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TUSB8020B: TUSB8020 cannot detect downstream device after plug in

Ben Kuo
Expert 7670 points

Part Number: TUSB8020B

Hi JMMN,

I create a external E2E post and loop customer in for issue discussion. We can close internal E2E post as below link and move discussion to this post.

https://e2e.ti.com/support/interface-group/interface---internal/f/interface---internal-forum/1078464/tusb8020b-cannot-find-usb-device-after-plug-in/3996445#3996445

Could you help to confirm if there are any risk on below item?

> we short pin #28 and #29 to CPU side directly without ac coupling cap. Is there any risk when no ac coupling cap on USB hub 3.0 Tx signal?

> If yes, is there any register to modify and allow this hardware design(no ac coupling cap) ?

Regards,

Ben

  • 0
    TI__Guru 60870 points

    Yes, the AC caps are required for the TX pins.  The hub *may* work without them but it would not be reliable. There is no way to change this.

    Has the USB 2.0 function been verified?

    Regards,

    JMMN

  • 0 in reply to JMMN
    TI__Expert 7670 points

    Hi JMMN,

    We have try to debug by BIOS and after enable xHCI compliance mode at CPU side. There are no error message pop out.

    We want to disable compliance mode of TUSB8020 to verify it.

    Could you let me know how to disable compliance mode of TUSB8020?

    Thanks.

    Regards,

    Ben

           

  • 0 in reply to Ben Kuo
    TI__Guru 60870 points

    Compliance mode cannot be disabled on the upstream port of the hub.  Compliance mode can be disabled on the downstream ports by enabling the DSPORTECR bit in the registers by EEPROM or SMBUS/I2C host: