MAXIM MAX9708ETN

19-3678; Rev 0; 7/05
KIT
ATION
EVALU
E
L
B
A
AVAIL
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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.
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 Patented 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
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
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
PKG
CODE
MAX9708ETN
-40°C to +85°C
56 TQFN-EP**
T5688-3
MAX9708ECB*
-40°C to +85°C
64 TQFP-EP**
C64E-6
*Future product—Contact factory for availability.
**EP = Exposed paddle.
Pin Configurations appear at end of data sheet.
Simplified Block Diagram
2
FS1, FS2
SYNC
MAX9708
SYNCOUT
RIGHT
CHANNEL
GAIN
CONTROL
MONO
G1, G2
TH0, TH1,
TH2
AUDIO
INPUT
CLASS D
MODULATOR
LEFT
CHANNEL
MONO
2
3
TEMP
G1, G2
TH0, TH1,
TH2
MAX9708
SYNCOUT
CLASS D
MODULATOR
VDIGITAL
OUTPUT
PROTECTION
STEREO MODE
2
FS1, FS2
SYNC
GAIN
CONTROL
OUTPUT
PROTECTION
2
3
TEMP
MONO MODE
________________________________________________________________ Maxim Integrated Products
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.
1
MAX9708
General Description
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
ABSOLUTE MAXIMUM RATINGS
PVDD, VDD to PGND, GND .......................................-0.3 to +30V
PVDD to VDD ..........................................................-0.3V to +0.3V
OUTR+, OUTR-, OUTL+,
OUTL- to PGND, GND...........................-0.3V to (PVDD + 0.3V)
C1N to GND .............................................-0.3V to (PVDD + 0.3V)
C1P to GND..............................(PVDD - 0.3V) to (CPVDD + 0.3V)
CPVDD to GND ..........................................(PVDD - 0.3V) to +40V
All Other Pins to GND.............................................-0.3V to +12V
Continuous Input Current (except PVDD, VDD, OUTR+,
OUTR-, OUTL+, and OUTL-) ...........................................20mA
Continuous Power Dissipation (TA = +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 (θJC)
56-Pin Thin QFN… .......................................................0.6°C/W
64-Pin TQFP….................................................................2°C/W
Lead Temperature (soldering, 10s) .................................+300°C
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
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, 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. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA
= +25°C.) (Note 1)
PARAMETER
Supply Voltage Range
Shutdown Current
SYMBOL
VDD
ISHDN
CONDITIONS
Inferred from PSRR test
MIN
TYP
10
SHDN = low
0.1
Shutdown to Full Operation
tSON
100
Mute to Full Operation
tMUTE
100
Input Impedance
RIN
Output Offset Voltage
VOS
Common-Mode Rejection Ratio
Switch On-Resistance
Switching Frequency
PSRR
CMRR
RDS
fSW
ms
ms
125
G1 = 1, G2 = 1
40
63
90
G1 = 1, G2 = 0
25
43
60
G1= 0, G2 = 0
12
21
30
600
200mVP-P ripple
(Note 2)
68
dB
50
50
70
dB
f = 20Hz to 20kHz, input referred
70
One power switch
0.3
0.75
200
220
FS1
FS2
0
0
1
1 (SSM)
200
1
0
160
0
1
250
FS1 = FS2 = high (SSM)
SYNCIN Lock Range
Equal to fSW x 4
mV
90
90
fRIPPLE = 20kHz
DC, input referred
kΩ
kΩ
±30
fRIPPLE = 1kHz
Oscillator Spread Bandwidth
2
µA
85
PVDD = 10V to 18V
Power-Supply Rejection Ratio
V
1
50
AC-coupled input, measured between
OUT_+ and OUT_-
UNITS
18
G1 = 0, G2 = 1
SHDN = GND
Output Pulldown Resistance
MAX
180
kHz
±2
600
_______________________________________________________________________________________
Ω
%
1200
kHz
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, 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. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA
= +25°C.) (Note 1)
PARAMETER
Gain
SYMBOL
AV
TEMP Flag Threshold
TFLAG
TEMP Flag Accuracy
MIN
TYP
MAX
G1 = 0, G2 = 1
CONDITIONS
21.6
22.0
22.3
G1 = 1, G2 = 1
24.9
25.0
25.6
G1 = 1, G2 = 0
29.2
29.5
29.9
G1 = 0, G2 = 0
35.9
36.0
36.6
TH2
TH1
TH0
0
0
0
+80
0
0
1
+90
0
1
0
+100
0
1
1
+110
1
0
0
+120
1
0
1
+129
1
1
0
+139
1
1
1
+150
From +80°C to +140°C
dB
°C
±6
TEMP Flag Hysteresis
UNITS
2
°C
°C
STEREO MODE (RLOAD = 8Ω)
Quiescent Current
Output Power
POUT
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio
THD+N
SNR
η
Efficiency
Left-Right Channel Gain
Matching
MUTE = 1, RLOAD = ∞
20
30
MUTE = 0
5
11
f = 1kHz, THD = 10%, TA = +25°C,
RLOAD = 8Ω, PVDD = 18V
f = 1kHz, BW = 22Hz to 22kHz,
RLOAD = 8Ω, POUT = 8W
RLOAD = 8Ω, POUT = 10W
21
W
0.1
%
22Hz to 22kHz
91
A-weighted
96
RLOAD = 8Ω, L > 60µH, POUT = 15W + 15W,
f = 1kHz
POUT = 10W
20
mA
dB
87
%
0.02
dB
_______________________________________________________________________________________
3
MAX9708
ELECTRICAL CHARACTERISTICS (continued)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, 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. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA
= +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
Output Short-Circuit Current
Threshold
ISC
RLOAD = 0Ω
Click-and-Pop Level
KCP
Peak voltage, 32
samples/second,
A-weighted (Notes 2, 4)
MIN
TYP
MAX
2.4
Into shutdown
-63
Out of shutdown
-55
UNITS
A
dBV
MONO MODE (RLOAD = 4Ω, MONO = High)
Quiescent Current
Output Power
POUT
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio
Efficiency
MUTE = 1, RLOAD = ∞
20
MUTE = 0
5
f = 1kHz,
THD = 10%
RLOAD = 8Ω
23
RLOAD = 4Ω
42
f = 1kHz, BW = 22Hz to 22kHz,
RLOAD = 4Ω, POUT = 17W
SNR
η
RLOAD = 4Ω,
POUT = 10W
0.12
20Hz to 20kHz
91
A-weighted
95
4.8
A
Click-and-Pop Level
KCP
Peak voltage, 32
samples/second,
A-weighted (Notes 2, 4)
Into shutdown
-60
Out of shutdown
-63
dBV
DIGITAL INPUTS (SHDN, MUTE, G1, G2, FS1, FS2, TH0, TH1, TH2, SYNCIN, MONO)
Logic-Input Current
IIN
0 to 12V
VIL
dB
%
RLOAD = 0Ω
VIH
%
85
ISC
Logic-Input Low Voltage
W
RLOAD = 4Ω, L > 40µH, POUT = 42W,
f = 1kHz
Output Short-Circuit Current
Threshold
Logic-Input High Voltage
mA
1
µA
0.8
V
2.5
V
OPEN-DRAIN OUTPUTS (TEMP, SYNCOUT)
Open-Drain Output Low Voltage
Leakage Current
Note 1:
Note 2:
Note 3:
Note 4:
4
VOL
ILEAK
ISINK = 3mA
VPULLUP = 5.5V
0.4
0.2
V
µA
All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Inputs AC-coupled to GND.
The device is current limited. The maximum output power is obtained with an 8Ω load.
Testing performed with an 8Ω resistive load in series with a 68µH inductive load connected across BTL outputs. Mode transitions are controlled by SHDN.
_______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and
OUT_-, TA = +25°C, unless otherwise stated.)
10
RL = 8Ω
THD+N (%)
1
1
PVDD = 18V,
8Ω STEREO MODE,
POUT = 8.3W PER
CHANNEL
0.01
0.01
5
10
15
20
25
0.01
0
30
5
15
10
10
1k
10k
100k
OUTPUT POWER PER CHANNEL (W)
FREQUENCY (Hz)
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER
vs. SUPPLY VOLTAGE
NO-LOAD SUPPLY CURRENT
vs. SUPPLY VOLTAGE
70
60
50
40
30
PVDD = 18V, 8Ω
STEREO MODE
20
25
20
24
10% THD+N
15
10
1% THD+N
STEREO MODE
22
5
5
10
15
20
25
12
14
18
16
TA = -40°C
14
10
12
SHDN = 0
16
18
20
22
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
100
MAX9708 toc07
4.0
14
SUPPLY VOLTAGE (V)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
PVDD = 18V, 4Ω MONO MODE,
1kHz
10
3.0
2.5
THD+N (%)
SUPPLY CURRENT (nA)
16
SUPPLY VOLTAGE (V)
OUTPUT POWER PER CHANNEL (W)
3.5
18
10
10
30
TA = +25°C
TA = +85°C
20
12
0
10
MAX9708 toc06
80
RL = 8Ω
STEREO MODE
MAX9708 toc08
90
30
SUPPLY CURRENT (mA)
MAX9708 toc04
100
0
100
OUTPUT POWER PER CHANNEL (W)
OUTPUT POWER PER CHANNEL (W)
0
0.1
RL = 4Ω
0.1
0.1
1
MAX9708 toc05
THD+N (%)
10
EFFICIENCY (%)
PVDD = 12V,
STEREO MODE,
fIN = 1kHz
THD+N (%)
PVDD = 18V, 8Ω
STEREO MODE, 1kHz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
MAX9708 toc02
100
MAX9708 toc01
100
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
MAX9708 toc03
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
2.0
1
1.5
0.1
1.0
0.5
0.01
0
10
12
14
16
18
SUPPLY VOLTAGE (V)
20
22
0
10
20
30
40
50
60
OUTPUT POWER (W)
_______________________________________________________________________________________
5
MAX9708
Typical Operating Characteristics
Typical Operating Characteristics (continued)
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and
OUT_-, TA = +25°C, unless otherwise stated.)
0.1
0.1
10kHz RBW
20
OUTPUT AMPLITUDE (dBV)
PVDD = 18V,
4Ω MONO MODE,
POUT = 18W
THD+N (%)
THD+N (%)
1
30
MAX9708 toc10
PVDD = 12V,
MONO MODE,
fIN = 1kHz
RL = 4Ω
10
1
MAX9708 toc09
100
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY
10
MAX9708 toc11
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER
0
-10
-20
-30
-40
-50
-60
0.01
-70
0.01
5
10
15
20
25
10
100
1k
10k
100k
100k
1M
100M
10M
OUTPUT POWER (W)
FREQUENCY (Hz)
FREQUENCY (Hz)
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
OUTPUT FREQUENCY SPECTRUM
(SSM MODE)
OUTPUT FREQUENCY SPECTRUM
(FFM MODE)
0
-10
-20
-30
-40
-50
0
-40
-60
-80
MAX9708 toc14
-20
OUTPUT AMPLITUDE (dBV)
10
0
-20
OUTPUT AMPLITUDE (dBV)
10kHz RBW
20
MAX9708 toc13
30
MAX9708 toc12
0
OUTPUT AMPLITUDE (dBV)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
-40
-60
-80
-100
-100
-60
-70
1M
10M
FREQUENCY (Hz)
6
-120
-120
100k
100M
0
4
8
12
16
FREQUENCY (kHz)
20
24
0
4
8
12
16
FREQUENCY (kHz)
_______________________________________________________________________________________
20
24
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and
OUT_-, TA = +25°C, unless otherwise stated.)
70
60
50
40
40
30
20
MAX9708 toc17
MONO MODE,
10% THD+N,
PVDD = 18V
50
OUTPUT POWER (W)
OUTPUT POWER (W)
80
RL = 4Ω,
MONO MODE,
10% THD+N
50
60
MAX9708 toc16
90
EFFICIENCY (%)
60
MAX9708 toc15
100
OUTPUT POWER
vs. LOAD RESISTANCE
OUTPUT POWER
vs. SUPPLY VOLTAGE
EFFICIENCY vs. OUTPUT POWER
MAX9708
Typical Operating Characteristics (continued)
40
30
20
30
10
PVDD = 18V,
4Ω MONO MODE
20
10
0
0
10
20
30
40
50
60
0
10
12
14
16
OUTPUT POWER (W)
SUPPLY VOLTAGE (V)
OUTPUT POWER
vs. LOAD RESISTANCE
MUTE RESPONSE
18
4
6
8
25
MAX9708 toc18
STEREO MODE,
10% THD+N,
PVDD = 18V
12
10
LOAD RESISTANCE (Ω)
SHUTDOWN RESPONSE
MAX9708 toc19
30
OUTPUT POWER PER CHANNEL (W)
10
MAX9708 toc20
MUTE
5V/div
SHDN
5V/div
OUTPUT
50mV/div
OUTPUT
50mV/div
20
15
10
5
0
7
8
9
10
11
12
40ms/div
40ms/div
LOAD RESISTANCE (Ω)
_______________________________________________________________________________________
7
Typical Operating Characteristics (continued)
(PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO
= low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and
OUT_-, TA = +25°C, unless otherwise stated.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-70
-40
MAX9708 toc22
INPUT REFERRED
-65
CROSSTALK vs. FREQUENCY
-30
MAX9708 toc21
-60
-40
-50
-60
-50
-85
-90
CROSSTALK (dB)
PSRR (dB)
-75
-80
-60
-70
-80
-95
MAX9708 toc23
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
CMRR (dB)
-70
-80
-90
-90
-100
-100
-110
-100
-120
-110
-110
100
10
1k
10k
10
100k
100
1k
MAXIMUM STEADY-STATE OUTPUT POWER
vs. TEMPERATURE
30
25
20
15
10
MEASURED WITH THE EV KIT (TQFN
PACKAGE), JUNCTION TEMPERATURE
MAINTAINED AT +110°C
5
70
PVDD = 18V, 4Ω
MONO MODE, 1kHz,
FS1 = FS2 = 1
TH0 = TH1 = 1
TH2 = 0
60
OUTPUT POWER (W)
PVDD = 18V, 8Ω
STEREO MODE, 1kHz,
FS1 = FS2 = 1
TH0 = TH1 = 1
TH2 = 0
50
100k
40
30
20
MEASURED WITH THE EV KIT (TQFN
PACKAGE), JUNCTION TEMPERATURE
MAINTAINED AT +110°C
10
0
10k
MAXIMUM STEADY-STATE OUTPUT POWER
vs. TEMPERATURE
MAX9708 toc24
40
1k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
35
100
10
100k
10k
MAX9708 toc25
-105
OUTPUT POWER PER CHANNEL (W)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
0
30
40
50
60
70
30
AMBIENT TEMPERATURE (°C)
40
50
60
70
AMBIENT TEMPERATURE (°C)
Pin Description
PIN
NAME
FUNCTION
TQFP
TQFN
1, 8, 13, 16,
17, 32, 33, 41,
48, 49, 50, 55,
58, 63, 64
1, 12, 42, 43,
44, 55, 56
N.C.
2, 3, 4, 45, 46,
47, 56, 57
2, 3, 4, 39,
40, 41, 49, 50
PGND
Power Ground
5, 6, 7,
42, 43, 44
5, 6, 7,
36, 37, 38
PVDD
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.
8
No Connection. Not internally connected.
_______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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
CPVDD
12
11
14
13
SYNCIN
15
14
FS2
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
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
28
25
VDD
Analog Power Supply. Bypass to GND with a 0.1µF capacitor as close to pin as
possible.
29
26
INR-
Right-Channel Positive Input. In mono mode, INR+ is the positive input.
30
27
INR+
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 VREG 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
Charge-Pump Power Supply. Bypass to PVDD with a 1µF capacitor as close to the pin
as possible.
SYNCOUT Open-Drain, Slew-Rate Limited Clock Output. Pullup with a 10kΩ resistor to REG.
Clock Synchronization Input. Allows for synchronization of the internal oscillator with an
external clock. SYNCIN is internally pulled up to VREG with a 100kΩ resistor.
Frequency Select 2
Mono/Stereo Mode Input. Drive logic-high for mono mode. Drive logic-low for stereo
mode.
Soft-Start. Connect a 0.47µF capacitor to GND to utilize soft-start power-up sequence.
Right-Channel Negative Input. In mono mode, INR- is the negative input.
51, 52
45, 46
OUTR-
Right-Channel Negative Output
53, 54
47, 48
OUTR+
Right-Channel Positive Output
59, 60
51, 52
OUTL-
Left-Channel Negative Output
61, 62
53, 54
OUTL+
EP
EP
EP
Left-Channel Positive Output
Exposed Paddle. Connect to GND with multiple vias for best heat dissipation.
_______________________________________________________________________________________
9
MAX9708
Pin Description (continued)
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
MAX9708
Typical Application Circuits/Functional Diagrams
VDD
PVDD
0.1µF
47µF*
22, 23
(25, 26)
VDIGITAL
25 (28)
GND
5–7, 36–38
(5–7, 42-44)
VDD
PVDD
VDIGITAL
2–4, 39–41 49–50
(2–4, 45–47, 56–57)
PGND
10kΩ
15 (18) FS1
14 (15) FS2
13 (14)
SYNCOUT
CONTROL
SYNCIN
RF
1µF
+
LEFT
CHANNEL
1µF
-
11 (12)
17 (20) INL+
16 (19) INL-
MAX9708
PVDD
VBIAS
RIN
CLASS D
MODULATOR
AND H-BRIDGE
RIN
OUTL+
53, 54 (61, 62)
OUTL-
51, 52 (59, 60)
OUTR+
47, 48 (53, 54)
OUTR-
45, 46 (51, 52)
RF
RF
PVDD
1µF
+
RIGHT
CHANNEL
1µF
-
27 (30) INR+
RIN
MUX
26 (29) INR-
RIN
CLASS D
MODULATOR
AND H-BRIDGE
VBIAS
VDIGITAL
30 (35)
CPVDD
SHDN
31 (36)
MUTE
28 (31) G2
RF
CHARGE
PUMP
GAIN
CONTROL
29 (34) G1
18 (21) MONO
REGULATOR
TH0
35 (40)
34 (39)
TH1
TH2
33 (38)
VDIGITAL
9 (10)
C1N
8 (9)
REG
19, 20, 21 (22, 23, 24)
C1
0.1µF
CREG
0.01µF
32 (37)
10kΩ
SS
24 (27)
PVDD
C1P
TEMP
THERMAL SENSOR
10 (11)
C2
1µF
CSS
0.47µF
VDIGITAL
CONFIGURATION: TQFN STEREO MODE, SSM, INTERNAL OSCILLATOR, GAIN = 22dB, THERMAL SETTING = +120°C
( ) TQFP PACKAGE
*ADDITIONAL BULK CAPACITANCE
Figure 1. Typical Application and Functional Diagram in Stereo Mode
10
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
VDD
PVDD
47µF*
0.1µF
0.1µF
22, 23
(25, 26)
VDIGITAL
25 (28)
GND
15 (18) FS1
14 (15) FS2
5–7, 36–38
(5–7, 42–44)
VDD
PVDD
2–4, 39–41 49–50
(2–4, 45–47, 56–57)
VDIGITAL
PGND
10kΩ
SYNCOUT 11 (12)
CONTROL
13 (14) SYNCIN
RF
1µF
+
AUDIO
INPUT
1µF
-
17 (20) INR+
16 (19) INR-
MAX9708
PVDD
VBIAS
RIN
CLASS D
MODULATOR
AND H-BRIDGE
RIN
OUTL+
53, 54 (61, 62)
OUTL-
51, 52 (59, 60)
OUTR+
47, 48 (53, 54)
OUTR-
45, 46 (51, 52)
CPVDD
10 (11)
PVDD
RF
MUX
VDIGITAL
30 (35)
SHDN
31 (36)
MUTE
28 (31) G1
CHARGE
PUMP
GAIN
CONTROL
29 (34) G2
VDIGITAL
CLASS D
MODULATOR
AND H-BRIDGE
18 (21) MONO
REGULATOR
TH0
35 (40)
34 (39)
TH1
TH2
33 (38)
9 (10)
C1N
8 (9)
REG
19, 20, 21 (22, 23, 24)
C1
0.1µF
CREG
0.01µF
32 (37)
10kΩ
SS
24 (27)
PVDD
C1P
TEMP
THERMAL SENSOR
C2
1µF
CSS
0.47µF
VDIGITAL
VDIGITAL
CONFIGURATION: TQFN MONO MODE, SSM, INTERNAL OSCILLATOR, GAIN = 22dB, THERMAL SETTING = +120°C
( ) TQFP PACKAGE
*ADDITIONAL BULK CAPACITANCE
Figure 2. Typical Application and Functional Diagram in Mono Mode
______________________________________________________________________________________
11
MAX9708
Typical Application Circuits/Functional Diagrams (continued)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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
12
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.
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
Gain Selection
The MAX9708 features four pin-selectable gain settings;
see Table 2.
VDIGITAL
10kΩ
10kΩ
TO DIGITAL
INPUT
TEMP
0.1µF
Figure 3. An RC Filter Eliminates Transient During Switching
Table 1. MAX9708 Junction Temperature
Threshold Setting
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
G2
Spread-Spectrum Modulation (SSM) Mode
The MAX9708 features a unique, patented spreadspectrum (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 fixed-frequency 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.
Table 3. Switching Frequencies
Table 2. MAX9708 Gain Setting
G1
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.
GAIN (dB)
FS1
FS2
SYNCOUT
FREQUENCY (kHz)
MODULATION
Low
High
22
0
0
200
Fixed-Frequency
High
High
25
0
1
250
Fixed-Frequency
High
Low
29.5
1
0
160
Fixed-Frequency
Low
Low
36
1
1
200 ±4
Spread-Spectrum
______________________________________________________________________________________
13
MAX9708
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.
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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.
1µF
INR+
MAX9708
Applications Information
INR-
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 PVDD or VDD. If
PVDD and VDD are 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:
f−3dB =
14
1
1µF
Figure 4. Single-Ended Input Connections
Choose CIN so that 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 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 components 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.
2π RIN CIN
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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 PVDD to
PGND with a 0.1µF capacitor as close to each PVDD
pin as possible. A low-impedance, high-current powersupply connection to PVDD is assumed. Additional bulk
capacitance should be added as required depending
on the application and power-supply characteristics.
GND and PGND should be star-connected to system
ground. 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.
______________________________________________________________________________________
15
MAX9708
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.
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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:
• TA = +40°C
• POUT = 16W
• Efficiency (η) = 87%
• θJA = 21°C/W
First, the Class D amplifier’s power dissipation must be
calculated:
PDISS =
16W
POUT
− POUT =
− 16W = 2.4W
η
0.87
Then the power dissipation is used to calculate the die
temperature, TC, as follows:
TC = TA + PDISS × θJA = 40°C + 24W × 21°C / W = 90.4°C
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, 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.
16
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.
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
INR+
INR-
HIGHPASS
FILTER
RIGHT
AUDIO
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.
OUTR+
OUTR-
8Ω
FULLRANGE
SPEAKER
OUTL+
OUTL-
8Ω
FULLRANGE
SPEAKER
OUTR+
OUTR-
4Ω OR 8Ω
WOOFER
MONO
MAX9708
INL+
HIGHPASS
FILTER
LEFT
AUDIO
INLSYNCOUT
Σ
SYNCIN
INR+
INR-
LOWPASS
FILTER
MAX9708
VDIGITAL
MONO
INL+
INL-
OUTL+
OUTL-
Figure 5. Multiple Amplifiers Implement a 2.1 Audio System
______________________________________________________________________________________
17
MAX9708
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.
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
R1
56.2kΩ
R2, 56.2kΩ
R3
28kΩ
C1
47nF
C2
47nF
2
U1A
R4
28kΩ
RIGHT
AUDIO
INPUT
1
MAX4478
R5
56.2kΩ
BIAS
3
RIGHT
AUDIO
OUTPUT
R6, 56.2kΩ
R7
28kΩ
C3
47nF
C4
47nF
6
U1B
7
MAX4478
R8
56.2kΩ
BIAS
5
RIGHT AND LEFT OUTPUTS
ARE AC-COUPLED TO A
MAX9708 CONFIGURED AS
A STEREO AMPLIFIER
R9, 56.2kΩ
R10
28kΩ
C5
47nF
C6
47nF
9
U1C
R11
28kΩ
LEFT
AUDIO
INPUT
8
MAX4478
R12
56.2kΩ
BIAS
10
LEFT
AUDIO
OUTPUT
R13, 56.2kΩ
R14
28kΩ
C7
47nF
C8
47nF
13
U1D
14
MAX4478
R15
26.1kΩ
R16
13kΩ
BIAS
12
SUBWOOFER OUTPUT IS
AC-COUPLED TO A
MAX9708 CONFIGURED AS
A MONO AMPLIFIER
C9, 47nF
R17
26.1kΩ
R18
7.5kΩ
2
U2A
R19
26.1kΩ
C10
47nF
1
MAX4478
R20
13kΩ
BIAS
3
SUBWOOFER
AUDIO
OUTPUT
C11, 47nF
R21
28kΩ
R22
7.5kΩ
6
U2B
7
MAX4478
BIAS
5
NOTE:
OP-AMP POWER PINS OMITTED FOR CLARITY.
ALL RESISTORS ARE 1% OR BETTER.
ALL CAPACITORS ARE 5% OR BETTER.
Figure 6. Fully Differential Crossover Filters
18
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
35
34
33
G2
36
SHDN
37
TEMP
TH2
38
MUTE
TH1
39
TH0
40
PVDD
PGND
41
PVDD
PGND
42
PVDD
N.C.
PGND
TOP VIEW
32
31
30
29
N.C. 43
28 G1
N.C. 44
27 INR+
OUTR- 45
26 INR-
OUTR- 46
25 VDD
OUTR+ 47
24 SS
OUTR+ 48
23 GND
PGND 49
22 GND
PGND 50
21 REG
MAX9708
OUTL- 51
20 REG
OUTL- 52
19 REG
7
8
9
10
11
12
13
14
SYNCIN
FS2
6
N.C.
5
SYNCOUT
4
C1P
3
CPVDD
2
C1N
1
PVDD
INL-
15 FS1
PVDD
16
N.C. 56
PVDD
N.C. 55
PGND
INL+
PGND
MONO
17
N.C.
18
OUTL+ 54
PGND
OUTL+ 53
THIN QFN
______________________________________________________________________________________
19
MAX9708
Pin Configurations
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
MAX9708
Pin Configurations (continued)
N.C.
N.C.
OUTR-
OUTR+
OUTR-
OUTR+
N.C.
PGND
63 62 61 60 59 58
N.C.
64
PGND
OUTL-
OUTL-
N.C.
OUTL+
N.C.
OUTL+
TOP VIEW
57 56 55 54 53 52 51 50 49
N.C.
1
48 N.C.
PGND
2
47 PGND
PGND
3
46 PGND
PGND
4
45 PGND
PVDD
5
44 PVDD
PVDD
6
43 PVDD
PVDD
7
42 PVDD
N.C.
8
41 N.C.
C1N
9
MAX9708
40 TH0
C1P 10
39 TH1
CPVDD 11
38 TH2
SYNCOUT 12
37 TEMP
N.C. 13
36 MUTE
SYNCIN 14
35 SHDN
FS2 15
34 G2
N.C. 16
33 N.C.
N.C.
G1
INR+
INR-
VDD
SS
GND
GND
REG
REG
REG
INL+
MONO
FS1
INL-
N.C.
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
TQFP
Chip Information
PROCESS: BiCMOS
20
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
56L THIN QFN.EPS
______________________________________________________________________________________
21
MAX9708
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.)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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.)
22
______________________________________________________________________________________
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
64L TQFP.EPS
PACKAGE OUTLINE,
64L TQFP, 10x10x1.4mm
21-0083
B
1
2
______________________________________________________________________________________
23
MAX9708
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.)
MAX9708
20W/40W, Filterless, Spread-Spectrum,
Mono/Stereo, Class D Amplifier
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,
64L TQFP, 10x10x1.4mm
21-0083
B
2
2
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
© 2005 Maxim Integrated Products
Freed
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.