General Description
The LM48821 is a fully differential input stereo headphone
audio amplifier with an internal digitally controlled volume
control. The LM48821 is optimized to operate over a power
supply voltage range of 2.0V to 4.0V. This amplifier is capable
of delivering 53mW
RMS
per channel into a 32
Ω
load at 1%
THD when powered by a 3.0V power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal amount of
external components. To that end, the LM48821 features two
functions that optimize system cost and minimize PCB area:
an integrated, digitally controlled (I
2
C bus) volume control and
an amplifier generated negative power supply voltage that
eliminates output signal-coupling capacitors. Since the
LM48821 does not require bootstrap capacitors, snubber net-
works, or output coupling capacitors, it is optimally suited for
low-power, battery powered potable systems.
The LM48821 includes separate shutdown controls for each
stereo channel for micropower dissipation, an internal thermal
shutdown protection mechanism, and is unity gain stable.
Operating Conditions
■
Temperature Range
–40°C
≤
T
A
≤
85°C
■
Amplifier Power
Supply Voltage
2.0V
≤
V
DD
≤
5.0V
≤
4.0V
Board Features
The LM48821 demonstration board has all of the necessary
connections, using 0.100” headers, to apply the power supply
voltage, the audio input signals, and the I
2
C signal inputs. The
amplified audio signal is available on both a stereo head-
phone jack and auxiliary output connections.
Also included with the demonstration board is an I
2
C signal
generation board and software. With this board and the soft-
ware, the user can easily control the LM48821’s, shutdown
function, mute, and stereo volume control. Figure 3 shows the
software’s graphical user interface.
Schematic
Figure 2 shows the LM48821 Demonstration Board schemat-
ic. Refer to Table 3 for a list of the connections and their
functions.
30009846
Figure 2. The LM48821 Demonstration Board Schematic
www.national.com
2
AN-1589
