General Description
The MAX9759 mono Class D, audio power amplifier
provides Class AB amplifier audio performance with the
benefits of Class D efficiency, eliminating the need for a
heatsink and extending battery life. The MAX9759 delivers up to 3.2W of continuous power into a 4Ω load while
offering greater than 90% efficiency. Maxim’s next-generation, low-EMI modulation scheme allows the amplifier to operate without an external LC filter while still
meeting FCC EMI-radiated emission levels.
The MAX9759 offers two modulation schemes: a fixedfrequency modulation (FFM) mode and a spread-spectrum modulation (SSM) mode. The SSM mode flattens
the wideband spectral components, reducing EMI-radiated emissions due to the modulation frequency.
Furthermore, the MAX9759 oscillator can be synchronized to an external clock through the SYNC input,
allowing the switching frequency to range from
1000kHz to 1600kHz. The SYNC input and SYNC_OUT
output of the MAX9759 allow multiple Maxim Class D
amplifiers to be cascaded and frequency locked, minimizing interference due to clock intermodulation. The
MAX9759 utilizes fully differential input amplifiers, a fullbridged output, comprehensive click-and-pop suppression, and features four selectable gain settings (6dB,
12dB, 18dB, 24dB).
The MAX9759 features high 81dB PSRR, low 0.02%
THD+N, and SNR in excess of 90dB. Short-circuit and
thermal-overload protection prevents damage to the
device during a fault condition. The MAX9759 operates
from a single 5V supply, consumes 8.4mA of supply
current, and is available in a 16-pin thin QFN package
(4mm x 4mm x 0.8mm). The MAX9759 is fully specified
over the extended -40°C to +85°C temperature range.
Applications
Cell Phones/PDAs
Notebook PCs
Portable DVD Players
Flat-Panel PC Monitors
LCD TVs
LCD Projectors
Features
♦ 3.2W into 4Ω Load (THD+N = 10%)
♦ Filterless Amplifier Passes FCC Radiated
Emissions Standards with 7.6cm of Cable
♦ 92% Efficiency
♦ High PSRR (81dB at 1kHz)
♦ Low 0.02% THD+N
♦ External Clock Synchronization for Multiple,
Cascaded Maxim Class D Amplifiers
♦ 3.0V to 5.5V Single-Supply Operation
♦ Pin-Selectable Gain (6dB, 12dB, 18dB, 24dB)
♦ Integrated Click-and-Pop Suppression
♦ Low Quiescent Current (8.4mA)
♦ Low-Power Shutdown Mode (10µA)
♦ Mute Function
♦ Short-Circuit and Thermal-Overload Protection
♦ Available in Thermally Efficient Package
16-Pin TQFN (4mm x 4mm x 0.8mm)
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
________________________________________________________________ Maxim Integrated Products 1
MAX9759
DIFFERENTIAL
AUDIO INPUT
SYNC
INPUT
SYNC
OUTPUT
V
DD
OSCILLATOR
MODULATOR
AND H-BRIDGE
MONO SPEAKER
OUTPUT
GAIN
CONTROL
MUTE
CONTROL
SHDN
CONTROL
G1
G2
SHDN
MUTE
Simplified Block Diagram
Ordering Information
19-3691; Rev 1; 10/05
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART
TEMP RANGE
PIN-
PKG
CODE
MAX9759ETE+
T1644-4
Pin Configurations appear at end of data sheet.
+Denotes lead-free package.
*EP = Exposed paddle.
PACKAGE
-40°C to +85°C 16 TQFN-EP*
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
2 _______________________________________________________________________________________
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.
VDDto GND..............................................................................6V
PV
DD
to PGND .........................................................................6V
GND to PGND .......................................................-0.3V to +0.3V
All Other Pins to GND.................................-0.3V to (V
DD
+ 0.3V)
Continuous Current Into/Out of PV
DD
/PGND/OUT+/OUT-....1.7A
Duration of OUT+ or OUT- Short Circuit to
V
DD
/GND/PVDD/PGND............................................Continuous
Duration of Short Circuit Between OUT+ and OUT- ..Continuous
Continuous Power Dissipation (T
A
= +70°C)
16-Pin TQFN (derate 16.9mW/°C above +70°C) .....1349.1mW
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
ESD Protection (+IBM).........................................................±2kV
ELECTRICAL CHARACTERISTICS (VDD= 5.0V)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = 0V (FFM). Gain = 12dB (G1 = 0, G2 = 1). Speaker load resistor
(R
L
) connected between OUT+ and OUT-, unless otherwise noted, RL= ∞, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical val-
ues are at T
A
= +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range V
DD
Inferred from PSRR test 3.0 5.5 V
Quiescent Current I
DD
No load 8.4 12 mA
Mute Current I
MUTE
V
MUTE
= 0V 5.5 8 mA
Shutdown Current
(
)
V
SHDN
= 0V 0.1 10 µA
Shutdown to Full Operation t
SON
40 ms
Mute to Full Operation t
MUTE
40 ms
Common-Mode Rejection Ratio CMRR f = 1kHz, input referred, VIN = 200mV
P-P
67 dB
Input DC Bias Voltage V
CM
1.3 1.5 1.7 V
Gain = +24dB 14 20 26
Gain = +18dB 25 36 47
Gain = +12dB 40 60 80
Input Resistance R
IN
Gain = +6dB 60 90 120
kΩ
G1 = 0, G2 = 0
G1 = 1, G2 = 0
G1 = 0, G2 = 1
Voltage Gain A
V
G1 = 1, G2 = 1 +4 +6 +8
dB
Output Offset Voltage V
OS
TA = +25°C
±50 mV
VDD = 4.5V to 5.5V 62 90
f
RIPPLE
= 217Hz 79
f
RIPPLE
= 1kHz 81
Power-Supply Rejection Ratio
(Note 3)
PSRR
200mV
P-P
ripple
f
RIPPLE
= 20kHz 70
dB
I
SHDN
DD
+22 +24 +26
+16 +18 +20
+10 +12 +14
±10
MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (VDD= 5.0V) (continued)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = 0V (FFM). Gain = 12dB (G1 = 0, G2 = 1). Speaker load resistor
(R
L
) connected between OUT+ and OUT-, unless otherwise noted, RL= ∞, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical val-
ues are at T
A
= +25°C.) (Notes 1, 2)
PARAMETER
CONDITIONS
UNITS
RL = 3Ω 3.4
RL = 4Ω 2.6THD+N = 1%
R
L
= 8Ω 1.4
RL = 3Ω 4.3
RL = 4Ω 3.2
Output Power P
OUT
THD+N = 10%
R
L
= 8Ω 1.8
W
RL = 3Ω
RL = 4Ω
Total Harmonic Distortion Plus
Noise
fIN = 1kHz, either
FFM or SSM,
P
OUT
= 1W
R
L
= 8Ω
%
FFM 93
BW = 22Hz to
22kHz
SSM 89
FFM 96
Signal-to-Noise Ratio SNR
P
OUT
= 1W,
R
L
= 8Ω
A-weighted
SSM 92
dB
SYNC = GND (FFM mode)
SYNC = FLOAT (FFM mode)
Oscillator Frequency f
OSC
SYNC = VDD (SSM mode)
1200
kHz
SYNC Frequency Lock Range TTL-compatible clock input
kHz
Into shutdown -50
Click-and-Pop Level K
CP
Peak voltage,
A-weighted, 32 samples
-57
dBV
Efficiency η
P
OUT
= 1W, fIN = 1kHz, RL = 8Ω in series
with 68µH
92 %
DIGITAL INPUTS (SHDN, MUTE, G1, G2, SYNC)
SYNC, G1, G2 Input Voltage High
V
INH
VDD x 0.9 V
SYNC, G1, G2 Input Voltage Low
V
INL
V
SHDN, MUTE Voltage High V
INH
2V
SHDN, MUTE Voltage Low V
INL
0.8 V
SYNC Input Resistance
kΩ
SYNC Input Current ±35 µA
SHDN, MUTE, G1, G2 Input
Current
±1µA
SYNC Capacitance 10 pF
DIGITAL OUTPUTS (SYNC_OUT)
Output Voltage High V
OH
IOH = 3mA 2.4 V
Output Voltage Low V
OL
IOL = 3mA 0.4 V
SYNC_OUT Capacitive Drive TTL-compatible clock output
pF
SYMBOL
THD+N
per second (Notes 3, 4)
Out of shutdown
MIN TYP MAX
0.08
0.05
0.02
1000 1100 1200
1102 1500 1837
±70
1000 1600
200
100
VDD x 0.1
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (VDD= 3.3V)
(VDD= PVDD= SHDN = MUTE = 3.3V, GND = PGND = 0V, SYNC = GND (FFM). Gain = 12dB (G1 = 0, G2 = 1). Speaker load resistor (R
L
) connected between OUT+ and OUT-, unless otherwise noted. RL= ∞, TA= T
MIN
to T
MAX
, unless otherwise noted. Typical
values are at T
A
= +25°C.) (Notes 1, 2)
PARAMETER
CONDITIONS
UNITS
Quiescent Current I
DD
6mA
Mute Current I
MUTE
V
MUTE
= 0V 5 A
Shutdown Current I
SHDN
V
SHDN
= 0V 0.1 µA
Common-Mode Rejection Ratio CMRR f = 1kHz, input referred 67 dB
VDD = 3.0V to 5.5V 50 72 dB
f
RIPPLE
= 217Hz 79
f
RIPPLE
= 1kHz 81
Power-Supply Rejection Ratio PSRR
200mV
P-P
ripple
f
RIPPLE
= 20kHz 70
dB
RL = 3Ω 1.5
RL = 4Ω 1.1
THD+N = 1%
R
L
= 8Ω
RL = 3Ω 1.8
RL = 4Ω 1.3
Output Power P
OUT
THD+N = 10%
R
L
= 8Ω
W
RL = 3Ω
RL = 4Ω
Total Harmonic Distortion Plus
Noise
f = 1kHz, either
FFM or SSM,
P
OUT
= 500mW
R
L
= 8Ω
%
FFM 93
BW = 22Hz
to 22kHz
SSM 89
FFM 96
Signal-to-Noise Ratio SNR
P
OUT
= 500mW,
R
L
= 8Ω
SSM 92
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 R
L
= 4Ω, L = 33µH.
For R
L
= 8Ω, L = 68µH.
Note 3: Inputs AC-coupled to GND.
Note 4: Testing performed with 8Ω resistive load in series with a 68µH inductive load across BTL outputs. Mode transitions are con-
trolled by the SHDN pin.
SYMBOL
MIN TYP MAX
0.65
0.78
0.06
THD+N
0.04
0.02
A-weighted
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
_______________________________________________________________________________________ 5
Typical Operating Characteristics
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = VDD(SSM), unless otherwise noted. Gain = 12dB (G1 = 0, G2 = 1).
THD+N measurement bandwidth: 22Hz to 22kHz. Typical values are at T
A
= +25°C.) (See Typical Operating Circuit)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 5V
R
L
= 3Ω
P
OUT
= 1W
P
OUT
= 2.6W
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 3.3V
R
L
= 3
Ω
P
OUT
= 500mW
P
OUT
= 1.3W
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 5V
R
L
= 4
Ω
P
OUT
= 1W
P
OUT
= 2.2W
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 3.3V
R
L
= 4
Ω
P
OUT
= 500mW
P
OUT
= 700mW
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc05
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 5V
R
L
= 8
Ω
P
OUT
= 600mW
P
OUT
= 1.2W
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc06
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.001
0.1
1
10
10 100k
VDD = 3.3V
R
L
= 8
Ω
P
OUT
= 300mW
P
OUT
= 500mW
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9759 toc07
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
10
0.001
10 100k
VDD = 5V
R
L
= 8
Ω
P
OUT
= 1.2W
SSM
FFM
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc08
OUTPUT POWER (W)
THD+N (%)
4321
0.01
0.1
1
10
100
0.001
0
VDD = 5V
R
L
= 3
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc09
OUTPUT POWER (W)
THD+N (%)
1.51.00.5
0.01
0.1
1
10
100
0.001
02.0
VDD = 3.3V
R
L
= 3
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
6 _______________________________________________________________________________________
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc12
OUTPUT POWER (W)
THD+N (%)
1.51.00.5
0.01
0.1
1
10
100
0.001
02.0
VDD = 5V
R
L
= 8
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc13
OUTPUT POWER (W)
THD+N (%)
0.60.40.2
0.01
0.1
1
10
100
0.001
0 0.8
VDD = 3.3V
R
L
= 8
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc14
OUTPUT POWER (W)
THD+N (%)
1.51.00.5
0.01
0.1
1
10
100
0.001
02.0
VDD = 5V
f
IN
= 1kHz
R
L
= 8
Ω
f = 1180kHz, FFM
f = 1400kHz, FFM
EFFICIENCY vs. OUTPUT POWER
MAX9759 toc15
OUTPUT POWER (W)
EFFICIENCY (%)
4321
10
20
30
40
50
60
70
80
90
100
0
05
RL = 8
Ω
RL = 4
Ω
RL = 3
Ω
VDD = 5V
f
IN
= 1kHz
EFFICIENCY vs. OUTPUT POWER
MAX9759 toc16
OUTPUT POWER (W)
EFFICIENCY (%)
1.51.00.5
10
20
30
40
50
60
70
80
90
100
0
02.0
RL = 8
Ω
RL = 4
Ω
RL = 3
Ω
VDD = 3.3V
f
IN
= 1kHz
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9759 toc17
SUPPLY VOLTAGE (V)
EFFICIENCY (%)
5.55.0
4.5
4.03.5
40
50
60
70
80
90
100
30
3.0
RL = 8
Ω
RL = 4
Ω
fIN = 1kHz
THD+N = 1%
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9759 toc18
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.5
5.04.54.0
3.5
1
2
3
4
5
6
0
3.0
RL = 3
Ω
f
IN
= 1kHz
THD+N = 1%
THD+N = 10%
Typical Operating Characteristics (continued)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = VDD(SSM), unless otherwise noted. Gain = 12dB (G1 = 0, G2 = 1).
THD+N measurement bandwidth: 22Hz to 22kHz. Typical values are at T
A
= +25°C.) (See Typical Operating Circuit)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc10
OUTPUT POWER (W)
THD+N (%)
3
2
1
0.01
0.1
1
10
100
0.001
0
VDD = 5V
R
L
= 4
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9759 toc11
OUTPUT POWER (W)
THD+N (%)
1.00.5
0.01
0.1
1
10
100
0.001
0 1.5
VDD = 3.3V
R
L
= 4
Ω
fIN = 200Hz, 1kHz
fIN = 10kHz
MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
_______________________________________________________________________________________ 7
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
MAX9759 toc24
COMMON-MODE VOLTAGE (V)
THD+N (%)
321
0.01
0.1
1
10
100
0.001
04
VDD = 5V
R
L
= 8
Ω
f
IN
= 1kHz
P
OUT
= 300mW
DIFF INPUT
VDD = 5V
R
L
= 8
Ω
f
IN
= 1kHz
P
OUT
= 300mW
DIFF INPUT
VDD = 3.3V
R
L
= 8
Ω
f
IN
= 1kHz
P
OUT
= 300mW
DIFF INPUT
Typical Operating Characteristics (continued)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = VDD(SSM), unless otherwise noted. Gain = 12dB (G1 = 0, G2 = 1).
THD+N measurement bandwidth: 22Hz to 22kHz. Typical values are at T
A
= +25°C.) (See Typical Operating Circuit)
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9759 toc19
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.5
5.0
3.5 4.0
4.5
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
3.0
RL = 4
Ω
f
IN
= 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9759 toc20
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
5.55.0
4.54.03.5
0.5
1.0
1.5
2.0
2.5
0
3.0
RL = 8
Ω
f
IN
= 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9759 toc21
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
10
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0
1100
VDD = 5V
f
IN
= 1kHz
10% THD+N
1% THD+N
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9759 toc22
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
10
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0
1100
VDD = 3.3V
f
IN
= 1kHz
10% THD+N
1% THD+N
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. COMMON-MODE VOLTAGE
MAX9759 toc23
COMMON-MODE VOLTAGE (V)
THD+N (%)
321
0.01
0.1
1
10
100
0.001
04
VDD = 5V
R
L
= 8
Ω
f
IN
= 1kHz
P
OUT
= 300mW
DIFF INPUT
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
8 _______________________________________________________________________________________
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9759 toc25
FREQUENCY (Hz)
CMRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
INPUT REFERRED
V
IN
= 200mV
P-P
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9759 toc26
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-100
10 100k
OUTPUT REFERRED
INPUTS AC GROUNDED
Typical Operating Characteristics (continued)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = VDD(SSM), unless otherwise noted. Gain = 12dB (G1 = 0, G2 = 1).
THD+N measurement bandwidth: 22Hz to 22kHz. Typical values are at T
A
= +25°C.) (See Typical Operating Circuit)
MUTE RESPONSE
MAX9759 toc32
20ms/div
5V
0V
500mV/div
MAX9759
OUTPUT
MUTE
f = 1kHz
R
L
= 8Ω
SHUTDOWN RESPONSE
MAX9759 toc31
20ms/div
5V
0V
500mV/div
MAX9759
OUTPUT
SHDN
f = 1kHz
R
L
= 8Ω
OUTPUT FREQUENCY SPECTRUM
MAX9759 toc28
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-140
020k
SSM MODE
V
OUT
= -60dBV
f
IN
= 1kHz
R
L
= 8
Ω
UNWEIGHTED
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
MAX9759 toc29
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
100M10M
-50
-40
-30
-20
-10
0
10
20
30
40
-60
1M 1000M
RBW = 10kHz
OUTPUT FREQUENCY SPECTRUM
MAX9759 toc27
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-140
020k
FFM MODE
V
OUT
= -60dBV
f
IN
= 1kHz
R
L
= 8
Ω
UNWEIGHTED
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
MAX9759 toc30
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
100M10M
-50
-40
-30
-20
-10
0
10
20
30
40
-60
1M 1000M
RBW = 10kHz
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
_______________________________________________________________________________________ 9
MAX9759
2
16
3
15
7
6, 14 4
1µF
PGND
OUT+
OUT-
PV
DD
PV
DD
GND
IN+
V
DD
V
DD
18
IN-
SYNC
UVLO/POWER
MANAGEMENT
CLASS D
MODULATOR
PV
DD
9, 12
11
10
CLICK-AND-POP
SUPPRESSION
OSCILLATOR
10µF*
1µF
1µF
MUTE
5
SHDN
CONTROL
V
DD
GND
R
IN
R
IN
G1
G2
BIAS
NOTE: TYPICAL OPERATING CIRCUIT DEPICTS MAX9759 IN FFM MODE WITH fS = 1400kHz and +18dB OF GAIN.
*BULK CAPACITANCE, IF NEEDED.
SYNC_OUT
13
R
F
R
F
Typical Operating Circuit/Functional Diagram
Typical Operating Characteristics (continued)
(VDD= PVDD= SHDN = MUTE = 5V, GND = PGND = 0V, SYNC = VDD(SSM), unless otherwise noted. Gain = 12dB (G1 = 0, G2 = 1).
THD+N measurement bandwidth: 22Hz to 22kHz. Typical values are at T
A
= +25°C.) (See Typical Operating Circuit)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9759 toc33
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.5
5.04.54.03.5
5.0
5.5
6.0
6.5
7.0
7.5
8.0
8.5
9.0
4.5
3.0
FFM
TA = +85°C
TA = -40°C
TA = +25°C
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9759 toc34
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
5.35.14.94.7
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0
4.5 5.5
TA = +85°C
TA = +25°C
TA = -40°C
FFM
PACKAGE TEMPERATURE
vs. TIME
MAX9759 toc35
TIME (s)
PACKAGE TEMPERATURE (°C)
25020015010050
10
20
30
40
50
60
0
0300
RL = 8Ω AT 10% THD+N
RL = 4Ω AT 10% THD+N
RL = 3Ω AT 10% THD+N
MAX9759EVKIT
FREE AIR
T
A
= +25°C
f
IN
= 1kHz SINE WAVE
Detailed Description
Operating Modes
The MAX9759 filterless, Class D audio power amplifier
features several improvements to switch-mode amplifier
technology. The MAX9759 offers Class AB performance
with Class D efficiency, while occupying minimal board
space. A unique modulation scheme, synchronizable
switching frequency, and SSM mode create a compact,
flexible, low-noise, efficient audio power amplifier. The
differential input architecture reduces common-mode
noise pickup, and can be used without input-coupling
capacitors. The device can also be configured as a single-ended input amplifier.
Comparators monitor the MAX9759 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, gener-
ating a minimum-width pulse t
ON(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 t
ON(MIN)
.
This causes the net voltage across the speaker (V
OUT+
- V
OUT-
) to change.
Fixed-Frequency Modulation (FFM) Mode
The MAX9759 features two FFM modes. The FFM
modes are selected by setting SYNC = GND for a
1.1MHz switching frequency, and SYNC = FLOAT for a
1.5MHz 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 (FFM
Mode) graph in the Typical Operating Characteristics).
The MAX9759 allows the switching frequency to be
changed, 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.
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1VDDAnalog Power Supply. Bypass to GND with a 1µF ceramic capacitor.
2 IN+ Noninverting Audio Input
3 IN- Inverting Audio Input
4 GND Analog Ground
5 SHDN
Active-Low Shutdown Input. Drive SHDN low to shut down the MAX9759. Connect to V
DD
for normal
operation.
6, 14 PGND Power Ground
7 SYNC
Frequency Select and External Clock Input:
SYNC = GND: Fixed-frequency mode with f
S
= 1100kHz.
SYNC = FLOAT: Fixed-frequency mode with f
S
= 1500kHz.
SYNC = V
DD
: Spread-spectrum mode with fS = 1200kHz ±70kHz.
SYNC = Clocked: Fixed-frequency mode with f
S
= external clock frequency.
8 MUTE
Active-Low Mute Function. Drive MUTE low to disable the H-bridge outputs. Connect to V
DD
for
normal operation.
9, 12 PV
DD
H-Bridge Power Supply. Bypass to PGND with a 10µF ceramic capacitor.
10 OUT- Negative Speaker Output
11 OUT+ Positive Speaker Output
13
Internal Clock Output. Connect SYNC_OUT to the clock input of cascaded Maxim Class D
amplifiers. Float SYNC_OUT if unused.
15 G2 Gain Control 2 (See Table 2)
16 G1 Gain Control 1 (See Table 2)
EP EP
Exposed Paddle. Can be left floating or tied to GND. For optimum thermal performance, connect EP
to GND.
SYNC_OUT
MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 11
Spread-Spectrum Modulation (SSM) Mode
The MAX9759 features a unique spread-spectrum mode
that reduces peak component energy in the wideband
spectrum, improving EMI emissions that may be radiated by the speaker and cables by 5dB. Proprietary tech-
niques 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 = V
DD
. In SSM
mode, the switching frequency varies by ±70kHz around
the center frequency (1.2MHz). 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 (Figure 3).
OUT+
OUT-
V
IN-
V
IN+
V
OUT+
- V
OUT-
t
ON(MIN)
t
SW
Figure 1. MAX9759 Outputs with an Input Signal Applied
SYNC INPUT MODE
GND FFM with fS = 1100kHz
FLOAT FFM with fS = 1500kHz
V
DD
SSM with fS = 1200kHz ±70kHz
Clocked FFM with fS = external clock frequency
Table 1. Operating Modes
External Synchronization
The SYNC function allows the MAX9759 to allocate
spectral components of the switching harmonics to
insensitive frequency bands and facilitates synchronization to a system clock (allowing for a fully synchronous
system). Applying an external TTL clock of 1000kHz to
1600kHz to SYNC synchronizes the switching frequency
of the MAX9759. The period of the SYNC clock can be
randomized, enabling the MAX9759 to be synchronized
to another MAX9759 operating in SSM mode.
Cascading Amplifiers
The SYNC_OUT function of the MAX9759 allows for
multiple Maxim Class D amplifiers to be cascaded and
frequency locked. Synchronizing multiple Class D
amplifiers ensures that no beat frequencies within the
audio spectrum occur on the power-supply rails. Any
intermodulation distortion due to the interference of
several modulation frequencies is minimized as a
result. Leave the SYNC_OUT pin of the MAX9759 floating if the SYNC_OUT function is not applicable.
Filterless Modulation/Common-Mode Idle
The MAX9759 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 finite load current,
increasing power consumption. When no signal is pre-
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
12 ______________________________________________________________________________________
V
OUT+
- V
OUT-
t
SW
t
SW
t
SW
t
SW
V
IN-
V
IN+
OUT+
OUT-
t
ON(MIN)
Figure 2. MAX9759 Outputs with an Input Signal Applied (SSM Mode)
MAX9759
3.2W, High Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 13
sent at the input of the MAX9759, the outputs switch as
shown in Figure 4. Because the MAX9759 drives the
speaker differentially, the two outputs cancel each other,
resulting in no net Idle Mode™ voltage across the
speaker and minimal power consumption.
Efficiency
Efficiency of a Class D amplifier is mostly associated
with 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 output stage is mostly due to the I x R loss of the
MOSFET on-resistance and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%; however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (i.e., typical music reproduction levels), efficiency of a linear
amplifier can fall below 30%. The MAX9759 Class D
amplifier still exhibits >90% efficiencies under the same
conditions (Figure 5).
Gain Selection
The MAX9759 features an internally set, logic-selectable gain. The G1 and G2 logic inputs set the gain of
the MAX9759 speaker amplifier (Table 2).
Shutdown
The MAX9759 features a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low places the MAX9759 in a low-power (0.1µA)
shutdown mode. Drive SHDN high for normal operation.
30 60 80 100 120 140 160 180 280 300220200 240 260
15
20
25
30
35
40
45
50
AMPLITUDE (dBµV/m)
FREQUENCY (MHz)
MAX9759
OUTPUT SPECTRUM
FCC LIMIT
Figure 3. MAX9759 EMI Spectrum
VIN = 0V
OUT-
OUT+
V
OUT+
- V
OUT-
= 0V
Figure 4. MAX9759 Outputs with No Input Signal
0
30
20
10
50
40
90
80
70
60
100
0 0.2 0.4 0.8 1.20.6 1.0
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
VDD = 5V
f = 1kHz
R
L
= 8Ω
CLASS AB
MAX9759
Figure 5. MAX9759 Efficiency vs. Output Power
G2 G1 GAIN (dB)
00+24
01+18
10+12
11 +6
Table 2. Gain Selection
Idle Mode is a trademark of Maxim Integrated Products, Inc.
Mute
The MAX9759 features a mute function that disables
the H-bridge outputs of the switching amplifier. The
mute function only affects the power amplifiers of the
MAX9759; it does not shut down the device. Driving
MUTE low places the MAX9759 in a disabled output
mode. Drive MUTE high for normal operation.
Click-and-Pop Suppression
The MAX9759 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 40ms following startup, a soft-start function
gradually unmutes the input amplifiers.
For improved click-and-pop performance, sequence the
digital inputs of the SHDN and MUTE pins of the
MAX9759 during power-up and power-down of the
device such that transients are eliminated from each
power cycle. Apply power to the MAX9759 with both
SHDN and MUTE held low. Release SHDN before MUTE
such that minimal transients occur during startup of the
device. The mute function allows the MAX9759 to be
powered up with the H-bridge outputs of the switching
amplifier disabled. For power-down, sequence the power
cycle such that the amplifier is muted first and subsequently shut down before power is disconnected from the
IC. This power cycle eliminates any audible transients on
power-up and power-down of the MAX9759.
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. The traditional PWM
scheme uses large differential output swings (2 x V
DD
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 MAX9759 does not require an output filter for the short
speaker cable. 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 MAX9759 output is well
beyond the bandwidth of most speakers, voice coil
movement due to the switching frequency is very small.
Although this movement is small, a speaker not
designed to handle the additional power can be damaged. For optimum results, use a speaker with a series
inductance > 10µH 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 an 8Ω load 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 MAX9759 features a differential input structure,
making it compatible with many CODECs, and offers
improved noise immunity over a single-ended input
amplifier. High-frequency signals can be picked up by
the amplifier’s input traces and can 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 cancelled.
Single-Ended Input
The MAX9759 can be configured as a single-ended input
amplifier by capacitively coupling one input to GND while
simultaneously driving the other input (Figure 6).
DC-Coupled Input
The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC coupling
eliminates the input-coupling capacitors, reducing component count to potentially one external component (see
the System Diagram). However, the low-frequency rejec-
tion of the capacitors is lost, allowing low-frequency signals to feedthrough to the load.
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
14 ______________________________________________________________________________________
1µF
IN+
IN-
1µF
SINGLE-ENDED
AUDIO INPUT
MAX9759
Figure 6. Single-Ended Input
MAX9759
3.2W, High-Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 15
Component Selection
Input Filter
An input capacitor, C
IN
, in conjunction with the input
impedance of the MAX9759 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/(2πRINCIN)
Choose C
IN
such that f
-3dB
is well below the lowest fre-
quency 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.
IN+
IN-
OUT+
OUT-
SYNC_OUT
RIGHT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9759
V
DD
V
DD
PV
DD
IN+
IN-
OUT+
SYNC_OUT
SYNC
LEFT-CHANNEL
DIFFERENTIAL
AUDIO INPUT
MAX9759
V
DD
PV
DD
IN+
IN-
OUT+
SYNC_OUT
SYNC
DIFFERENTIAL
AUDIO INPUT
MAX9759
V
DD
PV
DD
SYNC
U1
U2
Figure 7. Master-Slave Configuration
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
OUTPUT POWER (W)
THD+N (%)
VDD = 5.0V
f = 1kHz
R
L
= 8Ω
SLAVE DEVICE
Figure 8. Total Harmonic Distortion Plus Noise vs. Output
Voltage
-150
10 100
1k
100k
CROSSTALK vs. FREQUENCY
-130
-110
-90
-30
FREQUENCY (Hz)
CROSSTALK (dB)
-70
-50
10k
VDD = 5V
R
L
= 8Ω
f = 1kHz
MASTER TO SLAVE
SLAVE TO MASTER
Figure 9. Crosstalk vs. Frequency
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
16 ______________________________________________________________________________________
Output Filter
The MAX9759 does not require an output filter for the
short speaker cable. The device passes FCC emissions
standards with 7.6cm of unshielded speaker cables.
However, output filtering can be used if a design is failing radiated emissions due to board layout, cable
length, or the circuit’s close proximity to EMI-sensitive
devices. Use an LC filter when radiated emissions are a
concern, or when long leads are used to connect the
amplifier to the speaker.
Supply Bypassing, Layout, and Grounding
Proper power-supply bypassing ensures low-distortion
operation. For optimum performance, bypass VDDto
GND and PVDDto PGND with separate 0.1µF 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
power-supply characteristics. GND and PGND should
be star-connected to system ground.
Use wide, low-resistance output traces. As load impedance decreases, the current drawn from the device outputs increase. At higher current, the resistance of the
output traces decrease the power delivered to the load.
Wide output, supply, and GND traces also improve the
power dissipation of the device.
The MAX9759 thin QFN package features an exposed
thermal pad on its underside. This pad lowers the
package’s thermal resistance by providing a direct
heat conduction path. Due to the high efficiency of the
MAX9759’s Class D Amplifier, an external heatsink is
not required. For optimum thermal performance, connect the exposed paddle to GND.
Stereo Configuration
Two MAX9759s can be configured as a stereo amplifier
(Figure 7). Device U1 is the master amplifier; its oscillator output, SYNC_OUT, drives the SYNC input of the
slave device (U2), synchronizing the switching frequencies of the two devices. Synchronizing two MAX9759s
ensures that no beat frequencies within the audio spectrum occur on the power-supply rails. This stereo 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 and SYNC_OUT connection (Figures 8, 9).
Multiple MAX9759s can be cascaded and frequency
locked in a similar fashion (Figure 7). Repeat the stereo
configuration outlined in Figure 7 for multiple cascading
amplifier applications.
Volume Control
If volume control is required, connect a potentiometer
between the differential inputs of the MAX9759, as seen
in Figure 10. In this configuration, each input “sees”
identical RC paths when the device is powered up. The
variable resistive element appears between the two
inputs, meaning the setting affects both inputs the same
way. This configuration significantly improves transient
performance on power-up or release from SHDN.
IN+
MAX9759
IN-
1µF
1µF
CW
22kΩ
50kΩ
22kΩ
Figure 10. Single-Ended Drive of MAX9759 Plus Volume
Control
MAX9759
3.2W, High-Efficiency, Low-EMI, Filterless,
Class D Audio Amplifier
______________________________________________________________________________________ 17
System Diagram
MAX9759
V
DD
V
DD
V
DD
AV
DD
1µF
OUT-R
8Ω SPEAKER
1µF
1µF
AV
SS
IN+
IN-
G2
G1
MUTE
SHDN
PGND
AV
SS
GND
PV
DD
V
DD
OUT+
OUT-
SYNC
SYNC_OUT
MAX9759
V
DD
V
DD
1µF
CENTER OUT
4Ω SPEAKER
1µF
1µF
AV
SS
IN+
IN-
G2
G1
MUTE
SHDN
PGND GND
PV
DD
V
DD
OUT+
OUT-
SYNC
SYNC
SYNC_OUT
MAX9759
V
DD
V
DD
1µF
OUT-L
8Ω SPEAKER
1µF
1µF
AV
SS
IN+
IN-
G2
G1
MUTE
SHDN
PGND GND
PV
DD
V
DD
OUT+
OUT-
SYNC_OUT
OUT-R
EAPD
CENTER OUT
OUT-L
2.1
AUDIO
CODEC
NOTE: SYSTEM DIAGRAM DEPICTS MAX9759 IN SSM MODE WITH f
S
= 1200 ±70kHz AND +12dB OF GAIN.
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
18 ______________________________________________________________________________________
THIN QFN
TOP VIEW
MAX9759
13
14
15
1234
5
6
16
12 11 10 9
8
7
PGND
SYNC_OUT
G2
V
DD
IN+
IN-
GND
OUT+
OUT-
PV
DD
G1
SYNC
MUTE
PGND
SHDN
PV
DD
Pin Configuration
Chip Information
TRANSISTOR COUNT: 4219
PROCESS: BiCMOS
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
______________________________________________________________________________________ 19
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages
.)
24L QFN THIN.EPS
PACKAGE OUTLINE,
21-0139
2
1
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
MAX9759
3.2W, High-Efficiency, Low-EMI,
Filterless, Class D Audio Amplifier
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages
.)
PACKAGE OUTLINE,
21-0139
2
2
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
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