19-3203; Rev 0; 1/08
MAX9724A Evaluation Kit
General Description
The MAX9724A evaluation kit (EV kit) is a fully assem-
bled and tested printed-circuit board (PCB) that uses
the MAX9724A IC to drive a stereo headphone in
portable applications. The MAX9724A is a 60mW stereo
headphone amplifier with adjustable gain and
DirectDrive™ outputs. Maxim’s DirectDrive technology
eliminates the need for bulky DC-blocking capacitors at
the output of the amplifier.
The EV kit is configured for a -1.5V/V gain and is
designed to operate from a 2.7V to 5.5V DC power sup-
ply. The EV kit is capable of delivering up to 60mW per
channel into a 32Ω load and achieving 0.02% THD+N.
The MAX9724A EV kit can also be used to evaluate the
MAX9724B fixed-gain amplifier. Contact Maxim for a
free sample of the MAX9724B IC.
♦
2.7V to 5.5V Operation
♦
Adjustable -1.5V/V Gain
♦
60mW per Channel into a 32Ω Load
♦
0.02% THD+N
♦
Fully Assembled and Tested
Features
♦
No DC-Blocking Output Capacitors Required
Evaluates: MAX9724A/MAX9724B
Ordering Information
PART
MAX9724AEVKIT+
TYPE
EV Kit
+Denotes
lead-free and RoHS-compliant.
Component List
DESIGNATION QTY
C1, C2, C4
3
DESCRIPTION
1µF ±10%, 10V X5R ceramic
capacitors (0603)
Murata GRM188R61A105K
0.1µF ±10%, 10V X5R ceramic
capacitor (0402)
Murata GRM155R61A104K
0.47µF ±10%, 10V X5R ceramic
capacitors (0603)
Murata GRM188R61A474K
3-pin header
Stereo headphone jack (3.5mm)
DESIGNATION QTY
OUTL, OUTR,
SGND
R1, R3
R2, R4
U1
—
—
0
2
2
1
1
1
DESCRIPTION
Not installed, test points
10kΩ ±1% resistors (0603)
15kΩ ±1% resistors (0603)
60mW, DirectDrive, stereo headphone
amplifier (12-pin TQFN-EP*)
Maxim MAX9724AETC+
Shunt (JU1)
PCB: MAX9724A Evaluation Kit+
C3
1
C5, C6
JU1
OUT
2
1
1
*EP
= Exposed paddle.
Component Supplier
SUPPLIER
Murata Mfg. Co., Ltd.
PHONE
770-436-1300
WEBSITE
www.murata.com
Note:
Indicate that you are using the MAX9724A when contacting this component supplier.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX9724A Evaluation Kit
Evaluates: MAX9724/MAX9724B
Quick Start
Required Equipment
Before beginning, the following equipment is needed:
• 2.7V to 5.5V, 500mA power supply
• 32Ω stereo headphones with a 3.5mm plug
• Audio signal source
Test points OUTR, OUTL, and SGND are provided to
easily measure the output signals.
The MAX9724A EV kit can evaluate the fixed-gain
MAX9724B IC, also in a 12-pin thin QFN package. The
MAX9724B features a fixed gain of -1.5V/V. See the
Evaluating the MAX9724B
section for more information.
Shutdown (
SHDN
)
Procedure
Jumper JU1 controls the shutdown pin (SHDN) of the
MAX9724A that enables and disables the MAX9724A
IC. See Table 1 for jumper JU1 configurations.
The MAX9724A 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 installed on jumper JU1, pins
2-3 (IC disabled).
2) Set the power-supply output to 5V.
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.
6) Connect the audio source ground, left signal, and right
signal to the SGND, INL, and INR 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 across pins 1-2 (IC
enabled).
11) Verify that the headphones are playing the audio
source signal.
Table 1. Jumper JU1 Shutdown Selection
SHUNT POSITION
1-2
2-3
SHDN
PIN
Connected to VDD
Connected to GND
MAX9724A
FUNCTION
Enabled
Disabled
Gain Setting
The default gain-setting resistors R1–R4 configure the gain
for both the left and right channels to -1.5V/V. The gain
can be changed by replacing these resistors with other
surface-mount 0603 resistors. Resistors with a tolerance of
1% or better are recommended for optimum performance.
Use Table 2 and the following equation to select new gain-
setting resistors for the corresponding channel.
Table 2. Gain-Setting Resistors
CHANNEL
Right
Left
RIN
R1
R3
RF
R2
R4
Detailed Description
The MAX9724A EV kit features the MAX9724A IC stereo
headphone amplifier. The MAX9724A features
adjustable gain and 60mW DirectDrive outputs.
DirectDrive generates an internal negative supply
(-VDD) from the positive supply (VDD), thus biasing the
amplifier output. Zero-voltage biasing eliminates the
need for bulky DC-blocking capacitors at the amplifier
output. The MAX9724A operates from a 2.7V to 5.5V
supply with a low quiescent current of 3.5mA. The
MAX9724A comes in a 12-pin thin QFN package suit-
able for portable applications.
The EV kit’s gain for each channel is set to -1.5V/V. The
left- and right-channel gain can be adjusted by modifying
the ratio of the corresponding gain-setting resistors R1–R4.
R1 and R2 set the right-channel gain and R3 and R4 set
the left-channel gain. The IC delivers up to 60mW per
channel into a 32Ω load while achieving 0.02% THD+N.
2
RF = -A • RIN
where RIN
≥
10kΩ and A is the desired negative gain.
Refer to the
Output Dynamic Range
and
Maximum
Output Swing
sections in the MAX9724A/MAX9724B IC
data sheet for limitations on setting the gain.
Evaluating the MAX9724B
The MAX9724A EV kit can evaluate the fixed-gain
MAX9724B IC after performing the following:
1) Replace U1 with the MAX9724B IC.
2) Remove resistors R2 and R4.
3) Replace resistors R1 and R3 with 0Ω 0603 surface-
mount resistors.
The MAX9724B features a fixed-gain of -1.5V/V. Contact
Maxim for a free sample of the MAX9724BETC+.
_______________________________________________________________________________________
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