Intel IXP46X Computer Hardware User Manual


 
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—Category
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
HDD February 2007
60 Document Number: 305261; Revsion: 004
Place noisy parts (clock, processor, video, etc.) at least 1.5 – 3 inches away from
the edge of the printed circuit board.
Do not place noisy components close to internal/external cables
Any loose cables picks up noise and act as an antenna to radiate that noise
Be aware of the peak in-rush surge current into the device pins. This surge
current may inject high-frequency switching noise into power planes of the
printed circuit board.
Place high-current components near the power sources.
Do not share the same physical components (such as buffers and inverters)
between high-speed and low-speed signals. Use separate parts.
Place clock drivers and receivers such that clock trace length is minimized.
Place clock generation circuits near a ground stitch location. Place a localized
ground plane around the clock circuits and connect the localized plane to system
ground plane.
Install clock circuits directly on the printed circuit board, not on sockets.
Clock crystals should lie flat against the board to provide better coupling of
electromagnetic fields to the board.
4.5 Stack-Up Selection
Stack-up selection directly affects the trace geometry which, in turn, affects the
characteristic impedance requirement for the printed-circuit board. Additionally, the
“clean,” noise-free-planes design and placement is significantly important as
components run at higher speeds requiring more power.
Considerations include:
Low-speed, printed-circuit-board construction — for example two-layer boards:
Advantages:
•Inexpensive
Manufactured by virtually all printed-circuit-board vendors
Disadvantages:
Figure 19. Component Placement on a PCB
B2264-01
PCB
High Frequency
Components
Medium Frequency
Low FrequencyAnalog Circuit
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