19-3681; Rev 0; 12/05
KIT
ATION
EVALU
E
L
B
A
IL
AVA
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
The MAX9706/MAX9707 combine three high-efficiency
Class D amplifiers with an active crossover to provide
stereo highpass outputs, and a mono lowpass output.
All three channels deliver up to 2.3W at 1% THD+N per
channel into 4Ω when operating from a 5V supply.
An internal active filter processes the stereo inputs (left
and right) into stereo highpass and mono lowpass outputs. The crossover frequency is pin-selectable to four
different frequencies to accommodate a variety of
speaker configurations. The internal Class D amplifiers
feature low-EMI, spread-spectrum outputs. No output
filters are required.
The MAX9706 features Maxim’s DirectDrive™ headphone
amplifier, providing ground-referenced headphone outputs without the need for bulky DC-coupling capacitors.
The headphone outputs are capable of delivering
95mW per channel into 16Ω from a 3.3V supply, and
are protected against ESD up to ±8kV.
The MAX9706/MAX9707 feature pin-programmable
gain, synchronization inputs and outputs, and a shutdown mode that reduces supply current to less than
1µA. All amplifiers feature click-and-pop suppression
circuitry. Both devices are fully specified over the -40°C
to +85°C extended temperature range and are available in the thermally enhanced 36-pin (6mm x 6mm x
0.8mm) thin QFN package.
Applications
Notebook Audio Solutions
Multimedia Monitors
2.1 Speaker Solutions
Portable DVD Players
Desktop PCs
Table-Top LCD TVs
Features
♦ Triple Class D Amplifiers Deliver 3 x 2.3W into 4Ω
♦ Internal Active Crossover Filter with Adjustable
Crossover Frequency
♦ Low-EMI, Spread-Spectrum Modulation
♦ Low 0.02% THD+N
♦ High PSRR (71dB)
♦ DirectDrive Headphone Amplifier (MAX9706)
♦ Enhanced Click-and-Pop Suppression
♦ Input and Output Modulator Synchronization
♦ Low-Power Shutdown Mode
♦ Up To 90% Efficiency
♦ Space-Saving (6mm x 6mm x 0.8mm) 36-Pin Thin
QFN Package
Ordering Information
PART
HP AMP
MAX9706ETX+
Yes
PIN-PACKAGE
36 Thin QFN
PKG CODE
T3666N-1
MAX9707ETX+
No
36 Thin QFN
T3666N-1
+Denotes lead-free package.
Note: These devices operate over the -40°C to +85°C temperature range.
Functional Diagrams and Pin Configurations appear at end
of data sheet.
Block Diagram
MAX9706
MAX9707
AUDIO IN
FULL-RANGE
TRANSDUCERS
AUDIO IN
LOW-FREQUENCY
TRANSDUCER
FREQUENCY
SELECT
SHDN
HEADPHONE
FULL-RANGE
TRANSDUCERS
LOW-FREQUENCY
TRANSDUCER
FREQUENCY
SELECT
SHDN
________________________________________________________________ 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
MAX9706/MAX9707
General Description
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ABSOLUTE MAXIMUM RATINGS
VDD, PVDD, HPVDD, CPVDD to GND ........................-0.3V to +6V
GND to PGND, CPGND.........................................-0.3V to +0.3V
CPVSS, VSS to GND..................................................-6V to +0.3V
C1N to GND ...........................................(CPVSS - 0.3V) to +0.3V
C1P to GND ...........................................-0.3V to (CPVDD + 0.3V)
HPL, HPR.....................................................................-3V to +3V
All Other Pins to GND.................................-0.3V to (VDD + 0.3V)
OUT_+, OUT_ -, Short Circuit to GND or PVDD ...........Continuous
OUT_+ Short Circuit to OUT_-....................................Continuous
HPR, HPL Short Circuit to GND..................................Continuous
MONO_OUT Short Circuit to GND or VDD ....................Continuous
Continuous Current (PVDD, OUT_+, OUT_-, PGND).............1.7A
Continuous Current (MONO_OUT, CPVDD, C1N, C1P,
CPGND, CPVSS, VSS, HPVDD, HPR, HPL) ......................0.85A
Continuous Current (all other pins) .....................................20mA
Continuous Power Dissipation (TA = +70°C)
Single-Layer Board
36-Pin TQFN (derate 26.3mW/°C above +70°C) .......2105mW
Multilayer Board
36-Pin TQFN (derate 35.7mW/°C above +70°C) .......2857mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
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
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
GND, FS0 = FS1 = GND (800Hz), MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT_+ and
OUT_-, unless otherwise noted, RL = ∞. Headphone load RLH connected between HPR/HPL to GND, RLH = ∞. CBIAS = 1µF to GND,
C1 = 1µF, C2 = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.) (Note 1)
PARAMETER
Speaker Amplifier Supply Voltage
Range
Headphone Amplifier Supply
Voltage Range
SYMBOL
VDD, PVDD Inferred from PSRR test
HPVDD,
CPVDD
Quiescent Supply Current
IDD
Shutdown Supply Current
ISHDN
Input Resistance
CONDITIONS
Inferred from PSRR test (MAX9706)
TYP
MAX
UNITS
4.5
5.5
V
3.0
5.5
V
Speaker mode
25
35
Headphone mode, HPS = VDD (MAX9706)
7
12
0.5
3
µA
25
35
kΩ
SHDN = GND
RIN
Turn-On Time, Shutdown to Full
Operation
MIN
15
Speaker mode
87
Headphone mode (MAX9706)
87
mA
ms
SPEAKER AMPLIFIERS (OUTL_, OUTR_, OUTM_)
Output Power (Note 2)
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio
POUT
THD+N
SNR
RL = 8Ω, THD+N = 1%
1.4
RL = 4Ω, THD+N = 1%
2.3
POUT = 1W,
bandwidth = 22Hz to
22kHz (Note 2)
RL = 8Ω, POUT = 1W
(Note 2)
RL = 8Ω
0.06
RL = 4Ω
0.07
%
Bandwidth =
22Hz to 22kHz
87
A-weighted
92
VDD = PVDD = 4.5V to 5.5V, TA = +25°C
Power-Supply Rejection Ratio
2
PSRR
100mVP-P ripple
(Note 3)
W
50
dB
71
f = 2kHz, OUTL_, OUTR_
51
f = 100Hz, OUTM_
65
_______________________________________________________________________________________
dB
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
GND, FS0 = FS1 = GND (800Hz), MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT_+ and
OUT_-, unless otherwise noted, RL = ∞. Headphone load RLH connected between HPR/HPL to GND, RLH = ∞. CBIAS = 1µF to GND,
C1 = 1µF, C2 = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
Speaker Path Gain (Note 4)
CONDITIONS
MIN
GAIN2 = 0
GAIN1 = 0
9
GAIN2 = 0
GAIN1 = 1
10.5
GAIN2 = 1
GAIN1 = 0
12
GAIN2 = 1
GAIN1 = 1
13.5
Channel-to-Channel Gain
Tracking
Crosstalk
CL
η
Efficiency
Class D Center Frequency
MAX
fOSC
MGAIN = GND
-4.5
MGAIN = float
-6
MGAIN = VDD
-7.5
%
dB
Right to left, left to right, fIN = 10kHz,
POUT = 1W
70
dB
No sustained oscillations
200
pF
RL = 8Ω, POUT = 3 x 1W, f = 800Hz
90
RL = 4Ω, POUT = 3 x 1W, f = 800Hz
88
%
FFM, SYNC_IN = GND
955
1100
1270
FFM, SYNC_IN = float
1140
1340
1540
kHz
1500
kHz
SSM, SYNC_IN = VDD
Class D Spreading Bandwidth
UNITS
dB
0.3
MONO Gain Offset (Note 5)
Maximum Capacitive Load
TYP
1150
SSM mode, SYNC_IN = VDD
SYNC_IN Frequency Lock Range
±50
1000
Output Offset Voltage
VOS
OUT_+ to OUT_-
Click-and-Pop Level
KCP
Peak voltage,
A-weighted, 32 samples
per second (Note 6)
kHz
14
Into shutdown
47
Out of shutdown
50
FS0 = 0
FS1 = 0
800
FS0 = 0
FS1 = 1
1066.7
FS0 = 1
FS1 = 0
1600
FS0 = 1
FS1 = 1
2133.3
mV
dBV
CROSSOVER FILTERS
Cutoff Frequency Accuracy
Crossover Frequency
Left-to-Right Cutoff Frequency
Tracking
(Note 7)
fXO
±15
±0.5
%
Hz
%
_______________________________________________________________________________________
3
MAX9706/MAX9707
ELECTRICAL CHARACTERISTICS (continued)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
GND, FS0 = FS1 = GND (800Hz), MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT_+ and
OUT_-, unless otherwise noted, RL = ∞. Headphone load RLH connected between HPR/HPL to GND, RLH = ∞. CBIAS = 1µF to GND,
C1 = 1µF, C2 = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
35
50
MAX
UNITS
HEADPHONE AMPLIFIERS (MAX9706) (HPS = VDD)
Output Power
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio
POUT
THD+N
SNR
HPVDD = 3.3V to 5V,
TA = +25°C, THD+N = 1%
(Notes 2, 7)
RL = 32Ω
mW
RL = 16Ω
95
VOUT = 1VRMS, f = 1kHz,
bandwidth = 22Hz to
22kHz
RL = 32Ω
0.02
RL = 16Ω
0.04
VOUT = 1VRMS
Bandwidth =
22Hz to 22kHz
96
A-weighted
100
%
HPVDD = 3V to 5.5V
Power-Supply Rejection Ratio
PSRR
Headphone Path Gain (Note 8)
Output Offset Voltage
VOSHP
Crosstalk
70
f = 1kHz, 100mVP-P ripple (Note 3)
80
65
GAIN2 = 0
0
GAIN2 = 1
3
±0.7
CL
dB
dB
±3
mV
HPL to HPR, HPR to HPL, fIN = 1kHz,
POUT = 32mW, RL = 32Ω
-60
dB
0.5
V/µs
No sustained oscillations
300
pF
Slew Rate
Maximum Capacitive Load
90
f = 20kHz, 100mVP-P ripple (Note 3)
HP_ to GND, TA = +25°C
dB
HPS Pullup Impedance
600
kΩ
Debounce Time
65
ms
1.4
kΩ
fOSC / 2
kHz
HPS = GND or SHDN = GND
Output Impedance in Shutdown
Charge-Pump Switching
Frequency
Click-and-Pop Level
fCP
KCP
Peak voltage,
A-weighted, 32 samples
per second (Note 6)
Into shutdown
52
Out of
shutdown
52
dBV
LINE-LEVEL MONO OUTPUT (MONO_OUT)
MONO_OUT Signal-Path Gain
0
Maximum Output Level
Total Harmonic Distortion Plus
Noise
Ω
1
VRMS
VOUT = 1VRMS, fIN = 100Hz, RL = 10kΩ,
bandwidth = 22Hz to 22kHz
0.01
%
Maximum Capacitive Load
No sustained oscillations
200
pF
4
RL = 10kΩ
THD+N
CL
dB
0.1
Output Impedance
_______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
GND, FS0 = FS1 = GND (800Hz), MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT_+ and
OUT_-, unless otherwise noted, RL = ∞. Headphone load RLH connected between HPR/HPL to GND, RLH = ∞. CBIAS = 1µF to GND,
C1 = 1µF, C2 = 1µF. TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS (GAIN1, GAIN2, FS0, FS1, SHDN, SYNC_IN, MGAIN)
Input-Voltage High
VINH
Input-Voltage Low
VINL
2
Input Leakage Current
GAIN1, GAIN2, FS0, FS1, SHDN
Input Current
SYNC_IN, MGAIN
Pullup Impedance
SYNC_IN, MGAIN
V
0.8
V
±1
µA
±50
200
µA
kΩ
DIGITAL OUTPUT (SYNC_OUT)
Output-Voltage High
VOH
IOH = 1mA
Output-Voltage Low
VOL
IOL = 1mA
Note 1:
Note 2:
Note 3:
Note 4:
VDD x
0.9
V
VDD x
0.1
V
All devices are 100% tested at TA = +25°C. Limits over temperature are guaranteed by design.
Measured at 2kHz for OUTL_, OUTR_, HPL, and HPR; measured at 100Hz for OUTM_.
PSRR is measured with the inputs AC-grounded.
Left/right signal-path gain is defined as:
(VOUT _ + ) − (VOUT _ − )
VIN _
MONO signal-path gain is defined as:
(VOUTM + ) − (VOUTM − )
(VINL ) + (VINR )
Note 5: MONO gain offset is measured with respect to speaker-path gain.
Note 6: Speaker mode testing performed with an 8Ω resistive load in series with a 68µH inductive load connected across BTL output.
Headphone mode testing performed with a 32Ω resistive load connected between HP_ and GND. Mode transitions are controlled
by SHDN.
Note 7: Headphone-path gain is defined as:
VHP
VIN _
Note 8: Guaranteed by design only.
_______________________________________________________________________________________
5
MAX9706/MAX9707
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics—Speaker Mode
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
VDD = 5V
RL = 4Ω
OUTPUT POWER = 1.5W
VDD = 5V
RL = 8Ω
OUTPUT POWER = 900mW
0.1
OUTL AND OUTR
0.1
0.01
OUTM
1k
10k
100k
100
1k
10k
0
100k
0.5
1.0
1.5
2.0
2.5
3.0
FREQUENCY (Hz)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
fIN = 2kHz
0.1
fIN = 200Hz
MAX9706 toc05
1
SYNC_IN = FLOAT
0.1
0.01
fIN = 10kHz
SYNC_IN = VDD
0.9
10
1
SYNC_IN = 2MHz
0.1
0.01
SYNC_IN = GND
0.001
0.6
VDD = 5V
RL = 8Ω
fIN = 1kHz
SYNC_IN = 1.4MHz
SYNC_IN = 0.8MHz
0.001
0.3
100
THD+N (%)
1
VDD = 5V
RL = 8Ω
fIN = 1kHz
10
THD+N (%)
10
0.01
100
MAX9706 toc06
FREQUENCY (Hz)
VDD = 5V
RL = 8Ω
0
0.1
0.001
10
MAX9706 toc04
100
100
fIN = 2kHz
fIN = 200Hz
fIN = 10kHz
0.001
10
1
0.01
OUTM
0.001
VDD = 5V
RL = 4Ω
10
THD+N (%)
OUTL AND OUTR
0.01
1.2
OUTPUT POWER (W)
6
100
1
THD+N (%)
THD+N (%)
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9706 toc03
10
MAX9706 toc01
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9706 toc02
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
THD+N (%)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
1.5
1.8
0.001
0
0.5
1.0
OUTPUT POWER (W)
1.5
2.0
0
0.5
1.0
OUTPUT POWER (W)
_______________________________________________________________________________________
1.5
2.0
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
OUTPUT POWER
vs. SUPPLY VOLTAGE
2.0
1.5
THD+N = 1%
2.5
2.0
1.0
1.0
0.5
0.5
0
THD+N = 1%
4.9
5.1
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
PSRR (dB)
50
40
30
POUT = POUTL + POUTR + POUTM
fIN = 800Hz
0
1
2
3
OUTPUT POWER (W)
4
OUTL
OUTR
5.1
5.3
5.5
0
SSM MODE
VOUT = -60dB
f = 1kHz
RL = 8Ω
UNWEIGHTED
-20
-40
-60
-80
-100
-120
-110
-120
5
4.9
OUTPUT FREQUENCY SPECTRUM
-90
-100
20
10
OUTM
-40
-50
-60
-70
-80
4.7
SUPPLY VOLTAGE (V)
VRIPPLE = 100mVP-P
RL = 8Ω
-30
60
THD+N = 1%
4.5
MAX9706 toc11
MAX9706 toc10
0
-10
-20
RL = 4Ω RL = 8Ω
70
1.0
5.5
5.3
EFFICIENCY vs. OUTPUT POWER
80
0
4.7
SUPPLY VOLTAGE (V)
90
1.5
0
4.5
LOAD RESISTANCE (Ω)
100
THD+N = 10%
2.0
0.5
OUTPUT MAGNITUDE (dBV)
100
10
f = 1kHz
RL = 8Ω
2.5
0
1
EFFICIENCY (%)
3.0
1.5
3.0
MAX9706 toc12
2.5
THD+N = 10%
OUTPUT POWER (W)
THD+N = 10%
OUTPUT POWER (W)
OUTPUT POWER (W)
3.0
f = 1kHz
RL = 4Ω
3.5
MAX9706 toc08
VDD = 5V
f = 1kHz
3.5
4.0
MAX9706 toc07
4.0
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9706 toc09
OUTPUT POWER
vs. LOAD RESISTANCE
-140
10
100
1k
FREQUENCY (Hz)
10k
100k
0
5
10
15
20
FREQUENCY (kHz)
_______________________________________________________________________________________
7
MAX9706/MAX9707
Typical Operating Characteristics—Speaker Mode (continued)
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
Typical Operating Characteristics—Speaker Mode (continued)
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
-80
-100
-120
MAX9706 toc14
-10
-20
-30
-40
-50
5
10
-50
-80
0
1
10
100
1000
0
1
FREQUENCY (MHz)
TURN-ON/-OFF RESPONSE
20
fXO = 800Hz
100
1000
AMPLITUDE vs. FREQUENCY
20
0
-10
-20
0
-10
-20
-30
-30
-40
-40
-50
fXO = 2.1kHz
10
AMPLITUDE (dBV)
200mA/div
AMPLITUDE (dBV)
10
2V/div
10
FREQUENCY (MHz)
AMPLITUDE vs. FREQUENCY
MAX9706 toc16
-50
10
100
1k
FREQUENCY (Hz)
8
-40
-70
FREQUENCY (kHz)
20ms/div
-30
-60
20
15
-20
-70
MAX9706 toc17
0
0
-10
-60
-80
-140
RBW = 10kHz
INPUT AC-GROUNDED
10
MAX9706 toc18
-60
0
20
OUTPUT AMPLITUDE (dBV)
-40
RBW = 10kHz
INPUT AC-GROUNDED
10
OUTPUT AMPLITUDE (dBV)
SSM MODE
VOUT = -60dB
f = 1kHz
RL = 8Ω
A-WEIGHTED
-20
20
MAX9706 toc13
0
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
MAX9706 toc15
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
OUTPUT FREQUENCY SPECTRUM
OUTPUT MAGNITUDE (dBV)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
10k
100k
10
100
1k
FREQUENCY (Hz)
_______________________________________________________________________________________
10k
100k
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
HPVDD = 3.3V
RL = 16Ω
HPVDD = 3.3V
RL = 32Ω
10
OUTPUT POWER = 25mW
0.1
0.01
0.1
OUTPUT POWER = 10mW
0.01
OUTPUT POWER = 75mW
HPVDD = 5V
RL = 16Ω
1
THD+N (%)
1
THD+N (%)
THD+N (%)
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9706 toc21
10
MAX9706 toc19
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9706 toc20
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
OUTPUT POWER = 20mW
0.1
0.01
OUTPUT POWER = 80mW
OUTPUT POWER = 35mW
0.001
0.001
1k
10k
100k
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
100
0.01
100
1
fIN = 1kHz
0.1
fIN = 200Hz
0.01
HPVDD = 3.3V
RL = 32Ω
10
THD+N (%)
10
THD+N (%)
OUTPUT POWER = 10mW
HPVDD = 3.3V
RL = 16Ω
MAX9706 toc24
FREQUENCY (Hz)
1
THD+N (%)
100
FREQUENCY (Hz)
HPVDD = 5V
RL = 32Ω
0.1
0.001
10
MAX9706 toc23
10
100
MAX9706 toc22
10
1
fIN = 1kHz
0.1
fIN = 10kHz
0.01
fIN = 10kHz
OUTPUT POWER = 35mW
fIN = 200Hz
0.001
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
0
15
30
45
60
75
90 105 120 135
OUTPUT POWER (mW)
0
10
20
30
40
50
60
70
OUTPUT POWER (mW)
_______________________________________________________________________________________
9
MAX9706/MAX9707
Typical Operating Characteristics—Headphone Mode
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
Typical Operating Characteristics—Headphone Mode (continued)
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
fIN = 10kHz
0.1
fIN = 1kHz
0.01
1
fIN = 10kHz
0.1
140
fIN = 1kHz
100
THD+N = 10%
80
60
40
0.01
20
fIN = 200Hz
fIN = 200Hz
0.001
20
40
60
80
100
120
10
20
30
40
0
50
60
OUTPUT POWER (mW)
OUTPUT POWER
vs. LOAD RESISTANCE
OUTPUT POWER
vs. HEADPHONE SUPPLY VOLTAGE
THD+N = 1%
THD+N = 10%
60
40
0
110
VRIPPLE ON VDD AND HPVDD = 100mVP-P
INPUTS AC-GROUNDED
-20
RL = 16Ω
-40
PSRR (dB)
100
90
70
LEFT
-60
-80
RL = 32Ω
50
THD+N = 1%
20
10
100
LOAD RESISTANCE (Ω)
1000
RIGHT
-100
-120
30
0
1000
100
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9706 toc29
120
130
OUTPUT POWER (mW)
HPVDD = 5V
f = 1kHz
10
70
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
140
80
0
MAX9706 toc28
0
THD+N = 1%
MAX9706 toc30
0.001
10
HPVDD = 3.3V
f = 1kHz
120
MAX9706 toc27
10
THD+N (%)
1
HPVDD = 5V
RL = 32Ω
OUTPUT POWER (mW)
HPVDD = 5V
RL = 16Ω
10
THD+N (%)
100
MAX9706 toc25
100
OUTPUT POWER
vs. LOAD RESISTANCE
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9706 toc26
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
OUTPUT POWER (mW)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
3.0
3.5
4.0
4.5
HPVDD (V)
5.0
5.5
10
100
1k
FREQUENCY (Hz)
______________________________________________________________________________________
10k
100k
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
VRIPPLE = 100mVP-P
INPUTS AC-GROUNDED
-20
RL = 32Ω
POUT = 32mW
-10
CROSSTALK (dB)
PSRR (dB)
-60
RIGHT
-80
-30
-40
LEFT TO RIGHT
-50
-60
-100
-120
1k
10k
100k
100
30
HPS = GND
HPVDD = 3.3V
20
HPS = VDD
VDD = 5V
10
1k
10k
50
C1 = C2 = 0.22µF
100k
15
20
25
30
35
40
45
FREQUENCY (Hz)
LOAD (Ω)
OUTPUT FREQUENCY SPECTRUM
TURN-ON/-OFF RESPONSE
50
MAX9706 toc36
0
VOUT = -60dBV
f = 1kHz
RL = 32Ω
-20
OUTPUT MAGNITUDE (dBV)
SUPPLY CURRENT (mA)
MAX9706 toc34
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE = IVDD + IHPVDD
60
20
10
FREQUENCY (Hz)
40
70
MAX9706 toc35
100
C1 = C2 = 0.47µF
30
RIGHT TO LEFT
-80
10
80
40
-70
LEFT
f = 1kHz
THD+N = 1%
C1 = C2 = 1µF
90
OUTPUT POWER (mW)
-20
-40
100
MAX9706 toc32
0
MAX9706 toc31
0
OUTPUT POWER
vs. CHARGE-PUMP CAPACITANCE
CROSSTALK vs. FREQUENCY
MAX9706 toc33
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
-40
2V/div
-60
-80
1V/div
-100
-120
-140
0
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
0
5
10
15
20
100ms/div
FREQUENCY (kHz)
______________________________________________________________________________________
11
MAX9706/MAX9707
Typical Operating Characteristics—Headphone Mode (continued)
(VDD = PVDD = HPVDD = 5V, GND = PGND = CPGND = 0V, SHDN = VDD, GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (800Hz),
MGAIN = float (-6dB), SYNC_IN = VDD (SSM), speaker load RL connected between OUT+ and OUT-, unless otherwise noted, RL = ∞.
Headphone load RLH connected between HPR/HPL to GND. CBIAS = 1µF to GND, 1µF capacitor between C1P and C1N, CVSS = 1µF.
TA = TMIN to TMAX, unless otherwise noted. Typical values at TA = +25°C.)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Pin Description
PIN
NAME
FUNCTION
MAX9706
MAX9707
1
1
BIAS
Internal Bias. Bypass BIAS to GND with a 1µF capacitor.
2
2
GND
Ground. Star connect to PGND (see the Supply Bypassing, Layout, and Grounding section).
3
3
VDD
Main Power Supply. Connect VDD to a low-noise 5V source. Bypass VDD to GND with a 1µF
capacitor.
4
4
5, 23, 31
5, 23, 31
6
7
Synchronization Clock Output. Connect SYNC_OUT to other Class D amplifiers to maintain
SYNC_OUT synchronization. SYNC_OUT is a CMOS output proportional to VDD. Float SYNC_OUT, if not
used.
PGND
Power Ground. PGND is the ground connection for the speaker amplifiers.
6
OUTL-
Left-Speaker Negative Terminal
7
OUTL+
Left-Speaker Positive Terminal
8, 20, 34
8, 20, 34
PVDD
Output Power Supply. PVDD is the power connection for the speaker amplifiers. Connect to
VDD. Bypass each PVDD to its corresponding PGND with a 1µF capacitor.
9
—
CPVDD
Charge-Pump Positive Supply. Connect CPVDD to HPVDD. Bypass CPVDD to CPGND with a
1µF capacitor.
10
—
C1P
Charge-Pump Flying Capacitor Positive Terminal. Connect a 1µF capacitor from C1P to C1N.
11
—
CPGND
12
—
C1N
13
—
CPVSS
14
14
SYNC_IN
Frequency Select or External Clock Input. Connect SYNC_IN to GND, VDD, leave floating, or
drive with an externally generated clock to control the switching frequency of the Class D
amplifiers. See Table 1.
15
—
HPS
Headphone Sense. HPS is a digital input with a pullup resistor to detect the connection of a
headphone. When HPS is high, the headphone amplifier is enabled and the Class D speaker
amplifiers are disabled. See the Headphone Sense Input (HPS) section.
12
Charge-Pump Ground. Connect to PGND.
Charge-Pump Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1N to C1P.
Negative Supply Charge-Pump Output. Bypass CPVSS to PGND with a 1µF capacitor.
Connect CPVSS to VSS.
16
—
VSS
Headphone Amplifier Negative Supply. Connect VSS to CPVSS.
17
—
HPR
Right Headphone Output
18
—
HPL
Left Headphone Output
19
—
HPVDD
Positive Supply for Headphone Amplifiers. Connect HPVDD to VDD. Bypass HPVDD to PGND
with a 0.1µF capacitor.
21
21
OUTR+
Right-Speaker Positive Terminal
22
22
OUTR-
Right-Speaker Negative Terminal
Shutdown Input. Drive SHDN low to put the MAX9706/MAX9707 in low-power shutdown mode.
Drive SHDN high or connect to VDD to enable normal operation.
24
24
SHDN
25
25
FS0
26
26
FS1
Crossover Frequency Select. Connect FS0 and FS1 to GND or VDD to set the crossover
frequency. See Table 4.
______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
PIN
NAME
FUNCTION
MAX9706
MAX9707
27
27
INR
28
28
MGAIN
Mono Gain Control. Connect MGAIN to GND, VDD, or leave floating to set the gain of the
MONO channel with respect to the left and right channels. See Table 3.
29
29
GAIN2
Amplifier Gain-Control Input. Connect GAIN1 and GAIN2 to GND or VDD to set the gain of the
left and right channels. See Tables 2 and 4.
30
30
GAIN1
Amplifier Gain-Control Input. Connect GAIN1 and GAIN2 to GND or VDD to set the gain of the
left and right channels. See Tables 2 and 4.
32
32
OUTM-
Mono-Speaker Negative Terminal
33
33
OUTM+
Mono-Speaker Positive Terminal
35
35
MONO_OUT
Mono Line-Level Output. MONO_OUT is the monaural output of the summed left and right lowfrequency signals.
36
36
INL
Left-Channel Audio Input. Connect the left-channel audio signal to INL with a series capacitor.
INL has a 25kΩ typical input impedance.
—
9–13,
16–19
N.C.
No Connection. Not internally connected.
—
15
I.C.
Internally Connected. Connect to GND.
EP
EP
EP
Exposed Pad. The external pad lowers the package’s thermal impedance by providing a
direct heat conduction path from the die to the PC board. The exposed pad is not internally
connected. Connect the exposed pad to GND.
Right-Channel Audio Input. Connect the right-channel audio signal to INR with a series
capacitor. INR has a 25kΩ typical input impedance.
Detailed Description
The MAX9706/MAX9707 combine three high-efficiency
Class D amplifiers with an active crossover to provide
stereo highpass outputs, and a mono lowpass output
(Figure 1). All three channels deliver up to 2.3W per
channel into 4Ω when operating from a 5V supply.
An internal active filter processes the stereo inputs (left
and right) into stereo highpass and mono lowpass outputs. The crossover frequency is pin-selectable to four
different frequencies to accommodate a variety of
speaker configurations.
The internal Class D amplifiers feature low-EMI, spreadspectrum outputs. No output filters are required.
The MAX9706 features Maxim’s DirectDrive headphone
amplifier, providing ground-referenced headphone outputs without the need for bulky coupling capacitors.
The headphone outputs are capable of delivering
95mW per channel into 16Ω from a 3.3V supply, and
are protected against ESD up to ±8kV.
MAX9706
MAX9707
HPF
CLASS D
AMPLIFIER
LPF
CLASS D
AMPLIFIER
HPF
CLASS D
AMPLIFIER
LEFT IN
RIGHT IN
Figure 1. Speaker Arrangement
______________________________________________________________________________________
13
MAX9706/MAX9707
Pin Description (continued)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Class D Speaker Amplifier
Operating Modes
Spread-spectrum modulation and synchronizable switching frequency significantly reduce EMI emissions.
Comparators monitor the audio inputs and compare the
complementary input voltages to a sawtooth waveform.
The comparators trip when the input magnitude of the
sawtooth exceeds their corresponding input voltage. Both
comparators reset at a fixed time after the rising edge of
the second comparator trip point, generating a minimumwidth pulse (tON(MIN),100ns typ) at the output of the second comparator (Figure 2). As the input voltage increases
or decreases, the duration of the pulse at one output
increases while the other output pulse duration remains
the same. This causes the net voltage across the speaker
(VOUT+ - VOUT-) to change. The minimum-width pulse
helps the device to achieve high levels of linearity.
Fixed-Frequency (FFM) Mode
The MAX9706/MAX9707 feature two fixed-frequency
modes. Connect SYNC_IN to GND to select a 1.1MHz
switching frequency. Float SYNC to select a 1.34MHz
switching frequency. The frequency spectrum of the
MAX9706/MAX9707 consists of the fundamental
switching frequency and its associated harmonics (see
the Wideband Output Spectrum graph in the Typical
Operating Characteristics). Program the switching frequency so the harmonics do not fall within a sensitive
frequency band (Table 1). Audio reproduction is not
affected by changing the switching frequency.
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT_+ - VOUT_-
Figure 2. Outputs with an Input Signal Applied (FFM Mode)
14
______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
tSW
tSW
Table 1. Operating Modes
SYNC_IN
MODE
GND
FFM with fOSC = 1100kHz
FLOAT
FFM with fOSC = 1340kHz
VDD
SSM with fOSC = 1150kHz ±50kHz
Clocked
FFM with fOSC = external clock frequency
tSW
tSW
VIN_-
VIN_+
OUT_-
OUT_+
tON(MIN)
VOUT_+ - VOUT_-
Figure 3. Output with an Input Signal Applied (SSM Mode)
______________________________________________________________________________________
15
MAX9706/MAX9707
Spread-Spectrum (SSM) Mode
The MAX9706/MAX9707 feature a unique spread-spectrum mode that flattens the wideband spectral components, improving EMI emissions that can be radiated by
the speaker and cables. Enable SSM mode by setting
SYNC_IN = VDD (Table 1). In SSM mode, the switching
frequency varies randomly by ±50kHz around the center frequency (1.15MHz). The modulation scheme
remains the same, but the period of the sawtooth waveform changes from cycle to cycle (Figure 3). 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. A proprietary amplifier
topology ensures this does not corrupt the noise floor in
the audio bandwidth.
External Clock Mode
The SYNC_IN input allows the MAX9706/MAX9707 to
be synchronized to an external clock, or another Maxim
Class D amplifier. This creates a fully synchronous system, minimizing clock intermodulation, and allocating
spectral components of the switching harmonics to
insensitive frequency bands. Applying a TTL clock signal between 1MHz and 1.5MHz to SYNC_IN synchronizes the MAX9706/MAX9707. The period of the
SYNC_IN clock can be randomized, allowing the
MAX9706/MAX9707 to be synchronized to another
Maxim Class D amplifier operating in SSM mode.
SYNC_OUT allows several MAX9706/MAX9707s to be
cascaded. The synchronized output minimizes any
interference due to clock intermodulation caused by
the switching spread between single devices. The
modulation scheme remains the same when using
SYNC_OUT, and audio reproduction is not affected.
Leave SYNC_OUT floating if not used.
Filterless Modulation/Common-Mode Idle
The MAX9706/MAX9707 use Maxim’s unique modulation scheme that eliminates the LC filter required by traditional Class D amplifiers, improving efficiency,
reducing component count, conserving board space
and system cost. Conventional Class D amplifiers output a 50% duty-cycle square wave when no signal is
present. With no filter, the square wave appears across
the load as a DC voltage, resulting in finite load current,
increasing power consumption, especially when idling.
When no signal is present at the input of the
MAX9706/MAX9707, the outputs switch as shown in
Figure 4. Because the MAX9706/MAX9707 drive the
speaker differentially, the two outputs cancel each
other, resulting in no net idle-mode voltage across the
speaker, minimizing power consumption.
Efficiency
Efficiency loss of a Class D amplifier is due to the
switching 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 Class AB 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 MAX9706/MAX9707 still
exhibit >90% efficiencies under the same conditions
(Figure 5).
Signal Path Gain
The MAX9706/MAX9707 feature four selectable speaker gain and two headphone gain settings controlled by
two gain-control inputs GAIN1 and GAIN2 (see Table 2).
Note that the stereo headphone output is full bandwidth, but the stereo speaker outputs are highpass filtered by the crossover circuitry.
Table 2. Speaker Gain
SPEAKER
GAIN (dB)
MAX9706 HEADPHONE
GAIN (dB)
0
+9
0
1
+10.5
0
0
+12
+3
1
+13.5
+3
GAIN2
GAIN1
0
0
1
1
100
VIN_ = 0V
90
80
OUT_-
EFFICIENCY (%)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
MAX9706
POUT PER CHANNEL
70
60
50
40
30
OUT_+
20
VDD = 5V
fIN = 1kHz
RL = 8Ω
CLASS AB
TOTAL POUT
10
0
0
VOUT_+ - VOUT_- = 0V
Figure 4. Outputs with No Input Signal
16
0.2
0.4
0.6
0.8
OUTPUT POWER (W)
Figure 5. Efficiency vs. Class AB Efficiency
______________________________________________________________________________________
1.0
1.2
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
MAX9706/MAX9707
MGAIN
MONO SPEAKER GAIN
OFFSET (dB)
GND
-4.5
FLOATING
-6.0
VDD
-7.5
Table 4. Crossover Frequency Selection
AMPLITUDE (dB)
Table 3. Mono Speaker Gain
HP FUNCTION
2nd-ORDER SLOPE
LP FUNCTION
2nd-ORDER SLOPE
CROSSOVER
FREQUENCY (fXO) (Hz)
FS0
FS1
0
0
800
0
1
1066.7
1
0
1600
1
1
2133.3
FREQUENCY (Hz)
fX
Figure 6. Crossover Frequency
Mono Output
Headphone Amplifier (MAX9706)
The left and right channels are summed and passed
through a lowpass filter to generate the mono output.
The mono speaker gain offset is an attenuation of the
selected speaker gain. The MAX9706/MAX9707 offer
three options for this summing gain. Select mono output gain by setting MGAIN high, low, or leave floating
(see Table 3).
The left- and right-speaker impedance should be twice
that of the MONO channel (8Ω L/R, 4Ω MONO), then
from the same voltage swing, the mono speaker will
have 2 times the power. Over the left and right mono
channels, a 1.5dB increase improves matching
between the high- and low-frequency drivers.
In conventional single-supply headphone amplifiers,
the output-coupling capacitor is a major contributor of
audible clicks and pops. Upon startup, the amplifier
charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, during shutdown, the
capacitor is discharged to GND. This results in a DC
shift across the capacitor, which in turn appears as an
audible transient at the speaker. Since the MAX9706
headphone amplifier does not require output-coupling
capacitors, no audible transients appear.
The MAX9706 offers 0dB and 3dB headphone amplifier
gain settings controlled through the GAIN2 gain-select
input (see Table 2).
Crossover Frequency
DirectDrive
Traditional single-supply headphone amplifiers have
outputs biased at a nominal DC voltage (typically half
the supply) for maximum dynamic range. Large coupling capacitors are needed to block this DC bias from
the headphone. Without these capacitors, a significant
amount of DC current flows to the headphone, resulting
in unnecessary power dissipation and possible damage to both headphone and headphone amplifier.
Maxim’s DirectDrive architecture uses a charge pump
to create an internal negative supply voltage. This
allows the headphone outputs of the MAX9706 to be
biased at GND, almost doubling dynamic range while
operating from a single supply (Figure 7). With no DC
component, there is no need for the large DC-blocking capacitors. Instead of two large (220µF, typical)
The MAX9706/MAX9707 feature an internal active filter
with adjustable crossover frequency (fXO) for use with a
low-frequency transducer. The crossover filter consists of
a complementary 2nd-order lowpass and 2nd-order
highpass Butterworth filter (Figure 6). Crossover frequency is variable over the 800Hz to 2133.3Hz range to
accommodate different speaker types. There are four
selectable crossover frequencies selected by FS0 and
FS1 (Table 4).
The BTL outputs provide the option of phase-inverting
the mono (LF) output with respect to the main (L/R) outputs. Depending on the speaker placement and distance from the listener, this can smooth the crossover
transition between low and high frequencies.
______________________________________________________________________________________
17
tantalum-blocking capacitors, the MAX9706 charge
pump requires two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone amplifier. See the
Output Power vs. Charge-Pump Capacitance graph in
the Typical Operating Characteristics for details on sizing charge-pump capacitors. There is a low DC voltage
on the driver outputs due to amplifier offset. However,
the offset of the MAX9706 is typically 1.7mV, which,
when combined with a 32Ω load, results in less than
53µA of DC current flow to the headphones.
In addition to the cost and size disadvantages of the
DC-blocking capacitors required by conventional headphone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal (Figure 8). Previous attempts at eliminating the output-coupling capacitors involved biasing the
headphone return (sleeve) to the DC bias voltage of the
headphone amplifiers. This method raises some issues:
1) The sleeve is typically grounded to the chassis.
Using the midrail biasing approach, the sleeve
must be isolated from system ground, complicating product design.
VDD
VDD / 2
GND
CONVENTIONAL AMPLIFIER
BIASING SCHEME
+VDD
SGND
2)
During an ESD strike, the driver’s ESD structures
are the only path to system ground. Thus, the driver must be able to withstand the full ESD strike.
When using the headphone jack as a line out to other
equipment, the bias voltage on the sleeve may conflict
with the ground potential from other equipment, resulting in possible damage to the drivers.
Charge Pump
The MAX9706 features a low-noise charge pump. The
switching frequency of the charge pump is one-half the
switching frequency of the Class D amplifier, regardless
of the operating mode. When SYNC_IN is driven externally, the charge pump switches at 1/2 fSYNC_IN. When
SYNC_IN = V DD , the charge pump switches with a
spread-spectrum pattern. The nominal switching frequency is well beyond the audio range, and thus does
not interfere with the audio signals, resulting in an SNR of
96dB. The switch drivers feature a controlled switching
speed that minimizes noise generated by turn-on and
turn-off transients. By limiting the switching speed of the
charge pump, the di/dt noise caused by the parasitic
bond wire and trace inductance is minimized. Although
not typically required, additional high-frequency noise
attenuation can be achieved by increasing the size of the
charge-pump reservoir capacitor C2 (see the Functional
Diagram/Typical Operating Circuits). The charge pump is
active in both speaker and headphone modes.
-VDD
DirectDrive AMPLIFIER
BIASING SCHEME
Figure 7. Traditional Amplifier Output vs. MAX9706 DirectDrive
Output
0
-5
ATTENUATION (dB)
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
-10
-15
DirectDrive
330μF
220μF
100μF
33μF
-20
-25
-30
RL = 16Ω
-35
100
10
FREQUENCY (Hz)
Figure 8. Low-Frequency Rolloff
18
______________________________________________________________________________________
1000
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Click-and-Pop Suppression
The MAX9706/MAX9707 feature comprehensive clickand-pop suppression that eliminates audible transients
on startup and shutdown.
While in shutdown, the H-bridge is in a high-impedance
state. During startup or power-up, the input amplifiers
are muted and an internal loop sets the modulator bias
voltages to the correct levels, preventing clicks and
pops when the H-bridge is subsequently enabled.
VDD
MAX9706
600kΩ
SHDN
SHUTDOWN
CONTROL
HPS
HPL
HPR
1.4kΩ
1.4kΩ
Current Limit and Thermal Protection
The MAX9706/MAX9707 feature current limiting and
thermal protection to protect the device from short circuits and overcurrent conditions. If the current on any
output exceeds the current limit (1.5A typ) the internal
circuitry shuts off for 50µs then turns back on. If the
overload condition is still present after 50µs, the internal
circuitry shuts off again. The amplifier output pulses in
the event of a continuous overcurrent condition. The
headphone amplifier outputs become high impedance
in the event of an overcurrent condition. The speaker
amplifier’s current-limiting protection clamps the output
current without shutting down the outputs.
The MAX9706/MAX9707 feature thermal-shutdown protection with temperature hysteresis. A rising die temperature shuts down the device at +150°C. When the
die cools down to +143°C, the device is enabled. The
outputs pulsate as the temperature fluctuates between
the thermal limits.
Shutdown
The MAX9706/MAX9707 feature a 0.1µA shutdown
mode that reduces power consumption to extend battery life. Driving SHDN low disables the drive amplifiers,
bias circuitry, and charge pump and sets the headphone amplifier output impedance to 1.4kΩ.
Applications Information
Filterless Class D Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM output. The filters add cost, increase the solution size of
the amplifier, and can decrease efficiency. The traditional PWM scheme uses large differential output
swings (2 x VDD(P-P)) and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.
The MAX9706/MAX9707 do not require an output filter.
The devices rely on the inherent inductance of the
speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component
of the square-wave output. Eliminating the output filter
results in a smaller, less costly, more efficient solution.
Because the frequency of the MAX9706/MAX9707 output is well beyond the bandwidth of most speakers,
voice coil movement due to the square-wave frequency
is very small. Although this movement is small, a speaker not designed to handle the additional power can be
damaged. For optimum results, use a speaker with a
series inductance >10µH. Typical 8Ω speakers for
portable audio applications exhibit series inductances
in the 20µH to 100µH range.
Figure 9. HPS Configuration
______________________________________________________________________________________
19
MAX9706/MAX9707
Headphone Sense Input (HPS)
The headphone sense input (HPS) monitors the headphone jack, and automatically configures the MAX9706
based upon the voltage applied at HPS. A voltage of
less than 0.8V sets the MAX9706 to speaker mode and
disables the headphone amplifiers. A voltage of greater
than 2V disables the speaker amplifiers and enables
the headphone amplifiers. The HPS input features a
built-in 65ms debounce period to prevent audible
“chatter” when inserting or removing headphones.
For automatic headphone detection, connect HPS to
the control pin of a 3-wire headphone jack as shown in
Figure 9. With no headphone present, the output
impedance of the headphone amplifier pulls HPS to
less than 0.8V. When a headphone plug is inserted into
the jack, the control pin is disconnected from the tip
contact and HPS is pulled to VDD through the internal
600kΩ pullup. When driving HPS from an external logic
source, drive HPS low when the MAX9706 is shut
down. Place a 10kΩ resistor in series with HPS and the
headphone jack to ensure high ESD protection.
MAX9706/MAX9707
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Power Supplies
Supply Bypassing, Layout, and Grounding
The MAX9706/MAX9707 have different supplies for
each portion of the devices, allowing for the optimum
combination of headroom power dissipation and noise
immunity. The speaker amplifiers are powered from
PVDD. PVDD can range from 4.5V to 5.5V and must be
connected to the same potential as VDD. The headphone amplifiers are powered from HPVDD and VSS.
HPVDD is the positive supply of the headphone amplifiers and can range from 3V to 5.5V. VSS is the negative
supply of the headphone amplifiers. Connect VSS to
CPV SS . The charge pump is powered by CPV DD .
Connect CPV DD to V DD for normal operation. The
charge pump inverts the voltage at CPVDD, and the
resulting voltage appears at CPVSS. The remainder of
the device is powered by VDD.
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Large traces also aid in moving heat away from the package. Proper grounding
improves audio performance, minimizes crosstalk
between channels, and prevents any switching noise
from coupling into the audio signal. Connect PGND and
GND together at a single point on the PC board (star
configuration). Route all traces that carry switching
transients away from GND and the traces/components
in the audio signal path.
Component Selection
Input Filter
An input capacitor, CIN, in conjunction with the input
impedance of the MAX9706/MAX9707 forms a highpass filter that removes the DC bias from an incoming
signal. The AC-coupling capacitor allows the amplifier
to automatically bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of
the highpass filter is given by:
f−3dB =
1
2π × RIN × CIN
Choose CIN so f-3dB is well below the lowest frequency of
interest. Use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low frequencies.
Crossover Selection
Select the crossover filter to suit the chosen speaker.
Many small diameter speakers (as used in notebooks
and smaller displays) are self resonant (fO) at 800Hz to
1000Hz. Often these speakers have a slight peaking at
resonance, so choosing a crossover frequency at 2 x fO
can be effective. Ensure the mono channel speaker has
its fO much lower than crossover frequency (fC).
20
Connect the power-supply inputs V DD and PV DD
together and connect CPV DD and HPV DD together.
Bypass HPVDD and CPVDD with a 1µF capacitor in parallel with a 0.1µF capacitor to PGND. Bypass VDD and
PVDD with a 1µF capacitor to GND. Place the bypass
capacitors as close to the device as possible. Place a
bulk capacitor between PVDD and PGND if needed.
Use large, low-resistance output traces. Current drawn
from the outputs increase as load impedance decreases. High-output trace resistance decreases the power
delivered to the load. Large output, supply, and GND
traces allow more heat to move from the device to the
air, decreasing the thermal impedance of the circuit if
possible or connect to VSS.
The MAX9706/MAX9707 thin QFN-EP package features an exposed thermal pad on its underside. This
pad lowers the package’s thermal impedance by providing a direct heat conduction path from the die to
the PC board. The exposed thermal pad is not internally connected. Connect the exposed pad to GND.
BIAS Capacitor
BIAS is the output of the internally generated DC bias
voltage. The BIAS bypass capacitor, CBIAS improves
PSRR and THD+N by reducing power supply and other
noise sources at the common-mode bias node, and
also generates the clickless/popless, startup/shutdown
DC bias waveforms for the speaker amplifiers. Bypass
BIAS with a 1µF capacitor to GND.
______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
SUPPLIER
PHONE
FAX
Taiyo Yuden
800-348-2496
847-925-0899
www.t-yuden.com
TDK
807-803-6100
847-390-4405
www.component.tdk.com
Charge-Pump Capacitor Selection (MAX9706)
Use capacitors with an ESR less than 100mΩ for optimum performance. Low-ESR ceramic capacitors minimize the output resistance of the charge pump. Most
surface-mount ceramic capacitors satisfy the ESR
requirement. For best performance over the extended
temperature range, select capacitors with an X7R
dielectric. Table 5 lists suggested manufacturers.
Flying Capacitor (C1, MAX9706)
The value of the flying capacitor (C1) affects the output
resistance of the charge pump. A C1 value that is too
small degrades the device’s ability to provide sufficient
current drive, which leads to a loss of output voltage.
Increasing the value of C1 reduces the charge-pump output resistance to an extent. Above 1µF, the on-resistance
of the switches and the ESR of C1 and C2 dominate.
WEBSITE
Output Capacitor (C2, MAX9706)
The output capacitor value and ESR directly affect the
ripple at CPVSS. Increasing the value of C2 reduces
output ripple. Likewise, decreasing the ESR of C2
reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low
maximum output power levels. See the Output Power
vs. Charge-Pump Capacitance and Load Resistance
graph in the Typical Operating Characteristics. C2
must be equal to or greater than C1.
CPVDD Bypass Capacitor (MAX9706)
The CPVDD bypass capacitor lowers the output impedance of the power supply and reduces the impact of
the MAX9706’s charge-pump switching transients.
Bypass CPVDD with a capacitor to CPGND and place it
physically close to CPVDD and CPGND. Use a value
that is equal to C1.
______________________________________________________________________________________
21
MAX9706/MAX9707
Table 5. Suggested Capacitor Manufacturers
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
MAX9706/MAX9707
Functional Diagram/Typical Operating Circuits
4.5V TO 5.5V
CBIAS
1µF
1µF
10µF*
1µF
BIAS
VDD
PVDD
1
3
8, 20, 34
BIAS
GENERATOR
MAX9706
VDD
SYNC_IN 14
CIN
0.47µF
INL 36
4 SYNC_OUT
OSCILLATOR
AND SAWTOOTH
CLASS D
MODULATOR
AND H-BRIDGE
LOWPASS/
HIGHPASS
FILTER
CLASS D
MODULATOR
AND H-BRIDGE
MGAIN 28
CIN
0.47µF
INR 27
LOWPASS/
HIGHPASS
FILTER
HPVDD
SHDN 24
CLASS D
MODULATOR
AND H-BRIDGE
7 OUTL+
6 OUTL-
33 OUTM+
32 OUTM-
21 OUTR+
22 OUTR-
FS1 26
FS0 25
15 HPS
CONTROL
GAIN1 30
GAIN2 29
18 HPL
INL
HPVDD 19
CPVDD 9
C1P 10
1µF
0.1µF
C1
1µF
C1N 12
17 HPR
INR
CHARGE
PUMP
CPGND 11
35 MONO_OUT
13
16
2
5, 23, 31
CPVSS
VSS
GND
PGND
C2
1µF
*BULK CAPACITANCE IF NEEDED
TYPICAL OPERATING CIRCUIT SHOWN DEPICTS THE MAX9706 WITH:
SSM MODE WITH fOSC = 1150kHz, SPEAKER GAIN = +9dB, MONO SPEAKER GAIN OFFSET = -6.0dB,
HEADPHONE SPEAKER GAIN = +0dB, AND CROSSOVER FREQUENCY = 1066.7Hz.
22
______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
4.5V TO 5.5V
1µF
10µF*
1µF
VDD
PVDD
3
8, 20, 34
VDD
MAX9707
SYNC_IN 14
4 SYNC_OUT
OSCILLATOR
AND SAWTOOTH
CIN
0.47µF
INL 36
CLASS D
MODULATOR
AND H-BRIDGE
MGAIN 28
CIN
0.47µF
LOWPASS/
HIGHPASS
FILTER
INR 27
7 OUTL+
CLASS D
MODULATOR
AND H-BRIDGE
LOWPASS/
HIGHPASS
FILTER
CLASS D
MODULATOR
AND H-BRIDGE
SHDN 24
6 OUTL-
33 OUTM+
32 OUTM-
21 OUTR+
22 OUTR-
FS1 26
FS0 25
CONTROL
GAIN1 30
35 MONO_OUT
GAIN2 29
BIAS
GENERATOR
15 I.C.
9 N.C.
10 N.C.
11 N.C.
12
13
16
17
18
19
N.C. N.C. N.C. N.C. N.C. N.C.
1
BIAS
2
5, 23, 31
GND
PGND
CBIAS
1µF
*BULK CAPACITANCE IF NEEDED
TYPICAL OPERATING CIRCUIT SHOWN DEPICTS THE MAX9707 WITH:
SSM MODE WITH fOSC = 1150kHz, SPEAKER GAIN = +9dB, MONO SPEAKER GAIN OFFSET = -6.0dB,
AND CROSSOVER FREQUENCY = 1066.7Hz.
______________________________________________________________________________________
23
MAX9706/MAX9707
Functional Diagram/Typical Operating Circuits (continued)
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
27 26 25 24 23 22 21 20 19
27 26 25 24 23 22 21 20 19
GAIN1
PGND
30
16
31
15
OUTMOUTM+
32
PVDD
MONO_OUT
INL
34
12
35
11
C1N
CPGND
36
10
C1P
14
MAX9706
5
6
7
18
29
17
VSS
HPS
GAIN1
PGND
30
16
31
15
OUTMOUTM+
32
PVDD
34
12
MONO_OUT
INL
35
11
SYNC_IN
N.C.
N.C.
N.C.
36
10
N.C.
SYNC_IN
CPVSS
8
9
1
6mm x 6mm TQFN
14
MAX9707
33
BIAS
4
28
PVDD
3
MGAIN
GAIN2
CPVDD
2
GND
VDD
SYNC_OUT
PGND
OUTLOUTL+
BIAS
1
13
HPL
HPR
4
5
6
13
2
3
7
8
9
N.C.
17
PVDD
18
29
VDD
SYNC_OUT
PGND
OUTLOUTL+
28
GND
MGAIN
GAIN2
33
SHDN
PGND
OUTROUTR+
PVDD
N.C.
INR
TOP VIEW
FS1
FS0
SHDN
PGND
OUTROUTR+
PVDD
HPVDD
INR
TOP VIEW
FS1
FS0
MAX9706/MAX9707
Pin Configurations
N.C.
N.C.
N.C.
I.C.
6mm x 6mm TQFN
Chip Information
TRANSISTOR COUNT: 12,686
PROCESS: BICMOS
24
______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
QFN THIN.EPS
(NE-1) X e
E
E/2
k
D/2
CL
(ND-1) X e
D
D2
D2/2
e
b
E2/2
L
CL
k
E2
e
L
CL
CL
L1
L
L
e
A1
A2
e
A
PACKAGE OUTLINE
36, 40, 48L THIN QFN, 6x6x0.8mm
21-0141
F
1
2
NOTES:
1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
3. N IS THE TOTAL NUMBER OF TERMINALS.
4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1
SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE
ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE.
5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm
FROM TERMINAL TIP.
6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS.
9. DRAWING CONFORMS TO JEDEC MO220, EXCEPT FOR 0.4mm LEAD PITCH PACKAGE T4866-1.
10. WARPAGE SHALL NOT EXCEED 0.10 mm.
11. MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.
12. NUMBER OF LEADS SHOWN FOR REFERENCE ONLY.
PACKAGE OUTLINE
36, 40, 48L THIN QFN, 6x6x0.8mm
21-0141
F
2
2
The MAX9706/MAX9707 Thin QFN-EP package features an exposed thermal pad on its underside. This pad lowers the package’s thermal impedance by providing a direct heat conduction path from the die to the printed circuit board. The exposed
thermal pad is not internally connected. Connect the exposed pad to GND.
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 25
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX9706/MAX9707
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.)
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