is a don't care in the this case and FULLPWRMGMTz should be pulled high.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Expert 2415 points
    Yes permanently connected to USB interface between CPU and LTE modules for GANGED and FULLPWRMGMTz if pulled low in the above case what happens?
  • 0 in reply to Pang
    TI__Guru 60870 points
    If you pull FULLPWRMGMTz low, the hub will report in its descriptors that it supports per port power management. While this is incorrect, I have not seen any USB hub drivers that actually implement any behavior differently based on whether per port power management is enabled or not.

    Regards,
    JMMN
  • 0 in reply to JMMN
    Expert 2415 points

    I would like to confirm that the USB 3 interface to the LTE module from CPU has to be swapped for RX to TX and TX to RX, so it has to be swapped on both ends ( 1:2 mux) of the USB3.0 hub ports right? 

    CPU is the host and LTE is device, directly connected all the time, external power for the LTE and USB would be used. Please help to confirm as it's important for the design.

     The attached is for reference as what we had for the original design for the USB between CPU and module, now we want to add the hub in between.

  • 0 in reply to Pang
    TI__Guru 60870 points
    Hi,

    The TUSB8020B is not like a mux or splitter. It is an active part of the USB system, so RX of the upstream port goes to TX of the host and TX of the upstream port goes to the RX of the host. Likewise, the RX of the downstream port goes to TX of the device and TX of the downstream port goes to RX of the device. It would look like the bottom drawing in the photo that was attached.

    Regards,
    JMMN