LM4906LD National Semiconductor, LM4906LD Datasheet - Page 10

• Manufacturer Part Number: LM4906LD
• Description: 1W/ Bypass-Capacitor-less Audio Amplifier with Internal Selectable Gain
• Manufacturer: National Semiconductor

www.national.com
Application Information
C
reach its quiescent DC voltage (nominally 1/2 V
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the
capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
AUDIO POWER AMPLIFIER DESIGN
A 1W/8Ω Audio Amplifier
A designer must first determine the minimum supply rail to
obtain the specified output power. By extrapolating from the
Output Power vs Supply Voltage graphs in the Typical Per-
formance Characteristics section, the supply rail can be
easily found.
i.
Given:
A larger input coupling capacitor requires more charge to
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
100 Hz–20 kHz
FIGURE 2. REFERENCE DESIGN BOARD SCHEMATIC
(Continued)
±
1 Wrms
0.25 dB
DD
1 Vrms
20 kΩ
). This
8Ω
10
Extra supply voltage creates headroom that allows the
LM4906 to reproduce peaks in excess of 1W without pro-
ducing audible distortion. At this time, the designer must
make sure that the power supply choice along with the
output impedance does not violate the conditions explained
in the Power Dissipation section.
The gain of the LM4906 is internally set at either 6dB or
12dB.
The final design step is to address the bandwidth require-
ments which must be stated as a pair of −3dB frequency
points. Five times away from a −3dB point is 0.17dB down
from passband response which is better than the required
±
As stated in the External Components section, R
conjunction with C
0.25dB specified.
f
f
C
L
H
2
= 100Hz / 5 = 20Hz
= 20kHz * 5 = 100kHz
≥ 1 / (2π*20kΩ*20Hz) = 0.397µF; use 0.39µF
2
create a highpass filter.
200571C0
in
(20k) in