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MAX9725E Evaluation Kit
Quick Start
Required Equipment
Before beginning, the following equipment is needed:
? 0.9V to 1.8V, 500mA power supply
? 32 ? stereo headphones with a 3.5mm plug
either channel can be adjusted to a minimum of |-1V/V|.
The IC delivers up to 20mW per channel into a 32 ?
load while achieving 0.006% THD+N.
Test points OUTL, OUTR, and SGND are provided to
easily measure the output signals.
The MAX9725E EV kit can also evaluate the fixed-gain
?
Audio signal source (e.g., MP3 player, CD player, etc.)
MAX9725A, MAX9725B, MAX9725C, or MAX9725D
ICs. See the Evaluating the MAX9725A –MAX9725D
Procedure
The MAX9725E EV kit is fully assembled and tested.
Follow the steps below to verify board operation.
Caution: Do not turn on the power supply until all
connections are completed.
1) Verify that a shunt is not installed on jumper JU1 (IC
disabled).
section for more information.
Shutdown ( SHDN )
Jumper JU1 controls the shutdown pin ( SHDN ) of the
MAX9725E that enables and disables the MAX9725E
IC. See Table 1 for jumper JU1 configurations.
Table 1. Jumper JU1 Shutdown Selection
2) Set the power-supply output to 1.8V.
3) Disable the power-supply output.
4) Connect the power-supply ground to the PGND pad
and the power-supply positive output to the VDD pad.
5) Verify that the audio source output is disabled.
SHUNT POSITION
Installed
Not installed
SHDN PIN
Connected to VDD
Connected to GND
through R5
MAX9725E
FUNCTION
Enabled
Disabled
6) Connect the audio source ground, left signal, and
right signal to the SGND, VINL, and VINR pads,
respectively.
7) Plug the headphone into the OUT headphone jack.
8) Enable the power-supply output.
9) Enable the audio source.
10) Install a shunt on jumper JU1 (IC enabled).
11) Verify that the headphones are playing the stereo
audio source signal.
Detailed Description of Hardware
Gain Setting
The default gain-setting resistors (R1–R4) configure the
gain for both left and right channels to -1.82V/V. The gain
can be changed by replacing resistors R1–R4 with other
surface-mount 0603 resistors. Resistors with a tolerance
of 1% or better are recommended for optimum perfor-
mance. Use Table 2 and the equations that follow to
select new gain-setting resistors for the corresponding
channel.
Table 2. Component Function
The MAX9725E EV kit features the MAX9725E IC stereo
headphone amplifier in a tiny (1.54mm x 2.02mm x
0.6mm) 12-bump UCSP package for portable applica-
tions. The MAX9725E IC features adjustable gain and
CHANNEL
Right
Left
RIN
R2
R1
RFB
R3
R4
CIN
C6
C5
low-power DirectDrive outputs. DirectDrive generates
an internal negative supply (-VDD) from the positive
supply (VDD), thus biasing the output signal at 0V DC.
Zero-voltage biasing eliminates the need for bulky DC-
RIN >
1
2 π × 20 Hz × CIN
blocking capacitors at the output of the amplifier. The
MAX9725E operates from a 0.9V to 1.8V supply with a
RFB ≥ 10 k ?
low quiescent current of 2.3mA.
The EV kit’s gain for each channel is set to -1.82V/V.
The left- and right-channel gain can be adjusted by
RIN =
RFB
? A
modifying the ratio of the corresponding gain-setting
resistors, R1–R4. R1 and R4 set the left-channel gain;
R2 and R3 set the right-channel gain. The gain for
where A is the desired gain. The gain for either channel
can be adjusted to a minimum of |-1V/V|. Refer to the
MAX9725 IC data sheet for more details.
2
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