Power Supply Sequencing
The LM48821 uses two power supply voltages: V
DD
for the
analog circuitry and I
2
CV
DD
, which defines the digital control
logic high voltage level. To ensure proper functionality, apply
V
DD
first, followed by I
2
CV
DD
. If one power supply is used,
V
DD
and I
2
CV
DD
can be connected together. The part will
power-up with both channels shutdown, the volume control
set to minimum, and the mute function active.
I
2
C Signal Generation Board and
Software
The I
2
C signal generation and interface board, along with the
LM48821 software, will generate the address byte and the
data byte used in the I
2
C control data transaction. To use the
I
2
C signal generation and interface board, please plug it into
a PC’s parallel port (on either a notebook or a desktop com-
puter).
The software comes with an installer. To install, unzip the file
titled “LM48821_Software.” After the file unzips, double-click
the “setup.exe” file. After it launches, please follow the
installer’s instructions. Setup will create a folder named
“LM48821” in the “Program” folder on the “C” disk (if the de-
fault is used) along with a shortcut of the same name in the
“Programs” folder in the “Start” menu.
30009810
Figure 3. The LM48821 Software User's Interface
The LM48821 program includes controls for the amplifier’s
volume control, individual channel shutdown, and the mute
function. The control program's on-screen user interface is
shown in Figure 3.
The Default button is used to return the LM48821 to its power-
on reset state: minimum volume setting, shutdown on both
amplifiers active, and mute active.
The LM48821’s stereo VOLUME CONTROL has 32 steps
and a gain range of –76dB to 18dB. It is controlled using the
slider located at the bottom of the program’s window. Each
time the slider is moved from one tick mark to another, the
program updates the amplifier’s volume control.
LEFT CHANNEL, BOTH CHANNELS, and RIGHT CHAN-
NEL
controls each have two buttons. For the left and right
channel control, the “ON” button activates its respective chan-
nel, whereas the “OFF” button places its respective channel
in shutdown mode. Selecting the BOTH CHANNELS “ON”
button simultaneously activates both channels, whereas se-
lecting the “OFF” button places channels in shutdown mode.
PCB Layout Guidelines
This section provides general practical guidelines for PCB
layouts that use various power and ground traces. Designers
should note that these are only "rule-of-thumb" recommen-
dations and the actual results are predicated on the final
layout.
POWER AND GROUND CIRCUITS
Star trace routing techniques (returning individual traces back
to a central point rather than daisy chaining traces together in
a serial manner) can have a major positive impact on low-level
signal performance. Star trace routing refers to using individ-
ual traces that radiate from a signal point to feed power and
ground to each circuit or even device. This technique may
require greater design time, but should not increase the final
price of the board.
For good THD+N and low noise performance and to ensure
correct power-on behavior at the maximum allowed supply
voltage, a local 4.7
μ
F power supply bypass capacitor should
be connected as physically close as possible to the PV
DD
pin.
AVOIDING TYPICAL DESIGN/LAYOUT PROBLEMS
Avoid ground loops or running digital and analog traces par-
allel to each other (side-by-side) on the same PCB layer.
When traces must cross over each other, do so at 90 degrees.
Running digital and analog traces at 90 degrees to each other
from the top to the bottom side as much as possible will min-
imize capacitive noise coupling and crosstalk.
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