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19-2917; Rev 1; 1/04
500mW, Low EMI, Filterless, Class D Audio Amplifier
General Description
The MAX9712 mono class D audio power amplifier provides class AB amplifier performance with class D efficiency, conserving board space, and extending battery life. Using a class D architecture, the MAX9712 delivers up to 500mW into an 8 load while offering efficiencies above 85%. A patented, low EMI modulation scheme renders the traditional class D output filter unnecessary. The MAX9712 offers two modulation schemes: a fixedfrequency (FFM) mode, and a spread-spectrum (SSM) mode that reduces EMI-radiated emissions due to the modulation frequency. Furthermore, the MAX9712 oscillator can be synchronized to an external clock through the SYNC input, allowing the switching frequency to be user defined. The SYNC input also allows multiple MAX9712s to be cascaded and frequency locked, minimizing interference due to clock intermodulation. The device utilizes a fully differential architecture, a fullbridged output, and comprehensive click-and-pop suppression. The gain is internally set to +4V/V, further reducing external component count. The MAX9712 features high 72dB PSRR, a low 0.01% THD+N, and SNR in excess of 90dB. Short-circuit and thermal-overload protection prevent the device from damage during a fault condition. The MAX9712 is available in 10-pin TDFN (3mm 3mm 0.8mm), 10-pin MAX, and 12-bump UCSPTM (1.5mm 2mm 0.6mm) packages. The MAX9712 is specified over the extended -40C to +85C temperature range.
Features
Filterless Amplifier Passes FCC Radiated Emissions Standards with 100mm of Cable Unique Spread-Spectrum Mode Offers 5dB Emissions Improvement Over Conventional Methods Optional External SYNC Input Simple Master-Slave Setup for Stereo Operation 85% Efficiency Up to 500mW into 8 Low 0.01% THD+N High PSRR (72dB at 217Hz) Integrated Click-and-Pop Suppression Low Quiescent Current (4mA) Low-Power Shutdown Mode (0.1A) Short-Circuit and Thermal-Overload Protection Available in Thermally Efficient, Space-Saving Packages 10-Pin TDFN (3mm 3mm 0.8mm) 10-Pin MAX 12-Bump UCSP (1.5mm 2mm 0.6mm)
MAX9712
Ordering Information
PART MAX9712ETB MAX9712EUB MAX9712EBC-T TEMP RANGE -40C to +85C -40C to +85C -40C to +85C PIN/BUMPPACKAGE 10 TDFN 10 MAX 12 UCSP-12 TOP MARK AAI -- ABN
Applications
Cellular Phones PDAs MP3 Players Portable Audio
Simplified Block Diagram
VDD
Pin Configurations
TOP VIEW
MODULATOR AND H-BRIDGE
DIFFERENTIAL AUDIO INPUT
VDD 1 IN+ IN2 3 4 5
10 PVDD 9 OUTOUT+ PGND SYNC
MAX9712
8 7 6
SYNC INPUT
OSCILLATOR
GND
MAX9712
SHDN
TDFN/MAX
UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations continued at end of data sheet. 1
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
ABSOLUTE MAXIMUM RATINGS
VDD to GND..............................................................................6V 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 Into/Out of PVDD/PGND/OUT_ ........600mA 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) 10-Pin TDFN (derate 24.4mW/C above +70C) .....1951.2mW 10-Pin MAX (derate 5.6mW/oC above +70C) .........444.4mW 12-Bump UCSP (derate 6.1mW/C above +70C)........484mW Junction Temperature ......................................................+150C Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C Bump Temperature (soldering) Reflow ..........................................................................+235C
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 = GND (FFM), RL = 8, RL connected between OUT+ and OUT-, 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 Turn-On Time Input Resistance Input Bias Voltage Voltage Gain VDD IDD ISHDN tON RIN VBIAS AV TA = +25C Output Offset Voltage VOS TMIN TA TMAX MAX9712EUB/MAX9712ETB MAX9712EBC MAX9712EUB/MAX9712ETB MAX9712EBC 72 50 fRIPPLE = 217Hz fRIPPLE = 20kHz RL = 16, VDD = 5V Output Power POUT THD+N = 1% RL = 8 RL = 6 Total Harmonic Distortion Plus Noise fIN = 1kHz, either FFM or SSM RL = 8, POUT = 125mW RL = 6, POUT = 125mW 70 72 55 700 450 250 0.01 % 0.01 mW dB TA = +25C Either input 14 0.73 3.8 Inferred from PSRR test 2.5 4 0.1 30 20 0.83 4 11 15 0.93 4.2 40 65 65 95 dB mV 5.5 5.2 5 V mA A ms k V V/V SYMBOL CONDITIONS MIN TYP MAX UNITS
Common-Mode Rejection Ratio Power-Supply Rejection Ratio (Note 3)
CMRR PSRR
fIN = 1kHz, input referred VDD = 2.5V to 5.5V 200mVP-P ripple
THD+N
2
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500mW, Low EMI, Filterless, Class D Audio Amplifier
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL = 8, RL connected between OUT+ and OUT-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2)
PARAMETER SYMBOL CONDITIONS BW = 22Hz to 22kHz Signal-to-Noise Ratio SNR VOUT = 1.8VRMS A-weighted SYNC = GND Oscillator Frequency fOSC SYNC = float SYNC = VDD (SSM mode) SYNC Frequency Lock Range Efficiency DIGITAL INPUTS (SHDN, SYNC) Input Thresholds SHDN Input Leakage Current SYNC Input Current VIH VIL 2 0.8 1 5 V A A POUT = 300mW, fIN = 1kHz 800 85 FFM SSM FFM SSM 980 1280 MIN TYP 88 86 91 89 1100 1450 1220 120 2000 kHz % 1220 1620 kHz dB MAX UNITS
MAX9712
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 = 6, L = 47H. For RL = 8, L = 68H. For RL = 16, L = 136H. Note 3: PSRR is specified with the amplifier inputs connected to GND through CIN.
Typical Operating Characteristics
(VDD = 3.3V, VSYNC = GND, TA = +25C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9712 TOC01
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9712 TOC02
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
VDD = +3.3V RL = 8 POUT = 125mW 0.1
MAX9712 TOC03
1 VDD = +5V RL = 8
1 VDD = +3.3V RL = 8
1
0.1 THD+N (%) THD+N (%) POUT = 300mW
0.1 POUT = 300mW THD+N (%)
SSM MODE
0.01 POUT = 125mW
0.01 POUT = 125mW
0.01 FFM MODE
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
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3
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9712 TOC04
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9712 TOC05
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 3.3V RL = 6 10
MAX9712 TOC06
100 VDD = 3.3V RL = 8 10
100 VDD = 5V RL = 16 10
100
THD+N (%)
THD+N (%)
1 f = 10kHz
1
THD+N (%)
1
0.1
0.1
f = 10kHz
0.1
f = 10kHz
0.01 0.001 0 f = 1kHz 0.1 0.2 f = 100Hz
0.01 f = 1kHz 0.001 0.3 0.4 0.5 0 0.2 0.4 0.6 0.8 1.0 OUTPUT POWER (W) f = 100Hz
0.01 f = 1kHz 0.001 0 0.1 0.2 OUTPUT POWER (W) 0.3 0.4 f = 100Hz
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9712 TOC07
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9712 TOC08
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 3.3V RL = 8 SYNC = 3.3VP-P 50% DUTY CYCLE SQUARE WAVE
MAX9712 TOC09
100 VDD = 2.5V RL = 8 VCM = 1.25V NO INPUT CAPACITORS
100 VDD = 3.3V RL = 8 10
100 fSYNC = 2MHz
10
10
THD+N (%)
THD+N (%)
1 DIFFERENTIAL INPUT
1 FFM (SYNC FLOATING) SSM (SYNC = VDD)
THD+N (%)
1
fSYNC = 1.4MHz
0.1
0.1
0.1
0.01 0.001 0 0.1 0.2
SINGLE-ENDED
0.01 FFM (SYNC = GND) 0.001
0.01 fSYNC = 800kHz 0.001 0 0.1 0.2 0.3 0.4 0.5 0 0.1 0.2 0.3 0.4 0.5 0.6 OUTPUT POWER (W) OUTPUT POWER (W)
0.3
0.4
0.5
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. COMMON-MODE VOLTAGE
MAX9712 TOC10
EFFICIENCY vs. OUTPUT POWER
MAX9712TOC11
EFFICIENCY vs. OUTPUT POWER
90 80 EFFICIENCY (%) 70 60 50 40 30 20 RL = 6 RL = 16 RL = 8
MAX9712TOC12
10 VDD = 3.3V RL = 8 f = 1kHz POUT = 300mW DIFFERENTIAL INPUT
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 VDD = 5V f = 1kHz 0 0.1 0.2 0.3 0.4 0.5 0.6 RL = 8 RL = 16
100
THD+N (%)
1
0.1
10 0 0.7 0
VDD = 3.3V f = 1kHz 0.1 0.2 0.3 0.4 0.5
0.01 0 0.5 1.0 1.5 2.0 2.5 3.0 COMMON-MODE VOLTAGE (V)
0 OUTPUT POWER (W)
OUTPUT POWER (W)
4
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500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9712TOC13
EFFICIENCY vs. SYNC INPUT FREQUENCY
MAX9712TOC14
OUTPUT POWER vs. SUPPLY VOLTAGE
f = 1kHz 900 800 OUTPUT POWER (mW) 700 600 500 400 300 200 100 0 2000 2.5 3.1 3.7 4.3 4.9 5.5 SUPPLY VOLTAGE (V) RL = 6 RL = 8 RL = 16
MAX9712TOC15
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.5 3.0 3.5 4.0 4.5 5.0 f = 1kHz RL = 6 RL = 8 RL = 16
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VDD = 3.3V f = 1kHz POUT = 300mW RL = 8 800 1000 1200 1400 1600 1800
1000
5.5
SUPPLY VOLTAGE (V)
SYNC FREQUENCY (kHz)
OUTPUT POWER vs. LOAD RESISTANCE
900 800 OUTPUT POWER (mW) 700 600 500 400 300 200 100 0 0 10 20 30 40 50 60 70 80 90 100 LOAD RESISTANCE () VDD = 3.3V VDD = 5V CMRR (dB) f = 1kHz THD+N = 1%
MAX9712TOC16
COMMON-MODE REJECTION RATIO vs. FREQUENCY
MAX9712TOC17
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
-10 -20 -30 PSRR (dB) -40 -50 -60 -70 -80 -90 -100 OUTPUT REFERRED INPUTS AC GROUNDED VDD = 3.3V
MAX9712TOC18
1000
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 10 100 1k FREQUENCY (Hz) 10k INPUT REFERRED VIN = 200mVP-P
0
100k
10
100
1k FREQUENCY (Hz)
10k
100k
GSM POWER-SUPPLY REJECTION
MAX9712TOC19
OUTPUT FREQUENCY SPECTRUM
FFM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
MAX9712TOC20
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140
VDD
500mV/div
MAX9712 OUTPUT
100V/div
f = 217Hz INPUT LOW = 3V INPUT HIGH = 3.5V
2ms/div
DUTY CYCLE = 88% RL = 8
0
5k
10k 15k FREQUENCY (Hz)
20k
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500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Typical Operating Characteristics (continued)
(VDD = 3.3V, VSYNC = GND, TA = +25C, unless otherwise noted.)
WIDEBAND OUTPUT SPECTRUM (FFM MODE)
MAX9712TOC22
OUTPUT FREQUENCY SPECTRUM
MAX9712TOC21
OUTPUT FREQUENCY SPECTRUM
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 SSM MODE VOUT = -60dBV f = 1kHz RL = 8 A-WEIGHTED 0 -10 -20 OUTPUT AMPLITUDE (dB) -30 -40 -50 -60 -70 -80
-20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 0
SSM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
RBW = 10kHz
-90 -100 0 5 10 15 FREQUENCY (kHz) 20 1M 10M 100M 1G FREQUENCY (Hz)
5
10 15 FREQUENCY (kHz)
20
WIDEBAND OUTPUT SPECTRUM (SSM MODE)
MAX1972TOC24
TURN-ON/TURN-OFF RESPONSE
MAX9712TOC25
0 -10 -20 OUTPUT AMPLITUDE (dB) -30 -40 -50 -60 -70 -80 -90 -100 1M 10M 100M 1G FREQUENCY (Hz) RBW = 10kHz
3V
SHDN
0V
MAX9712 OUTPUT
250mV/div
f = 1kHz RL = 8
10ms/div
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9712TOC26
SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE
TA = +85C 0.14 SUPPLY CURRENT (A) 0.12 0.10 0.08 0.06 0.04 TA = +25C
MAX9712 TOC27
6.0 5.5 SUPPLY CURRENT (mA) 5.0 4.5 4.0 3.5 3.0 2.5 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 TA = -40C TA = +85C
0.16
TA = +25C
0.02 0 5.5 2.5 3.0 3.5 4.0
TA = -40C
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
6
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MAX1972 TOC23
0
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Functional Diagram
VDD
10F
1F 1 (C4) VDD 5 (B3) SHDN 10 (B1) PVDD CLICK AND POP SUPPRESSION 6 (C2) SYNC OSCILLATOR PVDD
UVLO/POWER MANAGEMENT
2 (B4) IN+ 3 (A4) INCLASS D MODULATOR PGND PVDD
8 OUT+ (C1)
OUT- 9 (A1)
MAX9712
PGND PGND 7 (B2) ( ) UCSP BUMP. GND 4 (A5)
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500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Pin Description
PIN TDFN/MAX 1 2 3 4 5 BUMP UCSP C4 B4 A4 A3 B3 NAME VDD IN+ INGND SHDN Analog Power Supply Noninverting Audio Input Inverting Audio Input Analog Ground Active-Low Shutdown Input. Connect to VDD for normal operation. Frequency Select and External Clock Input. SYNC = GND: Fixed-frequency mode with fS = 1100kHz. SYNC = Float: Fixed-frequency mode with fS = 1450kHz. SYNC = VDD: Spread-spectrum mode with fS = 1220kHz 120kHz. SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency. Power Ground Amplifier Output Positive Phase Amplifier Output Negative Phase H-Bridge Power Supply FUNCTION
6
C2
SYNC
7 8 9 10
B2 C1 A1 B1
PGND OUT+ OUTPVDD
Detailed Description
The MAX9712 filterless, class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9712 offers class AB performance with class D efficiency, while occupying minimal board space. A unique filterless modulation scheme, synchronizable switching frequency, and SSM mode create a compact, flexible, low-noise, efficient audio power amplifier. The differential input architecture reduces common-mode noise pick-up, and can be used without input-coupling capacitors. The device can also be configured as a single-ended input amplifier. Comparators monitor the MAX9712 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 (the first comparator to trip) while the other output pulse duration remains at tON(min). This causes the net voltage across the speaker (VOUT+ VOUT-) to change.
Operating Modes
Fixed-Frequency Modulation (FFM) Mode The MAX9712 features two FFM modes. The FFM modes are selected by setting SYNC = GND for a 1.1MHz switching frequency, and SYNC = FLOAT for a 1.45MHz switching frequency. In FFM mode, the frequency spectrum of the class D output consists of the fundamental switching frequency and its associated harmonics (see the Wideband FFT graph in the Typical Operating Characteristics). The MAX9712 allows the switching frequency to be changed by +32%, should the frequency of one or more of the harmonics fall in a sensitive band. This can be done at any time and does not affect audio reproduction. Spread-Spectrum Modulation (SSM) Mode The MAX9712 features a unique, patented spread-spectrum mode that flattens the wideband spectral components, improving EMI emissions that may be radiated by the speaker and cables by 5dB. Proprietary techniques ensure that the cycle-to-cycle variation of the switching period does not degrade audio reproduction or efficiency (see the Typical Operating Characteristics). Select SSM mode by setting SYNC = VDD. In SSM mode, the switching frequency varies randomly by 120kHz around the center frequency (1.22MHz). 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
8
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500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9712 Outputs with an Input Signal Applied
Table 1. Operating Modes
SYNC INPUT GND FLOAT VDD Clocked MODE FFM with fS = 1100kHz FFM with fS = 1450kHz SSM with fS = 1220kHz 120kHz FFM with fS = external clock frequency
system), or allocating the spectral components of the switching harmonics to insensitive frequency bands. Applying an external TTL clock of 800kHz to 2MHz to SYNC synchronizes the switching frequency of the MAX9712. The period of the SYNC clock can be randomized, enabling the MAX9712 to be synchronized to another MAX9712 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9712 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 square wave when no signal is present. With no filter, the square wave appears across
spread over a bandwidth that increases with frequency. Above a few MHz, the wideband spectrum looks like white noise for EMI purposes (Figure 3). External Clock Mode The SYNC input allows the MAX9712 to be synchronized to a system clock (allowing a fully synchronous
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9
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
tSW tSW tSW tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 2. MAX9712 Output with an Input Signal Applied (SSM Mode)
the load as a DC voltage, resulting in finite load current, increasing power consumption. When no signal is present at the input of the MAX9712, the outputs switch as shown in Figure 4. Because the MAX9712 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker, minimizing power consumption.
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 MAX9712 still exhibits >80% efficiencies under the same conditions (Figure 5).
Efficiency
Efficiency of a class D amplifier is attributed to the region of operation of the output stage transistors. In a class D amplifier, the output transistors act as currentsteering switches and consume negligible additional power. Any power loss associated with the class D output stage is mostly due to the I R loss of the MOSFET on-resistance, and quiescent current overhead.
10 ______________________________________________________________________________________
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
VIN = 0V
50.0 45.0 AMPLITUDE (dBV/m) 40.0 35.0 30.0 25.0 20.0 15.0 10.0 30.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0 FREQUENCY (MHz)
OUT-
OUT+
VOUT+ - VOUT- = 0V
Figure 3. MAX9712 with 76mm of Speaker Cable
Figure 4. MAX9712 Outputs with No Input Signal
Shutdown
The MAX9712 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9712 in a low-power (0.1A) shutdown mode. Connect SHDN to VDD for normal operation. The MAX9712 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 35ms following startup, a soft-start function gradually unmutes the input amplifiers.
EFFICIENCY (%)
EFFICIENCY vs. OUTPUT POWER
100 90 80 70 60 50 40 30 20 10 0 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W) VDD = 3.3V f = 1kHz RL - 8 CLASS AB MAX9712
Click-and-Pop Suppression
Applications Information
Filterless Operation
Traditional class D amplifiers require an output filter to recover the audio signal from the amplifier's 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 peak-to-peak) and causes large ripple currents. Any parasitic resistance in the filter components results in a loss of power, lowering the efficiency. The MAX9712 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.
Figure 5. MAX9712 Efficiency vs. Class AB Efficiency
Because the frequency of the MAX9712 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 may be damaged. For optimum results, use a speaker with a series inductance >10H. Typical 8 speakers exhibit series inductances in the range of 20H to 100H.
Power Conversion Efficiency
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
11
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500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
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), which is on the order of a few microamps.
1F SINGLE-ENDED AUDIO INPUT IN+
MAX9712
IN1F
Input Amplifier
Differential Input The MAX9712 features a differential input structure, making it compatible with many CODECs, and offering 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 MAX9712 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 Input 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 one external component (see the System Diagram). However, the low-frequency rejection of the capacitors is lost, allowing low-frequency signals to feedthrough to the load.
Figure 6. Single-Ended Input
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 in portable devices typically have a poor response below 150Hz. 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. Output Filter The MAX9712 does not require an output filter. The device passes FCC emissions standards with 100mm 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 the circuit is near EMI sensitive devices. Use an LC filter when radiated emissions are a concern, or when long leads are used to connect the amplifier to the speaker. Supply Bypassing/Layout Proper power-supply bypassing ensures low distortion operation. For optimum performance, bypass VDD to GND and PVDD to PGND with separate 0.1F capacitors as close to each pin as possible. A low-impedance, high-current power-supply connection to PVDD is assumed. Additional bulk capacitance should be added as required depending on the application and power-supply characteristics. GND and PGND should be star connected to system ground. Refer to the MAX9712 Evaluation Kit for layout guidance.
Component Selection
Input Filter An input capacitor, CIN, in conjunction with the input impedance of the MAX9712 forms a highpass filter that removes the DC bias from an incoming signal. The ACcoupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming zero-source impedance, the -3dB point of the highpass filter is given by: f-3dB = 1 2RINCIN
Choose CIN so f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the low-frequency response of the amplifier. Use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with
12
Stereo Configuration
Two MAX9712s can be configured as a stereo amplifier (Figure 7). Device U1 is the master amplifier; its unfil-
______________________________________________________________________________________
500mW, Low EMI, Filterless, Class D Audio Amplifier
VDD
1F VDD PVDD
RIGHT-CHANNEL DIFFERENTIAL AUDIO INPUT
IN+
MAX9712 OUT+
OUTSYNC
tered output drives the SYNC input of the slave device (U2), synchronizing the switching frequencies of the two devices. Synchronizing two MAX9712s ensures that no beat frequencies occur within the audio spectrum. This configuration works when the master device is in either FFM or SSM mode. There is excellent THD+N performance and minimal crosstalk between devices due to the SYNC connection (Figures 8 and 9). U2 locks onto only the frequency present at SYNC, not the pulse width. The internal feedback loop of device U2 ensures that the audio component of U1's output is rejected.
MAX9712
IN-
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 the Application Note: UCSP--A Wafer-Level Chip-Scale Package available on Maxim's website at www.maximic.com/ucsp.
1F VDD PVDD
LEFT-CHANNEL DIFFERENTIAL AUDIO INPUT
IN+
MAX9712 OUT+
OUTSYNC
Chip Information
TRANSISTOR COUNT: 3595 PROCESS: BiCMOS
IN-
Figure 7. Master-Slave Stereo Configuration
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
100 VDD = 3.3V f = 1kHz RL = 8 SLAVE DEVICE CROSSTALK (dB) 0 -20 -40 -60 -80 -100 -120 0 0.1 0.2 0.3 0.4 0.5 10
CROSSTALK vs. FREQUENCY
VDD = 3.3V RL = 8 f = 1kHz VIN = 500mVP-P
10
THD+N (%)
1
MASTER-TO-SLAVE
0.1
0.01 0.001 OUTPUT POWER (W)
SLAVE-TO-MASTER
100
1k FREQUENCY (Hz)
10k
100k
Figure 8. Master-Slave THD
Figure 9. Master-Slave Crosstalk
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13
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
System Diagram
VDD 0.1F AUX_IN 1F VDD 2.2k PVDD VDD
MAX4063
BIAS 2.2k 0.1F IN+ IN0.1F OUT OUT
CODEC/ BASEBAND PROCESSOR
IN+ INSHDN
MAX9712 OUT+
OUTSYNC
100k
VDD
MODE1 MODE2 VDD 10k CONTROLLER 1F 1F INL INR ALERT TIME C1P 220nF 1F CIN
1F VDD HPS
MAX9720 OUTL
OUTR PVDD SVDD
1F
Pin Configurations (continued)
TOP VIEW (BUMP SIDE DOWN)
1
MAX9712
2 3 4
OUTA PVDD B OUT+ C SYNC PGND
GND
IN-
SHDN
IN+
VDD
UCSP
14
______________________________________________________________________________________
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
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.)
12L, UCSP 4x3.EPS
PACKAGE OUTLINE, 4x3 UCSP 21-0104 F
1 1
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15
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
L D A A2
PIN 1 ID
D2
1
N
1
b
PIN 1 INDEX AREA
C0.35 [(N/2)-1] x e REF. e
E
DETAIL A
E2
A1
k
C L
C L
L e A e
L
SEMICONDUCTOR
PROPRIETARY INFORMATION TITLE:
DALLAS
PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
APPROVAL DOCUMENT CONTROL NO. REV.
21-0137
D
1 2
16
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6, 8, &10L, DFN THIN.EPS
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 0.20 MAX. 0.80 3.10 3.10 0.05 0.40
0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T633-1 T833-1 T1033-1 N 6 8 10 D2 1.500.10 1.500.10 1.500.10 E2 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.65 BSC 0.50 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEC MO229 / WEED-3 b 0.400.05 0.300.05 0.250.05 [(N/2)-1] x e 1.90 REF 1.95 REF 2.00 REF
SEMICONDUCTOR
PROPRIETARY INFORMATION TITLE:
DALLAS
PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm
APPROVAL DOCUMENT CONTROL NO. REV.
21-0137
D
2 2
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17
500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.)
10LUMAX.EPS
1 1
e
10
4X S
10
INCHES MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.0275 L1 0.037 REF b 0.007 0.0106 e 0.0197 BSC c 0.0035 0.0078 0.0196 REF S 0 6
MILLIMETERS MAX MIN 1.10 0.15 0.05 0.75 0.95 3.05 2.95 3.00 2.89 3.05 2.95 2.89 3.00 4.75 5.05 0.40 0.70 0.940 REF 0.177 0.270 0.500 BSC 0.090 0.200 0.498 REF 0 6
H y 0.500.1 0.60.1
1
1
0.60.1
TOP VIEW
BOTTOM VIEW
D2 GAGE PLANE A2 A b D1 A1
E2 c E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
I
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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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