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19-3457; Rev 3; 3/09
1.3W, Filterless, Stereo Class D Audio Power Amplifier
General Description
The MAX9701 stereo Class D audio power amplifier provides Class AB amplifier audio performance with the benefits of Class D efficiency, eliminating the need for a heatsink while extending battery life. The MAX9701 delivers up to 1.3W per channel into an 8 load while offering 87% efficiency. Maxim's next-generation, lowEMI modulation scheme allows the amplifier to operate without an external LC filter while still meeting FCC EMI emission levels. The MAX9701 offers two modulation schemes: a fixed-frequency (FFM) mode, and a spread-spectrum (SSM) mode that reduces EMI-radiated emissions. The MAX9701 oscillator can be synchronized to an external clock through the SYNC input, allowing synchronization of multiple Maxim Class D amplifiers. The sync output (SYNC_OUT) can be used for a master-slave application where more channels are required. The MAX9701 features a fully differential architecture, a full bridge-tied load (BTL) output, and comprehensive click-and-pop suppression. 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 and thermal-overload protection prevent the device from being damaged during a fault condition. The MAX9701 is available in 24-pin thin QFN-EP (4mm x 4mm x 0.8mm), and 20-bump UCSPTM (2mm x 2.5mm x 0.6mm) packages. The MAX9701 is specified over the extended -40C to +85C temperature range.
Features
o Patented Spread-Spectrum Modulation Lowers Radiated Emissions o Single-Supply Operation (2.5V to 5.5V) o 1.3W Stereo Output (8, VDD = 5V, THD+N = 1%) o No LC Output Filter Required o 87% Efficiency (RL = 8, POUT = 1000mW) o Less Than 0.1% THD+N o High 80dB PSRR o Fully Differential Inputs o Integrated Click-and-Pop Suppression o Typical Low Quiescent Current (9mA) o Typical Low-Power Shutdown Mode (0.1A) o Short-Circuit and Thermal-Overload Protection o Available in Thermally Efficient, Space-Saving Packages 24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm) 20-Bump UCSP (2mm x 2.5mm x 0.6mm)
MAX9701
Ordering Information
PART MAX9701EBP+TG45 MAX9701ETG+ TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 20 UCSP 24 TQFN-EP*
Applications
Cellular Phones Notebooks Handheld Gaming Consoles Docking Stations MP3 Players
+Denotes lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
Block Diagram
VDD
MAX9701
INR+ RIGHT MODULATOR AND H-BRIDGE INR-
Pin Configurations appear at end of data sheet.
GAIN1 GAIN2
GAIN
INL+ LEFT MODULATOR AND H-BRIDGE INLOSCILLATOR
SYNC
SYNC_OUT
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products 1
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.
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
ABSOLUTE MAXIMUM RATINGS
VDD to GND..............................................................................6V VDD to PVDD ..........................................................-0.3V to +0.3V PVDD to PGND .........................................................................6V GND to PGND .......................................................-0.3V to +0.3V All Other Pins to GND.................................-0.3V to (VDD + 0.3V) Continuous Current In/Out of PVDD, PGND, OUT_ .........800mA Continuous Input Current (all other pins)..........................20mA Duration of OUT_ Short Circuit to GND or PVDD ........Continuous Duration of Short Circuit Between OUT+ and OUT- ......Continuous Continuous Power Dissipation (TA = +70C) 20-Bump UCSP (derate 10mW/C above +70C) ...........800mW 24-Pin Thin QFN (derate 20.8mW/C above +70C) ..1666.7mW Junction Temperature ......................................................+150C Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Bump Temperature (soldering) Reflow............................+235C Lead Temperature (soldering, 10s) .................................+300C
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 = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between OUT+ and OUT-, RL = , TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2)
PARAMETER GENERAL Supply Voltage Range Quiescent Current Shutdown Current Common-Mode Rejection Ratio Input Bias Voltage Turn-On Time Output Offset Voltage VDD IDD ISHDN CMRR VBIAS tON VOS TA = +25oC TMIN < TA < TMAX VDD = 2.5V to 5.5V, VIN = 0V Power-Supply Rejection Ratio PSRR 100mVP-P ripple, VIN = 0V THD+N = 1%, TA = +25oC fRIPPLE = 217Hz fRIPPLE = 20kHz VDD = 3.3V VDD = 5V RL = 8 RL = 4 RL = 8 RL = 4 60 80 72 50 460 750 1300 2200 0.08 0.15 86 86 88.5 88.5 950 1200 1100 1400 1200 60 200 1000 1600 1250 1600 kHz dB % mW dB fIN = 1kHz 1.125 Inferred from PSRR test VDD = 3.3V, per channel VDD = 5V, per channel 2.5 4.5 6.3 0.1 66 1.25 40 10 30 55 1.375 5.5 8 10 10 V mA A dB V ms mV SYMBOL CONDITIONS MIN TYP MAX UNITS
Output Power (Note 3)
POUT
Total Harmonic Distortion Plus Noise (Note 3)
THD+N
RL = 8 (POUT = 300mW), f = 1kHz RL = 4 (POUT = 400mW), f = 1kHz BW = 22Hz to 22kHz FFM SSM FFM SSM
Signal-to-Noise Ratio
SNR
VOUT = 1VRMS A-weighted SYNC = GND SYNC = unconnected
Oscillator Frequency
fOSC SYNC = VDD
Minimum On-Time SYNC Frequency Lock Range
tMIN fSYNC
ns kHz
2
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between OUT+ and OUT-, RL = , TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2)
PARAMETER SYNC_OUT Capacitance Drive Capacitive Drive SYMBOL CSYNC_OUT CL Bridge-tied capacitance Single ended Peak reading, THD+N = 1% Into shutdown A-weighted, 32 samples Out of per second (Note 4) shutdown VDD = 3.3V, POUT = 500mW per channel, fIN = 1kHz, RL = 8 VDD = 5V, POUT = 1000mW per channel, fIN = 1kHz, RL = 8 GAIN1 = 0, GAIN2 = 0 Input Resistance RIN GAIN1 = 1, GAIN2 = 0 GAIN1 = 0, GAIN2 = 1 GAIN1 = 1, GAIN2 = 1 GAIN1 = 0, GAIN2 = 0 Gain AV GAIN1 = 1, GAIN2 = 0 GAIN1 = 0, GAIN2 = 1 GAIN1 = 1, GAIN2 = 1 Channel-to-Channel Gain Tracking Crosstalk L to R, R to L, f = 10kHz, RL = 8, POUT = 300mW VINH VINL 2 0.8 1 VIN = GND, normal operation VIN = VDD, normal operation DIGITAL OUTPUTS (SYNC_OUT) Output-Voltage High Output-Voltage Low VOH VOL IOH = 3mA, VDD = 3.3V IOL = 3mA 2.4 0.08 V V -15 -7 A 12 25 10.5 CONDITIONS MIN TYP 100 200 400 66.16 dB 66.26 87 % 87.4 15 25 37.4 50 18 12 6 0 1 70 % dB dB 19.5 k MAX UNITS pF pF
MAX9701
Click-and-Pop Level
KCP
Efficiency
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2) Input-Voltage High Input-Voltage Low Input Leakage Current (SHDN, GAIN1, GAIN2) Input Leakage Current (SYNC) V V A
Note 1: All devices are 100% production tested at +25C. 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 = 4, L = 33H. For RL = 8, L = 68H. Note 3: When driving speakers below 4 with large signals, exercise care to avoid violating the absolute maximum rating for continuous output current. Note 4: Testing performed with 8 resistive load in series with 68H inductive load connected across the BTL output. Mode transitions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage under normal operation at rated power level) / (peak voltage during mode transition, no input signal)]. Units are expressed in dB. _______________________________________________________________________________________ 3
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Typical Operating Characteristics
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9701 toc01
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9701 toc02
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
VDD = 3.3V RL = 4
MAX9701 toc03
10 VDD = 5V RL = 4
10 VDD = 5V RL = 8
10
1 THD+N (%) THD+N (%) OUTPUT POWER = 600mW
1 THD+N (%) OUTPUT POWER = 500mW 0.1 OUTPUT POWER = 100mW OUTPUT POWER = 300mW
1 OUTPUT POWER = 600mW
0.1
0.1 OUTPUT POWER = 100mW OUTPUT POWER = 100mW OUTPUT POWER = 250mW 10 100 1k FREQUENCY (Hz) 10k 100k OUTPUT POWER = 300mW 0.01 10 100 1k FREQUENCY (Hz) 10k 100k
0.01 10 100 1k FREQUENCY (Hz) 10k 100k
0.01
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9701 toc04
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9701 toc05
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 5V RL = 4 10
MAX9701 toc06
10 VDD = 3.3V RL = 8
10 VDD = 5V RL = 8 POUT = 800mW 1 THD+N (%)
100
1 THD+N (%) OUTPUT POWER = 400mW 0.1 OUTPUT POWER = 100mW OUTPUT POWER = 250mW 0.01 10 100 1k FREQUENCY (Hz) 10k 100k
THD+N (%)
fIN = 10kHz 1
FFM 0.1
0.1 SSM 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 0 0.5 1.0 1.5 2.0 fIN = 20kHz
fIN = 1kHz
2.5
3.0
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9701 toc07
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9701 toc08
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 3.3V RL = 8 10 THD+N (%)
MAX9701 toc09
100 VDD = 5V RL = 8 10 fIN = 10kHz THD+N (%) 1
100 VDD = 3.3V RL = 4 10 THD+N (%)
100
1
fIN = 10kHz
fIN = 1kHz
1
fIN = 10kHz
0.1 fIN = 20kHz fIN = 1kHz
0.01
0.1
fIN = 20kHz
0.1 fIN = 1kHz fIN = 20kHz 0.01
0.001 0 0.5 1.0 OUTPUT POWER (W) 1.5 2.0
0.01 0 0.2 0.4 0.6 0.8 1.0 1.2 OUTPUT POWER (W)
0
100
200
300
400
500
600
700
OUTPUT POWER (mW)
4
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
MAX9701
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9701 toc10
EFFICIENCY vs. OUTPUT POWER
90 80 EFFICIENCY (%) 70 60 50 40 30 RL = 4 RL = 8
MAX9701 toc11
EFFICIENCY vs. OUTPUT POWER
90 80 EFFICIENCY (%) 70 60 50 40 30 20 RL = 4 RL = 8
MAX9701 toc12
100 VDD = 5V RL = 8 fIN = 1kHz
100
100
10
THD+N (%)
1 SSM 0.1 FFM
0.01
20 10 VDD = 5V fIN = 1kHz 0 0.5 1.0 1.5 2.0 2.5
10 0 0 0.2 0.4 0.6 0.8
VDD = 3.3V fIN = 1kHz 1.0 1.2
0.001 0 0.4 0.8 1.2 1.6 2.0 OUTPUT POWER (W)
0 OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9701 toc13
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9701 toc14
OUTPUT POWER vs. LOAD RESISTANCE
VDD = 5V fIN = 1kHz
MAX9701 toc15
3.5 3.0 OUTPUT POWER (W) 2.5 2.0 1.5 1.0 THD+N = 1% 0.5 0 2.5 3.0 3.5 4.0 4.5 5.0 THD+N = 10% RL = 4 AV = 12dB fIN = 1kHz
2.0 RL = 8 AV = 12dB fIN = 1kHz
3.0 2.5 OUTPUT POWER (W) 2.0 1.5 1.0 0.5 0 THD+N = 1% THD+N = 10%
1.6 OUTPUT POWER (W)
1.2
THD+N = 10%
0.8 THD+N = 1%
0.4
0 5.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V)
0
20
40
60
80
100
LOAD RESISTANCE ()
OUTPUT POWER vs. LOAD RESISTANCE
MAX9701 toc16
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX9701 toc17
COMMON-MODE REJECTION RATIO vs. FREQUENCY
-10 -20 -30 CMRR (dB) -40 -50 -60 -70 -80 -90 -100 VDD = 3.3V VDD = 5V VCM = 100mVP-P RL = 8
MAX9701 toc18
2.0 fIN = 1kHz 1.6 OUTPUT POWER (W) THD+N = 10%
0 -10 -20 -30 PSRR (dB) -40 -50 -60 -70 VRIPPLE = 100mVP-P RL = 8
0
1.2
0.8
THD+N = 1%
0.4
-80 -90
0 0 20 40 60 80 100 LOAD RESISTANCE ()
-100 10 100 1k FREQUENCY (Hz) 10k 100k
10
100
1k FREQUENCY (Hz)
10k
100k
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5
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
CROSSTALK vs. FREQUENCY
MAX9701 toc19
CROSSTALK vs. INPUT AMPLITUDE
-40 -50 CROSSTALK (dB) -60 -70 -80 -90 -100 -110 LEFT TO RIGHT RL = 8 fIN = 1kHz
MAX9701 toc20
-30 -40 -50 CROSSTALK (dB) -60 -70 -80 -90 -100 -110 -120 -130 10 100 1k FREQUENCY (Hz) 10k RIGHT TO LEFT LEFT TO RIGHT POUT = 300mW RL = 8
-30
RIGHT TO LEFT
-120 -130 100k -94 -74 -54 -34 -14 6 INPUT AMPLITUDE (dB)
OUTPUT FREQUENCY SPECTRUM
MAX9701 toc21
OUTPUT FREQUENCY SPECTRUM
FFM MODE VOUT = -60dBV f = 1kHz RL = 8 A-WEIGHTED
MAX9701 toc22
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 0 5k 10k FREQUENCY (Hz) 15k FFM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140
20k
0
5k
10k FREQUENCY (Hz)
15k
20k
OUTPUT FREQUENCY SPECTRUM
MAX9701 toc23
OUTPUT FREQUENCY SPECTRUM
SSM MODE VOUT = -60dBV f = 1kHz RL = 8 A-WEIGHTED
MAX9701 toc24
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 0 5k 10k FREQUENCY (Hz) 15k SSM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140
20k
0
5k
10k FREQUENCY (Hz)
15k
20k
6
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
WIDEBAND OUTPUT SPECTRUM (SSM MODE)
MAX9701 toc25
MAX9701
WIDEBAND OUTPUT SPECTRUM (FFM MODE)
0 -10 OUTPUT MAGNITUDE (dB) -20 -30 -40 -50 -60 -70 -80 -90 -100 1k 10k 100k 1M FREQUENCY (Hz) RBW = 10kHz INPUT AC GROUNDED 0 -10 OUTPUT MAGNITUDE (dB) -20 -30 -40 -50 -60 -70 -80 -90 -100 1k
RBW = 10kHz INPUT AC GROUNDED
10k
100k
1M
FREQUENCY (Hz)
TURN-ON/TURN-OFF RESPONSE
MAX9701 toc27
SUPPLY CURRENT vs. SUPPLY VOLTAGE
BOTH CHANNELS 2V/div 0V 17 SUPPLY CURRENT (mA)
MAX9701 toc28
20
SHDN
14 SSM 11 FFM
MAX9701 OUTPUT
250mV/div
8
5 10ms/div 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
BOTH CHANNELS SHUTDOWN CURRENT (A) 4
MAX9701 toc29
5
3
2
1
0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
MAX9701 toc26
7
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Pin Description
PIN TQFN 1 UCSP A2 NAME SHDN FUNCTION Active-Low Shutdown. Connect to VDD for normal operation. 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. No Connection. Not internally connected. Left-Channel Amplifier Output Positive Phase H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1F capacitor to PGND. Power Ground Left-Channel Amplifier Output Negative Phase Analog Ground Clock Signal Output Right-Channel Amplifier Output Negative Phase Right-Channel Amplifier Output Positive Phase Gain-Select Input 1 Gain-Select Input 2 Right-Channel Inverting Input Right-Channel Noninverting Input Analog Power Supply. Connect to PVDD. Bypass with a 10F capacitor to GND. Left-Channel Noninverting Input Left-Channel Inverting Input Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply Bypassing, Layout, and Grounding section).
2
B3
SYNC
3, 8, 11, 16 4 5, 14 6, 13 7 9, 22 10 12 15 17 18 19 20 21 23 24 EP
-- A3 A4, D4 B4, C4 A5 B1, B5 C5 D5 D3 C3 D2 D1 C2 C1 B2 A1 --
N.C. OUTL+ PVDD PGND OUTLGND SYNC_OUT OUTROUTR+ GAIN1 GAIN2 INRINR+ VDD INL+ INLEP
8
_______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio Power Amplifier
Functional Diagram
MAX9701
VDD
10F
0.1F
VDD SYNC OSCILLATOR AND SAWTOOTH
PVDD SYNC_OUT
470nF INL+
RIN
VBIAS CLASS D MODULATOR AND H-BRIDGE
OUTL+ OUTL-
470nF
INL-
RIN
470nF INR+
RIN CLASS D MODULATOR AND H-BRIDGE RIN VBIAS
OUTR+ OUTR-
470nF INR-
VBIAS BIAS GENERATOR
GAIN1 GAIN2 SHDN GND PGND GAIN CONTROL
MAX9701
_______________________________________________________________________________________
9
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9701 Outputs with an Input Signal Applied
Detailed Description
The MAX9701 filterless, stereo Class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9701 offers Class AB performance with Class D efficiency, while occupying minimal board space. A unique, filterless modulation scheme, synchronizable switching frequency, and spread-spectrum switching mode create a compact, flexible, low-noise, efficient audio power amplifier. The differential input architecture reduces common-mode noise pickup, and can be used without input-coupling capacitors. The inputs can also be configured to accept a single-ended input signal.
Comparators monitor the MAX9701 inputs and compare the complementary input voltages to the 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 (tON(MIN)) at the output of the second comparator (Figure 1). 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.
10
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
tSW tSW tSW tSW
VIN_-
VIN_+
OUT_-
OUT_+
tON(MIN)
VOUT_+ - VOUT_-
Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode)
Operating Modes
Fixed-Frequency (FFM) Mode The MAX9701 features two fixed-frequency modes. Connect SYNC to GND to select a 1.1MHz switching frequency. Leave SYNC unconnected to select a 1.4MHz switching frequency. The frequency spectrum of the MAX9701 consists of the fundamental switching frequency and its associated harmonics (see the Wideband Output Spectrum (FFM Mode) 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.
Table 1. Operating Modes
SYNC GND Unconnected VDD Clocked MODE FFM with fOSC = 1100kHz FFM with fOSC = 1400kHz SSM with fOSC = 1200kHz 60kHz FFM with fOSC = external clock frequency
______________________________________________________________________________________
11
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
VIN_ = 0V
50.0 45.0 40.0 AMPLITUDE (dBV/m) 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 30 60 80 100 120 140 160 180 200 220 240 260 280 300
OUT_-
OUT_+
FREQUENCY (MHz)
VOUT_+ - VOUT_- = 0V
Figure 3. MAX9701 with 76mm of Speaker Cable with TDK Common-Mode Choke: TDK ACM4532-801-20-X
Figure 4. MAX9701 Outputs with No Input Signal
Spread-Spectrum (SSM) Mode The MAX9701 features a unique, patented spreadspectrum mode that flattens the wideband spectral components, improving EMI emissions that may be radiated by the speaker and cables. This mode is enabled by setting SYNC = V DD (Table 1). In SSM mode, the switching frequency varies randomly by 60kHz around the center frequency (1.2MHz). The modulation scheme remains the same, but the period of the sawtooth waveform changes from cycle to cycle (Figure 2). 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 (Figure 3). A proprietary amplifier topology ensures this does not corrupt the noise floor in the audio bandwidth.
SYNC_OUT SYNC_OUT allows several MAX9701s as well as other Class D amplifiers (such as the MAX9700) to be cascaded. The synchronized output minimizes interference due to clock intermodulation caused by the switching spread between single devices. Using SYNC_OUT, the modulation scheme remains the same and audio reproduction is not affected by changing the switching frequency.
Filterless Modulation/Common-Mode Idle
The MAX9701 uses 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, 180 out-of-phase 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, which increases power consumption especially when idling. When no signal is present at the input of the MAX9701, the amplifiers will output an in-phase square wave as shown in Figure 4. Because the MAX9701 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker, minimizing power consumption.
Synchronous Switching Mode
SYNC The SYNC input allows the MAX9701 to be synchronized to a user-defined clock, or another Maxim Class D amplifier, creating 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 1000kHz and 1600kHz to SYNC synchronizes the MAX9701. The period of the SYNC clock can be randomized, allowing the MAX9701 to be synchronized to another Maxim Class D amplifier operating in SSM mode.
Efficiency
Efficiency 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 output stage is mostly due to the I2R loss of the MOSFET onresistance, and quiescent-current overhead.
12
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
EFFICIENCY vs. OUTPUT POWER
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W) CLASS AB VDD = 3.3V f = 1kHz RL - 8 MAX9701
The MAX9701 does not require an output filter. The device relies 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 MAX9701 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 >10H. Typical 8 speakers, for portable audio applications, exhibit series inductances in the range of 20H to 100H.
MAX9701
Figure 5. MAX9701 Efficiency vs. Class AB Efficiency
Output Offset
Unlike a Class AB amplifier, the output offset voltage of a Class D amplifier does not noticeably increase quiescent current draw when a load is applied. This is due to the power conversion of the Class D amplifier. For example, an 8mV DC offset across an 8 load results in 1mA extra current consumption in a Class AB device. In the Class D case, an 8mV offset into 8 equates to an additional power drain of 8W. Due to the high efficiency of the Class D amplifier, this represents an additional quiescent current draw of: 8W/(VDD / 100 x ), which is on the order of a few A.
The theoretical best efficiency of a linear amplifier is 78%, however that efficiency is only exhibited at peak output powers. Under normal operating levels (typical music reproduction levels), efficiency falls below 30%, whereas the MAX9701 still exhibits >80% efficiencies under the same conditions (Figure 5).
Shutdown
The MAX9701 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9701 in a low-power (0.1A) shutdown mode. Connect SHDN to VDD for normal operation.
Selectable Gain
The MAX9701 features four selectable gain settings, minimizing external component count. Gains of 0dB, 3dB, 12dB, and 18dB are set through gain-select inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be hard-wired or digitally controlled. Table 2 shows the suggested gain settings to attain a maximum output power from a given peak input voltage and given load at VDD = 3.3V and THD+N = 10%.
Click-and-Pop Suppression
The MAX9701 features 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. For 40ms following startup, a soft-start function gradually unmutes the input amplifiers.
Table 2. Gain Settings
GAIN1 0 1 0 1 0 1 0 1 GAIN2 0 0 1 1 0 0 1 1 GAIN (dB) +18 +12 +6 0 +18 +12 +6 0 INPUT (VRMS) 0.305 0.615 1.213 2.105 0.345 0.686 1.360 2.705 RL () 4 4 4 4 8 8 8 8 POUT (mW) 1100 1100 1100 1100 725 725 725 725
Applications Information
Filterless 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.
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13
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
0.47F SINGLE-ENDED LEFT AUDIO INPUT 0.47F SINGLE-ENDED RIGHT AUDIO INPUT INR+ INL0.47F 0.47F OUTRGAIN2 GAIN1 SHDN 2.5V TO 5.5V VDD PVDD 10F 0.1F SYNC GND PGND 10F 0.1F SYNC 2.5V TO 5.5V OUTRGAIN2 GAIN1 SHDN VDD PVDD GND PGND INRCODEC INR+ INL+ OUTL+ INL+ INLOUTL+
MAX9701
OUTLINROUTR+
MAX9701
OUTLOUTR+
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB.
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.
Figure 6. Single-Ended Input
Figure 7. DC-Coupled Inputs
Input Amplifier
Differential Input The MAX9701 features a differential input structure, making it compatible with many CODECs and offers improved noise immunity over a single-ended input amplifier. In devices such as cellular phones, high-frequency signals from the RF transmitter can be picked up by the amplifier's input traces. The signals appear at the amplifier's inputs as common-mode noise. A differential input amplifier amplifies the difference of the two inputs, any signal common to both inputs is canceled. Single-Ended Input The MAX9701 can be configured as a single-ended input amplifier by capacitively coupling either input to GND, and driving the other input (Figure 6). DC-Coupled Inputs The input amplifier can accept DC-coupled inputs that are biased within the amplifier's common-mode range (see the Typical Operating Characteristics). DC coupling eliminates the input-coupling capacitors, reducing component count to potentially two external components (Figure 7). However, the highpass filtering effect of the capacitors is lost, allowing low-frequency signals to feed through to the load.
Component Selection
Input Filter An input capacitor, C IN , in conjunction with the MAX9701 input impedance (RIN) 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 2RINCIN
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. Other considerations when designing the input filter include the constraints of the overall system and the actual frequency band of interest. Although high-fidelity audio calls for a flat-gain response between 20Hz and 20kHz, portable voice-reproduction devices such as cellular phones and two-way radios need only concentrate on the frequency range of the spoken human voice (typically 300Hz to 3.5kHz). In addition, speakers used
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1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
5V CIN 2200pF INL+ CIN 2200pF INR+ CIN 2200pF INLCIN 2200pF INROUTRSYNC SYNC_OUT OUTR+ 8 OUTL+ 10F
MAX9701
OUTL10F
8
R3 10k R1 20k R4 39k R2 20k C2 0.01F 1.25V SYNC C2 1nF 1F IN+
5V VDD
MAX9700
OUT+ 4
MAX4238
1F INOUT-
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V. FFM MODE WITH fOSC = 1100kHz.
Figure 8. 2.1 Channel Application Circuit
in portable devices typically have a poor response below 300Hz. Taking these two factors into consideration, the input filter may not need to be designed for a 20Hz to 20kHz response, saving both board space and cost due to the use of smaller capacitors.
2.1 Channel Configuration
The typical 2.1 channel application circuit (Figure 8) shows the MAX9701 configured as a mid-/high-frequency amplifier and the MAX9700 configured as a mono bass amplifier. Input capacitors (CIN) set the highpass cutoff frequency according to the following equation: f= 1 2 x RIN x CIN
Output Filter The MAX9701 does not require an output filter. The device passes FCC emissions standards with 76mm of unshielded speaker cables. However, output filtering can be used if a design is failing radiated emissions due to board layout or cable length, or if the circuit is near EMI-sensitive devices. Use a ferrite bead filter when radiated frequencies above 10MHz are of concern. Use an LC filter or a common-mode choke when radiated emissions below 10MHz are of concern, or when long leads (>76mm) connect the amplifier to the speaker.
where R IN is the typical input resistance of the MAX9701. The 10F capacitors on the output of the MAX9701 ensure a two-pole highpass filter.
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1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Low frequencies are summed through a two-pole lowpass filter and sent to the MAX9700 mono speaker amplifier. The passband gain of the lowpass filter is unity for in-phase stereo signals, -2 x R3 R1 where R1 = R2 and R3 = R1//R2. The cutoff frequency of the lowpass filter is set by the following equation: f= 1 x 2 1 C1 x C2 x R 3 x R4 Bypass VDD with 10F to GND and PVDD with 0.1F to PGND. Place the bypass capacitors as close to the MAX9701 as possible. Use large, low-resistance output traces. Current drawn from the outputs increases 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 MAX9701 to the air, decreasing the thermal impedance of the circuit. The MAX9701 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. Connect the exposed thermal pad to the GND plane.
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 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. Route all traces that carry switching transients away from GND and the traces/components in the audio signal path.
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommended reflow temperature profile as well as the latest information on reliability testing results, refer to Application Note: UCSP--A Wafer-Level Chip-Scale Package available on Maxim's website at www.maxim-ic.com/ucsp.
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
System Diagram
MAX9701
VDD
10F 0.1F VDD 0.1F AUX_IN VCC 470nF INR+ 2.2k BIAS 2.2k 0.1F IN+ IN0.1F 470nF INL+ GAIN1 GND GAIN2 SHDN GND SYNC PGND PVDD
0.1F
MAX9701
MAX4060
OUT CODEC
470nF INR470nF INL-
OUTR+ OUTR-
OUTLOUTL+
VDD 1F
VDD SHDN 1F INL 1F INR CONTROLLER PVSS SVSS C1P CIN 1F OUTL
MAX9722B
OUTR
1F
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1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Pin Configurations
TOP VIEW
OUTR+ GAIN2 GAIN1 PVDD N.C. PGND
TOP VIEW (BUMPS ON BOTTOM)
1 2
MAX9701
3 4 5
18 INR- 19 INR+ 20 VDD 21 GND 22 INL+ 23 INL- 24 1 SHDN
17
16
15
14
13 12 OUTR11 N.C. 10 SYNC_OUT B GND INL+ SYNC PGND GND A INLSHDN OUTL+ PVDD OUTL-
MAX9701
9 8 7
GND N.C. OUTLD INRGAIN2 OUTR+ PVDD OUTRC VDD INR+ GAIN1 PGND SYNC _OUT
2 SYNC
3 N.C.
4 OUTL+
5 PVDD
6 PGND
UCSP
TQFN
Chip Information
TRANSISTOR COUNT: 5688 PROCESS: BiCMOS
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
PACKAGE TYPE 24 TQFN-EP 20 UCSP PACKAGE CODE T2444-4 B20-1 DOCUMENT NO. 21-0139 21-0095
MAX9701
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19
24L QFN THIN.EPS
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
20
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1.3W, Filterless, Stereo Class D Audio Power Amplifier
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
5x4 UCSP.EPS
MAX9701
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21
1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701
Revision History
REVISION NUMBER 3 REVISION DATE 3/09 DESCRIPTION Added G45 option to Ordering Information PAGES CHANGED 1
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.
22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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