5.6.1 Component Placement considerations
Components placement can affect signal quality, emissions and can decrease EMI problems.
1.
If the magnetics are a discrete component than the distance from the connector RJ45 should be kept to under 25mm of
separation.
2.
To decrease EMI problems the distance between magnetics and Phy should be at least 25mm or greater to isolate the PHY
from magnetics.
3.
The distance between Phy and RJ45 connector should always be within 200 mm.
4.
The differential transmit pair should be keep at least 25mm from the edge of PCB up to the magnetics. If the magnetics are
integrated into RJ45 the differential pair should be routed to the back of integrated magnetics RJ45 connector , away from the
board of PCB.
5.
The 49.9 ohm pull-up resistors on the differential lines should be placed within 10 mm of the Phy device
6.
The signals RX & TX should be independently matched in length to within 6mm
See the following figure
Figure 9
The PHY used in the module is the
SMSC LAN8710
.
For more information refer to the
SMSC Ethernet Physical Layer Layout Guidelines
.
For a list of magnetics selected to operate with the SMSC LAN8710, refer to the Application note
AN 8-13 Suggested Magnetics.
* this is figure 2.3 from SMSC Ethernet Physical Layer Layout Guidelines
D N :
2 8
