General Description
The MAX9722A/MAX9722B stereo headphone amplifiers
are designed for portable equipment where board space
is at a premium. The MAX9722A/MAX9722B use a
unique DirectDrive architecture to produce a ground-ref-
erenced output from a single supply, eliminating the
need for large DC-blocking capacitors, which saves
cost, board space, and component height. Additionally,
the gain of the amplifier is set internally
(-2V/V, MAX9722B) or adjusted externally (MAX9722A).
The MAX9722A/MAX9722B deliver up to 70mW per
channel into a 16Ωload or 130mW into a 32Ωload and
have low 0.009% THD+N. An 80dB at 217Hz power-sup-
ply rejection ratio (PSRR) allows these devices to operate
from noisy digital supplies without an additional linear
regulator. The MAX9722A/MAX9722B include ±8kV ESD
protection on the headphone outputs. Comprehensive
anticlick-and-pop circuitry suppresses audible clicks
and pops on startup and shutdown. A low-power shut-
down mode reduces the supply current to 0.1µA.
The MAX9722A/MAX9722B operate from a single 2.4V
to 5.5V supply, consume only 5.5mA of supply current,
feature short-circuit and thermal-overload protection,
and are specified over the extended -40°C to +85°C
temperature range. The devices are available in tiny
16-pin thin QFN (3mm ✕3mm ✕0.8mm) and 16-pin
TSSOP packages.
Applications
Features
♦2.4V to 5.5V Single-Supply Operation
♦High PSRR (80dB at 217Hz) Eliminates LDO
♦No Bulky DC-Blocking Capacitors Required
♦Ground-Referenced Outputs Eliminate DC Bias
Voltage on Headphone Ground Pin
♦No Degradation of Low-Frequency Response Due
to Output Capacitors
♦Differential Inputs for Enhanced Noise
Cancellation
♦Adjustable Gain (MAX9722A) or Fixed -2V/V Gain
(MAX9722B)
♦130mW per Channel into 32Ω
♦Low 0.009% THD+N
♦Integrated Click-and-Pop Suppression
♦Low Quiescent Current (5.5mA)
♦Short-Circuit and Thermal-Overload Protection
♦±8kV ESD-Protected Amplifier Outputs (Human
Body Model)
♦Available in a Space-Saving 16-Pin Thin QFN
(3mm ✕3mm ✕0.8mm) Package
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
LEFT
AUDIO
INPUT
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
FIXED GAIN ELIMINATES
EXTERNAL RESISTOR
NETWORK.
RIGHT
AUDIO
INPUT
SHDN MAX9722B
Simplified Diagram
19-3049; Rev 2; 10/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Note: All devices are specified over the -40°C to +85°C operating
temperature range.
*EP = Exposed paddle.
Pin Configurations and Typical Application Circuit appear at
end of data sheet.
PART PIN-PACKAGE
TOP
MARK
PKG
CODE
MAX9722AETE
16 Thin QFN-EP* (3mm
✕ 3mm ✕ 0.8mm)
AAX
T1633-5
MAX9722AEUE
16 TSSOP —
U16-1
MAX9722BETE
16 Thin QFN-EP* (3mm
✕ 3mm ✕ 0.8mm)
AAY
T1633-5
MAX9722BEUE
16 TSSOP —
U16-1
Notebook and
Desktop PCs
MP3 Players
Flat-Panel Monitors
Cellular Phones
Smart Phones
PDAs
Portable Audio
Equipment
EVALUATION KIT
AVAILABLE
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, resistive load referenced to ground, for
MAX9722A gain = -1V/V (RIN = RF= 10kΩ), for MAX9722B gain = -2V/V (internally set), TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
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.
PGND to SGND .....................................................-0.3V to +0.3V
PVDD and SVDD to PGND or SGND .........................-0.3V to +6V
PVSS and SVSS to PGND..........................................+0.3V to -6V
IN_ to SGND ................................(SVSS - 0.3V) to (SVDD + 0.3V)
OUT_ to PGND ......................................................-3.0V to +3.0V
SHDN to SGND..........................(SGND - 0.3V) to (SVDD + 0.3V)
C1P to PGND ...........................................-0.3V to (PVDD + 0.3V)
C1N to PGND............................................(SVSS - 0.3V) to +0.3V
PVDD to SVDD...........................................................................0V
PVSS to SVSS ............................................................................0V
Output Short Circuit to GND.......................................Continuous
Continuous Power Dissipation (TA= +70°C)
16-Pin Thin QFN (derate 14.7mW/°C above +70°C)....1176mW
16-Pin TSSOP (derate 9.4mW/°C above +70°C) .........755mW
Junction Temperature ......................................................+150°C
Operating Temperature Range............................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range VDD Guaranteed by PSRR test
2.4 5.5
V
Quiescent Supply Current IDD RL = ∞
5.5
13
mA
Shutdown Supply Current ISHDN SHDN = SGND
0.1
2µA
SHDN Input Logic High VIH 2V
SHDN Input Logic Low VIL
0.8
V
SHDN Input Leakage Current -1
+0.05
+1 µA
SHDN to Full Operation Time tSON 80 µs
AMPLIFIERS
Voltage Gain AVMAX9722B (Note 2)
-1.98
-2
-2.02
V/V
Gain Matching MAX9722B, between the right and left channels ±2%
Between IN_+ and IN_-, AC-coupled (MAX9722A) ±0.5 ±2.5
Input Offset Voltage VIS
Between IN_+ and IN_-, AC-coupled (MAX9722B) ±1.5
±5
mV
Input Bias Current IBIAS IN_+ and IN_- 50 nA
Input Impedance RIN MAX9722B, measured at IN_ 10
14.4
20 kΩ
Input Common-Mode Voltage
Range VCM
-0.5 +0.7
V
Common-Mode Rejection Ratio
CMRR
Input referred, MAX9722A, TA = +25°C
-60 -70
dB
DC, VDD = 2.4V to 5.5V, input referred
-80 -90
f = 217Hz, 100mVP-P ripple, input referred
-80
Power-Supply Rejection Ratio
(Note 3) PSRR
f = 10kHz, 100mVP-P ripple, input referred
-50
dB
RL = 16Ω, THD+N = 1%, TA = +25°C 60 70
Output Power POUT RL = 32Ω, THD+N = 1%, TA = +25°C
130
mW
Output Voltage VOUT RL = 1kΩ2
VRMS
Output Impedance in Shutdown
10 kΩ
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, resistive load referenced to ground, for
MAX9722A gain = -1V/V (RIN = RF= 10kΩ), for MAX9722B gain = -2V/V (internally set), TA= -40°C to +85°C, unless otherwise noted.
Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
Note 1: All specifications are 100% tested at TA= +25°C; temperature limits are guaranteed by design.
Note 2: Gain for the MAX9722A is adjustable.
Note 3: The amplifier inputs are AC-coupled to ground through CIN_.
Note 4: Measurement bandwidth is 22Hz to 22kHz.
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
RL = 16Ω, POUT = 55mW, f = 1kHz
0.03
Total Harmonic Distortion Plus
Noise (Note 4)
THD+N
RL = 32Ω, POUT = 125mW, f = 1kHz
0.009
%
Signal-to-Noise Ratio SNR RL = 32Ω, POUT = 20mW, f = 22Hz to 22kHz
100
dB
Noise Vn22Hz to 22kHz bandwidth, input AC grounded 6
µVRMS
Slew Rate SR
0.5
V/µs
Maximum Capacitive Load CLNo sustained oscillation
200
pF
Charge-Pump Oscillator
Frequency fOSC
505 600 800
kHz
Crosstalk RL = 32Ω, VIN = 200mVP-P, f = 10kHz, AV = 1 78 dB
ESD Protection Human Body Model (OUTR and OUTL) ±8kV
Thermal-Shutdown Threshold
145
°C
Thermal-Shutdown Hysteresis 5°C
Typical Operating Characteristics
(MAX9722A, PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, gain = -1V/V, single-ended input,
THD+N measurement bandwidth = 22Hz to 22kHz, TA= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 3V
AV = -1V/V
RL = 16Ω
POUT = 30mW
POUT = 5mW
POUT = 15mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 3V
AV = -1V/V
RL = 32Ω
POUT = 40mW
POUT = 5mW
POUT = 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 5V
AV = -1V/V
RL = 16Ω
POUT = 40mW
POUT = 5mW
POUT = 60mW
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(MAX9722A, PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, gain = -1V/V, single-ended input,
THD+N measurement bandwidth = 22Hz to 22kHz, TA= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 5V
AV = -2V/V
RL = 16Ω
POUT = 40mW
POUT = 5mW
POUT = 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc05
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 5V
AV = -1V/V
RL = 32Ω
POUT = 80mW
POUT = 5mW
POUT = 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc06
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
VDD = 5V
AV = -2V/V
RL = 32Ω
POUT = 80mW
POUT = 5mW
POUT = 20mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc07
OUTPUT POWER (mW)
THD+N (%)
605040302010
0.001
0.01
0.1
1
10
100
0.0001
070
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 3V
AV = -1V/V
RL = 16Ω
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc08
OUTPUT POWER (mW)
THD+N (%)
60 705040302010
0.001
0.01
0.1
1
10
100
0.0001
0 80
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 3V
AV = -1V/V
RL = 32Ω
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc09
OUTPUT POWER (mW)
THD+N (%)
605040302010
0.001
0.01
0.1
1
10
100
0.0001
070
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 5V
AV = -1V/V
RL = 16Ω
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc10
OUTPUT POWER (mW)
THD+N (%)
605040302010
0.001
0.01
0.1
1
10
100
0.0001
070
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 5V
AV = -2V/V
RL = 16Ω
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc11
OUTPUT POWER (mW)
THD+N (%)
12010080604020
0.001
0.01
0.1
1
10
100
0.0001
0140
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 5V
AV = -1V/V
RL = 32Ω
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc12
OUTPUT POWER (mW)
THD+N (%)
12010080604020
0.001
0.01
0.1
1
10
100
0.0001
0 140
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 5V
AV = -2V/V
RL = 32Ω
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
_______________________________________________________________________________________ 5
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9722 toc13
OUTPUT POWER (mW)
THD+N (%)
605040302010
0.001
0.01
0.1
1
10
100
0.0001
070
f = 10kHz
f = 20Hz
f = 1kHz
VDD = 5V
AV = -1V/V
RL = 16Ω
DIFFERENTIAL
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. COMMON-MODE VOLTAGE
MAX9722 toc14
COMMON-MODE VOLTAGE (V)
THD+N (%)
0.30.1-0.1-0.3
0.001
0.01
0.1
1
10
100
0.0001
-0.5 0.5
RL = 16Ω
RL = 32Ω
VDD = 5V
AV = -1V/V
f = 1kHz
DIFFERENTIAL
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9722 toc15
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.43.23.02.82.6
10
20
30
40
50
60
70
80
90
100
0
2.4 3.6
THD+N = 10%
THD+N = 1%
f = 1kHz
RL = 16Ω
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9722 toc16
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
4.43.93.42.9
20
40
60
80
100
120
140
160
180
200
0
2.4 4.9
THD+N = 10%
THD+N = 1%
f = 1kHz
RL = 32Ω
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9722 toc17
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
100
10
20
30
40
50
60
70
80
90
100
0
10 1000
THD+N = 10%
THD+N = 1%
VDD = 3V
f = 1kHz
AV = -1V/V
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9722 toc18
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
100
20
40
60
80
100
120
140
160
180
200
0
10 1000
VDD = 5V
f = 1kHz
AV = -1V/V
THD+N = 1%
THD+N = 10%
POWER DISSIPATION
vs. OUTPUT POWER
MAX9722 toc19
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
605040302010
50
100
150
200
250
300
0
070
VDD = 3V
f = 1kHz
POUT = PL + PR
RL = 16Ω
RL = 32Ω
POWER DISSIPATION
vs. OUTPUT POWER
MAX9722 toc20
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
80604020
100
200
300
400
500
600
0
0100
VDD = 5V
f = 1kHz
POUT = PL + PR
RL = 16Ω
RL = 32Ω
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9722 toc21
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
VDD = 3V
AV = -1V/V
RL = 32Ω
RIGHT
LEFT
Typical Operating Characteristics (continued)
(MAX9722A, PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, gain = -1V/V, single-ended input,
THD+N measurement bandwidth = 22Hz to 22kHz, TA= +25°C, unless otherwise noted.)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(MAX9722A, PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, gain = -1V/V, single-ended input,
THD+N measurement bandwidth = 22Hz to 22kHz, TA= +25°C, unless otherwise noted.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9722 toc22
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
VDD = 5V
AV = -1V/V
RL = 32Ω
RIGHT
LEFT
CROSSTALK vs. FREQUENCY
MAX9722 toc23
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
VDD = 3V
AV = -1V/V
VIN = 200mVP-P
RL = 32Ω
RIGHT TO LEFT
LEFT TO RIGHT
CROSSTALK vs. FREQUENCY
MAX9722 toc24
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
VDD = 5V
AV = -1V/V
VIN = 200mVP-P
RL = 32Ω
RIGHT TO LEFT
LEFT TO RIGHT
GAIN FLATNESS vs. FREQUENCY
MAX9722 toc25
FREQUENCY (Hz)
GAIN (dB)
10k100 1k
-3
-2
-1
0
1
2
3
4
-4
10 100k
VDD = 5V
AV = -1V/V
RL = 32Ω
CHARGE-PUMP OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
MAX9722 toc26
SUPPLY VOLTAGE (V)
OUTPUT RESISTANCE (Ω)
5.24.84.0 4.43.2 3.62.8
1
2
3
4
5
6
7
8
9
10
0
2.4 5.6
VIN = GND
IPVSS = 10mA
C1 = C2 = 2.2μF
NO LOAD
OUTPUT POWER vs. LOAD RESISTANCE
MAX9722 toc27
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
403020
10
20
30
40
50
60
0
10 50
VDD = 3V
f = 1kHz
AV = -1V/V
THD+N = 1%
C1 = C2 = 1μF
C1 = C2 = 0.68μF
C1 = C2 = 0.47μF
C1 = C2 = 2.2μF
OUTPUT SPECTRUM vs. FREQUENCY
MAX9722 toc28
FREQUENCY (kHz)
OUTPUT (dBc)
15105
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
-100
020
VDD = 5V
RL = 32Ω
VOUT = 1mVRMS
f = 1kHz
AV = -1V/V
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9722 toc29
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
54123
1
2
3
4
5
6
7
8
0
0
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9722 toc30
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (nA)
4321
2
4
6
8
10
12
14
16
18
20
0
05
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
_______________________________________________________________________________________ 7
Pin Description
Typical Operating Characteristics (continued)
(MAX9722A, PVDD = SVDD = +5V, PGND = SGND = 0V, SHDN = SVDD, C1 = C2 = 1µF, RL= ∞, gain = -1V/V, single-ended input,
THD+N measurement bandwidth = 22Hz to 22kHz, TA= +25°C, unless otherwise noted.)
EXIT SHUTDOWN TRANSIENT
MAX9722 toc31
200μs/div
SHDN
2V/div
OUT
500mV/div
SHUTDOWN TRANSIENT
MAX9722 toc32
400μs/div
SHDN
2V/div
OUT
500mV/div
POWER-UP/DOWN TRANSIENT
MAX9722 toc33
20ms/div
VDD
2V/div
OUT
5mV/div
PIN
THIN QFN
TSSOP
NAME FUNCTION
13PV
DD
Charge-Pump Power Supply. Powers charge-pump inverter, charge-pump logic, and oscillator.
Connect to positive supply (2.4V to 5.5V). Bypass with a 1µF capacitor to PGND as close to the
pin as possible.
2 4 C1P Flying Capacitor Positive Terminal
3 5 PGND Power Ground. Connect to ground.
4 6 C1N Flying Capacitor Negative Terminal
57PV
SS Charge-Pump Output. Connect to SVSS.
6 8 SGND Signal Ground. Connect to ground.
7 9 INR+ Noninverting Right-Channel Audio Input
8 10 INR- Inverting Right-Channel Audio Input
9, 13
11, 15
SVDD Amplifier Positive Power Supply. Connect to positive supply (2.4V to 5.5V). Bypass with a 1µF
capacitor to SGND as close to the pin as possible.
10 12 OUTR Right-Channel Output
11 13 SVSS Amplifier Negative Power Supply. Connect to PVSS.
12 14 OUTL Left-Channel Output
14 16 INL- Inverting Left-Channel Audio Input
15 1 INL+ Noninverting Left-Channel Audio Input
16 2 SHDN Active-Low Shutdown Input
——EP
Exposed Paddle. The exposed paddle can be either connected to PVSS or a small electrically
isolated copper plane. Do not connect to PGND, SGND, PVDD, or SVDD.
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
8 _______________________________________________________________________________________
Detailed Description
The MAX9722A/MAX9722B stereo headphone amplifiers
feature Maxim’s DirectDrive architecture, eliminating the
large output-coupling capacitors required by conven-
tional single-supply headphone amplifiers. The devices
consist of two class AB headphone amplifiers, undervolt-
age lockout (UVLO)/shutdown control, charge pump,
and comprehensive click-and-pop suppression circuitry
(see Typical Application Circuit). The charge pump
inverts the positive supply (PVDD), creating a negative
supply (PVSS). The headphone amplifiers operate from
these bipolar supplies with their outputs biased about
GND (Figure 1). The benefit of this GND bias is that the
amplifier outputs do not have a DC component, typically
VDD/2. The large DC-blocking capacitors required with
conventional headphone amplifiers are unnecessary,
thus conserving board space, reducing system cost,
and improving frequency response. The device features
an undervoltage lockout that prevents operation from an
insufficient power supply and click-and-pop suppression
that eliminates audible transients on startup and shut-
down. Additionally, the MAX9722A/MAX9722B feature
thermal-overload and short-circuit protection and can
withstand ±8kV ESD strikes at the output pins.
Differential Input
The MAX9722 can be configured as a differential input
amplifier (Figure 2), making it compatible with many
CODECs. A differential input offers improved noise
immunity over a single-ended input. In devices such as
cellular phones, high-frequency signals from the RF
transmitter can couple into the amplifier’s input traces.
The signals appear at the amplifier’s inputs as com-
mon-mode noise. A differential input amplifier amplifies
the difference of the two inputs, and signals common to
both inputs are cancelled. Configured differentially, the
gain of the MAX9722 is set by:
AV= RF1/RIN1
RIN1 must be equal to RIN2, and RF1 must be equal to
RF2.
The common-mode rejection ratio (CMRR) is limited by
the external resistor matching. For example, the worst-
case variation of 1% tolerant resistors results in 40dB
CMRR, while 0.1% resistors result in 60dB CMRR. For
best matching, use resistor arrays.
The RIN1 and RF1 of the MAX9722B are internal, set
RIN2 = 15kΩand RF2 = 30kΩ. However, for best
results, use the MAX9722A.
+VDD OR 3V
-VDD OR -3V
GND
VOUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
VDD/2
VDD
GND
VOUT
Figure 1. Conventional Driver Output Waveform vs. MAX9722A/
MAX9722B Output Waveform
RIN1 = RIN2, RF1 = RF2
*RIN1 AND RF1 ARE INTERNAL FOR MAX9722B.
IN-
IN+
OUT
RF1*
RIN2
RIN1*
RF2
Figure 2. Differential Input Configuration
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typi-
cally half the supply) for maximum dynamic range.
Large coupling capacitors are needed to block this DC
bias from the headphone. Without these capacitors, a
significant amount of DC current flows to the head-
phone, resulting in unnecessary power dissipation and
possible damage to both the headphone and the head-
phone amplifier.
Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage, allowing the
MAX9722A/MAX9722B outputs to be biased about
GND. With no DC component, there is no need for the
large DC-blocking capacitors. Instead of two large
(220µF, typ) tantalum capacitors, the MAX9722A/
MAX9722B charge pump requires two small ceramic
capacitors, conserving board space, reducing cost, and
improving the frequency response of the headphone
amplifier. See the Output Power vs. Load Resistance
graph in the Typical Operating Characteristics for
details of the possible capacitor sizes. There is a low
DC voltage on the amplifier outputs due to amplifier off-
set. However, the offset of the MAX9722A is typically
0.5mV, which, when combined with a 32Ωload, results
in less than 15.6µA of DC current flow to the head-
phones. Previous attempts to eliminate the output-cou-
pling capacitors involved biasing the headphone return
(sleeve) to the DC-bias voltage of the headphone ampli-
fiers. This method raises some issues:
• The sleeve is typically grounded to the chassis.
Using this biasing approach, the sleeve must be iso-
lated from system ground, complicating product
design.
• During an ESD strike, the amplifier’s ESD structures
are the only path to system ground. Thus, the amplifi-
er must be able to withstand the full ESD strike.
• 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.
• When using a combination microphone and speaker
headset, the microphone typically requires a GND
reference. The amplifier DC bias on the sleeve con-
flicts with the microphone requirements (Figure 3).
Low-Frequency Response
In addition to the cost and size disadvantages of the DC-
blocking capacitors required by conventional head-
phone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal:
1) The impedance of the headphone load and the DC-
blocking capacitor form a highpass filter with the
-3dB point set by:
where RLis the impedance of the headphone and
COUT is the value of the DC-blocking capacitor.
The highpass filter is required by conventional single-
ended, single power-supply headphone amplifiers to
block the midrail DC-bias component of the audio sig-
nal from the headphones. The drawback to the filter is
that it can attenuate low-frequency signals. Larger val-
ues of COUT reduce this effect but result in physically
larger, more expensive capacitors. Figure 4 shows the
relationship between the size of COUT and the resulting
low-frequency attenuation. Note that the -3dB point for
a 16Ωheadphone with a 100µF blocking capacitor is
100Hz, well within the normal audio band, resulting in
low-frequency attenuation of the reproduced signal.
fRC
dB L OUT
-3
1
2
=π
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
_______________________________________________________________________________________ 9
HEADPHONE DRIVER
MICROPHONE
AMPLIFIER
MICROPHONE
AMPLIFIER
OUTPUT
AUDIO
INPUT
AUDIO
INPUT
MICROPHONE
BIAS
MAX9722
Figure 3. Earbud Speaker/Microphone Combination Headset
Configuration
MAX9722A/MAX9722B
2) The voltage coefficient of the DC-blocking capaci-
tor contributes distortion to the reproduced audio
signal as the capacitance value varies and the
function of the voltage across the capacitor
changes. The reactance of the capacitor dominates
at frequencies below the -3dB point and the voltage
coefficient appears as frequency-dependent distor-
tion. Figure 5 shows the THD+N introduced by two
different capacitor dielectric types. Note that below
100Hz, THD+N increases rapidly. The combination
of low-frequency attenuation and frequency-depen-
dent distortion compromises audio reproduction in
portable audio equipment that emphasizes low-fre-
quency effects such as in multimedia laptops, MP3,
CD, and DVD players. By eliminating the DC-block-
ing capacitors through DirectDrive technology,
these capacitor-related deficiencies are eliminated.
Charge Pump
The MAX9722A/MAX9722B feature a low-noise charge
pump. The 600kHz switching frequency is well beyond
the audio range and, thus, does not interfere with the
audio signals. Also, the 600kHz switching frequency
does not interfere with the 450kHz AM transceivers.
The switch drivers feature a controlled switching speed
that minimizes noise generated by turn-on and turn-off
transients. By limiting the switching speed of the
charge pump, the di/dt noise caused by the parasitic
bond wire and trace inductance is minimized. Although
not typically required, additional high-frequency noise
attenuation can be achieved by increasing the value of
C2 (see Typical Application Circuit).
Click-and-Pop Suppression
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor is a major contributor of audible
clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, on shutdown, the capacitor is dis-
charged to GND. This results in a DC shift across the
capacitor, which, in turn, appears as an audible tran-
sient at the speaker. Since the MAX9722A/MAX9722B
do not require output-coupling capacitors, this problem
does not arise.
Additionally, the MAX9722A/MAX9722B feature exten-
sive click-and-pop suppression that eliminates any audi-
ble transient sources internal to the device. The
Power-Up/Down Transient graph in the Typical
Operating Characteristics shows that there is minimal
DC shift and no spurious transients at the output upon
startup or shutdown.
In most applications, the output of the preamplifier driving
the MAX9722A/MAX9722B has a DC bias of typically half
the supply. At startup, the input-coupling capacitor is
charged to the preamplifier’s DC-bias voltage through the
feedback resistor of the MAX9722A/MAX9722B, resulting
in a DC shift across the capacitor and an audible
click/pop. Delaying the rise of SHDN 4 to 5 time con-
stants (80ms to 100ms) based on RIN and CIN, relative to
the startup of the preamplifier, eliminates this click/pop
caused by the input filter.
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
10 ______________________________________________________________________________________
0
-30
10 100 1k 10k 100k
LOW-FREQUENCY ROLLOFF
(RL = 16Ω)
-24
-27
-12
-15
-18
-21
-6
-9
-3
FREQUENCY (Hz)
ATTENUATION (dB)
DirectDrive
330μF
220μF
100μF
33μF
Figure 4. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
TANTALUM
ALUM/ELEC
Figure 5. Distortion Contributed by DC-Blocking Capacitors
Shutdown
The MAX9722A/MAX9722B feature shutdown control
allowing audio signals to be shut down or muted.
Driving SHDN low disables the amplifiers and the
charge pump, sets the amplifier output impedance to
10kΩ, and reduces the supply current. In shutdown
mode, the supply current is reduced to 0.1µA. The
charge pump is enabled once SHDN is driven high.
Applications Information
Power Dissipation
Under normal operating conditions, linear power ampli-
fiers can dissipate a significant amount of power. The
maximum 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:
where TJ(MAX) is +145°C, TAis the ambient tempera-
ture, and θJA is the reciprocal of the derating factor in
°C/W as specified in the Absolute Maximum Ratings
section. For example, θJA of the thin QFN package is
+63.8°C/W, and 99.3°C/W for the TSSOP package.
The MAX9722A/MAX9722B have two power dissipation
sources: the charge pump and two amplifiers. If power
dissipation for a given application exceeds the maxi-
mum allowed for a particular package, either reduce
SVDD, increase load impedance, decrease the ambient
temperature, or add heatsinking to the device. Large
output, supply, and ground traces improve the maxi-
mum power dissipation in the package.
Thermal-overload protection limits total power dissipa-
tion in the MAX9722A/MAX9722B. When the junction
temperature exceeds +145°C, the thermal-protection
circuitry disables the amplifier output stage. The ampli-
fiers are enabled once the junction temperature cools
by 5°C. This results in a pulsing output under continu-
ous thermal-overload conditions.
Output Power
The device has been specified for the worst-case sce-
nario—when both inputs are in-phase. Under this con-
dition, the amplifiers simultaneously draw current from
the charge pump, leading to a slight loss in SVSS head-
room. In typical stereo audio applications, the left and
right signals have differences in both magnitude and
phase, subsequently leading to an increase in the max-
imum attainable output power. Figure 6 shows the two
extreme cases for in- and out-of-phase. In reality, the
available power lies between these extremes.
Powering Other Circuits
from a Negative Supply
An additional benefit of the MAX9722A/MAX9722B is
the internally generated, negative supply voltage
(PVSS). This voltage provides the ground-referenced
output level. PVSS can, however, be used to power
other devices within a design limit current drawn from
PVSS to 5mA; exceeding this affects the headphone
amplifier operation. A typical application is a negative
supply to adjust the contrast of LCD modules.
PVSS is roughly proportional to PVDD and is not a regulat-
ed voltage. The charge-pump output impedance must be
taken into account when powering other devices from
PVSS. The charge-pump output impedance plot appears
in the Typical Operating Characteristics. For best results,
use 1µF charge-pump capacitors.
UVLO
The MAX9722A/MAX9722B feature an UVLO function
that prevents the device from operating if the supply
voltage is less than 2.2V (typ). This feature ensures
proper operation during brownout conditions and pre-
vents deep battery discharge. Once the supply voltage
reaches the UVLO threshold, the MAX9722A/
MAX9722B charge pump is turned on and the ampli-
fiers are powered.
PT
DISSPKG MAX J MAX
JA
() ()
=-T
A
θ
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
______________________________________________________________________________________ 11
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9722 fig06
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.83.62.6 2.8 3.0 3.2 3.4
20
40
60
80
100
120
140
160
0
2.4 4.0
fIN = 1kHz
RL = 32Ω
THD+N = 10%
INPUTS
IN PHASE
INPUTS 180°
OUT OF PHASE
Figure 6. Output Power vs. Supply Voltage With Inputs In/Out
of Phase
MAX9722A/MAX9722B
Component Selection
Input Filtering
The input capacitor (CIN), in conjunction with the input
resistor (RIN), forms a highpass filter that removes the DC
bias from an incoming signal (see the Typical Application
Circuit). The AC-coupling capacitor allows the device to
bias the signal to an optimum DC level. Assuming zero
source impedance, the -3dB point of the highpass filter is
given by:
Choose CIN so f-3dB is well below the lowest frequency of
interest. For the MAX9722B, use the value of RIN as given
in the Electrical Characteristics table. Setting f-3dB too
high affects the device’s low-frequency response. Use
capacitors whose dielectrics have low-voltage coeffi-
cients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as ceram-
ics, can result in increased distortion at low frequencies.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩfor optimum
performance. Low-ESR ceramic capacitors minimize the
output resistance of the charge pump. For best perfor-
mance over the extended temperature range, select
capacitors with an X7R dielectric. Table 1 lists suggested
manufacturers.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the charge
pump’s load regulation and output resistance. A C1 value
that is too small degrades the device’s ability to provide
sufficient current drive, which leads to a loss of output
voltage. Increasing the value of C1 improves load regula-
tion and reduces the charge-pump output resistance to
an extent. See the Output Power vs. Load Resistance
graph in the Typical Operating Characteristics. Above
1µF, the on-resistance of the switches and the ESR of C1
and C2 dominate.
Hold Capacitor (C2)
The hold capacitor value and ESR directly affect the rip-
ple at PVSS. Increasing the value of C2 reduces output
ripple. Likewise, decreasing the ESR of C2 reduces both
ripple and output resistance. Lower capacitance values
can be used in systems with low maximum output power
levels. See the Output Power vs. Load Resistance graph
in the Typical Operating Characteristics.
Power-Supply Bypass Capacitor
The power-supply bypass capacitor (C3) lowers the
output impedance of the power supply and reduces the
impact of the MAX9722A/MAX9722Bs’ charge-pump
switching transients. Bypass PVDD with C3, the same
value as C1, and place it physically close to the PVDD
and PGND pins.
Amplifier Gain
The gain of the MAX9722B is internally set at -2V/V. All
gain-setting resistors are integrated into the device,
reducing external component count. The internally set
gain, in combination with DirectDrive, results in a head-
phone amplifier that requires only five tiny 1µF capaci-
tors to complete the amplifier circuit: two for the charge
pump, two for audio input coupling, and one for power-
supply bypassing (see the Typical Application Circuit).
The gain of the MAX9722A amplifier is set externally as
shown in Figure 7, the gain is:
AV= -RF/RIN
Choose feedback resistor values of 10kΩ. Values other
than 10kΩincrease output offset voltage due to the input
bias current, which, in turn, increases the amount of DC
current flow to the load.
fRC
dB IN IN
-3
1
2
=π
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
12 ______________________________________________________________________________________
Table 1. Suggested Capacitor Manufacturers
SUPPLIER PHONE FAX WEBSITE
Murata 770-436-1300 770-436-3030 www.murata.com
Taiyo Yuden 800-348-2496 847-925-0899 www.t-yuden.com
TDK 847-803-6100 847-390-4405 www.component.tdk.com
LEFT
AUDIO
INPUT
RIGHT
AUDIO
INPUT
OUTL
INL-
INL+
INR+
INR-
OUTR
RIN
RF
RF
RIN MAX9722A
Figure 7. Gain Setting for the MAX9722A
Common-Mode Sense
When the headphone jack is used as a line out to inter-
face between other equipment (notebooks, desktops,
and stereo receivers), potential differences between
the equipment grounds can create ground loops and
excessive ground-current flow. The MAX9722A’s INR+
and INL+ inputs are connected together to form a com-
mon-mode input that senses and corrects for the differ-
ence between the headphone return and device
ground (see Figure 8). Connect INR+ and INL+ through
a resistive voltage-divider between the headphone jack
return and SGND of the device. For optimum common-
mode rejection, use the same value resistors for R1and
RF, and R2and RIN. For the MAX9722B, RIN = 15kΩ
and RF= 30kΩ. Improve DC CMRR by adding a
capacitor between SGND and R2(see the Typical
Application Circuit). If ground sensing is not required,
connect INR+ and INL+ directly to SGND.
Common-Mode Noise Rejection
Figure 9 shows a theoretical connection between two
devices, for example, a notebook computer (transmit-
ter, on the left) and an amplifier (receiver, on the right),
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
______________________________________________________________________________________ 13
LEFT
AUDIO
INPUT
RIGHT
AUDIO
INPUT
SHDN
R2
R1
MAX9722A
Figure 8. Common-Mode Sense Input Eliminates Ground-Loop
Noise
VNOISE
VNOISE
0.1Ω
0.1Ω
0.1Ω
0.1ΩVREF_IN = (VNOISE x 0.99)
VIN = VAUDIO + (VNOISE x 0.98)
RESISTOR IS
INSERTED
BETWEEN THE
JACK SLEEVE
AND
GND = 9.8Ω
VAUDIO
VAUDIO
GND NOISE COMPONENT IN
OUTPUT = VNOISE/100
EXAMPLE CONNECTION:
IMPROVEMENT FROM
ADDING MAX9722 WITH
SERIES RESISTANCE
•
•
•
•
9.8Ω RESISTOR ADDS TO HP CROSSTALK, BUT DIFFERENTIAL
SENSING AT THE JACK SLEEVE CORRECTS FOR THIS (ONE CHANNEL
ONLY SHOWN).
CURRENT FLOW (IN SIGNAL CABLE SCREEN) DUE TO VNOISE
IS GREATLY REDUCED.
NOISE COMPONENT IN THE RECEIVER OUTPUT IS REDUCED BY 34dB
OVER THE PREVIOUS EXAMPLE WITH THE VALUES SHOWN.
•
•
9.8Ω
0.10Ω RESISTANCE FROM CABLE SCREEN.
0.10Ω RESISTANCE DUE TO GND CABLING AT RECEIVER.
VNOISE REPRESENTS THE POTENTIAL DIFFERENCE BETWEEN
THE TWO GNDS.
VREF_IN = VNOISE/2
VIN = VAUDIO
GND NOISE COMPONENT IN
OUTPUT = VNOISE/2
MAX9722A
Figure 9. Common-Mode Noise Rejection
MAX9722A/MAX9722B
such as the headphone socket used as a line output to
a home hi-fi system. In the upper diagram, any differ-
ence between the two GND references (represented by
VNOISE) causes current to flow through the screen of
cable between the two devices. This can cause noise
pickup at the receiver due to the potential divider
action of the audio screen cable impedance and the
GND wiring of the amplifier.
Introducing impedance between the jack socket and
GND of the notebook helps (as shown in the lower dia-
gram). This has the following effect:
Current flow (from GND potential differences) in the
cable screen is reduced, which is a safety issue.
It allows the MAX9722A/MAX9722B differential sensing
to reduce the GND noise seen by the receiver (amplifier).
The other side effect is that the differential headphone
jack sensing corrects the headphone crosstalk (from
introducing the resistance on the jack GND return).
Only one channel is depicted in Figure 9.
Figure 9 has some example numbers for resistance,
but the audio designer has control over only one series
resistance applied to the headphone jack return. Note
that this resistance can be bypassed for ESD purposes
at frequencies much higher than audio if required. The
upper limit for this added resistance is the amount of
output swing the headphone amplifier tolerates when
driving low-impedance loads. Any headphone return
current appears as a voltage across this resistor.
Piezoelectric Speaker Amplifier
Low-profile piezoelectric speakers can provide quality
sound for portable electronics. However, piezoelectric
speakers typically require large voltage swings
(>8VP-P) across the speaker element to produce usable
sound pressure levels. Power sources in portable
devices are usually low voltage in nature. Operating
from batteries, conventional amplifiers cannot provide
sufficient voltage swing to drive a piezoelectric speak-
er. However, the MAX9722’s DirectDrive architecture
can be configured to drive a piezoelectric speaker with
up to 12VP-P while operating from a single 5V supply.
The stereo MAX9722 features an inverting charge
pump that takes the positive +5V supply and creates a
negative -5V supply. Each output of the MAX9722 can
swing 6VP-P. This may be sufficient to drive a piezo-
electric speaker. If a higher output voltage is desired,
configuring the MAX9722A as a bridge-tied load (BTL)
amplifier (Figure 10) doubles the maximum output
swing as seen by the load to 12VP-P. In a BTL configu-
ration, the right channel of the MAX9722 serves as the
master amplifier, setting the gain of the device, driving
one side of the speaker, and providing signal to the left
channel. The left channel is configured as a unity-gain
follower, inverting the output of the right channel and
driving the other leg of the speaker. Use precision
resistors to set the gain of the left channel to ensure low
distortion and good matching.
The MAX9722 was tested with a Panasonic WM-R57A
piezoelectric speaker, and the resulting THD+N curves
are shown (Figures 11 and 12). Note in both graphs, as
frequency increases, the THD+N increases. This is due
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
14 ______________________________________________________________________________________
MAX9722A
INR
OUTR
INL
OUTL
AUDIO
INPUT
1μF10kΩ
10kΩ
10kΩ
10kΩ
Figure 10. MAX9722 BTL Configuration
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT VOLTAGE
MAX9722 fig11
OUTPUT POWER (mW)
THD+N (%)
12108642
0.0010
0.0100
0.1000
1
10
100
0.0001
014
VDD = 5V
AV = -1V/V
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
f = 100Hz
f = 20Hz
f = 1kHz
Figure 11. MAX9722 THD+N vs. Output Voltage
to the capacitive nature of the piezoelectric speaker, as
frequency increases, the speaker impedance decreas-
es, resulting in a larger current draw from the amplifier.
Furthermore, the capacitive nature of the speaker can
cause the MAX9722 to become unstable. In these
tests, the MAX9722 exhibited instabilities when driving
the WM-R57A. A simple inductor/resistor network in
series with the speaker isolates the speaker’s capaci-
tance from the amplifier, and ensures the device output
sees a resistive load of about 10Ωat high frequency
maintaining stability. Although the MAX9722 was not
stable with the WM-R57A, a different speaker with dif-
ferent characteristics may result in stable operation,
and elimination of the isolation components.
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 all components
associated with the charge pump (C2 and C3) to the
PGND plane. Connect PVDD and SVDD together at the
device. Connect PVSS and SVSS together at the device.
Bypassing of both supplies is accomplished by charge-
pump capacitors C2 and C3 (see the Typical Application
Circuit). Place capacitors C2 and C3 as close to the
device as possible. Route PGND and all traces that carry
switching transients away from SGND and the traces
and components in the audio signal path. Refer to the
MAX9722A Evaluation Kit for layout guidelines.
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
______________________________________________________________________________________ 15
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 fig12
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.0001
0.001
0.01
0.1
1
10
10 100k
VDD = 5V
AV = -1V/V
VOUT(P-P) = 2V
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
A 500mV/div
4μs/div
500mV/div
2μs/div
B
MAX9722A
INR
OUTR
INL
OUTL
AUDIO
INPUT
1μF10kΩ
10kΩ
10kΩ
10kΩ
10Ω
100μH
Figure 12. MAX9722 THD+N vs. Frequency
Figure 13. MAX9722 Capacitive-Load Stability Waveform:
(a) Falling Edge, (b) Rising Edge
Figure 14. Isolation Network Improves Stability
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
16 ______________________________________________________________________________________
System Diagram
MAX9710
MAX961
OUTR+
OUTR-
OUTL-
OUTL+
INR
INL
BIAS
PVDD
VDD
SHDN
15kΩ
15kΩ
15kΩ
15kΩ
VDD
0.1μF
0.1μF
0.1μF
1μF
MAX4060
MAX9722B
Q
Q
IN+
IN-
0.1μF
INL+
INR+
OUTL
OUTR
C1P CIN
PVSS
PVDD
SVDD
SVSS
SHDN
1μF
1μF
1μF
INL-
INR-
AUX_IN
BIAS
IN+
IN-
2.2kΩ
0.1μF
0.1μF
0.1μF
CODEC
OUT
1μF
100kΩ
100kΩ
VDD
VDD
10kΩ
10kΩ
1μF
VDD
VDD
1μF
The thin QFN package features an exposed paddle that
improves thermal efficiency of the package. The
MAX9722A/MAX9722B do not require additional
heatsinking. The exposed paddle can be either connect-
ed to PVSS or a small electrically isolated copper plane.
Do not connect to PGND, SGND, PVDD, or SVDD.
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
______________________________________________________________________________________ 17
Typical Application Circuit
CHARGE
PUMP
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
C1N
C1P
PVSS SVSS PGND SGND
*FOR MAX9722A, RIN AND RF ARE EXTERNAL TO THE DEVICE.
( ) FOR TSSOP PACKAGE.
INR-
PVDD SVDD SHDN
SVSS
SVDD
SGND
INL-
RIN
15kΩ
RF
30kΩ
RIN*
15kΩ
OUTR
LEFT
CHANNEL
AUDIO IN
RIGHT
CHANNEL
AUDIO IN
HEADPHONE
JACK
16
(2)
1
(3)
2
(4)
3
(5)
4
(6)
5
(7)
11
(13)
12
(14)
9, 13
(11, 15)
14
(16)
10
(12)
6
(8)
C1
1μF
C2
1μF
2.4V TO 5.5V
C3
1μF
CIN
1μF
SVSS
SVDD
OUTL
CIN
1μF
8
(10)
INR+
7
(9)
RF*
30kΩ
MAX9722A
MAX9722B
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
18 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 1100
PROCESS: BiCMOS
Pin Configurations
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
INL+ INL-
SVDD
OUTL
SVSS
OUTR
SVDD
INR-
INR+
TOP VIEW
MAX9722A
MAX9722B
SHDN
PVDD
C1N
C1P
PGND
PVSS
SGND
16
15
14
13
SHDN
INL+
INL-
SVDD
9
10
11
12
SVDD
OUTR
SVSS
OUTL
4
3
2
1
C1N
PGND
C1P
PVDD
5
6
7
8
PVSS
SGND
INR+
INR-
MAX9722A
MAX9722B
TSSOP THIN QFN
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
______________________________________________________________________________________ 19
TSSOP4.40mm.EPS
PACKAGE OUTLINE, TSSOP 4.40mm BODY
21-0066
1
1
I
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
20 ______________________________________________________________________________________
12x16L QFN THIN.EPS
0.10 C0.08 C
0.10 M C A B
D
D/2
E/2
E
A1
A2
A
E2
E2/2
L
k
e
(ND - 1) X e
(NE - 1) X e
D2
D2/2
b
L
e
L
C
L
e
C
L
L
C
L
C
PACKAGE OUTLINE
21-0136 2
1
I
8, 12, 16L THIN QFN, 3x3x0.8mm
MARKING
AAAA
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
EXPOSED PAD VARIATIONS
CODES
PKG.
T1233-1
MIN.
0.95
NOM.
1.10
D2
NOM.
1.10
MAX.
1.25
MIN.
0.95
MAX.
1.25
E2
12N
k
A2
0.25
NE
A1
ND
0
0.20 REF
--
3
0.02
3
0.05
L
e
E
0.45
2.90
b
D
A
0.20
2.90
0.70
0.50 BSC.
0.55
3.00
0.65
3.10
0.25
3.00
0.75
0.30
3.10
0.80
16
0.20 REF
0.25 -
0
4
0.02
4
-
0.05
0.50 BSC.
0.30
2.90
0.40
3.00
0.20
2.90
0.70
0.25
3.00
0.75
3.10
0.50
0.80
3.10
0.30
PKG
REF. MIN.
12L 3x3
NOM. MAX. NOM.
16L 3x3
MIN. MAX.
0.35 x 45°
PIN ID JEDEC
WEED-1
T1233-3 1.10 1.25 0.95 1.10 0.35 x 45°1.25 WEED-10.95
T1633F-3 0.65
T1633-4 0.95
0.80 0.95 0.65 0.80
1.10 1.25 0.95 1.10
0.225 x 45°
0.95 WEED-2
0.35 x 45°
1.25 WEED-2
T1633-2 0.95 1.10 1.25 0.95 1.10 0.35 x 45°
1.25 WEED-2
PACKAGE OUTLINE
21-0136
2
2
I
8, 12, 16L THIN QFN, 3x3x0.8mm
WEED-11.25
1.100.95 0.35 x 45°
1.251.10
0.95
T1233-4
T1633FH-3 0.65 0.80 0.95 0.225 x 45°
0.65 0.80 0.95 WEED-2
NOTES:
1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
3. N IS THE TOTAL NUMBER OF TERMINALS.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO
JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED
WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE.
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm
FROM TERMINAL TIP.
6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS .
9. DRAWING CONFORMS TO JEDEC MO220 REVISION C.
10. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.
11. NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY.
12. WARPAGE NOT TO EXCEED 0.10mm.
0.25 0.30 0.35
2
0.25
0
0.20 REF
--
0.02 0.05
0.35
8
2
0.55 0.75
2.90
2.90 3.00 3.10
0.65 BSC.
3.00 3.10
8L 3x3
MIN.
0.70 0.75 0.80
NOM. MAX.
TQ833-1 1.250.25 0.70 0.35 x 45°WEEC1.250.700.25
T1633-5 0.95 1.10 1.25 0.35 x 45°WEED-2
0.95 1.10 1.25
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
Revision History
Pages changed at Rev 2: 1, 13, 16, 19, 20, 21