General Description
The MAX9712 mono class D audio power amplifier provides class AB amplifier performance with class D efficiency, 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 low EMI modulation scheme renders the
traditional class D output filter unnecessary.
The MAX9712 offers two modulation schemes: a fixedfrequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions due to the
modulation frequency. Furthermore, the MAX9712 oscillator 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, minimizing interference due to clock intermodulation. The
device utilizes a fully differential architecture, a fullbridged output, and comprehensive click-and-pop suppression. 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 available 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.
Applications
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
500mW, Low EMI, Filterless,
Class D Audio Amplifier
________________________________________________________________ Maxim Integrated Products 1
1
2
3
4
5
10
9
8
7
6
PV
DD
OUT-
OUT+
PGNDGND
IN-
IN+
V
DD
MAX9712
TDFN/μMAX
TOP VIEW
SYNCSHDN
Pin Configurations
Ordering Information
MAX9712
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
V
DD
OSCILLATOR
MODULATOR
AND H-BRIDGE
Simplified Block Diagram
19-2917; Rev 1; 1/04
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.
Cellular Phones
PDAs
MP3 Players
Portable Audio
PART
PIN/BUMPPACKAGE
TOP
MARK
MAX9712ETB
10 TDFN AAI
MAX9712EUB
10 µMAX —
MAX9712EBC-T
ABN
Pin Configurations continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C 12 UCSP-12
500mW, Low EMI, Filterless,
Class D Audio Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= PVDD= SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected between OUT+ and OUT-, TA=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
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.
VDDto 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
MAX9712
PARAMETER
CONDITIONS
UNITS
GENERAL
Supply Voltage Range V
DD
Inferred from PSRR test 2.5 5.5 V
Quiescent Current I
DD
4 5.2 mA
Shutdown Current I
SHDN
0.1 5 µA
Turn-On Time t
ON
30 ms
Input Resistance R
IN
TA = +25°C 14 20 kΩ
Input Bias Voltage V
BIAS
Either input
V
Voltage Gain A
V
3.8 4 4.2 V/V
±40
TA = +25°C
M AX 9712E BC
±65
±65
Output Offset Voltage V
OS
T
MIN
≤ TA ≤
T
MAX M AX 9712E BC ±95
mV
Common-Mode Rejection Ratio CMRR fIN = 1kHz, input referred 72 dB
VDD = 2.5V to 5.5V 50 70
f
RIPPLE
= 217Hz 72
Power-Supply Rejection Ratio
(Note 3)
PSRR
200mV
P-P
ripple
f
RIPPLE
= 20kHz 55
dB
RL = 8Ω
Output Power P
OUT
THD+N = 1%
R
L
= 6Ω
mW
RL = 8Ω,
P
OUT
= 125mW
Total Harmonic Distortion Plus
Noise
fIN = 1kHz, either
FFM or SSM
R
L
= 6Ω,
P
OUT
= 125mW
%
SYMBOL
MIN TYP MAX
0.73 0.83 0.93
M AX 9712E U B/M AX 9712E TB ±11
±15
450
250
0.01
0.01
THD+N
M AX 9712E U B/M AX 9712E TB
RL = 16Ω, VDD = 5V 700
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= PVDD= SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected between OUT+ and OUT-, TA=
T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
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 RL= 16Ω, L = 136µH.
Note 3: PSRR is specified with the amplifier inputs connected to GND through C
IN
.
PARAMETER
CONDITIONS
UNITS
FFM 88
BW = 22Hz
to 22kHz
SSM 86
FFM 91
Signal-to-Noise Ratio SNR V
OUT
= 1.8V
RMS
SSM 89
dB
SYNC = GND 980
SYNC = float
Oscillator Frequency f
OSC
SYNC = VDD (SSM mode)
kHz
SYNC Frequency Lock Range 800
kHz
Efficiency η P
OUT
= 300mW, fIN = 1kHz 85 %
DIGITAL INPUTS (SHDN, SYNC)
V
IH
2
Input Thresholds
V
IL
0.8
V
SHDN Input Leakage Current ±1µA
SYNC Input Current ±5µA
Typical Operating Characteristics
(VDD= 3.3V, V
SYNC
= GND, TA= +25°C, unless otherwise noted.)
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9712 TOC01
FREQUENCY (Hz)
THD+N (%)
VDD = +5V
R
L
= 8Ω
P
OUT
= 300mW
P
OUT
= 125mW
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9712 TOC02
FREQUENCY (Hz)
THD+N (%)
VDD = +3.3V
R
L
= 8Ω
P
OUT
= 300mW
P
OUT
= 125mW
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9712 TOC03
FREQUENCY (Hz)
THD+N (%)
VDD = +3.3V
R
L
= 8Ω
P
OUT
= 125mW
SSM MODE
FFM MODE
SYMBOL
A-weighted
MIN TYP MAX
1100 1220
1280 1450 1620
1220
±120
2000
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= 3.3V, V
SYNC
= GND, TA= +25°C, unless otherwise noted.)
100
00.1 0.2 0.3 0.4 0.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC04
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
R
L
= 8Ω
f = 10kHz
f = 1kHz
f = 100Hz
100
0 0.2 0.4 0.6 0.8 1.0
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC05
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
R
L
= 16Ω
f = 10kHz
f = 1kHz
f = 100Hz
100
0 0.1 0.2 0.3 0.4
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC06
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
R
L
= 6Ω
f = 1kHz
f = 100Hz
f = 10kHz
100
0 0.1 0.2 0.3 0.4 0.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC07
OUTPUT POWER (W)
THD+N (%)
VDD = 2.5V
R
L
= 8Ω
V
CM
= 1.25V
NO INPUT CAPACITORS
DIFFERENTIAL
INPUT
SINGLE-ENDED
100
0 0.1 0.2 0.3 0.4 0.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC08
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
R
L
= 8Ω
FFM
(SYNC FLOATING)
FFM
(SYNC = GND)
SSM
(SYNC = V
DD
)
100
00.10.2 0.3 0.4 0.5 0.6
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9712 TOC09
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
R
L
= 8Ω
SYNC = 3.3V
P-P
50% DUTY CYCLE
SQUARE WAVE
f
SYNC
= 1.4MHz
f
SYNC
= 2MHz
f
SYNC
= 800kHz
10
00.51.01.52.02.53.0
1
0.1
0.01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
MAX9712 TOC10
COMMON-MODE VOLTAGE (V)
THD+N (%)
VDD = 3.3V
R
L
= 8Ω
f = 1kHz
P
OUT
= 300mW
DIFFERENTIAL INPUT
0
30
20
10
50
40
90
80
70
60
100
00.10.20.3 0.4 0.5 0.6 0.7
EFFICIENCY vs. OUTPUT POWER
MAX9712TOC11
OUTPUT POWER (W)
EFFICIENCY (%)
RL = 8Ω
VDD = 5V
f = 1kHz
RL = 16Ω
0
30
20
10
50
40
90
80
70
60
100
00.10.20.3 0.4 0.5
EFFICIENCY vs. OUTPUT POWER
MAX9712TOC12
OUTPUT POWER (W)
EFFICIENCY (%)
RL = 8Ω
RL = 6Ω
VDD = 3.3V
f = 1kHz
RL = 16Ω
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 5
0
30
20
10
50
40
90
80
70
60
100
2.5 3.0 3.5 4.0 4.5 5.0 5.5
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9712TOC13
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
RL = 8Ω
f = 1kHz
RL = 6Ω RL = 16Ω
0
30
20
10
50
40
90
80
70
60
100
800 1000 1200 1400 18001600 2000
EFFICIENCY
vs. SYNC INPUT FREQUENCY
MAX9712TOC14
SYNC FREQUENCY (kHz)
EFFICIENCY (%)
RL = 8Ω
VDD = 3.3V
f = 1kHz
P
OUT
= 300mW
0
500
400
200
100
300
700
600
900
800
1000
2.5 3.1 3.7 4.3 4.9 5.5
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9712TOC15
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
f = 1kHz
RL = 6Ω
RL = 8Ω
RL = 16Ω
0
300
200
100
500
400
900
800
700
600
1000
01020 4030 80706050 10090
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9712TOC16
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
VDD = 5V
VDD = 3.3V
f = 1kHz
THD+N = 1%
0
-100
10 100 1k 10k 100k
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
-80
MAX9712TOC17
FREQUENCY (Hz)
CMRR (dB)
-60
-40
-20
-30
-50
-70
-90
-10
INPUT REFERRED
V
IN
= 200mV
P-P
0
-100
10 100 1k 10k 100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-80
MAX9712TOC18
FREQUENCY (Hz)
PSRR (dB)
-60
-40
-20
-30
-50
-70
-90
-10
OUTPUT REFERRED
INPUTS AC GROUNDED
V
DD
= 3.3V
GSM POWER-SUPPLY REJECTION
MAX9712TOC19
MAX9712
OUTPUT
V
DD
100µV/div
500mV/div
2ms/div
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
DUTY CYCLE = 88%
R
L
= 8Ω
-140
-100
-120
-60
-80
-20
-40
0
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC20
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
05k10k15k 20k
FFM MODE
V
OUT
= -60dBV
f = 1kHz
R
L
= 8Ω
UNWEIGHTED
Typical Operating Characteristics (continued)
(VDD= 3.3V, V
SYNC
= GND, TA= +25°C, unless otherwise noted.)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= 3.3V, V
SYNC
= GND, TA= +25°C, unless otherwise noted.)
-140
-100
-120
-60
-80
-20
-40
0
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC22
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dBV)
051015 20
SSM MODE
V
OUT
= -60dBV
f = 1kHz
R
L
= 8Ω
A-WEIGHTED
0
-100
1M 10M 100M 1G
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
-80
MAX1972 TOC23
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dB)
-60
-40
-20
-30
-50
-70
-90
-10
RBW = 10kHz
0
-100
1M 10M 100M 1G
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
-80
MAX1972TOC24
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dB)
-60
-40
-20
-30
-50
-70
-90
-10
RBW = 10kHz
TURN-ON/TURN-OFF RESPONSE
MAX9712TOC25
MAX9712
OUTPUT
SHDN
0V
250mV/div
3V
10ms/div
f = 1kHz
R
L
= 8Ω
3.0
3.5
4.5
4.0
5.5
5.0
6.0
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9712TOC26
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
2.5 3.0 3.5 4.0 4.5 5.0 5.5
TA = +85°C
TA = +25°C
TA = -40°C
0
0.06
0.04
0.02
0.10
0.08
0.14
0.12
0.16
2.5 3.0 3.5 4.0 4.5 5.0 5.5
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9712 TOC27
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
µ
A)
TA = +85°C
TA = -40°C
TA = +25°C
-140
-100
-120
-60
-80
-20
-40
0
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC21
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dBV)
051015 20
SSM MODE
V
OUT
= -60dBV
f = 1kHz
R
L
= 8Ω
UNWEIGHTED
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 7
Functional Diagram
MAX9712
2
(B4)
5
(B3)
3
(A4)
7
(B2)
10µF
( ) UCSP BUMP.
1µF
PGND
OUT+
OUT-
PV
DD
PGND
PGND
PV
DD
4
(A5)
GND
IN+
V
DD
V
DD
1
(C4)
SHDN
IN-
UVLO/POWER
MANAGEMENT
CLASS D
MODULATOR
PV
DD
SYNC
10
(B1)
6
(C2)
8
(C1)
9
(A1)
CLICK AND POP
SUPPRESSION
OSCILLATOR
MAX9712
Detailed Description
The MAX9712 filterless, class D audio power amplifier
features several improvements to switch-mode amplifier
technology. The MAX9712 offers class AB performance
with class D efficiency, while occupying minimal board
space. A unique filterless modulation scheme, synchronizable switching frequency, and SSM mode create a
compact, flexible, low-noise, efficient audio power
amplifier. The differential input architecture reduces
common-mode noise pick-up, and can be used without
input-coupling capacitors. The device can also be configured as a single-ended input amplifier.
Comparators monitor the MAX9712 inputs and compare the complementary input voltages to the sawtooth
waveform. The comparators trip when the input magnitude of the sawtooth exceeds their corresponding input
voltage. Both comparators reset at a fixed time after the
rising edge of the second comparator trip point, generating a minimum-width pulse t
ON(min)
at the output of
the second comparator (Figure 1). As the input voltage
increases or decreases, the duration of the pulse at one
output increases (the first comparator to trip) while the
other output pulse duration remains at t
ON(min)
. This
causes the net voltage across the speaker (V
OUT+
-
V
OUT-
) to change.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode
The MAX9712 features two FFM modes. The FFM
modes are selected by setting SYNC = GND for a
1.1MHz switching frequency, and SYNC = FLOAT for a
1.45MHz switching frequency. In FFM mode, the frequency spectrum of the class D output consists of the
fundamental switching frequency and its associated
harmonics (see the Wideband FFT graph in the Typical
Operating Characteristics). The MAX9712 allows the
switching frequency to be changed by +32%, should
the frequency of one or more of the harmonics fall in a
sensitive band. This can be done at any time and does
not affect audio reproduction.
Spread-Spectrum Modulation (SSM) Mode
The MAX9712 features a unique spread-spectrum mode
that flattens the wideband spectral components, improving EMI emissions that may be radiated by the speaker
and cables by 5dB. Proprietary techniques ensure that
the cycle-to-cycle variation of the switching period does
not degrade audio reproduction or efficiency (see the
Typical Operating Characteristics). Select SSM mode by
setting SYNC = VDD. In SSM mode, the switching frequency varies randomly by ±120kHz around the center
frequency (1.22MHz). The modulation scheme remains
the same, but the period of the sawtooth waveform
changes from cycle to cycle (Figure 2). Instead of a
large amount of spectral energy present at multiples of
the switching frequency, the energy is now spread over
500mW, Low EMI, Filterless,
Class D Audio Amplifier
8 _______________________________________________________________________________________
Pin Description
PIN BUMP
TDFN/µMAX
UCSP
NAME FUNCTION
1C4V
DD
Analog Power Supply
2 B4 IN+ Noninverting Audio Input
3 A4 IN- Inverting Audio Input
4 A3 GND Analog Ground
5B3SHDN Active-Low Shutdown Input. Connect to VDD for normal operation.
6 C2 SYNC
Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with f
S
= 1100kHz.
SYNC = Float: Fixed-frequency mode with f
S
= 1450kHz.
SYNC = V
DD
: Spread-spectrum mode with fS = 1220kHz ±120kHz.
SYNC = Clocked: Fixed-frequency mode with f
S
= external clock frequency.
7 B2 PGND Power Ground
8 C1 OUT+ Amplifier Output Positive Phase
9 A1 OUT- Amplifier Output Negative Phase
10 B1 PV
DD
H-Bridge Power Supply
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 9
a bandwidth that increases with frequency. Above a few
MHz, the wideband spectrum looks like white noise for
EMI purposes (Figure 3).
External Clock Mode
The SYNC input allows the MAX9712 to be synchronized to a system clock (allowing a fully synchronous
system), or allocating the spectral components of the
switching harmonics to insensitive frequency bands.
Applying an external TTL clock of 800kHz to 2MHz to
SYNC synchronizes the switching frequency of the
MAX9712. The period of the SYNC clock can be randomized, enabling the MAX9712 to be synchronized to
another MAX9712 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9712 uses Maxim’s unique modulation
scheme that eliminates the LC filter required by
traditional class D amplifiers, improving efficiency,
reducing component count, conserving board space
and system cost. Conventional class D amplifiers output a 50% duty cycle square wave when no signal is
present. With no filter, the square wave appears across
Figure 1. MAX9712 Outputs with an Input Signal Applied
OUT+
OUT-
V
IN-
V
IN+
V
OUT+
- V
OUT-
t
ON(MIN)
t
SW
SYNC INPUT
MODE
GND FFM with fS = 1100kHz
FLOAT FFM with fS = 1450kHz
V
DD
SSM with fS = 1220kHz ±120kHz
Clocked FFM with fS = external clock frequency
Table 1. Operating Modes
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
10 ______________________________________________________________________________________
the load as a DC voltage, resulting in finite load current,
increasing power consumption. When no signal is present at the input of the MAX9712, the outputs switch as
shown in Figure 4. Because the MAX9712 drives the
speaker differentially, the two outputs cancel each
other, resulting in no net idle mode voltage across the
speaker, minimizing power consumption.
Efficiency
Efficiency of a class D amplifier is attributed to the
region of operation of the output stage transistors. In a
class D amplifier, the output transistors act as currentsteering switches and consume negligible additional
power. Any power loss associated with the class D output stage is mostly due to the I ✕R loss of the MOSFET
on-resistance, and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music reproduction levels), efficiency falls below 30%,
whereas the MAX9712 still exhibits >80% efficiencies
under the same conditions (Figure 5).
Figure 2. MAX9712 Output with an Input Signal Applied (SSM Mode)
V
OUT+
- V
OUT-
t
SW
t
SW
t
SW
t
SW
V
IN-
V
IN+
OUT+
OUT-
t
ON(MIN)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 11
Shutdown
The MAX9712 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9712 in a low-power (0.1µA) shutdown
mode. Connect SHDN to VDDfor normal operation.
Click-and-Pop Suppression
The MAX9712 features comprehensive click-and-pop
suppression that eliminates audible transients on startup and shutdown. While in shutdown, the H-bridge is in
a high-impedance state. During startup, or power-up,
the input amplifiers are muted and an internal loop sets
the modulator bias voltages to the correct levels, preventing clicks and pops when the H-bridge is subsequently enabled. For 35ms following startup, a soft-start
function gradually unmutes the input amplifiers.
Applications Information
Filterless Operation
Traditional class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost, increase the solution size of the amplifier, and can decrease efficiency. The traditional PWM
scheme uses large differential output swings (2 x V
DD
peak-to-peak) and causes large ripple currents. Any
parasitic resistance in the filter components results in a
loss of power, lowering the efficiency.
The MAX9712 does not require an output filter. The
device relies on the inherent inductance of the speaker
coil and the natural filtering of both the speaker and the
human ear to recover the audio component of the
square-wave output. Eliminating the output filter results
in a smaller, less costly, more efficient solution.
Because the frequency of the MAX9712 output is well
beyond the bandwidth of most speakers, voice coil
movement due to the square-wave frequency is very
small. Although this movement is small, a speaker not
designed to handle the additional power may be damaged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ω speakers exhibit series
inductances in the range of 20µH to 100µH.
Power Conversion Efficiency
Unlike a class AB amplifier, the output offset voltage of
a class D amplifier does not noticeably increase quiescent current draw when a load is applied. This is due to
Figure 3. MAX9712 with 76mm of Speaker Cable
30.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 280.0 300.0220.0200.0 240.0 260.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
AMPLITUDE (dBµV/m)
FREQUENCY (MHz)
Figure 4. MAX9712 Outputs with No Input Signal
VIN = 0V
OUT-
OUT+
V
OUT+
- V
OUT-
= 0V
Figure 5. MAX9712 Efficiency vs. Class AB Efficiency
0
30
20
10
50
40
90
80
70
60
100
00.10.2 0.3 0.4 0.5
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
MAX9712
CLASS AB
VDD = 3.3V
f = 1kHz
R
L
- 8Ω
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
12 ______________________________________________________________________________________
the power conversion of the class D amplifier. For example, an 8mV DC offset across an 8Ω load results in 1mA
extra current consumption in a class AB device. In the
class D case, an 8mV offset into 8Ω equates to an additional power drain of 8µW. Due to the high efficiency of
the class D amplifier, this represents an additional quiescent current draw of: 8µW/(VDD/100η), which is on the
order of a few microamps.
Input Amplifier
Differential Input
The MAX9712 features a differential input structure,
making it compatible with many CODECs, and offering
improved noise immunity over a single-ended input
amplifier. In devices such as cellular phones, high-frequency signals from the RF transmitter can be picked
up by 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, any signal common to both inputs is canceled.
Single-Ended Input
The MAX9712 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 6).
DC-Coupled Input
The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC coupling eliminates the input-coupling capacitors, reducing component count to potentially one external
component (see the System Diagram). However, the
low-frequency rejection of the capacitors is lost, allowing low-frequency signals to feedthrough to the load.
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9712 forms a highpass filter that
removes the DC bias from an incoming signal. The ACcoupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming zero-source
impedance, the -3dB point of the highpass filter is
given by:
Choose CINso f
-3dB
is well below the lowest frequency
of interest. Setting f
-3dB
too high affects the low-frequency response of the amplifier. Use capacitors
whose dielectrics have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
high-voltage coefficients, such as ceramics, may result
in increased distortion at low frequencies.
Other considerations when designing the input filter
include the constraints of the overall system and the
actual frequency band of interest. Although high-fidelity
audio calls for a flat-gain response between 20Hz and
20kHz, portable voice-reproduction devices such as
cellular phones and two-way radios need only concentrate on the frequency range of the spoken human
voice (typically 300Hz to 3.5kHz). In addition, speakers
used in portable devices typically have a poor response
below 150Hz. Taking these two factors into consideration, the input filter may not need to be designed for a
20Hz to 20kHz response, saving both board space and
cost due to the use of smaller capacitors.
Output Filter
The MAX9712 does not require an output filter. The
device passes FCC emissions standards with 100mm
of unshielded speaker cables. However, output filtering
can be used if a design is failing radiated emissions
due to board layout or cable length, or the circuit is
near EMI sensitive devices. Use an LC filter when radiated emissions are a concern, or when long leads are
used to connect the amplifier to the speaker.
Supply Bypassing/Layout
Proper power-supply bypassing ensures low distortion
operation. For optimum performance, bypass VDD to
GND and PVDD to PGND with separate 0.1µF capacitors as close to each pin as possible. A low-impedance, high-current power-supply connection to PVDD is
assumed. Additional bulk capacitance should be
added as required depending on the application and
power-supply characteristics. GND and PGND should
be star connected to system ground. Refer to the
MAX9712 Evaluation Kit for layout guidance.
Stereo Configuration
Two MAX9712s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its unfil-
f
RC
dB
IN IN
−=3
1
2π
Figure 6. Single-Ended Input
1µF
IN+
IN-
1µF
SINGLE-ENDED
AUDIO INPUT
MAX9712
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 13
tered output drives the SYNC input of the slave device
(U2), synchronizing the switching frequencies of the two
devices. Synchronizing two MAX9712s ensures that no
beat frequencies occur within the audio spectrum. This
configuration works when the master device is in either
FFM or SSM mode. There is excellent THD+N performance and minimal crosstalk between devices due to
the SYNC connection (Figures 8 and 9). U2 locks onto
only the frequency present at SYNC, not the pulse
width. The internal feedback loop of device U2 ensures
that the audio component of U1’s output is rejected.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest
information on reliability testing results, refer to the
Application Note: UCSP—A Wafer-Level Chip-Scale
Package available on Maxim’s website at www.maximic.com/ucsp.
Chip Information
TRANSISTOR COUNT: 3595
PROCESS: BiCMOS
Figure 7. Master-Slave Stereo Configuration
IN+
IN-
OUT+
OUT-
SYNC
1µF
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9712
V
DD
V
DD
PV
DD
IN+
IN-
OUT+
OUT-
SYNC
1µF
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9712
V
DD
PV
DD
Figure 8. Master-Slave THD
100
00.1 0.2 0.3 0.4 0.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
f = 1kHz
R
L
= 8Ω
SLAVE DEVICE
Figure 9. Master-Slave Crosstalk
0
-120
-100
10 100 1k 10k 100k
CROSSTALK vs. FREQUENCY
-80
FREQUENCY (Hz)
CROSSTALK (dB)
-60
-40
-20
MASTER-TO-SLAVE
SLAVE-TO-MASTER
VDD = 3.3V
R
L
= 8Ω
f = 1kHz
V
IN
= 500mV
P-P
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
14 ______________________________________________________________________________________
IN+
IN-
SHDN
OUT+
OUT-
SYNC
1µF
MAX9712
V
DD
V
DD
V
DD
V
DD
PV
DD
INL
C1P
CIN
ALERT
HPS
OUTR
SV
DD
1µF
1µF
MAX9720
OUTL
MODE1
MODE2
V
DD
PV
DD
INR
TIME
1µF
1µF
220nF
100kΩ
10kΩ
1µF
µCONTROLLER
CODEC/
BASEBAND
PROCESSOR
OUT
OUT
IN+
0.1µF
2.2kΩ
2.2kΩ
0.1µF
BIAS
AUX_IN
IN-
0.1µF
MAX4063
V
DD
System Diagram
MAX9712
TOP VIEW
(BUMP SIDE DOWN)
UCSP
GND
IN-
OUT-
1
A
B
C
234
OUT+ V
DD
SYNC
PV
DD
SHDN IN+
PGND
Pin Configurations (continued)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 15
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
.)
12L, UCSP 4x3.EPS
F
1
1
21-0104
PACKAGE OUTLINE, 4x3 UCSP
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
16 ______________________________________________________________________________________
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
.)
6, 8, &10L, DFN THIN.EPS
PROPRIETARY INFORMATION
TITLE:
APPROVAL
DOCUMENT CONTROL NO. REV.
2
1
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137 D
L
C
L
C
SEMICONDUCTOR
DALLAS
A2
A
PIN 1
INDEX
AREA
D
E
A1
D2
b
E2
[(N/2)-1] x e
REF.
e
k
1N1
L
e
L
A
L
PIN 1 ID
C0.35
DETAIL A
e
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 17
DOCUMENT CONTROL NO.APPROVAL
TITLE:
PROPRIETARY INFORMATION
REV.
2
2
COMMON DIMENSIONS
SYMBOL
MIN. MAX.
A
0.70 0.80
D
2.90 3.10
E
2.90 3.10
A1
0.00 0.05
L
0.20 0.40
PKG. CODE
6
N
T633-1 1.50±0.10D22.30±0.10
E2
0.95 BSCeMO229 / WEEA
JEDEC SPEC
0.40±0.05b1.90 REF
[(N/2)-1] x e
1.50±0.10
MO229 / WEEC
1.95 REF0.30±0.05
0.65 BSC
2.30±0.10T833-1 8
PACKAGE VARIATIONS
21-0137
0.25±0.05 2.00 REFMO229 / WEED-30.50 BSC1.50±0.10 2.30±0.1010T1033-1
0.25 MIN.
k
A2 0.20 REF.
D
SEMICONDUCTOR
DALLAS
PACKAGE OUTLINE, 6, 8 & 10L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
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
.)
MAX9712
500mW, Low EMI, Filterless,
Class D Audio Amplifier
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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
.)
10LUMAX.EPS
PACKAGE OUTLINE, 10L uMAX/uSOP
1
1
21-0061
I
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
TOP VIEW
FRONT VIEW
1
0.498 REF
0.0196 REF
S
6∞
SIDE VIEW
α
BOTTOM VIEW
0∞ 0∞ 6∞
0.037 REF
0.0078
MAX
0.006
0.043
0.118
0.120
0.199
0.0275
0.118
0.0106
0.120
0.0197 BSC
INCHES
1
10
L1
0.0035
0.007
e
c
b
0.187
0.0157
0.114
H
L
E2
DIM
0.116
0.114
0.116
0.002
D2
E1
A1
D1
MIN
-A
0.940 REF
0.500 BSC
0.090
0.177
4.75
2.89
0.40
0.200
0.270
5.05
0.70
3.00
MILLIMETERS
0.05
2.89
2.95
2.95
-
MIN
3.00
3.05
0.15
3.05
MAX
1.10
10
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
H
4X S
e
D2
D1
b
A2
A
E2
E1
L
L1
c
α
GAGE PLANE
A2 0.030 0.037 0.75 0.95
A1
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