Routing of receive and transmit differential pair is critical in systems where immunity to noise and robustness in general is required. The receive and transmit should be separated from each other by at least 1.27 mm and they should be routed to achieve the overall 100 ohm differential impedance and 50 ohm single-ended impedance. The isolation transformer should be placed within 2.5 mm of the RJ45 connector, and the filtering caps should be placed as close to the transfer as possible. Special attention must be paid to how the ground and power planes are routed. Do not extend the power plane under the Ethernet signals unless there is a solid ground plane between the differential Ethernet signals & the power plane. The ground plane should not discontinue under or near the differential signals between the MCU & the transformer.