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| 19-3405; Rev 3; 5/09 KIT ATION EVALU E AILABL AV 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier General Description Features o Filterless Amplifier Passes FCC-Radiated Emissions Standards with 24in of Cable o Unique Spread-Spectrum Mode and Active Emissions Limiting (AEL) Achieves Better than 20dB Margin Under FCC Limits o Zero Dead Time (ZDT) H-Bridge Maintains Stateof-the-Art Efficiency and THD+N o Simple Master-Slave Setup for Stereo Operation o Up to 90% Efficiency o 2.3W into 4 (1% THD+N) o Low 0.02% THD+N (POUT = 1W, VDD = 5.0V) o High PSRR (75dB at 217Hz) o Integrated Click-and-Pop Suppression o Low Quiescent Current (5.4mA) o Low-Power Shutdown Mode (0.3A) o Short-Circuit and Thermal-Overload Protection o Available in Thermally Efficient, Space-Saving Packages 10-Pin TDFN (3mm x 3mm x 0.8mm) 12-Bump UCSP (1.5mm x 2mm x 0.6mm) o Pin-for-Pin Compatible with the MAX9700 and MAX9712 MAX9705 The MAX9705 3rd-generation, ultra-low EMI, mono, Class D audio power amplifier provides Class AB performance with Class D efficiency. The MAX9705 delivers 2.3W into a 4 load and offers efficiencies above 85%. Active emissions limiting (AEL) circuitry greatly reduces EMI by actively controlling the output FET gate transitions under all possible transient output-voltage conditions. AEL prevents high-frequency emissions resulting from conventional Class D free-wheeling behavior in the presence of an inductive load. Zero dead time (ZDT) technology maintains state-of-the-art efficiency and THD+N performance by allowing the output FETs to switch simultaneously without cross-conduction. A patented spreadspectrum modulation scheme eliminates the need for output filtering found in traditional Class D devices. These design concepts reduce an application's component count and extend battery life. The MAX9705 offers two modulation schemes: a fixedfrequency (FFM) mode and a spread-spectrum (SSM) mode that further reduces EMI-radiated emissions due to the modulation frequency. The MAX9705 oscillator can be synchronized to an external clock through the SYNC input, allowing the switching frequency to be externally defined. The SYNC input also allows multiple MAX9705s to be cascaded and frequency locked, minimizing interference due to clock intermodulation. The device utilizes a fully differential architecture, a full-bridged output, and comprehensive click-and-pop suppression. The gain of the MAX9705 is set internally (MAX9705A: 6dB, MAX9705B: 12dB, MAX9705C: 15.6dB, MAX9705D: 20dB), further reducing external component count. The MAX9705 is available in 10-pin TDFN (3mm x 3mm x 0.8mm), and 12-bump UCSPTM (1.5mm x 2mm x 0.6mm) packages. The MAX9705 is specified over the extended -40C to +85C temperature range. Ordering Information PART MAX9705AETB+T MAX9705AEBC+T MAX9705BETB+T TEMP RANGE -40oC to +85oC -40oC to +85oC -40oC to +85oC PINPACKAGE 10 TDFN 12 UCSP 10 TDFN TOP MARK ACY ACH ACX MAX9705BEBC+T -40oC to +85oC 12 UCSP ACG Ordering Information continued at end of data sheet. +Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. Applications Cellular Phones PDAs MP3 Players Portable Audio AMPLITUDE (dBV/m) 50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 30.0 FCC EMI LIMIT EMI Spectrum Diagram Selector Guide appears at end of data sheet. UCSP is a trademark of Maxim Integrated Products, Inc. MAXIM'S NEW ULTRA-LOW OUTPUT SPECTRUM 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) ________________________________________________________________ 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. 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 ABSOLUTE MAXIMUM RATINGS VDD to GND..............................................................................6V PVDD to PGND .........................................................................6V GND to PGND .......................................................-0.3V to +0.3V PVDD to VDD ..........................................................-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 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 = V SHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL = , 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 VDD IDD ISHDN tON RIN VBIAS TA = +25C Either input MAX9705A MAX9705B MAX9705C MAX9705D 12 0.88 0.73 0.61 0.48 1.9 3.8 5.7 9.5 Inferred from PSRR test 2.5 5.4 0.3 30 20 1.0 0.83 0.71 0.56 2.0 4.0 6.0 10 10 56 50 75 75 60 600 950 mW dB 1.12 0.93 0.81 0.64 2.1 4.2 6.3 10.5 69 mV dB 5.5 7 10 V mA A ms k SYMBOL CONDITIONS MIN TYP MAX UNITS Input Bias Voltage V MAX9705A Voltage Gain AV MAX9705B MAX9705C MAX9705D Output Offset Voltage Common-Mode Rejection Ratio Power-Supply Rejection Ratio (Note 3) VOS CMRR PSRR TA = +25C fIN = 1kHz, input referred VDD = 2.5V to 5.5V, TA = +25C 200mVP-P ripple fRIPPLE = 217Hz fRIPPLE = 20kHz RL = 8 Output Power POUT THD+N = 1%, fIN = 1kHz RL = 4 MAX9705_ETB+T and MAX9705_EUB+ only RL = 8, POUT = 450mW RL = 4, POUT = 375mW Into shutdown Out of shutdown V/V Total Harmonic Distortion Plus Noise THD+N fIN = 1kHz, either FFM or SSM Peak voltage, A-weighted (Notes 3, 4) 0.02 % 0.025 -68 dB -60.5 176 V/s Click/Pop Level Output Slew Rate KCP SR 2 _______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier ELECTRICAL CHARACTERISTICS (continued) (VDD = PVDD = V SHDN = 3.3V, VGND = VPGND = 0, SYNC = GND (FFM), RL = , RL connected between OUT+ and OUT-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2) PARAMETER Rise/Fall Time SYMBOL tRISE, tFALL 10% to 90% BW = 22Hz to 22kHz A-weighted SYNC = GND Oscillator Frequency SYNC Frequency Lock Range Efficiency DIGITAL INPUTS (SHDN, SYNC) Input Thresholds SHDN Input Leakage Current SYNC Input Current (Note 5) VIH VIL 0.1 -1.25 2 0.8 10 10 V A A POUT = 800mW, fIN = 1kHz, RL = 8 fOSC SYNC = VDD (SSM mode) 800 89 FFM SSM FFM SSM 980 CONDITIONS MIN TYP 15 91 89 93 91 1100 1220 120 2000 1220 kHz kHz % dB MAX UNITS ns MAX9705 Signal-to-Noise Ratio SNR VOUT = 2VRMS ELECTRICAL CHARACTERISTICS (V DD = PV DD = V SHDN = 5V, V GND = V PGND = 0, SYNC = GND (FFM), R L = , R L 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 Power-Supply Rejection Ratio SYMBOL IDD ISHDN PSRR 200mVP-P ripple f = 217Hz f = 20kHz RL = 16 Output Power POUT THD+N = 1%, f = 1kHz RL = 8 RL = 4 MAX9705_ETB+T and MAX9705_EUB+ only RL = 8, POUT = 1.0W RL = 4, POUT = 1.75W FFM SSM FFM SSM CONDITIONS MIN TYP 7 0.55 75 60 750 1400 mW 2300 0.02 0.05 94 91 97 93 dB MAX UNITS mA A dB Total Harmonic Distortion Plus Noise THD+N f = 1kHz, either FFM or SSM VOUT = 3VRMS % Signal-to-Noise Ratio SNR 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: Inputs AC-coupled to GND. Note 4: Testing performed with 8 resistive load in series with 68H inductive load connected across BTL output. Mode transitions are controlled by SHDN pin. 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. Note 5: SYNC has a 1M resistor to VREF = 1.25V. _______________________________________________________________________________________ 3 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 Typical Operating Characteristics (VDD = 3.3V, SYNC = VDD (SSM), differential input, TA = +25C, unless otherwise noted. Typical Operating Characteristics for 4 load condition apply to the MAX9705_ETB+T only.) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9705toc01 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9705toc02 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9705toc03 100 fIN = 1kHz 100 100 10 10 10 THD+N (%) THD+N (%) THD+N (%) 1 1 1 0.1 0.1 0.1 0.01 VDD = 3.3V RL = 8 0.001 0 0.2 0.4 0.6 0.8 1.0 1.2 OUTPUT POWER (W) 0.01 fIN = 1kHz 0.001 0 0.5 1.0 OUTPUT POWER (W) 1.5 2.0 VDD = 5.0V RL = 8 0.01 0.001 0 0.2 fIN = 1kHz VDD = 2.5V RL = 4 0.4 OUTPUT POWER (W) 0.6 0.8 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9705toc04 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9705toc05 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 3.3V RL = 8 fIN = 1kHz MAX9705toc06 100 100 100 10 10 10 THD+N (%) 1 THD+N (%) THD+N (%) 1 1 SSM 0.1 FFM 0.1 0.1 0.01 0.001 0 0.5 fIN = 1kHz 0.01 VDD = 3.3V RL = 4 0.001 1.0 1.5 0 0.5 1.0 1.5 2.0 2.5 3.0 fIN = 1kHz VDD = 5.0V RL = 4 0.01 0.001 0 0.2 0.4 0.6 0.8 1.0 1.2 OUTPUT POWER (W) OUTPUT POWER (W) OUTPUT POWER (W) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9705toc07 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9705toc08 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 2.5V RL = 4 MAX9705toc09 100 VDD = 3.3V RL = 8 10 THD+N (%) 100 VDD = 5.0V RL = 8 10 THD+N (%) 100 10 THD+N (%) POUT = 50mW 1 POUT = 300mW 0.1 1 POUT = 100mW 1 POUT = 250mW 0.1 POUT = 450mW 0.1 POUT = 1W 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 4 _______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier Typical Operating Characteristics (continued) (VDD = 3.3V, SYNC = VDD (SSM), differential input, TA = +25C, unless otherwise noted. Typical Operating Characteristics for 4 load condition apply to the MAX9705_ETB+T only.) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9705toc10 MAX9705 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9705toc11 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 3.3V RL = 8 POUT = 450mW 10 MAX9705toc12 100 VDD = 3.3V RL = 4 10 THD+N (%) 100 VDD = 5.0V RL = 4 10 THD+N (%) POUT = 250mW 1 POUT = 1.75W 0.1 100 1 POUT = 100mW POUT = 800mW THD+N (%) 1 FFM 0.1 0.1 SSM 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 10 100 1k FREQUENCY (Hz) 10k 100k 0.01 10 100 1k FREQUENCY (Hz) 10k 100k TOTAL HARMONIC DISTORTION PLUS NOISE vs. COMMON-MODE VOLTAGE MAX9705toc13 EFFICIENCY vs. OUTPUT POWER MAX9705toc14 EFFICIENCY vs. OUTPUT POWER 90 80 EFFICIENCY (%) 70 60 50 40 30 20 RL = 4 RL = 8 MAX9705toc15 100 VDD = 3.3V to 5V fIN = 1kHz POUT = 500mW GAIN = 6dB RL = 8 100 90 80 EFFICIENCY (%) 70 60 50 40 30 RL = 4 RL = 8 100 10 THD+N (%) 1 0.1 0.01 0.001 0 0.5 1.0 1.5 2.0 2.5 COMMON-MODE VOLTAGE (V) 20 10 0 0 0.2 0.4 0.6 0.8 1.0 OUTPUT POWER (W) VDD = 3.3V fIN = 1kHz 10 0 0 0.5 1.0 1.5 2.0 VDD = 5.0V fIN = 1kHz 2.5 3.0 OUTPUT POWER (W) EFFICIENCY vs. SUPPLY VOLTAGE 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) fIN = 1kHz THD+N = 1% RL = 4 EFFICIENCY (%) RL = 8 MAX9705toc16 EFFICIENCY vs. SYNC FREQUENCY MAX9705toc17 EFFICIENCY vs. SYNC FREQUENCY 90 80 EFFICIENCY (%) 70 60 50 40 30 RL = 4 RL = 8 MAX9705toc18 100 100 90 80 70 60 50 40 30 20 10 0 800 1000 1200 1400 1600 1800 VDD = 3.3V fIN = 1kHz THD+N = 1% RL = 4 RL = 8 100 20 10 0 800 1000 1200 1400 1600 VDD = 5.0V fIN = 1kHz THD+N = 1% 1800 2000 2000 SYNC FREQUENCY (kHz) SYNC FREQUENCY (kHz) _______________________________________________________________________________________ 5 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 Typical Operating Characteristics (continued) (VDD = 3.3V, SYNC = VDD (SSM), differential input, TA = +25C, unless otherwise noted. Typical Operating Characteristics for 4 load condition apply to the MAX9705_ETB+T only.) OUTPUT POWER vs. SUPPLY VOLTAGE MAX9705toc19 OUTPUT POWER vs. SUPPLY VOLTAGE MAX9705toc20 OUTPUT POWER vs. LOAD RESISTANCE 3.5 OUTPUT POWER (W) 3.0 2.5 2.0 3.3V 1.5 1.0 fIN = 1kHz ZLOAD = 33H IN SERIES WITH RL THD+N = 1% 5.0V MAX9705 toc21 2.0 1.8 1.6 OUTPUT POWER (W) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 2.5 3.0 3.5 4.0 4.5 5.0 fIN = 1kHz RL = 8 THD+N = 1% THD+N = 10% 3.5 3.0 OUTPUT POWER (W) 2.5 THD+N = 10% 2.0 1.5 1.0 0.5 0 fIN = 1kHz RL = 4 2.5 3.0 3.5 4.0 4.5 5.0 THD+N = 1% 4.0 0.5 0 5.5 1 10 100 1000 5.5 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) LOAD RESISTANCE () POWER-SUPPLY REJECTION RATIO vs. FREQUENCY MAX9705 toc22 FIXED-FREQUENCY-MODE OUTPUT SPECTRUM vs. FREQUENCY 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 RL = 8 VDD = 5.0V fIN = 1kHz BW = 22Hz to 22kHz MAX9705 toc23 0 -10 -20 -30 PSRR (dB) -40 -50 -60 -70 -80 -90 -100 10 100 1k FREQUENCY (Hz) 10k VDD = 3.3V VIN = 200mVP-P RL = 8 20 100k 0 5 10 FREQUENCY (kHz) 15 20 SPREAD-SPECTRUM-MODE OUTPUT SPECTRUM vs. FREQUENCY MAX9705 toc24 SPREAD-SPECTRUM-MODE OUTPUT SPECTRUM vs. FREQUENCY 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 RL = 8 VDD = 5.0V fIN = 1kHz A-WEIGHTED MAX9705 toc25 20 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 0 5 10 FREQUENCY (kHz) 15 RL = 8 VDD = 5.0V fIN = 1kHz BW = 22Hz to 22kHz 20 20 0 5 10 FREQUENCY (kHz) 15 20 6 _______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 Typical Operating Characteristics (continued) (VDD = 3.3V, SYNC = VDD (SSM), differential input, TA = +25C, unless otherwise noted. Typical Operating Characteristics for 4 load condition apply to the MAX9705_ETB+T only.) WIDEBAND OUTPUT SPECTRUM FIXED-FREQUENCY MODE MAX9705 toc26 WIDEBAND OUTPUT SPECTRUM SPREAD-SPECTRUM MODE MAX9705 toc27 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 0 10 100 RL = 8 VDD = 5.0V INPUTS AC GROUNDED 0 -20 AMPLITUDE (dBV) -40 -60 -80 -100 -120 -140 RL = 8 VDD = 5.0V INPUTS AC GROUNDED 0 10 100 1000 1000 FREQUENCY (MHz) FREQUENCY (MHz) SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX9705 toc28 SUPPLY CURRENT vs. TEMPERATURE 6.75 SUPPLY CURRENT (mA) 6.50 6.25 6.00 5.75 5.50 5.25 5.00 5.5 -40 -15 SYNC = GND (FFM)) SYNC = VDD (SSM) VDD = 3.3V NO LOAD INPUTS AC GROUNDED MAX9705 toc29 10 9 SUPPLY CURRENT (mA) SYNC = VDD (SSM) 8 7 6 SYNC = GND (FFM) 5 4 2.5 3.5 4.5 SUPPLY VOLTAGE (V) NO LOAD INPUTS AC GROUNDED 7.00 10 35 60 85 TEMPERATURE (C) SHUTDOWN CURRENT vs. SUPPLY VOLTAGE 0.90 SHUTDOWN CURRENT (A) 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) NO LOAD INPUTS AC GROUNDED SHDN = GND TA = +25C MAX9705 OUTPUT TA = +85C TA = -40C MAX9705 toc30 TURN-ON/TURN-OFF RESPONSE MAX9705 toc31 1.00 3V SHDN 0V 250mV/div f = 1kHz RL = 8 10ms/div _______________________________________________________________________________________ 7 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 Functional Diagram 2.5V TO 5.5V 1F 1 (A1) VDD 5 (B2) SHDN 10 (B4) PVDD CLICK-AND-POP SUPPRESSION 6 (A3) SYNC OSCILLATOR PVDD UVLO/POWER MANAGEMENT LOW-EMI DRIVER 1F 2 (B1) IN+ 3 (C1) INCLASS D MODULATOR PGND PVDD 8 OUT+ (A4) 1F OUT- 9 (C4) LOW-EMI DRIVER MAX9705 PGND PGND 7 (B3) GND 4 (C2) ( ) UCSP BUMP. FIGURE SHOWS MAX9705 CONFIGURED FOR SPREAD-SPECTRUM OPERATION. 8 _______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier Pin Description PIN TDFN 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 = 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 Exposed Pad. Internally connected to ground. Connect to a large ground plane to maximize thermal performance. Not intended as an electrical connection point (TDFN only). FUNCTION MAX9705 6 A3 SYNC 7 8 9 10 -- B3 A4 C4 B4 -- PGND OUT+ OUTPVDD EP Detailed Description The MAX9705 ultra-low-EMI, filterless, Class D audio power amplifier features several improvements to switchmode amplifier technology. The MAX9705 features output driver active emissions limiting circuitry to reduce EMI. Zero dead time technology maintains state-of-the-art efficiency and THD+N performance by allowing the output FETs to switch simultaneously without cross-conduction. A unique filterless modulation scheme, synchronizable switching frequency, and spread-spectrum mode create a compact, flexible, low-noise, efficient audio power amplifier while occupying minimal board space. The differential input architecture reduces common-mode noise pickup with or without the use of input-coupling capacitors. The MAX9705 can also be configured as a singleended input amplifier without performance degradation. Thermal-overload and short-circuit protection prevent the MAX9705 from being damaged during a fault condition. The amplifier is disabled if the die temperature reaches +125C. The die must cool by 10C before normal operation can continue. The output of the MAX9705 shuts down if the output current reaches approximately 2A. Each output FET has its own short-circuit protection. This protection scheme allows the amplifier to survive shorts to either supply rail. After a thermal overload or short circuit, the device remains disabled for a minimum of 50s before attempting to return to normal operation. The amplifier will shut down immediately and wait another 50s before turning on if the fault condition is still present. This operation will cause the output to pulse during a persistent fault. Comparators monitor the MAX9705 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 FFM mode is selected by setting SYNC = GND for a 1.1MHz 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 Output Spectrum FixedFrequency Mode graph in the Typical Operating Characteristics). _______________________________________________________________________________________ 9 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 tSW VIN- VIN+ OUT- OUT+ tON(MIN) VOUT+ - VOUT- Figure 1. MAX9705 Outputs with an Input Signal Applied Table 1. Operating Modes SYNC INPUT GND VDD Clocked MODE FFM with fS = 1100kHz SSM with fS = 1220kHz 120kHz FFM with fS = external clock frequency 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 (see the EMI Spectrum Diagram). Spread-Spectrum Modulation (SSM) Mode The MAX9705 features a unique, patented spread-spectrum mode that flattens the wideband spectral components, improving EMI emissions 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 External Clock Mode The SYNC input allows the MAX9705 to be synchronized to a system clock moving 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 MAX9705. The period of the SYNC clock can be randomized, enabling the MAX9705 to be synchronized to another MAX9705 operating in SSM mode. 10 ______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 tSW tSW tSW tSW VIN- VIN+ OUT- OUT+ tON(MIN) VOUT+ - VOUT- Figure 2. MAX9705 Output with an Input Signal Applied (SSM Mode) Filterless Modulation/Common-Mode Idle The MAX9705 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 the load as a DC voltage, resulting in a finite load current, increasing power consumption. When no signal is present at the input of the MAX9705, the outputs switch as shown in Figure 3. Because the MAX9705 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle-mode voltage across the speaker, minimizing power consumption. 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 I2R loss of the MOSFET on-resistance and supply current. 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 MAX9705 still exhibits >70% efficiencies under the same conditions (Figure 4). Shutdown The MAX9705 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9705 in a low-power (0.3A) shutdown mode. Connect SHDN to VDD for normal operation. Efficiency Efficiency of a Class D amplifier is attributed to the region of operation of the output stage transistors. In a ______________________________________________________________________________________ 11 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 EFFICIENCY vs. OUTPUT POWER VIN = 0V 100 90 80 EFFICIENCY (%) 70 60 50 40 30 CLASS AB MAX9705 OUT- OUT+ 20 10 0 0 0.2 0.4 0.6 VDD = 3.3V fIN = 1kHz RL = 8 0.8 1.0 VOUT+ - VOUT- = 0V OUTPUT POWER (W) Figure 3. MAX9705 Outputs with No Input Signal Figure 4. MAX9705 Efficiency vs. Class AB Efficiency Click-and-Pop Suppression The MAX9705 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 30ms following startup, a soft-start function gradually unmutes the input amplifiers. 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 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. 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 and THD+N performance. 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 MAX9705 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 MAX9705 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 12 Input Amplifier Differential Input The MAX9705 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 MAX9705 can be configured as a single-ended input amplifier by capacitively coupling either input to GND and driving the other input (Figure 5). ______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier Note that the single-ended voltage range of the MAX9705A is 3VP-P. This limits the achievable output power for this device. Use higher gain versions (MAX9705B, MAX9705C, MAX9705D) if higher output power is desired in a single-ended application. MAX9705 1F SINGLE-ENDED AUDIO INPUT IN+ MAX9705 IN1F 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 feed through to the load. Figure 5. Single-Ended Input Component Selection Input Filter An input capacitor, CIN, in conjunction with the input resistance of the MAX9705 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 2 RIN CIN tion, 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 MAX9705 does not require an output filter. The device passes FCC emissions standards with 24in of unshielded twisted-pair speaker cables. However, an output filter can be used if a design is failing radiated emissions due to board layout or excessive cable length, or the circuit is near EMI-sensitive devices. Supply Bypassing/Layout Proper power-supply bypassing ensures low-distortion operation. For optimum performance, bypass VDD to GND and PVDD to PGND with separate 1F capacitors as close to each pin as possible. A low-impedance, high-current power-supply connection to PV DD is assumed. Additional bulk capacitance should be added as required depending on the application and powersupply characteristics. GND and PGND should be star connected to system ground. Refer to the MAX9705 evaluation kit for layout guidance. Choose CIN so f-3dB is well below the lowest frequency of interest. Setting f -3dB too high affects the lowfrequency response of the amplifier. 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. If a ceramic capacitor is selected due to size constraints, use the largest package possible to minimize voltage coefficient effects. In addition, use X7R dielectrics as opposed to Y5V or Z5U. 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 considera- Stereo Configuration Two MAX9705s can be configured as a stereo amplifier (Figure 6). 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 MAX9705s 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 7 and 8). 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. ______________________________________________________________________________________ 13 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 VDD 1F VDD PVDD RIGHT-CHANNEL DIFFERENTIAL AUDIO INPUT IN+ MAX9705 OUT+ IN- OUTSYNC 1F VDD PVDD LEFT-CHANNEL DIFFERENTIAL AUDIO INPUT IN+ MAX9705 OUT+ IN- OUTSYNC Figure 6. Master-Slave Stereo Configuration TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER 100 0 VDD = 3.3V SLAVE DEVICE fIN = 1kHz SYNC = GND (FFM) RL = 8 -10 -20 -30 CROSSTALK (dB) -40 -50 -60 -70 -80 0.01 -90 -100 0.001 0 0.2 0.4 OUTPUT POWER (W) 0.6 0.8 -110 10 CROSSTALK vs. FREQUENCY VDD = 3.3V VIN = 500mVP-P fIN = 1kHz SYNC = GND (FFM) RL = 8 10 THD+N (%) 1 0.1 MASTER TO SLAVE SLAVE TO MASTER 100 1k FREQUENCY (Hz) 10k 100k Figure 7. Master-Slave THD+N Figure 8. Master-Slave Crosstalk 14 ______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 1F CW 1F 50k INCW IN22k MAX9705 IN+ 1F 1F 50k 22k IN+ MAX9705 Figure 9a. Single-Ended Drive of MAX9705 Plus Volume Figure 9b. Improved Single-Ended Drive of MAX9705 Plus Volume Pin Configurations TOP VIEW PGND SYNC OUT+ PVDD OUT- Selector Guide PART MAX9705AETB+T MAX9705AEBC+T MAX9705BETB+T MAX9705BEBC+T MAX9705CETB+T MAX9705CEBC+T PIN-PACKAGE 10 TDFN 12 UCSP 10 TDFN 12 UCSP 10 TDFN 12 UCSP 10 TDFN 12 UCSP GAIN (dB) 6 6 12 12 15.6 15.6 20 20 10 9 8 7 6 MAX9705 + 1 VDD 2 IN+ 3 IN4 GND 5 SHDN MAX9705DETB+T MAX9705DEBC+T Ordering Information (continued) PART TEMP RANGE -40oC to +85oC -40 C to +85 C -40oC to +85oC -40oC to +85oC o o TDFN TOP VIEW (BUMP SIDE DOWN) 1 PINPACKAGE 10 TDFN 12 UCSP 10 TDFN 12 UCSP TOP MARK ACZ ACI ADA ACJ MAX9705 2 3 4 MAX9705CETB+T MAX9705CEBC+T MAX9705DETB+T MAX9705DEBC+T VDD A IN+ B INC GND SHDN SYNC OUT+ PGND PVDD +Denotes a lead(Pb)-free/RoHS-compliant package. T = Tape and reel. OUT- UCSP ______________________________________________________________________________________ 15 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 System Diagram VDD VDD 0.1F AUX_IN 1F VDD IN+ OUT INSHDN PVDD MAX9705 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 16 ______________________________________________________________________________________ 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier Chip Information PROCESS: BiCMOS 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 10 TDFN 12 UCSP PACKAGE CODE T1033-1 B12-11 DOCUMENT NO. 21-0137 21-0104 MAX9705 ______________________________________________________________________________________ 17 2.3W, Ultra-Low-EMI, Filterless, Class D Audio Amplifier MAX9705 Revision History REVISION NUMBER 2 3 REVISION DATE 8/08 5/09 Removed MAX package option Removed SYNC unconnected mode DESCRIPTION PAGES CHANGED 1-7, 9, 10, 15 3, 7, 9, 10, 14 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) 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. |
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