MAX9723_V01 [MAXIM]
Stereo DirectDrive Headphone Amplifier with BassMax, Volume Control, and I2C;
| 型号： | MAX9723_V01 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Stereo DirectDrive Headphone Amplifier with BassMax, Volume Control, and I2C |
| 文件： | 总26页 (文件大小：1992K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
General Description
The MAX9723 stereo DirectDrive headphone amplifier
Features
®
● 62mW, DirectDrive Headphone Amplifier Eliminates
Bulky DC-Blocking Capacitors
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.
● 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)
The headphone amplifier uses Maxim’s DirectDrive archi-
tecture that produces a ground-referenced output from a
single supply, eliminating the need for large DC-blocking
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.
2
● I C/SMBus-Compatible Interface
● Available in Space-Saving, Thermally Efficient
Packages:
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
• 16-Bump UCSP (2mm x 2mm x 0.62mm)
• 16-Pin Thin QFN (4mm x 4mm x 0.8mm)
Ordering Information
2
control are enabled through the I C/SMBus™-compatible
interface. Shutdown is controlled through either the hard-
ware or software interfaces.
PIN-
PACKAGE
PKG
CODE
PART**
TEMP RANGE
MAX9723_EBE-T -40°C to +85°C 16 UCSP-16 B16-1
MAX9723_ETE+ -40°C to +85°C 16 TQFN T1644-4
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.
*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.
Applications
● PDA Audio
Pin Configurations appears at end of data sheet.
● Portable CD Players
● Mini Disc Players
● MP3-Enabled Cellular
● Phones
Block Diagram
1.8V TO 3.6V SUPPLY
● MP3 Players
SCL
2
I C INTERFACE
SDA
BBL
Selector Guide
∑
∑
PART
SLAVE ADDRESS
MAXIMUM GAIN (dB)
OUTL
BassMax
MAX9723A
MAX9723B
MAX9723C
MAX9723D
1001100
0
0
1001101
INL
1001100
+6
+6
OUTR
BBR
VOLUME
CONTROL
1001101
INR
DirectDrive is a registered trademark of Maxim Integrated
Products, Inc.
SMBus is a trademark of Intel Corp.
BassMax
MAX9723
UCSP is a trademark of Maxim Integrated Products, Inc.
19-3509; Rev 5; 2/20
MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Absolute Maximum Ratings
SGND to PGND .....................................................-0.3V to +0.3V
Continuous Current Into/Out of:
V
to PGND...........................................................-0.3V to +4V
V
, C1P, PGND, C1N, PV , SV , or OUT_...........±0.85A
DD
DD SS SS
PV to SV .......................................................-0.3V to +0.3V
Any Other Pin................................................................±20mA
SS
SS
C1P to PGND.............................................-0.3V to (V
+ 0.3V)
Continuous Power Dissipation (T = +70°C)
DD
A
C1N to PGND...........................................(PV - 0.3V) to +0.3V
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)
SS
PV , SV to PGND..............................................+0.3V to -4V
SS
SS
IN_ to SGND.................................(SV - 0.3V) to (V
+ 0.3V)
SS
DD
SDA, SCL to PGND..................................................-0.3V to +4V
SHDN to PGND..........................................-0.3V to (V + 0.3V)
DD
OUT_ to SGND............................................................-3V to +3V
BB_ to SGND...............................................................-2V to +2V
Duration of OUT_ Short Circuit to _GND ....................Continuous
Reflow ..........................................................................+230°C
Lead Temperature (soldering, 10s) .................................+300°C
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
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)
A
MIN
MAX A
PARAMETER
GENERAL
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
Quiescent Supply Current
Shutdown Supply Current
Turn-On Time
V
1.8
3.6
V
DD
I
No load
= 0V
4
5
6.5
mA
µA
µs
µs
°C
°C
DD
I
V
8.5
DD_SHDN
SHDN
t
200
35
ON
Turn-Off Time
t
OFF
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
HEADPHONE AMPLIFIER
T
+143
12
THRES
T
HYST
Gain = 0dB,
MAX9723A/
MAX9723B
±0.7
±0.8
±4.5
±5
Measured between
OUT_ and SGND
(Note 2)
Output Offset Voltage
V
mV
OS
Gain = +6dB,
MAX9723C/
MAX9723D
Input Resistance
R
All volume levels
DC, V
10
17
±10
90
27
kΩ
IN
BBR, BBL Input Bias Current
I
±100
nA
BIAS_BB
= 1.8V to 3.6V
73
DD
f = 217Hz, 100mV
ripple,
P-P
87
86
61
V
= 3.0V
DD
Power-Supply Rejection Ratio
PSRR
(Note 2)
dB
f = 1kHz, 100mV
ripple,
P-P
V
= 3.0V
DD
f = 20kHz, 100mV
ripple,
P-P
V
= 3.0V
DD
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Electrical Characteristics (continued)
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C.) (Note 1)
A
MIN
MAX A
PARAMETER
Output Power
SYMBOL
CONDITIONS
MIN
TYP
59
MAX
UNITS
R = 32Ω
THD+N = 1%,
= 1kHz
L
P
mW
OUT
f
R = 16Ω (Note 5)
38
60
IN
L
R = 16Ω, P
= 35mW, f = 1kHz
IN
0.006
0.004
0
Total Harmonic Distortion Plus
Noise
L
OUT
THD+N
%
R = 32Ω, P
= 45mW, f = 1kHz
IN
L
OUT
Gain range bit 5 = 1
Gain range bit 5 = 0
Gain range bit 5 = 1
Gain range bit 5 = 0
BW = 22Hz to 22kHz
A-weighted
MAX9723A/
MAX9723B
dB
dB
dB
-5
Maximum Gain
A
MAX
+6
MAX9723C/
MAX9723D
+1
99
R = 32Ω,
L
Signal-to-Noise Ratio
SNR
V
= 1V
RMS
100
0.35
300
OUT
Slew Rate
SR
V/µs
pF
Capacitive Drive
No sustained oscillations
V
= 0V, measured from OUT_ to
= 0V, measured from OUT_ to
Into
SHDN
Output Resistance in Shutdown
Output Capacitance in Shutdown
R
C
20
60
kΩ
OUT_SHDN
SGND
V
SHDN
pF
OUT_SHDN
SGND
-69
-71
-70
-69
600
shutdown
MAX9723A/
MAX9723B
R = 32Ω,
L
Out of
shutdown
peak voltage,
A-weighted,
32 samples
per second
(Notes 2, 4)
Click/Pop Level
K
dB
CP
Into
shutdown
MAX9723C/
MAX9723D
Out of
shutdown
Charge-Pump Switching
Frequency
f
505
700
kHz
CP
L to ≥ or ≥ to L, f = 10kHz,
= 1V , R = 32Ω, both channels
Crosstalk
XTALK
V
80
dB
OUT
P-P
L
loaded
DIGITAL INPUTS (SHDN, SDA, SCL)
0.7 x
Input High Voltage
V
V
IH
V
DD
0.3 x
Input Low Voltage
V
V
IL
V
DD
Input Leakage Current
DIGITAL OUTPUTS (SDA)
Output Low Voltage
P1
µA
V
I
= 3mA
OL
0.4
V
OL
Output High Current
I
V
= V
DD
1
µA
OH
SDA
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Timing Characteristics
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V. gain = 0dB, maximum volume, BassMax disabled. Load con-
DD
nected between OUT_ and SGND where specified. T = T
to T
, unless otherwise noted. Typical values are at T = +25°C, see
A
MIN
MAX A
Timing Diagram.) (Notes 1, 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Serial Clock Frequency
f
0
400
kHz
SCL
Bus Free Time Between a STOP
and a START Condition
t
1.3
µs
µs
BUF
START Condition Hold Time
t
t
0.6
HD:STA
Low Period of the SCL Clock
t
1.3
µs
µs
LOW
High Period of the SCL Clock
t
0.6
HIGH
Setup Time for a Repeated
START Condition
0.6
µs
SU:STA
Data Hold Time
t
0
0.9
µs
ns
HD:DAT
Data Setup Time
t
100
SU:DAT
Maximum Rise Time of SDA and
SCL Signals
t
300
300
ns
ns
r
Maximum Fall Time of SDA and
SCL Signals
t
f
Setup Time for STOP Condition
Pulse Width of Suppressed Spike
t
0.6
µs
ns
SU:STO
t
100
400
SP
Maximum Capacitive Load for
Each Bus Line
C
pF
L_BUS
Note 1: All specifications are 100% tested at T = +25°C. Temperature limits are guaranteed by design.
A
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 T = +25°C.
A
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Typical Operating Characteristics
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. Outputs in phase, both channels loaded. T = +25°C, unless otherwise noted.) (See Func-
A
tional Diagram/Typical Operating Circuit)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
1
0.1
1
0.1
1
0.1
V
= 2.4V
V
= 3V
V
= 2.4V
DD
DD
DD
R = 32Ω
R = 16Ω
R = 16Ω
L
L
L
P
OUT
= 20mW
P
OUT
= 10mW
P
OUT
= 10mW
0.01
0.001
0.01
0.001
0.01
0.001
P
OUT
= 37mW
P
OUT
= 25mW
P
OUT
= 23mW
10
100
1k
10k
100k
10
100
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
1
0.1
100
10
100
10
V
R
= 3V
= 32Ω
V
= 2.4V
V
= 2.4V
DD
DD
DD
R = 16Ω
R = 32Ω
L
L
L
1
1
P
OUT
= 10mW
f
= 1kHz
IN
f
= 1kHz
f
= 20Hz
IN
IN
0.1
0.1
f
= 10kHz
f
= 10kHz
IN
IN
f
IN
= 20Hz
0.01
0.001
0.01
0.001
0.01
0.001
P
OUT
= 30mW
10
100
1k
FREQUENCY (Hz)
10k
100k
0
20
40
60
0
20
40
60
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
POWER DISSIPATION
vs. OUTPUT POWER
100
10
100
10
180
160
140
120
100
80
V
= 3V
V
f
= 2.4V
= 1kHz
DD
V
= 3V
DD
DD
R = 16Ω
L
R = 32Ω
IN
L
P
OUT
= P
+ P
OUTL OUTR
R = 16Ω
L
OUTPUTS IN PHASE
1
1
R = 32Ω
L
f
= 1kHz
IN
f
= 10kHz
f
= 1kHz
IN
IN
0.1
0.1
60
f
= 20Hz
f
= 10kHz
IN
IN
f
= 20Hz
IN
40
0.01
0.001
0.01
0.001
20
0
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
OUTPUT POWER (mW)
OUTPUT POWER (mW)
OUTPUT POWER (mW)
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Typical Operating Characteristics (continued)
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. Outputs in phase, both channels loaded. T = +25°C, unless otherwise noted.) (See Func-
A
tional Diagram/Typical Operating Circuit)
POWER DISSIPATION
vs. OUTPUT POWER
OUTPUT POWER
vs. LOAD RESISTANCE
80
70
60
50
40
30
20
10
0
300
250
200
150
100
50
V
f
= 3V
= 1kHz
= P
DD
V
= 2.4V
DD
IN
f = 1kHz
IN
P
OUT
+ P
OUTL OUTR
R = 16Ω
L
OUTPUTS IN PHASE
R = 32Ω
L
THD+N = 10%
THD+N = 1%
0
0
20
40
60
80
100
120
10
100
1k
OUTPUT POWER (mW)
LOAD RESISTANCE (W)
OUTPUT POWER
OUTPUT POWER
vs. LOAD RESISTANCE
vs. SUPPLY VOLTAGE
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
V
= 3V
= 1kHz
DD
f
IN
THD+N = 10%
THD+N = 10%
THD+N = 1%
THD+N = 1%
f
= 1kHz
IN
R = 16Ω
L
10
100
1k
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
OUTPUT POWER
vs. SUPPLY VOLTAGE
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
140
120
100
80
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
R = 32Ω
L
THD+N = 10%
60
THD+N = 1%
= 1kHz
40
f
20
IN
R = 32Ω
L
0
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE (V)
10
100
1k
10k
100k
FREQUENCY (Hz)
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Typical Operating Characteristics (continued)
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. Outputs in phase, both channels loaded. T = +25°C, unless otherwise noted.) (See Func-
A
tional Diagram/Typical Operating Circuit)
CROSSTALK
CROSSTALK
vs. FREQUENCY
vs. FREQUENCY
0
-20
0
-20
V
= 1V
V = 1V
IN P-P
IN
P-P
R = 32Ω
A = 0dB
R = 32Ω
L
L
A = -10dB
-40
-40
RIGHT TO LEFT
A = 0dB
RIGHT TO LEFT
A = -10dB
-60
-60
-80
-80
-100
-120
-100
-120
LEFT TO RIGHT
A = -10dB
LEFT TO RIGHT
A = 0dB
10
10
0
100
1k
FREQUENCY (Hz)
10k
100k
100k
20
10
10
0
100
1k
FREQUENCY (Hz)
10k
100k
BASS BOOST FREQUENCY
RESPONSE
GAIN FLATNESS
vs. FREQUENCY
20
15
10
5
1
0
R2 = 36kΩ
C3 = 0.068µF
NO LOAD
R1 = 47kΩ
-1
-2
-3
-4
-5
-6
-7
R2 = 22kΩ
C3 = 0.1µF
R2 = 10kΩ
C3 = 0.22µF
0
BassMax DISABLED
-5
-10
100
1k
10k
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
OUTPUT SPECTRUM
vs. FREQUENCY
CHARGE-PUMP OUTPUT VOLTAGE
vs. OUTPUT CURRENT
-40
-50
0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
NO HEADPHONE LOAD
CHARGE-PUMP LOAD
CONNECTED
R = 32Ω
L
V
= 3V
= 1kHz
DD
-60
f
IN
BETWEEN PV AND PGND
SS
-70
-80
-90
-100
-110
-120
-130
-140
5
10
15
25 50 75 100 125 150 175 200
OUTPUT CURRENT (mA)
FREQUENCY (kHz)
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Typical Operating Characteristics (continued)
(V
= SHDN = 3V, PGND = SGND = 0V, C1 = C2 = 1μF, BB_ = 0V, gain = 0dB, maximum volume, BassMax disabled. Load connected
DD
between OUT_ and SGND where specified. Outputs in phase, both channels loaded. T = +25°C, unless otherwise noted.) (See Func-
A
tional Diagram/Typical Operating Circuit)
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCE
POWER-UP/POWER-DOWN
WAVEFORM
MAX9723 toc23
75
70
65
60
55
50
45
40
35
C1 = C2 = 2.2µF
C1 = C2 = 1µF
V
DD
2V/div
C1 = C2 = 0.68µF
V
OUT
10mV/div
V
= 3V
= 1kHz
DD
f
IN
THD+N = 1%
10
20
30
40 50
20ms/div
LOAD RESISTANCE (Ω)
EXITING SHUTDOWN
ENTERING SHUTDOWN
MAX9723 toc24
MAX9723 toc25
V
SHDN
2V/div
V
SHDN
2V/div
V
OUT_
V
OUT_
200mV/div
200mV/div
40µs/div
20µs/div
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
4.5
4.0
3.5
3.0
2.5
2.0
8
7
6
5
4
3
2
1
0
NO LOAD
INPUTS GROUNDED
NO LOAD
INPUTS GROUNDED
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE (V)
1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6
SUPPLY VOLTAGE (V)
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Pin Description
PIN
BUMP
NAME
FUNCTION
THIN QFN
UCSP
D1
1
2
3
4
5
6
7
V
Power-Supply Input. Bypass V
to PGND with a 1µF capacitor.
DD
DD
C1
C1P
PGND
C1N
Charge-Pump Flying Capacitor Positive Terminal
Power Ground. Connect to SGND.
B1
A1
Charge-Pump Flying Capacitor Negative Terminal
Serial Clock Input. Connect a 10kI pullup resistor from SCL to V
B2
SCL
.
DD
A2
PV
Charge-Pump Output. Connect to SV . Bypass PV with a 1µF capacitor to PGND.
SS
SS
SS
A3
SDA
Serial-Data Input. Connect a 10kΩ pullup resistor from SDA to V
.
DD
Shutdown. Drive SHDN low to disable the MAX9723. Connect SHDN to V
is high for normal operation (see the Command Register section).
while bit 7
DD
8
B3
SHDN
9
A4
B4
C4
D4
SGND
INL
Signal Ground. Connect to PGND.
Left-Channel Input
10
11
12
INR
Right-Channel Input
SV
Headphone Amplifier Negative Power-Supply Input. Connect to PV
.
SS
SS
Right BassMax Input. Connect an external lowpass filter 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).
13
C3
BBR
14
D3
D2
OUTR
OUTL
Right Headphone Output
Left Headphone Output
15
Left BassMax Input. Connect an external lowpass filter 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).
16
C2
—
BBL
EP
EP
Exposed Paddle. Connect EP to SV or leave unconnected.
SS
The MAX9723 DirectDrive outputs are biased at SGND
Detailed Description
(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.
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
2
An I C-compatible interface allows serial communica-
tion between the MAX9723 and a microcontroller. The
2
MAX9723 is available with two different I C addresses
2
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
I C-compatible interface (see the Functional Diagram/
Typical Operating Circuit). A negative power supply
(PV ) is created internally by inverting the positive sup-
SS
ply (V ). Powering the amplifiers from V
and PV
DD
DD
SS
increases the dynamic range of the amplifiers to almost
twice that of other single-supply amplifiers, increasing the
total available output power.
Maxim Integrated
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
phone amplifiers limit low-frequency response and can
distort the audio signal.
V
V
DD
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:
/2
DD
GND
CONVENTIONAL AMPLIFIER BIASING SCHEME
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.
+V
DD
SGND
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).
-V
DD
DirectDrive BIASING SCHEME
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.
Figure 1. Traditional Amplifier Output vs. MAX9723 DirectDrive
Output
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.
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).
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.
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
2
to enable the MAX9723. The I C 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.
In addition to the cost and size disadvantages, the
DC-blocking capacitors required by conventional head-
Maxim Integrated
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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.
MAX9723
R
R
AUDIO
INPUT
OUT_
BB_
R1
R2
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.
BassMax
ENABLE
C3
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
Figure 2. BassMax External Connections
through the MAX9723’s input impedance (R ) during start-
IN
using positive feedback from OUT_ to BB_. Figure 2
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 R x C , relative to the start of the preamplifier.
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.
IN
IN
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.
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.
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 I C-compatible interface to program the com-
mand register to enable/disable the BassMax circuit.
Serial Interface
The MAX9723 features an I C/SMBus-compatible, 2-wire
2
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
2
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
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
SDA
SCL
t
BUF
t
t
SU, STA
SU, DAT
t
t
SP
HD, STA
t
SU, STO
t
t
HD, DAT
LOW
t
HIGH
t
HD, STA
t
R
t
F
START
CONDITION
REPEATED
START
STOP
START
CONDITION CONDITION
CONDITION
Figure 3. 2-Wire Serial-Interface Timing Diagram
master, typically a microcontroller, generates SCL and
initiates data transfer on the bus.
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.
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.
Early STOP Conditions
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 high-voltage spikes on the bus lines,
and minimize crosstalk and undershoot of the bus signals.
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.
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-
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.
2
tion). SDA and SCL idle high when the I C 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
Acknowledge
The acknowledge bit (ACK) is a clocked 9th bit that the
MAX9723 uses to handshake receipt of each byte of
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
S
Sr
P
CLOCK PULSE FOR
ACKNOWLEDGMENT
START
CONDITION
SCL
SCL
1
2
8
9
NOT ACKNOWLEDGE
SDA
SDA
ACKNOWLEDGE
Figure 4. START, STOP, and REPEATED START Conditions
Figure 5. Acknowledge
Table 3. Shutdown Control, SHDN = 1
Table 1. MAX9723 Address Map
MODE
B7
0
MAX9723 SLAVE ADDRESS
PART
MAX9723 Disabled
MAX9723 Enabled
A6
A5
A4
A3
A2
A1
A0 R/W
1
MAX9723A
MAX9723B
MAX9723C
MAX9723D
1
0
0
1
1
0
0
1
0
1
0
0
0
0
1
0
0
1
1
0
1
0
0
1
1
0
Table 4. BassMax Control
1
0
0
1
1
0
MODE
B6
0
BassMax Disabled
BassMax Enabled
Table 2. MAX9723 Command Register
1
B7
B6
B5
B4 B3 B2 B1 B0
BassMax MAXIMUM
SHUTDOWN
VOLUME
ENABLE
GAIN
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.
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).
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.
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.
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-
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Table 5. MAX9723A and MAX9723B
Maximum Gain Control
MAXIMUM GAIN (dB)
B5
0
COMMAND BYTE IS STORED ON
RECEIPT OF STOP CONDITION
B7 B6 B5 B4 B3 B2 B1 B0
ACK COMMAND BYTE ACK P
-5
0
ACKNOWLEDGE FROM MAX9723
1
S
SLAVE ADDRESS
0
ACKNOWLEDGE
FROM MAX9723
R/W
Table 6. MAX9723C and MAX9723D
Maximum Gain Control
MAXIMUM GAIN (dB)
B5
0
+1
+6
Figure 6. Write Data Format Example
1
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).
temperature, or add heatsinking. Large output, supply,
and ground traces decrease θ , allowing more heat to be
JA
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.
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.
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.
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:
V
= 2 2(P
×R )
OUT_(P−P)
OUT_1% L
where P
is the output power that causes 1%
OUT_1%
THD+N, R is the load resistance, and V
is
L
OUT_(P-P)
T
− T
A
J(MAX)
the peak output voltage. After V
is identified,
P
=
OUT_(P-P)
D(MAX)
θ
JA
determine the peak input voltage that can be amplified
without clipping:
where T
is +150°C, T is the ambient temperature,
J(MAX)
A
and θ is the reciprocal of the derating factor in °C/W as
V
JA
OUT_(P−P)
V
=
IN_(P−P)
specified in the Absolute Maximum Ratings section. For
A
V
example, θ for the thin QFN package is +59°C/W.
JA
20
10
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
where V
is the largest peak voltage that can be
amplified without clipping, and A is the voltage gain
IN_(P-P)
V
V
, increase load impedance, decrease the ambient
DD
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Table 7. MAX9723A and MAX9723B Gain
Settings (B5 = 1, Max Gain = 0dB)
Table 8. MAX9723A and MAX9723B Gain
Settings (B5 = 0, Max Gain = -5dB)
B0
(LSB)
GAIN
(dB)
B0
(LSB)
GAIN
(dB)
B4
B3
B2
B1
B4
B3
B2
B1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
0
-0.5
-1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
-5
-6
-7
-1.5
-2
-9
-11
-13
-15
-17
-19
-21
-23
-25
-27
-29
-31
-33
-35
-37
-39
-41
-43
-45
-47
-50
-53
-56
-59
-62
-65
-68
-71
MUTE
-2.5
-3
-4
-5
-6
-7
-9
-11
-13
-15
-17
-19
-21
-23
-25
-27
-29
-31
-33
-35
-37
-39
-41
-43
-45
-47
MUTE
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 (C ) and internal gain-setting
resistor form a highpass filter that removes any DC bias
IN
from an input signal (see the Functional Diagram/ Typical
Operating Circuit). C allows the MAX9723 to bias the
IN
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│ 15
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Table 9. MAX9723C and MAX9723D Gain
Settings (B5 = 1, Max Gain = +6dB)
Table 10. MAX9723C and MAX9723D Gain
Settings (B5 = 0, Max Gain = +1dB)
B0
(LSB)
GAIN
(dB)
B0
(LSB)
GAIN
(dB)
B4
B3
B2
B1
B4
B3
B2
B1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
6
5.5
5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
-1
4.5
4
-3
-5
3.5
3
-7
-9
2
-11
-13
-15
-17
-19
-21
-23
-25
-27
-29
-31
-33
-35
-37
-39
-41
-44
-47
-50
-53
-56
-59
-62
-65
MUTE
1
0
-1
-3
-5
-7
-9
-11
-13
-15
-17
-19
-21
-23
-25
-27
-29
-31
-33
-35
-37
-39
-41
MUTE
signal to an optimum DC level. The -3dB point of the high-
pass filter, assuming zero-source impedance, is given by:
Table 11. Initial Power-Up Command
Register Status
1
MODE
B7
B6
B5
B4
B3
B2
B1
B0
f
=
−3dB
2π ×R × C
IN
IN
Power-On
Reset
1
1
1
1
1
1
1
1
Maxim Integrated
│ 16
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
MAX9723AAND MAX9723B TRANSFER FUNCTION
MAX9723CAND MAX9723D TRANSFER FUNCTION
(B5 = 1)
(B5 = 1)
toc01
toc02
10
0
10
0
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
0
6
12
18
CODE
24
30
0
6
12
18
CODE
24
30
Figure 7. MAX9723A/MAX9723B Transfer Function with B5 = 1
Figure 9. MAX9723C/MAX9723D Transfer Function with B5 = 1
MAX9723AAND MAX9723B TRANSFER FUNCTION
MAX9723CAND MAX9723D TRANSFER FUNCTION
(B5 = 0)
(B5 = 0)
toc03
toc04
0
10
-10
-20
-30
-40
-50
-60
-70
-80
0
-10
-20
-30
-40
-50
-60
-70
0
6
12
18
CODE
24
30
0
6
12
18
CODE
24
30
Figure 8. MAX9723A/MAX9723B Transfer Function with B5 = 0
Figure 10. MAX9723C/MAX9723D Transfer Function with B5 = 0
where R is a minimum of 10kΩ. Choose C such
Charge-Pump Flying Capacitor
IN
IN
that f
Setting f
is well below the lowest frequency of interest.
-3dB
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 charge-pump output
impedance. See the Output Power vs. Charge-Pump
Capacitance and Load Resistance graph in the Typical
Operating Characteristics.
too high affects the amplifier’s low-frequency
-3dB
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.
Maxim Integrated
│ 17
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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 low-frequency gain.
GAIN PROFILE WITH AND
WITHOUT BassMax
10
8
f
POLE
6
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).
f
WITH
BassMax
ZERO
4
2
0
MAX9723A
-2
-4
-6
-8
-10
WITHOUT
BassMax
CMD REGISTER
CODE = 0xFF
R1 = 47kΩ
R2 = 22kΩ
C3 = 0.1mF
Capacitor C3 forms a pole and a zero according to the
following equations:
1
10
100
1k
10k
R1− R2
2π × C3 ×R1×R2
R1+ R2
FREQUENCY (Hz)
f
f
=
=
POLE
ZERO
Figure 11. BassMax, Gain Profile Example
2π × C3 ×R1×R2
Charge-Pump Hold Capacitor
f
is the frequency at which the gain boost begins
POLE
to roll off. f
is the frequency at which the bass-
The hold capacitor’s value and ESR directly affect the rip-
ZERO
boost 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.
ple at PV . Ripple is reduced by increasing the value of
SS
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.
Custom Maximum Gain Setting Using
BassMax
BassMax Gain-Setting Components
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:
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):
R1+ R2
R1− R2
A
= 20×log
V_BOOST
RA + RB
RA − RB
where A
frequencies. A
the volume setting. The absolute gain at low frequencies
is equal to:
is the voltage gain boost in dB at low
V_BOOST
A
= A
+ 20×log
V_VOL
V_TOTAL
is added to the gain realized by
V_BOOST
where A
is the gain due to the volume setting, and
V_VOL
A
is the absolute passband gain in dB.
V_TOTAL
A
= A
+ A
V_VOL V_BOOST
V_TOTAL
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
where A
A
is the gain due to the volume setting, and
V_VOL
is the absolute gain at low frequencies. To
V_TOTAL
maintain circuit stability, the ratio:
not attenuated. For a typical application, set f
equal
POLE
R2/(R1 + R2)
to or below 20Hz.
must not exceed 1/2. A ratio equaling 1/3 is recommend-
ed. The switch that shorts BB_ to SGND, when BassMax
Maxim Integrated
│ 18
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
FREQUENCY RESPONSE OF FIGURE 12
10
MAX9723
R
9
8
7
6
5
R
AUDIO
INPUT
OUT_
BB_
CA
RA
MAX9723A
4
3
2
1
0
CMD REGISTER
CODE = 0xFF
RA = 47kΩ
RB = 22kΩ
CA = 0.33mF
BassMax
ENABLE
RB
0.1
1
10
100
1k
10k
FREQUENCY (Hz)
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)
1
CA =
2 π f
× (RA − RB)
POLE
R2 (kΩ)
39
A
GAIN (dB)
20.6
15.1
11.3
V
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.
33
27
Layout and Grounding
Proper layout and grounding are essential for optimum
22
8.8
performance. Connect PGND and SGND together at a
15
5.7
single point on the PC board. Connect PV
to SV
SS
SS
10
3.7
and bypass with a 1μF capacitor to PGND. Bypass V
DD
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.
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
82
68
56
47
22
10
38
106
130
156
190
230
490
1060
47
56
The thin QFN package features an exposed paddle that
improves thermal efficiency. Ensure that the exposed
paddle is electrically isolated from PGND, SGND, and
68
V
. Connect the exposed paddle to SV
when the
81
DD
SS
board layout dictates that the exposed paddle cannot
be left floating.
174
384
Maxim Integrated
│ 19
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Functional Diagram/Typical Operating Circuit
1.8V TO 3.6V
ANALOG INPUT
C
R5
10kΩ
R6
10kΩ
IN
C5
1µF
0.47µF
SCL
INR
SDA
V
DD
R
V
DD
V
DD
2
I C INTERFACE
R
SHDN
OUTR
BBR
R3
47kΩ
SV
SS
SV
SS
C4
0.1µF
R4
22kΩ
MAX9723
V
DD
V
DD
V
DD
BBL
R2
22kΩ
C3
0.1µF
C1P
C1N
C1
1µF
CHARGE PUMP
SV
SS
R1
R
47kΩ
SV
SS
OUTL
SGND PGND PV
SV
SS
INL
R
SS
C2
1µF
C
IN
BASS BOOST CIRCUIT TUNED
FOR +8.8dB AT 106Hz.
0.47µF
ANALOG INPUT
UCSP Applications Information
Chip 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).
TRANSISTOR COUNT: 7165
PROCESS: BiCMOS
Maxim Integrated
│ 20
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
System Diagram
1.8V TO
3.6V
C5
1µF
R5
10kΩ
R6
10kΩ
V
DD
SDA
SCL
2
I C
MASTER
OUTL
BBL
C
IN
R3
47kΩ
0.47µF
INL
MAX9723
C
IN
CODEC
R4
22kΩ
0.47µF
C4
0.1µF
INR
OUTR
BBR
C1P
C1N
C1
1µF
R1
47kΩ
PV
SS
SV
SS
PGND SGND
C3
0.1µF
C2
1µF
R2
22kΩ
Pin Configurations
TOP VIEW
(BUMP SIDE DOWN)
TOP VIEW
1
2
3
4
16 15 14 13
+
PV
A
B
C
D
C1N
SDA
SGND
INL
SS
V
1
12 SV
DD
SS
11 INR
10 INL
C1P
2
3
4
MAX9723_
PGND
PGND
C1P
SCL
SHDN
9
SGND
C1N
MAX9723_
5
6
7
8
BBL
BBR
INR
THIN QFN
V
DD
SV
SS
OUTL
OUTR
UCSP
Maxim Integrated
│ 21
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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.
PACKAGE TYPE
16 TQFN
PACKAGE CODE
T1644-4
OUTLINE NO.
21-0139
LAND PATTERN NO.
90-0070
16 UCSP
B16-1
21-0101
Refer to Application Note 1891
Maxim Integrated
│ 22
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MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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.
Maxim Integrated
│ 23
www.maximintegrated.com
MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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.
Maxim Integrated
│ 24
www.maximintegrated.com
MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
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.
Maxim Integrated
│ 25
www.maximintegrated.com
MAX9723
Stereo DirectDrive Headphone Amplifier
with BassMax, Volume Control, and I C
2
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
Updated TQFN pin configuration, and corrected Typical Operating Circuit and System
Diagram pin names
2
8/08
20, 21
3
4
5
7/14
7/14
2/20
Removed automotive reference in Applications section
Updated Table 8, Table 10, and replaced Figures 7 through 10
Updated Ordering Information table
1
15, 16, 17
1
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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 specifications 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.
2020 Maxim Integrated Products, Inc.
│ 26
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