MAXIM MAX9722BETE

19-3049; Rev 0; 10/03
ILABLE
N KIT AVA
EVALUATIO
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
Features
♦ 2.4V to 5.5V Single-Supply Operation
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.
♦ Low Quiescent Current (5.5mA)
Applications
Notebook and
Desktop PCs
MP3 Players
Flat-Panel Monitors
Cellular Phones
♦ 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
♦ 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
Simplified Diagram
Smart Phones
PDAs
Portable Audio
Equipment
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
LEFT
AUDIO
INPUT
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX9722AETE -40°C to +85°C
16 Thin QFN-EP*
(3mm ✕ 3mm ✕
0.8mm)
MAX9722AEUE -40°C to +85°C
16 TSSOP
MAX9722BETE -40°C to +85°C
16 Thin QFN-EP*
(3mm ✕ 3mm ✕
0.8mm)
MAX9722BEUE -40°C to +85°C
16 TSSOP
*EP = Exposed paddle.
TOP
MARK
SHDN
MAX9722B
AAX
—
AAY
RIGHT
AUDIO
INPUT
FIXED GAIN ELIMINATES
EXTERNAL RESISTOR
NETWORK.
—
Pin Configurations and Typical Operating Circuit appear at
end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX9722A/MAX9722B
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, patented DirectDrive architecture to produce a
ground-referenced 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 16Ω load or 130mW into a 32Ω load and
have low 0.009% THD+N. An 80dB at 217Hz power-supply 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 shutdown mode reduces the supply current to 0.1µA.
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
ABSOLUTE MAXIMUM RATINGS
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
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
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
(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)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range
VDD
Guaranteed by PSRR test
Quiescent Supply Current
IDD
RL = ∞
Shutdown Supply Current
ISHDN
SHDN Input Logic High
VIH
SHDN Input Logic Low
VIL
SHDN = SGND
5.5
V
5.5
13
mA
0.1
2
µA
2
SHDN Input Leakage Current
SHDN to Full Operation Time
2.4
-1
tSON
V
+0.05
0.8
V
+1
µA
80
µs
AMPLIFIERS
Voltage Gain
AV
Gain Matching
Input Offset Voltage
VIS
IBIAS
Input Impedance
RIN
Input Common-Mode Voltage
Range
VCM
Power-Supply Rejection Ratio
(Note 3)
CMRR
PSRR
Output Power
POUT
Output Voltage
VOUT
Output Impedance in Shutdown
2
-1.98
-2
-2.02
±2
MAX9722B, between the right and left channels
Input Bias Current
Common-Mode Rejection Ratio
MAX9722B (Note 2)
%
Between IN_+ and IN_-, AC-coupled (MAX9722A)
±0.5
±2.5
Between IN_+ and IN_-, AC-coupled (MAX9722B)
±1.5
±5
IN_+ and IN_MAX9722B, measured at IN_
50
10
14.4
-0.5
Input referred, MAX9722A, TA = +25°C
-60
-70
DC, VDD = 2.4V to 5.5V, input referred
-80
-90
f = 217Hz, 100mVP-P ripple, input referred
-80
f = 10kHz, 100mVP-P ripple, input referred
-50
RL = 16Ω, THD+N = 1%, TA = +25°C
RL = 32Ω, THD+N = 1%, TA = +25°C
RL = 1kΩ
60
70
130
V/V
mV
nA
20
kΩ
+0.7
V
dB
dB
mW
2
VRMS
10
kΩ
_______________________________________________________________________________________
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
(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)
PARAMETER
SYMBOL
Total Harmonic Distortion Plus
Noise (Note 4)
THD+N
Signal-to-Noise Ratio
SNR
Noise
Vn
Slew Rate
SR
Maximum Capacitive Load
CL
Charge-Pump Oscillator
Frequency
CONDITIONS
MIN
TYP
RL = 16Ω, POUT = 55mW, f = 1kHz
0.03
RL = 32Ω, POUT = 125mW, f = 1kHz
0.009
RL = 32Ω, POUT = 20mW, f = 22Hz to 22kHz
505
fOSC
UNITS
%
100
dB
6
µVRMS
0.5
V/µs
200
pF
22Hz to 22kHz bandwidth, input AC grounded
No sustained oscillation
MAX
600
800
kHz
Crosstalk
RL = 32Ω, VIN = 200mVP-P, f = 10kHz, AV = 1
78
dB
ESD Protection
Human Body Model (OUTR and OUTL)
±8
kV
Thermal-Shutdown Threshold
145
°C
Thermal-Shutdown Hysteresis
5
°C
Note 1:
Note 2:
Note 3:
Note 4:
All specifications are 100% tested at TA = +25°C; temperature limits are guaranteed by design.
Gain for the MAX9722A is adjustable.
The amplifier inputs are AC-coupled to ground through CIN_.
Measurement bandwidth is 22Hz to 22kHz.
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.)
0.01
0.1
0.01
POUT = 40mW
1k
FREQUENCY (Hz)
0.1
MAX9722 toc03
POUT = 60mW
0.01
0.001
0.0001
0.0001
100
1
POUT = 5mW
POUT = 20mW
0.001
0.0001
10
VDD = 5V
AV = -1V/V
RL = 16Ω
POUT = 40mW
POUT = 30mW
0.001
1
10
POUT = 5mW
POUT = 15mW
0.1
VDD = 3V
AV = -1V/V
RL = 32Ω
THD+N (%)
POUT = 5mW
10
THD+N (%)
THD+N (%)
1
VDD = 3V
AV = -1V/V
RL = 16Ω
MAX9722 toc01
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc02
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
3
MAX9722A/MAX9722B
ELECTRICAL CHARACTERISTICS (continued)
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.)
0.01
VDD = 5V
AV = -1V/V
RL = 32Ω
1
THD+N (%)
POUT = 20mW
10
1
POUT = 5mW
0.1
POUT = 20mW
0.01
POUT = 5mW
0.1
POUT = 20mW
0.01
POUT = 40mW
0.001
0.0001
100
1k
10k
100k
0.0001
10
100
1k
10k
100k
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
0.1
f = 1kHz
f = 1kHz
0.1
0.01
VDD = 3V
AV = -1V/V
RL = 16Ω
f = 20Hz
0.001
0.0001
10
20
30
40
50
60
0.01
0.001
VDD = 3V
AV = -1V/V
RL = 32Ω
f = 20Hz
0.0001
70
0
10
20
30
40
50
60
70
f = 20Hz
0.001
VDD = 5V
AV = -1V/V
RL = 16Ω
0.0001
80
0
10
20
30
40
50
60
70
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = 5V
AV = -1V/V
RL = 32Ω
10
THD+N (%)
1
f = 1kHz
0.1
1
f = 10kHz
f = 1kHz
0.1
0.01
0.01
f = 20Hz
0.001
20
30
40
50
OUTPUT POWER (mW)
60
70
f = 1kHz
0.1
0.001
f = 20Hz
0.0001
10
f = 10kHz
0.01
0.001
0.0001
VDD = 5V
AV = -2V/V
RL = 32Ω
10
THD+N (%)
f = 10kHz
100
MAX9722 toc11
MAX9722 toc10
100
MAX9722 toc12
OUTPUT POWER (mW)
VDD = 5V
AV = -2V/V
RL = 16Ω
0
f = 10kHz
1
f = 10kHz
0.1
0.01
10
THD+N (%)
THD+N (%)
f = 10kHz
100
MAX9722 toc08
MAX9722 toc07
100
1
1
100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
f = 1kHz
10
10k
FREQUENCY (Hz)
1
100
1k
FREQUENCY (Hz)
10
0
100
FREQUENCY (Hz)
100
THD+N (%)
0.001
0.0001
10
4
POUT = 80mW
POUT = 80mW
0.001
VDD = 5V
AV = -2V/V
RL = 32Ω
MAX9722 toc09
0.1
10
THD+N (%)
POUT = 5mW
1
THD+N (%)
VDD = 5V
AV = -2V/V
RL = 16Ω
MAX9722 toc04
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc06
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 toc05
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
THD+N (%)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
f = 20Hz
0.0001
0
20
40
60
80
100
OUTPUT POWER (mW)
120
140
0
20
40
60
80
100
OUTPUT POWER (mW)
_______________________________________________________________________________________
120
140
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
1
f = 1kHz
THD+N (%)
0.1
0.01
90
80
RL = 16Ω
0.1
0.01
RL = 32Ω
0.001
20
30
40
50
60
-0.5
-0.1
0.1
0.3
2.4
0.5
2.6
2.8
3.0
3.2
THD+N = 1%
100
80
60
f = 1kHz
RL = 32Ω
20
70
THD+N = 10%
60
50
THD+N = 1%
40
30
160
2.9
3.4
3.9
4.4
140
THD+N = 1%
100
80
60
40
10
20
0
10
4.9
THD+N = 10%
120
20
0
0
VDD = 5V
f = 1kHz
AV = -1V/V
180
OUTPUT POWER (mW)
80
200
MAX9722 toc17
MAX9722 toc16
THD+N = 10%
140
VDD = 3V
f = 1kHz
AV = -1V/V
90
MAX9722 toc18
OUTPUT POWER
vs. LOAD RESISTANCE
100
1000
100
100
10
1000
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
LOAD RESISTANCE (Ω)
POWER DISSIPATION
vs. OUTPUT POWER
POWER DISSIPATION
vs. OUTPUT POWER
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
RL = 16Ω
150
100
RL = 32Ω
0
-20
-30
400
RL = 16Ω
300
RL = 32Ω
200
50
100
0
0
VDD = 3V
AV = -1V/V
RL = 32Ω
-10
PSRR (dB)
200
VDD = 5V
f = 1kHz
POUT = PL + PR
500
POWER DISSIPATION (mW)
VDD = 3V
f = 1kHz
POUT = PL + PR
MAX9722 toc20
600
MAX9722 toc19
300
3.6
3.4
OUTPUT POWER
vs. LOAD RESISTANCE
40
POWER DISSIPATION (mW)
-0.3
OUTPUT POWER
vs. SUPPLY VOLTAGE
OUTPUT POWER (mW)
OUTPUT POWER (mW)
70
SUPPLY VOLTAGE (V)
160
250
f = 1kHz
RL = 16Ω
COMMON-MODE VOLTAGE (V)
180
2.4
30
OUTPUT POWER (mW)
200
120
40
0
0.0001
10
THD+N = 1%
50
10
0.0001
0
60
20
0.001
f = 20Hz
THD+N = 10%
70
MAX9722 toc21
THD+N (%)
1
10
100
MAX9722 toc15
f = 10kHz
VDD = 5V
AV = -1V/V
f = 1kHz
DIFFERENTIAL
OUTPUT POWER (mW)
10
100
MAX9722 toc14
VDD = 5V
AV = -1V/V
RL = 16Ω
DIFFERENTIAL
MAX9722 toc13
100
OUTPUT POWER
vs. SUPPLY VOLTAGE
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. COMMON-MODE VOLTAGE
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
-40
-50
RIGHT
-60
-70
LEFT
-80
-90
0
10
20
30
40
50
OUTPUT POWER (mW)
60
70
-100
0
20
40
60
OUTPUT POWER (mW)
80
100
10
100
1k
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
5
MAX9722A/MAX9722B
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.)
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.)
CROSSTALK vs. FREQUENCY
-20
-40
-50
-60
-70
-40
-50
-60
-20
RIGHT TO LEFT
-70
RIGHT
-80
-80
-90
-90
LEFT
10k
100
1k
100k
10k
FREQUENCY (Hz)
GAIN FLATNESS vs. FREQUENCY
CHARGE-PUMP OUTPUT RESISTANCE
vs. SUPPLY VOLTAGE
10
1
0
-1
-2
8
100
1k
OUTPUT POWER vs. LOAD RESISTANCE
60
C1 = C2 = 2.2µF
50
7
6
5
4
3
40
30
C1 = C2 = 0.68µF
C1 = C2 = 1µF
C1 = C2 = 0.47µF
20
10
100
1k
10k
100k
2.4
2.8
3.2
3.6
4.0
4.4
4.8
5.2
10
5.6
20
30
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
OUTPUT SPECTRUM vs. FREQUENCY
SUPPLY CURRENT vs. SUPPLY VOLTAGE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
-30
-40
-50
-60
-70
5
4
3
2
10
FREQUENCY (kHz)
15
20
16
14
12
10
8
6
2
0
0
5
18
4
1
-100
MAX9722 toc30
MAX9722 toc29
6
-80
-90
20
SUPPLY CURRENT (nA)
-20
7
SUPPLY CURRENT (mA)
-10
8
MAX9722 toc28
VDD = 5V
RL = 32Ω
VOUT = 1mVRMS
f = 1kHz
AV = -1V/V
0
50
40
FREQUENCY (Hz)
10
0
VDD = 3V
f = 1kHz
AV = -1V/V
THD+N = 1%
0
0
10
100k
10k
1
-4
6
LEFT TO RIGHT
10
2
-3
RIGHT TO LEFT
FREQUENCY (Hz)
VIN = GND
IPVSS = 10mA
C1 = C2 = 2.2µF
NO LOAD
9
OUTPUT RESISTANCE (Ω)
2
-60
-90
FREQUENCY (Hz)
VDD = 5V
AV = -1V/V
RL = 32Ω
3
10
100k
-50
-100
OUTPUT POWER (mW)
1k
-40
-80
LEFT TO RIGHT
MAX9722 toc26
4
100
MAX9722 toc25
10
-30
-70
-100
-100
GAIN (dB)
-30
VDD = 5V
AV = -1V/V
VIN = 200mVP-P
RL = 32Ω
-10
MAX9722 toc27
CROSSTALK (dB)
PSRR (dB)
-30
VDD = 3V
AV = -1V/V
VIN = 200mVP-P
RL = 32Ω
-10
CROSSTALK (dB)
-20
CROSSTALK vs. FREQUENCY
0
MAX9722 toc23
VDD = 5V
AV = -1V/V
RL = 32Ω
-10
0
MAX9722 toc22
0
MAX9722 toc24
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OUTPUT (dBc)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
0
1
2
3
4
SUPPLY VOLTAGE (V)
5
0
1
2
3
4
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
EXIT SHUTDOWN TRANSIENT
POWER-UP/DOWN TRANSIENT
SHUTDOWN TRANSIENT
MAX9722 toc31
MAX9722 toc33
MAX9722 toc32
SHDN
2V/div
SHDN
2V/div
VDD
2V/div
OUT
500mV/div
OUT
500mV/div
OUT
5mV/div
200µs/div
20ms/div
400µs/div
Pin Description
PIN
NAME
FUNCTION
3
PVDD
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.
4
C1P
Flying Capacitor Positive Terminal
3
5
PGND
Power Ground. Connect to ground.
4
6
C1N
Flying Capacitor Negative Terminal
5
7
PVSS
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
Amplifier Negative Power Supply. Connect to PVSS.
THIN QFN
TSSOP
1
2
11
13
SVSS
12
14
OUTL
14
16
INL-
15
1
INL+
16
2
SHDN
—
—
EP
Left-Channel Output
Inverting Left-Channel Audio Input
Noninverting Left-Channel Audio Input
Active-Low Shutdown Input
Exposed Paddle. Leave this connection unconnected or solder to a piece of electrically
isolated copper. Do not connect to any voltage potential.
_______________________________________________________________________________________
7
MAX9722A/MAX9722B
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
Detailed Description
The MAX9722A/MAX9722B stereo headphone amplifiers
feature Maxim’s patented DirectDrive architecture, eliminating the large output-coupling capacitors required by
conventional single-supply headphone amplifiers. The
devices consist of two class AB headphone amplifiers,
undervoltage 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 V DD /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 clickand-pop suppression that eliminates audible transients
on startup and shutdown. Additionally, the MAX9722A/
MAX9722B feature thermal-overload and short-circuit
protection and can withstand ±8kV ESD strikes at the
output pins.
VDD
VOUT
VDD/2
GND
CONVENTIONAL DRIVER-BIASING SCHEME
+VDD OR 3V
VOUT
GND
-VDD OR -3V
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 common-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 worstcase 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
R IN2 = 15kΩ and R F2 = 30kΩ. However, for best
results, use the MAX9722A.
8
DirectDrive BIASING SCHEME
Figure 1. Conventional Driver Output Waveform vs. MAX9722A/
MAX9722B Output Waveform
RF1*
RIN1*
INOUT
RIN2
IN+
RF2
RIN1 = RIN2, RF1 = RF2
*RIN1 AND RF1 ARE INTERNAL FOR MAX9722B.
Figure 2. Differential Input Configuration
_______________________________________________________________________________________
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
Maxim’s patented 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.
Charge-Pump Capacitance and 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 offset. However, the offset of the MAX9722A is typically
0.5mV, which, when combined with a 32Ω load, results
in less than 15.6µA of DC current flow to the headphones. Previous attempts to eliminate the output-coupling capacitors involved biasing the headphone return
(sleeve) to the DC-bias voltage of the headphone
amplifiers. This method raises some issues:
• The sleeve is typically grounded to the chassis.
Using this biasing approach, the sleeve must be isolated from system ground, complicating product
design.
• During an ESD strike, the amplifier’s ESD structures
are the only path to system ground. Thus, the amplifier 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 conflict 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 conflicts with the microphone requirements (Figure 3).
Low-Frequency Response
In addition to the cost and size disadvantages of the DCblocking capacitors required by conventional head-
MAX9722A/MAX9722B
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typically 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 headphone, resulting in unnecessary power dissipation and
possible damage to both the headphone and the headphone amplifier.
MICROPHONE
BIAS
MICROPHONE
AMPLIFIER
MICROPHONE
AMPLIFIER
OUTPUT
AUDIO
INPUT
MAX9722
AUDIO
INPUT
HEADPHONE DRIVER
Figure 3. Earbud Speaker/Microphone Combination Headset
Configuration
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 DCblocking capacitor form a highpass filter with the
-3dB point set by:
f-3dB =
1
2πRLCOUT
where R L is the impedance of the headphone and
COUT is the value of the DC-blocking capacitor.
The highpass filter is required by conventional singleended, single power-supply headphone amplifiers to
block the midrail DC-bias component of the audio signal from the headphones. The drawback to the filter is
that it can attenuate low-frequency signals. Larger values 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 16Ω headphone with a 100µF blocking capacitor is
100Hz, well within the normal audio band, resulting in
low-frequency attenuation of the reproduced signal.
_______________________________________________________________________________________
9
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
LOW-FREQUENCY ROLLOFF
(RL = 16Ω)
0
10
-3
DirectDrive
-6
-9
1
330µF
-12
THD+N (%)
ATTENUATION (dB)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
220µF
-15
100µF
-18
0.1
TANTALUM
0.01
33µF
-21
-24
0.001
ALUM/ELEC
-27
-30
0.0001
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 4. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
2) The voltage coefficient of the DC-blocking capacitor 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 distortion. 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-dependent distortion compromises audio reproduction in
portable audio equipment that emphasizes low-frequency effects such as in multimedia laptops, MP3,
CD, and DVD players. By eliminating the DC-blocking 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).
10
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 5. Distortion Contributed by DC-Blocking Capacitors
Click-and-Pop Suppression
In conventional single-supply audio amplifiers, the output-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 discharged to GND. This results in a DC shift across the
capacitor, which, in turn, appears as an audible transient at the speaker. Since the MAX9722A/MAX9722B
do not require output-coupling capacitors, this problem
does not arise.
Additionally, the MAX9722A/MAX9722B feature extensive click-and-pop suppression that eliminates any audible transient sources internal to the device. The
Power-Up/Down Waveform 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 constants (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
Power Dissipation
Under normal operating conditions, linear power amplifiers 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:
PDISSPKG(MAX) =
TJ(MAX) - TA
fIN = 1kHz
RL = 32Ω
THD+N = 10%
MAX9722 fig06
140
OUTPUT POWER (mW)
Applications Information
OUTPUT POWER vs. SUPPLY VOLTAGE
160
INPUTS 180°
OUT OF PHASE
120
100
80
60
INPUTS
IN PHASE
40
20
0
2.4
2.6
2.8
3.0
3.2
3.4
3.6
3.8
4.0
SUPPLY VOLTAGE (V)
Figure 6. Distortion Contributed by DC-Blocking Capacitors
θJA
where TJ(MAX) is +145°C, TA is the ambient temperature, and θJA is the reciprocal of the derating factor in
°C/W as specified in the Absolute Maximum Ratings
section. For example, θJA of the thin QFN package is
+63.8°C/W, and 99.3°C/W for the TSSOP package.
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.
The MAX9722A/MAX9722B have two power dissipation
sources: the charge pump and two amplifiers. If power
dissipation for a given application exceeds the maximum 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 maximum power dissipation in the package.
Thermal-overload protection limits total power dissipation in the MAX9722A/MAX9722B. When the junction
temperature exceeds +145°C, the thermal-protection
circuitry disables the amplifier output stage. The amplifiers are enabled once the junction temperature cools
by 5°C. This results in a pulsing output under continuous thermal-overload conditions.
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 regulated 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.
Output Power
The device has been specified for the worst-case scenario—when both inputs are in-phase. Under this condition, the amplifiers simultaneously draw current from
the charge pump, leading to a slight loss in SVSS headroom. 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-
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 prevents deep battery discharge. Once the supply voltage
reaches the UVLO threshold, the MAX9722A/
MAX9722B charge pump is turned on and the amplifiers are powered.
Powering Other Circuits
from a Negative Supply
UVLO
______________________________________________________________________________________
11
MAX9722A/MAX9722B
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.
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
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:
f-3dB =
1
2πRINCIN
RF
LEFT
AUDIO
INPUT
RIN
INL-
MAX9722A
OUTL
INL+
INR+
OUTR
RIGHT
AUDIO
INPUT
RIN
INR-
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 DC Electrical Characteristics table. Setting f-3dB too
high affects the device’s low-frequency response. Use
capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as ceramics, can result in increased distortion at low frequencies.
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.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for optimum
performance. Low-ESR ceramic capacitors minimize the
output resistance of the charge pump. For best performance over the extended temperature range, select
capacitors with an X7R dielectric. Table 1 lists suggested
manufacturers.
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.
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 regulation and reduces the charge-pump output resistance to
an extent. See the Output Power vs. Charge-Pump
Capacitance and 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 ripple 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
RF
Figure 7. Gain Setting for the MAX9722A
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 headphone amplifier that requires only five tiny 1µF capacitors to complete the amplifier circuit: two for the charge
pump, two for audio input coupling, and one for powersupply 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 10kΩ increase output offset voltage due to the input
bias current, which, in turn, increases the amount of DC
current flow to the load.
Table 1. Suggested Capacitor Manufacturers
PHONE
FAX
Murata
SUPPLIER
770-436-1300
770-436-3030
WEBSITE
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
12
______________________________________________________________________________________
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
MAX9722A
LEFT
AUDIO
INPUT
SHDN
R1
RIGHT
AUDIO
INPUT
R2
Common-Mode Noise Rejection
Figure 9 shows a theoretical connection between two
devices, for example, a notebook computer (transmitter, on the left) and an amplifier (receiver, on the right),
Figure 8. Common-Mode Sense Input Eliminates Ground-Loop
Noise
EXAMPLE CONNECTION:
VIN = VAUDIO
VAUDIO
GND NOISE COMPONENT IN
OUTPUT = VNOISE/2
0.1Ω
VNOISE
0.1Ω
VREF_IN = VNOISE/2
• 0.10Ω RESISTANCE FROM CABLE SCREEN.
• 0.10Ω RESISTANCE DUE TO GND CABLING AT RECEIVER.
• VNOISE REPRESENTS THE POTENTIAL DIFFERENCE BETWEEN
THE TWO GNDS.
IMPROVEMENT FROM
ADDING MAX9722 WITH
SERIES RESISTANCE
MAX9722A
VIN = VAUDIO + (VNOISE x 0.98)
VAUDIO
GND NOISE COMPONENT IN
OUTPUT = VNOISE /100
0.1Ω
RESISTOR IS
INSERTED
BETWEEN THE
JACK SLEEVE
AND
GND = 9.8Ω
9.8Ω
VNOISE
0.1Ω
VREF_IN = (VNOISE x 0.99)
• 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.
Figure 9. Common-Mode Noise Rejection
______________________________________________________________________________________
13
MAX9722A/MAX9722B
Common-Mode Sense
When the headphone jack is used as a line out to interface 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 common-mode input that senses and corrects for the difference 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 commonmode rejection, use the same value resistors for R1 and
RIN, and R2 and RF. For the MAX9722B, RIN = 15kΩ
and R F = 30kΩ. Improve DC CMRR by adding a
capacitor between SGND and R 2 (see the Typical
Application Circuit). If ground sensing is not required,
connect INR+ and INL+ directly to SGND.
10kΩ
1µF
AUDIO
INPUT
10kΩ
INR
OUTR
10kΩ
INL
10kΩ
OUTL
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 speaker. 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 piezoelectric 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 configuration, 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
14
MAX9722A
Figure 10. MAX9722 BTL Configuration
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT VOLTAGE
100
MAX9722 fig11
such as the headphone socket used as a line output to
a home hi-fi system. In the upper diagram, any difference 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 diagram). This has the following effect:
Current flow (from GND potential differences) in the
cable screen is reduced, which is a safety issue.
VDD = 5V
AV = -1V/V
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
10
1
THD+N (%)
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
f = 1kHz
0.1000
0.0100
f = 20Hz
0.0010
f = 100Hz
0.0001
0
2
4
6
8
10
12
14
OUTPUT POWER (mW)
Figure 11. MAX9722 THD+N vs. Output Voltage
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
MAX9722A/MAX9722B
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9722 fig12
10
THD+N (%)
VDD = 5V
AV = -1V/V
1 VOUT(P-P) = 2V
OUTPUTS DRIVING
PIEZOELECTRIC SPEAKER
A
0.1
500mV/div
0.01
0.001
4µs/div
0.0001
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 12. MAX9722 THD+N vs. Frequency
B
to the capacitive nature of the piezoelectric speaker, as
frequency increases, the speaker impedance decreases, 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 capacitance from the amplifier, and ensures the device output
sees a resistive load of about 10Ω at high frequency
maintaining stability. Although the MAX9722 was not
stable with the WM-R57A, a different speaker with different 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 chargepump 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
MAX9722 evaluation kit for layout guidelines.
500mV/div
2µs/div
Figure 13. MAX9722 Capacitive-Load Stability Waveform:
(a) Falling Edge, (b) Rising Edge
10kΩ
AUDIO
INPUT
1µF 10kΩ
INR
10Ω
OUTR
10kΩ
100µH
INL
10kΩ
OUTL
MAX9722A
Figure 14. Isolation Network Improves Stability
______________________________________________________________________________________
15
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
MAX9722A/MAX9722B
System Diagram
VDD
0.1µF
15kΩ
0.1µF 15kΩ
INR
VDD
PVDD
0.1µF
1µF
OUTR-
MAX9710
BIAS
AUX_IN
OUTR+
1µF
SHDN
OUT
OUTL-
0.1µF 15kΩ
MAX4060
BIAS
OUTL+
INL
VDD
15kΩ
CODEC
VDD
2.2kΩ
10kΩ
0.1µF
IN-
IN+
VDD
10kΩ
Q
IN0.1µF
MAX961
Q
100kΩ
100kΩ
IN+
0.1µF
INL+
INR-
SHDN
1µF
INL-
MAX9722B OUTL
1µF
VDD
OUTR
INR-
PVSS
1µF
PVDD
SVDD
SVSS
C1P
CIN
1µF
1µF
The thin QFN package features an exposed paddle
that improves thermal efficiency of the package. The
MAX9722A/MAX9722B do not require additional
16
heatsinking. Ensure the exposed paddle is isolated
from GND or SVDD. Do not connect the exposed paddle to GND or SVDD.
______________________________________________________________________________________
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
CIN
1µF
2.4V TO 5.5V
LEFT
CHANNEL
AUDIO IN
C3
1µF
1
(3)
9, 13
(11, 15)
16
(2)
14
(16)
PVDD
SVDD
SHDN
INL-
R F*
30kΩ
SVDD
RIN*
15kΩ
12
OUTL (14)
HEADPHONE
JACK
UVLO/
SHUTDOWN
CONTROL
2
(4) C1P
SVSS
CHARGE
PUMP
C1
1µF
CLICK-AND-POP
SUPPRESSION
4
(6) C1N
SVDD
SGND
OUTR
RIN
15kΩ
MAX9722A
MAX9722B
10
(12)
SVSS
RF
30kΩ
PVSS
5
(7)
SVSS PGND
3
(5)
11
(13)
SGND
6
(8)
INR+
7
(9)
C2
1µF
RIGHT
CHANNEL
AUDIO IN
INR8
(10)
CIN
1µF
*FOR MAX9722A, RIN AND RF ARE EXTERNAL TO THE DEVICE.
( ) FOR TSSOP PACKAGE.
______________________________________________________________________________________
17
MAX9722A/MAX9722B
Typical Application Circuit
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
3
C1N
4
C1N 6
11 SVDD
PVSS 7
10 INR-
SGND 8
9
INR+
TSSOP
INL-
SVDD
14
13
8
PGND
12 OUTR
MAX9722A
MAX9722B
INR-
PGND 5
13 SVSS
7
2
MAX9722A
MAX9722B
INR+
C1P
C1P 4
INL+
1
15
PVDD
14 OUTL
6
15 SVDD
PVDD 3
SGND
SHDN 2
SHDN
16 INL-
16
INL+ 1
5
TOP VIEW
PVSS
MAX9722A/MAX9722B
Pin Configurations
THIN QFN
Chip Information
TRANSISTOR COUNT: 1100
PROCESS: BiCMOS
18
______________________________________________________________________________________
12
OUTL
11
SVSS
10
OUTR
9
SVDD
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
TSSOP4.40mm.EPS
______________________________________________________________________________________
19
MAX9722A/MAX9722B
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.)
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.)
12x16L QFN THIN.EPS
MAX9722A/MAX9722B
5V, Differential Input, DirectDrive, 130mW
Stereo Headphone Amplifiers with Shutdown
D2
0.10 M C A B
b
D
D2/2
D/2
E/2
E2/2
CL
-A-
(NE - 1) X e
E
E2
L
-B-
k
e
CL
(ND - 1) X e
CL
CL
0.10 C
0.08 C
A
A2
A1
L
L
e
e
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE
12 & 16L, QFN THIN, 3x3x0.8 mm
APPROVAL
DOCUMENT CONTROL NO.
21-0136
REV.
1
C
2
EXPOSED PAD VARIATIONS
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.
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE
12 & 16L, QFN THIN, 3x3x0.8 mm
APPROVAL
DOCUMENT CONTROL NO.
21-0136
REV.
C
2
2
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.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.