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Original question:

TPS2544: Mode switch related issue ： CDP mode to SDP1 mode

TPS2544: Mode switch related issue ： USB eyes waveform fail

user5865831
Prodigy 30 points
Part Number: TPS2544

         The USB eyes waveform will be fail when we used the TPS2544 on our MB. And if remove it, the result is pass.  Please check the attachment to get the waveform.

         The USB  signal Line length is 2840Mils on our mother board, and the Max spec can be to 6000mils.

          I think the reason is  IC attenuation.

          Do you have any suggestion for us?

TPS2544 Eyes waveform:

         

Remove TPS2544 Waveform:

  • 0
    TI__Mastermind 26650 points
    I do see the expected 0.2 to 0.3dB of insertion loss based on this capture and about the expected amount of bandwidth compression which shows in the edge rate and should show up as an increase in ISI.

    I think that this eye diagram shows higher ISI than should be generated by the TPS2544 and I think that it might be due to impedance mismatch somewhere in the system.

    How well controlled is the impedance match on your motherboard?
    Do you have secondary pin diodes or some other ESD structure in the system?

    I don't see any indication that the TPS2544 is the cause of this failure, it is more likely a system level interaction with the SP2544
  • 0 in reply to Chuck Branch
    Prodigy 30 points

    This USB impedance is 80 ohm, that have matched the AMD SPEC. And the rang is +/-10%.

    we have removed the ESD, The waveform is still failure.

    Could you help to provide the layout guide about the TPS2544? I want to double check it.

    TPS2544 SCH:

  • 0 in reply to user5865831
    TI__Mastermind 26650 points
    80 ohms is not a typical routing impedance. Almost every USB part is 90 ohms and this is the recommendation of the TPS2544. This is most likely the cause of the compliance failure that you are seeing.

    The EVM users guide (www.ti.com/.../slvu660a.pdf) has layout guidelines in section 4.2.