LM4904 National Semiconductor, LM4904 Datasheet - Page 17

• Manufacturer Part Number: LM4904
• Description: 1 Watt Audio Power Amplifier
• Manufacturer: National Semiconductor

Application Information
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.
Part Description
LM4904 Audio AMP
Tantalum Capcitor, 1µF
Ceramic Capacitor, 0.39µF
Resistor, 20kΩ, 1/10W
Resistor, 100kΩ, 1/10W
Jumper Header Vertical Mount 2X1 0.100“ spacing
Mono LM4904 Reference Design Boards
(Continued)
Bill of Material
Quantity
1
2
1
2
1
1
17
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 digi-
tal 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
components and circuit traces.
Avoiding Typical Design / Layout Problems
Avoid ground loops or running digital and analog traces
parallel 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
minimize capacitive noise coupling and cross talk.
Reference Designator
U1
C1, C3
C2
R2, R3
R1
J1
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