General Description
The MAX9705 3rd-generation, ultra-low EMI, mono, Class
D audio power amplifier provides Class AB performance
with Class D efficiency. The MAX9705 delivers 2.3W into
a 4Ωload and offers efficiencies above 85%. Active
emissions limiting (AEL) circuitry greatly reduces EMI by
actively controlling the output FET gate transitions under
all possible transient output-voltage conditions. AEL pre-
vents high-frequency emissions resulting from conven-
tional Class D free-wheeling behavior in the presence of
an inductive load. Zero dead time (ZDT) technology
maintains state-of-the-art efficiency and THD+N perfor-
mance by allowing the output FETs to switch simultane-
ously without cross-conduction. A spread-spectrum
modulation scheme eliminates the need for output filter-
ing found in traditional Class D devices. These design
concepts reduce an application’s component count and
extend battery life.
The MAX9705 offers two modulation schemes: a fixed-
frequency (FFM) mode and a spread-spectrum (SSM)
mode that further reduces EMI-radiated emissions due to
the modulation frequency. The MAX9705 oscillator can
be synchronized to an external clock through the SYNC
input, allowing the switching frequency to be externally
defined. The SYNC input also allows multiple MAX9705s
to be cascaded and frequency locked, minimizing inter-
ference 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 MAX9705 is set internally (MAX9705A: 6dB,
MAX9705B: 12dB, MAX9705C: 15.6dB, MAX9705D:
20dB), further reducing external component count.
The MAX9705 is available in 10-pin TDFN (3mm x 3mm x
0.8mm), and 12-bump UCSP™ (1.5mm x 2mm x 0.6mm)
packages. The MAX9705 is specified over the extended
-40°C to +85°C temperature range.
Applications
Features
♦Filterless Amplifier Passes FCC-Radiated
Emissions Standards with 24in of Cable
♦Unique Spread-Spectrum Mode and Active
Emissions Limiting (AEL) Achieves Better than
20dB Margin Under FCC Limits
♦Zero Dead Time (ZDT) H-Bridge Maintains State-
of-the-Art Efficiency and THD+N
♦Simple Master-Slave Setup for Stereo Operation
♦Up to 90% Efficiency
♦2.3W into 4Ω (1% THD+N)
♦Low 0.02% THD+N (POUT = 1W, VDD = 5.0V)
♦High PSRR (75dB at 217Hz)
♦Integrated Click-and-Pop Suppression
♦Low Quiescent Current (5.4mA)
♦Low-Power Shutdown Mode (0.3µA)
♦Short-Circuit and Thermal-Overload Protection
♦Available in Thermally Efficient, Space-Saving
Packages
10-Pin TDFN (3mm x 3mm x 0.8mm)
12-Bump UCSP (1.5mm x 2mm x 0.6mm)
♦Pin-for-Pin Compatible with the MAX9700 and
MAX9712
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-3405; Rev 3; 5/09
EVALUATION KIT
AVAILABLE
Cellular Phones
PDAs
MP3 Players
Portable Audio
PART
TEMP RANGE
PIN-
PACKAGE
TOP
MARK
MAX9705AETB+T
-40oC to +85oC
10 TDFN ACY
MAX9705AEBC+T
-40oC to +85oC
12 UCSP
ACH
MAX9705BETB+T
-40oC to +85oC
10 TDFN ACX
MAX9705BEBC+T
-40oC to +85oC
12 UCSP
ACG
Ordering Information continued at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Selector Guide appears at end of data sheet.
30.0 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
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
FREQUENCY (MHz)
AMPLITUDE (dBμV/m)
FCC EMI LIMIT
MAXIM'S NEW ULTRA-LOW
OUTPUT SPECTRUM
EMI Spectrum Diagram
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL= ∞, 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
PVDD to VDD ..........................................................-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
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
MAX9705
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 2.5 5.5 V
Quiescent Current IDD 5.4 7 mA
Shutdown Current ISHDN 0.3 10 µA
Turn-On Time tON 30 ms
Input Resistance RIN TA = +25°C 12 20 kΩ
MAX9705A 0.88 1.0 1.12
MAX9705B 0.73 0.83 0.93
MAX9705C 0.61 0.71 0.81
Input Bias Voltage VBIAS Either input
MAX9705D 0.48 0.56 0.64
V
MAX9705A 1.9 2.0 2.1
MAX9705B 3.8 4.0 4.2
MAX9705C 5.7 6.0 6.3
Voltage Gain AV
MAX9705D 9.5 10 10.5
V/V
Output Offset Voltage VOS TA = +25°C ±10 ±69 mV
Common-Mode Rejection Ratio CMRR fIN = 1kHz, input referred 56 dB
VDD = 2.5V to 5.5V, TA = +25°C 50 75
fRIPPLE = 217Hz 75
Power-Supply Rejection Ratio
(Note 3) PSRR 200mVP-P ripple fRIPPLE = 20kHz 60
dB
RL = 8Ω600
Output Power POUT THD+N = 1%,
fIN = 1kHz
RL = 4Ω
MAX9705_ETB+T and
MAX9705_EUB+ only
950 mW
RL = 8Ω,
POUT = 450mW 0.02
Total Harmonic Distortion
Plus Noise THD+N fIN = 1kHz, either
FFM or SSM RL = 4Ω,
POUT = 375mW 0.025
%
Into shutdown -68
Click/Pop Level KCP
Peak voltage,
A-weighted
(Notes 3, 4) Out of shutdown -60.5
dB
Output Slew Rate SR 176 V/µs
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = VSHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL= ∞, 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 +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: Inputs AC-coupled to GND.
Note 4: Testing performed with 8Ωresistive load in series with 68µH inductive load connected across BTL output. Mode transitions
are controlled by SHDN pin. KCP level is calculated as 20 x log[(peak voltage under normal operation at rated power
level)/(peak voltage during mode transition, no input signal)]. Units are expressed in dB.
Note 5: SYNC has a 1MΩresistor to VREF = 1.25V.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Rise/Fall Time tRISE, tFALL 10% to 90% 15 ns
FFM 91
BW = 22Hz
to 22kHz SSM 89
FFM 93
Signal-to-Noise Ratio SNR VOUT = 2VRMS
A-weighted SSM 91
dB
SYNC = GND 980 1100 1220
Oscillator Frequency fOSC SYNC = VDD (SSM mode) 1220
±120
kHz
SYNC Frequency Lock Range 800 2000 kHz
Efficiency ηPOUT = 800mW, fIN = 1kHz, RL = 8Ω89 %
DIGITAL INPUTS (SHDN, SYNC)
VIH 2
Input Thresholds VIL 0.8 V
SHDN Input Leakage Current 0.1 ±10 µA
SYNC Input Current (Note 5) -1.25 ±10 µA
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = VSHDN = 5V, VGND = VPGND = 0, SYNC = GND (FFM), RL= ∞, 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 7mA
Shutdown Current ISHDN 0.55 µA
f = 217Hz 75
Power-Supply Rejection Ratio PSRR 200mVP-P ripple f = 20kHz 60 dB
RL = 16Ω750
RL = 8Ω1400
Output Power POUT THD+N = 1%,
f = 1kHz RL = 4Ω
MAX9705_ETB+T and
MAX9705_EUB+ only
2300
mW
RL = 8Ω, POUT = 1.0W 0.02
Total Harmonic Distortion
Plus Noise THD+N f = 1kHz, either
FFM or SSM RL = 4Ω, POUT = 1.75W 0.05 %
FFM 94
BW = 22Hz to
22kHz SSM 91
FFM 97
Signal-to-Noise Ratio SNR VOUT =
3VRMS A-weighted SSM 93
dB
100
0 0.5 1.0 1.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9705toc04
OUTPUT POWER (W)
THD+N (%)
VDD = 3.3V
RL = 4Ω
fIN = 1kHz
100
01.00.5 2.01.5 2.5 3.0
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9705toc05
OUTPUT POWER (W)
THD+N (%)
fIN = 1kHz VDD = 5.0V
RL = 4Ω
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc07
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 3.3V
RL = 8Ω
POUT = 100mW
POUT = 450mW
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc08
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 5.0V
RL = 8Ω
POUT = 250mW
POUT = 1W
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc09
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 2.5V
RL = 4Ω
POUT = 50mW
POUT = 300mW
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD = 3.3V, SYNC = VDD (SSM), differential input, TA= +25°C, unless otherwise noted.
Typical Operating Characteristics
for 4Ω
load condition apply to the MAX9705_ETB+T only.)
100
0 0.4 0.8 1.00.2 0.6 1.2
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9705toc01
OUTPUT POWER (W)
THD+N (%)
fIN = 1kHz
VDD = 3.3V
RL = 8Ω
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
MAX9705toc02
OUTPUT POWER (W)
THD+N (%)
fIN = 1kHz VDD = 5.0V
RL = 8Ω
100
0 0.2 0.4 0.6 0.8
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9705toc03
OUTPUT POWER (W)
THD+N (%)
fIN = 1kHz
VDD = 2.5V
RL = 4Ω
MAX9705
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = VDD (SSM), differential input, TA= +25°C, unless otherwise noted.
Typical Operating Characteristics
for 4Ω
load condition apply to the MAX9705_ETB+T only.)
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc10
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 3.3V
RL = 4Ω
POUT = 100mW
POUT = 800mW
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc11
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 5.0V
RL = 4Ω
POUT = 250mW
POUT = 1.75W
100
0.01
10 100 10k 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
1
10
MAX9705toc12
FREQUENCY (Hz)
THD+N (%)
1k
VDD = 3.3V
RL = 8Ω
POUT = 450mW
FFM
SSM
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 5
100
0 0.5 1.51.0 2.0 2.5
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. COMMON-MODE VOLTAGE
MAX9705toc13
COMMON-MODE VOLTAGE (V)
THD+N (%)
VDD = 3.3V to 5V
fIN = 1kHz
POUT = 500mW
GAIN = 6dB
RL = 8Ω
0
30
20
10
40
50
60
70
80
90
100
0 0.40.2 0.6 0.8 1.0
EFFICIENCY
vs. OUTPUT POWER
MAX9705toc14
OUTPUT POWER (W)
EFFICIENCY (%)
VDD = 3.3V
fIN = 1kHz
RL = 8Ω
RL = 4Ω
0
30
20
10
40
50
60
70
80
90
100
0 1.00.5 1.5 2.0 2.5 3.0
EFFICIENCY
vs. OUTPUT POWER
MAX9705toc15
OUTPUT POWER (W)
EFFICIENCY (%)
VDD = 5.0V
fIN = 1kHz
RL = 8Ω
RL = 4Ω
0
30
20
10
40
50
60
70
80
90
100
2.5 3.53.0 4.0 4.5 5.0 5.5
EFFICIENCY
vs. SUPPLY VOLTAGE
MAX9705toc16
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
fIN = 1kHz
THD+N = 1%
RL = 8Ω
RL = 4Ω
0
30
20
10
40
50
60
70
80
90
100
800 12001000 1400 1600 1800 2000
EFFICIENCY
vs. SYNC FREQUENCY
MAX9705toc17
SYNC FREQUENCY (kHz)
EFFICIENCY (%)
VDD = 3.3V
fIN = 1kHz
THD+N = 1%
RL = 8Ω
RL = 4Ω
0
30
20
10
40
50
60
70
80
90
100
800 12001000 1400 1600 1800 2000
EFFICIENCY
vs. SYNC FREQUENCY
MAX9705toc18
SYNC FREQUENCY (kHz)
EFFICIENCY (%)
VDD = 5.0V
fIN = 1kHz
THD+N = 1%
RL = 8Ω
RL = 4Ω
-140
-120
-100
-80
-60
-40
-20
0
20
0 5 10 15 20
SPREAD-SPECTRUM-MODE OUTPUT
SPECTRUM vs. FREQUENCY
MAX9705 toc25
FREQUENCY (kHz)
AMPLITUDE (dBV)
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
A-WEIGHTED
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
6 _______________________________________________________________________________________
0
0.6
0.4
0.2
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.5 3.53.0 4.0 4.5 5.0 5.5
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9705toc19
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
fIN = 1kHz
RL = 8Ω
THD+N = 1%
THD+N = 10%
0
1.5
1.0
0.5
2.0
2.5
3.0
3.5
2.5 3.53.0 4.0 4.5 5.0 5.5
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9705toc20
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
fIN = 1kHz
RL = 4Ω
THD+N = 1%
THD+N = 10%
4.0
0
1 100 1000
OUTPUT POWER
vs. LOAD RESISTANCE
1.5
1.0
3.0
2.0
3.5
0.5
2.5
MAX9705 toc21
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
10
fIN = 1kHz
ZLOAD = 33µH IN
SERIES WITH RL
THD+N = 1%
3.3V
5.0V
0
-10
-100
10 100 10k 100k
POWER-SUPPLY REJECTION
RATIO vs. FREQUENCY
-90
-50
-70
-80
-40
-60
-20
-30
MAX9705 toc22
FREQUENCY (Hz)
PSRR (dB)
1k
VDD = 3.3V
VIN = 200mVP-P
RL = 8Ω
-140
-120
-100
-80
-60
-40
-20
0
20
0 5 10 15 20
FIXED-FREQUENCY-MODE OUTPUT
SPECTRUM vs. FREQUENCY
MAX9705 toc23
FREQUENCY (kHz)
AMPLITUDE (dBV)
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
BW = 22Hz to 22kHz
-140
-120
-100
-80
-60
-40
-20
0
20
0 5 10 15 20
SPREAD-SPECTRUM-MODE OUTPUT
SPECTRUM vs. FREQUENCY
MAX9705 toc24
FREQUENCY (kHz)
AMPLITUDE (dBV)
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
BW = 22Hz to 22kHz
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = VDD (SSM), differential input, TA= +25°C, unless otherwise noted.
Typical Operating Characteristics
for 4Ω
load condition apply to the MAX9705_ETB+T only.)
MAX9705
0
-140
0 100 1000
WIDEBAND OUTPUT SPECTRUM
FIXED-FREQUENCY MODE
-80
-100
-20
-60
-120
-40
MAX9705 toc26
FREQUENCY (MHz)
AMPLITUDE (dBV)
10
RL = 8Ω
VDD = 5.0V
INPUTS AC GROUNDED
0
-140
0 100 1000
WIDEBAND OUTPUT SPECTRUM
SPREAD-SPECTRUM MODE
-80
-100
-20
-60
-120
-40
MAX9705 toc27
FREQUENCY (MHz)
AMPLITUDE (dBV)
10
RL = 8Ω
VDD = 5.0V
INPUTS AC GROUNDED
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 7
4
5
6
7
8
9
10
2.5 3.5 4.5 5.5
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9705 toc28
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
SYNC = VDD (SSM)
SYNC = GND (FFM)
NO LOAD
INPUTS AC GROUNDED 5.00
5.25
5.50
5.75
6.25
6.00
6.50
6.75
7.00
-40 -15 10 35 60 85
SUPPLY CURRENT
vs. TEMPERATURE
MAX9705 toc29
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
SYNC = VDD (SSM)
SYNC = GND (FFM))
VDD = 3.3V
NO LOAD
INPUTS AC GROUNDED
0
0.10
0.20
0.30
0.50
0.40
0.60
0.80
0.70
0.90
1.00
2.5 3.0 3.5 4.0 4.5 5.0 5.5
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX9705 toc30
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (µA)
TA = +25°C
TA = +85°C
TA = -40°C
NO LOAD
INPUTS AC GROUNDED
SHDN = GND
TURN-ON/TURN-OFF RESPONSE
MAX9705 toc31
MAX9705
OUTPUT
SHDN
0V
250mV/div
3V
10ms/div
f = 1kHz
RL = 8Ω
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = VDD (SSM), differential input, TA= +25°C, unless otherwise noted.
Typical Operating Characteristics
for 4Ω
load condition apply to the MAX9705_ETB+T only.)
Functional Diagram
MAX9705
2
(B1)
5
(B2)
3
(C1)
7
(B3)
( ) UCSP BUMP.
FIGURE SHOWS MAX9705 CONFIGURED FOR SPREAD-SPECTRUM OPERATION.
1µF
PGND
OUT+
OUT-
PVDD
PGND
PGND
PVDD
4
(C2)
GND
IN+
VDD
2.5V TO 5.5V
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
LOW-EMI
DRIVER
LOW-EMI
DRIVER
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
8 _______________________________________________________________________________________
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 9
Detailed Description
The MAX9705 ultra-low-EMI, filterless, Class D audio
power amplifier features several improvements to switch-
mode amplifier technology. The MAX9705 features output
driver active emissions limiting circuitry to reduce EMI.
Zero dead time technology maintains state-of-the-art effi-
ciency and THD+N performance by allowing the output
FETs to switch simultaneously without cross-conduction.
A unique filterless modulation scheme, synchronizable
switching frequency, and spread-spectrum mode create
a compact, flexible, low-noise, efficient audio power
amplifier while occupying minimal board space. The dif-
ferential input architecture reduces common-mode noise
pickup with or without the use of input-coupling capaci-
tors. The MAX9705 can also be configured as a single-
ended input amplifier without performance degradation.
Thermal-overload and short-circuit protection prevent the
MAX9705 from being damaged during a fault condition.
The amplifier is disabled if the die temperature reaches
+125°C. The die must cool by 10°C before normal opera-
tion can continue. The output of the MAX9705 shuts down
if the output current reaches approximately 2A. Each out-
put FET has its own short-circuit protection. This protec-
tion scheme allows the amplifier to survive shorts to either
supply rail. After a thermal overload or short circuit, the
device remains disabled for a minimum of 50µs before
attempting to return to normal operation. The amplifier will
shut down immediately and wait another 50µs before turn-
ing on if the fault condition is still present. This operation
will cause the output to pulse during a persistent fault.
Comparators monitor the MAX9705 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 FFM mode is selected by setting SYNC = GND for a
1.1MHz switching frequency. In FFM mode, the frequen-
cy spectrum of the Class D output consists of the funda-
mental switching frequency and its associated
harmonics (see the Wideband Output Spectrum Fixed-
Frequency Mode graph in the
Typical Operating
Characteristics
).
Pin Description
PIN BUMP
TDFN UCSP NAME FUNCTION
1A1V
DD Analog Power Supply
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 = 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
——EP
Exposed Pad. Internally connected to ground. Connect to a large ground plane to
maximize thermal performance. Not intended as an electrical connection point
(TDFN only).
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
10 ______________________________________________________________________________________
Spread-Spectrum Modulation (SSM) Mode
The MAX9705 features a unique spread-spectrum mode
that flattens the wideband spectral components, improving
EMI emissions 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 fre-
quency 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 a
bandwidth that increases with frequency. Above a few
megahertz, the wideband spectrum looks like white noise
for EMI purposes (see the
EMI Spectrum Diagram
).
External Clock Mode
The SYNC input allows the MAX9705 to be synchronized
to a system clock moving 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
MAX9705. The period of the SYNC clock can be ran-
domized, enabling the MAX9705 to be synchronized to
another MAX9705 operating in SSM mode.
Figure 1. MAX9705 Outputs with an Input Signal Applied
OUT+
OUT-
VIN-
VIN+
VOUT+ - VOUT-
tON(MIN)
tSW
SYNC INPUT
MODE
GND FFM with fS = 1100kHz
VDD SSM with fS = 1220kHz ±120kHz
Clocked FFM with fS = external clock frequency
Table 1. Operating Modes
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 11
Filterless Modulation/Common-Mode Idle
The MAX9705 uses Maxim’s unique modulation scheme
that eliminates the LC filter required by traditional
Class D amplifiers, improving efficiency, reducing com-
ponent count, and conserving board space and system
cost. Conventional Class D amplifiers output a 50% duty
cycle square wave when no signal is present. With no fil-
ter, the square wave appears across the load as a DC
voltage, resulting in a finite load current, increasing
power consumption. When no signal is present at the
input of the MAX9705, the outputs switch as shown in
Figure 3. Because the MAX9705 drives the speaker dif-
ferentially, the two outputs cancel each other, resulting
in no net idle-mode voltage across the speaker, minimiz-
ing 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 I2R loss of the MOSFET
on-resistance and supply current.
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 MAX9705 still exhibits >70% efficiencies
under the same conditions (Figure 4).
Shutdown
The MAX9705 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9705 in a low-power (0.3µA) shutdown
mode. Connect SHDN to VDD for normal operation.
Figure 2. MAX9705 Output with an Input Signal Applied (SSM Mode)
VOUT+ - VOUT-
tSW tSW tSW tSW
VIN-
VIN+
OUT+
OUT-
tON(MIN)
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
12 ______________________________________________________________________________________
Click-and-Pop Suppression
The MAX9705 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 30ms 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 and THD+N perfor-
mance. 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, lower-
ing the efficiency.
The MAX9705 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 MAX9705 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
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 MAX9705 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 MAX9705 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND and driving the other input (Figure 5).
Figure 3. MAX9705 Outputs with No Input Signal
VIN = 0V
OUT-
OUT+
VOUT+ - VOUT- = 0V
Figure 4. MAX9705 Efficiency vs. Class AB Efficiency
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
0.80.60.40.2
10
20
30
40
50
60
70
80
90
100
0
01.0
VDD = 3.3V
fIN = 1kHz
RL = 8Ω
CLASS AB
MAX9705
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 13
Note that the single-ended voltage range of the
MAX9705A is 3VP-P. This limits the achievable output
power for this device. Use higher gain versions
(MAX9705B, MAX9705C, MAX9705D) if higher output
power is desired in a single-ended application.
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, reduc-
ing component count to potentially one external
component (see the
System Diagram
). However, the
low-frequency rejection of the capacitors is lost, allow-
ing low-frequency signals to feed through to the load.
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
resistance of the MAX9705 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-
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. If a ceramic
capacitor is selected due to size constraints, use the
largest package possible to minimize voltage coeffi-
cient effects. In addition, use X7R dielectrics as
opposed to Y5V or Z5U.
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 MAX9705 does not require an output filter. The
device passes FCC emissions standards with 24in of
unshielded twisted-pair speaker cables. However, an
output filter can be used if a design is failing radiated
emissions due to board layout or excessive cable
length, or the circuit is near EMI-sensitive devices.
Supply Bypassing/Layout
Proper power-supply bypassing ensures low-distortion
operation. For optimum performance, bypass VDD to
GND and PVDD to PGND with separate 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 MAX9705
evaluation kit for layout guidance.
Stereo Configuration
Two MAX9705s can be configured as a stereo amplifier
(Figure 6). 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 MAX9705s 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 7 and 8). 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.
fRC
dB IN IN
−=
3
1
2π
Figure 5. Single-Ended Input
1µF
IN+
IN-
1µF
SINGLE-ENDED
AUDIO INPUT
MAX9705
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
Figure 6. Master-Slave Stereo Configuration
IN+
IN-
OUT+
OUT-
SYNC
1µF
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9705
VDD
VDD PVDD
IN+
IN-
OUT+
OUT-
SYNC
1µF
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9705
VDD PVDD
Figure 7. Master-Slave THD+N
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
OUTPUT POWER (W)
THD+N (%)
0.60.40.2
0.01
0.1
1
10
100
0.001
00.8
VDD = 3.3V
SLAVE DEVICE
fIN = 1kHz
SYNC = GND (FFM)
RL = 8Ω
CROSSTALK vs. FREQUENCY
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-110
10 100k
VDD = 3.3V
VIN = 500mVP-P
fIN = 1kHz
SYNC = GND (FFM)
RL = 8Ω
MASTER TO SLAVE
SLAVE TO MASTER
Figure 8. Master-Slave Crosstalk
14 ______________________________________________________________________________________
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 15
Figure 9a. Single-Ended Drive of MAX9705 Plus Volume
IN+
1µF
1µF
MAX9705
IN-
CW
50kΩ
IN+
MAX9705
IN-
1µF
1µF
CW
22kΩ
50kΩ
22kΩ
Figure 9b. Improved Single-Ended Drive of MAX9705 Plus
Volume
Ordering Information (continued)
PART TEMP RANGE PIN-
PACKAGE
TOP
MARK
MAX9705CETB+T -40oC to +85oC 10 TDFN ACZ
MAX9705CEBC+T -40oC to +85oC 12 UCSP ACI
MAX9705DETB+T -40oC to +85oC 10 TDFN ADA
MAX9705DEBC+T -40oC to +85oC 12 UCSP ACJ
Selector Guide
PART PIN-PACKAGE GAIN (dB)
MAX9705AETB+T 10 TDFN 6
MAX9705AEBC+T 12 UCSP 6
MAX9705BETB+T 10 TDFN 12
MAX9705BEBC+T 12 UCSP 12
MAX9705CETB+T 10 TDFN 15.6
MAX9705CEBC+T 12 UCSP 15.6
MAX9705DETB+T 10 TDFN 20
MAX9705DEBC+T 12 UCSP 20
+
MAX9705
TOP VIEW
TOP VIEW
(BUMP SIDE DOWN)
UCSP
SYNC OUT+
VDD
1
A
B
C
234
IN- OUT-
GND
IN+ SHDN PVDD
PGND
1234 5
10987 6
PVDD
OUT+
PGND
VDD
IN-
GND
MAX9705
OUT-IN+
SYNCSHDN
TDFN
Pin Configurations
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
16 ______________________________________________________________________________________
MAX4063
MAX9705
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
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 17
Chip Information
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in
the package code indicates RoHS status only. Package draw-
ings may show a different suffix character, but the drawing per-
tains to the package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
10 TDFN T1033-1 21-0137
12 UCSP B12-11 21-0104
MAX9705
2.3W, Ultra-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
© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 8/08 Removed µMAX package option 1–7, 9,
10, 15
3 5/09 Removed SYNC unconnected mode 3, 7, 9, 10, 14