MAX9700BEBC+T ,1.2W, Low-EMI, Filterless, Class D Audio AmplifierELECTRICAL CHARACTERISTICS(V = PV = V = 3.3V, V = V = 0V, SYNC = GND (FFM), R = 8Ω, R connected bet ..
MAX9700BETB ,1.2W, Low-EMI, Filterless, Class D Audio AmplifierBlock Diagram Selector Guide appears at end of data sheet.Pin ConfigurationsVDDTOP VIEWDIFFERENTIAL ..
MAX9700BETB+ ,1.2W, Low-EMI, Filterless, Class D Audio AmplifierApplicationsMAX9700BEUB -40 C to +85 C 10 µMAX —o oCellular Phones MP3 Players MAX9700BEBC-T -40 C ..
MAX9700BETB+T ,1.2W, Low-EMI, Filterless, Class D Audio Amplifierfeatures high 72dB PSRR, a low 0.01%THD+N, and SNR in excess of 90dB. Short-circuit andPIN- TOPPART ..
MAX9700BEUB+ ,1.2W, Low-EMI, Filterless, Class D Audio AmplifierELECTRICAL CHARACTERISTICS (continued)(V = PV = V = 3.3V, V = V = 0V, SYNC = GND (FFM), R = 8Ω, R c ..
MAX9700BEUB+ ,1.2W, Low-EMI, Filterless, Class D Audio AmplifierBlock Diagramat end of data sheet.VDDPin ConfigurationsTOP VIEWDIFFERENTIAL MODULATORAUDIO INPUT AN ..
MB89153 ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12506-4EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89150/1 ..
MB89163 ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12405-2EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89160/1 ..
MB89163 ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12405-2EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89160/1 ..
MB89163PFV ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12405-2EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89160/1 ..
MB89165 ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12405-2EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89160/1 ..
MB89165A ,8-bit Proprietary MicrocontrollerFUJITSU SEMICONDUCTORDS07-12405-2EDATA SHEET8-bit Proprietary MicrocontrollerCMOS2F MC-8L MB89160/1 ..
MAX9700AEBC+T-MAX9700AETB+T-MAX9700BEBC+-MAX9700BEBC+T-MAX9700BETB+-MAX9700BETB+T-MAX9700BEUB+-MAX9700BEUB+T-MAX9700CETB+-MAX9700CETB+T-MAX9700DETB+T-MAX9700DEUB
1.2W, Low-EMI, Filterless, Class D Audio Amplifier
General DescriptionThe 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
FeaturesFilterless Amplifier Passes FCC RadiatedEmissions Standards with 100mm of CableUnique Spread-Spectrum Mode Offers 5dB
Emissions Improvement Over ConventionalMethodsOptional External SYNC InputSimple Master-Slave Setup for Stereo Operation94% Efficiency1.2W into 8ΩLow 0.01% THD+NHigh PSRR (72dB at 217Hz)Integrated Click-and-Pop SuppressionLow Quiescent Current (4mA)Low-Power Shutdown Mode (0.1µA)Short-Circuit and Thermal-Overload ProtectionAvailable 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 AmplifierPVDD
OUT-
OUT+
PGNDGND
IN-
IN+
VDD
MAX9700
TDFN/μMAXTOP VIEW
SYNCSHDN
Pin Configurations
Ordering InformationMAX9700
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
VDD
OSCILLATOR
MODULATOR
AND H-BRIDGE
Block Diagram19-3030; Rev 2; 10/08
Cellular Phones
PDAs
MP3 Players
Portable Audio
PARTTEMP RANGEPIN-
PACKAGE
TOP
MARKMAX9700AETB-40oC to +85oC10 TDFN-EP*ACM
MAX9700AEUB-40oC to +85oC10 µMAX—
MAX9700AEBC-T-40oC to +85oC12 UCSP—
MAX9700BETB-40oC to +85oC10 TDFN-EP*ACI
MAX9700BEUB-40oC to +85oC10 µMAX—
MAX9700BEBC-T-40oC to +85oC12 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.
*EP = Exposed pad.
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= PVDD= VSHDN= 3.3V, VGND= VPGND= 0V, SYNC = GND (FFM), RL= 8Ω, RLconnected between OUT+ and OUT-,= TMINto 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.
VDDto GND..............................................................................6V
PVDDto 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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
GENERALSupply Voltage RangeVDDInferred from PSRR test2.55.5V
Quiescent CurrentIDD45.2mA
Shutdown CurrentISHDN0.110µA
Turn-On TimetON30ms
Input ResistanceRINTA = +25°C1220kΩ
Input Bias VoltageVBIASEither input0.730.830.93V
MAX9700A6
MAX9700B12
MAX9700C15.6Voltage GainAV
MAX9700D20
TA = +25°C±11±80Output Offset VoltageVOSTMIN ≤ TA ≤ TMAX±120mV
Common-Mode Rejection RatioCMRRfIN = 1kHz, input referred72dB
VDD = 2.5V to 5.5V, TA = +25°C5070
fRIPPLE = 217Hz72Power-Supply Rejection Ratio
(Note 3)PSRR200mVP-P ripplefRIPPLE = 20kHz55
RL = 8Ω450Output PowerPOUTTHD+N = 1%RL = 6Ω800mW
RL = 8Ω,
POUT = 125mW0.01
Total Harmonic Distortion
Plus NoiseTHD+NfIN = 1kHz, either
FFM or SSMRL = 6Ω,
POUT = 125mW0.01
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, RLconnected between OUT+ and OUT-,= TMINto 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.
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSFFM89BW = 22Hz
to 22kHzSSM87
FFM92Signal-to-Noise RatioSNRVOUT = 2VRMS
A-weightedSSM90
SYNC = GND98011001220
SYNC = unconnected128014501620Oscillator FrequencyfOSC
SYNC = VDD (SSM mode)1220
±120
kHz
SYNC Frequency Lock Range8002000kHz
EfficiencyηPOUT = 500mW, fIN = 1kHz94%
DIGITAL INPUTS (SHDN, SYNC)VIH2Input ThresholdsVIL0.8V
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)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSQuiescent CurrentIDD5.2mA
Shutdown CurrentISHDN0.1µA
Common-Mode Rejection RatioCMRRf = 1kHz, input referred72dB
f = 217Hz72Power-Supply Rejection RatioPSRR200mVP-P ripplef = 20kHz55dB
RL = 16Ω700
RL = 8Ω1200Output PowerPOUTTHD+N = 1%
RL = 6Ω1600
RL = 8Ω, POUT = 125mW0.015Total Harmonic Distortion
Plus NoiseTHD+Nf = 1kHz, either
FFM or SSMRL = 4Ω, POUT = 125mW0.02%
FFM92.5BW = 22Hz to
22kHzSSM90.5
FFM95.5Signal-to-Noise RatioSNRVOUT =
3VRMS
A-weightedSSM93.5
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc04
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
RL = 8Ω
f = 1kHz
f = 10kHz
f = 100Hz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc05
OUTPUT POWER (W)
THD+N (%)
VDD = 5V
RL = 16Ω
f = 10kHz
f = 1kHzf = 100Hz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT VOLTAGE
MAX9700 toc06
OUTPUT POWER (W)
THD+N (%)
f = 10kHz
f = 1kHz
f = 100Hz
VDD = 5V
RL = 4Ω
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc07
THD+N (%)
VDD = 2.5V
RL = 8Ω
VCM = 1.25V
NO INPUT CAPACITORS
DIFFERENTIAL
INPUT
SINGLE ENDED
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc08
THD+N (%)
VDD = 5V
f = 1kHz
RL = 8Ω
FFM
(SYNC UNCONNECTED)
SSM
FFM
(SYNC = GND)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9700 toc09
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
Typical Operating Characteristics(VDD= 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
0.001100k10k1001k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCYMAX9700 toc01
FREQUENCY (Hz)
THD+N (%)
VDD = +5V
RL = 8Ω
POUT = 300mW
POUT = 125mW
0.001100k10k1001k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCYMAX9700 toc02
FREQUENCY (Hz)
THD+N (%)
VDD = +3.3V
RL = 8Ω
POUT = 300mW
POUT = 125mW
0.001100k10k1001k
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCYMAX9700 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.)0.51.01.52.02.53.0
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
EFFICIENCY vs. OUTPUT POWERMAX9700toc11
OUTPUT POWER (W)
EFFICIENCY (%)
RL = 4ΩRL = 8Ω
VDD = 3.3V
f = 1kHz
EFFICIENCY vs. OUTPUT POWERMAX9700toc12
OUTPUT POWER (W)
EFFICIENCY (%)
RL = 8Ω
RL = 4Ω
VDD = 5V
f = 1kHz
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9700 toc13
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
RL = 8Ω
f = 1kHz
POUT = MAX (THD+N = 1%)
RL = 4Ω
EFFICIENCY
vs. SYNC INPUT FREQUENCY
MAx9700 toc14
SYNC FREQUENCY (kHz)
EFFICIENCY (%)
VDD = 3.3V
f = 1kHz
POUT = 300mW
RL = 8Ω
OUTPUT POWER vs.
SUPPLY VOLTAGEMAX9700toc15
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
RL = 4Ω
THD+N = 10%
RL = 4Ω
THD+N = 1%
RL = 8Ω
THD+N = 10%
RL = 8Ω
THD+N = 1%
f = 1kHz
OUTPUT POWER vs. LOAD RESISTANCEMAX9700toc16
OUTPUT POWER (mW)8070605040302010
VDD = 5V
f = 1kHz
THD+N = 1%
VDD = 3.3V
-1001001k10k100k
COMMON-MODE REJECTION RATIO
vs. FREQUENCYMAX9700TOC17
CMRR (dB)-60
-10INPUT REFERRED
VIN = 200mVP-P
-1001001k10k100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCYMAX9700TOC18
PSRR (dB)-60
-10OUTPUT REFERRED
INPUTS AC GROUNDED
VDD = 3.3V
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio AmplifierOUTPUT FREQUENCY SPECTRUM
MAX9700 toc22
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)5k10k15k20k
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
-10010M100M1G
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)MAX9700 toc23
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dB)
-10RBW = 10kHz
-10010M100M1G
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)MAX9700 toc24
OUTPUT AMPLITUDE (dB)
-10RBW = 10kHz
TURN-ON/TURN-OFF RESPONSEMAX9700 toc25
MAX9700
OUTPUT
SHDN
250mV/div
10ms/divf = 1kHz
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc21
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)5k10k15k20k
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
GSM POWER-SUPPLY REJECTIONMAX9700 toc19
MAX9700
OUTPUT
VDD
100μV/div
500mV/div
2ms/divf = 217Hz
INPUT LOW = 3V
INPUT HIGH = 3.5V
DUTY CYCLE = 88%
RL = 8Ω
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc20
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)5k10k15k20k
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
Typical Operating Characteristics (continued)(VDD= 3.3V, SYNC = GND (SSM), TA= +25°C, unless otherwise noted.)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9700 toc26
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
TA = +85°C
TA = +25°C
TA = -40°C
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9700 toc27
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (
TA = +85°C
TA = -40°C
TA = +25°C
Functional DiagramMAX9700
(B1)
(B2)
(C1)
(B3)
( ) UCSP BUMP.
1μF
PGND
OUT+
OUT-
PVDD
PGND
PGND
PVDD
(C2)
GND
IN+
VDD
VDD
(A1)
SHDN
IN-
UVLO/POWER
MANAGEMENT
CLASS D
MODULATOR
PVDDSYNC
(B4)
(A3)
(A4)
(C4)
CLICK-AND-POP
SUPPRESSIONOSCILLATOR
1μF
1μF
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifier
Detailed DescriptionThe 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) ModeThe MAX9700 features two FFM modes. The FFM modes
are selected by setting SYNC = GND for a 1.1MHz
switching frequency, and SYNC = UNCONNECTEDfor 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) ModeThe 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
PINBUMP
TDFN/µMAXUCSPNAMEFUNCTION1A1VDDAnalog Power Supply. Connect to an external power supply. Bypass to GND with a
1µF capacitor.B1IN+Noninverting Audio InputC1IN-Inverting Audio InputC2GNDAnalog Ground
5B2SHDNActive-Low Shutdown Input. Connect to VDD for normal operation.A3SYNC
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.B3PGNDPower GroundA4OUT+Amplifier-Output Positive PhaseC4OUT-Amplifier-Output Negative PhaseB4PVDDH-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 Amplifierscheme 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 ModeThe 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 IdleThe 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 INPUTMODEGNDFFM with fS = 1100kHz
UNCONNECTEDFFM with fS = 1450kHz
VDDSSM with fS = 1220kHz ±120kHz
ClockedFFM with fS = external clock frequency
Table 1. Operating Modes
MAX9700
1.2W, Low-EMI, Filterless,
Class D Audio Amplifieroutput 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.
EfficiencyEfficiency 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-
tSWtSWtSWtSW
VIN-
VIN+
OUT+
OUT-
tON(MIN)
Idle Mode is a trademark of Maxim Integrated Products.
