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MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
General Description
Features
The MAX9700 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 MAX9700 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 MAX9700s
to be cascaded and frequency locked, minimizing
interference due to clock intermodulation. The device
utilizes a fully differential architecture, a full-bridged
output, and comprehensive click-and-pop suppression.
The gain of the MAX9700 is set internally (MAX9700A:
6dB, MAX9700B: 12dB, MAX9700C: 15.6dB, MAX9700D:
20dB), further reducing external component count.
Ordering Information
The MAX9700 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 MAX9700
delivers 1.2W into an 8Ω load while offering efficiencies
above 90%. A low-EMI modulation scheme renders the
traditional class D output filter unnecessary.
The MAX9700 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 MAX9700 is available
in 10-pin TDFN (3mm x 3mm x 0.8mm), 10-pin μMAX®,
and 12-bump UCSP™ (1.5mm x 2mm x 0.6mm) packages.
The MAX9700 is specified over the extended -40°C to
+85°C temperature range.
Applications
●● Cellular Phones
●● PDAs
●● MP3 Players
●● Portable Audio
Block Diagram
●● 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
●● 94% Efficiency
●● 1.2W 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 x 3mm x 0.8mm)
• 10-Pin μMAX
• 12-Bump UCSP (1.5mm x 2mm x 0.6mm)
TEMP RANGE
PINPACKAGE
MAX9700AETB+
-40°C to +85°C
10 TDFN-EP*
MAX9700AEUB+
-40°C to +85°C
10 µMAX
—
MAX9700AEBC+T
-40°C to +85°C
12 UCSP
—
MAX9700BETB+
-40°C to +85°C
10 TDFN-EP*
MAX9700BEUB+
-40°C to +85°C
10 µMAX
—
MAX9700BEBC+T
-40°C to +85°C
12 UCSP
—
PART
TOP VIEW
VDD 1
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
MODULATOR
AND H-BRIDGE
OSCILLATOR
MAX9700
IN+
2
IN-
3
GND
SHDN
10 PVDD
9
OUT-
8
OUT+
4
7
PGND
5
6
SYNC
MAX9700
TDFN/µMAX
Pin Configurations continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
μMAX is a registered trademark of Maxim Integrated Products, Inc.
19-3030; Rev 3; 3/18
ACM
ACI
*EP = Exposed pad.
Ordering Information continued and Selector Guide appears
at end of data sheet.
Pin Configurations
VDD
TOP
MARK
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Absolute Maximum Ratings
VDD to GND.............................................................................6V
PVDD to PGND.........................................................................6V
GND to PGND.......................................................-0.3V to +0.3V
All Other Pins to GND............................... -0.3V to (VDD + 0.3V)
Continuous Current Into/Out of PVDD/PGND/OUT_.......±600mA
Continuous Input Current (all other pins)..........................±20mA
Duration of OUT_ Short Circuit to GND or PVDD......Continuous
Duration of Short Circuit Between OUT+ and OUT-..... Continuous
Continuous Power Dissipation (TA = +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C)....1951.2mW
10-Pin μMAX (derate 5.6mW/oC 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
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-,
TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
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
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VDD
Inferred from PSRR test
2.5
IDD
ISHDN
tON
RIN
VBIAS
AV
VOS
CMRR
PSRR
POUT
THD+N
5.5
V
4
5.2
mA
0.1
10
30
TA = +25°C
Either input
12
20
0.73
0.83
MAX9700A
6
MAX9700B
12
MAX9700C
15.6
MAX9700D
20
TA = +25°C
±11
TMIN ≤ TA ≤ TMAX
VDD = 2.5V to 5.5V, TA = +25°C
200mVP-P ripple
THD+N = 1%
fIN = 1kHz, either
FFM or SSM
kΩ
0.93
72
50
±80
mV
dB
70
fRIPPLE = 217Hz
72
RL = 8Ω
450
RL = 6Ω
800
RL = 8Ω,
POUT = 125mW
0.01
RL = 6Ω,
POUT = 125mW
0.01
fRIPPLE = 20kHz
V
dB
±120
fIN = 1kHz, input referred
µA
ms
dB
55
mW
%
Maxim Integrated │ 2
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Electrical Characteristics (continued)
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-,
TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
Signal-to-Noise Ratio
SNR
Oscillator Frequency
fOSC
CONDITIONS
VOUT = 2VRMS
MIN
BW = 22Hz
to 22kHz
A-weighted
TYP
FFM
89
SSM
87
FFM
92
SSM
90
980
1100
1220
SYNC = unconnected
1280
1450
1620
1220
±120
SYNC = VDD (SSM mode)
800
η
DIGITAL INPUTS (SHDN, SYNC)
POUT = 500mW, fIN = 1kHz
2000
94
VIH
Input Thresholds
SHDN Input Leakage Current
0.8
SYNC Input Current
kHz
kHz
%
2
VIL
UNITS
dB
SYNC = GND
SYNC Frequency Lock Range
Efficiency
MAX
V
±1
µA
±5
µA
Electrical Characteristics
(VDD = PVDD = VSHDN = 5V, VGND = VPGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-, TA = TMIN
to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
Quiescent Current
Shutdown Current
SYMBOL
CONDITIONS
IDD
ISHDN
CMRR
f = 1kHz, input referred
Power-Supply Rejection Ratio
PSRR
200mVP-P ripple
Output Power
POUT
THD+N = 1%
Signal-to-Noise Ratio
THD+N
SNR
TYP
5.2
Common-Mode Rejection Ratio
Total Harmonic Distortion
Plus Noise
MIN
VOUT =
3VRMS
µA
dB
72
55
1200
RL = 8Ω, POUT = 125mW
0.015
mW
1600
RL = 4Ω, POUT = 125mW
A-weighted
dB
700
RL = 8Ω
BW = 22Hz to
22kHz
mA
72
f = 20kHz
RL = 6Ω
f = 1kHz, either
FFM or SSM
UNITS
0.1
f = 217Hz
RL = 16Ω
MAX
0.02
FFM
92.5
SSM
90.5
FFM
95.5
SSM
93.5
%
dB
Note 1: All devices are 100% production tested at TA = +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 RL = 4Ω, L = 33μH.
For RL = 8Ω, L = 68μH. For RL = 16Ω, L = 136μH.
Note 3: PSRR is specified with the amplifier inputs connected to GND through CIN.
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Maxim Integrated │ 3
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics
(VDD = 3.3V, SYNC = GND (SSM), TA = +25°C, unless otherwise noted.)
VDD = +3.3V
RL = 8Ω
0.01
POUT = 300mW
10
100
POUT = 125mW
1k
10k
10
100
1k
10k
0.001
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
0.01
0.001
0.5
1.0
1.5
MAX9700 toc05
f = 10kHz
0.001
2.0
VDD = 5V
RL = 4Ω
10
1
f = 100Hz
0.1
f = 10kHz
0.01
0.01
f = 10kHz
0
1
0.1
100
THD+N (%)
f = 1kHz
f = 100Hz
VDD = 5V
RL = 16Ω
10
THD+N (%)
1
0.1
100
MAX9700 toc04
VDD = 5V
RL = 8Ω
MAX9700 toc06
FREQUENCY (Hz)
10
0
0.2
f = 1kHz
f = 100Hz
f = 1kHz
0.4
0.6
0.8
0.001
1.0
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
10
1
DIFFERENTIAL
INPUT
0.1
0.01
0.001
0.1
0.2
0.3
OUTPUT POWER (W)
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0.4
VDD = 5V
f = 1kHz
RL = 8Ω
FFM
(SYNC = GND)
1
SSM
0.1
0.01
SINGLE ENDED
0
100
10
THD+N (%)
VDD = 2.5V
RL = 8Ω
VCM = 1.25V
NO INPUT CAPACITORS
0.5
0.001
0.5
1.0
1.5
OUTPUT POWER (W)
VDD = 5V
f = 1kHz
RL = 8Ω
10
fSYNC = 1.4MHz
1
fSYNC = 800kHz
0.1
0.01
FFM
(SYNC UNCONNECTED)
0
100
THD+N (%)
100
MAX9700 toc09
OUTPUT POWER (W)
MAX9700 toc07
OUTPUT POWER (W)
MAX9700 toc08
THD+N (%)
0.001
100k
FFM MODE
FREQUENCY (Hz)
100
THD+N (%)
SSM MODE
0.01
0.01
POUT = 125mW
0.001
VDD = +3.3V
RL = 8Ω
POUT = 125mW
THD+N (%)
THD+N (%)
POUT = 300mW
1
0.1
0.1
THD+N (%)
0.1
1
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9700 toc03
VDD = +5V
RL = 8Ω
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9700 toc02
1
MAX9700 toc01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
fSYNC = 2MHz
2.0
0.001
0
0.5
1.0
1.5
2.0
OUTPUT POWER (W)
Maxim Integrated │ 4
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25°C, unless otherwise noted.)
70
RL = 8Ω
60
RL = 4Ω
50
40
30
20
0.5
1.0
1.5
2.0
2.5
MAX9700toc12
30
VDD = 5V
f = 1kHz
10
0
1.5
0
1.0
0.5
1.5
2.0
OUTPUT POWER vs.
SUPPLY VOLTAGE
MAX9700 toc13
100
80
RL = 8Ω
EFFICIENCY (%)
RL = 4Ω
60
90
50
40
30
70
60
50
40
VDD = 3.3V
f = 1kHz
POUT = 300mW
RL = 8Ω
30
20
f = 1kHz
POUT = MAX (THD+N = 1%)
10
3.0
3.5
4.0
4.5
5.0
10
0
5.5
3.5
800
1000
1200
1400
1600
1800
f = 1kHz
RL = 4Ω
THD+N = 10%
3.0
RL = 4Ω
THD+N = 1%
2.5
RL = 8Ω
THD+N = 10%
2.0
1.5
1.0
0.5
0
2000
3.0
2.5
EFFICIENCY
vs. SYNC INPUT FREQUENCY
70
2.5
1.2
40
EFFICIENCY vs. SUPPLY VOLTAGE
20
RL = 8Ω
THD+N = 1%
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SYNC FREQUENCY (kHz)
SUPPLY VOLTAGE (V)
OUTPUT POWER vs. LOAD RESISTANCE
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-20
800
VDD = 3.3V
0
MAX9700TOC17
-10
VDD = 5V
1200
INPUT REFERRED
VIN = 200mVP-P
-20
-30
-30
-40
-40
-50
-60
-50
-60
-70
-70
400
-80
-80
-90
-90
0
-100
-100
0
10 20 30 40 50 60 70 80 90 100
LOAD RESISTANCE (Ω)
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10
100
1k
FREQUENCY (Hz)
10k
100k
OUTPUT REFERRED
INPUTS AC GROUNDED
VDD = 3.3V
-10
PSRR (dB)
1600
0
MAX9700toc16
f = 1kHz
THD+N = 1%
MAX9700TOC18
SUPPLY VOLTAGE (V)
CMRR (dB)
OUTPUT POWER (mW)
0.9
50
OUTPUT POWER (W)
80
2000
0.6
60
OUTPUT POWER (W)
90
0
0.3
0
RL = 4Ω
COMMON-MODE VOLTAGE (V)
100
EFFICIENCY (%)
0
3.0
RL = 8Ω
70
20
MAx9700 toc14
0
80
VDD = 3.3V
f = 1kHz
10
0.01
90
EFFICIENCY (%)
0.1
MAX9700toc11
80
EFFICIENCY vs. OUTPUT POWER
100
OUTPUT POWER (W)
THD+N (%)
1
90
EFFICIENCY (%)
VDD = 3.3V
RL = 8Ω
f = 1kHz
POUT = 300mW
DIFFERENTIAL INPUT
EFFICIENCY vs. OUTPUT POWER
100
MAX9700 toc10
10
MAX9700toc15
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
10
100
1k
10k
100k
FREQUENCY (Hz)
Maxim Integrated │ 5
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25°C, unless otherwise noted.)
GSM POWER-SUPPLY REJECTION
0
OUTPUT MAGNITUDE (dBV)
500mV/div
VDD
MAX9700 toc20
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc19
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
-20
-40
-60
-80
-100
MAX9700
OUTPUT
100mV/div
-140
-60
-80
-100
-40
-60
-80
-100
-120
-120
-140
-140
0
5k
10k
15k
FREQUENCY (Hz)
-20
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
0
RBW = 10kHz
-10
-20
-30
-40
-50
-60
-70
-80
0
5k
10k
15k
FREQUENCY (Hz)
-100
20k
1M
10M
100M
1G
FREQUENCY (Hz)
TURN-ON/TURN-OFF RESPONSE
RBW = 10kHz
-10
20k
-90
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
0
OUTPUT AMPLITUDE (dB)
20k
10k
15k
FREQUENCY (Hz)
MAX9700 toc25
-40
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
-20
MAX9700 toc24
OUTPUT MAGNITUDE (dBV)
-20
0
OUTPUT AMPLITUDE (dB)
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
OUTPUT MAGNITUDE (dBV)
0
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc21
OUTPUT FREQUENCY SPECTRUM
5k
MAX9700 toc23
0
DUTY CYCLE = 88%
RL = 8Ω
MAX9700 toc22
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
2ms/div
-120
SHDN
3V
-30
-40
-50
0V
-60
-70
MAX9700
OUTPUT
-80
250mV/div
-90
-100
1M
10M
100M
FREQUENCY (Hz)
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1G
f = 1kHz
RL = 8Ω
10ms/div
Maxim Integrated │ 6
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25°C, unless otherwise noted.)
5.0
TA = +25°C
4.5
TA = -40°C
4.0
3.5
3.0
TA = +85°C
0.14
SUPPLY CURRENT (µA)
TA = +85°C
0.12
0.10
TA = +25°C
0.08
0.06
0.04
TA = -40°C
0.02
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
MAX9700 toc27
5.5
0.16
MAX9700 toc26
6.0
SUPPLY CURRENT (mA)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
Functional Diagram
VDD
1µF
5
(B2) SHDN
1
(A1)
10
(B4)
6
(A3)
VDD
PVDD
SYNC
UVLO/POWER
MANAGEMENT
CLICK-AND-POP
SUPPRESSION
OSCILLATOR
PVDD
1µF
2
(B1) IN+
1µF
3
(C1) IN-
CLASS D
MODULATOR
8
OUT+ (A4)
PGND
PVDD
OUT- 9
(C4)
MAX9700
PGND
7
(B3)
GND
PGND
4
(C2)
( ) UCSP BUMP.
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Maxim Integrated │ 7
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Pin Description
PIN
BUMP
TDFN/µMAX
UCSP
1
NAME
FUNCTION
A1
VDD
Analog Power Supply. Connect to an external power supply. Bypass to GND with a
1µF capacitor.
2
B1
IN+
Noninverting Audio Input
3
C1
IN-
Inverting Audio Input
4
C2
GND
5
B2
SHDN
Active-Low Shutdown Input. Connect to VDD for normal operation.
Analog Ground
6
A3
SYNC
Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with fS = 1100kHz.
SYNC = Unconnected: Fixed-frequency mode with fS = 1450kHz.
SYNC = VDD: Spread-spectrum mode with fS = 1220kH ±120kHz.
SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency.
7
B3
PGND
Power Ground
8
A4
OUT+
Amplifier-Output Positive Phase
9
C4
OUT-
Amplifier-Output Negative Phase
10
B4
PVDD
H-Bridge Power Supply. Connect to VDD.
—
—
EP
Exposed Pad. Internallly connected to GND. Connect to a large ground plane to
maximize thermal performance. Not intended as an electrical connection point.
(TDFN package only.)
Detailed Description
The MAX9700 filterless, class D audio power amplifier
features several improvements to switch-mode amplifier
technology. The MAX9700 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 pickup, and can be used without input-coupling
capacitors. The device can also be configured as a singleended input amplifier.
Comparators monitor the MAX9700 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 tON(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 tON(MIN). This causes
the net voltage across the speaker (VOUT+ - VOUT-) to
change.
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Operating Modes
Fixed-Frequency Modulation (FFM) Mode
The MAX9700 features two FFM modes. The FFM modes
are selected by setting SYNC = GND for a 1.1MHz switching
frequency, and SYNC = UNCONNECTED 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
MAX9700 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 MAX9700 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 sawMaxim Integrated │ 8
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9700 Outputs with an Input Signal Applied
Table 1. Operating Modes
SYNC INPUT
GND
UNCONNECTED
VDD
Clocked
External Clock Mode
MODE
FFM with fS = 1100kHz
FFM with fS = 1450kHz
SSM with fS = 1220kHz ±120kHz
FFM with fS = external clock frequency
tooth 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 a bandwidth that increases with frequency.
Above a few megahertz, the wideband spectrum looks
like white noise for EMI purposes (Figure 3).
www.maximintegrated.com
The SYNC input allows the MAX9700 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 MAX9700. The
period of the SYNC clock can be randomized, enabling
the MAX9700 to be synchronized to another MAX9700
operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9700 uses Maxim’s modulation scheme that
eliminates the LC filter required by traditional class
D amplifiers, improving efficiency, reducing component
count, and conserving board space and system cost.
Conventional class D amplifiers output a 50% duty cycle
Maxim Integrated │ 9
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
tSW
tSW
tSW
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 2. MAX9700 Output with an Input Signal Applied (SSM Mode)
square wave when no signal is present. With no filter,
the square wave appears across the load as a DC voltage, resulting in finite load current, increasing power
consumption. When no signal is present at the input of
the MAX9700, the outputs switch as shown in Figure 4.
Because the MAX9700 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 current-steering
switches and consume negligible additional power. Any
power loss associated with the class D output stage is
mostly due to the I x 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 MAX9700 still exhibits >90% efficiencies under the
same conditions (Figure 5).
Idle Mode is a trademark of Maxim Integrated Products
www.maximintegrated.com
Maxim Integrated │ 10
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
VIN = 0V
50.0
AMPLITUDE (dBV/m)
45.0
40.0
35.0
OUT-
30.0
25.0
20.0
15.0
10.0
30.0
OUT+
60.0
80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0
FREQUENCY (MHz)
VOUT+ - VOUT- = 0V
Figure 3. MAX9700 EMI Spectrum
Figure 4. MAX9700 Outputs with No Input Signal
Shutdown
The MAX9700 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9700 in a low-power (0.1μA) shutdown
mode. Connect SHDN to VDD for normal operation.
The MAX9700 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.
90
80
EFFICIENCY (%)
Click-and-Pop Suppression
EFFICIENCY vs. OUTPUT POWER
100
MAX9700
70
60
50
CLASS AB
40
30
VDD = 3.3V
f = 1kHz
RL - 8Ω
20
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
OUTPUT POWER (W)
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 VDD
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 MAX9700 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.
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Figure 5. MAX9700 Efficiency vs. Class AB Efficiency
Because the frequency of the MAX9700 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 can be damaged. For
optimum results, use a speaker with a series inductance
>10μH. Typical 8Ω speakers exhibit series inductances in
the 20μH to 100μH range.
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 the
Maxim Integrated │ 11
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
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 quiescentcurrent draw of 8μW/(VDD/100η), which is on the order of
a few microamps.
SINGLE-ENDED
AUDIO INPUT
1µF
IN+
MAX9700
IN1µF
Input Amplifier
Differential Input
The MAX9700 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 MAX9700 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 MAX9700 forms a highpass filter that
removes the DC bias from an incoming signal. The
AC-coupling 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:
f −3dB =
1
2πR INC IN
Choose CIN so 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
www.maximintegrated.com
Figure 6. Single-Ended Input
whose dielectrics have low-voltage coefficients, such as
tantalum or aluminum electrolytic. Capacitors with highvoltage 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 MAX9700 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, highcurrent 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 MAX9700 evaluation kit for
layout guidance.
Maxim Integrated │ 12
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Stereo Configuration
Two MAX9700s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its unfiltered output drives the SYNC input of the slave device
(U2), synchronizing the switching frequencies of the two
devices. Synchronizing two MAX9700s 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.
VDD
1µF
VDD
PVDD
MAX9700
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
IN+
OUT+
IN-
OUTSYNC
Designing with Volume Control
The MAX9700 can easily be driven by single-ended
sources (Figure 6), but extra care is needed if the source
impedance “seen” by each differential input is unbalanced,
such as the case in Figure 10a, where the MAX9700 is
used with an audio taper potentiometer acting as a volume control. Functionally, this configuration works well,
but can suffer from click-pop transients at power-up (or
coming out of SHDN) depending on the volume-control
setting. As shown, the click-pop performance is fine for
either max or min volume, but worsens at other settings.
1µF
VDD
PVDD
MAX9700
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
IN+
OUT+
IN-
OUTSYNC
Figure 7. Master-Slave Stereo Configuration
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
100
VDD = 3.3V
f = 1kHz
RL = 8Ω
SLAVE DEVICE
1
0.1
-40
MASTER-TO-SLAVE
-60
-80
-100
0.01
0.001
VDD = 3.3V
RL = 8Ω
f = 1kHz
VIN = 500mVP-P
-20
CROSSTALK (dB)
THD+N (%)
10
CROSSTALK vs. FREQUENCY
0
-120
0
0.1
0.2
0.3
OUTPUT POWER (W)
Figure 8. Master-Slave THD+N
www.maximintegrated.com
0.4
0.5
SLAVE-TO-MASTER
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 9. Master-Slave Crosstalk
Maxim Integrated │ 13
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
One solution is the configuration shown in Figure 10b.
The potentiometer is connected between the differential
inputs, and these “see” identical RC paths when the
device powers up. The variable resistive element appears
between the two inputs, meaning the setting affects both
inputs the same way. The potentiometer is audio taper,
as in Figure 10a. This significantly improves transient
performance on power-up or release from SHDN. A similar approach can be applied when the MAX9700 is driven
differentially and a volume control is required.
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, PC 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.maximintegrated.com/ucsp.
1µF
CW
22kΩ
1µF
IN-
50kΩ
IN-
CW
MAX9700
50kΩ
MAX9700
1µF
IN+
IN+
22kΩ
1µF
Figure 10a. Single-Ended Drive of MAX9700 Plus Volume
Figure 10b. Improved Single-Ended Drive of MAX9700 Plus
Volume
Ordering Information (continued)
Selector Guide
TOP
MARK
PIN-PACKAGE
GAIN (dB)
MAX9700AETB+
PART
10 TDFN-EP*
6
ACN
MAX9700AEUB+
10 µMAX
6
TEMP RANGE
PINPACKAGE
MAX9700CETB+
-40°C to +85°C
10 TDFN-EP*
MAX9700CEUB+
-40°C to +85°C
10 µMAX
—
MAX9700AEBC+T
MAX9700CEBC+T
-40°C to +85°C
12 UCSP
—
MAX9700BETB+
MAX9700DETB+
-40°C to +85°C
10 TDFN-EP*
ACO
MAX9700DEUB+
-40°C to +85°C
10 µMAX
—
MAX9700DEBC+T
-40°C to +85°C
12 UCSP
—
PART
*EP = Exposed pad.
12 UCSP
6
10 TDFN-EP*
12
MAX9700BEUB+
10 µMAX
12
MAX9700BEBC+T
12 UCSP
12
MAX9700CETB+
10 TDFN-EP*
15.6
MAX9700CEUB+
10 µMAX
15.6
MAX9700CEBC+T
12 UCSP
15.6
MAX9700DETB+
10 TDFN-EP*
20
MAX9700DEUB+
10 µMAX
20
MAX9700DEBC+T
12 UCSP
20
*EP = Exposed pad.
www.maximintegrated.com
Maxim Integrated │ 14
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
System Diagram
VDD
1µF
VDD
0.1µF
AUX_IN
OUT
BIAS
MAX4063
2.2kΩ
PVDD
IN+
OUT+
MAX9700
IN-
OUT
2.2kΩ
VDD
OUT-
SHDN
SYNC
CODEC/
BASEBAND
PROCESSOR
0.1µF
IN+
VDD
IN0.1µF
1µF
INL
MAX9722
1µF
1µF
VDD
SHDN
OUTL
OUTR
INR
µCONTROLLER
PVSS
SVSS
C1P
CIN
1µF
1µF
Pin Configurations (continued)
TOP VIEW
(BUMP SIDE DOWN)
1
VDD
TRANSISTOR COUNT: 3595
PROCESS: BiCMOS
MAX9700
2
Chip Information
3
4
SYNC
OUT+
PGND
PVDD
A
IN+
SHDN
IN-
GND
B
OUT-
C
UCSP
www.maximintegrated.com
Maxim Integrated │ 15
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE
PACKAGE CODE
DOCUMENT NO.
12 UCSP
B12-11
21-0104
10 TDFN-EP
T1033-1
21-0137
10 μMAX
U10-2
21-0061
www.maximintegrated.com
Maxim Integrated │ 16
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Revision History
REVISION REVISION
NUMBER
DATE
DESCRIPTION
PAGES
CHANGED
0
10/03
Initial release
1
6/04
Changes made to TOCs and specs
3–8, 14, 15
—
2
10/08
Addition of EP information to pin description table
1, 2, 3, 8, 14
3
3/18
Updated Ordering Information
1, 14
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
© 2018 Maxim Integrated Products, Inc. │ 17
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