Datasheet

Table Of Contents

LM4890

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SNAS138L –SEPTEMBER 2001–REVISED MAY 2013

Table 1. Mono LM4890 Reference Design Boards

Bill of Material for all 3 Demo Boards (continued)

Bill of Material for all 3 Demo Boards

Item Part Number Part Description Qty Ref Designator

1 551011208-001 LM4890 Mono Reference Design Board 1

10 482911183-001 LM4890 Audio AMP 1 U1

20 151911207-001 Tant Cap 1uF 16V 10 1 C1

21 151911207-002 Cer Cap 0.39uF 50V Z5U 20% 1210 1 C2

25 152911207-001 Tant Cap 1uF 16V 10 1 C3

30 472911207-001 Res 20K Ohm 1/10W 5 3 R1, R2, R3

35 210007039-002 Jumper Header Vertical Mount 2X1 0.100 2 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 (bringing 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 digital 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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