LM4869 datasheet(14/20 Pages) NSC

14 / 20 page

Typical Performance Characteristics

MH Specific Characteristics (Continued)

Cross Talk vs Frequency

200428D5

DD = 3V, RL =8

Ω,A

V = 15.6dB,

A = Left channel driven, right channel measured;

B = Right channel driven, left channel measured

200428D6

DD = 3V, RL =8

Ω,A

V = 21.6dB,

A = Left channel driven, right channel measured;

B = Right channel driven, left channel measured

Power Dissipation Derating Curves

200428E4

DD = 5V, RL =8

Ω,f

IN = 1kHz,

(from top to bottom at 40˚C): 3in x 3in four-layer PCB

with bottom and two inner layers connected to the package’s DAP,

1.5in x 1.5in two-layer PCB with bottom and top layer

planes connected to the package’s DAP

Application Information

PCB LAYOUT AND SUPPLY REGULATION

CONSIDERATIONS FOR DRIVING 3W AND 4W LOADS

Power dissipated by a load is a function of the voltage swing

across the load and the load’s impedance. As load imped-

ance decreases, load dissipation becomes increasingly de-

pendent on the interconnect (PCB trace and wire) resistance

between the amplifier output pins and the load’s connec-

tions. Residual trace resistance causes a voltage drop,

which results in power dissipated in the trace and not in the

load as desired. For example, 0.1

Ω trace resistance reduces

the output power dissipated by a 4

Ω load from 2.1W to 2.0W.

This problem of decreased load dissipation is exacerbated

as load impedance decreases. Therefore, to maintain the

highest load dissipation and widest output voltage swing,

PCB traces that connect the output pins to a load must be as

wide as possible.

Poor power supply regulation also adversely affects maxi-

mum output power. A poorly regulated supply’s output volt-

age decreases with increasing load current. Reduced supply

voltage causes decreased headroom, output signal clipping,

and reduced output power. Even with tightly regulated sup-

plies, trace resistance creates the same effects as poor

supply regulation. Therefore, making the power supply

traces as wide as possible helps maintain full output voltage

swing.

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