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Polycom using SN65LVPE502CPRUSB 3.0 redriver issue

Darren Mock
Prodigy 30 points


I am having an issue with a SN65LVPE502CPR USB 3.0 re-driver on our Dreamhouse board.  I’ve attached the appropriate schematic page.  The 3m cable is on the left side of the re-driver.  The trace length from the hub side to the re-driver is around 6.5”.  The circuit works without the re-driver, so I’m assuming the settings for the re-driver are incorrect.

 

3323.Millennium Dream House _ Pg08_ USB 3.pdf

 

Some other information:

 

1)      I verified that the DE, OS and EQ pins are truly at VCC/2 since they are also connected to the FPGA.

2)      The schematic incorrectly shows R196 as being DNP’d.  It is installed.

3)      When we tested without the re-driver, we shorted across C187, C189, C185 and C186.

4)      We tested with all 6 pins tri-stated, and all 6 pins pulled up.

 

I believe the issue is that the two channels shouldl be set differently, since the “trace” lengths on each end is different, i.e. Ch1 input  = 3m, Ch1 output = 6.5”, Ch2 input = 6.5”, Ch2 output = 3m.

  • 0
    TI__Guru* 76130 points

    Hello Darren,

    You need to populate AC coupling capacitors on RX1+/- lines (the left side of the redriver).

    You are right about the two channels can be set differently, but because your system works without the redriver then it should work also with the default settings which are leaving all the DE, EQ and OS pins floating.

    Can you try this.

    Regards.

  • 0 in reply to Elias Villegas M.
    TI__Expert 4011 points

    The customer says the following:

    We have DC blocking caps on the TX side of those lines on the Bob side (before the 3m cable).  The system will not work with all the control lines floating.  I have to tie DE1 high (Deemphasis = -6dB) in order for it to work.

    Let us know what might be wrong?

  • 0 in reply to JatanNaik
    TI__Guru* 76130 points

    Hello Jatan,

    Would you please elaborate more when they say "...the circuit works without the re-driver..."  Does that mean that they are replacing the re-driver with only wires?

    The DE, EQ and OS setting have to be selected according the system needs, does their application works when they tie DE to 3.3V ?  Is there a problem with this?

    Regards.

  • 0
    TI__Expert 4011 points
    Hi Elias,

    I am at Polycom right now—would you be available for a quick call?  Thanks.
     
    Regards,
     
    Jatan Naik
    Analog Field Applications Engineer
    Texas Instruments
    12357 Riata Trace Pkwy.
    Austin, TX 78727
    512-219-3052 (o)
    512-947-9099 (m)
    From: ELIAS VILLEGAS [mailto:bounce-1662752@e2e.ti.com]
    Sent: Tuesday, July 24, 2012 9:40 AM
    To: int_highspeed_interconn_forum@e2e.ti.com
    Subject: RE: [INT - High Speed Interface Forum] Polycom using SN65LVPE502CPRUSB 3.0 redriver issue
     

    Hello Jatan,

    Would you please elaborate more when they say "...the circuit works without the re-driver..."  Does that mean that they are replacing the re-driver with only wires?

    The DE, EQ and OS setting have to be selected according the system needs, does their application works when they tie DE to 3.3V ?  Is there a problem with this?

    Regards.

  • 0
    TI__Expert 4011 points
    Elias,
     
    Yes, the board worked when the redriver was bypassed with only wires.
    The customer says that the part works with DE1 high and the other setting pins floating.  However, they want to know why the settings would be the same for both directions since the Tx and Rx drivers are driving (and receiving) different trace/cable lengths?  How can they determine the proper settings for the other pins?
     
    Regards,
     
    Jatan Naik
    Analog Field Applications Engineer
    Texas Instruments
    12357 Riata Trace Pkwy.
    Austin, TX 78727
    512-219-3052 (o)
    512-947-9099 (m)
    From: ELIAS VILLEGAS [mailto:bounce-1662752@e2e.ti.com]
    Sent: Tuesday, July 24, 2012 9:40 AM
    To: int_highspeed_interconn_forum@e2e.ti.com
    Subject: RE: [INT - High Speed Interface Forum] Polycom using SN65LVPE502CPRUSB 3.0 redriver issue
     

    Hello Jatan,

    Would you please elaborate more when they say "...the circuit works without the re-driver..."  Does that mean that they are replacing the re-driver with only wires?

    The DE, EQ and OS setting have to be selected according the system needs, does their application works when they tie DE to 3.3V ?  Is there a problem with this?

    Regards.

  • 0 in reply to JatanNaik
    TI__Expert 6240 points

    Hi, Elias, Jatan,

    What's the root cause of the issue? My customer also meet the similar issue.

    Best Regards,

    Barry Xiao

  • 0 in reply to Barry Xiao
    TI__Guru* 76130 points

    Hello Barry,

    Please specify what is the issue and what is the set up of your customer, schematics will be good to have as well, how are they configuring the EQ and DE pins?

    Regards.