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19-3030; Rev 1; 6/04
1.2W, Low-EMI, Filterless, Class D Audio Amplifier
General Description
The MAX9700 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 MAX9700 delivers 1.2W into an 8 load while offering efficiencies above 90%. A patented, low-EMI modulation scheme renders the traditional class D output filter unnecessary. The MAX9700 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 MAX9700 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 MAX9700s 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 of the MAX9700 is set internally (MAX9700A: 6dB, MAX9700B: 12dB, MAX9700C: 15.6dB, MAX9700D: 20dB), further reducing external component count. The MAX9700 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 MAX9700 is available in 10-pin TDFN (3mm 3mm 0.8mm), 10-pin MAX, and 12-bump UCSPTM (1.5mm 2mm 0.6mm) packages. The MAX9700 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 94% Efficiency 1.2W 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)
MAX9700
Ordering Information
PART MAX9700AETB MAX9700AEUB MAX9700AEBC-T MAX9700BETB MAX9700BEUB MAX9700BEBC-T TEMP RANGE -40oC to +85oC -40oC to +85oC -40oC to +85oC -40 C to +85 C -40oC to +85oC -40oC to +85oC
o o
PINPACKAGE 10 TDFN 10 MAX 12 UCSP-12 10 TDFN 10 MAX 12 UCSP-12
TOP MARK ACM -- -- ACI -- --
Applications
Cellular Phones PDAs MP3 Players Portable Audio
Ordering Information continued at end of data sheet. Selector Guide appears at end of data sheet.
Block Diagram
VDD
Pin Configurations
TOP VIEW
DIFFERENTIAL AUDIO INPUT
MODULATOR AND H-BRIDGE
VDD 1 IN+ IN2 3 4 5
10 PVDD 9 OUTOUT+ PGND SYNC
MAX9700
8 7 6
SYNC INPUT
OSCILLATOR
GND
MAX9700
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.
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
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 VDD IDD ISHDN tON RIN VBIAS TA = +25C Either input MAX9700A Voltage Gain AV MAX9700B MAX9700C MAX9700D Output Offset Voltage Common-Mode Rejection Ratio Power-Supply Rejection Ratio (Note 3) Output Power VOS CMRR PSRR TA = +25C TMIN TA TMAX fIN = 1kHz, input referred VDD = 2.5V to 5.5V, TA = +25C 200mVP-P ripple THD+N = 1% fRIPPLE = 217Hz fRIPPLE = 20kHz RL = 8 RL = 6 RL = 8, POUT = 125mW RL = 6, POUT = 125mW 50 72 70 72 55 450 800 0.01 % 0.01 mW dB 12 0.73 Inferred from PSRR test 2.5 4 0.1 30 20 0.83 6 12 15.6 20 11 80 120 mV dB dB 0.93 5.5 5.2 10 V mA A ms k V SYMBOL CONDITIONS MIN TYP MAX UNITS
POUT
Total Harmonic Distortion Plus Noise
THD+N
fIN = 1kHz, either FFM or SSM
2
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1.2W, 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 = 2VRMS 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 = 500mW, fIN = 1kHz 800 94 FFM SSM FFM SSM 980 1280 MIN TYP 89 87 92 90 1100 1450 1220 120 2000 kHz % 1220 1620 kHz dB MAX UNITS
MAX9700
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = SHDN = 5V, 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 Quiescent Current Shutdown Current Common-Mode Rejection Ratio Power-Supply Rejection Ratio SYMBOL IDD ISHDN CMRR PSRR f = 1kHz, input referred 200mVP-P ripple f = 217Hz f = 20kHz RL = 16 Output Power Total Harmonic Distortion Plus Noise POUT THD+N = 1% f = 1kHz, either FFM or SSM RL = 8 RL = 6 THD+N RL = 8, POUT = 125mW RL = 4, POUT = 125mW FFM SSM FFM SSM CONDITIONS MIN TYP 5.2 0.1 72 72 55 700 1200 1600 0.015 0.02 92.5 90.5 95.5 93.5 dB % mW MAX UNITS mA A dB dB
Signal-to-Noise Ratio
SNR
VOUT = 3VRMS
BW = 22Hz to 22kHz A-weighted
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. For RL = 16, L = 136H. Note 3: PSRR is specified with the amplifier inputs connected to GND through CIN.
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3
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
Typical Operating Characteristics
(VDD = 3.3V, SYNC = GND (SSM), TA = +25C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9700 toc01
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9700 toc02
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
VDD = +3.3V RL = 8 POUT = 125mW 0.1
MAX9700 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
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9700 toc04
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9700 toc05
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT VOLTAGE
VDD = 5V RL = 4 10
MAX9700 toc06
100 VDD = 5V RL = 8
100 VDD = 5V RL = 16 10
100
10
THD+N (%)
THD+N (%)
1 f = 1kHz 0.1 f = 100Hz
THD+N (%)
1
1 f = 100Hz
0.1
f = 10kHz
0.1
0.01
f = 10kHz
0.01 f = 1kHz f = 100Hz 0.001
0.01 f = 1kHz 0.001 0 0.2 0.4 0.6 0.8 1.0 0 0.5 1.0 1.5 2.0
f = 10kHz
0.001 0 0.5 1.0 OUTPUT POWER (W) 1.5 2.0
2.5
3.0
3.5
OUTPUT POWER (W)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9700 toc07
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9700 toc08
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 5V f = 1kHz RL = 8 fSYNC = 1.4MHz THD+N (%) 1 fSYNC = 800kHz 0.1
MAX9700 toc09
100 VDD = 2.5V RL = 8 VCM = 1.25V NO INPUT CAPACITORS
100 VDD = 5V f = 1kHz RL = 8 FFM (SYNC = GND) SSM 0.1
100
10
10
10
THD+N (%)
THD+N (%)
1 DIFFERENTIAL INPUT
1
0.1
0.01 0.001 0 0.1 0.2
SINGLE ENDED
0.01 FFM (SYNC FLOATING) 0.001
0.01 fSYNC = 2MHz 0.001 0 0.5 1.0 OUTPUT POWER (W) 1.5 2.0 0 0.5 1.0 OUTPUT POWER (W) 1.5 2.0
0.3
0.4
0.5
OUTPUT POWER (W)
4
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. COMMON-MODE VOLTAGE
MAX9700 toc10
MAX9700
EFFICIENCY vs. OUTPUT POWER
MAX9700toc11
EFFICIENCY vs. OUTPUT POWER
90 80 EFFICIENCY (%) 70 60 50 40 30 20 RL = 4 RL = 8
MAX9700toc12
10 VDD = 3.3V RL = 8 f = 1kHz POUT = 300mW DIFFERENTIAL INPUT
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 VDD = 3.3V f = 1kHz 0 0.3 0.6 0.9 1.2 RL = 8 RL = 4
100
THD+N (%)
1
0.1
10 0 1.5 0 0.5 1.0 1.5 2.0
VDD = 5V f = 1kHz 2.5 3.0
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)
EFFICIENCY vs. SUPPLY VOLTAGE
MAX9700 toc13
EFFICIENCY vs. SYNC INPUT FREQUENCY
MAX9700 toc14
OUTPUT POWER vs. SUPPLY VOLTAGE
f = 1kHz RL = 4 THD+N = 10% RL = 4 THD+N = 1% RL = 8 THD+N = 10%
MAX9700toc15
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.5 3.0 3.5 f = 1kHz POUT = MAX (THD+N = 1%) 4.0 4.5 5.0 RL = 4 RL = 8
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
3.5 3.0 OUTPUT POWER (W) 2.5 2.0 1.5 1.0 0.5 0
RL = 8 THD+N = 1% 2.5 3.0 3.5 4.0 4.5 5.0 5.5
5.5
2000
SUPPLY VOLTAGE (V)
SYNC FREQUENCY (kHz)
SUPPLY VOLTAGE (V)
OUTPUT POWER vs. LOAD RESISTANCE
f = 1kHz THD+N = 1% 1600 OUTPUT POWER (mW) VDD = 5V CMRR (dB) 1200
MAX9700toc16
COMMON-MODE REJECTION RATIO vs. FREQUENCY
MAX9700TOC17
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
MAX9700TOC18
2000
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 INPUT REFERRED VIN = 200mVP-P
0
800 VDD = 3.3V 400
0 0 10 20 30 40 50 60 70 80 90 100 LOAD RESISTANCE ()
-100 10 100 1k FREQUENCY (Hz) 10k 100k
10
100
1k FREQUENCY (Hz)
10k
100k
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5
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25C, unless otherwise noted.)
GSM POWER-SUPPLY REJECTION
MAX9700 toc19
OUTPUT FREQUENCY SPECTRUM
FFM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
MAX9700 toc20
0 500mV/div -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140
VDD
MAX9700 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
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc21
OUTPUT FREQUENCY SPECTRUM
MAX9700 toc22
WIDEBAND OUTPUT SPECTRUM (FFM MODE)
-10 -20 OUTPUT AMPLITUDE (dB) -30 -40 -50 -60 -70 -80 RBW = 10kHz
MAX9700 toc23
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 0 5k 10k 15k FREQUENCY (Hz) SSM MODE VOUT = -60dBV f = 1kHz RL = 8 UNWEIGHTED
0 -20 OUTPUT MAGNITUDE (dBV) -40 -60 -80 -100 -120 -140 SSM MODE VOUT = -60dBV f = 1kHz RL = 8 A-WEIGHTED
0
-90 -100 0 5k 10k 15k FREQUENCY (Hz) 20k 1M 10M 100M 1G FREQUENCY (Hz)
20k
WIDEBAND OUTPUT SPECTRUM (SSM MODE)
-10 -20 OUTPUT AMPLITUDE (dB) -30 -40 -50 -60 -70 -80 -90 -100 1M 10M 100M 1G FREQUENCY (Hz) MAX9700 OUTPUT RBW = 10kHz
MAX9700 toc24
TURN-ON/TURN-OFF RESPONSE
MAX9700 toc25
0
3V
SHDN
0V
250mV/div
f = 1kHz RL = 8
10ms/div
6
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier
Typical Operating Characteristics (continued)
(VDD = 3.3V, SYNC = GND (SSM), TA = +25C, unless otherwise noted.)
MAX9700
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9700 toc26
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
MAX9700 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)
Functional Diagram
VDD
1F 1 (A1) VDD 5 (B2) SHDN 10 (B4) PVDD CLICK-AND-POP SUPPRESSION 6 (A3) SYNC OSCILLATOR PVDD
UVLO/POWER MANAGEMENT
1F
2 (B1) IN+ 3 (C1) INCLASS D MODULATOR PGND PVDD
8 OUT+ (A4)
1F
OUT- 9 (C4)
MAX9700
PGND PGND 7 (B3) ( ) UCSP BUMP. GND 4 (C2)
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
Pin Description
PIN TDFN/MAX 1 2 3 4 5 BUMP UCSP A1 B1 C1 C2 B2 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
A3
SYNC
7 8 9 10
B3 A4 C4 B4
PGND OUT+ OUTPVDD
Detailed Description
The MAX9700 filterless, class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9700 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 pickup, and can be used without input-coupling capacitors. The device can also be configured as a single-ended input amplifier. Comparators monitor the MAX9700 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 MAX9700 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 MAX9700 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 MAX9700 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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1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9700 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 MAX9700. The period of the SYNC clock can be randomized, enabling the MAX9700 to be synchronized to another MAX9700 operating in SSM mode.
Filterless Modulation/Common-Mode Idle
The MAX9700 uses Maxim's unique, patented modulation scheme that eliminates the LC filter required by traditional class D amplifiers, improving efficiency, reducing component count, and 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 megahertz, the wideband spectrum looks like white noise for EMI purposes (Figure 3). External Clock Mode The SYNC input allows the MAX9700 to be synchronized to a system clock (allowing a fully synchronous
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9
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
tSW tSW tSW tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 2. MAX9700 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 MAX9700, the outputs switch as shown in Figure 4. Because the MAX9700 drives the speaker differentially, the two outputs cancel each other, resulting in no net Idle ModeTM voltage across the speaker, minimizing power consumption.
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 current-
steering 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. 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 MAX9700 still exhibits >90% efficiencies under the same conditions (Figure 5).
Idle Mode is a trademark of Maxim Integrated Products.
10
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
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. MAX9700 EMI Spectrum
Figure 4. MAX9700 Outputs with No Input Signal
Shutdown
The MAX9700 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9700 in a low-power (0.1A) shutdown mode. Connect SHDN to VDD for normal operation. The MAX9700 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 0.6 0.7 OUTPUT POWER (W) VDD = 3.3V f = 1kHz RL - 8 CLASS AB MAX9700
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 MAX9700 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. MAX9700 Efficiency vs. Class AB Efficiency
Because the frequency of the MAX9700 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 exhibit series inductances in the 20H to 100H range.
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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1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
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+
MAX9700
IN1F
Input Amplifier
Differential Input The MAX9700 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 MAX9700 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
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 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 MAX9700 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 MAX9700 evaluation kit for layout guidance.
Component Selection
Input Filter An input capacitor, CIN, in conjunction with the input impedance of the MAX9700 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
12
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier
Stereo Configuration
VDD
MAX9700
1F VDD PVDD
RIGHT-CHANNEL DIFFERENTIAL AUDIO INPUT
IN+
MAX9700 OUT+
OUTSYNC
IN-
Two MAX9700s can be configured as a stereo amplifier (Figure 7). Device U1 is the master amplifier; its unfiltered output drives the SYNC input of the slave device (U2), synchronizing the switching frequencies of the two devices. Synchronizing two MAX9700s 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.
Designing with Volume Control
1F VDD PVDD
LEFT-CHANNEL DIFFERENTIAL AUDIO INPUT
IN+
MAX9700 OUT+
OUTSYNC
IN-
The MAX9700 can easily be driven by single-ended sources (Figure 6), but extra care is needed if the source impedance "seen" by each differential input is unbalanced, such as the case in Figure 10a, where the MAX9700 is used with an audio taper potentiometer acting as a volume control. Functionally, this configuration works well, but can suffer from click-pop transients at power-up (or coming out of SHDN) depending on the volume-control setting. As shown, the click-pop performance is fine for either max or min volume, but worsens at other settings.
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+N
Figure 9. Master-Slave Crosstalk
______________________________________________________________________________________
13
1.2W, Low-EMI, Filterless, Class D Audio Amplifier
One solution is the configuration shown in Figure 10b. The potentiometer is connected between the differential inputs, and these "see" identical RC paths when the device powers up. The variable resistive element appears between the two inputs, meaning the setting affects both inputs the same way. The potentiometer is audio taper, as in Figure 10a. This significantly improves transient performance on power-up or release from SHDN. A similar approach can be applied when the MAX9700 is driven differentially and a volume control is required.
MAX9700
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, PC 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.maxim-ic.com/ucsp.
1F CW 1F 50k IN-
22k IN-
CW
MAX9700
IN+ 1F 1F
50k 22k IN+
MAX9700
Figure 10a. Single-Ended Drive of MAX9700 Plus Volume
Figure 10b. Improved Single-Ended Drive of MAX9700 Plus Volume
Ordering Information (continued)
PART MAX9700CETB MAX9700CEUB MAX9700CEBC-T MAX9700DETB MAX9700DEUB MAX9700DEBC-T TEMP RANGE -40 C to +85 C -40oC to +85oC -40oC to +85oC -40 C to +85 C -40oC to +85oC -40oC to +85oC
o o o o
Selector Guide
PART MAX9700AETB MAX9700AEUB MAX9700AEBC-T MAX9700BETB MAX9700BEUB MAX9700BEBC-T MAX9700CETB MAX9700CEUB MAX9700CEBC-T MAX9700DETB MAX9700DEUB MAX9700DEBC-T PIN-PACKAGE 10 TDFN 10 MAX 12 UCSP-12 10 TDFN 10 MAX 12 UCSP-12 10 TDFN 10 MAX 12 UCSP-12 10 TDFN 10 MAX 12 UCSP-12 GAIN (dB) 6 6 6 12 12 12 15.6 15.6 15.6 20 20 20
PINPACKAGE 10 TDFN 10 MAX 12 UCSP-12 10 TDFN 10 MAX 12 UCSP-12
TOP MARK ACN -- -- ACO -- --
14
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1.2W, Low-EMI, Filterless, Class D Audio Amplifier
System Diagram
VDD
MAX9700
VDD 0.1F AUX_IN
1F VDD IN+ OUT INSHDN PVDD
MAX9700
OUT+ OUTSYNC
2.2k BIAS 2.2k 0.1F IN+
OUT
CODEC/ BASEBAND PROCESSOR
MAX4063
VDD IN-
0.1F SHDN 1F INL 1F INR CONTROLLER
VDD
1F
OUTL
MAX9722
OUTR PVSS SVSS
C1P
CIN
1F
1F
Pin Configurations (continued)
TOP VIEW (BUMP SIDE DOWN)
1
Chip Information
TRANSISTOR COUNT: 3595 PROCESS: BiCMOS
MAX9700
2 3 4
VDD A IN+ B INC GND SHDN
SYNC
OUT+
PGND
PVDD
OUT-
UCSP
______________________________________________________________________________________
15
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
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
16
______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Class D Audio Amplifier
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.) 6, 8, &10L, DFN THIN.EPS
C L
MAX9700
D
N
PIN 1 INDEX AREA
E
DETAIL A
E2
C L
L A e e
L
PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
21-0137
F
1
2
______________________________________________________________________________________
17
1.2W, Low-EMI, Filterless, Class D Audio Amplifier MAX9700
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 MAX. 0.80 3.10 3.10 0.05
0.40 0.20 0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T633-1 T833-1 T1033-1 T1433-1 T1433-2 N 6 8 10 14 14 D2 1.500.10 1.500.10 1.500.10 1.700.10 1.700.10 E2 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.65 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEC MO229 / WEED-3 ------b 0.400.05 0.300.05 0.250.05 0.200.03 0.200.03 [(N/2)-1] x e 1.90 REF 1.95 REF 2.00 REF 2.40 REF 2.40 REF
PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
F
2
2
18
______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Class D Audio Amplifier
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.)
MAX9700
e
10
4X S
10
INCHES MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 D1 0.120 0.116 0.118 D2 0.114 E1 0.116 0.120 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 2.89 3.00 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 0 0.500.1 0.60.1
1
1
0.60.1
TOP VIEW
BOTTOM VIEW
D2 GAGE PLANE A2 A b A1 D1
E2
c
E1 L1
L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0061
1 1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 19 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
10LUMAX.EPS

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