Connections
Connecting to the world is accomplished through the 100mil headers on the LM4681 demonstration board. The functions of the
different headers are detailed in Table 1.
TABLE 1. LM4681 Demonstration Board Connections
Jumper Designation
Function or Use
JP1
Power supply connection. Connect an external power supply’s
positive voltage source to the JP1 pin labeled “VDD” and the
supply’s ground source to the pin labeled “GND.”
JP2
This is the connection to the amplifier’s input A (labeled as the
“LF_IN” input on the demonstration board). Apply an external
signal source’s positive voltage to the JP2 pin labeled “IN” and the
signal source’s ground reference to the pin labeled “GND.”
JP3
This is the connection to the amplifier’s output A (labeled as the
"LEFT_OUT” output on the demonstration board). Connect the JP3
pin labeled “+” to the positive input of an external signal
measurement device. Connect the JP3 pin labeled “-” to the
negative input of an external signal measurement device.
JP4
This is the connection to the amplifier’s input B (labeled as the
“RT_IN” input on the demonstration board). Apply an external
signal source’s positive voltage to the JP4 pin labeled “IN” and the
signal source’s ground reference to the pin labeled “GND.”
JP5
This is the connection to the amplifier’s output B (labeled as the
“RIGHT_OUT” output on the demonstration board). Connect the
JP5 pin labeled “+” to the positive input of an external signal
measurement device. Connect the JP5 pin labeled “-” to the
negative input of an external signal measurement device.
JP6
If an external I
2
C power supply voltage is used, connect this
supply’s positive voltage source to the JP6 pin labeled “I2CVDD”
and the supply’s ground source to the pin labeled “GND.” If no
external supply is used, leave this jumper’s pins unconnected.
JP7
This header is used for the I
2
C signal inputs. JP7-pin 1 is for an
I
2
CV
DD
that is generated by the I
2
C signal source, JP7-pin 2 is for
the SCL signal, JP7-pin 3 is for GND, JP7-pin 4 is for the ADR
signal, and JP7-pin 6 is for the SDA signal.
JP8
This three-pin jumper selects either I
2
C or SPI digital interface
protocol. Short pins 1 and 2 together SPI protocol is used. Short
pins 2 and 3 together when I
2
C protocol is used.
Power Supply Sequencing
The LM4681 uses two power supply voltage: V
DD
for the
Class D power amplifier and the Class AB headphone am-
plifier and I
2
CV
DD
for the digital controls (volume, shutdown,
etc.). To ensure proper functionality, apply I
2
CV
DD
first, fol-
lowed by V
DD
. The part will power-up with shutdown active,
the volume control set to minimum, and mute active.
I
2
C Signal Generation Board and
Software
The I
2
C signal generation and interface board, along with the
LM4681 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 “LM4681_Software_ver1-1.” 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 “LM4681” 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.
AN-1488
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