Crystal LAN CS8920, Техническое справочное руководство, Страница: 22 / 67

AN84REV1 22
CS8920 Technical Reference Manual
2.2.2.1 Two layered printed circuit
board (PCB)
A two layered PCB has signal traces on the
component and solder side of the PCB. Fill
unused areas with copper planes.
Typically, planes on the component side of
the PCB are connected to ground and those
on the solder side are connected to VCC or
+5 volts.
Provide each pair of power pin with a 0.1
µ
F bypass capacitor. Place each bypass
capacitor as close as possible to the
corresponding power pin pair. Connect the
capacitor to the pads of the power pins by
short, wide traces, the other end of these
traces should be connected to VCC and
GND planes. Figure 2.2.2 and Figure 2.2.3
illustrate ground and power (Vcc) plane
connections, respectively
.
2.2.2.2 Multi-layered printed circuit
board
A multi-layered printed circuit board (PCB)
typically has separate ground and power
(VCC) planes. Multi-layered PCBs are
required when the component and trace
density is high. Often discrete components
like resistors and capacitors are placed on
the solder side of a printed circuit board.
For a multi layer PCB with all components
on one side of the board, follow the power
connection guide lines as explained in
section 2.2.2.1. Instead of connecting the
ground and VCC to the copper fills on the
component and solder side of the board,
connect them to the internal ground and
VCC planes. Figures 2.2.4 through 2.2.9
show the four layers of the four-layer card.
For a multi-layered board the discrete
components are to be placed on the solder
side of the PCB, bypass capacitors for the
CS8920 can be placed on the solder side of
the PCB. Each bypass capacitor should be
placed beneath the CS8920 and closest to
its corresponding power pin pair. Figures
2.2.10 and 2.2.11 illustrate the placement
and routing of one bypass capacitor.