SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
2.2.3.2. Gigabit Ethernet Schematic Example (Discrete Magnetics)
If discrete magnetics are used instead of a RJ-45 Ethernet jack with
integrated magnetics, special care has to be taken to route the signals
between the magnetics and the jack. These signals are required to be
high voltage isolated from the other signals. It is therefore necessary to
place a dedicated ground plane under these signals which has a minimum
separation of 2mm from every other signal and plane. Additionally, a
separate shield ground for the
LAN
device is needed. Try to place the
magnetics as close as possible to the Ethernet jack. This reduces the
length of the signal traces between the magnetics and jack.
Figure 9: Separation of Magnetics Ground