LM4890 datasheet(25/31 Pages) NSC

25 / 31 page

Application Information (Continued)

Mono LM4890 Reference Design Boards

Bill of Material for all 3 Demo Boards

Item

Part Number

Part Description

Qty

Ref Designator

551011208-001 LM4890 Mono Reference Design Board

482911183-001 LM4890 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

R1, R2, R3

210007039-002 Jumper Header Vertical Mount 2X1 0.100

J1, J2

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

RECOMMENDATIONS

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.

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.

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