19-2917; Rev 1; 1/04 500mW, Low EMI, Filterless, Class D Audio Amplifier 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 8Ω 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 µMAX, and 12-bump UCSP™ (1.5mm ✕ 2mm ✕ 0.6mm) packages. The MAX9712 is specified over the extended -40°C to +85°C temperature range. Applications Cellular Phones MP3 Players PDAs Portable Audio Simplified Block Diagram 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 8Ω ♦ Low 0.01% THD+N ♦ High PSRR (72dB at 217Hz) ♦ Integrated Click-and-Pop Suppression ♦ Low Quiescent Current (4mA) ♦ Low-Power Shutdown Mode (0.1µA) ♦ Short-Circuit and Thermal-Overload Protection ♦ Available in Thermally Efficient, Space-Saving Packages 10-Pin TDFN (3mm ✕ 3mm ✕ 0.8mm) 10-Pin µMAX 12-Bump UCSP (1.5mm ✕ 2mm ✕ 0.6mm) Ordering Information TEMP RANGE PIN/BUMPPACKAGE MAX9712ETB -40°C to +85°C 10 TDFN AAI MAX9712EUB -40°C to +85°C 10 µMAX — MAX9712EBC-T -40°C to +85°C 12 UCSP-12 PART VDD TOP MARK ABN Pin Configurations TOP VIEW DIFFERENTIAL AUDIO INPUT MODULATOR AND H-BRIDGE VDD 1 IN+ SYNC INPUT OSCILLATOR MAX9712 10 PVDD 2 MAX9712 9 OUT- IN- 3 8 OUT+ GND 4 7 PGND SHDN 5 6 SYNC TDFN/µMAX UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations continued at end of data sheet. ________________________________________________________________ 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 MAX9712 General Description MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier 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 = +70°C) 10-Pin TDFN (derate 24.4mW/°C above +70°C) .....1951.2mW 10-Pin µMAX (derate 5.6mW/oC above +70°C) .........444.4mW 12-Bump UCSP (derate 6.1mW/°C above +70°C)........484mW Junction Temperature ......................................................+150°C Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Bump Temperature (soldering) Reflow ..........................................................................+235°C 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 = 8Ω, RL connected between OUT+ and OUT-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS GENERAL Supply Voltage Range VDD 5.5 V Quiescent Current IDD Inferred from PSRR test 2.5 4 5.2 mA Shutdown Current ISHDN 0.1 5 µA Turn-On Time tON Input Resistance RIN TA = +25°C 14 20 VBIAS Either input 0.73 0.83 Input Bias Voltage Voltage Gain 30 AV 3.8 TA = +25°C Output Offset Voltage Common-Mode Rejection Ratio Power-Supply Rejection Ratio (Note 3) Output Power Total Harmonic Distortion Plus Noise 2 VOS CMRR TMIN ≤ TA ≤ TMAX POUT THD+N kΩ 0.93 V V/V 4 4.2 MAX9712EUB/MAX9712ETB ±11 ±40 MAX9712EBC ±15 ±65 ±65 MAX9712EUB/MAX9712ETB 200mVP-P ripple THD+N = 1% fIN = 1kHz, either FFM or SSM mV ±95 MAX9712EBC fIN = 1kHz, input referred VDD = 2.5V to 5.5V PSRR ms 72 50 dB 70 fRIPPLE = 217Hz 72 fRIPPLE = 20kHz 55 RL = 16Ω, VDD = 5V 700 RL = 8Ω 450 RL = 6Ω 250 RL = 8Ω, POUT = 125mW 0.01 RL = 6Ω, POUT = 125mW 0.01 dB mW % _______________________________________________________________________________________ 500mW, Low EMI, Filterless, Class D Audio Amplifier (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = GND (FFM), RL = 8Ω, RL connected between OUT+ and OUT-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS BW = 22Hz to 22kHz Signal-to-Noise Ratio SNR VOUT = 1.8VRMS A-weighted Oscillator Frequency fOSC MIN FFM TYP MAX 88 SSM 86 FFM 91 SSM dB 89 SYNC = GND 980 1100 1220 SYNC = float 1280 1450 1620 SYNC Frequency Lock Range 800 η kHz 1220 ±120 SYNC = VDD (SSM mode) Efficiency UNITS POUT = 300mW, fIN = 1kHz 2000 kHz 85 % DIGITAL INPUTS (SHDN, SYNC) VIH Input Thresholds 2 V 0.8 VIL SHDN Input Leakage Current ±1 µA SYNC Input Current ±5 µA Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design. Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For RL = 6Ω, L = 47µH. For RL = 8Ω, L = 68µH. For RL = 16Ω, L = 136µH. Note 3: PSRR is specified with the amplifier inputs connected to GND through CIN. Typical Operating Characteristics (VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.) 1 1 1 VDD = +5V RL = 8Ω VDD = +3.3V RL = 8Ω VDD = +3.3V RL = 8Ω POUT = 125mW 0.1 POUT = 300mW 0.01 THD+N (%) THD+N (%) 0.1 THD+N (%) 0.1 POUT = 300mW POUT = 125mW FFM MODE 0.001 0.001 10 100 1k FREQUENCY (Hz) SSM MODE 0.01 0.01 POUT = 125mW 0.001 10k 100k MAX9712 TOC03 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9712 TOC02 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9712 TOC01 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY 10 100 1k FREQUENCY (Hz) 10k 100k 10 100 1k 10k 100k FREQUENCY (Hz) _______________________________________________________________________________________ 3 MAX9712 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (continued) (VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.) 1 f = 10kHz 10 1 10 1 0.1 0.1 f = 1kHz 0.3 0.4 0.5 f = 100Hz f = 1kHz f = 100Hz 0.001 0.2 f = 10kHz 0.01 f = 100Hz f = 1kHz 0 0.001 0 0.2 0.4 0.6 0.8 1.0 0 0.1 0.2 0.3 0.4 OUTPUT POWER (W) OUTPUT POWER (W) OUTPUT POWER (W) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER DIFFERENTIAL INPUT FFM (SYNC FLOATING) SSM (SYNC = VDD) fSYNC = 800kHz 0.4 0.5 0.001 0 0.1 OUTPUT POWER (W) TOTAL HARMONIC DISTORTION PLUS NOISE vs. COMMON-MODE VOLTAGE 0.3 0.4 0.5 0.1 80 RL = 8Ω 60 50 40 2.0 2.5 COMMON-MODE VOLTAGE (V) 3.0 80 0.6 RL = 16Ω 70 RL = 8Ω 60 RL = 6Ω 50 40 VDD = 3.3V f = 1kHz 10 0 0 1.5 0.5 20 VDD = 5V f = 1kHz 10 1.0 0.4 30 20 0.01 0.3 90 RL = 16Ω 70 0.2 100 MAX9712TOC11 90 30 0.5 0.1 EFFICIENCY vs. OUTPUT POWER EFFICIENCY vs. OUTPUT POWER EFFICIENCY (%) VDD = 3.3V RL = 8Ω f = 1kHz POUT = 300mW DIFFERENTIAL INPUT 0 0 OUTPUT POWER (W) 100 MAX9712 TOC10 10 1 0.2 OUTPUT POWER (W) EFFICIENCY (%) 0.3 0.1 0.01 0.001 0.2 fSYNC = 2MHz fSYNC = 1.4MHz FFM (SYNC = GND) 0.001 0.1 1 0.01 SINGLE-ENDED 0 10 MAX9712 TOC09 MAX9712 TOC08 1 VDD = 3.3V RL = 8Ω SYNC = 3.3VP-P 50% DUTY CYCLE SQUARE WAVE MAX9712TOC12 0.01 10 0.1 100 THD+N (%) 1 0.1 VDD = 3.3V RL = 8Ω THD+N (%) VDD = 2.5V RL = 8Ω VCM = 1.25V NO INPUT CAPACITORS 10 100 MAX9712 TOC07 100 4 VDD = 3.3V RL = 6Ω 0.01 0.001 THD+N (%) f = 10kHz 0.1 0.01 100 MAX9712 TOC05 VDD = 5V RL = 16Ω THD+N (%) THD+N (%) 10 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER THD+N (%) VDD = 3.3V RL = 8Ω 0.1 100 MAX9712 TOC04 100 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER MAX9712 TOC06 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER THD+N (%) MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W) 0.6 0.7 0 0.1 0.2 0.3 OUTPUT POWER (W) _______________________________________________________________________________________ 0.4 0.5 500mW, Low EMI, Filterless, Class D Audio Amplifier EFFICIENCY vs. SYNC INPUT FREQUENCY RL = 16Ω 60 50 40 60 50 40 30 20 20 10 10 f = 1kHz 3.5 4.0 4.5 5.0 1600 RL = 6Ω 0 1800 2000 2.5 3.1 3.7 4.3 4.9 OUTPUT POWER vs. LOAD RESISTANCE COMMON-MODE REJECTION RATIO vs. FREQUENCY POWER-SUPPLY REJECTION RATIO vs. FREQUENCY 400 0 -20 -20 -30 -30 -40 -40 -50 -60 -50 -60 300 -70 -70 200 -80 -80 100 -90 -90 0 -100 -100 10 20 30 40 50 60 70 80 90 100 10 100 1k 10k 100k 10 FREQUENCY (Hz) LOAD RESISTANCE (Ω) 1k 10k 100k OUTPUT FREQUENCY SPECTRUM MAX9712TOC19 0 FFM MODE VOUT = -60dBV f = 1kHz RL = 8Ω UNWEIGHTED -20 OUTPUT MAGNITUDE (dBV) 500mV/div MAX9712 OUTPUT 100 FREQUENCY (Hz) GSM POWER-SUPPLY REJECTION VDD OUTPUT REFERRED INPUTS AC GROUNDED VDD = 3.3V -10 -40 MAX9712TOC20 VDD = 3.3V INPUT REFERRED VIN = 200mVP-P 5.5 MAX9712TOC18 0 -10 CMRR (dB) 600 0 RL = 8Ω 300 SUPPLY VOLTAGE (V) VDD = 5V 500 1400 400 SYNC FREQUENCY (kHz) 800 700 1200 500 SUPPLY VOLTAGE (V) f = 1kHz THD+N = 1% 900 1000 600 100 RL = 8Ω 800 5.5 RL = 16Ω 700 200 PSRR (dB) 1000 3.0 MAX9712TOC16 2.5 VDD = 3.3V f = 1kHz POUT = 300mW 0 0 OUTPUT POWER (mW) 70 30 800 OUTPUT POWER (mW) RL = 8Ω RL = 6Ω 80 f = 1kHz 900 MAX9712TOC17 70 1000 MAX9712TOC14 80 90 EFFICIENCY (%) 90 EFFICIENCY (%) 100 MAX9712TOC13 100 OUTPUT POWER vs. SUPPLY VOLTAGE MAX9712TOC15 EFFICIENCY vs. SUPPLY VOLTAGE -60 -80 -100 100µV/div -120 -140 f = 217Hz INPUT LOW = 3V INPUT HIGH = 3.5V 2ms/div DUTY CYCLE = 88% RL = 8Ω 0 5k 10k 15k FREQUENCY (Hz) 20k _______________________________________________________________________________________ 5 MAX9712 Typical Operating Characteristics (continued) (VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VDD = 3.3V, VSYNC = GND, TA = +25°C, unless otherwise noted.) -40 -60 -80 -100 SSM MODE VOUT = -60dBV f = 1kHz RL = 8Ω A-WEIGHTED -20 -40 0 RBW = 10kHz -10 -20 OUTPUT AMPLITUDE (dB) -20 0 MAX9712TOC22 SSM MODE VOUT = -60dBV f = 1kHz RL = 8Ω UNWEIGHTED OUTPUT MAGNITUDE (dBV) MAX9712TOC21 0 WIDEBAND OUTPUT SPECTRUM (FFM MODE) OUTPUT FREQUENCY SPECTRUM -60 -80 -100 MAX1972 TOC23 OUTPUT FREQUENCY SPECTRUM OUTPUT MAGNITUDE (dBV) -30 -40 -50 -60 -70 -80 -120 -120 -140 -140 0 5 10 15 FREQUENCY (kHz) 20 -90 -100 0 5 10 15 FREQUENCY (kHz) WIDEBAND OUTPUT SPECTRUM (SSM MODE) -20 OUTPUT AMPLITUDE (dB) 10M 100M FREQUENCY (Hz) MAX9712TOC25 MAX1972TOC24 RBW = 10kHz -10 1M 20 TURN-ON/TURN-OFF RESPONSE 0 SHDN 3V -30 -40 -50 0V -60 -70 MAX9712 OUTPUT -80 250mV/div -90 -100 10M 100M 1G SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE SUPPLY CURRENT vs. SUPPLY VOLTAGE TA = +25°C 4.5 TA = -40°C 4.0 TA = +85°C 0.14 SUPPLY CURRENT (µA) TA = +85°C 5.0 0.16 MAX9712TOC26 6.0 5.5 10ms/div f = 1kHz RL = 8Ω FREQUENCY (Hz) MAX9712 TOC27 1M SUPPLY CURRENT (mA) MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier 0.12 0.10 TA = +25°C 0.08 0.06 0.04 3.5 0 3.0 2.5 6 TA = -40°C 0.02 3.0 3.5 4.0 4.5 SUPPLY VOLTAGE (V) 5.0 5.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 1G 500mW, Low EMI, Filterless, Class D Audio Amplifier VDD 10µF 1µF 5 (B3) SHDN 1 (C4) 10 (B1) 6 (C2) VDD PVDD SYNC UVLO/POWER MANAGEMENT CLICK AND POP SUPPRESSION OSCILLATOR PVDD 2 (B4) IN+ CLASS D MODULATOR 3 (A4) IN- 8 OUT+ (C1) PGND PVDD OUT- 9 (A1) MAX9712 PGND PGND 7 (B2) GND 4 (A5) ( ) UCSP BUMP. _______________________________________________________________________________________ 7 MAX9712 Functional Diagram 500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712 Pin Description PIN BUMP TDFN/µMAX UCSP 1 C4 VDD 2 B4 IN+ Noninverting Audio Input 3 A4 IN- Inverting Audio Input 4 A3 GND 5 B3 SHDN Active-Low Shutdown Input. Connect to VDD for normal operation. NAME FUNCTION Analog Power Supply Analog Ground 6 C2 SYNC 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. 7 B2 PGND Power Ground 8 C1 OUT+ Amplifier Output Positive Phase 9 A1 OUT- Amplifier Output Negative Phase 10 B1 PVDD H-Bridge Power Supply 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. 8 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 _______________________________________________________________________________________ 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 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 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 _______________________________________________________________________________________ 9 MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier 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 AMPLITUDE (dBµV/m) 45.0 40.0 35.0 30.0 OUT- 25.0 20.0 15.0 10.0 30.0 OUT+ 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) 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 (0.1µA) shutdown mode. Connect SHDN to VDD for normal operation. 100 Click-and-Pop Suppression 70 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. 90 80 EFFICIENCY (%) 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 vs. OUTPUT POWER MAX9712 60 50 40 CLASS AB 30 VDD = 3.3V f = 1kHz RL - 8Ω 20 10 0 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W) 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 >10µH. Typical 8Ω speakers exhibit series inductances in the range of 20µH to 100µH. 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 MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier the power conversion of the class D amplifier. For example, an 8mV DC offset across an 8Ω load results in 1mA extra current consumption in a class AB device. In the class D case, an 8mV offset into 8Ω equates to an additional power drain of 8µW. Due to the high efficiency of the class D amplifier, this represents an additional quiescent current draw of: 8µW/(VDD/100η), which is on the order of a few microamps. 1µF SINGLE-ENDED AUDIO INPUT IN+ MAX9712 IN1µF 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. 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 2πRINCIN 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 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 0.1µF 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. 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 1µF RIGHT-CHANNEL DIFFERENTIAL AUDIO INPUT VDD PVDD IN+ MAX9712 OUT+ IN- OUT- UCSP Applications Information SYNC 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. 1µF LEFT-CHANNEL DIFFERENTIAL AUDIO INPUT VDD PVDD IN+ MAX9712 OUT+ IN- OUT- Chip Information TRANSISTOR COUNT: 3595 PROCESS: BiCMOS SYNC Figure 7. Master-Slave Stereo Configuration TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER CROSSTALK vs. FREQUENCY 100 0 VDD = 3.3V f = 1kHz RL = 8Ω SLAVE DEVICE CROSSTALK (dB) THD+N (%) 10 VDD = 3.3V RL = 8Ω f = 1kHz VIN = 500mVP-P -20 1 0.1 0.01 -40 MASTER-TO-SLAVE -60 -80 -100 0.001 SLAVE-TO-MASTER -120 0 0.1 0.2 0.3 OUTPUT POWER (W) Figure 8. Master-Slave THD 0.4 0.5 10 100 1k 10k 100k FREQUENCY (Hz) Figure 9. Master-Slave Crosstalk ______________________________________________________________________________________ 13 MAX9712 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. 500mW, Low EMI, Filterless, Class D Audio Amplifier MAX9712 System Diagram VDD VDD 0.1µF AUX_IN 1µF VDD PVDD IN+ MAX9712 OUT+ IN- OUT- SHDN SYNC 2.2kΩ MAX4063 BIAS OUT 2.2kΩ CODEC/ BASEBAND PROCESSOR 0.1µF OUT IN+ IN- 100kΩ 0.1µF 1µF VDD 10kΩ µCONTROLLER 1µF 1µF MODE1 VDD MODE2 HPS INL MAX9720 OUTL INR OUTR ALERT PVDD TIME SVDD C1P CIN 220nF 1µF 1µF Pin Configurations (continued) TOP VIEW (BUMP SIDE DOWN) 1 MAX9712 2 OUT- 3 4 GND IN- SHDN IN+ A PVDD PGND OUT+ SYNC B VDD C UCSP 14 VDD ______________________________________________________________________________________ 500mW, Low EMI, Filterless, Class D Audio Amplifier 12L, UCSP 4x3.EPS PACKAGE OUTLINE, 4x3 UCSP 21-0104 F 1 ______________________________________________________________________________________ 1 15 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.) 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 MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier L A D D2 A2 PIN 1 ID 1 N 1 C0.35 b E PIN 1 INDEX AREA [(N/2)-1] x e REF. E2 DETAIL A e k A1 CL CL L L e e A DALLAS SEMICONDUCTOR PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY 16 APPROVAL DOCUMENT CONTROL NO. 21-0137 ______________________________________________________________________________________ REV. D 1 2 500mW, Low EMI, Filterless, Class D Audio Amplifier COMMON DIMENSIONS SYMBOL A MIN. 0.70 MAX. 0.80 D 2.90 3.10 E 2.90 3.10 A1 0.00 0.05 L k 0.20 0.40 0.25 MIN. A2 0.20 REF. PACKAGE VARIATIONS PKG. CODE N D2 E2 e JEDEC SPEC b T633-1 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF T833-1 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF T1033-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 2.00 REF [(N/2)-1] x e DALLAS SEMICONDUCTOR PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 6, 8 & 10L, TDFN, EXPOSED PAD, 3x3x0.80 mm APPROVAL DOCUMENT CONTROL NO. 21-0137 REV. D 2 ______________________________________________________________________________________ 2 17 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.) 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.) e 10LUMAX.EPS MAX9712 500mW, Low EMI, Filterless, Class D Audio Amplifier 4X S 10 INCHES 10 H ÿ 0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS 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 α 0∞ 6∞ 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∞ E2 GAGE PLANE A2 c A b D1 A1 α E1 L L1 FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, 10L uMAX/uSOP APPROVAL DOCUMENT CONTROL NO. 21-0061 REV. I 1 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.