DVD Recorder User Manual
13
Appendix B: PCB Layout Suggestion
The following PCB layout guidelines should be followed
to obtain a good PSRR and EM immunity resulting in
good electrical performance. Things to note:
1. The ground plane should be continuous under the
part, but should not extend under the shield trace.
2. The shield trace is a wide, low inductance trace back
to the system ground. CX1, CX2, CX3, and CX4 are
optional supply lter capacitors; they may be left out
if a clean power supply is used.
3. Vled can be connected to either unfiltered or un-
regulated power supply. If Vled and Vcc share the
same power supply, CX3 need not be used and the
connections for CX1 and CX2 should be before the
current limiting resistor R1. In a noisy environment,
including capacitor CX2 can enhance supply rejec-
Figure 16. PCB layout suggestion.
The area underneath the module at the second layer,
and 3 cm in all directions around the module is dened
as the critical ground plane zone. The ground plane
should be maximized in this zone. Refer to application
note AN1114 or the Lite-On Technologies' IrDA Data Link
Design Guide for details. The layout below is based on a
2-layer PCB.
tion. CX1 is generally a ceramic capacitor of low in-
ductance providing a wide frequency response while
CX2 and CX3 are tantalum capacitors of big volume
and fast frequency response. The use of a tantalum
capacitor is more critical on the Vled line, which car-
ries a high current. CX4 is an optional ceramic capaci-
tor, similar to CX1, for the IOVcc line.
4. Preferably a multi-layered board should be used to
provide sufficient ground plane. Use the layer un-
derneath and near the transceiver module as Vcc,
and sandwich that layer between ground connected
board layers.
Refer to the diagram below for an example of a 4
layer board.
TOP LAYER
CONNECT THE METAL SHIELD AND MODULE
GROUND PIN TO BOTTOM GROUND LAYER.
LAYER 2
CRITICAL GROUND PLANE ZONE. DO NOT
CONNECT DIRECTLY TO THE MODULE
GROUND PIN.
LAYER 3
KEEP DATA BUS AWAY FROM CRITICAL
GROUND PLANE ZONE.
BOTTOM LAYER (GND)