General Description
The MAX9700 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 MAX9700 delivers
1.2W into an 8Ωload while offering efficiencies above
90%. A low-EMI modulation scheme renders the tradi-
tional class D output filter unnecessary.
The MAX9700 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 MAX9700 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
MAX9700s 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 MAX9700 is set internally
(MAX9700A: 6dB, MAX9700B: 12dB, MAX9700C:
15.6dB, MAX9700D: 20dB), further reducing external
component count.
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 avail-
able in 10-pin TDFN (3mm ✕3mm ✕0.8mm), 10-pin
µMAX®, and 12-bump UCSP™ (1.5mm ✕2mm ✕ 0.6mm)
packages. The MAX9700 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
♦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)
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
________________________________________________________________
Maxim Integrated Products
1
1
2
3
4
5
10
9
8
7
6
PVDD
OUT-
OUT+
PGNDGND
IN-
IN+
VDD
MAX9700
TDFN/μMAX
TOP VIEW
SYNCSHDN
Pin Configurations
Ordering Information
MAX9700
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
VDD
OSCILLATOR
MODULATOR
AND H-BRIDGE
Block Diagram
19-3030; Rev 2; 10/08
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
TEMP RANGE
PIN-
PACKAGE
TOP
MARK
MAX9700AETB
-40oC to +85oC 10 TDFN-EP*
ACM
MAX9700AEUB
-40oC to +85oC
10 µMAX —
MAX9700AEBC-T
-40oC to +85oC
12 UCSP —
MAX9700BETB
-40oC to +85oC 10 TDFN-EP*
ACI
MAX9700BEUB
-40oC to +85oC
10 µMAX —
MAX9700BEBC-T
-40oC to +85oC
12 UCSP —
Pin Configurations continued at end of data sheet.
Ordering Information continued and Selector Guide appears
at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
*EP = Exposed pad.
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected between OUT+ and OUT-,
TA= TMIN to TMAX, 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.
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
MAX9700
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 2.5 5.5 V
Quiescent Current IDD 45.2mA
Shutdown Current ISHDN 0.1 10 µA
Turn-On Time tON 30 ms
Input Resistance RIN TA = +25°C 12 20 kΩ
Input Bias Voltage VBIAS Either input
0.73 0.83 0.93
V
MAX9700A 6
MAX9700B 12
MAX9700C
15.6
Voltage Gain AV
MAX9700D 20
dB
TA = +25°C
±11 ±80
Output Offset Voltage VOS TMIN ≤ TA ≤ TMAX
±120
mV
Common-Mode Rejection Ratio CMRR fIN = 1kHz, input referred 72 dB
VDD = 2.5V to 5.5V, TA = +25°C 50 70
fRIPPLE = 217Hz 72
Power-Supply Rejection Ratio
(Note 3) PSRR 200mVP-P ripple fRIPPLE = 20kHz 55
dB
RL = 8Ω
450
Output Power POUT THD+N = 1% RL = 6Ω
800
mW
RL = 8Ω,
POUT = 125mW
0.01
Total Harmonic Distortion
Plus Noise
THD+N
fIN = 1kHz, either
FFM or SSM RL = 6Ω,
POUT = 125mW
0.01
%
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected between OUT+ and OUT-,
TA= TMIN to TMAX, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
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.
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
FFM 89
BW = 22Hz
to 22kHz SSM 87
FFM 92
Signal-to-Noise Ratio SNR VOUT = 2VRMS
A-weighted
SSM 90
dB
SYNC = GND 980
1100 1220
SYNC = unconnected
1280 1450 1620
Oscillator Frequency fOSC
SYNC = VDD (SSM mode)
1220
±120
kHz
SYNC Frequency Lock Range 800
2000
kHz
Efficiency ηPOUT = 500mW, fIN = 1kHz 94 %
DIGITAL INPUTS (SHDN, SYNC)
VIH 2
Input Thresholds VIL 0.8 V
SHDN Input Leakage Current ±1µA
SYNC Input Current ±5µA
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = VSHDN = 5V, VGND = VPGND = 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected 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
Quiescent Current IDD 5.2 mA
Shutdown Current ISHDN 0.1 µA
Common-Mode Rejection Ratio CMRR f = 1kHz, input referred 72 dB
f = 217Hz 72
Power-Supply Rejection Ratio PSRR
200mVP-P ripple
f = 20kHz 55 dB
RL = 16Ω
700
RL = 8Ω
1200
Output Power POUT THD+N = 1%
RL = 6Ω
1600
mW
RL = 8Ω, POUT = 125mW 0.015
Total Harmonic Distortion
Plus Noise
THD+N
f = 1kHz, either
FFM or SSM
RL = 4Ω, POUT = 125mW 0.02
%
FFM
92.5
BW = 22Hz to
22kHz SSM
90.5
FFM
95.5
Signal-to-Noise Ratio SNR VOUT =
3VRMS A-weighted SSM
93.5
dB
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
MAX9700 toc05
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
RL = 16Ω
f = 10kHz
f = 1kHz f = 100Hz
100
0 0.5 1.0 1.5 2.0
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE
MAX9700 toc06
OUTPUT POWER (W)
THD+N (%)
2.5 3.0 3.5
f = 10kHz
f = 1kHz
f = 100Hz
VDD = 5V
RL = 4Ω
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
MAX9700 toc07
OUTPUT POWER (W)
THD+N (%)
VDD = 2.5V
RL = 8Ω
VCM = 1.25V
NO INPUT CAPACITORS
DIFFERENTIAL
INPUT
SINGLE ENDED
100
0 0.5 1.0 1.5 2.0
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc08
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
f = 1kHz
RL = 8Ω
FFM
(SYNC UNCONNECTED)
SSM
FFM
(SYNC = GND)
100
0 0.5 1.0 1.5 2.0
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc09
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
f = 1kHz
RL = 8Ω
fSYNC = 800kHz
fSYNC = 2MHz
fSYNC = 1.4MHz
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD = 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9700 toc01
FREQUENCY (Hz)
THD+N (%)
VDD = +5V
RL = 8Ω
POUT = 300mW
POUT = 125mW
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9700 toc02
FREQUENCY (Hz)
THD+N (%)
VDD = +3.3V
RL = 8Ω
POUT = 300mW
POUT = 125mW
0.001
10 100k10k100 1k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
1
0.1
0.01
MAX9700 toc03
FREQUENCY (Hz)
THD+N (%)
VDD = +3.3V
RL = 8Ω
POUT = 125mW
SSM MODE
FFM MODE
MAX9700
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
10
0 0.5 1.0 1.5 2.0 2.5 3.0
1
0.1
0.01
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
MAX9700 toc10
COMMON-MODE VOLTAGE (V)
THD+N (%)
VDD = 3.3V
RL = 8Ω
f = 1kHz
POUT = 300mW
DIFFERENTIAL INPUT
1.2W, 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
MAX9700 toc13
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
RL = 8Ω
f = 1kHz
POUT = MAX (THD+N = 1%)
RL = 4Ω
0
-100
10 100 1k 10k 100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-80
MAX9700TOC18
FREQUENCY (Hz)
PSRR (dB)
-60
-40
-20
-30
-50
-70
-90
-10 OUTPUT REFERRED
INPUTS AC GROUNDED
VDD = 3.3V
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
6 _______________________________________________________________________________________
-140
-100
-120
-60
-80
-20
-40
0
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc22
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
0 5k 10k 15k 20k
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
0
-100
1M 10M 100M 1G
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
-80
MAX9700 toc24
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dB)
-60
-40
-20
-30
-50
-70
-90
-10 RBW = 10kHz
TURN-ON/TURN-OFF RESPONSE
MAX9700 toc25
MAX9700
OUTPUT
SHDN
0V
250mV/div
3V
10ms/div
f = 1kHz
RL = 8Ω
GSM POWER-SUPPLY REJECTION
MAX9700 toc19
MAX9700
OUTPUT
VDD
100μV/div
500mV/div
2ms/div
f = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
DUTY CYCLE = 88%
RL = 8Ω
-140
-100
-120
-60
-80
-20
-40
0
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc20
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
0 5k 10k 15k 20k
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 7
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
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
MAX9700 toc27
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (μA)
TA = +85°C
TA = -40°C
TA = +25°C
Functional Diagram
MAX9700
2
(B1)
5
(B2)
3
(C1)
7
(B3)
( ) UCSP BUMP.
1μF
PGND
OUT+
OUT-
PVDD
PGND
PGND
PVDD
4
(C2)
GND
IN+
VDD
VDD
1
(A1)
SHDN
IN-
UVLO/POWER
MANAGEMENT
CLASS D
MODULATOR
PVDD SYNC
10
(B4)
6
(A3)
8
(A4)
9
(C4)
CLICK-AND-POP
SUPPRESSION OSCILLATOR
1μF
1μF
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
8 _______________________________________________________________________________________
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, synchro-
nizable 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 con-
figured as a single-ended input amplifier.
Comparators monitor the MAX9700 inputs and com-
pare the complementary input voltages to the sawtooth
waveform. The comparators trip when the input magni-
tude 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, gener-
ating 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.
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 fre-
quency 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 efficien-
cy (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
Pin Description
PIN BUMP
TDFN/µMAX
UCSP NAME FUNCTION
1A1V
DD 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 Analog Ground
5B2SHDN Active-Low Shutdown Input. Connect to VDD for normal operation.
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 = 1220kHz ±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.)
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 9
scheme remains the same, but the period of the saw-
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).
External Clock Mode
The SYNC input allows the MAX9700 to be synchro-
nized 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 ran-
domized, 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
Figure 1. MAX9700 Outputs with an Input Signal Applied
OUT+
OUT-
VIN-
VIN+
VOUT+ - VOUT-
tON(MIN)
tSW
SYNC INPUT MODE
GND FFM with fS = 1100kHz
UNCONNECTED
FFM with fS = 1450kHz
VDD SSM with fS = 1220kHz ±120kHz
Clocked FFM with fS = external clock frequency
Table 1. Operating Modes
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
10 ______________________________________________________________________________________
output a 50% duty cycle 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 pre-
sent 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 out-
put 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 MAX9700 still exhibits >90% efficiencies
under the same conditions (Figure 5).
Figure 2. MAX9700 Output with an Input Signal Applied (SSM Mode)
VOUT+ - VOUT-
tSW tSW tSW tSW
VIN-
VIN+
OUT+
OUT-
tON(MIN)
Idle Mode is a trademark of Maxim Integrated Products.
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 11
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.
Click-and-Pop Suppression
The MAX9700 features comprehensive click-and-pop
suppression that eliminates audible transients on start-
up 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, pre-
venting clicks and pops when the H-bridge is subse-
quently 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 amplifi-
er, 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.
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 dam-
aged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ωspeakers 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 quies-
cent current draw when a load is applied. This is due to
Figure 3. MAX9700 EMI Spectrum
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. MAX9700 Outputs with No Input Signal
VIN = 0V
OUT-
OUT+
VOUT+ - VOUT- = 0V
Figure 5. MAX9700 Efficiency vs. Class AB Efficiency
0
30
20
10
50
40
90
80
70
60
100
0 0.1 0.2 0.4 0.60.3 0.5 0.7
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
MAX9700
CLASS AB
VDD = 3.3V
f = 1kHz
RL - 8Ω
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
12 ______________________________________________________________________________________
the power conversion of the class D amplifier. For exam-
ple, an 8mV DC offset across an 8Ωload results in 1mA
extra current consumption in a class AB device. In the
class D case, an 8mV offset into 8Ωequates to an addi-
tional power drain of 8µW. Due to the high efficiency of
the class D amplifier, this represents an additional quies-
cent-current draw of 8µW/(VDD/100η), which is on the
order of a few microamps.
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-fre-
quency 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 differ-
ential 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 cou-
pling 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-frequen-
cy 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 sig-
nal to an optimum DC level. Assuming zero source
impedance, the -3dB point of the highpass filter is
given by:
Choose CIN so f-3dB is well below the lowest frequency
of interest. Setting f-3dB too high affects the low-fre-
quency 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 concen-
trate 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 considera-
tion, 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 radi-
ated 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 capaci-
tors as close to each pin as possible. A low-imped-
ance, 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
MAX9700 evaluation kit for layout guidance.
fRC
dB IN IN
−=
3
1
2π
Figure 6. Single-Ended Input
1μF
IN+
IN-
1μF
SINGLE-ENDED
AUDIO INPUT
MAX9700
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 13
Stereo Configuration
Two MAX9700s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its unfil-
tered 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 perfor-
mance 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.
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 configura-
tion 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 perfor-
mance is fine for either max or min volume, but worsens
at other settings.
Figure 7. Master-Slave Stereo Configuration
IN+
IN-
OUT+
OUT-
SYNC
1μF
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9700
VDD
VDD PVDD
IN+
IN-
OUT+
OUT-
SYNC
1μF
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9700
VDD PVDD
Figure 8. Master-Slave THD+N
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
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
f = 1kHz
RL = 8Ω
SLAVE DEVICE
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
RL = 8Ω
f = 1kHz
VIN = 500mVP-P
Figure 9. Master-Slave Crosstalk
MAX9700
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 con-
trol is required.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, PC board tech-
niques, bump-pad layout, and recommended reflow tem-
perature 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.maxim-ic.com/ucsp.
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
14 ______________________________________________________________________________________
Figure 10a. Single-Ended Drive of MAX9700 Plus Volume
IN+
1μF
1μF
MAX9700
IN-
CW
50kΩ
IN+
MAX9700
IN-
1μF
1μF
CW
22kΩ
50kΩ
22kΩ
Figure 10b. Improved Single-Ended Drive of MAX9700 Plus
Volume
Ordering Information (continued)
PART
TEMP RANGE
PIN-
PACKAGE
TOP
MARK
MAX9700CETB
-40oC to +85oC 10 TDFN-EP*
ACN
MAX9700CEUB
-40oC to +85oC
10 µMAX —
MAX9700CEBC-T
-40oC to +85oC
12 UCSP —
MAX9700DETB
-40oC to +85oC 10 TDFN-EP*
ACO
MAX9700DEUB
-40oC to +85oC
10 µMAX —
MAX9700DEBC-T
-40oC to +85oC
12 UCSP —
Selector Guide
PART PIN-PACKAGE
GAIN (dB)
MAX9700AETB 10 TDFN-EP* 6
MAX9700AEUB 10 µMAX 6
MAX9700AEBC-T 12 UCSP 6
MAX9700BETB 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.
*EP = Exposed pad.
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 15
Chip Information
TRANSISTOR COUNT: 3595
PROCESS: BiCMOS
MAX4063
MAX9700
MAX9722
CODEC/
BASEBAND
PROCESSOR
AUX_IN
BIAS
IN+
IN-
OUT
IN+
VDD
OUT+
OUT-
INL
INR
C1P CIN
SVSS
PVSS
OUTR
OUTL
VDD
VDD
0.1μF
0.1μF
0.1μF
2.2kΩ
2.2kΩ
VDD
VDD
μCONTROLLER
IN-
PVDD
SYNC
OUT
1μF
1μF
1μF
1μF
1μF
1μF
SHDN
SHDN
System Diagram
MAX9700
TOP VIEW
(BUMP SIDE DOWN)
UCSP
SYNC OUT+
VDD
1
A
B
C
234
IN- OUT-
GND
IN+ SHDN PVDD
PGND
Pin Configurations (continued)
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
16 ______________________________________________________________________________________
12L, UCSP 4x3.EPS
F
11
21-0104
PACKAGE OUTLINE, 4x3 UCSP
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
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
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 17
6, 8, &10L, DFN THIN.EPS
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
18 ______________________________________________________________________________________
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 N D2 E2 eJEDEC SPEC b[(N/2)-1] x e
PACKAGE VARIATIONS
0.25 MIN.k
A2 0.20 REF.
2.00 REF0.25–0.050.50 BSC2.30–0.1010T1033-1
2.40 REF0.20–0.05- - - - 0.40 BSC1.70–0.10 2.30–0.1014T1433-1
1.50–0.10 MO229 / WEED-3
0.40 BSC - - - - 0.20–0.05 2.40 REFT1433-2 14 2.30–0.101.70–0.10
T633-2 6 1.50–0.10 2.30–0.10 0.95 BSC MO229 / WEEA 0.40–0.05 1.90 REF
T833-2 8 1.50–0.10 2.30–0.10 0.65 BSC MO229 / WEEC 0.30–0.05 1.95 REF
T833-3 8 1.50–0.10 2.30–0.10 0.65 BSC MO229 / WEEC 0.30–0.05 1.95 REF
2.30–0.10 MO229 / WEED-3 2.00 REF0.25–0.050.50 BSC1.50–0.1010T1033-2
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
MAX9700
10LUMAX.EPS
α
α
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 19
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
MAX9700
1.2W, 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.
20
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER REVISION 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