General DescriptionThe MAX9701 stereo Class D audio power amplifier pro-vides Class AB amplifier audio performance with thebenefits of Class D efficiency, eliminating the need for aheatsink while extending battery life. The MAX9701delivers up to 1.3W per channel into an 8Ω load whileoffering 87% efficiency. Maxim’s next-generation, low-EMI modulation scheme allows the amplifier to operatewithout an external LC filter while still meeting FCC EMIemission levels.
The MAX9701 offers two modulation schemes: a fixed-fre-quency (FFM) mode, and a spread-spectrum (SSM)mode that reduces EMI-radiated emissions. TheMAX9701 oscillator can be synchronized to an externalclock through the SYNC input, allowing synchronization ofmultiple Maxim Class D amplifiers. The sync output(SYNC_OUT) can be used for a master-slave applicationwhere more channels are required. The MAX9701 fea-tures a fully differential architecture, a full bridge-tied load(BTL) output, and comprehensive click-and-pop suppres-sion. The device features internally set gains of 0dB, 6dB,12dB, and 18dB selected through two gain-select inputs,further reducing external component count.
The MAX9701 features high 80dB PSRR, less than 0.1%THD+N, and SNR in excess of 88dB. Short-circuit andthermal-overload protection prevent the device frombeing damaged during a fault condition. The MAX9701 isavailable in 24-pin thin QFN-EP (4mm x 4mm x 0.8mm)and 20-bump UCSP™ (2mm x 2.5mm x 0.6mm) pack-ages. The MAX9701 is specified over the extended -40°C to +85°C temperature range.
ApplicationsCellular Phones
Notebooks
Handheld Gaming Consoles
Docking Stations
MP3 Players
Features♦ Spread-Spectrum Modulation Lowers Radiated
Emissions
♦ Single-Supply Operation (2.5V to 5.5V)
♦ 1.3W Stereo Output (8Ω, VDD = 5V, THD+N = 1%)
♦ No LC Output Filter Required
♦ 87% Efficiency (RL = 8Ω, POUT = 1000mW)
♦ Less Than 0.1% THD+N
♦ High 80dB PSRR
♦ Fully Differential Inputs
♦ Integrated Click-and-Pop Suppression
♦ Typical Low Quiescent Current (9mA)
♦ Typical Low-Power Shutdown Mode (0.1µA)
♦ Short-Circuit and Thermal-Overload Protection
♦ Available in Thermally Efficient, Space-SavingPackages
24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm)20-Bump UCSP (2mm x 2.5mm x 0.6mm)
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
________________________________________________________________ Maxim Integrated Products 1
MAX9701
GAIN2GAIN1
VDD
GAIN
RIGHTMODULATOR
AND H-BRIDGE
SYNC OSCILLATOR
LEFTMODULATOR
AND H-BRIDGE
INR+
INR-
INL+
INL-
SYNC_OUT
Block Diagram
Ordering Information
19-3457; Rev 3; 3/09
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX9701EBP+TG45 -40°C to +85°C 20 UCSP
MAX9701ETG+ -40°C to +85°C 24 TQFN-EP*
Pin Configurations appear at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
+Denotes lead(Pb)-free/RoHS-compliant package.*EP = Exposed pad.
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ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected betweenOUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.
VDD to GND..............................................................................6VVDD to PVDD ..........................................................-0.3V to +0.3VPVDD to PGND .........................................................................6VGND to PGND .......................................................-0.3V to +0.3VAll Other Pins to GND.................................-0.3V to (VDD + 0.3V)Continuous Current In/Out of PVDD, PGND, OUT_.........±800mAContinuous Input Current (all other pins)..........................±20mADuration of OUT_ Short Circuit to GND or PVDD........ContinuousDuration of Short Circuit Between OUT+ and OUT- ......Continuous
Continuous Power Dissipation (TA = +70°C)20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW
Junction Temperature ......................................................+150°COperating Temperature Range ...........................-40°C to +85°CStorage Temperature Range .............................-65°C to +150°CBump Temperature (soldering) Reflow............................+235°CLead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 2.5 5.5 V
VDD = 3.3V, per channel 4.5 8Quiescent Current IDD
VDD = 5V, per channel 6.3 10mA
Shutdown Current ISHDN 0.1 10 μA
Common-Mode Rejection Ratio CMRR fIN = 1kHz 66 dB
Input Bias Voltage VBIAS 1.125 1.25 1.375 V
Turn-On Time tON 40 ms
TA = +25oC ±10 ±30Output Offset Voltage VOS
TMIN < TA < TMAX ±55mV
VDD = 2.5V to 5.5V, VIN = 0V 60 80
fRIPPLE = 217Hz 72Power-Supply Rejection Ratio PSRR 100mVP-P ripple,VIN = 0V fRIPPLE = 20kHz 50
dB
RL = 8Ω 460VDD = 3.3V
RL = 4Ω 750
RL = 8Ω 1300Output Power (Note 3) POUT
THD+N = 1%,TA = +25oC
VDD = 5VRL = 4Ω 2200
mW
RL = 8Ω (POUT = 300mW), f = 1kHz 0.08Total Harmonic Distortion PlusNoise (Note 3)
THD+NRL = 4Ω (POUT = 400mW), f = 1kHz 0.15
%
FFM 86BW = 22Hzto 22kHz SSM 86
FFM 88.5Signal-to-Noise Ratio SNR VOUT = 1VRMS
A-weightedSSM 88.5
dB
SYNC = GND 950 1100 1250SYNC = unconnected 1200 1400 1600
Oscillator Frequency fOSCSYNC = VDD
1200±60
kHz
Minimum On-Time tMIN 200 ns
SYNC Frequency Lock Range fSYNC 1000 1600 kHz
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
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Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For RL = 4Ω, L = 33μH.
For RL = 8Ω, L = 68μH.Note 3: When driving speakers below 4Ω with large signals, exercise care to avoid violating the absolute maximum rating for continuous
output current.Note 4: Testing performed with 8Ω resistive load in series with 68μH inductive load connected across the BTL output. Mode transi-
tions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage under normal operation at rated powerlevel) / (peak voltage during mode transition, no input signal)]. Units are expressed in dB.
ELECTRICAL CHARACTERISTICS (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected betweenOUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SYNC_OUT Capacitance Drive CSYNC_OUT 100 pF
Bridge-tied capacitance 200Capacitive Drive CL
Single ended 400pF
Into shutdown 66.16Click-and-Pop Level KCP
Peak reading, TH D + N = 1%A-weighted, 32 samplesper second (Note 4) Out of
shutdown66.26
dB
VDD = 3.3V, POUT = 500mW per channel,fIN = 1kHz, RL = 8Ω
87
Efficiency ηVDD = 5V, POUT = 1000mW per channel,fIN = 1kHz, RL = 8Ω
87.4
%
GAIN1 = 0, GAIN2 = 0 10.5 15 19.5
GAIN1 = 1, GAIN2 = 0 25
GAIN1 = 0, GAIN2 = 1 37.4Input Resistance RIN
GAIN1 = 1, GAIN2 = 1 50
kΩ
GAIN1 = 0, GAIN2 = 0 18
GAIN1 = 1, GAIN2 = 0 12
GAIN1 = 0, GAIN2 = 1 6Gain AV
GAIN1 = 1, GAIN2 = 1 0
dB
Channel-to-Channel GainTracking
1 %
CrosstalkL to R, R to L, f = 10kHz, RL = 8Ω,POUT = 300mW
70 dB
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High VINH 2 V
Input-Voltage Low VINL 0.8 V
Input Leakage Current(SHDN, GAIN1, GAIN2)
±1 μA
VIN = GND, normal operation -15 -7Input Leakage Current (SYNC)
VIN = VDD, normal operation 12 25μA
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High VOH IOH = 3mA, VDD = 3.3V 2.4 V
Output-Voltage Low VOL IOL = 3mA 0.08 V
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4 _______________________________________________________________________________________
Typical Operating Characteristics(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY
MAX
9701
toc0
1
FREQUENCY (Hz)
THD+
N (%
)
10k1k100
0.1
1
10
0.0110 100k
VDD = 5VRL = 4Ω
OUTPUT POWER = 300mWOUTPUT POWER = 100mW
OUTPUT POWER = 600mW
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY
MAX
9701
toc0
2
FREQUENCY (Hz)
THD+
N (%
)
10k1k100
0.1
1
10
0.0110 100k
VDD = 5VRL = 8Ω
OUTPUT POWER = 250mWOUTPUT POWER = 100mW
OUTPUT POWER = 500mW
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY
MAX
9701
toc0
3
FREQUENCY (Hz)
THD+
N (%
)
10k1k100
0.1
1
10
0.0110 100k
VDD = 3.3VRL = 4Ω
OUTPUT POWER = 300mWOUTPUT POWER = 100mW
OUTPUT POWER = 600mW
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY
MAX
9701
toc0
4
FREQUENCY (Hz)
THD+
N (%
)
10k1k100
0.1
1
10
0.0110 100k
VDD = 3.3VRL = 8Ω
OUTPUT POWER = 100mW
OUTPUT POWER = 400mW
OUTPUT POWER = 250mW
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. FREQUENCY
MAX
9701
toc0
5
FREQUENCY (Hz)
THD+
N (%
)
10k1k100
0.1
1
10
0.0110 100k
VDD = 5VRL = 8ΩPOUT = 800mW
FFM
SSM
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER
MAX
9701
toc0
6
OUTPUT POWER (W)
THD+
N (%
)
2.52.01.51.00.5
0.1
1
10
100
0.010 3.0
VDD = 5VRL = 4Ω
fIN = 10kHz
fIN = 20kHz
fIN = 1kHz
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER
MAX
9701
toc0
7
OUTPUT POWER (W)
THD+
N (%
)
1.51.00.5
0.01
0.1
1
10
100
0.0010 2.0
VDD = 5VRL = 8Ω
fIN = 10kHz
fIN = 20kHz fIN = 1kHz
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER
MAX
9701
toc0
8
OUTPUT POWER (W)
THD+
N (%
)
1.00.80.60.40.2
0.1
1
10
100
0.010 1.2
VDD = 3.3VRL = 4Ω
fIN = 10kHz
fIN = 20kHz
fIN = 1kHz
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER
MAX
9701
toc0
9
OUTPUT POWER (mW)
THD+
N (%
)
600500400300200100
0.1
1
10
100
0.010 700
VDD = 3.3VRL = 8Ω
fIN = 10kHz
fIN = 20kHz
fIN = 1kHz
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
_______________________________________________________________________________________ 5
Typical Operating Characteristics (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
TOTAL HARMONIC DISTORTIONPLUS NOISE vs. OUTPUT POWER
MAX
9701
toc1
0
OUTPUT POWER (W)
THD+
N (%
)
1.61.20.80.4
0.01
0.1
1
10
100
0.0010 2.0
VDD = 5VRL = 8ΩfIN = 1kHz
SSM
FFM
EFFICIENCY vs. OUTPUT POWER
MAX
9701
toc1
1
OUTPUT POWER (W)
EFFI
CIEN
CY (%
)
2.01.51.00.5
10
20
30
40
50
60
70
80
90
100
00 2.5
RL = 8Ω
RL = 4Ω
VDD = 5VfIN = 1kHz
EFFICIENCY vs. OUTPUT POWER
MAX
9701
toc1
2
OUTPUT POWER (W)
EFFI
CIEN
CY (%
)
1.00.80.60.40.2
10
20
30
40
50
60
70
80
90
100
00 1.2
RL = 8Ω
RL = 4Ω
VDD = 3.3VfIN = 1kHz
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX
9701
toc1
3
SUPPLY VOLTAGE (V)
OUTP
UT P
OWER
(W)
5.04.54.03.53.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
02.5 5.5
RL = 4ΩAV = 12dBfIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER vs. SUPPLY VOLTAGEM
AX97
01 to
c14
SUPPLY VOLTAGE (V)
OUTP
UT P
OWER
(W)
5.04.54.03.53.0
0.4
0.8
1.2
1.6
2.0
02.5 5.5
RL = 8ΩAV = 12dBfIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER vs. LOAD RESISTANCE
MAX
9701
toc1
5
LOAD RESISTANCE (Ω)
OUTP
UT P
OWER
(W)
80604020
0.5
1.0
1.5
2.0
2.5
3.0
00 100
VDD = 5VfIN = 1kHz
THD+N = 10%
THD+N = 1%
OUTPUT POWER vs. LOAD RESISTANCE
MAX
9701
toc1
6
LOAD RESISTANCE (Ω)
OUTP
UT P
OWER
(W)
80604020
0.4
0.8
1.2
1.6
2.0
00 100
fIN = 1kHz
THD+N = 10%
THD+N = 1%
POWER-SUPPLY REJECTION RATIOvs. FREQUENCY
MAX
9701
toc1
7
FREQUENCY (Hz)
PSRR
(dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-10010 100k
VRIPPLE = 100mVP-PRL = 8Ω
COMMON-MODE REJECTION RATIOvs. FREQUENCY
MAX
9701
toc1
8
FREQUENCY (Hz)
CMRR
(dB)
10k1k100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-10010 100k
VCM = 100mVP-PRL = 8Ω
VDD = 5V
VDD = 3.3V
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Typical Operating Characteristics (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
CROSSTALK vs. FREQUENCY
MAX
9701
toc1
9
FREQUENCY (Hz)
CROS
STAL
K (d
B)
10k1k100
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-13010 100k
RIGHT TO LEFT
LEFT TO RIGHT
POUT = 300mWRL = 8Ω
CROSSTALK vs. INPUT AMPLITUDE
MAX
9701
toc2
0
INPUT AMPLITUDE (dB)CR
OSST
ALK
(dB)
-14-34-54-74
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-130-94 6
RL = 8ΩfIN = 1kHz
RIGHT TO LEFT
LEFT TO RIGHT
OUTPUT FREQUENCY SPECTRUM
MAX
9701
toc2
1
FREQUENCY (Hz)
OUTP
UT M
AGNI
TUDE
(dBV
)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-1400 20k
FFM MODEVOUT = -60dBVf = 1kHzRL = 8ΩUNWEIGHTED
OUTPUT FREQUENCY SPECTRUM
MAX
9701
toc2
2
FREQUENCY (Hz)
OUTP
UT M
AGNI
TUDE
(dBV
)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-1400 20k
FFM MODEVOUT = -60dBVf = 1kHzRL = 8ΩA-WEIGHTED
OUTPUT FREQUENCY SPECTRUM
MAX
9701
toc2
3
FREQUENCY (Hz)
OUTP
UT M
AGNI
TUDE
(dBV
)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-1400 20k
SSM MODEVOUT = -60dBVf = 1kHzRL = 8ΩUNWEIGHTED
OUTPUT FREQUENCY SPECTRUM
MAX
9701
toc2
4
FREQUENCY (Hz)
OUTP
UT M
AGNI
TUDE
(dBV
)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-1400 20k
SSM MODEVOUT = -60dBVf = 1kHzRL = 8ΩA-WEIGHTED
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WIDEBAND OUTPUT SPECTRUM(FFM MODE)
MAX
9701
toc2
5
FREQUENCY (Hz)
OUTP
UT M
AGNI
TUDE
(dB)
100k10k
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-1001k 1M
RBW = 10kHzINPUT AC GROUNDED
WIDEBAND OUTPUT SPECTRUM(SSM MODE)
MAX
9701
toc2
6
FREQUENCY (Hz)OU
TPUT
MAG
NITU
DE (d
B)100k10k
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-1001k 1M
RBW = 10kHzINPUT AC GROUNDED
TURN-ON/TURN-OFF RESPONSE
MAX
9701
toc2
7
MAX9701OUTPUT
SHDN
0V
250mV/div
2V/div
10ms/div
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX
9701
toc2
8
SUPPLY VOLTAGE (V)
SUPP
LY C
URRE
NT (m
A)
5.04.54.03.53.0
8
11
14
17
20
52.5 5.5
SSM
FFM
BOTH CHANNELS
SHUTDOWN CURRENTvs. SUPPLY VOLTAGE
MAX
9701
toc2
9
SUPPLY VOLTAGE (V)
SHUT
DOW
N CU
RREN
T (μ
A)
5.04.54.03.53.0
1
2
3
4
5
02.5 5.5
BOTH CHANNELS
Typical Operating Characteristics (continued)(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
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Pin Description
PIN
TQFN UCSPNAME FUNCTION
1 A2 SHDN Active-Low Shutdown. Connect to VDD for normal operation.
2 B3 SYNC
Frequency Select and External Clock Input.SYNC = GND: Fixed-frequency mode with fS = 1100kHz.SYNC = Unconnected: Fixed-frequency mode with fS = 1400kHz.SYNC = VDD: Spread-spectrum mode with fS = 1200kHz ±60kHz.SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency.
3, 8, 11, 16 — N.C. No Connection. Not internally connected.
4 A3 OUTL+ Left-Channel Amplifier Output Positive Phase
5, 14 A4, D4 PVDD H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1μF capacitor to PGND.
6, 13 B4, C4 PGND Power Ground
7 A5 OUTL- Left-Channel Amplifier Output Negative Phase
9, 22 B1, B5 GND Analog Ground
10 C5 SYNC_OUT Clock Signal Output
12 D5 OUTR- Right-Channel Amplifier Output Negative Phase
15 D3 OUTR+ Right-Channel Amplifier Output Positive Phase
17 C3 GAIN1 Gain-Select Input 1
18 D2 GAIN2 Gain-Select Input 2
19 D1 INR- Right-Channel Inverting Input
20 C2 INR+ Right-Channel Noninverting Input
21 C1 VDD Analog Power Supply. Connect to PVDD. Bypass with a 10μF capacitor to GND.
23 B2 INL+ Left-Channel Noninverting Input
24 A1 INL- Left-Channel Inverting Input
EP — EPExposed Pad. Connect the exposed thermal pad to the GND plane (see the SupplyBypassing, Layout, and Grounding section).
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Functional Diagram
VBIAS
VBIAS
CLASS DMODULATOR
AND H-BRIDGE
CLASS DMODULATOR
AND H-BRIDGE
BIASGENERATOR
OSCILLATORAND
SAWTOOTH
GAINCONTROL
OUTL+
VBIAS
MAX9701
GND PGND
OUTR+
OUTL-
OUTR-
SYNC_OUT
PVDD
SYNC
INL+
INL-
INR+
INR-
GAIN1
GAIN2
SHDN
RIN
RIN
RIN
RIN
470nF
470nF
470nF
470nF
VDD
VDD
10μF 0.1μF
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Detailed DescriptionThe MAX9701 filterless, stereo Class D audio poweramplifier features several improvements to switch-modeamplifier technology. The MAX9701 offers Class AB per-formance with Class D efficiency, while occupying mini-mal board space. A unique, filterless modulationscheme, synchronizable switching frequency, andspread-spectrum switching mode create a compact,flexible, low-noise, efficient audio power amplifier. Thedifferential input architecture reduces common-modenoise pickup, and can be used without input-couplingcapacitors. The inputs can also be configured to accepta single-ended input signal.
Comparators monitor the MAX9701 inputs and comparethe complementary input voltages to the sawtooth wave-form. The comparators trip when the input magnitude ofthe sawtooth exceeds their corresponding input voltage.Both comparators reset at a fixed time after the risingedge of the second comparator trip point, generating aminimum-width pulse (tON(MIN)) at the output of the sec-ond comparator (Figure 1). As the input voltage increasesor decreases, the duration of the pulse at one outputincreases while the other output pulse duration remainsthe same. This causes the net voltage across the speaker(VOUT+ - VOUT-) to change. The minimum-width pulsehelps the device to achieve high levels of linearity.
1.3W, Filterless, Stereo Class D Audio Power Amplifier
10 ______________________________________________________________________________________
OUT+
OUT-
VIN-
VIN+
VOUT+ - VOUT-
tON(MIN)
tSW
Figure 1. MAX9701 Outputs with an Input Signal Applied
Operating ModesFixed-Frequency (FFM) Mode
The MAX9701 features two fixed-frequency modes.Connect SYNC to GND to select a 1.1MHz switching fre-quency. Leave SYNC unconnected to select a 1.4MHzswitching frequency. The frequency spectrum of theMAX9701 consists of the fundamental switching frequen-cy and its associated harmonics (see the WidebandOutput Spectrum (FFM Mode) graph in the TypicalOperating Characteristics). Program the switching fre-quency so the harmonics do not fall within a sensitive fre-quency band (Table 1). Audio reproduction is notaffected by changing the switching frequency.
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VOUT_+ - VOUT_-
tSW tSW tSW tSW
VIN_-
VIN_+
OUT_+
OUT_-
tON(MIN)
Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode)
Table 1. Operating Modes
SYNC MODE
GND FFM with fOSC = 1100kHz
Unconnected FFM with fOSC = 1400kHz
VDD SSM with fOSC = 1200kHz ±60kHz
Clocked FFM with fOSC = external clock frequency
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Spread-Spectrum (SSM) ModeThe MAX9701 features a unique spread-spectrummode that flattens the wideband spectral components,improving EMI emissions that may be radiated by thespeaker and cables. This mode is enabled by settingSYNC = VDD (Table 1). In SSM mode, the switching fre-quency varies randomly by ±60kHz around the centerfrequency (1.2MHz). The modulation scheme remainsthe same, but the period of the sawtooth waveformchanges from cycle to cycle (Figure 2). Instead of alarge amount of spectral energy present at multiples ofthe switching frequency, the energy is now spread overa bandwidth that increases with frequency. Above afew megahertz, the wideband spectrum looks like whitenoise for EMI purposes (Figure 3). A proprietary amplifi-er topology ensures this does not corrupt the noisefloor in the audio bandwidth.
Synchronous Switching ModeSYNC
The SYNC input allows the MAX9701 to be synchronizedto a user-defined clock, or another Maxim Class D ampli-fier, creating a fully synchronous system, minimizingclock intermodulation, and allocating spectral compo-nents of the switching harmonics to insensitive frequencybands. Applying a TTL clock signal between 1000kHzand 1600kHz to SYNC synchronizes the MAX9701. Theperiod of the SYNC clock can be randomized, allowingthe MAX9701 to be synchronized to another Maxim ClassD amplifier operating in SSM mode.
SYNC_OUTSYNC_OUT allows several MAX9701s as well as otherClass D amplifiers (such as the MAX9700) to be cas-caded. The synchronized output minimizes interfer-ence due to clock intermodulation caused by theswitching spread between single devices. UsingSYNC_OUT, the modulation scheme remains the sameand audio reproduction is not affected by changing theswitching frequency.
Filterless Modulation/Common-Mode IdleThe MAX9701 uses Maxim’s unique modulation schemethat eliminates the LC filter required by traditional class Damplifiers, improving efficiency, reducing componentcount, conserving board space and system cost.Conventional Class D amplifiers output a 50% duty cycle,180° out-of-phase square wave when no signal is pre-sent. With no filter, the square wave appears across theload as a DC voltage, resulting in finite load current,which increases power consumption especially whenidling. When no signal is present at the input of theMAX9701, the amplifiers will output an in-phase squarewave as shown in Figure 4. Because the MAX9701 drivesthe speaker differentially, the two outputs cancel eachother, resulting in no net idle mode voltage across thespeaker, minimizing power consumption.
EfficiencyEfficiency of a Class D amplifier is due to the switchingoperation of the output stage transistors. In a Class Damplifier, the output transistors act as current-steeringswitches and consume negligible additional power.Any power loss associated with the Class D outputstage is mostly due to the I2R loss of the MOSFET on-resistance and quiescent-current overhead.
1.3W, Filterless, Stereo Class D Audio Power Amplifier
12 ______________________________________________________________________________________
VIN_ = 0V
OUT_-
OUT_+
VOUT_+ - VOUT_- = 0V
Figure 4. MAX9701 Outputs with No Input Signal
FREQUENCY (MHz)
AMPL
ITUD
E (d
BμV/
m)
280260240200 22080 100 120 140 160 18060
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
0.0
30 300
Figure 3. MAX9701 with 76mm of Speaker Cable with TDKCommon-Mode Choke: TDK ACM4532-801-20-X
The theoretical best efficiency of a linear amplifier is78%; however, that efficiency is only exhibited at peakoutput powers. Under normal operating levels (typicalmusic reproduction levels), efficiency falls below 30%,whereas the MAX9701 still exhibits >80% efficienciesunder the same conditions (Figure 5).
ShutdownThe MAX9701 has a shutdown mode that reduces powerconsumption and extends battery life. Driving SHDN lowplaces the MAX9701 in a low-power (0.1μA) shutdownmode. Connect SHDN to VDD for normal operation.
Click-and-Pop SuppressionThe MAX9701 features comprehensive click-and-popsuppression that eliminates audible transients on startupand shutdown. While in shutdown, the H-bridge is in ahigh-impedance state. During startup, or power-up, theinput amplifiers are muted and an internal loop sets themodulator bias voltages to the correct levels, preventingclicks and pops when the H-bridge is subsequentlyenabled. For 40ms following startup, a soft-start functiongradually unmutes the input amplifiers.
Applications InformationFilterless Operation
Traditional Class D amplifiers require an output filter torecover the audio signal from the amplifier’s PWM out-put. The filters add cost, increase the solution size ofthe amplifier, and can decrease efficiency. The tradi-tional PWM scheme uses large differential outputswings (2 x VDD(P-P)) and causes large ripple currents.Any parasitic resistance in the filter components resultsin a loss of power, lowering the efficiency.
The MAX9701 does not require an output filter. Thedevice relies on the inherent inductance of the speakercoil and the natural filtering of both the speaker and thehuman ear to recover the audio component of thesquare-wave output. Eliminating the output filter resultsin a smaller, less costly, more efficient solution.
Because the frequency of the MAX9701 output is wellbeyond the bandwidth of most speakers, voice coilmovement due to the square-wave frequency is verysmall. Although this movement is small, a speaker notdesigned to handle the additional power can be dam-aged. For optimum results, use a speaker with a seriesinductance >10μH. Typical 8Ω speakers, for portableaudio applications, exhibit series inductances in therange of 20μH to 100μH.
Output OffsetUnlike a Class AB amplifier, the output offset voltage of aClass D amplifier does not noticeably increase quiescentcurrent draw when a load is applied. This is due to thepower conversion of the Class D amplifier. For example,an 8mV DC offset across an 8Ω load results in 1mA extracurrent consumption in a Class AB device. In the Class Dcase, an 8mV offset into 8Ω equates to an additionalpower drain of 8μW. Due to the high efficiency of theClass D amplifier, this represents an additional quiescentcurrent draw of: 8μW/(VDD / 100 x η), which is on theorder of a few μA.
Selectable GainThe MAX9701 features four selectable gain settings,minimizing external component count. Gains of 0dB,3dB, 12dB, and 18dB are set through gain-selectinputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can behard-wired or digitally controlled. Table 2 shows thesuggested gain settings to attain a maximum outputpower from a given peak input voltage and given loadat VDD = 3.3V and THD+N = 10%.
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0
30
20
10
50
40
90
80
70
60
100
0 0.1 0.2 0.40.3 0.5
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFI
CIEN
CY (%
)
MAX9701
CLASS AB VDD = 3.3Vf = 1kHzRL - 8Ω
Figure 5. MAX9701 Efficiency vs. Class AB Efficiency
GAIN1 GAIN2GAIN(dB)
INPUT(VRMS)
RL(Ω)
POUT(mW)
0 0 +18 0.305 4 1100
1 0 +12 0.615 4 1100
0 1 +6 1.213 4 1100
1 1 0 2.105 4 1100
0 0 +18 0.345 8 725
1 0 +12 0.686 8 725
0 1 +6 1.360 8 725
1 1 0 2.705 8 725
Table 2. Gain Settings
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Input AmplifierDifferential Input
The MAX9701 features a differential input structure,making it compatible with many CODECs and offersimproved noise immunity over a single-ended inputamplifier. In devices such as cellular phones, high-fre-quency signals from the RF transmitter can be pickedup by the amplifier’s input traces. The signals appear atthe amplifier’s inputs as common-mode noise. A differ-ential input amplifier amplifies the difference of the twoinputs, any signal common to both inputs is canceled.
Single-Ended InputThe MAX9701 can be configured as a single-endedinput amplifier by capacitively coupling either input toGND, and driving the other input (Figure 6).
DC-Coupled InputsThe input amplifier can accept DC-coupled inputs thatare biased within the amplifier’s common-mode range(see the Typical Operating Characteristics). DC cou-pling eliminates the input-coupling capacitors, reduc-ing component count to potentially two externalcomponents (Figure 7). However, the highpass filteringeffect of the capacitors is lost, allowing low-frequencysignals to feed through to the load.
Component SelectionInput Filter
An input capacitor, CIN, in conjunction with theMAX9701 input impedance (RIN) forms a highpass filterthat removes the DC bias from an incoming signal. TheAC-coupling capacitor allows the amplifier to automati-cally bias the signal to an optimum DC level. Assumingzero-source impedance, the -3dB point of the highpassfilter is given by:
Choose CIN so f-3dB is well below the lowest frequency ofinterest. Use capacitors whose dielectrics have low-volt-age coefficients, such as tantalum or aluminum electrolyt-ic. Capacitors with high-voltage coefficients, such asceramics, may result in increased distortion at low fre-quencies.
Other considerations when designing the input filterinclude the constraints of the overall system and theactual frequency band of interest. Although high-fidelityaudio calls for a flat-gain response between 20Hz and20kHz, portable voice-reproduction devices such ascellular phones and two-way radios need only concen-trate on the frequency range of the spoken human voice(typically 300Hz to 3.5kHz). In addition, speakers used
fR CdB
IN IN− =3
12π
1.3W, Filterless, Stereo Class D Audio Power Amplifier
14 ______________________________________________________________________________________
MAX9701
0.1μF10μF
2.5V TO 5.5V
0.47μF
0.47μF
0.47μF
0.47μFSINGLE-ENDED
LEFT AUDIO INPUT
SINGLE-ENDEDRIGHT AUDIO INPUT
OUTL+
OUTL-
OUTR+
OUTR-
GAIN1
GND
PGND
SYNC
INL+
INR+
INL-
INR-
GAIN2
SHDN
VDD
PVDD
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB.
Figure 6. Single-Ended Input
MAX9701
0.1μF10μF
2.5V TO 5.5V
OUTL+
OUTL-
OUTR+
OUTR-
GAIN1
GND
PGND
SYNC
INL+
INR+
INL-
INR-
GAIN2
SHDN
VDD
PVDD
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dBCODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.
CODEC
Figure 7. DC-Coupled Inputs
in portable devices typically have a poor responsebelow 300Hz. Taking these two factors into considera-tion, the input filter may not need to be designed for a20Hz to 20kHz response, saving both board space andcost due to the use of smaller capacitors.
Output FilterThe MAX9701 does not require an output filter. Thedevice passes FCC emissions standards with 76mm ofunshielded speaker cables. However, output filteringcan be used if a design is failing radiated emissions dueto board layout or cable length, or if the circuit is nearEMI-sensitive devices. Use a ferrite bead filter whenradiated frequencies above 10MHz are of concern. Usean LC filter or a common-mode choke when radiatedemissions below 10MHz are of concern, or when longleads (>76mm) connect the amplifier to the speaker.
2.1 Channel ConfigurationThe typical 2.1 channel application circuit (Figure 8)shows the MAX9701 configured as a mid-/high-frequencyamplifier and the MAX9700 configured as a mono bassamplifier. Input capacitors (CIN) set the highpass cutofffrequency according to the following equation:
where RIN is the typical input resistance of theMAX9701. The 10μF capacitors on the output of theMAX9701 ensure a two-pole highpass filter.
fR CIN IN
=× ×
12π
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MAX9701
MAX9700
MAX4238
INR+
INL+
INL-
INR-
SYNC
5V
OUTL+
OUTL-
OUTR+
OUTR-
8Ω
8Ω
SYNC_OUT
10μF
10μFCIN
2200pF
1μF
1μF
5V
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.FFM MODE WITH fOSC = 1100kHz.
OUT+
OUT-
SYNC
IN+
IN-1.25V
R3 10kΩ
C2 1nF
R1 20kΩ
R2 20kΩ
R4 39kΩ
C2 0.01μF
VDD
CIN2200pF
CIN2200pF
CIN2200pF
4Ω
Figure 8. 2.1 Channel Application Circuit
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where R1 = R2 and R3 = R1//R2. The cutoff frequencyof the lowpass filter is set by the following equation:
Supply Bypassing, Layout, and GroundingProper layout and grounding are essential for optimumperformance. Use large traces for the power-supplyinputs and amplifier outputs to minimize losses due toparasitic trace resistance. Large traces also aid in movingheat away from the package. Proper grounding improvesaudio performance, minimizes crosstalk between chan-nels, and prevents any switching noise from coupling intothe audio signal. Connect PGND and GND together at asingle point on the PC board. Route all traces that carryswitching transients away from GND and the traces/com-ponents in the audio signal path.
Bypass VDD with 10μF to GND and PVDD with 0.1μF toPGND. Place the bypass capacitors as close to theMAX9701 as possible. Use large, low-resistance outputtraces. Current drawn from the outputs increases as loadimpedance decreases. High-output trace resistancedecreases the power delivered to the load. Large output,supply, and GND traces allow more heat to move fromthe MAX9701 to the air, decreasing the thermal imped-ance of the circuit.
The MAX9701 thin QFN-EP package features anexposed thermal pad on its underside. This pad lowersthe package’s thermal impedance by providing adirect heat conduction path from the die to the printedcircuit board. Connect the exposed thermal pad to theGND plane.
UCSP Applications InformationFor the latest application details on UCSP construction,dimensions, tape carrier information, printed circuit boardtechniques, bump-pad layout, and recommended reflowtemperature profile as well as the latest information onreliability testing results, refer to Application Note:UCSP—A Wafer-Level Chip-Scale Package available onMaxim’s website at www.maxim-ic.com/ucsp.
fC C R R
= ×× × ×
12
11 2 3 4π
− ×2 3
1
RR
1.3W, Filterless, Stereo Class D Audio Power Amplifier
16 ______________________________________________________________________________________
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MAX4060
MAX9701
MAX9722B
CODEC
AUX_IN
BIAS
IN+
IN-
VCC
OUTL-
OUTL+
OUTR+
OUTR-
INL
INR
C1P CINSVSS
PVSS
OUTR
OUTL
VDD
0.1μF
0.1μF
0.1μF
2.2kΩ
2.2kΩ
VDD
μCONTROLLER
INL+
SYNC
OUT
1μF
1μF
1μF
1μF
1μF
SHDN
SHDN
GND
470nF
470nF
470nF
470nF
GAIN1
GAIN2
INL-
INR-
INR+
0.1μF10μF
VDD
VDD PVDD
GND PGND
0.1μF
System Diagram
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Chip InformationTRANSISTOR COUNT: 5688
PROCESS: BiCMOS
GND INL+ SYNC PGND GND
VDD INR+ GAIN1 PGND SYNC_OUT
INR- GAIN2 OUTR+ PVDD OUTR-
INL- SHDN OUTL+ PVDD OUTL-A
B
C
D
1 2 3 4 5
MAX9701
UCSP
TOP VIEW(BUMPS ON BOTTOM)
MAX9701
18 17 16 15 14
19
TQFN
TOP VIEW
13
1 2 3 4 5 6
24
23
22
21
20
12
7
8
9
10
11
INL+
VDD
INR+
INR-
INL-
GND
N.C.
SYNC_OUT
N.C.
OUTR-
OUTL-
GND
SHDN
SYNC N.C.
OUTL
+
PVDD
PGND
GAIN
2
GAIN
1
N.C.
OUTR
+
PVDD
PGND
Pin Configurations
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
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24L
QFN
TH
IN.E
PS
Package InformationFor the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in thepackage code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to thepackage regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
24 TQFN-EP T2444-4 21-0139
20 UCSP B20-1 21-0095
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
20 ______________________________________________________________________________________
Package Information (continued)For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in thepackage code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to thepackage regardless of RoHS status.
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5x4
UC
SP
.EP
S
Package Information (continued)For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in thepackage code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to thepackage regardless of RoHS status.
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses areimplied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISIONNUMBER
REVISIONDATE
DESCRIPTIONPAGES
CHANGED
3 3/09 Added G45 option to Ordering Information 1