LM4869 NSC [National Semiconductor], LM4869 Datasheet - Page 14

• Manufacturer Part Number: LM4869
• Description: 1.9W Differential Input, BTL Output Stereo Audio Amplifier with Selectable Gain and Shutdown
• Manufacturer: NSC [National Semiconductor]

www.national.com
Typical Performance Characteristics
MH Specific Characteristics
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, 0.1Ω trace resistance reduces
the output power dissipated by a 4Ω load from 2.1W to 2.0W.
This problem of decreased load dissipation is exacerbated
A = Left channel driven, right channel measured;
B = Right channel driven, left channel measured
V
DD
Cross Talk vs Frequency
= 3V, R
L
with bottom and two inner layers connected to the package’s DAP,
= 8Ω, A
(from top to bottom at 40˚C): 3in x 3in four-layer PCB
1.5in x 1.5in two-layer PCB with bottom and top layer
V
= 15.6dB,
planes connected to the package’s DAP
Power Dissipation Derating Curves
V
200428D5
DD
(Continued)
= 5V, R
L
= 8Ω, f
14
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.
IN
A = Left channel driven, right channel measured;
B = Right channel driven, left channel measured
= 1kHz,
V
DD
200428E4
Cross Talk vs Frequency
= 3V, R
L
= 8Ω, A
V
= 21.6dB,
200428D6