Pcb Component Placement - Intel PXA27 Series Design Manual

PCB Design Guidelines
Figure 2-3. Recommended I/O Power Plane Layout
VCC_MEM
2.2.2

PCB Component Placement

PCB component placement requires careful planning to consider how signal and power traces map
to the ten power supply domains on the PXA27x processor. See
Figure 2-6
supply domain. Place the external circuits as close as possible to the output pins of the PXA27x
processor.
Recommendations for component placement for the PXA270 processor (VF-BGA, 13 mm x 13
mm) are:
•
Place memory components on the left side.
•
Place peripherals on the top or bottom side.
•
Place the LCD panel in the middle of the right side.
•
Place the USIM card interface on the upper right side.
•
Place the crystals and power controller signals on the lower right side.
See Figure
VSS_CORE balls are present on all sides of the package. If the VSS references for all domains are
connected to a single common ground plane, connections between all the VSS balls can be made
without difficulty. However, use two power planes to facilitate connection of all VCC supply balls
for each domain. When using two power planes, one continuous plane is assigned to the
VCC_CORE power domain. The second plane is divided for memory and peripheral I/O power
planes (see
Place the clock crystals and external load capacitors near the lower right corner of the package as
close as possible to their package balls. If possible, install these components (clock crystals and
external load capacitors) on the bottom of the board under the package to minimize trace
capacitance and noise coupling.
In general, reserve the space on the bottom layer of the PCB under the package for the high-
frequency decoupling caps and clock crystals. Install the high-frequency caps and clock crystals on
the bottom layer before installing bulk decoupling caps or other components.
I:2-4
VCC_IO
for illustrations showing how the processor balls are grouped on the package for each
2-4, Figure 2-5, and Figure 2-6
Figure 2-3).
VCC_IO
VCC_LCD
VCC_BATT
Figure
for illustrations showing how the VCC_CORE and
®
Intel PXA27x Processor Family Design Guide
2-4, Figure 2-5, and