General Description
The MAX9723 stereo DirectDrive® headphone amplifier
with BassMax and volume control is ideal for portable
audio applications where space is at a premium and
performance is essential. The MAX9723 operates from a
single 1.8V to 3.6V power supply and includes features
that reduce external component count, system cost,
board space, and improves audio reproduction.
The headphone amplifier uses Maxim’s DirectDrive archi-
tecture that produces a ground-referenced output from a
single supply, eliminating the need for large DCblocking
capacitors. The headphone amplifiers deliver 62mW into
a 16Ω load, feature low 0.006% THD+N, and high 90dB
PSRR. The MAX9723 features Maxim’s industry-leading
click-and-pop suppression.
The BassMax feature boosts the bass response of
the amplifier, improving audio reproduction when using
inexpensive headphones. The integrated volume control
features 32 discrete volume levels, eliminating the need
for an external potentiometer. BassMax and the volume
control are enabled through the I2C/SMBus™-compatible
interface. Shutdown is controlled through either the hard-
ware or software interfaces.
The MAX9723 consumes only 3.7mA of supply current at
1.8V, provides short-circuit and thermal-overload protection,
and is fully specified over the extended -40°C to +85°C tem-
perature range. The MAX9723 is available in a tiny (2mm x
2mm x 0.62mm) 16-bump chip-scale package (UCSP™) or
16-pin thin QFN (4mm x 4mm x 0.8mm) package.
Applications
Features
● 62mW, DirectDrive Headphone Amplifier Eliminates
Bulky DC-Blocking Capacitors
●1.8V to 3.6V Single-Supply Operation
●Integrated 32-Level Volume Control
● High 90dB PSRR at 1kHz
● Low 0.006% THD+N
●Industry-Leading Click-and-Pop Suppression
● ±8kV HBM ESD-Protected Headphone Outputs
●Short-Circuit and Thermal-Overload Protection
● Low-Power Shutdown Mode (5μA)
● Software-Enabled Bass Boost (BassMax)
●I2C/SMBus-Compatible Interface
● Available in Space-Saving, Thermally Efficient
Packages:
• 16-Bump UCSP (2mm x 2mm x 0.62mm)
• 16-Pin Thin QFN (4mm x 4mm x 0.8mm)
Pin Configurations appears at end of data sheet.
19-3509; Rev 3; 7/14
●PDA Audio
●Portable CD Players
●Mini Disc Players
● MP3-Enabled Cellular
●Phones
●MP3 Players
**Replace the ‘_’ with the one-letter code that denotes the slave
address and maximum programmable gain. See the Selector
Guide.
+Denotes a lead-free/RoHS-compliant package.
*Future product—contact factory for availability.
DirectDrive is a registered trademark of Maxim Integrated
Products, Inc.
SMBus is a trademark of Intel Corp.
UCSP is a trademark of Maxim Integrated Products, Inc.
PART SLAVE ADDRESS MAXIMUM GAIN (dB)
MAX9723A 1001100 0
MAX9723B 1001101 0
MAX9723C 1001100 +6
MAX9723D 1001101 +6
PART** TEMP RANGE PIN-
PACKAGE
PKG
CODE
MAX9723_EBE-T* -40°C to +85°C 16 UCSP-16 B16-1
MAX9723_ETE+ -40°C to +85°C 16 TQFN T1644-4
I2C INTERFACE
VOLUME
CONTROL
BassMax
BassMax
1.8V TO 3.6V SUPPLY
SCL
BBL
OUTL
BBR
OUTR
SDA
INL
INR
∑
∑
MAX9723
MAX9723 Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I2C
Block Diagram
Ordering Information
Selector Guide
EVALUATION KIT AVAILABLE
SGND to PGND .....................................................-0.3V to +0.3V
VDD to PGND...........................................................-0.3V to +4V
PVSS to SVSS.......................................................-0.3V to +0.3V
C1P to PGND.............................................-0.3V to (VDD + 0.3V)
C1N to PGND...........................................(PVSS - 0.3V) to +0.3V
PVSS, SVSS to PGND..............................................+0.3V to -4V
IN_ to SGND.................................(SVSS - 0.3V) to (VDD + 0.3V)
SDA, SCL to PGND..................................................-0.3V to +4V
SHDN to PGND..........................................-0.3V to (VDD + 0.3V)
OUT_ to SGND............................................................-3V to +3V
BB_ to SGND...............................................................-2V to +2V
Duration of OUT_ Short Circuit to _GND ....................Continuous
Continuous Current Into/Out of:
VDD, C1P, PGND, C1N, PVSS, SVSS, or OUT_...........±0.85A
Any Other Pin................................................................±20mA
Continuous Power Dissipation (TA = +70°C)
4 x 4 UCSP (derate 8.2mW/°C above +70°C)
..........
659.2mW
16-Pin Thin QFN (derate 16.9mW/°C above +70°C)....1349mW
Operating Temperature Range.............................-40°C to +85°C
Junction Temperature....................
......................
.............+150°C
Storage Temperature Range .............................-65°C to +150°C
Bump Temperature (soldering)
Reflow ..........................................................................+230°C
Lead Temperature (soldering, 10s) .............
....
..
..........
....+300°C
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage Range VDD 1.8 3.6 V
Quiescent Supply Current IDD No load 46.5 mA
Shutdown Supply Current IDD_SHDN VSHDN = 0V 5 8.5 µA
Turn-On Time tON 200 µs
Turn-Off Time tOFF 35 µs
Thermal Shutdown Threshold TTHRES +143 °C
Thermal Shutdown Hysteresis THYST 12 °C
HEADPHONE AMPLIFIER
Output Offset Voltage VOS
Measured between
OUT_ and SGND
(Note 2)
Gain = 0dB,
MAX9723A/
MAX9723B
±0.7 ±4.5
mV
Gain = +6dB,
MAX9723C/
MAX9723D
±0.8 ±5
Input Resistance RIN All volume levels 10 17 27 kΩ
BBR, BBL Input Bias Current IBIAS_BB ±10 ±100 nA
Power-Supply Rejection Ratio PSRR (Note 2)
DC, VDD = 1.8V to 3.6V 73 90
dB
f = 217Hz, 100mVP-P ripple,
VDD = 3.0V 87
f = 1kHz, 100mVP-P ripple,
VDD = 3.0V 86
f = 20kHz, 100mVP-P ripple,
VDD = 3.0V 61
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
2
Absolute Maximum Ratings
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Electrical Characteristics
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Output Power POUT THD+N = 1%,
fIN = 1kHz
RL = 32Ω 59 mW
RL = 16Ω (Note 5) 38 60
Total Harmonic Distortion Plus
Noise THD+N RL = 16Ω, POUT = 35mW, fIN = 1kHz 0.006 %
RL = 32Ω, POUT = 45mW, fIN = 1kHz 0.004
Maximum Gain AMAX
MAX9723A/
MAX9723B
Gain range bit 5 = 1 0 dB
Gain range bit 5 = 0 -5
MAX9723C/
MAX9723D
Gain range bit 5 = 1 +6 dB
Gain range bit 5 = 0 +1
Signal-to-Noise Ratio SNR RL = 32Ω,
VOUT = 1VRMS
BW = 22Hz to 22kHz 99 dB
A-weighted 100
Slew Rate SR 0.35 V/µs
Capacitive Drive No sustained oscillations 300 pF
Output Resistance in Shutdown ROUT_SHDN VSHDN = 0V, measured from OUT_ to
SGND 20 kΩ
Output Capacitance in Shutdown COUT_SHDN VSHDN = 0V, measured from OUT_ to
SGND 60 pF
Click/Pop Level KCP
RL = 32Ω,
peak voltage,
A-weighted,
32 samples
per second
(Notes 2, 4)
MAX9723A/
MAX9723B
Into
shutdown -69
dB
Out of
shutdown -71
MAX9723C/
MAX9723D
Into
shutdown -70
Out of
shutdown -69
Charge-Pump Switching
Frequency fCP 505 600 700 kHz
Crosstalk XTALK
L to ≥ or ≥ to L, f = 10kHz,
VOUT = 1VP-P, RL = 32Ω, both channels
loaded
80 dB
DIGITAL INPUTS (SHDN, SDA, SCL)
Input High Voltage VIH 0.7 x
VDD
V
Input Low Voltage VIL 0.3 x
VDD
V
Input Leakage Current P1 µA
DIGITAL OUTPUTS (SDA)
Output Low Voltage VOL IOL = 3mA 0.4 V
Output High Current IOH VSDA = VDD 1 µA
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
3
Electrical Characteristics (continued)
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load con-
nected between OUT_ and SGND where specified. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C, see
Timing Diagram.) (Notes 1, 3)
Note 1: All specifications are 100% tested at TA = +25°C. Temperature limits are guaranteed by design.
Note 2: Inputs AC-coupled to SGND.
Note 3: Guaranteed by design.
Note 4: Headphone mode testing performed with a 32Ω resistive load connected to GND. Mode transitions are controlled by SHDN.
The KCP level is calculated as: 20 x log [(level peak voltage during mode transition, no input signal)/(peak voltage under
normal operation at rated power)]. Units are expressed in dB.
Note 5: Output power MIN is specified at TA = +25°C.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Serial Clock Frequency fSCL 0 400 kHz
Bus Free Time Between a STOP
and a START Condition tBUF 1.3 µs
START Condition Hold Time tHD:STA 0.6 µs
Low Period of the SCL Clock tLOW 1.3 µs
High Period of the SCL Clock tHIGH 0.6 µs
Setup Time for a Repeated
START Condition tSU:STA 0.6 µs
Data Hold Time tHD:DAT 0 0.9 µs
Data Setup Time tSU:DAT 100 ns
Maximum Rise Time of SDA and
SCL Signals tr300 ns
Maximum Fall Time of SDA and
SCL Signals tf300 ns
Setup Time for STOP Condition tSU:STO 0.6 µs
Pulse Width of Suppressed Spike tSP 100 ns
Maximum Capacitive Load for
Each Bus Line CL_BUS 400 pF
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
4
Timing Characteristics
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specied. Outputs in phase, both channels loaded. TA = +25°C, unless otherwise noted.) (See Func-
tional Diagram/Typical Operating Circuit)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9723 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 2.4V
RL = 32Ω
POUT = 23mW
POUT = 10mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9723 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
RL = 16Ω
POUT = 37mW
POUT = 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9723 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
RL = 32Ω
POUT = 30mW
POUT = 10mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9723 toc05
OUTPUT POWER (mW)
THD+N (%)
4020
0.01
0.1
1
10
100
0.001
0 60
VDD = 2.4V
RL = 16Ω
fIN = 1kHz
fIN = 20Hz
fIN = 10kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9723 toc06
OUTPUT POWER (mW)
THD+N (%)
4020
0.01
0.1
1
10
100
0.001
0 60
VDD = 2.4V
RL = 32Ω
fIN = 1kHz
fIN = 10kHz
fIN = 20Hz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9723 toc07
OUTPUT POWER (mW)
THD+N (%)
80604020
0.01
0.1
1
10
100
0.001
0 100
VDD = 3V
RL = 16Ω
fIN = 10kHz
fIN = 1kHz
fIN = 20Hz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9723 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 2.4V
RL = 16Ω
POUT = 10mW
POUT = 25mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9723 toc08
OUTPUT POWER (mW)
THD+N (%)
80604020
0.01
0.1
1
10
100
0.001
0 100
VDD = 3V
RL = 32Ω
fIN = 10kHz
fIN = 1kHz
fIN = 20Hz
0
40
60
80
100
120
140
160
180
0 20 40 60 80
POWER DISSIPATION
vs. OUTPUT POWER
MAX9723 toc09
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
20
VDD = 2.4V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN PHASE
RL = 32Ω
RL = 16Ω
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
Maxim Integrated
│
5
www.maximintegrated.com
Typical Operating Characteristics
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specied. Outputs in phase, both channels loaded. TA = +25°C, unless otherwise noted.) (See Func-
tional Diagram/Typical Operating Circuit)
0
100
50
200
150
250
300
0 40 6020 80 100 120
POWER DISSIPATION
vs. OUTPUT POWER
MAX9723 toc10
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
RL = 16Ω
VDD = 3V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN PHASE
RL = 32Ω
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9723 toc11
LOAD RESISTANCE (W)
OUTPUT POWER (mW)
100
10
20
30
40
50
60
70
80
0
10 1k
VDD = 2.4V
fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9723 toc12
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
100
10
20
30
40
50
60
70
80
90
100
0
10 1k
VDD = 3V
fIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9723 toc13
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.43.22.8 3.02.2 2.4 2.62.0
10
20
30
40
50
60
70
80
90
100
0
1.8 3.6
THD+N = 10%
THD+N = 1%
fIN = 1kHz
RL = 16Ω
20
40
60
80
100
120
140
0
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9723 toc14
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.43.22.8 3.02.2 2.4 2.62.01.8 3.6
THD+N = 10%
THD+N = 1%
fIN = 1kHz
RL = 32Ω
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9723 toc15
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
RL = 32Ω
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
Maxim Integrated
│
6
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specied. Outputs in phase, both channels loaded. TA = +25°C, unless otherwise noted.) (See Func-
tional Diagram/Typical Operating Circuit)
CROSSTALK
vs. FREQUENCY
-100
-80
-60
-40
-20
0
-120
MAX9723 toc16
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k10010 100k
VIN = 1VP-P
RL = 32Ω
A = 0dB
LEFT TO RIGHT
A = 0dB
RIGHT TO LEFT
A = 0dB
CROSSTALK
vs. FREQUENCY
-100
-80
-60
-40
-20
0
-120
MAX9723 toc17
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k10010 100k
VIN = 1VP-P
RL = 32Ω
A = -10dB
LEFT TO RIGHT
A = -10dB
RIGHT TO LEFT
A = -10dB
BASS BOOST FREQUENCY
RESPONSE
-5
0
5
10
15
20
-10
MAX9723 toc18
FREQUENCY (Hz)
AMPLITUDE (dB)
10k1k10010 100k
NO LOAD
R1 = 47kΩ
BassMax DISABLED
R2 = 36kΩ
C3 = 0.068µF
R2 = 22kΩ
C3 = 0.1µF
R2 = 10kΩ
C3 = 0.22µF
GAIN FLATNESS
vs. FREQUENCY
-6
-5
-4
-3
-2
-1
0
1
-7
MAX9723 toc19
FREQUENCY (Hz)
AMPLITUDE (dB)
10k1k10010 100k
OUTPUT SPECTRUM
vs. FREQUENCY
MAX9723 toc20
FREQUENCY (kHz)
AMPLITUDE (dBV)
15105
-130
-120
-110
-100
-90
-80
-70
-60
-50
-40
-140
0 20
RL = 32Ω
VDD = 3V
fIN = 1kHz
CHARGE-PUMP OUTPUT VOLTAGE
vs. OUTPUT CURRENT
MAX9723 toc21
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
175150125100755025
-3.0
-2.5
-2.0
-1.5
-1.0
-0.5
0
-3.5
0 200
NO HEADPHONE LOAD
CHARGE-PUMP LOAD
CONNECTED
BETWEEN PVSS AND PGND
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
Maxim Integrated
│
7
www.maximintegrated.com
Typical Operating Characteristics (continued)
(VDD = SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
between OUT_ and SGND where specied. Outputs in phase, both channels loaded. TA = +25°C, unless otherwise noted.) (See Func-
tional Diagram/Typical Operating Circuit)
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCE
MAX9723 toc22
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
403020
40
45
50
55
60
65
70
75
35
10 50
C1 = C2 = 2.2µF
C1 = C2 = 0.68µF
C1 = C2 = 1µF
VDD = 3V
fIN = 1kHz
THD+N = 1%
POWER-UP/POWER-DOWN
WAVEFORM
MAX9723 toc23
20ms/div
VDD
2V/div
VOUT
10mV/div
EXITING SHUTDOWN
MAX9723 toc24
40µs/div
VOUT_
200mV/div
VSHDN
2V/div
ENTERING SHUTDOWN
MAX9723 toc25
20µs/div
VOUT_
200mV/div
VSHDN
2V/div
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9723 toc26
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.43.23.02.82.62.42.22.0
2.5
3.0
3.5
4.0
4.5
2.0
1.8 3.6
NO LOAD
INPUTS GROUNDED
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN CURRENT (µA)
1
2
3
4
5
6
7
8
0
MAX9723 toc27
SUPPLY VOLTAGE (V)
3.43.23.02.82.62.42.22.01.8 3.6
NO LOAD
INPUTS GROUNDED
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
Maxim Integrated
│
8
www.maximintegrated.com
Typical Operating Characteristics (continued)
Detailed Description
The MAX9723 stereo headphone amplifier features
Maxim’s DirectDrive architecture, eliminating the large
output-coupling capacitors required by conventional sin-
gle-supply headphone amplifiers. The MAX9723 consists
of two 62mW Class AB headphone amplifiers, hardware/
software shutdown control, inverting charge pump, inte-
grated 32-level volume control, BassMax circuitry, com-
prehensive click-and-pop suppression circuitry, and an
I2C-compatible interface (see the Functional Diagram/
Typical Operating Circuit). A negative power supply
(PVSS) is created internally by inverting the positive sup-
ply (VDD). Powering the amplifiers from VDD and PVSS
increases the dynamic range of the amplifiers to almost
twice that of other single-supply amplifiers, increasing the
total available output power.
The MAX9723 DirectDrive outputs are biased at SGND
(see Figure 1). The benefit of this 0V bias is that the ampli-
fier outputs do not have a DC component, eliminating the
need for large DC-blocking capacitors. Eliminating the
DC-blocking capacitors on the output saves board space,
system cost, and improves low-frequency response.
An I2C-compatible interface allows serial communica-
tion between the MAX9723 and a microcontroller. The
MAX9723 is available with two different I2C addresses
allowing two MAX9723 ICs to share the same bus (see
Table 1). The internal command register controls the
shutdown status of the MAX9723, enables the BassMax
circuitry, sets the maximum gain of the amplifier, and sets
the volume level (see Table 2). The MAX9723’s BassMax
circuitry improves audio reproduction by boosting the
bass response of the amplifier, compensating for any low-
frequency attenuation introduced by the headphone. The
PIN BUMP NAME FUNCTION
THIN QFN UCSP
1 D1 VDD Power-Supply Input. Bypass VDD to PGND with a 1µF capacitor.
2 C1 C1P Charge-Pump Flying Capacitor Positive Terminal
3 B1 PGND Power Ground. Connect to SGND.
4 A1 C1N Charge-Pump Flying Capacitor Negative Terminal
5B2 SCL Serial Clock Input. Connect a 10kI pullup resistor from SCL to VDD.
6 A2 PVSS Charge-Pump Output. Connect to SVSS. Bypass PVSS with a 1µF capacitor to PGND.
7 A3 SDA Serial-Data Input. Connect a 10kΩ pullup resistor from SDA to VDD.
8 B3 SHDN Shutdown. Drive SHDN low to disable the MAX9723. Connect SHDN to VDD while bit 7
is high for normal operation (see the Command Register section).
9 A4 SGND Signal Ground. Connect to PGND.
10 B4 INL Left-Channel Input
11 C4 INR Right-Channel Input
12 D4 SVSS Headphone Amplier Negative Power-Supply Input. Connect to PVSS.
13 C3 BBR
Right BassMax Input. Connect an external lowpass lter between OUTR and BBR to
apply bass boost to the right-channel output. Connect BBR to SGND if BassMax is not
used (see the BassMax (Bass Boost) section).
14 D3 OUTR Right Headphone Output
15 D2 OUTL Left Headphone Output
16 C2 BBL
Left BassMax Input. Connect an external lowpass lter between OUTL and BBL to
apply bass boost to the left-channel output. Connect BBL to SGND if BassMax is not
used (see the BassMax (Bass Boost) section).
EP —EP Exposed Paddle. Connect EP to SVSS or leave unconnected.
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
9
Pin Description
MAX9723A and MAX9723B have a maximum amplifier
gain of 0dB while the MAX9723C and MAX9723D have
a maximum gain of +6dB. Amplifier volume is digitally
programmable to any one of 32 levels.
DirectDrive
Traditional single-supply headphone amplifiers have their
outputs biased at a nominal DC voltage, typically half
the supply, for maximum dynamic range. Large cou-
pling capacitors are needed to block this DC bias from
the headphone. Without these capacitors, a significant
amount of DC current flows to the headphone, resulting
in unnecessary power dissipation and possible damage to
both headphone and headphone amplifier.
Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage. This allows
the MAX9723 headphone amplifier outputs to be biased
at 0V, almost doubling the dynamic range while operat-
ing from a single supply. With no DC component, there
is no need for the large DC-blocking capacitors. Instead
of two large (typically 220μF) tantalum capacitors, the
MAX9723 charge pump requires only two small 1μF
ceramic capacitors, thereby conserving board space,
reducing cost, and improving the low-frequency response
of the headphone amplifier. See the Output Power vs.
Charge-Pump Capacitance and Load Resistance graph
in the Typical Operating Characteristics for details of the
possible capacitor sizes.
In addition to the cost and size disadvantages, the
Cblocking capacitors required by conventional head-
phone amplifiers limit low-frequency response and can
distort the audio signal.
Previous attempts at eliminating the output-coupling
capacitors involved biasing the headphone return (sleeve)
to the DC bias voltage of the headphone amplifiers. This
method raises some issues:
1) The sleeve is typically grounded to the chassis. Using
the midrail biasing approach, the sleeve must be
isolated from system ground, complicating product
design. The DirectDrive output biasing scheme allows
the sleeve to be grounded.
2) During an ESD strike, the amplifier’s ESD structure is
the only path to system ground. The amplifier must be
able to withstand the full ESD strike. The MAX9723
headphone outputs can withstand an ±8kV ESD strike
(HBM).
3) When using the headphone jack as a line out to other
equipment, the bias voltage on the sleeve may con-
flict with the ground potential from other equipment,
resulting in possible damage to the amplifiers. The
DirectDrive outputs of the MAX9723 can be directly
coupled to other ground-biased equipment.
Charge Pump
The MAX9723 features a low-noise charge pump. The
600kHz switching frequency is well beyond the audio
range, and does not interfere with the audio signals.
This enables the MAX9723 to achieve a 99dB SNR.
The switch drivers feature a controlled switching speed
that minimizes noise generated by turn-on and turn-off
transients. Limiting the switching speed of the charge
pump minimizes di/dt noise caused by the parasitic
bond wire and trace inductance. Although not typically
required, additional high-frequency noise attenuation
can be achieved by increasing the size of C2 (see the
Functional Diagram/Typical Operating Circuit).
Shutdown
The MAX9723 features a 5μA, low-power shutdown mode
that reduces quiescent current consumption and extends
battery life. Shutdown is controlled by a hardware or
software interface. Driving SHDN low disables the drive
amplifiers, bias circuitry, charge pump, and sets the
headphone amplifier output impedance to 20kΩ. Similarly,
the MAX9723 enters shutdown when bit seven (B7) in
the control register is reset. SHDN and B7 must be high
to enable the MAX9723. The I2C interface is active and
the contents of the command register are not affected
when in shutdown. This allows the master to write to the
MAX9723 while in shutdown.
Figure 1. Traditional Amplifier Output vs. MAX9723 DirectDrive
Output
VDD
+VDD
-VDD
VDD/2
GND
SGND
CONVENTIONAL AMPLIFIER BIASING SCHEME
DirectDrive BIASING SCHEME
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
10
Click-and-Pop Suppression
The output-coupling capacitor is a major contributor of
audible clicks and pops in conventional single-supply
headphone amplifiers. The amplifier charges the coupling
capacitor to its output bias voltage at startup. During shut-
down the capacitor is discharged. This charging and dis-
charging results in a DC shift across the capacitor, which
appears as an audible transient at the speaker. Since the
MAX9723 headphone amplifier does not require output-
coupling capacitors, no audible transients occur.
Additionally, the MAX9723 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Power-
Down Waveform in the Typical Operating Characteristics
shows that there are minimal transients at the output upon
startup or shutdown.
In most applications, the preamplifier driving the MAX9723
has a DC bias of typically half the supply. The input-coupling
capacitor is charged to the preamplifier’s bias voltage
through the MAX9723’s input impedance (RIN) during start-
up. The resulting voltage shift across the capacitor creates
an audible click/pop. To avoid clicks/pops caused by the
input filter, delay the rise of SHDN by at least 4 time con-
stants, 4 x RIN x CIN, relative to the start of the preamplifier.
BassMax (Bass Boost)
Typical headphones do not have a flat-frequency response.
The small physical size of the diaphragm does not allow the
headphone speaker to efficiently reproduce low frequen-
cies. This physical limitation results in attenuated bass
response. The MAX9723 includes a bass boost feature
that compensates for the headphone’s poor bass response
by increasing the amplifier gain at low frequencies.
The DirectDrive output of the MAX9723 has more head-
room than typical single-supply headphone amplifiers.
This additional headroom allows boosting the bass fre-
quencies without the output-signal clipping.
Program the BassMax gain and cutoff frequency with
external components connected between OUT_ and BB_
(see the Functional Diagram/Typical Operating Circuit).
Use the I2C-compatible interface to program the com-
mand register to enable/disable the BassMax circuit.
BB_ is connected to the noninverting input of the output
amplifier when BassMax is enabled. BB_ is pulled to
SGND when BassMax is disabled. The typical application
of the BassMax circuit involves feeding a lowpass version
of the output signal back to the amplifier. This is realized
using positive feedback from OUT_ to BB_. Figure 2
shows the connections needed to implement BassMax.
Maximum Gain Control
The MAX9723A and MAX9723B have selectable maxi-
mum gains of -5dB or 0dB (see Table 5) while the
MAX9723C and MAX9723D have selectable maximum
gains of +1dB or +6dB (see Table 6). Bit 5 in the command
register selects between the two maximum gain settings.
Volume Control
The MAX9723 includes a 32-level volume control that
adjusts the gain of the output amplifiers according to
the code contained in the command register. Volume is
programmed through the command register bits [4:0].
Tables 7–10 show all of the available gain settings for the
MAX9723A–MAX9723D. The mute attenuation is typically
better than 100dB when driving a 32Ω load.
Serial Interface
The MAX9723 features an I2C/SMBus-compatible, 2-wire
serial interface consisting of a serial data line (SDA) and
a serial clock line (SCL). SDA and SCL facilitate commu-
nication between the MAX9723 and the master at clock
rates up to 400kHz. Figure 3 shows the 2-wire interface
timing diagram. The MAX9723 is a receive-only slave
device relying on the master to generate the SCL signal.
The MAX9723 cannot write to the SDA bus except to
acknowledge the receipt of data from the master. The
Figure 2. BassMax External Connections
C3
R2
R1
R
R
OUT_
BB_
AUDIO
INPUT
BassMax
ENABLE
MAX9723
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
11
master, typically a microcontroller, generates SCL and
initiates data transfer on the bus.
A master device communicates to the MAX9723 by trans-
mitting the proper address followed by the data word.
Each transmit sequence is framed by a START (S) or
REPEATED START (Sr) condition and a STOP (P) condi-
tion. Each word transmitted over the bus is 8 bits long and
is always followed by an acknowledge clock pulse.
The MAX9723 SDA line operates as both an input and an
open-drain output. A pullup resistor, greater than 500Ω, is
required on the SDA bus. The MAX9723 SCL line oper-
ates as an input only. A pullup resistor, greater than 500Ω,
is required on SCL if there are multiple masters on the bus,
or if the master in a single-master system has an open-
drain SCL output. Series resistors in line with SDA and
SCL are optional. Series resistors protect the digital inputs
of the MAX9723 from highvoltage spikes on the bus lines,
and minimize crosstalk and undershoot of the bus signals.
Bit Transfer
One data bit is transferred during each SCL cycle. The
data on SDA must remain stable during the high period
of the SCL pulse. Changes in SDA while SCL is high are
control signals (see the START and STOP Conditions sec-
tion). SDA and SCL idle high when the I2C bus is not busy.
Start and Stop Conditions
SDA and SCL idle high when the bus is not in use. A mas-
ter device initiates communication by issuing a START
condition. A START condition is a high-to-low transition
on SDA with SCL high. A STOP condition is a low-to-high
transition on SDA while SCL is high (Figure 4). A START
condition from the master signals the beginning of trans-
mission to the MAX9723. The master terminates trans-
mission and frees the bus by issuing a STOP condition.
The bus remains active if a REPEATED START condition
is generated instead of a STOP condition.
Early STOP Conditions
The MAX9723 recognizes a STOP condition at any point
during data transmission except if the STOP condition
occurs in the same high pulse as a START condition.
Slave Address
The MAX9723 is available with one of two preset slave
addresses (see Table 1). The address is defined as the
seven most significant bits (MSBs) followed by the Read/
Write (R/W) bit. The address is the first byte of informa-
tion sent to the MAX9723 after the START condition. The
MAX9723 is a slave device only capable of being written
to. The sent R/W bit must always be a zero when config-
uring the MAX9723.
The MAX9723 acknowledges the receipt of its address
even if R/W is set to 1. However, the MAX9723 will not
drive SDA. Addressing the MAX9723 with R/W set to 1
causes the master to receive all 1’s regardless of the
contents of the command register.
Acknowledge
The acknowledge bit (ACK) is a clocked 9th bit that the
MAX9723 uses to handshake receipt of each byte of
Figure 3. 2-Wire Serial-Interface Timing Diagram
SCL
SDA
START
CONDITION
STOP
CONDITION
REPEATED
START
CONDITION
START
CONDITION
tHD, STA
tSU, STA tHD, STA tSP
tBUF
tSU, STO
tLOW
tSU, DAT
tHD, DAT
tHIGH
tRtF
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
12
data (see Figure 5). The MAX9723 pulls down SDA dur-
ing the master-generated 9th clock pulse. The SDA line
must remain stable and low during the high period of the
acknowledge clock pulse. Monitoring ACK allows for detec-
tion of unsuccessful data transfers. An unsuccessful data
transfer occurs if a receiving device is busy or if a system
fault has occurred. In the event of an unsuccessful data
transfer, the bus master may reattempt communication.
Write Data Format
A write to the MAX9723 includes transmission of a START
condition, the slave address with the R/W bit reset to 0
(see Table 1), one byte of data to configure the command
register, and a STOP condition. Figure 6 illustrates the
proper format for one frame.
The MAX9723 only accepts write data, but it acknowl-
edges the receipt of its address byte with the R/W bit set
high. The MAX9723 does not write to the SDA bus in the
event that the R/W bit is set high. Subsequently, the mas-
ter reads all 1’s from the MAX9723. Always reset the R/W
bit to 0 to avoid this situation.
Command Register
The MAX9723 has one command register that is used to
enable/disable shutdown, enable/disable BassMax, and
set the maximum gain and volume. Table 2 describes the
function of the bits contained in the command register.
Reset B7 to 0 to shut down the MAX9723. The MAX9723
wakes up from shutdown when B7 is set to 1 provided
SHDN is high. SHDN must be high and B7 must be set
to 1 for the MAX9723 to operate normally (see Table 3).
Set B6 to 1 to enable BassMax (see Table 4). The output
signal’s low-frequency response will be boosted accord-
ing to the external components connected between OUT_
and BB_. See the BassMax Gain-Setting Components
section in the Applications Information section for details
on choosing the external components.
Figure 4. START, STOP, and REPEATED START Conditions Figure 5. Acknowledge
Table 1. MAX9723 Address Map
Table 2. MAX9723 Command Register
Table 3. Shutdown Control, SHDN = 1
Table 4. BassMax Control
PART MAX9723 SLAVE ADDRESS
A6 A5 A4 A3 A2 A1 A0 R/W
MAX9723A 1 0 0 1 1 0 0 0
MAX9723B 1 0 0 1 1 010
MAX9723C 1 0 0 1 1 0 0 0
MAX9723D 1 0 0 1 1 010
B7 B6 B5 B4 B3 B2 B1 B0
SHUTDOWN BassMax
ENABLE
MAXIMUM
GAIN VOLUME
MODE B7
MAX9723 Disabled 0
MAX9723 Enabled 1
MODE B6
BassMax Disabled 0
BassMax Enabled 1
SCL
SDA
S Sr P
1
SCL
START
CONDITION
SDA
2 8 9
CLOCK PULSE FOR
ACKNOWLEDGMENT
ACKNOWLEDGE
NOT ACKNOWLEDGE
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
13
The MAX9723A and MAX9723B have a maximum
gain setting of -5dB or 0dB, while the MAX9723C and
MAX9723D have a maximum gain setting of +1dB or
+6dB. B5 in the command register programs the maxi-
mum gain (see Tables 5 and 6).
Adjust the MAX9723’s amplifier gain with the volume
control bits [4:0]. The gain is adjustable to one of 32 steps
ranging from full mute to the maximum gain programmed
by B5. Tables 7–10 list all the possible gain settings for
the MAX9723. Figures 7–10 show the volume control
transfer functions for the MAX9723.
Power-On Reset
The contents of the MAX9723’s command register at
power-on are shown in Table 11.
Applications Information
Power Dissipation and Heat Sinking
Linear power amplifiers can dissipate a significant amount
of power under normal operating conditions. The maxi-
mum power dissipation for each package is given in the
Absolute Maximum Ratings section under Continuous
Power Dissipation or can be calculated by the following
equation:
J(MAX) A
D(MAX)
JA
TT
P
−
=θ
where TJ(MAX) is +150°C, T
A
is the ambient temperature,
and θJA is the reciprocal of the derating factor in °C/W as
specified in the Absolute Maximum Ratings section. For
example, θ
JA
for the thin QFN package is +59°C/W.
The MAX9723 has two power dissipation sources, the
charge pump and the two output amplifiers. If the power
dissipation exceeds the rated package dissipation, reduce
VDD, increase load impedance, decrease the ambient
temperature, or add heatsinking. Large output, supply,
and ground traces decrease θJA, allowing more heat to be
transferred from the package to surrounding air.
Output Dynamic Range
Dynamic range is the difference between the noise
floor of the system and the output level at 1% THD+N.
It is essential that a system’s dynamic range be known
before setting the maximum output gain. Output clipping
will occur if the output signal is greater than the dynamic
range of the system. The DirectDrive architecture of the
MAX9723 has increased dynamic range compared to
other single-supply amplifiers.
Use the THD+N vs. Output Power in the Typical Operating
Characteristics to identify the system’s dynamic range.
Find the output power that causes 1% THD+N for a given
load. This point will indicate what output power causes the
output to begin to clip. Use the following equation to deter-
mine the peak output voltage that causes 1% THD+N for
a given load.
OUT_(P P) OUT_1% L
V 2 2(P R )
−= ×
where POUT_1% is the output power that causes 1%
THD+N, RL is the load resistance, and VOUT_(P-P) is
the peak output voltage. After VOUT_(P-P) is identified,
determine the peak input voltage that can be amplified
without clipping:
V
OUT_(P P)
IN_(P P) A
20
V
V
10
−
−
=
where VIN_(P-P) is the largest peak voltage that can be
amplified without clipping, and AV is the voltage gain
Figure 6. Write Data Format Example
Table 5. MAX9723A and MAX9723B
Maximum Gain Control
Table 6. MAX9723C and MAX9723D
Maximum Gain Control
MAXIMUM GAIN (dB) B5
-5 0
01
MAXIMUM GAIN (dB) B5
+1 0
+6 1
S
ACK
0
ACKNOWLEDGE FROM MAX9723
R/WACKNOWLEDGE
FROM MAX9723
B7 B6 B5 B4 B3 B2
COMMAND BYTE IS STORED ON
RECEIPT OF STOP CONDITION
ACK
P
B1 B0
SLAVE ADDRESS COMMAND BYTE
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
14
of the amplifier in dB determined by the maximum gain
setting (Bit 5) or the combination of the maximum gain
setting plus bass boost (see the BassMax Gain-Setting
Components section).
Component Selection
Input-Coupling Capacitor
The AC-coupling capacitor (CIN) and internal gain-setting
resistor form a highpass filter that removes any DC bias
from an input signal (see the Functional Diagram/ Typical
Operating Circuit). CIN allows the MAX9723 to bias the
Table 7. MAX9723A and MAX9723B Gain
Settings (B5 = 1, Max Gain = 0dB)
Table 8. MAX9723A and MAX9723B Gain
Settings (B5 = 0, Max Gain = -5dB)
B4 B3 B2 B1 B0
(LSB)
GAIN
(dB)
111110
11110 -0.5
11101 -1
1110 0 -1.5
1101 1 -2
11010 -2.5
11001 -3
11000-4
10111-5
10110-6
10101 -7
1010 0 -9
1001 1 -11
10010-13
10001-15
10000-17
01 1 1 1 -19
01110-21
01101 -23
0110 0 -25
0101 1 -27
01010-29
010 0 1 -31
01000-33
00111-35
00110-37
00101 -39
0010 0 -41
0001 1 -43
00010 -45
00001 -47
0 0 0 0 0 MUTE
B4 B3 B2 B1 B0
(LSB)
GAIN
(dB)
11111-5
11110-6
11101 -7
1110 0 -9
1101 1 -11
11010-13
110 0 1-15
110 0 0 -17
101 1 1 -19
101 1 0-21
10101 -23
1010 0 -25
1001 1 -27
10010-29
10001 -31
10 0 0 0 -33
01 1 1 1 -35
01110-37
01101 -39
0110 0 -41
0101 1 -43
01010 -45
010 0 1 -47
010 0 0 -51
001 1 1 -55
001 1 0 -59
00101 -63
0010 0 -67
0001 1 -71
00010 -75
00001 -79
0 0 0 0 0 MUTE
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
15
signal to an optimum DC level. The -3dB point of the high-
pass filter, assuming zero-source impedance, is given by:
3dB IN IN
1
f2R C
−=π× ×
Table 9. MAX9723C and MAX9723D Gain
Settings (B5 = 1, Max Gain = +6dB)
Table 10. MAX9723C and MAX9723D Gain
Settings (B5 = 0, Max Gain = +1dB)
Table 11. Initial Power-Up Command
Register Status
B4 B3 B2 B1 B0
(LSB)
GAIN
(dB)
1 1 1 1 1 6
11110 5.5
111015
1110 0 4.5
1101 1 4
11010 3.5
110 0 1 3
110 0 0 2
101 1 1 1
101 1 0 0
10101 -1
1010 0 -3
10 0 1 1 -5
10 0 10-7
10001 -9
10 0 0 0 -11
01 1 1 1 -13
01110 -15
01 1 01 -17
01 1 0 0 -19
0101 1 -21
01010-23
010 0 1-25
010 0 0 -27
001 1 1 -29
001 1 0-31
00101 -33
0010 0 -35
0001 1 -37
00010-39
00001 -41
0 0 0 0 0 MUTE
B4 B3 B2 B1 B0
(LSB)
GAIN
(dB)
1 1 1 1 1 1
11110 0
11101 -1
1110 0 -3
1101 1 -5
11010-7
110 0 1 -9
110 0 0 -11
101 1 1 -13
101 1 0 -15
10101 -17
1010 0 -19
1001 1 -21
10010-23
10001-25
10 0 0 0 -27
01 1 1 1 -29
01110-31
01101 -33
0110 0 -35
0101 1 -37
01010-39
010 0 1 -41
010 0 0 -45
001 1 1 -49
001 1 0 -53
00101-57
0010 0 -61
0001 1 -65
00010-69
00001 -73
0 0 0 0 0 MUTE
MODE B7 B6 B5 B4 B3 B2 B1 B0
Power-On
Reset 1 1 1 1 1 1 1 1
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
16
where RIN is a minimum of 10kΩ. Choose CIN such
that f-3dB is well below the lowest frequency of interest.
Setting f-3dB too high affects the amplifier’s low-frequency
response. Use capacitors with low-voltage coefficient
dielectrics. Film or C0G dielectric capacitors are good
choices for AC-coupling capacitors. Capacitors with high-
voltage coefficients, such as ceramics, can result in
increased distortion at low frequencies.
Charge-Pump Flying Capacitor
The charge-pump flying capacitor connected between
C1N and C1P affects the charge pump’s load regulation
and output impedance. Choosing a flying capacitor that
is too small degrades the MAX9723’s ability to provide
sufficient current drive and leads to a loss of output volt-
age. Increasing the value of the flying capacitor improves
load regulation and reduces the chargepump output
impedance. See the Output Power vs. Charge-Pump
Capacitance and Load Resistance graph in the Typical
Operating Characteristics.
Figure 7. MAX9723A/MAX9723B Transfer Function with B5 = 1
Figure 8. MAX9723A/MAX9723B Transfer Function with B5 = 0
Figure 9. MAX9723C/MAX9723D Transfer Function with B5 = 1
Figure 10. MAX9723C/MAX9723D Transfer Function with B5 = 0
MAX9723A AND MAX9723B
TRANSFER FUNCTION (B5 = 1)
CODE
GAIN (dB)
-20
-30
-40
10
0
-10
-50
0 6 12 18 24 30
MAX9723A AND MAX9723B
TRANSFER FUNCTION (B5 = 0)
CODE
GAIN (dB)
-40
-50
-60
-70
-80
0
-10
-30
-20
-90
0 6 12 18 24 30
GAIN PROFILE WITH AND
WITHOUT BassMax
FREQUENCY (Hz)
AV (dB)
1k10010
-8
-6
-4
-2
0
2
4
6
8
10
-10
1 10k
MAX9723A
CMD REGISTER
CODE = 0xFF
R1 = 47kΩ
R2 = 22kΩ
C3 = 0.1mF
fPOLE
fZERO
WITH
BassMax
WITHOUT
BassMax
MAX9723C AND MAX9723D
TRANSFER FUNCTION (B5 = 0)
CODE
0 6 12 18 24 30
GAIN (dB)
-30
-40
-50
-60
-70
10
0
-20
-10
-80
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
17
Charge-Pump Hold Capacitor
The hold capacitor’s value and ESR directly affect the rip-
ple at PVSS. Ripple is reduced by increasing the value of
the hold capacitor. Choosing a capacitor with lower ESR
reduces ripple and output impedance. Lower capacitance
values can be used in systems with low maximum output
power levels. See the Output Power vs. Charge-Pump
Capacitance and Load Resistance graph in the Typical
Operating Characteristics.
BassMax Gain-Setting Components
The bass-boost low-frequency response, when BassMax
is enabled, is set by the ratio of R1 to R2 by the following
equation (see Figure 2):
V_BOOST
R1 R2
A 20 logR1 R2
+
= × −
where AV_BOOST is the voltage gain boost in dB at low
frequencies. AV_BOOST is added to the gain realized by
the volume setting. The absolute gain at low frequencies
is equal to:
V_TOTAL V_VOL V_BOOST
A AA= +
where AV_VOL is the gain due to the volume setting, and
AV_TOTAL is the absolute gain at low frequencies. To
maintain circuit stability, the ratio:
R2/(R1 + R2)
must not exceed 1/2. A ratio equaling 1/3 is recommend-
ed. The switch that shorts BB_ to SGND, when BassMax
is disabled, can have an on-resistance as high as 300Ω.
Choose a value for R1 that is greater than 40kΩ to ensure
that positive feedback is negligible when BassMax is
disabled. Table 12 contains a list of R2 values, with R1 =
47kΩ, and the corresponding lowfrequency gain.
The low-frequency boost attained by the BassMax circuit
is added to the gain realized by the volume setting. Select
the BassMax gain so that the output signal will remain
within the dynamic range of the MAX9723. Output sig-
nal clipping will occur at low frequencies if the BassMax
gain boost is excessively large (see the Output Dynamic
Range section).
Capacitor C3 forms a pole and a zero according to the
following equations:
POLE
ZERO
R1 R2
f2 C3 R1 R2
R1 R2
f
2 C3 R1 R2
−
=π× × ×
+
=π× × ×
fPOLE is the frequency at which the gain boost begins to
roll off. fZERO is the frequency at which the bassboost
gain no longer affects the transfer function and the
volume-control gain dominates. Table 13 contains a list of
capacitor values and the corresponding poles and zeros
for a given DC gain. See Figure 11 for an example of a
gain profile using BassMax.
Custom Maximum Gain Setting Using
BassMax
The circuit in Figure 12 uses the BassMax function to
increase the maximum gain of the MAX9723. The gain
boost created with the circuit in Figure 12 is added to the
maximum gain selected by Bit 5 in the command register.
Set the maximum gain with RA and RB using the follow-
ing equation:
V_TOTAL V _VOL
RA RB
A A 20 log RA RB
+
= +×
−
where AV_VOL is the gain due to the volume setting, and
AV_TOTAL is the absolute passband gain in dB.
Capacitor CA blocks any DC offset from being gained,
but allows higher frequencies to pass. CA creates a pole
that indicates the low-frequency point of the pass band.
Choose CA so that the lowest frequencies of interest are
not attenuated. For a typical application, set fPOLE equal
to or below 20Hz.
Figure 11. BassMax, Gain Profile Example
GAIN PROFILE WITH AND
WITHOUT BassMax
FREQUENCY (Hz)
AV (dB)
1k10010
-8
-6
-4
-2
0
2
4
6
8
10
-10
1 10k
MAX9723A
CMD REGISTER
CODE = 0xFF
R1 = 47kΩ
R2 = 22kΩ
C3 = 0.1mF
fPOLE
fZERO
WITH
BassMax
WITHOUT
BassMax
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
18
POLE
1
CA
2 f (RA RB)
=π ×−
Figure 13 shows the frequency response of the circuit in
Figure 12. With RA = 47kΩ, RB = 22kΩ, and CA = 0.33μF,
the passband gain is set to 8.8dB.
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PC board. Connect PVSS to SVSS
and bypass with a 1μF capacitor to PGND. Bypass VDD
to PGND with a 1μF capacitor. Place the power-supply
bypass capacitor and the charge-pump capacitors as
close to the MAX9723 as possible. Route PGND and all
traces that carry switching transients away from SGND
and the audio signal path. Route digital signal traces
away from the audio signal path. Make traces perpen-
dicular to each other when routing digital signals over or
under audio signals.
The thin QFN package features an exposed paddle that
improves thermal efficiency. Ensure that the exposed
paddle is electrically isolated from PGND, SGND, and
VDD. Connect the exposed paddle to SVSS when the
board layout dictates that the exposed paddle cannot
be left floating.
Figure 12. Using BassMax to Increase MAX9723’s Maximum
Gain
Figure 13. Increasing the Maximum Gain Using BassMax
Table 12. BassMax Gain Examples
(R1 = 47kΩ)
Table 13. BassMax Pole and Zero
Examples for a Gain Boost of 8.8dB
(R1 = 47kΩ, R2 = 22kΩ)
C3 (nF) fPOLE (Hz) fZERO (Hz)
100 38 106
82 47 130
68 56 156
56 68 190
47 81 230
22 174 490
10 384 1060
R2 (kΩ) AV GAIN (dB)
39 20.6
33 15.1
27 11.3
22 8.8
15 5.7
10 3.7
CA
RB
RA
R
R
OUT_
BB_
AUDIO
INPUT
BassMax
ENABLE
MAX9723
FREQUENCY RESPONSE OF FIGURE 12
FREQUENCY (Hz)
AV (dB)
1k100101
1
2
3
4
5
6
7
8
9
10
0
0.1 10k
MAX9723A
CMD REGISTER
CODE = 0xFF
RA = 47kΩ
RB = 22kΩ
CA = 0.33mF
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
19
R5
10kΩ
R6
10kΩ
CIN
0.47µF
C4
0.1µF
R4
22kΩ
R3
47kΩ
R1
47kΩ
C5
1µF
C2
1µF
CIN
0.47µF
C1
1µF
1.8V TO 3.6V ANALOG INPUT
I2C INTERFACE
CHARGE PUMP
VDD
INR
SDA
SCL
VDD
VDD
SVSS
VDD
R
OUTR
BBR
BBL
OUTL
R
SVSS
VDD
SVSS
VDD
SVSS
SHDN
C1P
C1N
SGND PGND PVSS SVSS
C3
0.1µF
R2
22kΩ
ANALOG INPUT
BASS BOOST CIRCUIT TUNED
FOR +8.8dB AT 106Hz.
R
INL
R
MAX9723
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
20
Functional Diagram/Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 7165
PROCESS: BiCMOS
UCSP Applications Information
For the latest application details on UCSP construction, dimen-
sions, tape carrier information, PC board techniques, bump-
pad layout, and recommended reflow temperature profile, as
well as the latest information on reliability testing results, go
to Maxim’s website at www.maximintegrated.com/ucsp and
look up Application Note 1891: Understanding the Basics of the
Wafer-Level Chip-Scale Package (WL-CSP).
R3
47kΩ
R4
22kΩ
R1
47kΩ
C3
0.1µF
C4
0.1µF
R2
22kΩ
OUTL
VDD
PVSS
C2
1µF
C5
1µF
R6
10kΩ
R5
10kΩ
I2C
MASTER
CODEC
SVSS PGND SGND
BBL
OUTR
BBR
1.8V TO
3.6V
SDA
SCL
INL
INR
C1P
C1N
CIN
0.47µF
CIN
0.47µF
C1
1µF
MAX9723
12
11
10
9
SVSS
INR
INL
SGND
56 7 8
SCL
PVSS
SDA
SHDN
16 15 14 13
BBL
OUTL
OUTR
BBR
1
2
3
4
VDD
C1P
PGND
C1N
TOP VIEW
TOP VIEW
(BUMP SIDE DOWN)
THIN QFN
UCSP
SHDN
C1N PVSS SDA SGND
INLSCLPGND
C1P
VDD
BBL BBR INR
OUTL OUTR SVSS
1 2 3 4
A
B
C
D
+
MAX9723_
MAX9723_
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
21
System Diagram
Pin Congurations
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
16 TQFN T1644-4 21-0139 90-0070
16 UCSP B16-1 21-0101 Refer to Application Note 1891
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
22
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
23
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
24
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
www.maximintegrated.com Maxim Integrated
│
25
Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
28/08 Updated TQFN pin conguration, and corrected Typical Operating Circuit and System
Diagram pin names 20, 21
3 7/14 Removed automotive reference in Applications section 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I2C
© 2008 Maxim Integrated Products, Inc.
│
26
Revision History
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
