19-3457; Rev 3; 3/09 1.3W, Filterless, Stereo Class D Audio Power Amplifier The MAX9701 stereo Class D audio power amplifier provides Class AB amplifier audio performance with the benefits of Class D efficiency, eliminating the need for a heatsink while extending battery life. The MAX9701 delivers up to 1.3W per channel into an 8Ω load while offering 87% efficiency. Maxim’s next-generation, lowEMI modulation scheme allows the amplifier to operate without an external LC filter while still meeting FCC EMI emission levels. The MAX9701 offers two modulation schemes: a fixed-frequency (FFM) mode, and a spread-spectrum (SSM) mode that reduces EMI-radiated emissions. The MAX9701 oscillator can be synchronized to an external clock through the SYNC input, allowing synchronization of multiple Maxim Class D amplifiers. The sync output (SYNC_OUT) can be used for a master-slave application where more channels are required. The MAX9701 features a fully differential architecture, a full bridge-tied load (BTL) output, and comprehensive click-and-pop suppression. The device features internally set gains of 0dB, 6dB, 12dB, and 18dB selected through two gain-select inputs, further reducing external component count. The MAX9701 features high 80dB PSRR, less than 0.1% THD+N, and SNR in excess of 88dB. Short-circuit and thermal-overload protection prevent the device from being damaged during a fault condition. The MAX9701 is available in 24-pin thin QFN-EP (4mm x 4mm x 0.8mm), and 20-bump UCSP™ (2mm x 2.5mm x 0.6mm) packages. The MAX9701 is specified over the extended -40°C to +85°C temperature range. Applications Features o Patented Spread-Spectrum Modulation Lowers Radiated Emissions o Single-Supply Operation (2.5V to 5.5V) o 1.3W Stereo Output (8Ω, VDD = 5V, THD+N = 1%) o No LC Output Filter Required o 87% Efficiency (RL = 8Ω, POUT = 1000mW) o Less Than 0.1% THD+N o High 80dB PSRR o Fully Differential Inputs o Integrated Click-and-Pop Suppression o Typical Low Quiescent Current (9mA) o Typical Low-Power Shutdown Mode (0.1µA) o Short-Circuit and Thermal-Overload Protection o Available in Thermally Efficient, Space-Saving Packages 24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm) 20-Bump UCSP (2mm x 2.5mm x 0.6mm) Ordering Information PART TEMP RANGE PIN-PACKAGE MAX9701EBP+TG45 -40°C to +85°C 20 UCSP MAX9701ETG+ -40°C to +85°C 24 TQFN-EP* +Denotes lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Block Diagram Cellular Phones Notebooks VDD Handheld Gaming Consoles Docking Stations MAX9701 INR+ RIGHT MODULATOR AND H-BRIDGE MP3 Players INR- Pin Configurations appear at end of data sheet. GAIN1 GAIN2 GAIN INL+ LEFT MODULATOR AND H-BRIDGE INL- SYNC OSCILLATOR SYNC_OUT UCSP is a trademark of Maxim Integrated Products, Inc. ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX9701 General Description MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier ABSOLUTE MAXIMUM RATINGS VDD to GND..............................................................................6V VDD to PVDD ..........................................................-0.3V to +0.3V PVDD to PGND .........................................................................6V GND to PGND .......................................................-0.3V to +0.3V All Other Pins to GND.................................-0.3V to (VDD + 0.3V) Continuous Current In/Out of PVDD, PGND, OUT_ .........±800mA Continuous Input Current (all other pins)..........................±20mA Duration of OUT_ Short Circuit to GND or PVDD ........Continuous Duration of Short Circuit Between OUT+ and OUT- ......Continuous Continuous Power Dissipation (TA = +70°C) 20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW 24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW Junction Temperature ......................................................+150°C Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Bump Temperature (soldering) Reflow............................+235°C Lead Temperature (soldering, 10s) .................................+300°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 = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5.5 V GENERAL Supply Voltage Range Quiescent Current VDD IDD Shutdown Current ISHDN Common-Mode Rejection Ratio CMRR Input Bias Voltage VBIAS Turn-On Time Output Offset Voltage Inferred from PSRR test 2.5 VDD = 3.3V, per channel 4.5 8 VDD = 5V, per channel 6.3 10 0.1 10 fIN = 1kHz 66 1.125 tON VOS Output Power (Note 3) Total Harmonic Distortion Plus Noise (Note 3) PSRR POUT THD+N 100mVP-P ripple, VIN = 0V THD+N = 1%, TA = +25oC SNR VDD = 3.3V VDD = 5V 460 RL = 4Ω 750 RL = 8Ω 1300 RL = 4Ω 2200 RL = 4Ω (POUT = 400mW), f = 1kHz 0.15 FFM 86 SSM 86 FFM 88.5 SSM SYNC Frequency Lock Range fOSC 2 % dB 1100 1400 1250 1600 kHz 1200 ±60 tMIN fSYNC mW 88.5 950 1200 SYNC = VDD Minimum On-Time dB 50 RL = 8Ω 0.08 SYNC = GND SYNC = unconnected mV 80 RL = 8Ω (POUT = 300mW), f = 1kHz VOUT = 1VRMS V ms ±30 72 fRIPPLE = 20kHz A-weighted Oscillator Frequency 60 fRIPPLE = 217Hz BW = 22Hz to 22kHz Signal-to-Noise Ratio 1.375 ±55 TMIN < TA < TMAX µA dB 40 ±10 TA = +25oC VDD = 2.5V to 5.5V, VIN = 0V Power-Supply Rejection Ratio 1.25 mA 200 1000 _______________________________________________________________________________________ ns 1600 kHz 1.3W, Filterless, Stereo Class D Audio Power Amplifier (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2) PARAMETER SYNC_OUT Capacitance Drive Capacitive Drive SYMBOL KCP η Efficiency RIN Gain AV MAX 100 200 Single ended 400 Peak reading, THD+N = 1% Into shutdown A-weighted, 32 samples Out of per second (Note 4) shutdown UNITS pF pF 66.16 dB 66.26 VDD = 3.3V, POUT = 500mW per channel, fIN = 1kHz, RL = 8Ω 87 VDD = 5V, POUT = 1000mW per channel, fIN = 1kHz, RL = 8Ω 87.4 % 10.5 15 GAIN1 = 1, GAIN2 = 0 25 GAIN1 = 0, GAIN2 = 1 37.4 GAIN1 = 1, GAIN2 = 1 50 GAIN1 = 0, GAIN2 = 0 18 GAIN1 = 1, GAIN2 = 0 12 GAIN1 = 0, GAIN2 = 1 6 GAIN1 = 1, GAIN2 = 1 0 Channel-to-Channel Gain Tracking L to R, R to L, f = 10kHz, RL = 8Ω, POUT = 300mW Crosstalk TYP Bridge-tied capacitance GAIN1 = 0, GAIN2 = 0 Input Resistance MIN CSYNC_OUT CL Click-and-Pop Level CONDITIONS 19.5 kΩ dB 1 % 70 dB DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2) Input-Voltage High VINH Input-Voltage Low VINL 2 V Input Leakage Current (SHDN, GAIN1, GAIN2) VIN = GND, normal operation Input Leakage Current (SYNC) -15 0.8 V ±1 µA -7 µA VIN = VDD, normal operation 12 25 DIGITAL OUTPUTS (SYNC_OUT) Output-Voltage High VOH IOH = 3mA, VDD = 3.3V Output-Voltage Low VOL IOL = 3mA 2.4 V 0.08 V 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 = 4Ω, L = 33µH. For RL = 8Ω, L = 68µH. Note 3: When driving speakers below 4Ω with large signals, exercise care to avoid violating the absolute maximum rating for continuous output current. Note 4: Testing performed with 8Ω resistive load in series with 68µH inductive load connected across the BTL output. Mode transitions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage under normal operation at rated power level) / (peak voltage during mode transition, no input signal)]. Units are expressed in dB. _______________________________________________________________________________________ 3 MAX9701 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)). TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 5V RL = 4Ω VDD = 5V RL = 8Ω VDD = 3.3V RL = 4Ω 1 OUTPUT POWER = 600mW 0.1 THD+N (%) THD+N (%) 1 OUTPUT POWER = 500mW 0.1 0.1 OUTPUT POWER = 100mW OUTPUT POWER = 100mW 0.01 0.01 100 1k 10k 100k OUTPUT POWER = 300mW OUTPUT POWER = 100mW OUTPUT POWER = 250mW OUTPUT POWER = 300mW 10 100 1k 10k 0.01 100 10 100k 1k 10k 100k FREQUENCY (Hz) FREQUENCY (Hz) FREQUENCY (Hz) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER 10 MAX9701 toc04 10 VDD = 3.3V RL = 8Ω 100 MAX9701 toc05 10 OUTPUT POWER = 600mW VDD = 5V RL = 8Ω POUT = 800mW MAX9701 toc06 THD+N (%) 1 10 MAX9701 toc02 10 MAX9701 toc01 10 MAX9701 toc03 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 5V RL = 4Ω 10 THD+N (%) THD+N (%) OUTPUT POWER = 400mW THD+N (%) 1 1 FFM fIN = 10kHz 1 0.1 0.1 0.1 OUTPUT POWER = 100mW fIN = 1kHz SSM fIN = 20kHz OUTPUT POWER = 250mW 0.01 0.01 0.01 100 1k 10k 100 10 100k 1k 10k 0 100k 0.5 1.0 1.5 2.0 2.5 FREQUENCY (Hz) FREQUENCY (Hz) 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 VDD = 5V RL = 8Ω 10 VDD = 3.3V RL = 4Ω 100 VDD = 3.3V RL = 8Ω 10 3.0 MAX9701 toc09 100 MAX9701 toc07 100 MAX9701 toc08 10 10 1 0.1 fIN = 1kHz fIN = 10kHz 0.1 fIN = 1kHz fIN = 20kHz 0.01 1 THD+N (%) THD+N (%) fIN = 10kHz THD+N (%) MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier fIN = 10kHz 1 0.1 fIN = 20kHz fIN = 1kHz fIN = 20kHz 0.01 0.001 0 0.5 1.0 OUTPUT POWER (W) 4 1.5 2.0 0.01 0 0.2 0.4 0.6 0.8 OUTPUT POWER (W) 1.0 1.2 0 100 200 300 400 500 OUTPUT POWER (mW) _______________________________________________________________________________________ 600 700 1.3W, Filterless, Stereo Class D Audio Power Amplifier (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)). 0.1 MAX9701 toc11 80 RL = 4Ω 70 60 50 40 80 VDD = 5V fIN = 1kHz 10 0.8 1.2 1.6 0.5 1.0 2.0 0 2.5 2.5 THD+N = 10% 1.5 RL = 8Ω AV = 12dB fIN = 1kHz 1.6 1.2 THD+N = 1% THD+N = 10% 0.8 0 3.5 4.0 4.5 5.0 2.0 THD+N = 10% 1.5 THD+N = 1% 1.0 3.0 3.5 4.0 4.5 5.0 5.5 0 20 40 60 SUPPLY VOLTAGE (V) LOAD RESISTANCE (Ω) OUTPUT POWER vs. LOAD RESISTANCE POWER-SUPPLY REJECTION RATIO vs. FREQUENCY COMMON-MODE REJECTION RATIO vs. FREQUENCY -20 -30 CMRR (dB) THD+N = 1% -40 -50 -60 -40 -60 -70 -70 -80 -80 -90 -90 0 -100 -100 20 40 60 LOAD RESISTANCE (Ω) 80 100 10 100 1k FREQUENCY (Hz) 10k 100k VDD = 5V -50 0.4 0 VCM = 100mVP-P RL = 8Ω -10 -30 PSRR (dB) 0.8 MAX9701 toc18 -20 THD+N = 10% 1.2 VRIPPLE = 100mVP-P RL = 8Ω -10 0 MAX9701 toc17 1.6 0 MAX9701 toc16 fIN = 1kHz 100 80 SUPPLY VOLTAGE (V) 2.0 OUTPUT POWER (W) VDD = 5V fIN = 1kHz 0 2.5 5.5 1.2 1.0 0.5 0.5 0 0.8 2.5 THD+N = 1% 0.4 0.6 OUTPUT POWER vs. LOAD RESISTANCE 1.0 3.0 0.4 3.0 MAX9701 toc14 MAX9701 toc13 RL = 4Ω AV = 12dB fIN = 1kHz 2.5 0.2 OUTPUT POWER (W) 2.0 OUTPUT POWER (W) OUTPUT POWER (W) 1.5 OUTPUT POWER vs. SUPPLY VOLTAGE OUTPUT POWER vs. SUPPLY VOLTAGE 3.5 2.0 VDD = 3.3V fIN = 1kHz OUTPUT POWER (W) OUTPUT POWER (W) 3.0 40 0 0 2.0 OUTPUT POWER (W) 0.4 50 10 0 0 RL = 4Ω 60 20 20 0.001 70 30 30 FFM 0.01 RL = 8Ω 90 MAX9701 toc15 SSM 100 EFFICIENCY (%) 1 RL = 8Ω 90 EFFICIENCY (%) THD+N (%) 100 MAX9701 toc10 VDD = 5V RL = 8Ω fIN = 1kHz 10 EFFICIENCY vs. OUTPUT POWER EFFICIENCY vs. OUTPUT POWER 100 MAX9701 toc12 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 3.3V 10 100 1k 10k 100k FREQUENCY (Hz) _______________________________________________________________________________________ 5 MAX9701 Typical Operating Characteristics (continued) Typical Operating Characteristics (continued) (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)). CROSSTALK vs. FREQUENCY -60 -70 -80 LEFT TO RIGHT -90 RL = 8Ω fIN = 1kHz -40 -50 CROSSTALK (dB) -100 -60 -70 LEFT TO RIGHT -80 -90 -100 -110 -110 RIGHT TO LEFT -120 RIGHT TO LEFT -120 -130 -130 100 1k 10k 100k -94 FREQUENCY (Hz) MAX9701 toc21 FFM MODE VOUT = -60dBV f = 1kHz RL = 8Ω UNWEIGHTED -60 -80 -100 FFM MODE VOUT = -60dBV f = 1kHz RL = 8Ω A-WEIGHTED -20 OUTPUT MAGNITUDE (dBV) OUTPUT MAGNITUDE (dBV) 6 -14 0 -40 -60 -80 -100 -120 -120 -140 -140 0 5k 10k 15k 0 20k 5k OUTPUT FREQUENCY SPECTRUM 20k OUTPUT FREQUENCY SPECTRUM -60 -80 -100 -120 SSM MODE VOUT = -60dBV f = 1kHz RL = 8Ω A-WEIGHTED -20 OUTPUT MAGNITUDE (dBV) SSM MODE VOUT = -60dBV f = 1kHz RL = 8Ω UNWEIGHTED -40 15k 0 MAX9701 toc23 0 -20 10k FREQUENCY (Hz) FREQUENCY (Hz) -40 -60 -80 -100 -120 -140 -140 0 5k 10k FREQUENCY (Hz) 6 -34 OUTPUT FREQUENCY SPECTRUM OUTPUT FREQUENCY SPECTRUM -40 -54 INPUT AMPLITUDE (dB) 0 -20 -74 MAX9701 toc22 10 MAX9701 toc24 CROSSTALK (dB) -50 MAX9701 toc20 POUT = 300mW RL = 8Ω -40 CROSSTALK vs. INPUT AMPLITUDE -30 MAX9701 toc19 -30 OUTPUT MAGNITUDE (dBV) MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier 15k 20k 0 5k 10k 15k 20k FREQUENCY (Hz) _______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier (VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)). WIDEBAND OUTPUT SPECTRUM (SSM MODE) WIDEBAND OUTPUT SPECTRUM (FFM MODE) -20 RBW = 10kHz INPUT AC GROUNDED -10 -30 -40 -50 -60 -70 MAX9701 toc26 RBW = 10kHz INPUT AC GROUNDED -20 OUTPUT MAGNITUDE (dB) -30 -40 -50 -60 -70 -80 -80 -90 -90 -100 -100 10k 100k 10k 1k 1M 100k FREQUENCY (Hz) FREQUENCY (Hz) TURN-ON/TURN-OFF RESPONSE SUPPLY CURRENT vs. SUPPLY VOLTAGE SHDN BOTH CHANNELS 17 SUPPLY CURRENT (mA) 2V/div 0V MAX9701 OUTPUT 1M 20 MAX9701 toc27 1k MAX9701 toc28 OUTPUT MAGNITUDE (dB) 0 MAX9701 toc25 0 -10 250mV/div 14 SSM 11 FFM 8 5 10ms/div 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) SHUTDOWN CURRENT vs. SUPPLY VOLTAGE MAX9701 toc29 5 SHUTDOWN CURRENT (μA) BOTH CHANNELS 4 3 2 1 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 7 MAX9701 Typical Operating Characteristics (continued) 1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701 Pin Description PIN TQFN UCSP 1 A2 2 8 B3 NAME FUNCTION SHDN Active-Low Shutdown. Connect to VDD for normal operation. SYNC Frequency Select and External Clock Input. SYNC = GND: Fixed-frequency mode with fS = 1100kHz. SYNC = Unconnected: Fixed-frequency mode with fS = 1400kHz. SYNC = VDD: Spread-spectrum mode with fS = 1200kHz ±60kHz. SYNC = Clocked: Fixed-frequency mode with fS = external clock frequency. 3, 8, 11, 16 — N.C. 4 A3 OUTL+ No Connection. Not internally connected. 5, 14 A4, D4 PVDD H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor to PGND. 6, 13 B4, C4 PGND Power Ground 7 A5 OUTL- 9, 22 B1, B5 GND 10 C5 SYNC_OUT 12 D5 OUTR- Right-Channel Amplifier Output Negative Phase 15 D3 OUTR+ Right-Channel Amplifier Output Positive Phase 17 C3 GAIN1 Gain-Select Input 1 18 D2 GAIN2 19 D1 INR- Right-Channel Inverting Input 20 C2 INR+ Right-Channel Noninverting Input 21 C1 VDD Analog Power Supply. Connect to PVDD. Bypass with a 10µF capacitor to GND. 23 B2 INL+ Left-Channel Noninverting Input 24 A1 INL- Left-Channel Inverting Input EP — EP Left-Channel Amplifier Output Positive Phase Left-Channel Amplifier Output Negative Phase Analog Ground Clock Signal Output Gain-Select Input 2 Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply Bypassing, Layout, and Grounding section). _______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier VDD 10μF 0.1μF VDD INL+ 470nF CLASS D MODULATOR AND H-BRIDGE INL- INR+ RIN INR- RIN 470nF VBIAS RIN RIN 470nF SYNC_OUT OSCILLATOR AND SAWTOOTH SYNC 470nF PVDD CLASS D MODULATOR AND H-BRIDGE VBIAS OUTL+ OUTL- OUTR+ OUTR- VBIAS BIAS GENERATOR GAIN1 GAIN2 GAIN CONTROL MAX9701 SHDN GND PGND _______________________________________________________________________________________ 9 MAX9701 Functional Diagram MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier tSW VIN- VIN+ OUT- OUT+ tON(MIN) VOUT+ - VOUT- Figure 1. MAX9701 Outputs with an Input Signal Applied Detailed Description The MAX9701 filterless, stereo Class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9701 offers Class AB performance with Class D efficiency, while occupying minimal board space. A unique, filterless modulation scheme, synchronizable switching frequency, and spread-spectrum switching mode create a compact, flexible, low-noise, efficient audio power amplifier. The differential input architecture reduces common-mode noise pickup, and can be used without input-coupling capacitors. The inputs can also be configured to accept a single-ended input signal. 10 Comparators monitor the MAX9701 inputs and compare the complementary input voltages to the sawtooth waveform. The comparators trip when the input magnitude of the sawtooth exceeds their corresponding input voltage. Both comparators reset at a fixed time after the rising edge of the second comparator trip point, generating a minimum-width pulse (tON(MIN)) at the output of the second comparator (Figure 1). As the input voltage increases or decreases, the duration of the pulse at one output increases while the other output pulse duration remains the same. This causes the net voltage across the speaker (VOUT+ - VOUT-) to change. The minimum-width pulse helps the device to achieve high levels of linearity. ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier tSW tSW MAX9701 tSW tSW VIN_- VIN_+ OUT_- OUT_+ tON(MIN) VOUT_+ - VOUT_- Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode) Operating Modes Fixed-Frequency (FFM) Mode The MAX9701 features two fixed-frequency modes. Connect SYNC to GND to select a 1.1MHz switching frequency. Leave SYNC unconnected to select a 1.4MHz switching frequency. The frequency spectrum of the MAX9701 consists of the fundamental switching frequency and its associated harmonics (see the Wideband Output Spectrum (FFM Mode) graph in the Typical Operating Characteristics). Program the switching frequency so the harmonics do not fall within a sensitive frequency band (Table 1). Audio reproduction is not affected by changing the switching frequency. Table 1. Operating Modes SYNC MODE GND FFM with fOSC = 1100kHz Unconnected VDD Clocked FFM with fOSC = 1400kHz SSM with fOSC = 1200kHz ±60kHz FFM with fOSC = external clock frequency ______________________________________________________________________________________ 11 VIN_ = 0V 50.0 45.0 40.0 AMPLITUDE (dBμV/m) MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier 35.0 30.0 OUT_- 25.0 20.0 15.0 10.0 5.0 OUT_+ 0.0 30 60 80 100 120 140 160 180 200 220 240 260 280 300 FREQUENCY (MHz) VOUT_+ - VOUT_- = 0V Figure 3. MAX9701 with 76mm of Speaker Cable with TDK Common-Mode Choke: TDK ACM4532-801-20-X Spread-Spectrum (SSM) Mode The MAX9701 features a unique, patented spreadspectrum mode that flattens the wideband spectral components, improving EMI emissions that may be radiated by the speaker and cables. This mode is enabled by setting SYNC = V DD (Table 1). In SSM mode, the switching frequency varies randomly by ±60kHz around the center frequency (1.2MHz). The modulation scheme remains the same, but the period of the sawtooth waveform changes from cycle to cycle (Figure 2). Instead of a large amount of spectral energy present at multiples of the switching frequency, the energy is now spread over a bandwidth that increases with frequency. Above a few megahertz, the wideband spectrum looks like white noise for EMI purposes (Figure 3). A proprietary amplifier topology ensures this does not corrupt the noise floor in the audio bandwidth. Synchronous Switching Mode SYNC The SYNC input allows the MAX9701 to be synchronized to a user-defined clock, or another Maxim Class D amplifier, creating a fully synchronous system, minimizing clock intermodulation, and allocating spectral components of the switching harmonics to insensitive frequency bands. Applying a TTL clock signal between 1000kHz and 1600kHz to SYNC synchronizes the MAX9701. The period of the SYNC clock can be randomized, allowing the MAX9701 to be synchronized to another Maxim Class D amplifier operating in SSM mode. 12 Figure 4. MAX9701 Outputs with No Input Signal SYNC_OUT SYNC_OUT allows several MAX9701s as well as other Class D amplifiers (such as the MAX9700) to be cascaded. The synchronized output minimizes interference due to clock intermodulation caused by the switching spread between single devices. Using SYNC_OUT, the modulation scheme remains the same and audio reproduction is not affected by changing the switching frequency. Filterless Modulation/Common-Mode Idle The MAX9701 uses Maxim’s unique, patented modulation scheme that eliminates the LC filter required by traditional class D amplifiers, improving efficiency, reducing component count, conserving board space and system cost. Conventional Class D amplifiers output a 50% duty cycle, 180° out-of-phase square wave when no signal is present. With no filter, the square wave appears across the load as a DC voltage, resulting in finite load current, which increases power consumption especially when idling. When no signal is present at the input of the MAX9701, the amplifiers will output an in-phase square wave as shown in Figure 4. Because the MAX9701 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker, minimizing power consumption. Efficiency Efficiency of a Class D amplifier is due to the switching operation of the output stage transistors. In a Class D amplifier, the output transistors act as current-steering switches and consume negligible additional power. Any power loss associated with the Class D output stage is mostly due to the I2R loss of the MOSFET onresistance, and quiescent-current overhead. ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier 100 90 EFFICIENCY (%) 80 70 MAX9701 60 50 40 30 CLASS AB 20 10 VDD = 3.3V f = 1kHz RL - 8Ω 0 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W) Figure 5. MAX9701 Efficiency vs. Class AB Efficiency The theoretical best efficiency of a linear amplifier is 78%, however that efficiency is only exhibited at peak output powers. Under normal operating levels (typical music reproduction levels), efficiency falls below 30%, whereas the MAX9701 still exhibits >80% efficiencies under the same conditions (Figure 5). Shutdown The MAX9701 has a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the MAX9701 in a low-power (0.1µA) shutdown mode. Connect SHDN to VDD for normal operation. Click-and-Pop Suppression The MAX9701 features comprehensive click-and-pop suppression that eliminates audible transients on startup and shutdown. While in shutdown, the H-bridge is in a high-impedance state. During startup, or power-up, the input amplifiers are muted and an internal loop sets the modulator bias voltages to the correct levels, preventing clicks and pops when the H-bridge is subsequently enabled. For 40ms following startup, a soft-start function gradually unmutes the input amplifiers. Applications Information The MAX9701 does not require an output filter. The device relies on the inherent inductance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component of the square-wave output. Eliminating the output filter results in a smaller, less costly, more efficient solution. Because the frequency of the MAX9701 output is well beyond the bandwidth of most speakers, voice coil movement due to the square-wave frequency is very small. Although this movement is small, a speaker not designed to handle the additional power can be damaged. For optimum results, use a speaker with a series inductance >10µH. Typical 8Ω speakers, for portable audio applications, exhibit series inductances in the range of 20µH to 100µH. Output Offset Unlike a Class AB amplifier, the output offset voltage of a Class D amplifier does not noticeably increase quiescent current draw when a load is applied. This is due to the power conversion of the Class D amplifier. For example, an 8mV DC offset across an 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 / 100 x η), which is on the order of a few µA. Selectable Gain The MAX9701 features four selectable gain settings, minimizing external component count. Gains of 0dB, 3dB, 12dB, and 18dB are set through gain-select inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be hard-wired or digitally controlled. Table 2 shows the suggested gain settings to attain a maximum output power from a given peak input voltage and given load at VDD = 3.3V and THD+N = 10%. Table 2. Gain Settings GAIN1 GAIN2 GAIN (dB) INPUT (VRMS) RL (Ω) POUT (mW) 0 0 +18 0.305 4 1100 4 1100 Filterless Operation Traditional Class D amplifiers require an output filter to recover the audio signal from the amplifier’s PWM output. The filters add cost, increase the solution size of the amplifier, and can decrease efficiency. The traditional PWM scheme uses large differential output swings (2 x VDD(P-P)) and causes large ripple currents. Any parasitic resistance in the filter components results in a loss of power, lowering the efficiency. 1 0 +12 0.615 0 1 +6 1.213 4 1100 4 1100 1 1 0 2.105 0 0 +18 0.345 8 725 1 0 +12 0.686 8 725 8 725 8 725 0 1 +6 1.360 1 1 0 2.705 ______________________________________________________________________________________ 13 MAX9701 EFFICIENCY vs. OUTPUT POWER MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier 0.47μF SINGLE-ENDED LEFT AUDIO INPUT INL+ INL+ OUTL+ INL- OUTL+ 0.47μF SINGLE-ENDED RIGHT AUDIO INPUT CODEC INR+ INL- 0.47μF INR- MAX9701 INR+ MAX9701 OUTLINROUTR+ OUTLOUTR+ 0.47μF OUTR- OUTR- GAIN2 GAIN2 GAIN1 GAIN1 SHDN SHDN 2.5V TO 5.5V VDD PVDD 10μF GND PVDD PGND 10μF 0.1μF GND VDD 2.5V TO 5.5V PGND 0.1μF SYNC SYNC FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE. FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB. Figure 6. Single-Ended Input Figure 7. DC-Coupled Inputs Input Amplifier Component Selection Differential Input The MAX9701 features a differential input structure, making it compatible with many CODECs and offers improved noise immunity over a single-ended input amplifier. In devices such as cellular phones, high-frequency signals from the RF transmitter can be picked up by the amplifier’s input traces. The signals appear at the amplifier’s inputs as common-mode noise. A differential input amplifier amplifies the difference of the two inputs, any signal common to both inputs is canceled. Input Filter An input capacitor, C IN , in conjunction with the MAX9701 input impedance (RIN) forms a highpass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to automatically bias the signal to an optimum DC level. Assuming zero-source impedance, the -3dB point of the highpass filter is given by: Single-Ended Input The MAX9701 can be configured as a single-ended input amplifier by capacitively coupling either input to GND, and driving the other input (Figure 6). DC-Coupled Inputs The input amplifier can accept DC-coupled inputs that are biased within the amplifier’s common-mode range (see the Typical Operating Characteristics). DC coupling eliminates the input-coupling capacitors, reducing component count to potentially two external components (Figure 7). However, the highpass filtering effect of the capacitors is lost, allowing low-frequency signals to feed through to the load. 14 f−3dB = 1 2πRINCIN Choose CIN so f-3dB is well below the lowest frequency of interest. Use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies. Other considerations when designing the input filter include the constraints of the overall system and the actual frequency band of interest. Although high-fidelity audio calls for a flat-gain response between 20Hz and 20kHz, portable voice-reproduction devices such as cellular phones and two-way radios need only concentrate on the frequency range of the spoken human voice (typically 300Hz to 3.5kHz). In addition, speakers used ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701 5V CIN 2200pF 10μF INL+ OUTL+ CIN 2200pF 8Ω MAX9701 INR+ OUTL- CIN 2200pF 10μF INLOUTR+ CIN 2200pF 8Ω INROUTRSYNC SYNC_OUT R3 10kΩ 5V R1 20kΩ VDD R4 39kΩ R2 20kΩ SYNC C2 1nF 1μF IN+ C2 0.01μF 1.25V MAX4238 MAX9700 OUT+ 4Ω 1μF IN- OUT- NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V. FFM MODE WITH fOSC = 1100kHz. Figure 8. 2.1 Channel Application Circuit in portable devices typically have a poor response below 300Hz. Taking these two factors into consideration, the input filter may not need to be designed for a 20Hz to 20kHz response, saving both board space and cost due to the use of smaller capacitors. Output Filter The MAX9701 does not require an output filter. The device passes FCC emissions standards with 76mm of unshielded speaker cables. However, output filtering can be used if a design is failing radiated emissions due to board layout or cable length, or if the circuit is near EMI-sensitive devices. Use a ferrite bead filter when radiated frequencies above 10MHz are of concern. Use an LC filter or a common-mode choke when radiated emissions below 10MHz are of concern, or when long leads (>76mm) connect the amplifier to the speaker. 2.1 Channel Configuration The typical 2.1 channel application circuit (Figure 8) shows the MAX9701 configured as a mid-/high-frequency amplifier and the MAX9700 configured as a mono bass amplifier. Input capacitors (CIN) set the highpass cutoff frequency according to the following equation: f= 1 2π × RIN × CIN where R IN is the typical input resistance of the MAX9701. The 10µF capacitors on the output of the MAX9701 ensure a two-pole highpass filter. ______________________________________________________________________________________ 15 MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier Low frequencies are summed through a two-pole lowpass filter and sent to the MAX9700 mono speaker amplifier. The passband gain of the lowpass filter is unity for in-phase stereo signals, −2 × R3 R1 where R1 = R2 and R3 = R1//R2. The cutoff frequency of the lowpass filter is set by the following equation: f= 1 × 2π 1 C1 × C2 × R 3 × R4 Supply Bypassing, Layout, and Grounding Proper layout and grounding are essential for optimum performance. Use large traces for the power-supply inputs and amplifier outputs to minimize losses due to parasitic trace resistance. Large traces also aid in moving heat away from the package. Proper grounding improves audio performance, minimizes crosstalk between channels, and prevents any switching noise from coupling into the audio signal. Connect PGND and GND together at a single point on the PC board. Route all traces that carry switching transients away from GND and the traces/components in the audio signal path. 16 Bypass VDD with 10µF to GND and PVDD with 0.1µF to PGND. Place the bypass capacitors as close to the MAX9701 as possible. Use large, low-resistance output traces. Current drawn from the outputs increases as load impedance decreases. High-output trace resistance decreases the power delivered to the load. Large output, supply, and GND traces allow more heat to move from the MAX9701 to the air, decreasing the thermal impedance of the circuit. The MAX9701 thin QFN-EP package features an exposed thermal pad on its underside. This pad lowers the package’s thermal impedance by providing a direct heat conduction path from the die to the printed circuit board. Connect the exposed thermal pad to the GND plane. UCSP Applications Information For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommended reflow temperature profile as well as the latest information on reliability testing results, refer to Application Note: UCSP—A Wafer-Level Chip-Scale Package available on Maxim’s website at www.maxim-ic.com/ucsp. ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier VDD 10μF 0.1μF 0.1μF VDD PVDD 0.1μF AUX_IN VCC 470nF INR+ 2.2kΩ MAX4060 BIAS MAX9701 470nF OUTR- INROUT CODEC OUTR+ 470nF INL- 2.2kΩ OUTL- 470nF 0.1μF IN+ IN- INL+ OUTL+ GAIN1 GND GAIN2 0.1μF SHDN SYNC GND PGND VDD 1μF VDD SHDN 1μF INL OUTL 1μF MAX9722B INR OUTR μCONTROLLER PVSS SVSS C1P CIN 1μF 1μF ______________________________________________________________________________________ 17 MAX9701 System Diagram 1.3W, Filterless, Stereo Class D Audio Power Amplifier MAX9701 Pin Configurations TOP VIEW (BUMPS ON BOTTOM) GAIN2 GAIN1 N.C. OUTR+ PVDD PGND TOP VIEW 18 17 16 15 14 13 INR- 19 12 OUTR- INR+ 20 11 N.C. 10 SYNC_OUT VDD 21 MAX9701 7 OUTL- 1 2 SHDN SYNC 3 4 5 6 PGND INL- 24 PVDD N.C. N.C. GND 8 OUTL+ 9 INL+ 23 GND 22 MAX9701 1 2 3 4 5 A INL- SHDN OUTL+ PVDD OUTL- B GND INL+ SYNC PGND GND C VDD INR+ GAIN1 PGND SYNC _OUT D INR- GAIN2 OUTR+ PVDD OUTR- UCSP TQFN Chip Information TRANSISTOR COUNT: 5688 PROCESS: BiCMOS 18 ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier PACKAGE CODE DOCUMENT NO. 24 TQFN-EP T2444-4 21-0139 20 UCSP B20-1 21-0095 24L QFN THIN.EPS PACKAGE TYPE ______________________________________________________________________________________ 19 MAX9701 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. MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 20 ______________________________________________________________________________________ 1.3W, Filterless, Stereo Class D Audio Power Amplifier 5x4 UCSP.EPS ______________________________________________________________________________________ 21 MAX9701 Package Information (continued) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. MAX9701 1.3W, Filterless, Stereo Class D Audio Power Amplifier Revision History REVISION NUMBER REVISION DATE 3 3/09 DESCRIPTION Added G45 option to Ordering Information PAGES CHANGED 1 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. 22 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.