General Description
The LM4681 is a Class D audio amplifier with an internal,
digitally controlled volume control, and Class AB stereo
headphone amplifier. The LM4681 is optimized to operate
over a power supply voltage range of 9.0V to 15.5V. This
amplifier is capable of delivering 10W
RMS
per channel into
an 8
Ω
load at 10% THD when powered by a 14.0V power
supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. The LM4681 is a high-efficiency Class
D amplifier that is optimally suited for volume minimized
design such as flat panel displays that can not tolerate
heatsinks or portable system that must maximize battery life
while producing high acoustic output.
The LM4681 includes a digitally controlled (I
2
C) 32–step
volume control that optimizes system cost and minimizes
PCB area.
The LM4681 features a shutdown mode for micropower
dissipation, an internal thermal shutdown protection mecha-
nism, and output stage fault detect and current limit protec-
tion.
Operating Conditions
•
Temperature Range
–40˚C
≤
T
A
≤
85˚C
•
Amplifier Power Supply Voltage
9.0V
≤
V
DD
≤
15.5V
Board Features
The LM4681 demonstration board has all of the necessary
connections, using 100mil headers, to apply the power sup-
ply voltage, the audio input signals, and the I
2
C signal inputs.
The Class D amplifier’s output is available on 100 mil head-
ers. The Class AB headphone’s amplified audio signal is
available on both a stereo headphone jack and 100 mil
headers.
Also included with the demonstration board is an I
2
C signal
generation board and software. With this board and the
software, the user can easily control the LM4681’s shutdown
function and stereo volume control. Figure 3 shows the
software’s graphical user interface.
Schematic
Figure 2 shows the LM4681 Demonstration Board sche-
matic. Refer to Table 1 for a list of the connections and their
functions.
AN-1488
www.national.com
2