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DS320PR1601: pcie gen5 redriver

SHEKHA SHOUKATH
Intellectual 510 points
Part Number: DS320PR1601
Other Parts Discussed in Thread: , DS320PR810

Tool/software:

Hi,

We are developing a card using DS320PR1601 redriver, while routing it is noted that the track width is 6mils and intra pair spacing is4.5 mils.

Could somebody please tell whether any consideration has to be taken for maintaing width/spacing in PCIe Gen5?

Thanks and Regards,

Shekha Shoukath

  • 0
    TI__Mastermind 18890 points

    Hi Sheka,

    Trace width is related to impedance. The PCIe specification allows for between 68 and 105 Ohms of differential impedance but most commonly 85 Ohms is used. Depending on your stackup, the appropriate trace width may be somewhat different from one design to another. Impedance control of signal traces should be discussed in detail with your PCB designer/vendor.

    I don't think we have an explicit suggestion for intra-pair spacing, but I believe the general rule of thumb for differential signals is that intra-pair spacing should be somewhere around 1x-2x the trace width. On our DS320PR1601 EVM, the intra-pair spacing ranges around 1.2x-2.5x the trace width, depending on the position of the trace segments closer to the device BGA breakout or closer to the connectors.

    Spacing between differential pairs should be at least 5x the intrapair spacing.

    Let us know if you have more questions.

    Best,

    Evan Su

  • 0 in reply to Evan Su
    Intellectual 510 points

    Hi,

    I would like to know whether reducing the spacing between intra pair differential signals less than its track width result in any issue?

    Thanks and Regards,

    Shekha Shoukath

  • 0 in reply to SHEKHA SHOUKATH
    TI__Mastermind 18890 points

    Hi Sheka,

    I have not seen designs with intra-pair spacing of less than the individual trace width in my experience and would not recommend it in general. In extremely tight spots such as the device GBA breakout it's possible that the space could be limited, but there are usually options for necking the trace width in the software design rules that can help avoid this. Is there a specific reason or space constraint that you are thinking about?

    Best,

    Evan Su

  • 0 in reply to Evan Su
    Intellectual 510 points

    Hi,

     

     

     

    In order to attain characteristic  impedance of 85ohm, using Saturn pcb tool kit we calculated trace width and spacing as 6mils and 4.5 mils respectively.

     

    Why did you choose Roger over Megtron6  in DS320PR1601EVM?

     

    Which tool is used for SI analysis?

     

    Kindly provide ibis model of DS320PR1601.

     

     

     

    Thanks and Regards,

    Shekha Shoukath

  • 0 in reply to SHEKHA SHOUKATH
    TI__Mastermind 20901 points

    Hello Shekha,

    Megtron6 is used for the top and bottom layers of the DS320PR1601RSCEVM. Other materials such as Roger could be used as well - if desired.

    Keysight ADS is typically used for IBIS or IBIS-AMI modeling with our devices.

    I don't believe we have simulation models specifically available for the DS320PR1601, but the DS320PR810/822 IBIS-AMI model (smaller 8-channel device) should be a close substitute because there is similarity between their designs and performance. You can find this model in the same PCIE5-REDRIVERS-DESIGN folder, which can be accessed by request.

    Best,
    David