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DP83867E: Clarification on MDI Trace Impedance Requirements for DP83867E

Conor
Guru 12155 points
Part Number: DP83867E

Tool/software:

Hi,

I have questions regarding the MDI trace impedance requirements outlined in the datasheet (Rev. E), which states:

"MDI traces must be 50Ω to ground and 100Ω-differential controlled impedance."
(MDI traces should have 50Ω single-ended impedance to ground and 100Ω differential impedance.)

It is challenging to meet both single-ended 50Ω and differential 100Ω requirements simultaneously in PCB design. Could you please provide clarification on the following points?

  1. Tolerance: What is the acceptable tolerance range for single-ended 50Ω and differential 100Ω impedances (e.g., ±10%)?
  2. Priority: Should we prioritize achieving differential 100Ω over single-ended 50Ω, and what are the potential trade-offs?
  3. Issues with 100Ω Only: What specific issues might arise if the design focuses only on differential 100Ω and does not meet single-ended 50Ω?
  4. Guideline Differences: Why do some parts of the guidelines specify "differential 100Ω" while others require both "single-ended 50Ω and differential 100Ω"

Thanks,

Conor