19-2917; Rev 1; 1/04
500mW, Low EMI, Filterless,
Class D Audio Amplifier
General Description
The MAX9712 mono class D audio power amplifier pro-
vides class AB amplifier performance with class D effi-
ciency, conserving board space, and extending battery
life. Using a class D architecture, the MAX9712 delivers
up to 500mW into an 8Ω load while offering efficiencies
above 85%. A patented, low EMI modulation scheme
renders the traditional class D output filter unnecessary.
The MAX9712 offers two modulation schemes: a fixed-
frequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions due to the
modulation frequency. Furthermore, the MAX9712 oscil-
lator can be synchronized to an external clock through
the SYNC input, allowing the switching frequency to be
user defined. The SYNC input also allows multiple
MAX9712s to be cascaded and frequency locked, mini-
mizing interference due to clock intermodulation. The
device utilizes a fully differential architecture, a full-
bridged output, and comprehensive click-and-pop sup-
pression. The gain is internally set to +4V/V, further
reducing external component count.
The MAX9712 features high 72dB PSRR, a low 0.01%
THD+N, and SNR in excess of 90dB. Short-circuit and
thermal-overload protection prevent the device from
damage during a fault condition. The MAX9712 is avail-
able in 10-pin TDFN (3mm
✕
3mm
✕
0.8mm), 10-pin
µMAX, and 12-bump UCSP™ (1.5mm
✕
2mm
✕
0.6mm)
packages. The MAX9712 is specified over the extended
-40°C to +85°C temperature range.
Features
♦
Filterless Amplifier Passes FCC Radiated
Emissions Standards with 100mm of Cable
♦
Unique Spread-Spectrum Mode Offers 5dB
Emissions Improvement Over Conventional
Methods
♦
Optional External SYNC Input
♦
Simple Master-Slave Setup for Stereo Operation
♦
♦
♦
♦
♦
♦
♦
♦
♦
85% Efficiency
Up to 500mW into 8Ω
Low 0.01% THD+N
High PSRR (72dB at 217Hz)
Integrated Click-and-Pop Suppression
Low Quiescent Current (4mA)
Low-Power Shutdown Mode (0.1µA)
Short-Circuit and Thermal-Overload Protection
Available in Thermally Efficient, Space-Saving
Packages
10-Pin TDFN (3mm
✕
3mm
✕
0.8mm)
10-Pin µMAX
12-Bump UCSP (1.5mm
✕
2mm
✕
0.6mm)
MAX9712
Ordering Information
PART
MAX9712ETB
MAX9712EUB
MAX9712EBC-T
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN/BUMP-
PACKAGE
10 TDFN
10 µMAX
12 UCSP-12
TOP
MARK
AAI
—
ABN
Applications
Cellular Phones
PDAs
MP3 Players
Portable Audio
Simplified Block Diagram
V
DD
Pin Configurations
TOP VIEW
MODULATOR
AND H-BRIDGE
DIFFERENTIAL
AUDIO INPUT
V
DD
1
IN+
IN-
2
3
4
5
10
PV
DD
9
OUT-
OUT+
PGND
SYNC
MAX9712
8
7
6
SYNC
INPUT
OSCILLATOR
GND
MAX9712
SHDN
TDFN/µMAX
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations continued at end of data sheet.
1
________________________________________________________________
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.
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND..............................................................................6V
PV
DD
to PGND .........................................................................6V
GND to PGND .......................................................-0.3V to +0.3V
All Other Pins to GND.................................-0.3V to (V
DD
+ 0.3V)
Continuous Current Into/Out of PV
DD
/PGND/OUT_ ........±600mA
Continuous Input Current (all other pins)..........................±20mA
Duration of OUT_ Short Circuit to GND or PV
DD
........Continuous
Duration of Short Circuit Between OUT+ and OUT- ..Continuous
Continuous Power Dissipation (T
A
= +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C) .....1951.2mW
10-Pin µMAX (derate 5.6mW/
o
C above +70°C) .........444.4mW
12-Bump UCSP (derate 6.1mW/°C above +70°C)........484mW
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
Bump Temperature (soldering)
Reflow ..........................................................................+235°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= PV
DD
=
SHDN
= 3.3V, GND = PGND = 0V, SYNC = GND (FFM), R
L
= 8Ω, R
L
connected between OUT+ and OUT-, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Notes 1, 2)
PARAMETER
GENERAL
Supply Voltage Range
Quiescent Current
Shutdown Current
Turn-On Time
Input Resistance
Input Bias Voltage
Voltage Gain
V
DD
I
DD
I
SHDN
t
ON
R
IN
V
BIAS
A
V
T
A
= +25°C
Output Offset Voltage
V
OS
T
MIN
≤
T
A
≤
T
MAX
MAX9712EUB/MAX9712ETB
MAX9712EBC
MAX9712EUB/MAX9712ETB
MAX9712EBC
72
50
f
RIPPLE
= 217Hz
f
RIPPLE
= 20kHz
R
L
= 16Ω, V
DD
= 5V
Output Power
P
OUT
THD+N = 1%
R
L
= 8Ω
R
L
= 6Ω
Total Harmonic Distortion Plus
Noise
f
IN
= 1kHz, either
FFM or SSM
R
L
= 8Ω,
P
OUT
= 125mW
R
L
= 6Ω,
P
OUT
= 125mW
70
72
55
700
450
250
0.01
%
0.01
mW
dB
T
A
= +25°C
Either input
14
0.73
3.8
Inferred from PSRR test
2.5
4
0.1
30
20
0.83
4
±11
±15
0.93
4.2
±40
±65
±65
±95
dB
mV
5.5
5.2
5
V
mA
µA
ms
kΩ
V
V/V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
(Note 3)
CMRR
PSRR
f
IN
= 1kHz, input referred
V
DD
= 2.5V to 5.5V
200mV
P-P
ripple
THD+N
2
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
DD
=
SHDN
= 3.3V, GND = PGND = 0V, SYNC = GND (FFM), R
L
= 8Ω, R
L
connected between OUT+ and OUT-, T
A
=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
BW = 22Hz
to 22kHz
Signal-to-Noise Ratio
SNR
V
OUT
= 1.8V
RMS
A-weighted
SYNC = GND
Oscillator Frequency
f
OSC
SYNC = float
SYNC = V
DD
(SSM mode)
SYNC Frequency Lock Range
Efficiency
DIGITAL INPUTS (SHDN, SYNC)
Input Thresholds
SHDN
Input Leakage Current
SYNC Input Current
V
IH
V
IL
2
0.8
±1
±5
V
µA
µA
η
P
OUT
= 300mW, f
IN
= 1kHz
800
85
FFM
SSM
FFM
SSM
980
1280
MIN
TYP
88
86
91
89
1100
1450
1220
±120
2000
kHz
%
1220
1620
kHz
dB
MAX
UNITS
MAX9712
Note 1:
All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2:
Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R
L
= 6Ω, L = 47µH.
For R
L
= 8Ω, L = 68µH. For R
L
= 16Ω, L = 136µH.
Note 3:
PSRR is specified with the amplifier inputs connected to GND through C
IN
.
Typical Operating Characteristics
(V
DD
= 3.3V, V
SYNC
= GND, T
A
= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9712 TOC01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9712 TOC02
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
V
DD
= +3.3V
R
L
= 8Ω
P
OUT
= 125mW
0.1
MAX9712 TOC03
1
V
DD
= +5V
R
L
= 8Ω
1
V
DD
= +3.3V
R
L
= 8Ω
1
0.1
THD+N (%)
THD+N (%)
P
OUT
= 300mW
0.1
P
OUT
= 300mW
THD+N (%)
SSM MODE
0.01
P
OUT
= 125mW
0.01
P
OUT
= 125mW
0.01
FFM MODE
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
_______________________________________________________________________________________
3
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, V
SYNC
= GND, T
A
= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC04
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC05
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
V
DD
= 3.3V
R
L
= 6Ω
10
MAX9712 TOC06
100
V
DD
= 3.3V
R
L
= 8Ω
10
100
V
DD
= 5V
R
L
= 16Ω
10
100
THD+N (%)
THD+N (%)
1
f = 10kHz
1
THD+N (%)
1
0.1
0.1
f = 10kHz
0.1
f = 10kHz
0.01
0.001
0
f = 1kHz
0.1
0.2
f = 100Hz
0.01
f = 1kHz
0.001
0.3
0.4
0.5
0
0.2
0.4
0.6
0.8
1.0
OUTPUT POWER (W)
f = 100Hz
0.01
f = 1kHz
0.001
0
0.1
0.2
OUTPUT POWER (W)
0.3
0.4
f = 100Hz
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC07
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC08
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
V
DD
= 3.3V
R
L
= 8Ω
SYNC = 3.3V
P-P
50% DUTY CYCLE
SQUARE WAVE
MAX9712 TOC09
100
V
DD
= 2.5V
R
L
= 8Ω
V
CM
= 1.25V
NO INPUT CAPACITORS
100
V
DD
= 3.3V
R
L
= 8Ω
10
100
f
SYNC
= 2MHz
10
10
THD+N (%)
THD+N (%)
1
DIFFERENTIAL
INPUT
1
FFM
(SYNC FLOATING)
SSM
(SYNC = V
DD
)
THD+N (%)
1
f
SYNC
= 1.4MHz
0.1
0.1
0.1
0.01
0.001
0
0.1
0.2
SINGLE-ENDED
0.01
FFM
(SYNC = GND)
0.001
0.01
f
SYNC
= 800kHz
0.001
0
0.1
0.2
0.3
0.4
0.5
0
0.1
0.2
0.3
0.4
0.5
0.6
OUTPUT POWER (W)
OUTPUT POWER (W)
0.3
0.4
0.5
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
MAX9712 TOC10
EFFICIENCY vs. OUTPUT POWER
MAX9712TOC11
EFFICIENCY vs. OUTPUT POWER
90
80
EFFICIENCY (%)
70
60
50
40
30
20
R
L
= 6Ω
R
L
= 16Ω
R
L
= 8Ω
MAX9712TOC12
10
V
DD
= 3.3V
R
L
= 8Ω
f = 1kHz
P
OUT
= 300mW
DIFFERENTIAL INPUT
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
V
DD
= 5V
f = 1kHz
0
0.1
0.2
0.3
0.4
0.5
0.6
R
L
= 8Ω
R
L
= 16Ω
100
THD+N (%)
1
0.1
10
0
0.7
0
V
DD
= 3.3V
f = 1kHz
0.1
0.2
0.3
0.4
0.5
0.01
0
0.5
1.0
1.5
2.0
2.5
3.0
COMMON-MODE VOLTAGE (V)
0
OUTPUT POWER (W)
OUTPUT POWER (W)
4
_______________________________________________________________________________________
500mW, Low EMI, Filterless,
Class D Audio Amplifier
MAX9712
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, V
SYNC
= GND, T
A
= +25°C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9712TOC13
EFFICIENCY
vs. SYNC INPUT FREQUENCY
MAX9712TOC14
OUTPUT POWER
vs. SUPPLY VOLTAGE
f = 1kHz
900
800
OUTPUT POWER (mW)
700
600
500
400
300
200
100
0
2000
2.5
3.1
3.7
4.3
4.9
5.5
SUPPLY VOLTAGE (V)
R
L
= 6Ω
R
L
= 8Ω
R
L
= 16Ω
MAX9712TOC15
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
2.5
3.0
3.5
4.0
4.5
5.0
f = 1kHz
R
L
= 6Ω
R
L
= 8Ω
R
L
= 16Ω
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
V
DD
= 3.3V
f = 1kHz
P
OUT
= 300mW
R
L
= 8Ω
800
1000
1200
1400
1600
1800
1000
5.5
SUPPLY VOLTAGE (V)
SYNC FREQUENCY (kHz)
OUTPUT POWER
vs. LOAD RESISTANCE
900
800
OUTPUT POWER (mW)
700
600
500
400
300
200
100
0
0
10 20 30 40 50 60 70 80 90 100
LOAD RESISTANCE (Ω)
V
DD
= 3.3V
V
DD
= 5V
CMRR (dB)
f = 1kHz
THD+N = 1%
MAX9712TOC16
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9712TOC17
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-10
-20
-30
PSRR (dB)
-40
-50
-60
-70
-80
-90
-100
OUTPUT REFERRED
INPUTS AC GROUNDED
V
DD
= 3.3V
MAX9712TOC18
1000
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
10
100
1k
FREQUENCY (Hz)
10k
INPUT REFERRED
V
IN
= 200mV
P-P
0
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
GSM POWER-SUPPLY REJECTION
MAX9712TOC19
OUTPUT FREQUENCY SPECTRUM
FFM MODE
V
OUT
= -60dBV
f = 1kHz
R
L
= 8Ω
UNWEIGHTED
MAX9712TOC20
0
-20
OUTPUT MAGNITUDE (dBV)
-40
-60
-80
-100
-120
-140
V
DD
500mV/div
MAX9712
OUTPUT
100µV/div
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
2ms/div
DUTY CYCLE = 88%
R
L
= 8Ω
0
5k
10k
15k
FREQUENCY (Hz)
20k
_______________________________________________________________________________________
5
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