19-0515; Rev 0; 5/06
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
General Description
The MAX9746 mono Class D audio power amplifier pro-
vides Class AB amplifier performance with Class D effi-
ciency, conserving board space and extending battery
life. The MAX9746 is designed specifically for systems
using 1.8V logic interface. Using a Class D architecture,
the MAX9746 delivers 1.2W into an 8Ω load while offer-
ing efficiencies near 90%. A patented, low-EMI modula-
tion scheme renders the traditional Class D output filter
unnecessary.
The MAX9746 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 MAX9746 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
MAX9746s 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 of the MAX9746 is set internally
further reducing external component count.
The MAX9746 features high 72dB PSRR, a low 0.1%
THD+N, and SNR in excess of 90dB. Short-circuit and
thermal-overload protection prevent the device from
damage during a fault condition. The MAX9746 is avail-
able in a 12-bump UCSP™ (1.5mm
✕
2mm
✕
0.6mm)
package. The MAX9746 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
♦
88% Efficiency
♦
1.2W into 8Ω
♦
Low 0.1% THD+N
♦
High PSRR (72dB at 217Hz)
♦
Integrated Click-and-Pop Suppression
♦
1.8V Logic-Compatible
♦
Low Quiescent Current (4mA)
♦
Low-Power Shutdown Mode (0.1µA)
♦
Short-Circuit and Thermal-Overload Protection
♦
Available in Thermally Efficient, Space-Saving
12-Bump UCSP Package (1.5mm x 2mm x 0.6mm)
MAX9746
Ordering Information
PART
MAX9746BEBC+T
TEMP RANGE
-40
o
C to +85
o
C
PIN-PACKAGE
12 UCSP-12
+Denotes
lead-free package.
Applications
Cellular Phones
PDAs
MP3 Players
Portable Audio
Pin Configuration
TOP VIEW
(BUMP SIDE DOWN)
1
Block Diagram
V
DD
MAX9746
2
3
4
V
DD
DIFFERENTIAL
AUDIO INPUT
MODULATOR
AND H-BRIDGE
SYNC
OUT+
A
IN+
B
SHDN
PGND
PV
DD
SYNC
INPUT
OSCILLATOR
IN-
GND
OUT-
MAX9746
C
UCSP
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
Maxim Integrated Products
1
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.
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
MAX9746
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)
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
Output Offset Voltage
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
(Note 3)
Output Power
Total Harmonic Distortion
Plus Noise
V
DD
I
DD
I
SHDN
t
ON
R
IN
V
BIAS
A
V
V
OS
CMRR
T
A
= +25°C
T
MIN
≤
T
A
≤
T
MAX
f
IN
= 1kHz, input referred
V
DD
= 2.5V to 5.5V, T
A
= +25°C
PSRR
200mV
P-P
ripple
THD+N = 1%
f
IN
= 1kHz, either
FFM or SSM
f
RIPPLE
= 217Hz
f
RIPPLE
= 20kHz
R
L
= 8Ω
R
L
= 8Ω,
P
OUT
= 125mW
BW = 22Hz
to 22kHz
Signal-to-Noise Ratio
SNR
V
OUT
= 2V
RMS
A-weighted
SYNC = GND
Oscillator Frequency
f
OSC
SYNC = float
SYNC = V
DD
(SSM mode)
FFM
SSM
FFM
SSM
980
1280
50
72
70
72
55
530
0.1
89
87
92
90
1100
1450
1220
±120
1220
1620
kHz
dB
mW
%
dB
T
A
= +25°C
Either input
12
0.73
Inferred from PSRR test
2.5
4
0.1
30
20
0.83
12
±11
±80
±120
0.93
5.5
5.2
10
V
mA
µA
ms
kΩ
V
dB
mV
dB
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
P
OUT
THD+N
2
_______________________________________________________________________________________
1.2W, 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
SYNC Frequency Lock Range
Efficiency
DIGITAL INPUTS (SHDN, SYNC)
SHDN
Input Threshold
SHDN
Input Leakage Current
External clock
V
IH
V
IL
SYNC Input Threshold
Internal clock
SSM mode
FFM mode (1.1MHz)
FFM mode (1.45MHz)
SYNC Input Current
1.9
Tie to
V
DD
Tie to
GND
Float
±5
µA
0.4
1.4
0.4
V
V
IH
V
IL
1.4
0.4
±1
V
µA
η
P
OUT
= 500mW, f
IN
= 1kHz
SYMBOL
CONDITIONS
MIN
800
94
TYP
MAX
2000
UNITS
kHz
%
MAX9746
ELECTRICAL CHARACTERISTICS
(V
DD
= PV
DD
=
SHDN
= 5V,
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
Quiescent Current
Shutdown Current
Common-Mode Rejection Ratio
Power-Supply Rejection Ratio
Output Power
Total Harmonic Distortion
Plus Noise
SYMBOL
I
DD
I
SHDN
CMRR
PSRR
P
OUT
THD+N
f = 1kHz, input referred
200mV
P-P
ripple
THD+N = 1%
f = 1kHz, either
FFM or SSM
f = 217Hz
f = 20kHz
R
L
= 8Ω
R
L
= 8Ω, P
OUT
= 125mW
FFM
SSM
FFM
SSM
CONDITIONS
MIN
TYP
5.2
0.1
72
72
55
1200
0.1
92.5
90.5
95.5
93.5
dB
MAX
UNITS
mA
µA
dB
dB
mW
%
Signal-to-Noise Ratio
SNR
V
OUT
=
3V
RMS
BW = 22Hz to
22kHz
A-weighted
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
= 8Ω, L = 68µH.
Note 3:
PSRR is specified with the amplifier inputs connected to GND through C
IN
.
_______________________________________________________________________________________
3
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
MAX9746
Typical Operating Characteristics
(V
DD
= 3.3V, SYNC = V
DD
(SSM), T
A
= +25°C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9746 toc01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9746 toc02
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
V
DD
= 5V
R
L
= 8Ω
MAX9746 toc03
10
V
DD
= +3.3V
R
L
= 8Ω
1
THD+N (%)
P
OUT
= 300mW
0.1
P
OUT
= 125mW
10
V
DD
= +3.3V
R
L
= 8Ω
P
OUT
= 125mW
SSM (V
DD
)
100
10
1
THD+N (%)
THD+N (%)
1
f = 100Hz
0.1
0.1
f = 1kHz
0.01
f = 10kHz
0.01
0.01
FFM (GND)
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
0
0.3
1.3
0.5
0.8
1.0
OUTPUT POWER (W)
1.5
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9746 toc04
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
V
DD
= 3.3V
R
L
= 8Ω
MAX9746 toc05
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
V
DD
= 3.3V
R
L
= 8Ω
MAX9746 toc06
100
V
DD
= 3.3V
R
L
= 8Ω
100
100
10
f
IN
= 100Hz
10
10
SYNC = 2MHz
THD+N (%)
THD+N (%)
THD+N (%)
1
f
IN
= 1kHz
1
SYNC = FLOAT
1
0.1
f
IN
= 10kHz
0.1
SYNC = V
DD
0.1
SYNC = 800kHz
0.01
SYNC = 1.4MHz
0.01
0.001
0
0.1
0.2
0.3 0.4 0.5 0.6
OUTPUT POWER (W)
0.7 0.8
0.01
SYNC = GND
0.001
0
0.1
0.3
0.4
0.2
OUTPUT POWER (W)
0.5
0.6
0.001
0
0.1
0.3
0.4
0.2
OUTPUT POWER (W)
0.5
0.6
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
V
DD
= 3.3V
f
IN
= 1kHz
P
OUT
= 500mW
R
L
= 8Ω
DIFFERENTIAL INPUT
MAX9746 toc07
EFFICIENCY
vs. OUTPUT POWER
90
80
EFFICIENCY (%)
70
60
50
40
30
MAX9746 toc08
100
100
10
THD+N (%)
1
0.1
0.01
20
10
V
DD
= 3.3V
f
IN
= 1kHz
R
L
= 8Ω
0
0.1
0.2
0.3
0.4
0.5
0.6
0.001
0
0.5
1.0
1.5
2.0
COMMON-MODE VOLTAGE (V)
2.5
0
OUTPUT POWER (W)
4
_______________________________________________________________________________________
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
MAX9746
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, SYNC = V
DD
(SSM), T
A
= +25°C, unless otherwise noted.)
EFFICIENCY
vs. OUTPUT POWER
MAX9746 toc09
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX9746 toc10
EFFICIENCY
vs. SYNC FREQUENCY
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
5.5
800
1000
1200
1400
V
DD
= 3.3V
f
IN
= 1kHz
THD+N = 1%
R
L
= 8Ω
1600
1800
2000
MAX9746 toc11
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1.0
OUTPUT POWER (W)
V
DD
= 5.0V
f
IN
= 1kHz
R
L
= 8Ω
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
3.0
3.5
4.0
4.5
5.0
SUPPLY VOLTAGE (V)
f
IN
= 1kHz
THD+N = 1%
R
L
= 8Ω
90
SYNC FREQUENCY (kHz)
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9746 toc12
OUTPUT POWER
vs. LOAD RESISTANCE
f
IN
= 1kHz
Z
LOAD
= 3.3µH IN
SERIES WITH R
L
THD+N = 1%
MAX9746 toc13
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
-10
-20
-30
CMRR (dB)
-40
-50
-60
-70
INPUT REFERRED
V
IN
= 200mV
P-P
MAX9746 TOC14
1.8
1.6
1.4
OUTPUT POWER (W)
1.2
1.0
0.8
0.6
0.4
0.2
0
2.5
3.0
3.5
4.0
4.5
5.0
f
IN
= 1kHz
R
L
= 8Ω
THD+N = 1%
THD+N = 10%
2.5
0
2.0
OUTPUT POWER (W)
1.5
5.0V
1.0
3.3V
0.5
-80
-90
0
5.5
1
10
100
1000
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
-100
10
100
1k
FREQUENCY (Hz)
10k
100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-10
-20
-30
PSRR (dB)
-40
-50
-60
-70
-80
-90
-100
10
100
1k
FREQUENCY (Hz)
10k
100k
MAX9746
OUTPUT
OUTPUT REFERRED
INPUTS AC GROUNDED
V
DD
= 3.3V
MAX9746 TOC15
GSM POWER-SUPPLY REJECTION
MAX9746 toc16
0
V
DD
500mV/div
100µV/div
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
2ms/div
DUTY CYCLE = 88%
R
L
= 8Ω
_______________________________________________________________________________________
5
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