Cirrus Logic AN83 - Manual (Page 43)

AN83
AN83REV3 43
The 20.000 MHz crystal traces should be short,
have no via, and run on the component side.
Biasing resistor at RES pin of the CS8900A: A
4.99 K
Ω resistor is connected between pins RES
(pin #93) and AVSS3 (pin #94) of the CS8900A.
This resistor biases internal analog circuits of the
CS8900A, and should be placed as close as possi-
ble to RES pin (pin #93) of the CS8900A.
Routing of the 10BASE-T signals: Four signals
are used for 10BASE-T communication, two dif-
ferential transmit signals and two differential re-
ceive signals. An isolation transformer is placed
between the transmit and receive traces and a RJ-45
(modular phone jack) connector. The isolation
transformer should be placed as close as possible to
the RJ-45 connector. Both transmit and receive
signal traces should be routed so they are parallel
and of equal length. The signal traces should be on
the component side and should have direct and
short paths. The widths of the receive signal traces
should at least be 25 mil. while widths of the trans-
Figure 31. Placement of Decoupling Capacitor (Bottom side, under CS8900A)
Figure 32. Routing of Decoupling Capacitor (Top side, component side)