Power Supply Sequencing
The LM4985 uses two power supply voltage: V
DD
for the
analog circuitry and I
2
CV
DD
for the digital controls (volume,
shutdown, etc.). 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 shutdown active, the volume control set to
minimum, and the input MUX set so that IN1 and IN2 corre-
spond to OUT1 and OUT2, respectfully (normal stereo).
I
2
C Signal Generation Board and
Software
The I
2
C signal generation and interface board, along with the
LM4985 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
computer).
The software comes with an installer. To install, unzip the file
titled “LM4985_Software_ver1-52.” 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 “LM4985” in the “Program” folder on the “C” disk (if
the default is used) along with a shortcut of the same name
in the “Programs” folder in the “Start” menu.
20184927
Figure 3. The LM4985 Demonstration Board Schematic
The LM4985 program includes controls for the amplifier’s
volume control, shutdown, input MUX, selectable wake-up
time, amplifier output coupling and the I
2
C address bit. The
control program’s on-screen user interface is shown in Fig-
ure 3.
The Default button is used to return the LM4985 to its
power-on reset state (minimum volume setting, shutdown on
both amplifiers active, standard stereo mode, capacitively
coupled output, and minimum wake-up time.
The LM4985’s stereo
VOLUME CONTROL
has 32 steps
and a gain range of –76dB to 18dB. It is controlled using the
slider located at the top of the program’s window. Each time
the slider is moved from one tick mark to another, the pro-
gram updates the amplifier’s volume control.
The
CHANNEL SHUTDOWN CONTROL
has four radio but-
tons. From left to right, the first button controls the shutdown
function of both amplifiers. When selected, both amplifiers
are placed in shutdown mode. The middle pair of buttons
places a single amplifier channel in shutdown mode. The
first of the pair deactivates channel A’s shutdown and acti-
vates channel B’s shutdown. The second in the pair acti-
vates channel A’s shutdown and deactivates channel B’s
shutdown. The last shutdown button deactivates both chan-
nels’ shutdown, allowing full, two-channel amplifier opera-
tion.
There is a protocol that one must follow when placing an
individual amplifier channel in shutdown while the other
channel remains active. The protocol requires activating
both channel’s shutdown simultaneously, then deactivating
the shutdown of the channel whose output is desired (or
leaving the desired channel in shutdown mode). This proto-
col is required whether using this software or a user-created
routine. Further, when operating in the C-CUPL mode, a
short delay time is required before activating one channel
after placing both channels in shutdown. If the user finds that
both channels activate when only one was chosen, increase
the delay.
The next section,
CHANNEL SELECT
, is used to choose
which input signal is internally routed to which amplifier
channel. The power-on or reset state is standard stereo: the
signal applied to input IN A is routed to the OUT A amplifier
and the signal applied to input IN B is routed to the OUT B
amplifier. The other three modes are the signal applied to IN
A is routed to both channels, the signal applied to IN B is
routed to both channels, and reverse stereo (the signal
applied to IN A is routed to amplifier B and the signal applied
to IN B is routed to amplifier A).
AN-1452
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