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TUSB1046A-DCI: Request for TDR differential Impedance Measurement of the TUSB1046A-EVM TX and RX high speed pins

Guru 19775 points
Part Number: TUSB1046A-DCI

Hi Team,

Could you please share us the TDR differential impedance measurement data of the TUSB1046AEVM TX and RX pins ?

Customer says they fail the USB requirement that differential impedance drop down to 65 ohm (MIN) at the device.

We want to clarify whether this drop is due to their board design or the device internal parasitics.

Best Regards,

Kawai

  • Kawai-san

    Differential input impedance for the USB RX is 72 to 120ohm (present after a GEN2 device is detected on TXP/TXN) and differential impedance of the driver is 75 to 120ohm.

    Have they done TDR measurement of the bare board?

    Thanks
    David
  • Hi David-san,

    They haven't done the measurement with their bare board since they don't have one. All boards IC mounted.

    > Differential input impedance for the USB RX is 72 to 120ohm (present after a GEN2 device is detected on TXP/TXN)

    If TUSB1046 is used in receiver side, device TX is connected to USB GEN2 PHY.

    So, the impedance measurent result shouldn't drop down to 65 ohm. However, it is dropped outside the datasheet spec.

    Now, when measureing TDR on transmitter side, I believe there is no USB RX connection on the connector. In this case, how much is the ouput impedance of USB TX ?

    i.e. How can they test the impedance requirement ?

    It would be very helpful if you could take the TX/RX TDR data of the EVM for us. If it is inside the USB CT requirement, we can prove that it is their board layout problem.

    Best Regards,

    Kawai

  • David-san,

    Please allow me to get into this discussion.

    We measured the differential impedance using a TDR.
    The impedance was 100 ohm on the input connector. However, it dipped as low as 63 ohm
    on the IC pad point. 
    The impedance was influenced both PCB and device, because the device was mounted on the board.
    One way, to know how PCB and device influence this dip, de-solder the device. However, in worst scenario,
    board may get damage.

    An alternative way is to measure impedance using an evaluation board. If an evaluation board does not
    show such impedance dip, we can say that the PCB is major contributor of this dip.

    Therefore, we ask you to measure impedance of the EVM.
    Please provide us the impedance profile of an EVM.

    Mita

  • Kawai-san, Mita-san

    Could you please provide more detail on their impedance measurement setup? Is the TDR done with TUSB1046 in the off state? If so, please refer to the Common-mode input impedance with termination disabled (DC) in the TUSB1046 data sheet. The minimum is 25Kohm, and typical measurement is 56Kohm.

    Thanks
    David
  • Hi David-san,

    I can send you the TDR data. I will requeset friendship so that I can send you message.

    In the past model, they had a design without redriver which differential impedance met the USB requirements.

    The point is that there is a impedance dip which drops down to 63 ohm at the device pin, package, or internal parasitics.

    Best Regards,
    Kawai
  • Kawai-san

    I accepted your request, would you please provide a detailed TDR measurement setup?

    Thanks
    David
  • Hi David-san,

    Thanks for your support.

    I have sent you a message, could you please cnfirm and advise us ?

    Best Regards,
    Kawai
  • Hi David-san,

    Thanks for your kind support.

    Best Regards,
    Kawai