DP83630 MDI Connections

Hello,

Our reconmendation for MDI trace length is to keep the MDI traces as short as possible(see highlighted text).

For example, on the DP83630 EVM modules we used MDI trace lengths in the 2 inch range. Regardless of the

trace lengths you end up using, please follow the other MDI considerations as closely as possible.

Thank you,

John

2.1 PCB LAYOUT CONSIDERATIONS

• Place the 49.9 ohm,1% resistors, and 0.1μF decoupling

capacitor, near the PHYTER TD+/- and RD+/- pins and via

directly to the Vdd plane.

• Stubs should be avoided on all signal traces, especially

the differential signal pairs. 

• Within the pairs (e.g. TD+ & TD-) the trace lengths should

be run parallel to each other and matched in length.

Matched lengths minimize delay differences, avoiding an

increase in common mode noise and increased EMI. See

• Ideally there should be no crossover or via on the signal

paths. Vias present impedance discontinuities and should

be minimized. Route an entire trace pair on a single layer

if possible.

• PCB trace lengths should be kept as short as possible.

• Signal traces should not be run such that they cross a

plane split. See Figure 4. A signal crossing a plane split

may cause unpredictable return path currents and would

likely impact signal quality as well, potentially creating EMI

problems.

• MDI signal traces should have 50 ohm to ground or 100

ohm differential controlled impedance. 

Hello, thank you for your prompt reply.

I have one additional question regarding this description as below;

Do you have any particular tolerance on the trace length difference between each TD+ & TD- or RD+ & RD- pair?

Thank you in advance for your information.

Best regards,