MAX9706 [MAXIM]
3-Channel, 2.3W, Filterless Class D Amplifiers with Active Crossover; 3通道， 2.3W ，无需滤波的D类放大器，有源分频
| 型号： | MAX9706 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 3-Channel, 2.3W, Filterless Class D Amplifiers with Active Crossover |
| 文件： | 总25页 (文件大小：652K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3681; Rev 0; 12/05
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
General Description
Features
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 out-
puts. 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.
♦ 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
The MAX9706 features Maxim’s patented DirectDrive™
headphone amplifier, providing ground-referenced
headphone outputs without the need for bulky DC-cou-
pling 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 ±±kV.
♦ Up To 90% Efficiency
♦ Space-Saving (6mm x 6mm x 0.8mm) 36-Pin Thin
QFN Package
The MAX9706/MAX9707 feature pin-programmable
gain, synchronization inputs and outputs, and a shut-
down 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 +±5°C extended temperature range and are avail-
able in the thermally enhanced 36-pin (6mm x 6mm x
0.±mm) thin QFN package.
Ordering Information
PART
HP AMP PIN-PACKAGE
PKG CODE
T3666N-1
T3666N-1
MAX9706ETX+
MAX9707ETX+
Yes
No
36 Thin QFN
36 Thin QFN
+Denotes lead-free package.
Note: These devices operate over the -40°C to +85°C temper-
ature range.
Applications
Notebook Audio Solutions
2.1 Speaker Solutions
Desktop PCs
Multimedia Monitors
Portable DVD Players
Table-Top LCD TVs
Functional Diagrams and Pin Configurations appear at end
of data sheet.
Block Diagram
MAX9706
MAX9707
FULL-RANGE
TRANSDUCERS
AUDIO IN
FULL-RANGE
TRANSDUCERS
AUDIO IN
LOW-FREQUENCY
TRANSDUCER
LOW-FREQUENCY
TRANSDUCER
FREQUENCY
SELECT
FREQUENCY
SELECT
HEADPHONE
SHDN
SHDN
________________________________________________________________ Maxim Integrated Products
1
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.
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ABSOLUTE MAXIMUM RATINGS
V
, PV , HPV , CPV
to GND ........................-0.3V to +6V
Continuous Current (MONO_OUT, CPV , C1N, C1P,
DD
DD
DD
DD
DD
GND to PGND, CPGND.........................................-0.3V to +0.3V
CPV , V to GND..................................................-6V to +0.3V
CPGND, CPV , V , HPV , HPR, HPL)......................0.±5A
Continuous Current (all other pins).....................................20mA
SS SS DD
SS SS
C1N to GND ...........................................(CPV - 0.3V) to +0.3V
Continuous Power Dissipation (T = +70°C)
SS
A
C1P to GND...........................................-0.3V to (CPV
HPL, HPR.....................................................................-3V to +3V
All Other Pins to GND.................................-0.3V to (V + 0.3V)
+ 0.3V)
Single-Layer Board
36-Pin TQFN (derate 26.3mW/°C above +70°C) .......2105mW
Multilayer Board
DD
DD
OUT_+, OUT_ -, Short Circuit to GND or PV
OUT_+ Short Circuit to OUT_-....................................Continuous
HPR, HPL Short Circuit to GND..................................Continuous
Continuous
36-Pin TQFN (derate 35.7mW/°C above +70°C) .......2±57mW
Operating Temperature Range ...........................-40°C to +±5°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
DD ...........
MONO_OUT Short Circuit to GND or V
Continuous
DD ....................
Continuous Current (PV , OUT_+, OUT_-, PGND).............1.7A
DD
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
(V
= PV
= HPV
= 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
DD
DD
DD DD
GND, FS0 = FS1 = GND (±00Hz), MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT_+ and
L
DD
OUT_-, unless otherwise noted, R = ∞. Headphone load R connected between HPR/HPL to GND, R = ∞. C
= 1µF to GND,
L
to T
LH
LH
BIAS
C1 = 1µF, C2 = 1µF. T = T
A
, unless otherwise noted. Typical values at T = +25°C.) (Note 1)
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
Inferred from PSRR test
DD
MIN
TYP
MAX
5.5
UNITS
Speaker Amplifier Supply Voltage
Range
V
, PV
DD
4.5
V
Headphone Amplifier Supply
Voltage Range
HPV
CPV
,
DD
Inferred from PSRR test (MAX9706)
Speaker mode
3.0
15
5.5
V
DD
25
7
35
12
3
Quiescent Supply Current
I
mA
DD
Headphone mode, HPS = V
(MAX9706)
DD
Shutdown Supply Current
Input Resistance
I
SHDN = GND
0.5
25
±7
±7
µA
SHDN
R
35
kΩ
IN
Speaker mode
Turn-On Time, Shutdown to Full
Operation
ms
Headphone mode (MAX9706)
SPEAKER AMPLIFIERS (OUTL_, OUTR_, OUTM_)
R = ±Ω, THD+N = 1%
1.4
2.3
L
Output Power (Note 2)
P
W
%
OUT
R = 4Ω, THD+N = 1%
L
P
= 1W,
R = ±Ω
0.06
0.07
OUT
L
Total Harmonic Distortion Plus
Noise
THD+N
SNR
bandwidth = 22Hz to
22kHz (Note 2)
R = 4Ω
L
Bandwidth =
22Hz to 22kHz
±7
R = ±Ω, P
= 1W
L
OUT
Signal-to-Noise Ratio
dB
dB
(Note 2)
A-weighted
92
71
51
65
V
= PV
= 4.5V to 5.5V, T = +25°C
50
DD
DD
A
Power-Supply Rejection Ratio
PSRR
f = 2kHz, OUTL_, OUTR_
f = 100Hz, OUTM_
100mV
(Note 3)
ripple
P-P
2
_______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ELECTRICAL CHARACTERISTICS (continued)
(V
= PV
= HPV
= 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
DD
DD
DD DD
GND, FS0 = FS1 = GND (±00Hz), MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT_+ and
L
DD
OUT_-, unless otherwise noted, R = ∞. Headphone load R connected between HPR/HPL to GND, R = ∞. C
= 1µF to GND,
L
to T
LH
LH
BIAS
C1 = 1µF, C2 = 1µF. T = T
A
, unless otherwise noted. Typical values at T = +25°C.) (Note 1)
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
GAIN1 = 0
MIN
TYP
9
MAX
UNITS
GAIN2 = 0
GAIN2 = 0
GAIN2 = 1
GAIN2 = 1
GAIN1 = 1
GAIN1 = 0
GAIN1 = 1
10.5
12
Speaker Path Gain (Note 4)
dB
13.5
Channel-to-Channel Gain
Tracking
0.3
%
MGAIN = GND
MGAIN = float
-4.5
-6
MONO Gain Offset (Note 5)
dB
MGAIN = V
-7.5
DD
Right to left, left to right, f = 10kHz,
IN
Crosstalk
70
dB
pF
P
= 1W
OUT
Maximum Capacitive Load
C
No sustained oscillations
200
90
L
R = ±Ω, P
= 3 x 1W, f = ±00Hz
= 3 x 1W, f = ±00Hz
L
OUT
Efficiency
η
%
R = 4Ω, P
±±
L
OUT
FFM, SYNC_IN = GND
FFM, SYNC_IN = float
955
1100
1340
1150
±50
1270
Class D Center Frequency
f
1140
1540
kHz
OSC
SSM, SYNC_IN = V
DD
Class D Spreading Bandwidth
SSM mode, SYNC_IN = V
kHz
kHz
mV
DD
SYNC_IN Frequency Lock Range
Output Offset Voltage
1000
1500
V
OUT_+ to OUT_-
14
47
OS
Peak voltage,
Into shutdown
Click-and-Pop Level
K
A-weighted, 32 samples
per second (Note 6)
dBV
CP
Out of shutdown
50
CROSSOVER FILTERS
Cutoff Frequency Accuracy
(Note 7)
FS0 = 0
FS0 = 0
FS0 = 1
FS0 = 1
±15
%
FS1 = 0
FS1 = 1
FS1 = 0
FS1 = 1
±00
1066.7
1600
Crossover Frequency
f
Hz
XO
2133.3
Left-to-Right Cutoff Frequency
Tracking
±0.5
%
_______________________________________________________________________________________
3
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ELECTRICAL CHARACTERISTICS (continued)
(V
= PV
= HPV
= 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
DD
DD
DD DD
GND, FS0 = FS1 = GND (±00Hz), MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT_+ and
L
DD
OUT_-, unless otherwise noted, R = ∞. Headphone load R connected between HPR/HPL to GND, R = ∞. C
= 1µF to GND,
L
to T
LH
LH
BIAS
C1 = 1µF, C2 = 1µF. T = T
A
, unless otherwise noted. Typical values at T = +25°C.) (Note 1)
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
HEADPHONE AMPLIFIERS (MAX9706) (HPS = V
)
DD
HPV
= 3.3V to 5V,
R = 32Ω
L
35
50
DD
T
A
= +25°C, THD+N = 1%
Output Power
P
mW
%
OUT
R = 16Ω
95
(Notes 2, 7)
L
V
= 1V , f = 1kHz,
RMS
R = 32Ω
L
0.02
0.04
OUT
Total Harmonic Distortion Plus
Noise
THD+N
SNR
bandwidth = 22Hz to
22kHz
R = 16Ω
L
Bandwidth =
22Hz to 22kHz
96
Signal-to-Noise Ratio
V
= 1V
dB
dB
OUT
RMS
A-weighted
100
90
±0
65
0
HPV
= 3V to 5.5V
70
DD
Power-Supply Rejection Ratio
PSRR
f = 1kHz, 100mV
ripple (Note 3)
P-P
f = 20kHz, 100mV
GAIN2 = 0
ripple (Note 3)
P-P
Headphone Path Gain (Note ±)
Output Offset Voltage
Crosstalk
dB
mV
dB
GAIN2 = 1
3
V
HP_ to GND, T = +25°C
±0.7
±3
OSHP
A
HPL to HPR, HPR to HPL, f = 1kHz,
IN
-60
P
= 32mW, R = 32Ω
L
OUT
Slew Rate
0.5
300
600
65
V/µs
pF
Maximum Capacitive Load
HPS Pullup Impedance
Debounce Time
C
No sustained oscillations
L
kΩ
ms
kΩ
Output Impedance in Shutdown
HPS = GND or SHDN = GND
1.4
Charge-Pump Switching
Frequency
f
f
/ 2
kHz
CP
OSC
Into shutdown
52
Peak voltage,
Click-and-Pop Level
K
A-weighted, 32 samples
per second (Note 6)
dBV
CP
Out of
shutdown
52
LINE-LEVEL MONO OUTPUT (MONO_OUT)
MONO_OUT Signal-Path Gain
Output Impedance
0
0.1
1
dB
Ω
Maximum Output Level
R = 10kΩ
L
V
RMS
Total Harmonic Distortion Plus
Noise
V
= 1V
, f = 100Hz, R = 10kΩ,
OUT
RMS IN L
THD+N
0.01
200
%
bandwidth = 22Hz to 22kHz
Maximum Capacitive Load
C
No sustained oscillations
pF
L
4
_______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
ELECTRICAL CHARACTERISTICS (continued)
(V
= PV
= HPV
= 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (SPKR = +9dB, HP = 0dB), HPS =
DD
DD
DD DD
GND, FS0 = FS1 = GND (±00Hz), MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT_+ and
L
DD
OUT_-, unless otherwise noted, R = ∞. Headphone load R connected between HPR/HPL to GND, R = ∞. C
= 1µF to GND,
L
to T
LH
LH
BIAS
C1 = 1µF, C2 = 1µF. T = T
A
, unless otherwise noted. Typical values at T = +25°C.) (Note 1)
MIN
MAX A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
DIGITAL INPUTS (GAIN1, GAIN2, FS0, FS1, SHDN, SYNC_IN, MGAIN)
Input-Voltage High
V
2
V
INH
Input-Voltage Low
V
0.±
V
INL
Input Leakage Current
Input Current
GAIN1, GAIN2, FS0, FS1, SHDN
SYNC_IN, MGAIN
±1
µA
µA
kΩ
±50
Pullup Impedance
SYNC_IN, MGAIN
200
DIGITAL OUTPUT (SYNC_OUT)
V
x
DD
0.9
Output-Voltage High
Output-Voltage Low
V
I
I
= 1mA
= 1mA
V
V
OH
OH
V
x
DD
0.1
V
OL
OL
Note 1: All devices are 100% tested at T = +25°C. Limits over temperature are guaranteed by design.
A
Note 2: Measured at 2kHz for OUTL_, OUTR_, HPL, and HPR; measured at 100Hz for OUTM_.
Note 3: PSRR is measured with the inputs AC-grounded.
Note 4: Left/right signal-path gain is defined as:
V
− V
(
)
(
)
OUT_+
OUT_−
V
IN_
MONO signal-path gain is defined as:
V
− V
(
)
)
(
)
OUTM+
OUTM−
V
(
+ V
(
)
INL
INR
Note 5: MONO gain offset is measured with respect to speaker-path gain.
Note 6: Speaker mode testing performed with an ±Ω resistive load in series with a 6±µH 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:
V
HP
V
IN_
Note 8: Guaranteed by design only.
_______________________________________________________________________________________
5
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Speaker Mode
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T
, unless otherwise noted. Typical values at T = +25°C.)
A
MIN
MAX
A
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
10
1
10
1
100
10
V
= 5V
V
= 5V
V
= 5V
DD
L
DD
L
DD
L
R = 4Ω
OUTPUT POWER = 1.5W
R = 8Ω
OUTPUT POWER = 900mW
R = 4Ω
OUTL AND OUTR
OUTL AND OUTR
1
f
= 2kHz
IN
0.1
0.1
f
= 200Hz
IN
0.1
0.01
0.001
0.01
0.001
0.01
0.001
OUTM
OUTM
f
= 10kHz
IN
10
100
1k
10k
100k
10
100
1k
10k
100k
0
0.5
1.0
1.5
2.0
2.5
3.0
FREQUENCY (Hz)
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
100
10
1
100
10
100
10
V
= 5V
V
= 5V
DD
DD
V
= 5V
DD
R = 8Ω
R = 8Ω
L
L
R = 8Ω
L
f
IN
= 1kHz
f
IN
= 1kHz
1
1
SYNC_IN = 2MHz
SYNC_IN = FLOAT
f
= 2kHz
IN
0.1
0.1
0.1
0.01 SYNC_IN = V
0.001
0.01
0.001
0.01
0.001
SYNC_IN = 1.4MHz
DD
f
= 10kHz
1.5
IN
SYNC_IN = GND
1.0
f
= 200Hz
IN
SYNC_IN = 0.8MHz
0.5
0
0.5
1.5
2.0
0
1.0
1.5
2.0
0
0.3
0.6
0.9
1.2
1.8
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
6
_______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Speaker Mode (continued)
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T , unless otherwise noted. Typical values at T = +25°C.)
MAX A
A
MIN
OUTPUT POWER
OUTPUT POWER
OUTPUT POWER
vs. LOAD RESISTANCE
vs. SUPPLY VOLTAGE
vs. SUPPLY VOLTAGE
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
3.0
2.5
2.0
1.5
1.0
0.5
0
V
= 5V
DD
f = 1kHz
R = 4Ω
L
f = 1kHz
R = 8Ω
L
THD+N = 10%
f = 1kHz
THD+N = 10%
THD+N = 10%
THD+N = 1%
THD+N = 1%
THD+N = 1%
1
10
LOAD RESISTANCE (Ω)
100
4.5
4.7
4.9
5.1
5.3
5.5
4.5
4.7
4.9
5.1
5.3
5.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
EFFICIENCY vs. OUTPUT POWER
OUTPUT FREQUENCY SPECTRUM
0
100
90
80
70
60
50
40
30
20
10
0
0
-20
V
= 100mV
P-P
RIPPLE
SSM MODE
-10
-20
R = 8Ω
L
V
= -60dB
OUT
f = 1kHz
OUTM
R = 8Ω
-30
R = 8Ω
L
L
R = 4Ω
L
-40
UNWEIGHTED
-40
-50
-60
-60
OUTL
-80
-70
OUTR
-80
-100
-120
-140
-90
-100
-110
-120
P
= P
= 800Hz
+ P
+ P
OUTM
OUT
OUTL
OUTR
f
IN
10
100
1k
FREQUENCY (Hz)
10k
100k
0
1
2
3
4
5
0
5
10
15
20
OUTPUT POWER (W)
FREQUENCY (kHz)
_______________________________________________________________________________________
7
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Speaker Mode (continued)
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T
, unless otherwise noted. Typical values at T = +25°C.)
A
MIN
MAX
A
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
OUTPUT FREQUENCY SPECTRUM
20
10
20
10
0
-20
RBW = 10kHz
INPUT AC-GROUNDED
RBW = 10kHz
INPUT AC-GROUNDED
SSM MODE
= -60dB
f = 1kHz
V
OUT
0
0
R = 8Ω
L
-40
-10
-20
-30
-40
-50
-60
-70
-80
-10
-20
-30
-40
-50
-60
-70
-80
A-WEIGHTED
-60
-80
-100
-120
-140
0
1
10
100
1000
0
1
10
100
1000
0
5
10
15
20
FREQUENCY (MHz)
FREQUENCY (MHz)
FREQUENCY (kHz)
TURN-ON/-OFF RESPONSE
AMPLITUDE vs. FREQUENCY
AMPLITUDE vs. FREQUENCY
MAX9706 toc16
20
10
20
10
f
= 800Hz
f
= 2.1kHz
XO
XO
0
0
2V/div
-10
-20
-30
-40
-50
-10
-20
-30
-40
-50
200mA/div
10
100
1k
10k
100k
10
100
1k
10k
100k
20ms/div
FREQUENCY (Hz)
FREQUENCY (Hz)
8
_______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Headphone Mode
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T
, unless otherwise noted. Typical values at T = +25°C.)
A
MIN
MAX
A
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
10
1
10
1
10
1
HPV = 3.3V
DD
R = 16Ω
L
HPV = 3.3V
DD
R = 32Ω
L
HPV = 5V
DD
R = 16Ω
L
OUTPUT POWER = 25mW
OUTPUT POWER = 20mW
0.1
0.1
0.1
OUTPUT POWER = 10mW
0.01
0.001
0.01
0.001
0.01
0.001
OUTPUT POWER = 75mW
OUTPUT POWER = 80mW
OUTPUT POWER = 35mW
10
100
1k
10k
100k
10
100
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
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
10
1
100
10
100
10
HPV = 5V
DD
R = 32Ω
L
HPV = 3.3V
DD
R = 16Ω
L
HPV = 3.3V
DD
R = 32Ω
L
1
1
0.1
f
= 1kHz
OUTPUT POWER = 10mW
IN
f
= 200Hz
f
= 1kHz
IN
IN
0.1
0.1
f
= 10kHz
IN
0.01
0.001
0.01
0.001
0.01
0.001
f
= 10kHz
OUTPUT POWER = 35mW
IN
f
= 200Hz
30
IN
10
100
1k
FREQUENCY (Hz)
10k
100k
0
15 30 45 60 75 90 105 120 135
OUTPUT POWER (mW)
0
10
20
40
50
60
70
OUTPUT POWER (mW)
_______________________________________________________________________________________
9
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Headphone Mode (continued)
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T
, unless otherwise noted. Typical values at T = +25°C.)
A
MIN
MAX
A
OUTPUT POWER
vs. LOAD RESISTANCE
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
140
120
100
80
100
10
100
10
HPV = 3.3V
HPV = 5V
DD
R = 16Ω
L
HPV = 5V
DD
R = 32Ω
L
DD
f = 1kHz
1
1
THD+N = 10%
f
= 10kHz
IN
f
= 1kHz
60
IN
f
= 10kHz
IN
0.1
0.1
f
= 1kHz
IN
40
0.01
0.001
0.01
0.001
20
THD+N = 1%
f
= 200Hz
IN
f
= 200Hz
IN
0
10
100
1000
0
20
40
60
80
100
120
0
10
20
30
40
50
60
70
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
OUTPUT POWER (mW)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OUTPUT POWER
vs. HEADPHONE SUPPLY VOLTAGE
OUTPUT POWER
vs. LOAD RESISTANCE
0
-20
140
120
100
80
130
110
90
V
ON V AND HPV = 100mV
DD DD P-P
RIPPLE
HPV = 5V
f = 1kHz
THD+N = 1%
DD
INPUTS AC-GROUNDED
R = 16Ω
L
-40
THD+N = 10%
LEFT
-60
60
70
-80
40
R = 32Ω
L
RIGHT
10k
50
THD+N = 1%
-100
-120
20
0
30
10
100
1k
FREQUENCY (Hz)
100k
10
100
LOAD RESISTANCE (Ω)
1000
3.0
3.5
4.0
4.5
5.0
5.5
HPV (V)
DD
10 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Typical Operating Characteristics—Headphone Mode (continued)
(V = PV = HPV = 5V, GND = PGND = CPGND = 0V, SHDN = V , GAIN1 = GAIN2 = GND (+9dB), FS0 = FS1 = GND (±00Hz),
DD
DD
DD
DD
MGAIN = float (-6dB), SYNC_IN = V
(SSM), speaker load R connected between OUT+ and OUT-, unless otherwise noted, R = ∞.
DD
L
L
Headphone load R connected between HPR/HPL to GND. C
= 1µF to GND, 1µF capacitor between C1P and C1N, C = 1µF.
LH
BIAS
VSS
T = T
to T
, unless otherwise noted. Typical values at T = +25°C.)
A
MIN
MAX
A
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
OUTPUT POWER
vs. CHARGE-PUMP CAPACITANCE
CROSSTALK vs. FREQUENCY
0
-20
0
-10
-20
-30
-40
-50
-60
-70
-80
100
90
80
70
60
50
40
30
20
V
= 100mV
P-P
R = 32Ω
RIPPLE
L
OUT
f = 1kHz
C1 = C2 = 1µF
INPUTS AC-GROUNDED
P
= 32mW
THD+N = 1%
C1 = C2 = 0.47µF
-40
-60
RIGHT
LEFT TO RIGHT
-80
C1 = C2 = 0.22µF
-100
-120
LEFT
RIGHT TO LEFT
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
10k
100k
15
20
25
30
35
40
45
50
FREQUENCY (Hz)
LOAD (Ω)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
OUTPUT FREQUENCY SPECTRUM
TURN-ON/-OFF RESPONSE
MAX9706 toc36
0
-20
40
30
20
10
0
V
= -60dBV
OUT
SUPPLY VOLTAGE = I
+ I
VDD HPVDD
f = 1kHz
R = 32Ω
L
-40
2V/div
1V/div
HPS = GND
HPV = 3.3V
DD
-60
-80
-100
-120
-140
HPS = V
DD
V
= 5V
DD
0
5
10
15
20
100ms/div
3.0
3.5
4.0
4.5
5.0
5.5
FREQUENCY (kHz)
SUPPLY VOLTAGE (V)
______________________________________________________________________________________ 11
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Pin Description
PIN
NAME
FUNCTION
MAX9706 MAX9707
1
2
1
2
BIAS
GND
Internal Bias. Bypass BIAS to GND with a 1µF capacitor.
Ground. Star connect to PGND (see the Supply Bypassing, Layout, and Grounding section).
Main Power Supply. Connect V
capacitor.
to a low-noise 5V source. Bypass V
to GND with a 1µF
DD
DD
3
3
V
DD
Synchronization Clock Output. Connect SYNC_OUT to other Class D amplifiers to maintain
synchronization. SYNC_OUT is a CMOS output proportional to V . Float SYNC_OUT, if not
DD
4
4
SYNC_OUT
used.
5, 23, 31
5, 23, 31
PGND
OUTL-
OUTL+
Power Ground. PGND is the ground connection for the speaker amplifiers.
Left-Speaker Negative Terminal
6
7
6
7
Left-Speaker Positive Terminal
Output Power Supply. PV
is the power connection for the speaker amplifiers. Connect to
DD
±, 20, 34
9
±, 20, 34
—
PV
DD
V
. Bypass each PV
DD
to its corresponding PGND with a 1µF capacitor.
DD
Charge-Pump Positive Supply. Connect CPV
1µF capacitor.
to HPV . Bypass CPV to CPGND with a
DD DD
DD
CPV
DD
10
11
12
—
—
—
C1P
Charge-Pump Flying Capacitor Positive Terminal. Connect a 1µF capacitor from C1P to C1N.
Charge-Pump Ground. Connect to PGND.
CPGND
C1N
Charge-Pump Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1N to C1P.
Negative Supply Charge-Pump Output. Bypass CPV to PGND with a 1µF capacitor.
SS
13
—
CPV
SS
Connect CPV to V
.
SS
SS
Frequency Select or External Clock Input. Connect SYNC_IN to GND, V , leave floating, or
DD
drive with an externally generated clock to control the switching frequency of the Class D
amplifiers. See Table 1.
14
14
SYNC_IN
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.
15
—
16
17
1±
—
—
—
V
Headphone Amplifier Negative Supply. Connect V to CPV
SS
.
SS
SS
HPR
HPL
Right Headphone Output
Left Headphone Output
Positive Supply for Headphone Amplifiers. Connect HPV
with a 0.1µF capacitor.
to V . Bypass HPV
to PGND
DD
DD
DD
19
—
HPV
DD
21
22
21
22
OUTR+
OUTR-
Right-Speaker Positive Terminal
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 V to enable normal operation.
24
24
SHDN
DD
25
26
25
26
FS0
FS1
Crossover Frequency Select. Connect FS0 and FS1 to GND or V
frequency. See Table 4.
to set the crossover
DD
12 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Pin Description (continued)
PIN
NAME
INR
FUNCTION
MAX9706 MAX9707
Right-Channel Audio Input. Connect the right-channel audio signal to INR with a series
capacitor. INR has a 25kΩ typical input impedance.
27
2±
29
30
27
2±
29
30
Mono Gain Control. Connect MGAIN to GND, V , or leave floating to set the gain of the
DD
MONO channel with respect to the left and right channels. See Table 3.
MGAIN
GAIN2
GAIN1
Amplifier Gain-Control Input. Connect GAIN1 and GAIN2 to GND or V
left and right channels. See Tables 2 and 4.
to set the gain of the
to set the gain of the
DD
Amplifier Gain-Control Input. Connect GAIN1 and GAIN2 to GND or V
left and right channels. See Tables 2 and 4.
DD
32
33
32
33
OUTM-
Mono-Speaker Negative Terminal
Mono-Speaker Positive Terminal
OUTM+
Mono Line-Level Output. MONO_OUT is the monaural output of the summed left and right low-
frequency signals.
35
36
35
36
MONO_OUT
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.
I.C.
No Connection. Not internally connected.
Internally Connected. Connect to GND.
15
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.
EP
EP
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 out-
puts. The crossover frequency is pin-selectable to four
different frequencies to accommodate a variety of
speaker configurations.
MAX9706
MAX9707
CLASS D
AMPLIFIER
HPF
LPF
HPF
LEFT IN
CLASS D
AMPLIFIER
The internal Class D amplifiers feature low-EMI, spread-
spectrum outputs. No output filters are required.
RIGHT IN
The MAX9706 features Maxim’s patented 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 sup-
ply, and are protected against ESD up to ±±kV.
CLASS D
AMPLIFIER
Figure 1. Speaker Arrangement
______________________________________________________________________________________ 13
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Class D Speaker Amplifier
Operating Modes
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 fre-
quency so the harmonics do not fall within a sensitive
frequency band (Table 1). Audio reproduction is not
affected by changing the switching frequency.
Spread-spectrum modulation and synchronizable switch-
ing 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 minimum-
width pulse (t
,100ns typ) at the output of the sec-
ON(MIN)
ond 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
(V
- V
) to change. The minimum-width pulse
OUT-
OUT+
helps the device to achieve high levels of linearity.
t
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
- V
OUT_-
OUT_+
Figure 2. Outputs with an Input Signal Applied (FFM Mode)
14 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Spread-Spectrum (SSM) Mode
Table 1. Operating Modes
The MAX9706/MAX9707 feature a unique, patented
SYNC_IN
GND
FLOAT
MODE
spread-spectrum mode that flattens the wideband
spectral components, improving EMI emissions that
can be radiated by the speaker and cables. Enable
FFM with f
FFM with f
= 1100kHz
OSC
OSC
= 1340kHz
SSM mode by setting SYNC_IN = V
(Table 1). In
DD
V
SSM with f
= 1150kHz ±50kHz
= external clock frequency
DD
OSC
OSC
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.
Clocked
FFM with f
t
t
t
t
SW
SW
SW
SW
V
IN_-
V
IN_+
OUT_-
OUT_+
t
ON(MIN)
V
- V
OUT_-
OUT_+
Figure 3. Output with an Input Signal Applied (SSM Mode)
______________________________________________________________________________________ 15
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
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 sys-
tem, minimizing clock intermodulation, and allocating
spectral components of the switching harmonics to
insensitive frequency bands. Applying a TTL clock sig-
nal between 1MHz and 1.5MHz to SYNC_IN synchro-
nizes 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.
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 current-
steering switches and consume negligible additional
power. Any power loss associated with the Class D out-
put 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 7±%, however, that efficiency is only exhibit-
ed at peak output powers. Under normal operating lev-
els (typical music reproduction levels), efficiency falls
below 30%, whereas the MAX9706/MAX9707 still
exhibit >90% efficiencies under the same conditions
(Figure 5).
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.
Signal Path Gain
The MAX9706/MAX9707 feature four selectable speak-
er gain and two headphone gain settings controlled by
two gain-control inputs GAIN1 and GAIN2 (see Table 2).
Filterless Modulation/Common-Mode Idle
The MAX9706/MAX9707 use Maxim’s unique, patented
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.
Note that the stereo headphone output is full band-
width, but the stereo speaker outputs are highpass fil-
tered by the crossover circuitry.
Table 2. Speaker Gain
SPEAKER
GAIN (dB)
MAX9706 HEADPHONE
GAIN (dB)
GAIN2
GAIN1
0
0
1
1
0
1
0
1
+9
0
+10.5
+12
0
+3
+3
+13.5
100
90
80
70
60
50
40
30
20
10
V
IN_
= 0V
MAX9706
P
PER CHANNEL
OUT
OUT_-
OUT_+
V
f
= 5V
= 1kHz
DD
IN
L
CLASS AB
TOTAL P
R = 8Ω
OUT
0
0
0.2
0.4
0.6
0.8
1.0
1.2
OUTPUT POWER (W)
V - V = 0V
OUT_+ OUT_-
Figure 4. Outputs with No Input Signal
Figure 5. Efficiency vs. Class AB Efficiency
16 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Table 3. Mono Speaker Gain
MONO SPEAKER GAIN
MGAIN
OFFSET (dB)
GND
-4.5
-6.0
-7.5
HP FUNCTION
2nd-ORDER SLOPE
LP FUNCTION
2nd-ORDER SLOPE
FLOATING
V
DD
Table 4. Crossover Frequency Selection
CROSSOVER
FREQUENCY (f ) (Hz)
XO
FS0
FS1
0
0
1
1
0
1
0
1
±00
FREQUENCY (Hz)
f
X
1066.7
1600
Figure 6. Crossover Frequency
2133.3
Mono Output
Headphone Amplifier (MAX9706)
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, typi-
cally 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 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 out-
put 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 (±Ω 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.
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 cou-
pling 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 dam-
age to both headphone and headphone amplifier.
The MAX9706/MAX9707 feature an internal active filter
with adjustable crossover frequency (f ) for use with a
XO
low-frequency transducer. The crossover filter consists of
a complementary 2nd-order lowpass and 2nd-order
highpass Butterworth filter (Figure 6). Crossover fre-
quency is variable over the ±00Hz to 2133.3Hz range to
accommodate different speaker types. There are four
selectable crossover frequencies selected by FS0 and
FS1 (Table 4).
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply volt-
age. 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
The BTL outputs provide the option of phase-inverting
the mono (LF) output with respect to the main (L/R) out-
puts. Depending on the speaker placement and dis-
tance from the listener, this can smooth the crossover
transition between low and high frequencies.
______________________________________________________________________________________ 17
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
(220µF, typical) tantalum-blocking capacitors, the
MAX9706 charge pump requires two small ceramic
V
DD
capacitors, conserving board space, reducing cost,
and improving the frequency response of the head-
phone amplifier. See the Output Power vs. Charge-
Pump Capacitance graph in the Typical Operating
V
/ 2
DD
Characteristics for details on sizing charge-pump
capacitors. There is a low DC voltage on the driver out-
puts 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.
GND
CONVENTIONAL AMPLIFIER
BIASING SCHEME
In addition to the cost and size disadvantages of the
DC-blocking capacitors required by conventional head-
phone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio sig-
nal (Figure ±). Previous attempts at eliminating the out-
put-coupling capacitors involved biasing the
headphone return (sleeve) to the DC bias voltage of the
headphone amplifiers. This method raises some issues:
+V
DD
1) The sleeve is typically grounded to the chassis.
Using the midrail biasing approach, the sleeve
must be isolated from system ground, complicat-
ing product design.
SGND
2) During an ESD strike, the driver’s ESD structures
are the only path to system ground. Thus, the dri-
ver 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, result-
ing in possible damage to the drivers.
-V
DD
DirectDrive AMPLIFIER
BIASING SCHEME
Figure 7. Traditional Amplifier Output vs. MAX9706 DirectDrive
Output
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 exter-
0
-5
nally, the charge pump switches at 1/2 f
. When
SYNC_IN
SYNC_IN = V , the charge pump switches with a
DD
spread-spectrum pattern. The nominal switching fre-
quency 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.
-10
-15
DirectDrive
-20
-25
-30
-35
330µF
220µF
100µF
33µF
R = 16Ω
L
10
100
FREQUENCY (Hz)
1000
Figure 8. Low-Frequency Rolloff
18 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Headphone Sense Input (HPS)
The headphone sense input (HPS) monitors the head-
phone jack, and automatically configures the MAX9706
based upon the voltage applied at HPS. A voltage of
less than 0.±V 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.
Current Limit and Thermal Protection
The MAX9706/MAX9707 feature current limiting and
thermal protection to protect the device from short cir-
cuits 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.
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.±V. When a headphone plug is inserted into
the jack, the control pin is disconnected from the tip
The MAX9706/MAX9707 feature thermal-shutdown pro-
tection with temperature hysteresis. A rising die tem-
perature 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.
contact and HPS is pulled to V
through the internal
DD
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.
Shutdown
The MAX9706/MAX9707 feature a 0.1µA shutdown
mode that reduces power consumption to extend bat-
tery life. Driving SHDN low disables the drive amplifiers,
bias circuitry, and charge pump and sets the head-
phone amplifier output impedance to 1.4kΩ.
Click-and-Pop Suppression
The MAX9706/MAX9707 feature comprehensive click-
and-pop suppression that eliminates audible transients
on startup and shutdown.
While in shutdown, the H-bridge is in a high-impedance
state. During startup or power-up, the input amplifiers
are muted and an internal loop sets the modulator bias
voltages to the correct levels, preventing clicks and
pops when the H-bridge is subsequently enabled.
Applications Information
Filterless Class D Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM out-
put. The filters add cost, increase the solution size of
the amplifier, and can decrease efficiency. The tradi-
tional PWM scheme uses large differential output
swings (2 x V
) and causes large ripple currents.
DD(P-P)
V
DD
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.
MAX9706
600kΩ
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 speak-
er 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.
SHUTDOWN
CONTROL
SHDN
HPS
HPL
Because the frequency of the MAX9706/MAX9707 out-
put 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 speak-
er not designed to handle the additional power can be
damaged. For optimum results, use a speaker with a
series inductance >10µH. Typical ±Ω speakers for
portable audio applications exhibit series inductances
in the 20µH to 100µH range.
HPR
1.4kΩ
1.4kΩ
Figure 9. HPS Configuration
______________________________________________________________________________________ 19
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Power Supplies
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
Supply Bypassing, Layout, and Grounding
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 mov-
ing 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.
PV . PV
can range from 4.5V to 5.5V and must be
DD
DD
connected to the same potential as V . The head-
DD
phone amplifiers are powered from HPV
and V
.
SS
DD
HPV
is the positive supply of the headphone ampli-
DD
fiers and can range from 3V to 5.5V. V is the negative
SS
supply of the headphone amplifiers. Connect V
to
.
SS
DD
CPV . The charge pump is powered by CPV
SS
Connect CPV
to V
for normal operation. The
DD
DD
charge pump inverts the voltage at CPV , and the
DD
Connect the power-supply inputs V
and PV
DD
DD
resulting voltage appears at CPV . The remainder of
SS
together and connect CPV
and HPV
together.
DD
DD
the device is powered by V
.
DD
Bypass HPV
and CPV
with a 1µF capacitor in par-
DD
DD
allel with a 0.1µF capacitor to PGND. Bypass V
and
DD
Component Selection
P
with a 1µF capacitor to GND. Place the bypass
VDD
Input Filter
capacitors as close to the device as possible. Place a
bulk capacitor between PV and PGND if needed.
An input capacitor, C , in conjunction with the input
IN
DD
impedance of the MAX9706/MAX9707 forms a high-
pass 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:
Use large, low-resistance output traces. Current drawn
from the outputs increase as load impedance decreas-
es. 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 V
.
1
SS
f
=
−3dB
2π × R × C
The MAX9706/MAX9707 thin QFN-EP package fea-
tures an exposed thermal pad on its underside. This
pad lowers the package’s thermal impedance by pro-
viding a direct heat conduction path from the die to
the PC board. The exposed thermal pad is not inter-
nally connected. Connect the exposed pad to GND.
IN
IN
Choose C so f
is well below the lowest frequency of
IN
-3dB
interest. Use capacitors whose dielectrics have low-volt-
age coefficients, such as tantalum or aluminum electrolyt-
ic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low fre-
quencies.
BIAS Capacitor
BIAS is the output of the internally generated DC bias
Crossover Selection
Select the crossover filter to suit the chosen speaker.
Many small diameter speakers (as used in notebooks
voltage. The BIAS bypass capacitor, C
improves
BIAS
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.
and smaller displays) are self resonant (f ) at ±00Hz to
O
1000Hz. Often these speakers have a slight peaking at
resonance, so choosing a crossover frequency at 2 x f
O
can be effective. Ensure the mono channel speaker has
its f much lower than crossover frequency (f ).
O
C
20 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Table 5. Suggested Capacitor Manufacturers
SUPPLIER
Taiyo Yuden
TDK
PHONE
FAX
WEBSITE
±00-34±-2496
±07-±03-6100
±47-925-0±99
±47-390-4405
www.t-yuden.com
www.component.tdk.com
Charge-Pump Capacitor Selection (MAX9706)
Output Capacitor (C2, MAX9706)
Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize 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.
The output capacitor value and ESR directly affect the
ripple at CPV . Increasing the value of C2 reduces
SS
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.
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 out-
put resistance to an extent. Above 1µF, the on-resistance
of the switches and the ESR of C1 and C2 dominate.
CPV
Bypass Capacitor (MAX9706)
DD
The CPV
bypass capacitor lowers the output imped-
DD
ance of the power supply and reduces the impact of
the MAX9706’s charge-pump switching transients.
Bypass CPV
with a capacitor to CPGND and place it
DD
physically close to CPV
that is equal to C1.
and CPGND. Use a value
DD
______________________________________________________________________________________ 21
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Functional Diagram/Typical Operating Circuits
4.5V TO 5.5V
C
1µF
BIAS
1µF
10µF*
1µF
BIAS
1
V
3
PV
DD
DD
8, 20, 34
BIAS
GENERATOR
MAX9706
V
DD
SYNC_IN
INL
14
36
4
SYNC_OUT
OSCILLATOR
AND SAWTOOTH
C
IN
7
6
OUTL+
OUTL-
CLASS D
MODULATOR
AND H-BRIDGE
0.47µF
LOWPASS/
HIGHPASS
FILTER
33
32
OUTM+
OUTM-
CLASS D
MODULATOR
AND H-BRIDGE
MGAIN
INR
28
27
C
IN
0.47µF
LOWPASS/
HIGHPASS
FILTER
21
22
OUTR+
OUTR-
CLASS D
MODULATOR
AND H-BRIDGE
HPV
DD
SHDN
FS1
24
26
25
30
FS0
15
18
HPS
HPL
CONTROL
GAIN1
GAIN2
29
19
9
INL
HPV
DD
CPV
DD
C1P
10
17
35
HPR
INR
C1
1µF
CHARGE
PUMP
1µF
0.1µF
C1N
12
11
CPGND
MONO_OUT
13
16
2
5, 23, 31
PGND
CPV
V
GND
SS
SS
C2
1µF
*BULK CAPACITANCE IF NEEDED
TYPICAL OPERATING CIRCUIT SHOWN DEPICTS THE MAX9706 WITH:
SSM MODE WITH f = 1150kHz, SPEAKER GAIN = +9dB, MONO SPEAKER GAIN OFFSET = -6.0dB,
OSC
HEADPHONE SPEAKER GAIN = +0dB, AND CROSSOVER FREQUENCY = 1066.7Hz.
22 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Functional Diagram/Typical Operating Circuits (continued)
4.5V TO 5.5V
1µF
10µF*
1µF
V
3
PV
DD
DD
8, 20, 34
V
DD
MAX9707
SYNC_IN
INL
14
36
4
SYNC_OUT
OSCILLATOR
AND SAWTOOTH
C
IN
7
6
OUTL+
OUTL-
CLASS D
MODULATOR
AND H-BRIDGE
0.47µF
LOWPASS/
HIGHPASS
FILTER
33
32
OUTM+
OUTM-
CLASS D
MODULATOR
AND H-BRIDGE
MGAIN
INR
28
27
C
IN
0.47µF
LOWPASS/
HIGHPASS
FILTER
21
22
OUTR+
OUTR-
CLASS D
MODULATOR
AND H-BRIDGE
SHDN
FS1
24
26
25
30
29
FS0
CONTROL
GAIN1
GAIN2
35
MONO_OUT
BIAS
GENERATOR
15
9
I.C.
N.C.
N.C.
N.C.
10
11
12 13 16 17 18 19
1
2
5, 23, 31
N.C. N.C. N.C. N.C. N.C. N.C. BIAS
GND
PGND
C
BIAS
1µF
*BULK CAPACITANCE IF NEEDED
TYPICAL OPERATING CIRCUIT SHOWN DEPICTS THE MAX9707 WITH:
SSM MODE WITH f = 1150kHz, SPEAKER GAIN = +9dB, MONO SPEAKER GAIN OFFSET = -6.0dB,
OSC
AND CROSSOVER FREQUENCY = 1066.7Hz.
______________________________________________________________________________________ 23
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
Pin Configurations
TOP VIEW
TOP VIEW
27 26 25 24 23 22 21 20 19
27 26 25 24 23 22 21 20 19
MGAIN 28
GAIN2 29
GAIN1 30
PGND 31
OUTM- 32
18 HPL
17 HPR
MGAIN 28
GAIN2 29
GAIN1 30
PGND 31
OUTM- 32
18 N.C.
17 N.C.
16 N.C.
15 I.C.
16
V
SS
15 HPS
14 SYNC_IN
14 SYNC_IN
13 N.C.
12 N.C.
MAX9706
MAX9707
OUTM+
PV
OUTM+
PV
33
34
13 CPV
12 C1N
33
34
SS
DD
DD
CPGND
N.C.
MONO_OUT 35
INL 36
11
MONO_OUT 35
INL 36
11
10 C1P
10 N.C.
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
6mm x 6mm TQFN
6mm x 6mm TQFN
Chip Information
TRANSISTOR COUNT: 12,6±6
PROCESS: BICMOS
24 ______________________________________________________________________________________
3-Channel, 2.3W, Filterless Class D Amplifiers
with Active Crossover
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.)
(NE-1) X
e
E
E/2
k
D/2
C
(ND-1) X
e
D
D2
L
D2/2
e
b
E2/2
L
C
L
k
E2
e
L
C
C
L
L
L1
L
L
e
e
A
A1
A2
PACKAGE OUTLINE
36, 40, 48L THIN QFN, 6x6x0.8mm
1
F
21-0141
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
2
F
21-0141
2
The MAX9706/MAX9707 Thin QFN-EP package features an exposed thermal pad on its underside. This pad lowers the pack-
age’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.
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