19-3405; Rev 3; 5/09
KIT
ATION
EVALU
LE
B
A
IL
A
AV
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
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 4Ω load 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 prevents high-frequency emissions resulting from conventional 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 performance by allowing the output FETs to switch simultaneously without cross-conduction. A spread-spectrum
modulation scheme eliminates the need for output filtering 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 fixedfrequency (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 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 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.
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 Stateof-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
Ordering Information
TEMP RANGE
PINPACKAGE
MAX9705AETB+T
-40oC to +85oC
10 TDFN
ACY
MAX9705AEBC+T
-40oC to +85oC
12 UCSP
ACH
MAX9705BETB+T
-40oC to +85oC
10 TDFN
ACX
PART
TOP
MARK
MAX9705BEBC+T
-40oC to +85oC 12 UCSP
ACG
Ordering Information continued at end of data sheet.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Applications
MP3 Players
PDAs
Portable Audio
Selector Guide appears at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
EMI Spectrum Diagram
50.0
AMPLITUDE (dBμV/m)
Cellular Phones
45.0
40.0
FCC EMI LIMIT
35.0
30.0
25.0
20.0
15.0
10.0
5.0
MAXIM'S NEW ULTRA-LOW
OUTPUT SPECTRUM
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
FREQUENCY (MHz)
________________________________________________________________ Maxim Integrated Products
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.
1
MAX9705
General Description
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
ABSOLUTE MAXIMUM RATINGS
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
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
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 = V SHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL = ∞, 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
VDD
5.5
V
Quiescent Current
IDD
5.4
7
mA
Shutdown Current
ISHDN
0.3
10
µA
Turn-On Time
tON
Input Resistance
RIN
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
Click/Pop Level
Output Slew Rate
2
VBIAS
AV
VOS
CMRR
Inferred from PSRR test
30
TA = +25°C
POUT
THD+N
KCP
SR
ms
MAX9705A
12
0.88
0.73
0.61
0.48
1.9
20
1.0
0.83
0.71
0.56
2.0
1.12
0.93
0.81
0.64
2.1
MAX9705B
3.8
4.0
4.2
MAX9705C
5.7
6.0
6.3
MAX9705D
9.5
10
10.5
±10
±69
Either input
MAX9705A
MAX9705B
MAX9705C
MAX9705D
TA = +25°C
fIN = 1kHz, input referred
VDD = 2.5V to 5.5V, TA = +25°C
PSRR
2.5
200mVP-P ripple
THD+N = 1%,
fIN = 1kHz
fIN = 1kHz, either
FFM or SSM
Peak voltage,
A-weighted
(Notes 3, 4)
fRIPPLE = 217Hz
56
50
75
fRIPPLE = 20kHz
60
600
RL = 4Ω
MAX9705_ETB+T and
MAX9705_EUB+ only
950
Into shutdown
V
V/V
mV
dB
75
RL = 8Ω
RL = 8Ω,
POUT = 450mW
RL = 4Ω,
POUT = 375mW
kΩ
dB
mW
0.02
%
0.025
-68
dB
Out of shutdown
-60.5
176
_______________________________________________________________________________________
V/µs
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
(VDD = PVDD = V SHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL = ∞, RL connected between OUT+ and OUT-,
TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
Rise/Fall Time
SYMBOL
CONDITIONS
MIN
tRISE, tFALL 10% to 90%
Signal-to-Noise Ratio
SNR
BW = 22Hz
to 22kHz
VOUT = 2VRMS
FFM
91
SSM
FFM
89
93
SSM
SYNC = GND
fOSC
1100
ns
dB
1220
kHz
1220
±120
SYNC = VDD (SSM mode)
800
η
UNITS
91
980
SYNC Frequency Lock Range
Efficiency
MAX
15
A-weighted
Oscillator Frequency
TYP
POUT = 800mW, fIN = 1kHz, RL = 8Ω
2000
89
kHz
%
DIGITAL INPUTS (SHDN, SYNC)
VIH
Input Thresholds
2
VIL
0.8
SHDN Input Leakage Current
SYNC Input Current
(Note 5)
V
0.1
±10
µA
-1.25
±10
µA
ELECTRICAL CHARACTERISTICS
(V DD = PV DD = V SHDN = 5V, V GND = V PGND = 0, SYNC = GND (FFM), R L = ∞, R L 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
Quiescent Current
IDD
7
mA
Shutdown Current
ISHDN
0.55
µA
Power-Supply Rejection Ratio
Output Power
PSRR
POUT
Total Harmonic Distortion
Plus Noise
Signal-to-Noise Ratio
THD+N
SNR
200mVP-P ripple
THD+N = 1%,
f = 1kHz
f = 1kHz, either
FFM or SSM
VOUT =
3VRMS
f = 217Hz
75
f = 20kHz
60
RL = 16Ω
750
RL = 8Ω
1400
RL = 4Ω
MAX9705_ETB+T and
MAX9705_EUB+ only
2300
RL = 8Ω, POUT = 1.0W
0.02
RL = 4Ω, POUT = 1.75W
0.05
BW = 22Hz to
22kHz
A-weighted
dB
mW
FFM
94
SSM
91
FFM
97
SSM
93
%
dB
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 8Ω resistive 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 1MΩ resistor to VREF = 1.25V.
_______________________________________________________________________________________
3
MAX9705
ELECTRICAL CHARACTERISTICS (continued)
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.)
0.1
0.01
1
0.1
0.2
0.4
0.6
0.8
1.0
1.2
0.5
1.0
1.5
0
2.0
0.4
0.6
0.8
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
0.01
1
0.1
fIN = 1kHz
VDD = 3.3V
RL = 4Ω
0.001
0.5
1.0
1.5
MAX9705toc06
SSM
FFM
0.1
VDD = 5.0V
RL = 4Ω
0.001
0.001
0
1
0.01
0.01
fIN = 1kHz
VDD = 3.3V
RL = 8Ω
fIN = 1kHz
10
THD+N (%)
10
THD+N (%)
0.1
100
MAX9705toc05
100
MAX9705toc04
1
0
0.5
1.0
1.5
2.0
2.5
0
3.0
0.2
0.4
0.6
0.8
1.0
OUTPUT POWER (W)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
VDD = 5.0V
RL = 8Ω
POUT = 450mW
POUT = 250mW
1
POUT = 1W
0.1
0.01
THD+N (%)
POUT = 100mW
1
1k
FREQUENCY (Hz)
10k
100k
POUT = 50mW
1
POUT = 300mW
0.1
0.01
0.01
100
VDD = 2.5V
RL = 4Ω
10
10
THD+N (%)
10
100
MAX9705toc08
100
MAX9705toc07
VDD = 3.3V
RL = 8Ω
1.2
MAX9705toc09
OUTPUT POWER (W)
100
10
0.2
OUTPUT POWER (W)
10
THD+N (%)
0.001
0
OUTPUT POWER (W)
100
0.1
fIN = 1kHz
VDD = 2.5V
RL = 4Ω
0.001
0
0.1
VDD = 5.0V
RL = 8Ω
fIN = 1kHz
0.001
1
0.01
0.01
VDD = 3.3V
RL = 8Ω
4
10
THD+N (%)
10
THD+N (%)
1
100
MAX9705toc02
fIN = 1kHz
10
THD+N (%)
100
MAX9705toc01
100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9705toc03
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
THD+N (%)
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
FREQUENCY (Hz)
_______________________________________________________________________________________
10k
100k
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
VDD = 3.3V
RL = 4Ω
VDD = 5.0V
RL = 4Ω
VDD = 3.3V
RL = 8Ω
POUT = 450mW
10
POUT = 100mW
1
POUT = 800mW
THD+N (%)
10
THD+N (%)
POUT = 250mW
1
0.01
0.01
0.01
100
10k
1k
100k
10
100
10k
1k
10
100k
100
10k
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. COMMON-MODE VOLTAGE
EFFICIENCY
vs. OUTPUT POWER
EFFICIENCY
vs. OUTPUT POWER
0.1
RL = 4Ω
50
40
80
30
0.5
1.0
1.5
2.0
2.5
40
VDD = 5.0V
fIN = 1kHz
0
0
0.2
0.4
0.6
0.8
1.0
0
0.5
1.0
1.5
2.0
2.5
COMMON-MODE VOLTAGE (V)
OUTPUT POWER (W)
OUTPUT POWER (W)
EFFICIENCY
vs. SUPPLY VOLTAGE
EFFICIENCY
vs. SYNC FREQUENCY
EFFICIENCY
vs. SYNC FREQUENCY
EFFICIENCY (%)
60
50
40
60
50
40
30
30
20
20
fIN = 1kHz
THD+N = 1%
10
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
RL = 8Ω
90
80
RL = 4Ω
70
60
50
40
30
VDD = 3.3V
fIN = 1kHz
THD+N = 1%
10
0
0
100
RL = 4Ω
70
3.0
MAX9705toc18
80
RL = 4Ω
70
RL = 8Ω
EFFICIENCY (%)
80
90
MAX9705toc17
RL = 8Ω
90
100
MAX9705toc16
100
2.5
RL = 4Ω
50
10
0
0
60
20
VDD = 3.3V
fIN = 1kHz
10
0.001
70
30
20
0.01
RL = 8Ω
90
70
60
MAX9705toc15
80
100k
100
EFFICIENCY (%)
1
RL = 8Ω
90
EFFICIENCY (%)
VDD = 3.3V to 5V
fIN = 1kHz
POUT = 500mW
GAIN = 6dB
RL = 8Ω
10
100
MAX9705toc13
100
EFFICIENCY (%)
SSM
0.1
0.1
10
FFM
1
POUT = 1.75W
0.1
MAX9705toc14
THD+N (%)
10
100
MAX9705toc11
100
MAX9705toc10
100
THD+N (%)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9705toc12
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
20
VDD = 5.0V
fIN = 1kHz
THD+N = 1%
10
0
800
1000
1200
1400
1600
SYNC FREQUENCY (kHz)
1800
2000
800
1000
1200
1400
1600
1800
2000
SYNC FREQUENCY (kHz)
_______________________________________________________________________________________
5
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.)
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.)
OUTPUT POWER
vs. SUPPLY VOLTAGE
1.6
THD+N = 10%
1.0
THD+N = 1%
0.6
THD+N = 10%
2.0
1.5
3.0
THD+N = 1%
1.0
2.0
3.3V
1.5
1.0
0.4
0.5
fIN = 1kHz
RL = 8Ω
0.2
0
fIN = 1kHz
RL = 4Ω
0.5
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
2.5
3.0
SUPPLY VOLTAGE (V)
3.5
4.0
4.5
5.0
5.5
-20
-40
-50
-60
-70
-40
-60
-80
-100
-80
-120
-90
-100
-140
10
100
1k
10k
5
10
15
SPREAD-SPECTRUM-MODE OUTPUT
SPECTRUM vs. FREQUENCY
SPREAD-SPECTRUM-MODE OUTPUT
SPECTRUM vs. FREQUENCY
MAX9705 toc24
20
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
A-WEIGHTED
0
-20
AMPLITUDE (dBV)
-20
0
FREQUENCY (kHz)
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
BW = 22Hz to 22kHz
0
100k
FREQUENCY (Hz)
20
AMPLITUDE (dBV)
RL = 8Ω
VDD = 5.0V
fIN = 1kHz
BW = 22Hz to 22kHz
0
AMPLITUDE (dBV)
PSRR (dB)
20
MAX9705 toc22
VDD = 3.3V
VIN = 200mVP-P
RL = 8Ω
-30
-40
-60
-80
20
-40
-60
-80
-100
-100
-120
-120
-140
-140
0
5
10
FREQUENCY (kHz)
6
100
10
LOAD RESISTANCE (Ω)
FIXED-FREQUENCY-MODE OUTPUT
SPECTRUM vs. FREQUENCY
0
-20
1
SUPPLY VOLTAGE (V)
POWER-SUPPLY REJECTION
RATIO vs. FREQUENCY
-10
5.0V
2.5
MAX9705 toc23
0.8
2.5
fIN = 1kHz
ZLOAD = 33µH IN
SERIES WITH RL
THD+N = 1%
3.5
MAX9705 toc25
1.2
3.0
OUTPUT POWER (W)
1.4
4.0
OUTPUT POWER (W)
1.8
MAX9705toc20
3.5
MAX9705toc19
2.0
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9705 toc21
OUTPUT POWER
vs. SUPPLY VOLTAGE
OUTPUT POWER (W)
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
15
20
0
5
10
15
FREQUENCY (kHz)
_______________________________________________________________________________________
20
1000
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
WIDEBAND OUTPUT SPECTRUM
SPREAD-SPECTRUM MODE
WIDEBAND OUTPUT SPECTRUM
FIXED-FREQUENCY MODE
-60
-80
-40
-60
-80
-100
-100
RL = 8Ω
VDD = 5.0V
INPUTS AC GROUNDED
-120
RL = 8Ω
VDD = 5.0V
INPUTS AC GROUNDED
-120
-140
-140
100
10
0
1000
100
10
FREQUENCY (MHz)
FREQUENCY (MHz)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY CURRENT
vs. TEMPERATURE
7.00
MAX9705 toc28
10
9
SUPPLY CURRENT (mA)
SYNC = VDD (SSM)
8
7
6
SYNC = GND (FFM)
5
6.75
VDD = 3.3V
NO LOAD
INPUTS AC GROUNDED
6.50
6.25
6.00
SYNC = VDD (SSM)
5.75
5.50
SYNC = GND (FFM))
5.25
NO LOAD
INPUTS AC GROUNDED
4
1000
MAX9705 toc29
0
SUPPLY CURRENT (mA)
-20
AMPLITUDE (dBV)
AMPLITUDE (dBV)
-40
MAX9705 toc27
-20
5.00
2.5
3.5
4.5
-40
5.5
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
TURN-ON/TURN-OFF RESPONSE
85
MAX9705 toc31
MAX9705 toc30
1.00
0.90
SHUTDOWN CURRENT (µA)
0
MAX9705 toc26
0
0.80
3V
SHDN
TA = -40°C
0.70
0.60
TA = +85°C
0V
0.50
TA = +25°C
0.40
MAX9705
OUTPUT
0.30
0.20
250mV/div
NO LOAD
INPUTS AC GROUNDED
SHDN = GND
0.10
0
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
f = 1kHz
RL = 8Ω
10ms/div
_______________________________________________________________________________________
7
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.)
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
MAX9705
Functional Diagram
2.5V TO 5.5V
1µF
5
(B2) SHDN
1
(A1)
10
(B4)
6
(A3)
VDD
PVDD
SYNC
UVLO/POWER
MANAGEMENT
CLICK-AND-POP
SUPPRESSION
OSCILLATOR
PVDD
LOW-EMI
DRIVER
1µF
2
(B1) IN+
1µF
3
(C1) IN-
8
OUT+ (A4)
PGND
CLASS D
MODULATOR
PVDD
OUT- 9
(C4)
LOW-EMI
DRIVER
MAX9705
PGND
PGND
7
(B3)
GND
4
(C2)
( ) UCSP BUMP.
FIGURE SHOWS MAX9705 CONFIGURED FOR SPREAD-SPECTRUM OPERATION.
8
_______________________________________________________________________________________
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
PIN
BUMP
TDFN
UCSP
NAME
FUNCTION
1
A1
VDD
Analog Power Supply
2
B1
IN+
Noninverting Audio Input
Inverting Audio Input
3
C1
IN-
4
C2
GND
Analog Ground
5
B2
SHDN
Active-Low Shutdown Input. Connect to VDD for normal operation.
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
6
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).
Detailed Description
The MAX9705 ultra-low-EMI, filterless, Class D audio
power amplifier features several improvements to switchmode amplifier technology. The MAX9705 features output
driver active emissions limiting circuitry to reduce EMI.
Zero dead time technology maintains state-of-the-art efficiency 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 differential input architecture reduces common-mode noise
pickup with or without the use of input-coupling capacitors. The MAX9705 can also be configured as a singleended 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 operation can continue. The output of the MAX9705 shuts down
if the output current reaches approximately 2A. Each output FET has its own short-circuit protection. This protection 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 turning 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 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.
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 frequency spectrum of the Class D output consists of the fundamental switching frequency and its associated
harmonics (see the Wideband Output Spectrum FixedFrequency Mode graph in the Typical Operating
Characteristics).
_______________________________________________________________________________________
9
MAX9705
Pin Description
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9705 Outputs with an Input Signal Applied
Table 1. Operating Modes
SYNC INPUT
MODE
GND
FFM with fS = 1100kHz
VDD
SSM with fS = 1220kHz ±120kHz
Clocked
FFM with fS = external clock frequency
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 frequency varies randomly by ±120kHz around the center
frequency (1.22MHz). The modulation scheme remains
10
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 randomized, enabling the MAX9705 to be synchronized to
another MAX9705 operating in SSM mode.
______________________________________________________________________________________
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
tSW
tSW
MAX9705
tSW
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 2. MAX9705 Output with an Input Signal Applied (SSM Mode)
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 component 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 filter, 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 differentially, the two outputs cancel each other, resulting
in no net idle-mode voltage across the speaker, minimizing power consumption.
Efficiency
Efficiency of a Class D amplifier is attributed to the
region of operation of the output stage transistors. In a
Class D amplifier, the output transistors act as currentsteering switches and consume negligible additional
power. Any power loss associated with the Class D output stage is mostly due to the 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.
______________________________________________________________________________________
11
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
EFFICIENCY vs. OUTPUT POWER
VIN = 0V
100
MAX9705
90
EFFICIENCY (%)
80
OUT-
70
60
50
CLASS AB
40
30
OUT+
20
VDD = 3.3V
fIN = 1kHz
RL = 8Ω
10
0
0
Figure 3. MAX9705 Outputs with No Input Signal
Click-and-Pop Suppression
The MAX9705 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 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 amplifier, and can decrease efficiency and THD+N performance. 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 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
12
0.2
0.4
0.6
0.8
1.0
OUTPUT POWER (W)
VOUT+ - VOUT- = 0V
Figure 4. MAX9705 Efficiency vs. Class AB Efficiency
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 power conversion of the Class D amplifier. For example, an 8mV DC offset across an 8Ω load results in 1mA
extra current consumption in a Class AB device. In the
Class D case, an 8mV offset into 8Ω equates to an additional power drain of 8µW. Due to the high efficiency of
the Class D amplifier, this represents an additional quiescent-current draw of 8µW/(VDD/100η), which is on the
order of a few microamps.
Input Amplifier
Differential Input
The 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-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 MAX9705 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND and driving the other input (Figure 5).
______________________________________________________________________________________
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
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 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 ACcoupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming zero source
impedance, the -3dB point of the highpass filter is
given by:
f −3dB =
1
2π RIN CIN
Choose CIN so f-3dB is well below the lowest frequency
of interest. Setting f -3dB too high affects the lowfrequency 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 coefficient 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 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 considera-
MAX9705
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.
1µF
SINGLE-ENDED
AUDIO INPUT
IN+
MAX9705
IN1µF
Figure 5. Single-Ended Input
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 PV DD is
assumed. Additional bulk capacitance should be added
as required depending on the application and powersupply 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 unfiltered 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 performance 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.
______________________________________________________________________________________
13
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
VDD
1µF
VDD
IN+
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
PVDD
MAX9705
IN-
OUT+
OUTSYNC
1µF
VDD
IN+
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
IN-
PVDD
MAX9705
OUT+
OUTSYNC
Figure 6. Master-Slave Stereo Configuration
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
VDD = 3.3V
SLAVE DEVICE
fIN = 1kHz
SYNC = GND (FFM)
RL = 8Ω
VDD = 3.3V
VIN = 500mVP-P
fIN = 1kHz
SYNC = GND (FFM)
RL = 8Ω
-10
-20
-30
CROSSTALK (dB)
10
THD+N (%)
CROSSTALK vs. FREQUENCY
0
100
1
0.1
-40
-50
-60
MASTER TO SLAVE
-70
-80
0.01
-90
SLAVE TO MASTER
-100
-110
0.001
0
0.2
0.4
OUTPUT POWER (W)
Figure 7. Master-Slave THD+N
14
0.6
0.8
10
100
1k
10k
FREQUENCY (Hz)
Figure 8. Master-Slave Crosstalk
______________________________________________________________________________________
100k
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
MAX9705
1µF
CW
22kΩ
1µF
IN-
50kΩ
IN-
CW
50kΩ
MAX9705
1µF
IN+
MAX9705
IN+
22kΩ
1µF
Figure 9a. Single-Ended Drive of MAX9705 Plus Volume
Figure 9b. Improved Single-Ended Drive of MAX9705 Plus
Volume
Pin Configurations
Selector Guide
PART
6
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
SYNC
6
12 UCSP
PGND
10 TDFN
MAX9705AEBC+T
OUT+
GAIN (dB)
OUT-
PIN-PACKAGE
PVDD
TOP VIEW
MAX9705AETB+T
10
9
8
7
6
MAX9705BETB+T
MAX9705
4
5
SHDN
IN+
3
GND
2
IN-
1
VDD
+
Ordering Information (continued)
TDFN
PART
TOP VIEW
(BUMP SIDE DOWN)
1
MAX9705
2
3
VDD
SYNC
4
OUT+
A
IN+
SHDN
IN-
GND
PGND
PVDD
MAX9705CETB+T
TEMP RANGE
PINPACKAGE
-40oC to +85oC
10 TDFN
o
o
TOP
MARK
ACZ
MAX9705CEBC+T
-40 C to +85 C
12 UCSP
ACI
MAX9705DETB+T
-40oC to +85oC
10 TDFN
ADA
MAX9705DEBC+T
-40oC to +85oC
12 UCSP
ACJ
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
B
OUT-
C
UCSP
______________________________________________________________________________________
15
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
MAX9705
System Diagram
VDD
1µF
VDD
0.1µF
AUX_IN
OUT
2.2kΩ
OUT
BIAS
VDD
PVDD
IN+
OUT+
MAX9705
IN-
OUT-
SHDN
SYNC
CODEC/
BASEBAND
PROCESSOR
2.2kΩ
MAX4063
0.1µF
IN+
VDD
IN0.1µF
1µF
VDD
SHDN
1µF
INL
OUTL
1µF
MAX9722
INR
µCONTROLLER
OUTR
PVSS
SVSS
C1P
CIN
1µF
1µF
16
______________________________________________________________________________________
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
PROCESS: BiCMOS
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 drawings may show a different suffix character, but the drawing pertains 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
______________________________________________________________________________________
17
MAX9705
Package Information
Chip Information
MAX9705
2.3W, Ultra-Low-EMI, Filterless,
Class D Audio Amplifier
Revision History
REVISION
NUMBER
REVISION
DATE
2
8/08
Removed µMAX package option
3
5/09
Removed SYNC unconnected mode
DESCRIPTION
PAGES
CHANGED
1–7, 9,
10, 15
3, 7, 9, 10, 14
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.
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