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Question about ddr data lines routing rules 50ohm impedance of K2H.

Denny%20Yang99373
Expert 3805 points

Hi team,

Our K2H ddr design guide about data lines routing rules give below message.

But the driver of SDRAM recommended is 34/40ohm.

If customer use your recommended 34ohm / 40ohm for driver, how about changing the transmission traces into 40ohm single-ended for a better match?

thanks!

BR,
Denny

  • 0
    TI__Mastermind 42545 points
    Hi Denny,
    These impedance decisions are dependent on the preferences of the customer. We provide the impedances that we have used in our validation. Whichever you choose, you need to verify it through IBIS simulation. Some impedance tradeoffs are discussed in the JEDEC UDIMM spec. It also discusses different impedance strategies for various topologies. Using lower impedance for your traces could have other effects. If you choose a topology that allows the routing of 40 ohm traces at a narrow trace width to minimize the spread due to the spacing requirements, any signals that require 50 ohms may be too narrow to route.
    Regards,
    Bill