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TUSB8020B: TUSB8020B - hub sees devices (2.0) but drops intermittently

James Guyton
Prodigy 180 points

Part Number: TUSB8020B
Other Parts Discussed in Thread: AM6442,

Hi all, having some troubles with connecting usb devices using the TUSB8020B. We have a custom board with IC on it, with the AM6442 as the host processor.

We have an external USB port that we connect to when booting, then after boot we use a pair of HD3SS6126RUAR to reroute the USB2.0/3.0 signals to both the USB hub, and the USB hub to the external port as well as an onboard cell modem.

2.0/3.0 works fine from the AM64 out to the connector, when I swap to the USB hub the hub is detected at 2.0, but when mounting the USB drive or communicating with the modem, the devices disconnect.

I'm curious as to whether or not the crystal + loading capacitors are sufficient; using a ABM8-24.000MHz-12-B1U-T with 12pF might be a little low on the capacitance, swapping to 18pF I wasn't able to get the device to start, but subsequently dropping to 15pf and back to 12pf, I wasn't able to get the hub to be detected anymore.

What are other possibilities towards troubleshooting that I could attempt?

Image files are failing to be attached on the inital submit, so I'll try to find out how to get something uploaded here.

  • 0
    TI__Guru**** 161836 points

    I can not attach any files too this week.

    is this the test setup?

    AM6442 host --> USB connector--> HS3SS6126--> TUSB8020B--> modem

    12pf should be ok for crystal when USB2 works.

    For USB3, make sure SSTX from USB connector --> SSTX of HD3SS6126--> SSTX_UP of TUSB8020B.

    Best

    Brian

  • 0 in reply to Brian Zhou
    Prodigy 180 points

    Hi Brian, I'll try to diagram the connector:
    Setup at boot:
    (Host) 6442 -> HS3SS6126 -> HS3SS6126 -> connector 

    Setup after OS boot (and rootfs isn't a USB mount :P)

    (Host) 6442 -> HS3SS6126 -> TUSB8020B  -> HS3SS6126 -> connector (this is downstream port 1, USB2.0+3.0)

                                                                |

                                                            cell modem (downstream port 2, USB 2.0 only)



    I'm OK living without the USB3 after switching to the hub, but do need stable/reliable communication.

    I've had stable USB2 communication with the cell modem in the boot configuration, going out the connector and back onto the board to the device via a USB cable, to try to eliminate that as a potential source of issues.
    I can try to send some schematic snapshots/images via messaging if that helps?
    James

  • 0 in reply to James Guyton
    TI__Guru**** 161836 points

    Hi James:

       please send schematic and snapshots via  messaging.

    Best

    Brian