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Original question:

SN75LVCP601: LTOL

SN75LVCP601: The circurt design about HIGH-SPEED DIFFERENTIAL I/O

Lumina Gui
Genius 3640 points
Part Number: SN75LVCP601

Tool/software:

Dear TI Engineer,

We have a question about the circurt design about the HIGH-SPEED DIFFERENTIAL I/O of SN75LVCP601. From the SN75LVCP601EVM user guide we found that the RX1P (Positive) signal is connected to the TX - (Negative) terminal of the Host (Male/female Connector), while the RX1N (Negative) signal is connected to the TX+(Positive) terminal of the Host (Male/female Connector).

Does it means that we need to follow this specification to design HIGH-SPEED DIFFENTIAL I/O?

Thanks,

Kind Regards

  • 0
    Guru 316760 points

    The positive/negative signals are exchanged twice, on both the male and female connectors, so the end result is that the signals are correctly passed through.

    This was probably done to simplify routing on the EVM. The two signals behave the same electrically, so it does not matter whether you exchange +/− on the redriver.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 20901 points

    Hi Lumina,

    Yes, this was done to simplify the EVM layout. Please find an older E2E post on the same topic here.

    Best,
    David

  • 0 in reply to David Waier
    Genius 3640 points

    Hi David,

    Now we have encountered a new problem, when we configured the equalization, de-emphasis, de-emphasis width parameter. When connected to a SATA hard drive, it was not recognized upon startup. If reconfigured them according to Table 2 on the EVM, the SATA hard driver can be recognized normally.

    Could you help check the risks of following the Default Configuration on EVM for the equalization, de-emphasis, de-emphasis width parameter? Or do you have any better suggestions for those configuration?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Mastermind 20901 points

    Hello Lumina,

    Please allow me to ensure that I understand your setup and observations correctly.

    In your system's design, you select some EQ, De-Emphasis, and De-Emphasis width control settings and you are not able to detect your SATA drive. Could you please detail which EQ, De-Emphasis, and De-Emphasis width control settings you use?

    I would not say that there are risks to the 'Default' configuration for the EVM relative to any particular application. These 'Default' settings select an EQ boost of 0dB (low EQ boost), which may be suitable for applications with shorter traces.

    Best,
    David

  • 0 in reply to David Waier
    Genius 3640 points

    Hi David,

    We encountered a Fail during SI testing, mainly due to the amplitude being too wide causing edge compression. We believe that the driving capability of SN75LVCP601 exceeded the upper limit and caused the issue.

    Can the driver capability be reduced by setting equalization, de emphasis, and de emphasis width parameters?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Mastermind 20901 points

    Hello Lumina,

    Please try reducing the de-emphasis of the SN75LVCP601's TX driver by setting DE1/DE2 to either -2dB or -4dB. The EVM default should be 0dB, which is what I'm assuming is the setting you are currently using.

    Best,
    David