lm4891mm National Semiconductor Corporation, lm4891mm Datasheet - Page 16

• Manufacturer Part Number: lm4891mm
• Description: 1 Watt Audio Power Amplifier
• Manufacturer: National Semiconductor Corporation

www.national.com
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
take require a greater amount of design time but will not
increase the final price of the board. The only extra parts
required may be some jumpers.
Item
1
10
20
21
25
30
35
Part Number
551011208-001 LM4891 Mono Reference Design Board
482911183-001 LM4891 Audio AMP
151911207-001 Tant Cap 1uF 16V 10
151911207-002 Cer Cap 0.39uF 50V Z5U 20% 1210
152911207-001 Tant Cap 1uF 16V 10
472911207-001 Res 20K Ohm 1/10W 5
210007039-002 Jumper Header Vertical Mount 2X1 0.100 2
Part Description
Mono LM4891 Reference Design Boards
(Continued)
Bill of Material for all 3 Demo Boards
16
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 signals 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.
Qty
1
1
1
1
1
3
Ref Designator
U1
C1
C2
C3
R1, R2, R3
J1, J2