General Description
The MAX9708 mono/stereo, Class D audio power amplifier delivers up to 2 x 21W into an 8Ω stereo mode and
1 x 42W into a 4Ω load in mono mode while offering up to
87% efficiency. The MAX9708 provides Class AB amplifier performance with the benefits of Class D efficiency,
eliminating the need for a bulky heatsink and conserving
power. The MAX9708 operates from a single +10V to
+18V supply, driving the load in a BTL configuration.
The MAX9708 offers two modulation schemes: a fixedfrequency modulation (FFM) mode, and a spread-spectrum modulation (SSM) mode that reduces
EMI-radiated emissions. The MAX9708 can be synchronized to an external clock from 600kHz to 1.2MHz. A
synchronized output allows multiple units to be cascaded in the system.
Features include fully differential inputs, comprehensive
click-and-pop suppression, and four selectable-gain settings (22dB, 25dB, 29.5dB, and 36dB). A pin-programmable thermal flag provides seven different thermal
warning thresholds. Short-circuit and thermal-overload
protection prevent the device from being damaged
during a fault condition.
The MAX9708 is available in 56-pin TQFN (8mm x 8mm
x 0.8mm) and 64-pin TQFP (10mm x 10mm x 1.4mm)
packages, and is specified over the extended
-40°C to +85°C temperature range.
Applications
LCD TVs PDP TVs
Automotive PC/HiFi Audio Solutions
Features
♦ 2 x 21W Output Power in Stereo Mode
(8Ω, THD = 10%)
♦ 1 x 42W Output Power in Mono Mode
(4Ω, THD = 10%)
♦ High Efficiency: Up to 87%
♦ Filterless Class D Amplifier
♦ Unique Spread-Spectrum Mode
♦ Programmable Gain (+22dB, +25dB, +29.5dB,
+36dB)
♦ High PSRR (90dB at 1kHz)
♦ Differential Inputs Suppress Common-Mode
Noise
♦ Shutdown and Mute Control
♦ Integrated Click-and-Pop Suppression
♦ Low 0.1% THD+N
♦ Current Limit and Thermal Protection
♦ Programmable Thermal Flag
♦ SYNC Input/Output
♦ Available in Thermally Efficient, Space-Saving
Packages: 56-Pin TQFN and 64-Pin TQFP
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
________________________________________________________________ Maxim Integrated Products 1
CLASS D
MODULATOR
SYNCOUT
TEMP
OUTPUT
PROTECTION
GAIN
CONTROL
FS1, FS2
MAX9708
STEREO MODE
G1, G2
2
SYNC
RIGHT
CHANNEL
LEFT
CHANNEL
MONO
2
TH0, TH1,
TH2
3
PART
TEMP RANGE
PIN-PACKAGE
PKG
CODE
MAX9708ETN+
T5688-3
MAX9708ECB*
64 TQFP-EP**
C64E-6
Simplified Block Diagram
Ordering Information
19-3678; Rev 2; 3/06
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.
+Denotes lead-free package.
*Future product—Contact factory for availability.
**EP = Exposed paddle.
Pin Configurations appear at end of data sheet.
EVALUATION KIT
AVAILABLE
CLASS D
MODULATOR
SYNCOUT
TEMP
OUTPUT
PROTECTION
GAIN
CONTROL
FS1, FS2
MAX9708
MONO MODE
G1, G2
2
SYNC
AUDIO
INPUT
V
DIGITAL
MONO
2
TH0, TH1,
TH2
3
-40°C to +85°C 56 TQFN-EP**
-40°C to +85°C
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, MONO = low (stereo
mode),
SHDN = MUTE = high, G1 = low, G2 = high (AV= 22dB), FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are
connected between OUT_+ and OUT_-, unless otherwise stated. T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
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.
PVDD, VDDto PGND, GND .......................................-0.3 to +30V
PV
DD
to VDD..........................................................-0.3V to +0.3V
OUTR+, OUTR-, OUTL+,
OUTL- to PGND, GND...........................-0.3V to (PV
DD
+ 0.3V)
C1N to GND .............................................-0.3V to (PV
DD
+ 0.3V)
C1P to GND..............................(PV
DD
- 0.3V) to (CPVDD+ 0.3V)
CPV
DD
to GND ..........................................(PV
DD
- 0.3V) to +40V
All Other Pins to GND.............................................-0.3V to +12V
Continuous Input Current (except PV
DD
, VDD, OUTR+,
OUTR-, OUTL+, and OUTL-) ...........................................20mA
Continuous Power Dissipation (T
A
= +70°C)
56-Pin Thin QFN (derate 47.6mW/°C above +70°C) ......3.81W
64-Pin TQFP (derate 43.5mW/°C above +70°C).............3.48W
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature......................................................+150°C
Thermal Resistance (θ
JC
)
56-Pin Thin QFN… .......................................................0.6°C/W
64-Pin TQFP….................................................................2°C/W
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER
CONDITIONS
UNITS
Supply Voltage Range V
DD
Inferred from PSRR test 10 18 V
Shutdown Current I
SHDN
SHDN = low 0.1 1 µA
Shutdown to Full Operation t
SON
ms
Mute to Full Operation t
MUTE
ms
G1 = 0, G2 = 1 50 85 125
G1 = 1, G2 = 1 40 63 90
G1 = 1, G2 = 0 25 43 60
Input Impedance R
IN
G1= 0, G2 = 0 12 21 30
kΩ
Output Pulldown Resistance SHDN = GND
kΩ
Output Offset Voltage V
OS
AC-coupled input, measured between
OUT_+ and OUT_-
mV
PVDD = 10V to 18V 68 90
f
RIPPLE
= 1kHz 90
Power-Supply Rejection Ratio PSRR
200mV
P-P
ripple
(Note 2)
f
RIPPLE
= 20kHz 50
dB
DC, input referred 50 70
Common-Mode Rejection Ratio CMRR
f = 20Hz to 20kHz, input referred 70
dB
Switch On-Resistance R
DS
One power switch 0.3
Ω
FS1 FS2
00
220
1 1 (SSM)
10
Switching Frequency f
SW
01
kHz
Oscillator Spread Bandwidth FS1 = FS2 = high (SSM) ±2 %
SYNCIN Lock Range Equal to fSW x 4
kHz
SYMBOL
MIN TYP MAX
100
100
600
200
160
250
180 200
600 1200
±30
0.75
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, MONO = low (stereo
mode), SHDN = MUTE = high, G1 = low, G2 = high (A
V
= 22dB), FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are
connected between OUT_+ and OUT_-, unless otherwise stated. T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
CONDITIONS
UNITS
G1 = 0, G2 = 1
G1 = 1, G2 = 1
G1 = 1, G2 = 0
Gain A
V
G1 = 0, G2 = 0
dB
TH2 TH1 TH0
000
001
010
011
100
101
110
TEMP Flag Threshold T
FLAG
111
°C
TEMP Flag Accuracy From +80°C to +140°C ±6 °C
TEMP Flag Hysteresis 2°C
STEREO MODE (R
LOAD
= 8Ω)
MUTE = 1, R
LOAD
= ∞ 20 30
Quiescent Current
MUTE = 0 5 11
mA
Output Power P
OUT
f = 1kHz, THD = 10%, TA = +25°C,
R
LOAD
= 8Ω, PVDD = 18V
20 21 W
Total Harmonic Distortion Plus
Noise
f = 1kHz, BW = 22Hz to 22kHz,
R
LOAD
= 8Ω, P
OUT
= 8W
0.1 %
91
Signal-to-Noise Ratio SNR
A-weighted 96
dB
Efficiency η
f = 1kHz
87 %
Left-Right Channel Gain
Matching
P
OUT
= 10W
dB
SYMBOL
THD+N
R
LOAD
R
LOAD
OUT
= 10W
= 8Ω, P
= 8Ω, L > 60µH , P
22Hz to 22kHz
= 15W + 15W ,
OU T
MIN TYP MAX
21.6 22.0 22.3
24.9 25.0 25.6
29.2 29.5 29.9
35.9 36.0 36.6
+80
+90
+100
+110
+120
+129
+139
+150
0.02
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, MONO = low (stereo
mode), SHDN = MUTE = high, G1 = low, G2 = high (A
V
= 22dB), FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are
connected between OUT_+ and OUT_-, unless otherwise stated. T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
CONDITIONS
UNITS
Output Short-Circuit Current
Threshold
I
SC
R
LOAD
= 0Ω 2.4 A
Into shutdown -63
Click-and-Pop Level K
CP
Peak voltage, 32
samples/second,
-55
dBV
MONO MODE (R
LOAD
= 4Ω, MONO = High)
MUTE = 1, R
LOAD
= ∞ 20
Quiescent Current
MUTE = 0 5
mA
R
LOAD
= 8Ω 23
Output Power P
OUT
f = 1kHz,
R
LOAD
= 4Ω 42
W
Total Harmonic Distortion Plus
Noise
f = 1kHz, BW = 22Hz to 22kHz,
R
LOAD
= 4Ω, P
OUT
= 17W
%
91
Signal-to-Noise Ratio SNR
R
LOAD
= 4Ω,
P
OUT
= 10W
A-weighted 95
dB
Efficiency η
R
LOAD
= 4Ω, L > 40µH, P
OUT
= 42W,
f = 1kHz
85 %
Output Short-Circuit Current
Threshold
I
SC
R
LOAD
= 0Ω 4.8 A
Into shutdown -60
Click-and-Pop Level K
CP
Peak voltage, 32
samples/second,
A-weighted (Notes 2, 4)
-63
dBV
DIGITAL INPUTS (SHDN, MUTE, G1, G2, FS1, FS2, TH0, TH1, TH2, SYNCIN, MONO)
Logic-Input Current I
IN
0 to 12V 1 µA
Logic-Input High Voltage V
IH
2.5 V
Logic-Input Low Voltage V
IL
0.8 V
OPEN-DRAIN OUTPUTS (TEMP, SYNCOUT)
Open-Drain Output Low Voltage V
OL
I
SINK
= 3mA 0.4 V
Leakage Current I
LEAK
V
PULLUP
= 5.5V 0.2 µA
Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2: Inputs AC-coupled to GND.
Note 3: The device is current limited. The maximum output power is obtained with an 8Ω load.
Note 4: Testing performed with an 8Ω resistive load in series with a 68µH inductive load connected across BTL outputs. Mode tran-
sitions are controlled by SHDN.
SYMBOL
MIN TYP MAX
A-weighted (Notes 2, 4)
THD = 10%
Out of shutdown
20Hz to 20kHz
Out of shutdown
0.12
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
_______________________________________________________________________________________ 5
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9708 toc01
OUTPUT POWER PER CHANNEL (W)
THD+N (%)
252015105
0.1
1
10
100
0.01
030
PVDD = 18V, 8
Ω
STEREO MODE, 1kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9708 toc02
OUTPUT POWER PER CHANNEL (W)
THD+N (%)
105
0.1
1
10
100
0.01
015
PVDD = 12V,
STEREO MODE,
f
IN
= 1kHz
RL = 8
Ω
RL = 4
Ω
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9708 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
10 100k
1
0.01
PVDD = 18V,
8Ω STEREO MODE,
P
OUT
= 8.3W PER
CHANNEL
EFFICIENCY vs. OUTPUT POWER
MAX9708 toc04
OUTPUT POWER PER CHANNEL (W)
EFFICIENCY (%)
252015105
20
30
40
50
60
70
80
90
100
10
030
PVDD = 18V, 8
Ω
STEREO MODE
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9708 toc05
SUPPLY VOLTAGE (V)
OUTPUT POWER PER CHANNEL (W)
161412
5
10
15
20
25
30
0
10 18
RL = 8Ω
STEREO MODE
10% THD+N
1% THD+N
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9708 toc06
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
2018161412
12
14
16
18
20
22
24
10
10 22
STEREO MODE
TA = +25°C
TA = +85°C
TA = -40°C
Typical Operating Characteristics
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (R
L
) are between OUT_+ and
OUT_-, T
A
= +25°C, unless otherwise stated.)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9708 toc07
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (nA)
201812 14 16
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
10 22
SHDN = 0
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9708 toc08
OUTPUT POWER (W)
THD+N (%)
5040302010
0.1
1
10
100
0.01
060
PVDD = 18V, 4Ω MONO MODE,
1kHz
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
6 _______________________________________________________________________________________
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9708 toc10
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.1
10 100k
1
0.01
PVDD = 18V,
4Ω MONO MODE,
P
OUT
= 18W
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
MAX9708 toc11
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
10M1M
-60
-50
-40
-30
-20
-10
0
10
20
30
-70
100k 100M
10kHz RBW
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
MAX9708 toc12
FREQUENCY (Hz)
OUTPUT AMPLITUDE (dBV)
10M1M100k 100M
10kHz RBW
-60
-50
-40
-30
-20
-10
0
10
20
30
-70
OUTPUT FREQUENCY SPECTRUM
(SSM MODE)
MAX9708 toc13
FREQUENCY (kHz)
OUTPUT AMPLITUDE (dBV)
20161284
-100
-80
-60
-40
-20
0
-120
024
OUTPUT FREQUENCY SPECTRUM
(FFM MODE)
MAX9708 toc14
FREQUENCY (kHz)
OUTPUT AMPLITUDE (dBV)
20161284
-100
-80
-60
-40
-20
0
-120
024
Typical Operating Characteristics (continued)
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (R
L
) are between OUT_+ and
OUT_-, T
A
= +25°C, unless otherwise stated.)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9708 toc09
OUTPUT POWER (W)
THD+N (%)
2015105
0.1
1
10
100
0.01
025
PVDD = 12V,
MONO MODE,
f
IN
= 1kHz
R
L
= 4
Ω
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
_______________________________________________________________________________________ 7
EFFICIENCY vs. OUTPUT POWER
MAX9708 toc15
OUTPUT POWER (W)
EFFICIENCY (%)
5040302010
20
30
40
50
60
70
80
90
100
10
060
PVDD = 18V,
4Ω MONO MODE
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9708 toc16
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
161412
10
20
30
40
50
60
0
10 18
RL = 4Ω,
MONO MODE,
10% THD+N
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9708 toc17
LOAD RESISTANCE (Ω)
OUTPUT POWER (W)
1086
10
20
30
40
50
60
0
412
MONO MODE,
10% THD+N,
PV
DD
= 18V
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9708 toc18
LOAD RESISTANCE (Ω)
OUTPUT POWER PER CHANNEL (W)
111098
5
10
15
20
25
30
0
712
STEREO MODE,
10% THD+N,
PV
DD
= 18V
MUTE RESPONSE
MAX9708 toc19
40ms/div
MUTE
5V/div
OUTPUT
50mV/div
SHUTDOWN RESPONSE
MAX9708 toc20
40ms/div
SHDN
5V/div
OUTPUT
50mV/div
Typical Operating Characteristics (continued)
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (R
L
) are between OUT_+ and
OUT_-, T
A
= +25°C, unless otherwise stated.)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
8 _______________________________________________________________________________________
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
MAX9708 toc21
FREQUENCY (Hz)
CMRR (dB)
10k1k100
-105
-100
-95
-90
-85
-80
-75
-70
-65
-60
-110
10 100k
INPUT REFERRED
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9708 toc22
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-100
-90
-80
-70
-60
-50
-40
-30
-110
10 100k
CROSSTALK vs. FREQUENCY
MAX9708 toc23
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-110
-100
-90
-80
-70
-60
-50
-40
-120
10 100k
MAXIMUM STEADY-STATE OUTPUT POWER
vs. TEMPERATURE
MAX9708 toc24
AMBIENT TEMPERATURE (°C)
OUTPUT POWER PER CHANNEL (W)
6040
50
5
15
10
25
20
30
35
40
0
30 70
PVDD = 18V, 8
Ω
STEREO MODE, 1kHz,
FS1 = FS2 = 1
TH0 = TH1 = 1
TH2 = 0
MEASURED WITH THE EV KIT (TQFN
PACKAGE), JUNCTION TEMPERATURE
MAINTAINED AT +110°C
MAXIMUM STEADY-STATE OUTPUT POWER
vs. TEMPERATURE
MAX9708 toc25
AMBIENT TEMPERATURE (°C)
OUTPUT POWER (W)
60
40 50
10
20
40
30
50
60
70
0
30 70
PVDD = 18V, 4
Ω
MONO MODE, 1kHz,
FS1 = FS2 = 1
TH0 = TH1 = 1
TH2 = 0
MEASURED WITH THE EV KIT (TQFN
PACKAGE), JUNCTION TEMPERATURE
MAINTAINED AT +110°C
Typical Operating Characteristics (continued)
(PVDD= VDD= +18V, PGND = GND = 0V, CSS= 0.47µF, C
REG
= 0.01µF, C1 = 0.1µF, C2 = 1µF, R
LOAD
= ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (R
L
) are between OUT_+ and
OUT_-, T
A
= +25°C, unless otherwise stated.)
Pin Description
PIN
TQFP TQFN
NAME FUNCTION
1, 8, 13, 16,
17, 32, 33, 41,
48, 49, 50, 55,
58, 63, 64
1, 12, 42, 43,
44, 55, 56
N.C. No Connection. Not internally connected.
2, 3, 4, 45, 46,
47, 56, 57
2, 3, 4, 39,
PGND Power Ground
5, 6, 7,
42, 43, 44
5, 6, 7,
36, 37, 38
PV
DD
Positive Power Supply. Bypass to PGND with a 0.1µF and a 47µF capacitor with the
smallest capacitor placed as close to pins as possible.
40, 41, 49, 50
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
_______________________________________________________________________________________ 9
Pin Description (continued)
PIN
TQFP TQFN
NAME FUNCTION
9 8 C1N Charge-Pump Flying Capacitor C1, Negative Terminal
10 9 C1P Charge-Pump Flying Capacitor C1, Positive Terminal
11 10 CPV
DD
Charge-Pump Power Supply. Bypass to PVDD with a 1µF capacitor as close to the pin
as possible.
12 11
Open-Drain, Slew-Rate Limited Clock Output. Pullup with a 10kΩ resistor to REG.
14 13
Clock Synchronization Input. Allows for synchronization of the internal oscillator with an
external clock. SYNCIN is internally pulled up to V
REG
with a 100kΩ resistor.
15 14 FS2 Frequency Select 2
18 15 FS1 Frequency Select 1
19 16 INL- Left-Channel Negative Input (Stereo Mode Only)
20 17 INL+ Left-Channel Positive Input (Stereo Mode Only)
21 18 MONO
Mono/Stereo Mode Input. Drive logic-high for mono mode. Drive logic-low for stereo
mode.
22, 23, 24 19, 20, 21 REG Internal Regulator Output Voltage (6V). Bypass with a 0.01µF capacitor to GND.
25, 26 22, 23 GND Analog Ground
27 24 SS
Soft-Start. Connect a 0.47µF capacitor to GND to utilize soft-start power-up sequence.
28 25 V
DD
Analog Power Supply. Bypass to GND with a 0.1µF capacitor as close to pin as
possible.
29 26 INR- Right-Channel Negative Input. In mono mode, INR- is the negative input.
30 27 INR+ Right-Channel Positive Input. In mono mode, INR+ is the positive input.
31 28 G1 Gain Select Input 1
34 29 G2 Gain Select Input 2
35 30 SHDN
Active-Low Shutdown Input. Drive SHDN high for normal operation. Drive SHDN low to
place the device in shutdown mode.
36 31 MUTE
Active-Low Mute Input. Drive logic-low to place the device in mute. In mute mode,
Class D output stage is no longer switching. Drive high for normal operation. MUTE is
internally pulled up to V
REG
with a 100kΩ resistor.
37 32 TEMP Thermal Flag Output, Open Drain. Pull up with a 10kΩ resistor to REG.
38 33 TH2 Temperature Flag Threshold Select Input 2
39 34 TH1 Temperature Flag Threshold Select Input 1
40 35 TH0 Temperature Flag Threshold Select Input 0
51, 52 45, 46 OUTR- Right-Channel Negative Output
53, 54 47, 48
Right-Channel Positive Output
59, 60 51, 52 OUTL- Left-Channel Negative Output
61, 62 53, 54
Left-Channel Positive Output
EP EP EP Exposed Paddle. Connect to GND with multiple vias for best heat dissipation.
SYNCOUT
SYNCIN
OUTR+
OUTL+
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
10 ______________________________________________________________________________________
Typical Application Circuits/Functional Diagrams
OUTR+
OUTR-
OUTL-
OUTL+
SYNCIN
INL+
INL-
INR+
INR-
SHDN
G2
G1
SYNCOUT
PGND
R
IN
R
IN
R
IN
R
IN
V
BIAS
V
BIAS
TH0 TH1 TH2
TEMP
CPV
DD
PV
DD
PV
DD
PV
DD
PV
DD
PV
DD
V
DD
V
DD
C1P
C1N
REG
+
-
LEFT
CHANNEL
+
-
RIGHT
CHANNEL
V
DIGITAL
C2
1µF
C1
0.1µF
0.1µF
47µF*
1µF
1µF
1µF
1µF
C
REG
0.01µF
C
SS
0.47µF
V
DIGITAL
V
DIGITAL
V
DIGITAL
V
DIGITAL
GND
MONO
FS1
FS2
R
F
R
F
R
F
R
F
10kΩ
10kΩ
14 (15)
13 (14)
17 (20)
16 (19)
27 (30)
26 (29)
30 (35)
28 (31)
29 (34)
18 (21)
35 (40) 34 (39) 33 (38)
32 (37)
19, 20, 21 (22, 23, 24)
8 (9)
9 (10)
10 (11)
51, 52 (59, 60)
53, 54 (61, 62)
45, 46 (51, 52)
47, 48 (53, 54)
11 (12)
22, 23
(25, 26)
2–4, 39–41 49–50
(2–4, 45–47, 56–57)
5–7, 36–38
(5–7, 42-44)25 (28)
15 (18)
SS
24 (27)
MUTE
31 (36)
( ) TQFP PACKAGE
*ADDITIONAL BULK CAPACITANCE
CONFIGURATION: TQFN STEREO MODE, SSM, INTERNAL OSCILLATOR, GAIN = 22dB, THERMAL SETTING = +120°C
MAX9708
GAIN
CONTROL
CONTROL
CHARGE
PUMP
REGULATOR
THERMAL SENSOR
MUX
CLASS D
MODULATOR
AND H-BRIDGE
CLASS D
MODULATOR
AND H-BRIDGE
Figure 1. Typical Application and Functional Diagram in Stereo Mode
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 11
Typical Application Circuits/Functional Diagrams (continued)
OUTR+
OUTR-
OUTL-
OUTL+
SYNCIN
INR+
INR-
SHDN
G1
G2
SYNCOUT
PGND
R
IN
R
IN
V
BIAS
TH0 TH1 TH2
TEMP
CPV
DD
PV
DD
PV
DD
PV
DD
PV
DD
PV
DD
V
DD
V
DD
C1P
C1N
REG
+
-
AUDIO
INPUT
V
DIGITAL
C2
1µF
0.1µF
0.1µF
47µF*
1µF
1µF
C
REG
0.01µF
C1
0.1µF
C
SS
0.47µF
V
DIGITAL
V
DIGITAL
V
DIGITAL
V
DIGITAL
GND
MONO
FS1
FS2
R
F
R
F
10kΩ
10kΩ
14 (15)
13 (14)
17 (20)
16 (19)
30 (35)
28 (31)
29 (34)
18 (21)
35 (40) 34 (39) 33 (38)
32 (37)
19, 20, 21 (22, 23, 24)
8 (9)
9 (10)
10 (11)
51, 52 (59, 60)
53, 54 (61, 62)
45, 46 (51, 52)
47, 48 (53, 54)
11 (12)
22, 23
(25, 26)
2–4, 39–41 49–50
(2–4, 45–47, 56–57)
5–7, 36–38
(5–7, 42–44)25 (28)
15 (18)
SS
24 (27)
MUTE
31 (36)
V
DIGITAL
MAX9708
GAIN
CONTROL
CHARGE
PUMP
REGULATOR
THERMAL SENSOR
MUX
CONTROL
CLASS D
MODULATOR
AND H-BRIDGE
CLASS D
MODULATOR
AND H-BRIDGE
( ) TQFP PACKAGE
*ADDITIONAL BULK CAPACITANCE
CONFIGURATION: TQFN MONO MODE, SSM, INTERNAL OSCILLATOR, GAIN = 22dB, THERMAL SETTING = +120°C
Figure 2. Typical Application and Functional Diagram in Mono Mode
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
12 ______________________________________________________________________________________
Detailed Description
The MAX9708 filterless, Class D audio power amplifier
features several improvements to switch-mode amplifier technology. The MAX9708 is a two-channel, stereo
amplifier with 21W output power on each channel. The
amplifier can be configured to output 42W output
power in mono mode. The device offers Class AB performance with Class D efficiency, while occupying minimal board space. A unique filterless modulation
scheme and spread-spectrum switching 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.
Mono/Stereo Configuration
The MAX9708 features a mono mode that allows the
right and left channels to operate in parallel, achieving
up to 42W of output power. The mono mode is enabled
by applying logic-high to MONO. In this mode, an
audio signal applied to the right channel (INR+/INR-) is
routed to the H-bridge of both channels, while a signal
applied to the left channel (INL+/INL-) is ignored.
OUTL+ must be connected to OUTR+ and OUTL- must
be connected to OUTR- using heavy PC board traces
as close to the device as possible (see Figure 2).
When the device is placed in mono mode on a PC
board with outputs wired together, ensure that the
MONO pin can never be driven low when the device is
enabled. Driving the MONO pin low (stereo mode)
while the outputs are wired together in mono mode may
trigger the short circuit or thermal protection or both,
and may even damage the device.
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 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 MAX9708 still exhibits 87% efficiency under the
same conditions.
Shutdown
The MAX9708 features a shutdown mode that reduces
power consumption and extends battery life. Driving
SHDN low places the device in low-power (0.1µA) shutdown mode. Connect SHDN to digital high for normal
operation.
Mute Function
The MAX9708 features a clickless/popless mute mode.
When the device is muted, the outputs stop switching,
muting the speaker. Mute only affects the output stage
and does not shut down the device. To mute the
MAX9708, drive MUTE to logic-low. Driving MUTE low
during the power-up/down or shutdown/turn-on cycle
optimizes click-and-pop suppression.
Click-and-Pop Suppression
The MAX9708 features comprehensive click-and-pop
suppression that eliminates audible transients on startup and shutdown. While in shutdown, the H-bridge is
pulled to GND through a 330kΩ resistor. 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 subsequently enabled. Following startup, a
soft-start function gradually un-mutes the input amplifiers. The value of the soft-start capacitor has an impact
on the click-and-pop levels as well as startup time.
Thermal Sensor
The MAX9708 features an on-chip temperature sensor
that monitors the die temperature. When the junction
temperature exceeds a programmed level, TEMP is
pulled low. This flags the user to reduce power or shut
down the device. TEMP may be connected to SS or
MUTE for automatic shutdown during overheating. If
TEMP is connected to MUTE, during thermal-protection
mode, the audio is muted and the device is in mute
mode. If TEMP is connected to SS, during thermal-protection mode, the device is shut down but the thermal
sensor is still active.
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 13
TEMP returns high once the junction temperature cools
below the set threshold minus the thermal hysteresis. If
TEMP is connected to either MUTE or SS, the audio
output resumes. The temperature threshold is set by
the TH0, TH1, and TH2 inputs as shown in Table 1. An
RC filter may be used to eliminate any transient at the
TEMP output as shown in Figure 3.
Gain Selection
The MAX9708 features four pin-selectable gain settings;
see Table 2.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode
The MAX9708 features three switching frequencies in
the FFM mode (Table 3). In this mode, the frequency
spectrum of the Class D output consists of the fundamental switching frequency and its associated harmonics (see the Wideband Output Spectrum graph in the
Typical Operating Characteristics). Select one of the
three fixed switching frequencies such that the harmonics do not fall in a sensitive band. The switching frequency can be changed at any time without affecting
audio reproduction.
Spread-Spectrum Modulation (SSM) Mode
The MAX9708 features a unique spread-spectrum
(SSM) mode that flattens the wideband spectral components, improving EMI emissions that may be radiated
by the speaker and cables. This mode is enabled by
setting FS1 = FS2 = high. In SSM mode, the switching
frequency varies randomly by ±4% around the center
frequency (200kHz). 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 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. SSM mode reduces EMI compared to fixedfrequency mode. This can also help to randomize visual artifacts caused by radiated or supply-borne
interference in displays.
Synchronous Switching Mode
The MAX9708 SYNCIN input allows the Class D amplifier to switch at a frequency defined by an external clock
frequency. Synchronizing the amplifier with an external
clock source may confine the switching frequency to a
less sensitive band. The external clock frequency range
is from 600kHz to 1.2MHz and can have any duty cycle,
but the minimum pulse must be greater than 100ns.
SYNCOUT is an open-drain clock output for synchronizing external circuitry. Its frequency is four times the
amplifier’s switching frequency, and it is active in either
internal or external oscillator mode.
Figure 3. An RC Filter Eliminates Transient During Switching
Table 1. MAX9708 Junction Temperature
Threshold Setting
TEMP
0.1μF
10kΩ
10kΩ
V
DIGITAL
TO DIGITAL
INPUT
JUNCTION
TEMPERATURE
(°C)
TH2 TH1 TH0
80 Low Low Low
90 Low Low High
100 Low High Low
110 Low High High
120 High Low Low
129 High Low High
139 High High Low
150 High High High
Table 2. MAX9708 Gain Setting
G1 G2 GAIN (dB)
Low High 22
High High 25
High Low 29.5
Low Low 36
Table 3. Switching Frequencies
FS1
FS2
SYNCOUT
MODULATION
0 0 200 Fixed-Frequency
0 1 250 Fixed-Frequency
1 0 160 Fixed-Frequency
1 1 200 ±4 Spread-Spectrum
FREQUENCY (kHz)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
14 ______________________________________________________________________________________
Linear Regulator (REG)
The supply voltage range for the MAX9708 is from 10V
to 18V to achieve high-output power. An internal linear
regulator reduces this voltage to 6.3V for use with
small-signal and digital circuitry that does not require a
high-voltage supply. Bypass a 0.01µF capacitor from
REG to GND.
Applications Information
Logic Inputs
All of the digital logic inputs and output have an
absolute maximum rating of +12V. If the MAX9708 is
operating with a supply voltage between 10V and 12V,
digital inputs can be connected to PV
DD
or VDD. If
PVDDand VDDare greater than 12V, digital inputs and
outputs must connected to a digital system supply
lower than 12V.
Input Amplifier
Differential Input
The MAX9708 features a differential input structure,
making them compatible with many CODECs, and
offering improved noise immunity over a single-ended
input amplifier. In devices such as flat-panel displays,
noisy digital signals can be picked up by the amplifier’s
inputs. These signals appear at the amplifiers’ inputs as
common-mode noise. A differential input amplifier
amplifies only the difference of the two inputs, while any
signal common to both inputs is attenuated.
Single-Ended Input
The MAX9708 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND and driving the other input (Figure 4).
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9708, 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:
Choose C
IN
so 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 with dielectrics that 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.
Output Filter
The MAX9708 does not require an output filter.
However, output filtering can be used if a design is failing radiated emissions due to board layout or cable
length, or the circuit is near EMI-sensitive devices.
Refer to the MAX9708 Evaluation Kit for suggested filter
topologies. The tuning and component selection of the
filter should be optimized for the load. A purely resistor
load (8Ω) used for lab testing will require different com-
ponents than a real, complex load-speaker load.
Charge-Pump Capacitor Selection
The MAX9708 has an internal charge-pump converter
that produces a voltage level for internal circuitry. It
requires a flying capacitor (C1) and a holding capacitor
(C2). 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 performance over the extended temperature
range, select capacitors with an X7R dielectric. The
capacitors’ voltage rating must be greater than 36V.
f
RC
dB
IN IN
−
=
3
1
2 π
Figure 4. Single-Ended Input Connections
INR+
INR-
MAX9708
1µF
1µF
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 15
Sharing Input Sources
In certain systems, a single audio source can be
shared by multiple devices (speaker and headphone
amplifiers). 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 MAX9708 by driving
MUTE low. Driving MUTE low turns off the Class D output stage, but does not affect the input bias levels of
the MAX9708.
Frequency Synchronization
The MAX9708 outputs up to 21W on each channel in
stereo mode. If higher output power or a 2.1 solution is
needed, two MAX9708s can be used. Each MAX9708
is synchronized by connecting SYNCOUT from the first
MAX9708 to SYNCIN of the second MAX9708 (see
Figure 5).
Supply Bypassing/Layout
Proper power-supply bypassing ensures low-distortion
operation. For optimum performance, bypass PVDDto
PGND with a 0.1µF capacitor as close to each PV
DD
pin as possible. A low-impedance, high-current powersupply connection to PVDDis 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. For the TQFN package, solder the exposed
paddle (EP) to the ground plane using multiple-plated
through-hole vias. The exposed paddle must be soldered to the ground plane for rated power dissipation
and good ground return. Use wider PC board traces to
lower the parasitic resistance for the high-power output
pins (OUTR+, OUTR-, OUTL+, OUTL-). Refer to the
MAX9708 Evaluation Kit for layout guidance.
Thermal Considerations
Class D amplifiers provide much better efficiency and
thermal performance than a comparable Class AB
amplifier. However, the system’s thermal performance
must be considered with realistic expectations along
with its many parameters.
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. The
PC board must be optimized for best dissipation (see
the PC Board Thermal Considerations section).
Audio content, both music and voice, has a much lower
RMS value relative to its peak output power. Therefore,
while an audio signal 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
for real music or voice.
PC Board Thermal Considerations
The exposed pad is the primary route for conducting
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 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, provided 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 system’s constraints for signal routing.
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
out of the package, they do provide a small amount.
The total improvement would not exceed approximately
10%, but it could make the difference between acceptable performance and thermal problems.
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
16 ______________________________________________________________________________________
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 resistance 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 costeffective location for a heatsink. If an LC filter is used in
the design, placing the inductor in close proximity to the
IC can help draw heat away from the MAX9708.
Thermal Calculations
The die temperature of a Class D amplifier can be estimated with some basic calculations. For example, the
die temperature is calculated for the below conditions:
•T
A
= +40°C
•P
OUT
= 16W
• Efficiency (η) = 87%
• θJA= 21°C/W
First, the Class D amplifier’s power dissipation must be
calculated:
Then the power dissipation is used to calculate the die
temperature, T
C
, as follows:
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 I
2
R losses in the MOSFETs, which increases
efficiency. To keep the peak currents lower, choose the
highest impedance speaker that can still deliver the
desired output power within the voltage swing limits of
the Class D amplifier and its supply voltage.
Although most loudspeakers fall either 4Ω or 8Ω, there
are other impedances available that can provide a
more thermally efficient solution.
Another consideration is the load impedance across
the audio frequency band. A loudspeaker is a complex
electro-mechanical system with a variety of resonance.
In other words, an 8Ω speaker usually has 8Ω impedance within a very narrow range. This 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 multidriver audio system.
Systems Application Circuit
The MAX9708 can be configured into multiple amplifier
systems. One concept is a 2.1 audio system (Figure 5)
where a stereo audio source is split into three channels.
The left- and right-channel inputs are highpass filtered
to remove the bass content, and then amplified by the
MAX9708 in stereo mode. Also, the left- and right-channel inputs are summed together and lowpass filtered to
remove the high-frequency content, then amplified by a
second MAX9708 in mono mode.
The conceptual drawing of Figure 5 can be applied to
either single-ended or differential systems. Figure 6
illustrates the circuitry required to implement a fully
differential filtering system. By maintaining a fully differential path, the signal-to-noise ratio remains uncompromised and noise pickup is kept very low. However,
keeping a fully differential signal path results in almost
twice the component count, and therefore performance
must be weighed against cost and size.
The highpass and lowpass filters should have different
cutoff frequencies to ensure an equal power response
at the crossover frequency. The filters should be at
-6dB amplitude at the crossover frequency, which is
known as a Linkwitz-Riley alignment. In the example
circuit of Figure 6, the -3dB cutoff frequency for the
highpass filters is 250Hz, and the -3dB cutoff frequency
for the lowpass filter is 160Hz. Both the highpass filters
and the lowpass filters are at a -6dB amplitude at
approximately 200Hz. If the filters were to have the
same -3dB cutoff frequency, a measurement of sound
pressure level (SPL) vs. frequency would have a peak
at the crossover frequency.
The circuit in Figure 6 uses inverting amplifiers for their
ease in biasing. Note the phase labeling at the outputs
has been reversed. The resistors should be 1% or better
in tolerance and the capacitors 5% tolerance or better.
TTP C W CW C
C A DISS JA
=+ × =°+ ×° = °θ 40 24 21 90 4/.
P
P
P
W
WW
DISS
OUT
OUT
===−−
.
.
η
16
087
16 2 4
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 17
Mismatch in the components can cause discrepancies
between the nominal transfer function and actual performance. Also, the mismatch of the input resistors (R15,
R17, R19, and R21 in Figure 6) of the summing amplifier
and lowpass filter will cause some high-frequency sound
to be sent to the subwoofer.
The circuit in Figure 6 drives a pair of MAX9708 devices
similar to the circuit in Figure 5. The inputs to the
MAX9708 still require AC-coupling to prevent compromising the click-and-pop performance of the MAX9708.
The left and right drivers should be at an 8Ω to 12Ω
impedance, whereas the subwoofer can be 4Ω to 12Ω
depending on the desired output power, the available
power-supply voltage, and the sensitivity of the individual speakers in the system. The four gain settings of
the MAX9708 allow gain adjustments to match the sensitivity of the speakers.
Figure 5. Multiple Amplifiers Implement a 2.1 Audio System
MAX9708
MAX9708
HIGHPASS
FILTER
8Ω
FULLRANGE
SPEAKER
8Ω
FULLRANGE
SPEAKER
4Ω OR 8Ω
WOOFER
RIGHT
AUDIO
LEFT
AUDIO
HIGHPASS
FILTER
LOWPASS
FILTER
Σ
V
DIGITAL
OUTR+
OUTR-
OUTL+
OUTL-
OUTR+
OUTR-
OUTL+
OUTL-
INR+
INR-
MONO
INL+
INL-
INR+
SYNCIN
SYNCOUT
INR-
MONO
INL+
INL-
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
18 ______________________________________________________________________________________
Figure 6. Fully Differential Crossover Filters
BIAS
2
3
1
C1
47nF
R3
28kΩ
R2, 56.2kΩ
R1
56.2kΩ
C2
47nF
MAX4478
U1A
BIAS
6
5
7
C3
47nF
R7
28kΩ
R6, 56.2kΩ
RIGHT
AUDIO
OUTPUT
RIGHT
AUDIO
INPUT
R5
56.2kΩ
R4
28kΩ
C4
47nF
MAX4478
U1B
BIAS
9
10
8
C5
47nF
R10
28kΩ
R9, 56.2kΩ
R8
56.2kΩ
C6
47nF
MAX4478
U1C
BIAS
13
12
14
C7
47nF
R14
28kΩ
R13, 56.2kΩ
LEFT
AUDIO
OUTPUT
SUBWOOFER OUTPUT IS
AC-COUPLED TO A
MAX9708 CONFIGURED AS
A MONO AMPLIFIER
NOTE:
OP-AMP POWER PINS OMITTED FOR CLARITY.
ALL RESISTORS ARE 1% OR BETTER.
ALL CAPACITORS ARE 5% OR BETTER.
RIGHT AND LEFT OUTPUTS
ARE AC-COUPLED TO A
MAX9708 CONFIGURED AS
A STEREO AMPLIFIER
SUBWOOFER
AUDIO
OUTPUT
LEFT
AUDIO
INPUT
R12
56.2kΩ
R11
28kΩ
C8
47nF
MAX4478
U1D
BIAS
2
3
1
R17
26.1kΩ
R15
26.1kΩ
MAX4478
U2A
R16
13kΩ
C9, 47nF
C10
47nF
R18
7.5kΩ
BIAS
6
5
7
R21
28kΩ
R19
26.1kΩ
MAX4478
U2B
R20
13kΩ
C11, 47nF
R22
7.5kΩ
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 19
Pin Configurations
TOP VIEW
PGND
PGND
PGND
PV
DD
PV
DD
PV
DD
TH0
TH1
TH2
G2
TEMP
MUTE
SHDN
N.C.
3637383940 3233343541
18
19
20
21
22
23
24
25
26
27
OUTL+
THIN QFN
3031 29
INR+
INR-
V
DD
SS
GND
GND
REG
REG
REG
FS1
15
16
17
MONO
INL+
INL-
OUTL-
OUTL-
PGND
PGND
OUTR+
N.C.
N.C.
OUTL+
OUTR+
OUTR-
OUTR-
N.C.
28 G1N.C.
SYNCOUT
CPV
DD
C1P
C1N
PV
DD
PV
DD
FS2
SYNCIN
N.C.
PV
DD
PGND
PGND
PGND
N.C.
42
7654311109821312 141
53
52
51
50
49
48
47
46
45
44
56
55
54
43
MAX9708
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
20 ______________________________________________________________________________________
Chip Information
PROCESS: BiCMOS
Pin Configurations (continued)
5859606162 5455565763
38
39
40
41
42
43
44
45
46
47
CPV
DD
INL-
N.C.
TQFP
TOP VIEW
OUTL+
OUTL+
OUTL-
OUTL-
N.C.
PGND
PGND
N.C.
OUTR+
5253
49
5051
OUTR+
OUTR-
OUTR-
N.C.
N.C.
FS1
MONO
INL+
REG
REG
GND
REG
SS
GND
INR-
V
DD
G1
INR+
N.C.
PGND
PGND
PGND
PV
DD
PV
DD
PV
DD
N.C.
TH0
TH1
TH2
33
34
35
36
37
TEMP
MUTE
SHDN
G2
N.C.
C1P
C1N
N.C.
PV
DD
PV
DD
N.C.
FS2
SYNCIN
N.C.
SYNCOUT
PV
DD
PGND
PGND
PGND
48 N.C.N.C.
64
N.C.
N.C.
2322212019 2726252418 2928 32313017
11
10
9
8
7
6
5
4
3
2
16
15
14
13
12
1
MAX9708
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 21
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
.)
56L THIN QFN.EPS
PACKAGE OUTLINE
21-0135
2
1
E
56L THIN QFN, 8x8x0.8mm
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
22 ______________________________________________________________________________________
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
21-0135
2
2
E
56L THIN QFN, 8x8x0.8mm
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
______________________________________________________________________________________ 23
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
.)
64L TQFP.EPS
B
1
2
21-0083
PACKAGE OUTLINE,
64L TQFP, 10x10x1.4mm
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D 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.
24 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2006 Maxim Integrated Products Printed USA 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
.)
B
2
2
21-0083
PACKAGE OUTLINE,
64L TQFP, 10x10x1.4mm
Freed
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