AN2826 Freescale Semiconductor / Motorola, AN2826 Datasheet - Page 16

• Manufacturer Part Number: AN2826
• Description: DDR-SDRAM Layout Considerations for MCF547x/8x Processors
• Manufacturer: Freescale Semiconductor / Motorola

Summary
Figure 12. MCF547x/8x Validation Board Ground Plane
As with the previous diagram,
Figure 12
is an inverse plot and white represents filled copper. This diagram
shows the ground plane for the validation board. By flood filling the ground plane under the MPU and with
the various power planes (+3.3V, +2.5V & +1.5V) above it, the PCB itself creates a by-pass/decoupling
capacitor that will remove lower frequency noise (<1 MHz). The effectiveness of this will vary depending
on the material used to manufacture the PCB, but FR4 (fiberglass) has proved quite effective on our
evaluation and validation boards. As much of this layer is filled with copper as possible to minimize noise
on the ground plane.
4
Summary
This application note has outlined the considerations that must be made when designing with DDR
SDRAM and the MCF547x/548x family of processors. The major advantage of DDR SDRAM over SDR
SDRAM is the data bandwidth available, theoretically a doubling of bandwidth. This increase in
DDR-SDRAM Layout Considerations for MCF547x/8x Processors, Rev. 1
16
Freescale Semiconductor