General Description
The MAX9703/MAX9704 mono/stereo Class D audio
power amplifiers provide Class AB amplifier performance
with Class D efficiency, conserving board space and
eliminating the need for a bulky heatsink. Using a Class
D architecture, these devices deliver up to 15W while
offering up to 78% efficiency. Proprietary and protected
modulation and switching schemes render the traditional
Class D output filter unnecessary.
The MAX9703/MAX9704 offer two modulation schemes:
a fixed-frequency mode (FFM), and a spread-spectrum
mode (SSM) that reduces EMI-radiated emissions due
to the modulation frequency. The device utilizes a fully
differential architecture, a full bridged output, and compre-
hensive click-and-pop suppression.
The MAX9703/MAX9704 feature high 80dB PSRR, low
0.07% THD+N, and SNR in excess of 95dB. Short-circuit
and thermal-overload protection prevent the devices from
being damaged during a fault condition. The MAX9703 is
available in a 32-pin TQFN (5mm x 5mm x 0.8mm) pack-
age. The MAX9704 is available in a 32-pin TQFN (7mm x
7mm x 0.8mm) package. Both devices are specified over
the extended -40°C to +85°C temperature range.
Applications
Features
●Filterless Class D Amplifier
●Unique Spread-Spectrum Mode Offers 5dB
Emissions Improvement Over Conventional Methods
●Up to 78% Efficient (RL = 8Ω)
●Up to 88% Efficient (RL = 16Ω)
● 15W Continuous Output Power into 8Ω (MAX9703)
● 2x10W Continuous Output Power into 8Ω (MAX9704)
●Low 0.07% THD+N
●High PSRR (80dB at 1kHz)
●10V to 25V Single-Supply Operation
●Differential Inputs Minimize Common-Mode Noise
●Pin-Selectable Gain Reduces Component Count
●Industry-Leading Click-and-Pop Suppression
●Low Quiescent Current (24mA)
● Low-Power Shutdown Mode (0.2μA)
●Short-Circuit and Thermal-Overload Protection
●Available in Thermally Efficient, Space-Saving
Packages
• 32-Pin TQFN (5mm x 5mm x 0.8mm)–MAX9703
• 32-Pin TQFN (7mm x 7mm x 0.8mm)–MAX9704
Pin Configurations appears at end of data sheet.
19-3160; Rev 8; 5/14
●LCD TVs
●LCD Monitors
●Desktop PCs
●LCD Projectors
●Hands-Free Car Phone
Adapters
Note: All devices specified for over -40°C to +85°C operating
temperature range.
*EP = Exposed paddle.
+Denotes lead-free package.
PART PIN-PACKAGE AMP PKG CODE
MAX9703ETJ+ 32 TQFN-EP* Mono T3255-4
MAX9704ETJ+ 32 TQFN-EP* Stereo T3277-2
0.47µF INL+ OUTL+
OUTL-INL-
0.47µF H-BRIDGE
0.47µFINR+ OUTR+
OUTR-INR-
0.47µF H-BRIDGE
0.47µF IN+ OUT+
OUT-
IN-
0.47µF H-BRIDGE
MAX9704
MAX9703
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Amplifiers
Block Diagrams
Ordering Information
(All voltages referenced to PGND.)
VDD to PGND, AGND............................................................30V
OUTR_, OUTL_, C1N.................................-0.3V to (VDD + 0.3V)
C1P............................................(VDD - 0.3V) to (CHOLD + 0.3V)
CHOLD........................................................(VDD - 0.3V) to +40V
All Other Pins to PGND...........................................-0.3V to +12V
Duration of OUTR_/OUTL_
Short Circuit to PGND, VDD................................................10s
Continuous Input Current (VDD, PGND) ...............................1.6A
Continuous Input Current......................................................0.8A
Continuous Input Current (all other pins)..........................±20mA
Continuous Power Dissipation (TA = +70°C)
Single-Layer Board:
MAX9703 32-Pin TQFN (derate 21.3mW/°C
above +70°C)..........................................................1702.1mW
MAX9704 32-Pin TQFN (derate 27mW/°C
above +70°C)..........................................................2162.2mW
Multilayer Board:
MAX9703 32-Pin TQFN (derate 34.5mW/°C
above +70°C)..........................................................2758.6mW
MAX9704 32-Pin TQFN (derate 37mW/°C
above +70°C)..........................................................2963.0mW
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
(VDD = 15V, AGND = PGND = 0V, SHDN ≥ VIH, AV = 16dB, CSS = CIN = 0.47μF, CREG = 0.01μF, C1 = 100nF, C2 = 1μF, FS1 = FS2
= PGND (fS = 660kHz), RL connected between OUTL+ and OUTL- and OUTR+ and OUTR-, 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 Inferred from PSRR test 10 25 V
Quiescent Current IDD RL = OPEN MAX9703 14 22 mA
MAX9704 24 34
Shutdown Current ISHDN 0.2 1.5 µA
Turn-On Time tON
CSS = 470nF 100 ms
CSS = 180nF 50
Amplier Output Resistance in
Shutdown SHDN = PGND 150 330 kΩ
Input Impedance RIN
AV = 13dB 35 58 80
kΩ
AV = 16dB 30 48 65
AV = 19.1dB 23 39 55
AV = 29.6dB 10 15 22
Voltage Gain AV
G1 = L, G2 = L 29.4 29.6 29.8
dB
G1 = L, G2 = H 18.9 19.1 19.3
G1 = H, G2 = L 12.8 13 13.2
G1 = H, G2 = H 15.9 16 16.3
Gain Matching Between channels (MAX9704) 0.5 %
Output Offset Voltage VOS ±6 ±30 mV
Common-Mode Rejection Ratio CMRR fIN = 1kHz, input referred 60 dB
Power-Supply Rejection Ratio
(Note 3) PSRR
VDD = 10V to 25V 54 80
dB
200mVP-P ripple fRIPPLE = 1kHz 80
fRIPPLE = 20kHz 66
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Absolute Maximum Ratings
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 = 15V, AGND = PGND = 0V, SHDN ≥ VIH, AV = 16dB, CSS = CIN = 0.47μF, CREG = 0.01μF, C1 = 100nF, C2 = 1μF, FS1 = FS2
= PGND (fS = 660kHz), RL connected between OUTL+ and OUTL- and OUTR+ and OUTR-, 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 = 8Ω, L = 68μH.
For RL = 4Ω, L = 33μH.
Note 3: PSRR is specified with the amplifier inputs connected to AGND through CIN.
Note 4: The MAX9704 continuous 8Ω and 16Ω power measurements account for thermal limitations of the 32-pin TQFN-EP pack-
age. Continuous 4Ω power measurements account for short-circuit protection of the MAX9703/MAX9704 devices.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Continuous Output Power
(MAX9703) PCONT
THD+N = 10%, VDD
= 16V, f = 1kHz, TA =
+25°C, tCONT = 15min
(Note 4)
RL = 4Ω 10
WRL = 8Ω 15
RL = 16Ω, VDD = 24V 18
Continuous Output Power
(MAX9704) PCONT
THD+N = 10%, VDD
= 16V, f = 1kHz, TA =
+25°C, tCONT = 15min
(Note 4)
RL = 4Ω 2x5
WRL = 8Ω 2x10
RL = 16Ω, VDD = 24V 2x16
Total Harmonic Distortion Plus
Noise THD+N fIN = 1kHz, either FFM or SSM, RL = 8Ω,
POUT = 4W 0.07 %
Signal-to-Noise Ratio SNR RL = 8Ω, POUT =
10W, f = 1kHz
BW = 22Hz to
22kHz
FFM 94
dB
SSM 88
A-weighted FFM 97
SSM 91
Crosstalk Left to right, right to left, 8Ω load, fIN = 10kHz 65 dB
Oscillator Frequency fOSC
FS1 = L, FS2 = L 560 670 800
kHz
FS1 = L, FS2 = H 940
FS1 = H, FS2 = L 470
FS1 = H, FS2 = H (spread-spectrum mode) 670
±7%
Efciency η POUT = 15W, f = 1kHz, RL = 8Ω 78 %
POUT = 10W, f = 1kHz, RL = 16Ω 88
Regulator Output VREG 6 V
DIGITAL INPUTS (SHDN, FS_, G_)
Input Thresholds VIH 2.5 V
VIL 0.8
Input Leakage Current ±1 µA
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Electrical Characteristics (continued)
(33μH with 4Ω, 68μH with 8Ω, part in SSM mode, 136μH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9703/04 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01
10 100k
VDD = 15V
RL = 8Ω
AV = 16dB
POUT = 500mW
POUT = 8W
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9703/04 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01
10 100k
VDD = 20V
RL = 8Ω
AV = 16dB
POUT = 8W
POUT = 500mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9703/04 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01
10 100k
VDD = 20V
RL = 8Ω
AV = 16dB
POUT = 8W
SSM
FFM
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9703/04 toc05
OUTPUT POWER (W)
THD+N (%)
6
4 5
23
1
0.1
1
10
100
0.01
0 1097 8
VDD = 15V
RL = 4Ω
AV = 16dB
f = 10kHz
f = 1kHz
f = 100Hz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9703/04 toc06
OUTPUT POWER (W)
THD+N (%)
12345678910 11 12 13 14
0.1
1
10
0.01
0 15
VDD = 15V
RL = 8Ω
AV = 16dB
f = 100Hz
f = 1kHz
f = 10kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9703/04 toc07
OUTPUT POWER (W)
THD+N (%)
4
26 8 10 12 14 16 18
0.1
1
10
100
0.01
0 20
VDD = 20V
RL = 8Ω
AV = 16dB
f = 100Hz
f = 1kHz
f = 10kHz
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9703/04 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
1
10
0.01
10 100k
VDD = 15V
RL = 4Ω
AV = 16dB
POUT = 4W
POUT = 500mW
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9703/04 toc08
OUTPUT POWER (W)
THD+N (%)
1 2 345 6 7 8 91011 12 13 14 15 16 17 18 19
0.1
1
10
0.01
020
FFM (335kHz)
SSM
VDD = 20V
RL = 8Ω
AV = 16dB
f = 1kHz
EFFICIENCY vs. OUTPUT POWER
MAX9703/04 toc09
OUTPUT POWER (W)
EFFICIENCY (%)
8642 3 5 7 9
1
10
20
30
40
50
60
70
80
90
100
0
0 10
VDD = 12V
AV = 16dB
f = 1kHz
RL = 4Ω
RL = 8Ω
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Typical Operating Characteristics
(33μH with 4Ω, 68μH with 8Ω, part in SSM mode, 136μH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)
EFFICIENCY vs. OUTPUT POWER
MAX9703/04 toc10
OUTPUT POWER (W)
EFFICIENCY (%)
16
12
8
4
2610 14 18
10
20
30
40
50
60
70
80
90
100
0
0 20
VDD = 15V
AV = 16dB
f = 1kHz
RL = 16Ω
RL = 8Ω
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9703/04 toc11
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
0
6
4
2
8
10
12
14
16
18
20
10 1613 19 22 25
RL = 8Ω
RL = 16Ω
AV = 16dB
THD+N = 10%
20
18
16
14
12
10
8
6
4
2
0
1 10 100
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9703/04 toc12
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
THD+N = 1%
THD+N = 10%
VDD = 15V
AV = 16dB
24
22
20
18
16
14
12
10
8
6
4
2
0
1 10 100
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9703/04 toc13
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
VDD = 20V
AV = 16dB THD+N = 10%
THD+N = 1%
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9703/04 toc14
FREQUENCY (Hz)
CMRR (dB)
10k1k100
-70
-60
-50
-40
-30
-20
-10
0
-80
10 100k
VDD = 15V
RL = 8Ω
AV = 16dB
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9703/04 toc15
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-100
-80
-60
-40
-20
0
-120
10 100k
AV = 16dB
RL = 8Ω
200mVP-P INPUT
VDD = 15V
CROSSTALK vs. FREQUENCY
MAX9703/04 toc16
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-80
-100
-60
-40
-20
0
-120
10 100k
LEFT TO RIGHT
RIGHT TO LEFT
AV = 16dB
1% THD+N
VDD = 15V
8Ω LOAD
OUTPUT FREQUENCY SPECTRUM
MAX9703/04 toc17
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dB)
-120
-100
-80
-60
-40
-20
0
20
-140
181612 144 6 8 1020 20
FFM MODE
AV = 16dB
UNWEIGHTED
fIN = 1kHz
POUT = 5W
RL = 8Ω
OUTPUT FREQUENCY SPECTRUM
MAX9703/04 toc18
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dB)
-120
-100
-80
-60
-40
-20
0
20
-140
181612 144 6 8 1020 20
SSM MODE
AV = 16dB
UNWEIGHTED
fIN = 1kHz
POUT = 5W
RL = 8Ω
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Typical Operating Characteristics (continued)
(33μH with 4Ω, 68μH with 8Ω, part in SSM mode, 136μH with 16Ω, measurement BW = 22Hz to 22kHz, unless otherwise noted.)
OUTPUT FREQUENCY SPECTRUM
MAX9703/04 toc19
FREQUENCY (kHz)
OUTPUT MAGNITUDE (dB)
-120
-100
-80
-60
-40
-20
0
20
-140
181612 144 6 8 1020 20
SSM MODE
AV = 16dB
A-WEIGHTED
fIN = 1kHz
POUT = 5W
RL = 8Ω
100k 1M 10M 100M
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
MAX9703/04 toc20
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
0
-120
-100
-80
-60
-40
-20
RBW = 10kHz
VDD = 15V
100k 1M 10M
100M
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
MAX9703/04 toc21
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
0
-120
-100
-80
-60
-40
-20
RBW = 10kHz
VDD = 15V
TURN-ON/TURN-OFF RESPONSE
MAX9703/04 toc22
20ms/div
OUTPUT
1V/div
5V/div
SHDN
f = 1kHz
RL = 8Ω
CSS = 180pF
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9703/04 toc23
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
22191613
10
5
15
20
25
30
35
0
10 25
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX97703/04 toc24
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (µA)
18161412
0.10
0.05
0.15
0.20
0.25
0.30
0.35
0
10 20
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Typical Operating Characteristics (continued)
PIN NAME FUNCTION
MAX9703 MAX9704
1, 2, 23, 24 1, 2, 23, 24 PGND Power Ground
3, 4, 21, 22 3, 4, 21, 22 VDD Power-Supply Input
5 5 C1N Charge-Pump Flying Capacitor Negative Terminal
6 6 C1P Charge-Pump Flying Capacitor Positive Terminal
7 7 CHOLD Charge-Pump Hold Capacitor. Connect a 1µF capacitor from CHOLD to VDD.
8, 17, 20, 25,
26, 31, 32 8 N.C. No Connection. Not internally connected.
9 14 REG 6V Internal Regulator Output. Bypass with a 0.01µF capacitor to AGND.
10 13 AGND Analog Ground
11 — IN- Negative Input
12 — IN+ Positive Input
13 12 SS Soft-Start. Connect a 0.47µF capacitor from SS to PGND to enable soft-start feature.
14 11 SHDN Active-Low Shutdown. Connect SHDN to PGND to disable the device. Connect to a
logic-high for normal operation.
15 17 G1 Gain-Select Input 1
16 18 G2 Gain-Select Input 2
18 19 FS1 Frequency-Select Input 1
19 20 FS2 Frequency-Select Input 2
27, 28 — OUT- Negative Audio Output
29, 30 — OUT+ Positive Audio Output
— 9 INL- Left-Channel Negative Input
— 10 INL+ Left-Channel Positive Input
— 15 INR- Right-Channel Negative Input
— 16 INR+ Right-Channel Positive Input
— 25, 26 OUTR- Right-Channel Negative Audio Output
— 27, 28 OUTR+ Right-Channel Positive Audio Output
— 29, 30 OUTL- Left-Channel Negative Audio Output
— 31, 32 OUTL+ Left-Channel Positive Audio Output
— — EP Exposed Paddle. Connect to PGND.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
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Pin Description
Detailed Description
The MAX9703/MAX9704 filterless, Class D audio power
amplifiers feature several improvements to switchmode
amplifier technology. The MAX9703 is a mono amplifier,
the MAX9704 is a stereo amplifier. These devices offer
Class AB performance with Class D efficiency, while occu-
pying minimal board space. A unique filterless modulation
scheme and spread-spectrum switching mode create a
compact, flexible, lownoise, efficient audio power ampli-
fier. The differential input architecture reduces common-
mode noise pickup, and can be used without input-cou-
pling capacitors. The devices can also be configured as a
single-ended input amplifier.
Comparators monitor the device inputs and compare the
complementary input voltages to the triangle waveform.
The comparators trip when the input magnitude of the
triangle exceeds their corresponding input voltage.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode
The MAX9703/MAX9704 feature three FFM modes with
different switching frequencies (Table 1). 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 (FFM
Mode) graph in the Typical Operating Characteristics).
The MAX9703/ MAX9704 allow the switching frequency
to be changed by ±35%, 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 MAX9703/MAX9704 feature a unique spread-spec-
trum mode that flattens the wideband spectral compo-
nents, improving EMI emissions that may be radiated by
the speaker and cables. This mode is enabled by setting
FS1 = FS2 = H. In SSM mode, the switching frequency
varies randomly by ±7% around the center frequency
(670kHz). The modulation scheme remains the same, but
the period of the triangle waveform changes from cycle to
cycle. Instead of a large amount of spectral energy pres-
ent at multiples of the switching frequency, the energy
is now spread over a bandwidth that increases with fre-
quency. Above a few megahertz, the wideband spectrum
looks like white noise for EMI purposes (see Figure 1).
Efciency
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 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 MAX9704 still exhibits >78% efficiency under the
same conditions (Figure 2).
Table 1. Operating Modes
FS1 FS2 SWITCHING MODE
(kHz)
L L 670
L H 940
H L 470
H H 670 ±7%
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
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Figure 1. MAX9704 EMI Spectrum, 9in PC Board trace, 3in Twisted-Pair Speaker Cable
VDD
CIN L1*
L2*
1000pF
1000pF
L3*
L4*
1000pF
*L1–L4 = 0.05Ω DCR, 70Ω AT 100MHz, 3A FAIR RITE FERRITE BEAD (2512067007Y3).
1000pF
CIN
CIN
CIN
FREQUENCY (MHz)
AMPLITUDE (dBuV/m)
900800100 200 300 500 600400 700
10
15
20
25
30
35
40
5
30 1000
CE LIMIT
MAX9704 OUTPUT
SPECTRUM
MAX9704
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
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Shutdown
The MAX9703/MAX9704 have a shutdown mode that
reduces power consumption and extends battery life.
Driving SHDN low places the device in low-power
(0.2μA) shutdown mode. Connect SHDN to a logic high
for normal operation.
Click-and-Pop Suppression
The MAX9703/MAX9704 feature comprehensive clicka-
nd-pop suppression that eliminates audible transients on
startup and shutdown. While in shutdown, the Hbridge is
pulled to PGND through 330kΩ. 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 Hbridge is subse-
quently enabled. Following startup, a soft-start function
gradually unmutes the input amplifiers. The value of the
soft-start capacitor has an impact on the click/pop levels.
For optimum performance, CSS should be at least 0.18μF
with a voltage rating of at least 7V.
Mute Function
The MAX9703/MA9704 features a clickless/popless mute
mode. When the device is muted, the outputs stop
switching, muting the speaker. Mute only affects the out-
put stage and does not shut down the device. To mute
the MAX9703/MAX9704, drive SS to PGND by using a
MOSFET pulldown (Figure 3). Driving SS to PGND during
the power-up/down or shutdown/turn-on cycle optimizes
click-and-pop suppression.
Applications Information
Filterless Operation
Traditional class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM out-
put. The filters add cost, increase the solution size of the
amplifier, and can decrease efficiency. The traditional
PWM scheme uses large differential output swings (2
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 MAX9703/MAX9704 do not require an output fil-
ter. The devices rely 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 MAX9703/MAX9704 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 > 30μH. Typical 8Ω speakers exhibit series
inductances in the range of 30μH to 100μH. Optimum
efficiency is achieved with speaker inductances > 60μH.
Internal Regulator Output (VREG)
The MAX9703/MAX9704 feature an internal, 6V regula-
tor output (VREG). The MAX9703/MAX9704 REG output
pin simplifies system design and reduces system cost by
providing a logic voltage high for the MAX9703/ MAX9704
logic pins (G_, FS_). VREG is not available as a logic
voltage high in shutdown mode. Do not apply VREG as a
6V potential to surrounding system components. Bypass
REG with a 6.3V, 0.01μF capacitor to AGND.
Figure 2. MAX9704 Efficiency vs. Class AB Efficiency
Figure 3. MAX9703/MAX9704 Mute Circuit
0
30
20
10
40
50
60
70
80
90
100
06810 12 14 16 18
2 4 20
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
VDD = 15V
f = 1kHz
RL = 8Ω
MAX9704
CLASS AB
SS
0.18µF
GPIO
MUTE SIGNAL
MAX9703/
MAX9704
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Gain Selection
The MAX9703/MAX9704 feature an internally set, logic-
selectable gain. The G1 and G2 logic inputs set the gain
of the MAX9703/MAX9704 speaker amplifier (Table 2).
Output Offset
Unlike a Class AB amplifier, the output offset voltage of
Class D amplifiers 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/100 x η), which is in the order
of a few microamps.
Input Amplier
Differential Input
The MAX9703/MAX9704 feature a differential input struc-
ture, making them compatible with many CODECs, and
offering improved noise immunity over a single-ended
input amplifier. In devices such as PCs, noisy digital sig-
nals can be picked up by the amplifier’s input traces. The
signals appear at the amplifiers’ inputs as commonmode
noise. A differential input amplifier amplifies the difference
of the two inputs, any signal common to both inputs is
canceled.
Single-Ended Input
The MAX9703/MAX9704 can be configured as singleen-
ded input amplifiers by capacitively coupling either input
to AGND and driving the other input (Figure 4).
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9703/MAX9704, forms a highpass
filter that removes the DC bias from an incoming signal.
The AC-coupling capacitor allows the amplifier to bias
the signal to an optimum DC level. Assuming zero-source
impedance, the -3dB point of the highpass filter is given by:
-
3dB IN IN
1
f2R C
=π
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 with dielectrics
that have low-voltage coefficients, such as tantalum or
aluminum electrolytic. Capacitors with highvoltage coef-
ficients, such as ceramics, may result in increased distor-
tion at low frequencies.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for optimum
performance. Low-ESR ceramic capacitors minimize
the output resistance of the charge pump. For best per-
formance over the extended temperature range, select
capacitors with an X7R dielectric.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability to
provide sufficient current drive. Increasing the value of C1
improves load regulation and reduces the chargepump
output resistance to an extent. Above 1μF, the onresis-
tance of the switches and the ESR of C1 and C2 dominate.
Hold Capacitor (C2)
The output capacitor value and ESR directly affect the
ripple at CHOLD. Increasing C2 reduces output ripple.
Likewise, decreasing the ESR of C2 reduces both ripple
and output resistance. Lower capacitance values can be
used in systems with low maximum output power levels.
Output Filter
The MAX9703/MAX9704 do not require an output filter
and can pass FCC emissions standards with unshielded
speaker cables. However, output filtering can be used if a
Figure 4. Single-Ended Input
Table 2. Gain Selection
G1 G2 GAIN (dB)
0 0 29.6
0 1 19.1
1 0 13
1 1 16
IN+
IN-
0.47µF
0.47µF
SINGLE-ENDED
AUDIO INPUT
MAX9703/
MAX9704
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design is failing radiated emissions due to board layout or
cable length, or the circuit is near EMIsensitive devices.
Use a ferrite bead filter when radiated frequencies above
10MHz are of concern. Use an LC filter when radiated
frequencies below 10MHz are of concern, or when long
leads connect the amplifier to the speaker. Refer to the
MAX9704 Evaluation Kit schematic for details of this filter.
Sharing Input Sources
In certain systems, a single audio source can be shared
by multiple devices (speaker and headphone ampli-
fiers). When sharing inputs, it is common to mute the
unused device, rather than completely shutting it down,
preventing the unused device inputs from distorting the
input signal. Mute the MAX9703/MAX9704 by driving SS
low through an open-drain output or MOSFET (see the
System Diagram). Driving SS low turns off the Class D
output stage, but does not affect the input bias levels of
the MAX9703/MAX9704. Be aware that during normal
operation, the voltage at SS can be up to 7V, depending
on the MAX9703/MAX9704 supply.
Supply Bypassing/Layout
Proper power-supply bypassing ensures low distortion
operation. For optimum performance, bypass VDD to
PGND with a 0.1μF capacitor as close to each VDD pin
as possible. A low-impedance, high-current power-supply
connection to VDD is assumed. Additional bulk capaci-
tance should be added as required depending on the
application and power-supply characteristics. AGND and
PGND should be star connected to system ground. Refer
to the MAX9704 Evaluation Kit for layout guidance.
Class D Amplier Thermal
Considerations
Class D amplifiers provide much better efficiency and ther-
mal performance than a comparable Class AB amplifier.
However, the system’s thermal performance must be consid-
ered with realistic expectations and include consideration of
many parameters. This section examines Class D amplifiers
using general examples to illustrate good design practices.
Continuous Sine Wave vs. Music
When a Class D amplifier is evaluated in the lab, often
a continuous sine wave is used as the signal source.
While this is convenient for measurement purposes, it
represents a worst-case scenario for thermal loading on
the amplifier. It is not uncommon for a Class D amplifier
to enter thermal shutdown if driven near maximum output
power with a continuous sine wave.
Audio content, both music and voice, has a much lower
RMS value relative to its peak output power. Figure
5 shows a sine wave and an audio signal in the time
domain. Both are measured for RMS value by the oscil-
loscope. Although the audio signal has a slightly higher
peak value than the sine wave, its RMS value is almost
half that of the sine wave. Therefore, while an audio sig-
nal may reach similar peaks as a continuous sine wave,
the actual thermal impact on the Class D amplifier is
highly reduced. If the thermal performance of a system
is being evaluated, it is important to use actual audio
signals instead of sine waves for testing. If sine waves
must be used, the thermal performance will be less than
the system’s actual capability.
PC Board Thermal Considerations
The exposed pad is the primary route of keeping heat
away from the IC. With a bottom-side exposed pad, the
PC board and its copper becomes the primary heatsink
for the Class D amplifier. Solder the exposed pad to a
large copper polygon. Add as much copper as possible
from this polygon to any adjacent pin on the Class D
amplifier as well as to any adjacent components, pro-
vided these connections are at the same potential. These
copper paths must be as wide as possible. Each of these
paths contributes to the overall thermal capabilities of
the system.
The copper polygon to which the exposed pad is attached
should have multiple vias to the opposite side of the PC
board, where they connect to another copper polygon.
Make this polygon as large as possible within the sys-
tem’s constraints for signal routing.
Figure 5. RMS Comparison of Sine Wave vs. Audio Signal
20ms/div
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Additional improvements are possible if all the traces from
the device are made as wide as possible. Although the IC
pins are not the primary thermal path of the package, they
do provide a small amount. The total improvement would
not exceed about 10%, but it could make the difference
between acceptable performance and thermal problems.
Auxiliary Heatsinking
If operating in higher ambient temperatures, it is possible
to improve the thermal performance of a PC board with
the addition of an external heatsink. The thermal resis-
tance to this heatsink must be kept as low as possible to
maximize its performance. With a bottom-side exposed
pad, the lowest resistance thermal path is on the bottom
of the PC board. The topside of the IC is not a significant
thermal path for the device, and therefore is not a costef-
fective location for a heatsink.
Thermal Calculations
The die temperature of a Class D amplifier can be esti-
mated with some basic calculations. For example, the die
temperature is calculated for the below conditions:
● TA = +40°C
● POUT = 2x8W = 16W
● RL = 16Ω
● Efficiency (η) = 87%
● θJA = 27°C/W
First, the Class D amplifier’s power dissipation must be
calculated.
OUT
DISS OUT
P 16W
P P 16W 2.4W
0.87
= − = −=
η
Then the power dissipation is used to calculate the die
temperature, TC, as follows:
TC = TA + PDISS x θJA
= 40°C + 2.4W x 27°C/W
= 104.8°C
Decreasing the ambient temperature or reducing θJA
will improve the die temperature of the MAX9704. θJA
can be reduced by increasing the copper size/weight of
the ground plane connected to the exposed paddle of
the MAX9704 TQFN package. Additionally, θJA can be
reduced by attaching a heatsink, adding a fan, or mount-
ing a vertical PC board.
Load Impedance
The on-resistance of the MOSFET output stage in Class
D amplifiers affects both the efficiency and the peak-
current capability. Reducing the peak current into the load
reduces the I2R losses in the MOSFETs, thereby increas-
ing efficiency. To keep the peak currents lower, choose
the highest impedance speaker which can still deliver the
desired output power within the voltage swing limits of the
Class D amplifier and its supply voltage.
Although most loudspeakers are either 4Ω or 8Ω, there
are other impedances available which can provide a more
thermally efficient solution.
Another consideration is the load impedance across
the audio frequency band. A loudspeaker is a complex
electromechanical system with a variety of resonances.
In other words, an 8Ω speaker is usually only 8Ω imped-
ance within a very narrow range, and often extends well
below 8Ω, reducing the thermal efficiency below what is
expected. This lower-than-expected impedance can be
further reduced when a crossover network is used in a
multi-driver audio system.
Optimize MAX9703/MAX9704 Efciency with
Load Impedance and Supply Voltage
To optimize the efficiency of the MAX9703/MAX9704,
load the output stage with 12Ω to 16Ω speakers. The
MAX9703/MAX9704 exhibits highest efficiency perfor-
mance when driving higher load impedance (see the
Typical Operating Characteristics). If a 12Ω to 16Ω load is
not available, select a lower supply voltage when driving
6Ω to 10Ω loads.
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0.47µF
LOGIC INPUTS SHOWN FOR AV = 16dB (SSM).
VIN = LOGIC HIGH > 2.5V.
†CHOOSE CAPACITOR VOLTAGE RATING VDD.
*SYSTEM-LEVEL REQUIREMENT.
IN+
11
12
18
14
15
16
13
10 AGND
9
6
5
19
IN-
FS1
VREG
VREG
VREG
VREG
FS2
G1
G2
SS
REG
VREG
0.47µF MODULATOR
OSCILLATOR
CHARGE PUMP
C1P C1
0.1µF
25V†
C1N
0.18µF
10V
GAIN
CONTROL
SHUTDOWN
CONTROL
0.01µF
10V
SHDN
H-BRIDGE
OUT+
OUT+
OUT-
OUT-
30
29
28
27
PGND VDD VDD PGND
1 3 4 21 22 23 242
10V TO 25V
100µF*
25V†
0.1µF
25V†
0.1µF
25V†
C2
1µF
25V†
CHOLD
VDD
7
MAX9703
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Functional Diagrams
0.47µF
LOGIC INPUTS SHOWN FOR AV = 16dB (SSM).
VIN = LOGIC HIGH > 2.5V.
†CHOOSE CAPACITOR VOLTAGE RATING VDD.
*SYSTEM-LEVEL REQUIREMENT.
INL+10
9
19
11
17
18
12
13 AGND
14
6
5
20
INL-
FS1
VREG
VREG
VREG
VREG
FS2
G1
G2
SS
REG
0.47µF MODULATOR
OSCILLATOR
CHARGE PUMP
C1P
C1
0.1µF
25V†
C1N
0.18µF
10V
GAIN
CONTROL
SHUTDOWN
CONTROL
0.01µF
10V
SHDN
H-BRIDGE
OUTL+
OUTL+
OUTL-
OUTL-
32
31
30
29
PGND VDD VDD PGND
1 3 4 21 22 23 242
10V TO 25V
100µF*
25V†
0.1µF
25V†
0.1µF
25V†
C2
1µF
25V†
CHOLD
VDD
7
0.47µF INR+
15
16
INR-
0.47µF MODULATOR H-BRIDGE
OUTR+
OUTR+
OUTR-
OUTR-
28
27
26
25
VREG
MAX9704
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Functional Diagrams (continued)
0.47µF
VDD
INL-
VDD
OUTL-
SHDN
OUTL+INL+
CODEC
OUTL-
OUTL+
OUTR+
OUTR-
INR+ OUTR+
OUTR-
0.18µF
5V
VDD
OUTL
OUTR
PVSS
SVSS
INL+
INL-
INR+
INR-
C1P
1µF
1µF
CIN
100kΩ
INR-
0.47µF
0.47µF
0.47µF
1µF
SS
SHDN
LOGIC INPUTS SHOWN FOR AV = 16dB (SSM).
*BULK CAPACITANCE, IF NEEDED.
1µF
30kΩ30kΩ
15kΩ
15kΩ
1µF
1µF
1µF
100µF*
MAX9704
MAX9722B
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System Diagram
PGND
PGND
VDD
VDD
N.C.
FS2
FS1
N.C.
PGND
PGND
VDD
VDD
C1N
CHOLD
N.C.
9
10
11
12
13
14
15
REG.
AGND
IN-
IN+
SS
SHDN
G1
32
31
30
29
28
27
26
N.C.
N.C.
OUT+
OUT+
OUT-
OUT-
N.C.
25
12 3 4 5 6 7 8
24 23 22 21 20 19 18 17
N.C. 16 G2
TOP VIEW
TQFN (5mm x 5mm)
C1P
TQFN (7mm x 7mm)
PGND
PGND
VDD
VDD
FS2
FS1
G2
G1
PGND
PGND
VDD
VDD
C1N
CHOLD
N.C.
9
10
11
12
13
14
15
INL-
INL+
SHDN
SS
AGND
REG.
INR-
32
31
30
29
28
27
26
OUTL+
OUTL+
OUTL-
OUTL-
OUTR+
OUTR+
OUTR-
25
12 3 4 5 6 7 8
24 23 22 21 20 19 18 17
OUTR- 16 INR+
C1P
MAX9703 MAX9704
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
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Pin Congurations
Chip Information
MAX9703 TRANSISTOR COUNT: 3093
MAX9704 TRANSISTOR COUNT: 4630
PROCESS: BiCMOS
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Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
32 TQFN-EP (Mono) T3255-4 21-0144 90-0012
32 TQFN-EP (Stereo) T3277-2 21-0140 90-0125
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Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
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Package Information (continued)
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing
pertains to the package regardless of RoHS status.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
8 5/14 Removed automotive reference in Applications section and corrected
package code 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
MAX9703/MAX9704 10W Stereo/15W Mono, Filterless,
Spread-Spectrum, Class D Ampliers
© 2014 Maxim Integrated Products, Inc.
│
24
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
