18.104.22.168 MDI Layout Guidelines
The Media Dependent Interface (MDI) connects the DP83869 to the transformer and the Ethernet network.
- MDI traces must be 50 Ω to ground and 100-Ω differential controlled impedance.
- Route MDI traces to transformer on the same layer.
- Use a metal shielded RJ-45 connector, and connect the shield to chassis ground.
- Use magnetics with integrated common-mode choking devices.
- Void supplies and ground beneath magnetics.
- Do not overlap the circuit and chassis ground planes, keep them isolated. Instead, make chassis ground an isolated island and make a void between the chassis and circuit ground. Connecting circuit and chassis planes using a size 1206 resistor and capacitor on either side of the connector is a good practice.