10.4.2 Ethernet Design Layout Recommendations
When designing the Ethernet interface, consider the following recommendations:
- ETH_TX_P, ETH_TX_N, ETH_RX_P and ETH_RX_N should be routed on the top layer without any vias.
- ETH_TX_P and ETH_TX_N should be matched in length to within 120 mils.
- ETH_RX_P and ETH_RX_N should be matched in length to within 120 mils.
- ETH_TX_x and ETH_RX_x must be symmetrical in shape and routing path.
- Place the TX_P and TX_N signals at least two times the trace width away from other signals for noise immunity.
- Place signals at least two times the trace width away from any copper plane.
- Place the TX and RX signals at least three times the trace width away from other signals for noise immunity.
- Check that the ETH_TX_x and ETH_RX_x
line impedance is the same for all signal layers.
Recommended differential impedance for net: 100Ω ± 5%.