LM4910 datasheet(19/22 Pages) NSC

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Application Information (Continued)

LM4910 Reference Design Boards

Bill of Materials

Part Description

Qty

Ref Designator

LM4910 Mono Reference Design Board

LM4910 Audio AMP

Tantalum Cap 1µF 16V 10

Ceramic Cap 0.39µF 50V Z50 20

Resistor 20k

Ω 1/10W 5

Ri, Rf

Resistor 100k

Ω 1/10W 5

Rpu

Jumper Header Vertical Mount 2X1, 0.100

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.

Minimization of THD

PCB trace impedance on the power, ground, and all output

traces should be minimized to achieve optimal THD perfor-

mance. Therefore, use PCB traces that are as wide as

possible for these connections. As the gain of the amplifier is

increased, the trace impedance will have an ever increasing

adverse affect on THD performance. At unity-gain (0dB) the

parasitic trace impedance effect on THD performance is

reduced but still a negative factor in the THD performance of

the LM4910 in a given application.

GENERAL MIXED SIGNAL LAYOUT

RECOMMENDATION

Power and Ground Circuits

For two 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

greatly enhance 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 may

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. Further, place 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

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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