DP83867CSRGZR.B datasheet(114/129 Pages) TI2

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Figure 8-10. Avoiding Stubs in a Differential Signal Pair

Signals on different layers must not cross each other without at least one return path plane between them.

Coupling between traces is also an important factor. Unwanted coupling can cause cross talk problems.

Differential pairs must have a constant coupling distance between them.

For convenience and efficient layout process, start by routing the critical signals first.

8.4.1.2 Return Path

A general best practice is to have a solid return path beneath all signal traces. This return path can be a

continuous ground or DC power plane. Reducing the width of the return path width can potentially affect the

impedance of the signal trace. This effect is more prominent when the width of the return path is comparable to

the width of the signal trace. Breaks in return path beneath the signal traces can be avoided at all cost. A signal

crossing a plane split can cause unpredictable return path currents and can likely impact signal quality as well,

potentially creating EMI problems. See Figure 8-11

Figure 8-11. Differential Signal Pair-Plane Crossing

8.4.1.3 Transformer Layout

There can be no metal layer running beneath the transformer. Transformers can inject noise in metal beneath

them which can affect the performance of the system.

8.4.1.4 Metal Pour

All metal pours which are not signals or power can be tied to ground. There can be no floating metal on the

system. There can be no metal between the differential traces.

DP83867CS, DP83867IS, DP83867E

SNLS504F – OCTOBER 2015 – REVISED JANUARY 2025

www.ti.com

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