Notes On Board Wiring - Renesas R-IN32M4-CL2 User Manual

R-IN32M4-CL2 User's Manual: Board design edition
6.5

Notes on Board Wiring

Pay attention to the following notes when placing the wiring on the board.
• Avoid long wiring runs. We recommend to place the pulse transformer and the connector immediately as close as
possible to R-IN32M4-CL2.
• The components should be placed so that differential signal traces of TxP/N and RxP/N do not cross.
• Differential signal traces should be routed straight and as short as possible.
• Bends in lines should be at angles of at least 135 degrees. (Figure 6.7)
• Differential signal traces between the R-IN32M4-CL2, pulse transformer, and RJ-45 connector should be designed
with a differential impedance of 100Ω ± 10% and with an impedance of 50Ω relating to GND.
• Differential signal traces between the R-IN32M4-CL2 and pulse transformer, and those between the pulse
transformer and RJ-45 connector, should be equal in length. 0.5 mm is the maximum deviation. Each of the
differential signal traces in each pair must be as nearly equal in length as is possible.
• As well as equal lengths, the designs of signal lines for differential signals should be symmetrical. They should run
parallel to each other and be routed in the same layer. Placement of components, via holes, and the like should also
be symmetrical.
• Branches in signal lines act as stubs and should thus be avoided
• Place traces for differential signals with a separation from those for other signals. We recommend the width of the
gap to another signal line be at least five times the width of each differential signal trace.
• Differential signal traces should not cross edges of the power/GND planes. The GND plane is desirable as the layer
below the differential signal trace.
• Do not place any wiring, including any part of the power and GND planes, below the pulse transformer.
• Differential signal traces should be routed via as few via holes as possible. If via holes are essential, pay attention to
the following points.
We recommend via holes for the related power and GND planes to be placed near the signal vias. The width
-
between the via holes for a signal and GND should be equal to the distance between the layers to avoid a
discontinuity in the impedance.
- Metal planes close to the differential signal via holes could affect the impedance.
The diameter of a via hole should be almost equal to the width of the trace.
-
Figure 6.6 Example of Wiring for Differential Signals (1)
R18UZ0046EJ0200
Dec. 28, 2018
R-IN32M4-CL2
1 mm
N P
Shorten the N trace.
Traces for the differential signal in the above
space should be of equal length.
6. Gigabit Ethernet PHY Pins
Pulse transformer
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