lm4995tmx National Semiconductor Corporation, lm4995tmx Datasheet - Page 14

• Manufacturer Part Number: lm4995tmx
• Description: Boomer-r Audio Power Amplifier Series1.3 W Audio Power Amplifier
• Manufacturer: National Semiconductor Corporation

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PCB LAYOUT GUIDELINES
This section provides practical guidelines for mixed signal
PCB layout that involves various digital/analog power and
ground traces. Designers should note that these are only
"rule-of-thumb" recommendations and the actual results will
depend heavily on the final layout.
GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION
Power and Ground Circuits
For 2 layer mixed signal design, it is important to isolate the
digital power and ground trace paths from the analog power
and ground trace paths. Star trace routing techniques (bring-
ing individual traces back to a central point rather than daisy
chaining traces together in a serial manner) can have a major
impact on low level signal performance. Star trace routing
refers to using individual traces to feed power and ground to
each circuit or even device. This technique will require a
greater amount of design time but will not increase the final
price of the board. The only extra parts required will be some
jumpers.
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Single-Point Power / Ground Connections
The analog power traces should be connected to the digital
traces through a single point (link). A "Pi-filter" can be helpful
in minimizing High Frequency noise coupling between the
analog and digital sections. It is further recommended to put
digital and analog power traces over the corresponding digital
and analog ground traces to minimize noise coupling.
Placement of Digital and Analog Components
All digital components and high-speed digital signal traces
should be located as far away as possible from analog com-
ponents and circuit traces.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces par-
allel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other do it at 90 degrees.
Running digital and analog traces at 90 degrees to each other
from the top to the bottom side as much as possible will min-
imize capacitive noise coupling and cross talk.