19-3160; Rev 7; 3/06 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers Features The MAX9703/MAX9704 mono/stereo Class D audio power amplifiers provide Class AB amplifier performance with Class D efficiency, conserving board space and eliminating the need for a bulky heatsink. Using a Class D architecture, these devices deliver up to 15W while offering up to 78% efficiency. Proprietary and protected modulation and switching schemes render the traditional Class D output filter unnecessary. The MAX9703/MAX9704 offer two modulation schemes: a fixed-frequency mode (FFM), and a spread-spectrum mode (SSM) that reduces EMI-radiated emissions due to the modulation frequency. The device utilizes a fully differential architecture, a full bridged output, and comprehensive click-and-pop suppression. The MAX9703/MAX9704 feature high 80dB PSRR, low 0.07% THD+N, and SNR in excess of 95dB. Short-circuit and thermal-overload protection prevent the devices from being damaged during a fault condition. The MAX9703 is available in a 32-pin TQFN (5mm x 5mm x 0.8mm) package. The MAX9704 is available in a 32-pin TQFN (7mm x 7mm x 0.8mm) package. Both devices are specified over the extended -40C to +85C temperature range. Filterless Class D Amplifier Unique Spread-Spectrum Mode Offers 5dB Emissions Improvement Over Conventional Methods Up to 78% Efficient (RL = 8) Up to 88% Efficient (RL = 16) 15W Continuous Output Power into 8 (MAX9703) 2x10W Continuous Output Power into 8 (MAX9704) Low 0.07% THD+N High PSRR (80dB at 1kHz) 10V to 25V Single-Supply Operation Differential Inputs Minimize Common-Mode Noise Pin-Selectable Gain Reduces Component Count Industry-Leading Click-and-Pop Suppression Low Quiescent Current (24mA) Low-Power Shutdown Mode (0.2A) Short-Circuit and Thermal-Overload Protection Available in Thermally Efficient, Space-Saving Packages 32-Pin TQFN (5mm x 5mm x 0.8mm)-MAX9703 32-Pin TQFN (7mm x 7mm x 0.8mm)-MAX9704 Applications LCD TVs Hands-Free Car Phone Adaptors LCD Monitors Automotive Desktop PCs LCD Projectors Ordering Information PIN-PACKAGE AMP PKG CODE MAX9703ETJ+ 32 TQFN-EP* Mono T3255-3 MAX9704ETJ+ 32 TQFN-EP* Stereo T3277-2 PART Note: All devices specified for over -40C to +85C operating temperature range. *EP = Exposed paddle. +Denotes lead-free package. Block Diagrams 0.47F IN+ OUTL+ H-BRIDGE 0.47F MAX9703 0.47F MAX9704 INL+ INL- OUTL- INR+ OUTR+ OUT+ H-BRIDGE 0.47F IN- OUT- 0.47F H-BRIDGE 0.47F INR- OUTR- Pin Configurations appear 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 MAX9703/MAX9704 General Description MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers ABSOLUTE MAXIMUM RATINGS (All voltages referenced to PGND.) VDD to PGND, AGND .............................................................30V OUTR_, OUTL_, C1N..................................-0.3V to (VDD + 0.3V) C1P............................................(VDD - 0.3V) to (CHOLD + 0.3V) CHOLD ........................................................(VDD - 0.3V) to +40V All Other Pins to PGND...........................................-0.3V to +12V Duration of OUTR_/OUTL_ Short Circuit to PGND, VDD ................................................10s Continuous Input Current (VDD, PGND) ...............................1.6A Continuous Input Current......................................................0.8A Continuous Input Current (all other pins)..........................20mA Continuous Power Dissipation (TA = +70C) Single-Layer Board: MAX9703 32-Pin TQFN (derate 21.3mW/C above +70C)..........................................................1702.1mW MAX9704 32-Pin TQFN (derate 27mW/C above +70C)..........................................................2162.2mW Multilayer Board: MAX9703 32-Pin TQFN (derate 34.5mW/C above +70C)..........................................................2758.6mW MAX9704 32-Pin TQFN (derate 37mW/C above +70C)..........................................................2963.0mW Junction Temperature ......................................................+150C Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C 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 = 15V, AGND = PGND = 0V, SHDN VIH, AV = 16dB, CSS = CIN = 0.47F, CREG = 0.01F, C1 = 100nF, C2 = 1F, FS1 = FS2 = PGND (fS = 660kHz), RL connected between OUTL+ and OUTL- and OUTR+ and OUTR-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 25 V GENERAL Supply Voltage Range VDD Quiescent Current IDD Shutdown Current ISHDN Turn-On Time tON Amplifier Output Resistance in Shutdown Input Impedance RIN Inferred from PSRR test RL = OPEN 10 MAX9703 14 22 MAX9704 24 34 0.2 1.5 CSS = 470nF 100 CSS = 180nF 50 Voltage Gain AV Gain Matching 150 330 AV = 13dB 35 58 80 AV = 16dB 30 48 65 AV = 19.1dB 23 39 55 Output Offset Voltage Common-Mode Rejection Ratio Power-Supply Rejection Ratio (Note 3) 2 10 15 22 29.4 29.6 29.8 G1 = L, G2 = H 18.9 19.1 19.3 G1 = H, G2 = L 12.8 13 13.2 G1 = H, G2 = H 15.9 16 16.3 0.5 6 VOS CMRR fIN = 1kHz, input referred VDD = 10V to 25V PSRR k G1 = L, G2 = L Between channels (MAX9704) 200mVP-P ripple 60 54 A ms SHDN = PGND AV = 29.6dB mA k dB % 30 mV dB 80 fRIPPLE = 1kHz 80 fRIPPLE = 20kHz 66 _______________________________________________________________________________________ dB 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers (VDD = 15V, AGND = PGND = 0V, SHDN VIH, AV = 16dB, CSS = CIN = 0.47F, CREG = 0.01F, C1 = 100nF, C2 = 1F, FS1 = FS2 = PGND (fS = 660kHz), RL connected between OUTL+ and OUTL- and OUTR+ and OUTR-, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (Notes 1, 2) PARAMETER Continuous Output Power (MAX9703) Continuous Output Power (MAX9704) Total Harmonic Distortion Plus Noise SYMBOL PCONT PCONT THD+N Signal-to-Noise Ratio SNR CONDITIONS THD+N = 10%, VDD = RL = 4 16V, f = 1kHz, TA = RL = 8 +25C, tCONT = 15min RL = 16, VDD = 24V (Note 4) RL = 8, POUT = 10W, f = 1kHz fOSC Efficiency Regulator Output W 2x5 2x10 W 2x16 0.07 % 94 SSM 88 FFM 97 SSM 91 Left to right, right to left, 8 load, fIN = 10kHz Oscillator Frequency UNITS 18 FFM FS1 = L, FS2 = L MAX 15 fIN = 1kHz, either FFM or SSM, RL = 8, POUT = 4W BW = 22Hz to 22kHz TYP 10 THD+N = 10%, VDD = RL = 4 16V, f = 1kHz, TA = RL = 8 +25C, tCONT = 15min RL = 16, VDD = 24V (Note 4) A-weighted Crosstalk MIN dB 65 560 670 FS1 = L, FS2 = H 940 FS1 = H, FS2 = L 470 FS1 = H, FS2 = H (spread-spectrum mode) 670 7% POUT = 15W, f = 1kHz, RL = 8 78 POUT = 10W, f = 1kHz, RL = 16 88 dB 800 kHz % VREG 6 V DIGITAL INPUTS (SHDN, FS_, G_) VIH Input Thresholds VIL Input Leakage Current 2.5 0.8 1 V A 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 = 8, L = 68H. For RL = 4, L = 33H. Note 3: PSRR is specified with the amplifier inputs connected to AGND through CIN. Note 4: The MAX9704 continuous 8 and 16 power measurements account for thermal limitations of the 32-pin TQFN-EP package. Continuous 4 power measurements account for short-circuit protection of the MAX9703/MAX9704 devices. _______________________________________________________________________________________ 3 MAX9703/MAX9704 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (33H with 4, 68H with 8, part in SSM mode, 136H with 16, measurement BW = 22Hz to 22kHz, unless otherwise noted.) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 15V RL = 4 AV = 16dB VDD = 15V RL = 8 AV = 16dB 10 1 THD+N (%) POUT = 4W POUT = 8W 0.1 0.1 POUT = 500mW POUT = 500mW 0.01 0.01 1k 10k 0.01 10 100k 100 1k 10k 100k 10 100 1k 10k 100k FREQUENCY (Hz) FREQUENCY (Hz) FREQUENCY (Hz) TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER VDD = 15V RL = 4 AV = 16dB 10 10 MAX9703/04 toc06 VDD = 20V RL = 8 AV = 16dB POUT = 8W MAX9703/04 toc05 100 MAX9703/04 toc04 10 100 POUT = 8W 0.1 POUT = 500mW 10 VDD = 20V RL = 8 AV = 16dB 1 THD+N (%) THD+N (%) 1 MAX9703/04 toc03 10 MAX9703/04 toc01 10 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY MAX9703/04 toc02 TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY VDD = 15V RL = 8 AV = 16dB f = 10kHz THD+N (%) THD+N (%) SSM THD+N (%) 1 1 f = 10kHz 1 f = 1kHz 0.1 0.1 0.1 f = 1kHz FFM f = 100Hz f = 100Hz 0.01 0.01 10 100 1k 10k 1 2 3 4 5 6 7 8 9 OUTPUT POWER (W) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER f = 10kHz MAX9703/04 toc07 VDD = 20V RL = 8 AV = 16dB 10 OUTPUT POWER (W) EFFICIENCY vs. OUTPUT POWER VDD = 20V RL = 8 AV = 16dB f = 1kHz f = 1kHz SSM 0.1 FFM (335kHz) f = 100Hz 6 8 10 12 14 16 18 OUTPUT POWER (W) 4 70 60 50 RL = 4 40 20 VDD = 12V AV = 16dB f = 1kHz 0 0.01 4 80 10 0.01 2 RL = 8 90 30 0.1 0 100 EFFICIENCY (%) THD+N (%) 1 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 10 MAX9703/04 toc08 FREQUENCY (Hz) 100 10 0 100k MAX9703/04 toc09 0.01 THD+N (%) MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 20 0 1 2 3 4 5 6 7 8 9 10111213141516171819 20 OUTPUT POWER (W) 0 1 2 3 4 5 6 7 OUTPUT POWER (W) _______________________________________________________________________________________ 8 9 10 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 50 40 30 VDD = 15V AV = 16dB f = 1kHz 10 RL = 16 10 8 6 AV = 16dB THD+N = 10% 2 8 10 16 18 12 14 20 OUTPUT POWER (W) 16 19 SUPPLY VOLTAGE (V) OUTPUT POWER vs. LOAD RESISTANCE COMMON-MODE REJECTION RATIO vs. FREQUENCY 0 -40 100 -20 MAX9703/04 toc12 -60 -80 -100 -120 100 10 1k 10k -80 RIGHT TO LEFT -100 -40 MAX9703/04 toc17 -20 -60 -80 -100 SSM MODE AV = 16dB UNWEIGHTED fIN = 1kHz POUT = 5W RL = 8 0 -20 -40 -60 -80 -100 -140 -140 100k 100k -120 -120 -120 10k OUTPUT FREQUENCY SPECTRUM 20 OUTPUT MAGNITUDE (dB) -60 FFM MODE AV = 16dB UNWEIGHTED fIN = 1kHz POUT = 5W RL = 8 0 OUTPUT MAGNITUDE (dB) LEFT TO RIGHT 20 1k FREQUENCY (Hz) OUTPUT FREQUENCY SPECTRUM -40 10k 100 10 100k FREQUENCY (Hz) MAX9703/04 toc16 AV = 16dB 1% THD+N VDD = 15V 8 LOAD FREQUENCY (Hz) AV = 16dB RL = 8 200mVP-P INPUT VDD = 15V -40 CROSSTALK vs. FREQUENCY CROSSTALK (dB) 0 -80 10 1k 100 POWER-SUPPLY REJECTION RATIO vs. FREQUENCY -70 100 10 -60 THD+N = 1% 10 THD+N = 1% LOAD RESISTANCE () -30 LOAD RESISTANCE () -20 6 1 -50 1 8 25 -20 0 0 22 VDD = 15V RL = 8 AV = 16dB -10 CMRR (dB) THD+N = 10% 13 PSRR (dB) VDD = 20V AV = 16dB 10 0 10 MAX9703/04 toc14 6 4 MAX9703/04 toc13 24 22 20 18 16 14 12 10 8 6 4 2 2 12 2 0 0 14 4 4 0 OUTPUT POWER (W) RL = 8 12 THD+N = 10% 16 MAX9703/04 toc18 20 14 VDD = 15V AV = 16dB 18 MAX9703/04 toc15 RL = 8 60 16 OUTPUT POWER (W) EFFICIENCY (%) 70 18 OUTPUT POWER (W) 80 20 MAX9703/04 toc11 RL = 16 90 20 MAX9703/04 toc10 100 OUTPUT POWER vs. LOAD RESISTANCE OUTPUT POWER vs. SUPPLY VOLTAGE EFFICIENCY vs. OUTPUT POWER 0 2 4 6 8 10 12 14 16 18 20 FREQUENCY (kHz) 0 2 4 6 8 10 12 14 16 18 20 FREQUENCY (kHz) _______________________________________________________________________________________ 5 MAX9703/MAX9704 Typical Operating Characteristics (continued) (33H with 4, 68H with 8, part in SSM mode, 136H with 16, measurement BW = 22Hz to 22kHz, unless otherwise noted.) Typical Operating Characteristics (continued) (33H with 4, 68H with 8, part in SSM mode, 136H with 16, measurement BW = 22Hz to 22kHz, unless otherwise noted.) -60 -80 -100 -40 -60 -80 -140 2 4 100k TURN-ON/TURN-OFF RESPONSE MAX9703/04 toc22 1M 10M 1V/div OUTPUT SHUTDOWN CURRENT vs. SUPPLY VOLTAGE 25 20 15 10 0.30 MAX9703/04 toc21 0.25 0.20 0.15 0.10 0 10 13 16 19 SUPPLY VOLTAGE (V) 6 0.35 0.05 0 20ms/div 100M SUPPLY CURRENT vs. SUPPLY VOLTAGE 5 f = 1kHz RL = 8 10M FREQUENCY (Hz) MAX9703/04 toc23 SUPPLY CURRENT (mA) 5V/div 1M FREQUENCY (Hz) 30 SHDN -80 100k 100M 35 CSS = 180pF -60 -120 -120 6 8 10 12 14 16 18 20 FREQUENCY (kHz) SHUTDOWN CURRENT (A) 0 -40 -100 -100 -120 RBW = 10kHz VDD = 15V -20 MAX97703/04 toc24 -40 -20 0 OUTPUT AMPLITUDE (dBV) -20 RBW = 10kHz VDD = 15V MAX9703/04 toc20 0 0 OUTPUT AMPLITUDE (dBV) SSM MODE AV = 16dB A-WEIGHTED fIN = 1kHz POUT = 5W RL = 8 MAX9703/04 toc19 20 WIDEBAND OUTPUT SPECTRUM (SSM MODE) WIDEBAND OUTPUT SPECTRUM (FFM MODE) OUTPUT FREQUENCY SPECTRUM OUTPUT MAGNITUDE (dB) MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 22 25 10 12 14 16 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 18 20 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers PIN NAME FUNCTION MAX9703 MAX9704 1, 2, 23, 24 1, 2, 23, 24 3, 4, 21, 22 3, 4, 21, 22 VDD Power-Supply Input 5 5 C1N Charge-Pump Flying Capacitor Negative Terminal 6 6 C1P Charge-Pump Flying Capacitor Positive Terminal 7 7 CHOLD 8, 17, 20, 25, 26, 31, 32 8 N.C. PGND Power Ground Charge-Pump Hold Capacitor. Connect a 1F capacitor from CHOLD to VDD. No Connection. Not internally connected. 9 14 REG 10 13 AGND Analog Ground 6V Internal Regulator Output. Bypass with a 0.01F capacitor to AGND. 11 -- IN- Negative Input 12 -- IN+ Positive Input 13 12 SS Soft-Start. Connect a 0.47F capacitor from SS to PGND to enable soft-start feature. 14 11 SHDN Active-Low Shutdown. Connect SHDN to PGND to disable the device. Connect to a logic-high for normal operation. 15 17 G1 Gain-Select Input 1 16 18 G2 Gain-Select Input 2 18 19 FS1 Frequency-Select Input 1 19 20 FS2 Frequency-Select Input 2 27, 28 -- OUT- 29, 30 -- OUT+ -- 9 INL- -- 10 INL+ Left-Channel Positive Input -- 15 INR- Right-Channel Negative Input -- 16 INR+ Right-Channel Positive Input -- 25, 26 OUTR- Right-Channel Negative Audio Output -- 27, 28 OUTR+ Right-Channel Positive Audio Output -- 29, 30 OUTL- Left-Channel Negative Audio Output -- 31, 32 OUTL+ Left-Channel Positive Audio Output -- -- EP Exposed Paddle. Connect to GND. Negative Audio Output Positive Audio Output Left-Channel Negative Input _______________________________________________________________________________________ 7 MAX9703/MAX9704 Pin Description MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers Detailed Description The MAX9703/MAX9704 filterless, Class D audio power amplifiers feature several improvements to switchmode amplifier technology. The MAX9703 is a mono amplifier, the MAX9704 is a stereo amplifier. These devices offer Class AB performance with Class D efficiency, while occupying minimal board space. A unique filterless modulation scheme and spread-spectrum switching mode create a compact, flexible, lownoise, efficient audio power amplifier. The differential input architecture reduces common-mode noise pickup, and can be used without input-coupling capacitors. The devices can also be configured as a single-ended input amplifier. Comparators monitor the device inputs and compare the complementary input voltages to the triangle waveform. The comparators trip when the input magnitude of the triangle exceeds their corresponding input voltage. Operating Modes Fixed-Frequency Modulation (FFM) Mode The MAX9703/MAX9704 feature three FFM modes with different switching frequencies (Table 1). 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 (FFM Mode) graph in the Typical Operating Characteristics). The MAX9703/ MAX9704 allow the switching frequency to be changed by 35%, 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 MAX9703/MAX9704 feature a unique spread-spectrum mode that flattens the wideband spectral components, improving EMI emissions that may be radiated 8 Table 1. Operating Modes FS2 SWITCHING MODE (kHz) L L 670 L H 940 FS1 H L 470 H H 670 7% by the speaker and cables. This mode is enabled by setting FS1 = FS2 = H. In SSM mode, the switching frequency varies randomly by 7% around the center frequency (670kHz). The modulation scheme remains the same, but the period of the triangle waveform changes from cycle to cycle. 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 Figure 1). 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 I2R loss of the MOSFET on-resistance, and quiescent current overhead. The theoretical best efficiency of a linear amplifier is 78%; however, that efficiency is only exhibited at peak output powers. Under normal operating levels (typical music reproduction levels), efficiency falls below 30%, whereas the MAX9704 still exhibits >78% efficiency under the same conditions (Figure 2). _______________________________________________________________________________________ 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers MAX9703/MAX9704 VDD CIN L1* CIN L2* 1000pF 1000pF MAX9704 CIN L3* 1000pF CIN L4* 1000pF *L1-L4 = 0.05 DCR, 70 AT 100MHz, 3A FAIR RITE FERRITE BEAD (2512067007Y3). 40 AMPLITUDE (dBuV/m) 35 CE LIMIT 30 25 20 15 MAX9704 OUTPUT SPECTRUM 10 5 30 100 200 300 400 500 600 700 800 900 1000 FREQUENCY (MHz) Figure 1. MAX9704 EMI Spectrum, 9in PC Board trace, 3in Twisted-Pair Speaker Cable _______________________________________________________________________________________ 9 EFFICIENCY vs. OUTPUT POWER SS 100 90 GPIO MUTE SIGNAL MAX9704 80 0.18F MAX9703/ MAX9704 70 EFFICIENCY (%) MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 60 50 Figure 3. MAX9703/MAX9704 Mute Circuit CLASS AB 40 Applications Information 30 20 VDD = 15V f = 1kHz RL = 8 10 0 0 2 4 6 8 10 12 14 16 18 20 OUTPUT POWER (W) Figure 2. MAX9704 Efficiency vs. Class AB Efficiency Shutdown The MAX9703/MAX9704 have a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low places the device in low-power (0.2A) shutdown mode. Connect SHDN to a logic high for normal operation. Click-and-Pop Suppression The MAX9703/MAX9704 feature comprehensive clickand-pop suppression that eliminates audible transients on startup and shutdown. While in shutdown, the Hbridge is pulled to PGND through 330k. 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 Hbridge is subsequently enabled. Following startup, a soft-start function gradually unmutes the input amplifiers. The value of the soft-start capacitor has an impact on the click/pop levels. For optimum performance, CSS should be at least 0.18F with a voltage rating of at least 7V. Mute Function The MAX9703/MA9704 features a clickless/popless mute mode. When the device is muted, the outputs stop switching, muting the speaker. Mute only affects the output stage and does not shut down the device. To mute the MAX9703/MAX9704, drive SS to PGND by using a MOSFET pulldown (Figure 3). Driving SS to PGND during the power-up/down or shutdown/turn-on cycle optimizes click-and-pop suppression. 10 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 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 MAX9703/MAX9704 do not require an output filter. The devices rely 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 MAX9703/MAX9704 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 > 30H. Typical 8 speakers exhibit series inductances in the range of 30H to 100H. Optimum efficiency is achieved with speaker inductances > 60H. Internal Regulator Output (VREG) The MAX9703/MAX9704 feature an internal, 6V regulator output (VREG). The MAX9703/MAX9704 REG output pin simplifies system design and reduces system cost by providing a logic voltage high for the MAX9703/ MAX9704 logic pins (G_, FS_). VREG is not available as a logic voltage high in shutdown mode. Do not apply VREG as a 6V potential to surrounding system components. Bypass REG with a 6.3V, 0.01F capacitor to AGND. ______________________________________________________________________________________ 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 0.47F SINGLE-ENDED AUDIO INPUT IN+ MAX9703/ IN- MAX9704 Table 2. Gain Selection 0.47F G1 G2 GAIN (dB) 0 0 29.6 0 1 19.1 1 0 13 1 1 16 Output Offset Unlike a Class AB amplifier, the output offset voltage of Class D amplifiers 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 in the order of a few microamps. Input Amplifier Differential Input The MAX9703/MAX9704 feature a differential input structure, making them compatible with many CODECs, and offering improved noise immunity over a single-ended input amplifier. In devices such as PCs, noisy digital signals can be picked up by the amplifier's input traces. The signals appear at the amplifiers' inputs as commonmode noise. A differential input amplifier amplifies the difference of the two inputs, any signal common to both inputs is canceled. Single-Ended Input The MAX9703/MAX9704 can be configured as singleended input amplifiers by capacitively coupling either input to AGND and driving the other input (Figure 4). Component Selection Input Filter An input capacitor, CIN, in conjunction with the input impedance of the MAX9703/MAX9704, forms a highpass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the signal to an optimum DC level. Assuming Figure 4. Single-Ended Input zero-source impedance, the -3dB point of the highpass filter is given by: 1 f -3dB = 2RINCIN Choose CIN so f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the low-frequency response of the amplifier. Use capacitors with dielectrics that have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with highvoltage coefficients, such as ceramics, may result in increased distortion at low frequencies. Charge-Pump Capacitor Selection Use capacitors with an ESR less than 100m for optimum performance. Low-ESR ceramic capacitors minimize the output resistance of the charge pump. For best performance over the extended temperature range, select capacitors with an X7R dielectric. Flying Capacitor (C1) The value of the flying capacitor (C1) affects the load regulation and output resistance of the charge pump. A C1 value that is too small degrades the device's ability to provide sufficient current drive. Increasing the value of C1 improves load regulation and reduces the chargepump output resistance to an extent. Above 1F, the onresistance of the switches and the ESR of C1 and C2 dominate. Hold Capacitor (C2) The output capacitor value and ESR directly affect the ripple at CHOLD. Increasing C2 reduces output ripple. Likewise, decreasing the ESR of C2 reduces both ripple and output resistance. Lower capacitance values can be used in systems with low maximum output power levels. Output Filter The MAX9703/MAX9704 do not require an output filter and can pass FCC emissions standards with unshielded speaker cables. However, output filtering can be ______________________________________________________________________________________ 11 MAX9703/MAX9704 Gain Selection The MAX9703/MAX9704 feature an internally set, logicselectable gain. The G1 and G2 logic inputs set the gain of the MAX9703/MAX9704 speaker amplifier (Table 2). MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers used if a design is failing radiated emissions due to board layout or cable length, or the circuit is near EMIsensitive devices. Use a ferrite bead filter when radiated frequencies above 10MHz are of concern. Use an LC filter when radiated frequencies below 10MHz are of concern, or when long leads connect the amplifier to the speaker. Refer to the MAX9704 Evaluation Kit schematic for details of this filter. Sharing Input Sources In certain systems, a single audio source can be shared by multiple devices (speaker and headphone amplifiers). When sharing inputs, it is common to mute the unused device, rather than completely shutting it down, preventing the unused device inputs from distorting the input signal. Mute the MAX9703/MAX9704 by driving SS low through an open-drain output or MOSFET (see the System Diagram). Driving SS low turns off the Class D output stage, but does not affect the input bias levels of the MAX9703/MAX9704. Be aware that during normal operation, the voltage at SS can be up to 7V, depending on the MAX9703/MAX9704 supply. Supply Bypassing/Layout Proper power-supply bypassing ensures low distortion operation. For optimum performance, bypass VDD to PGND with a 0.1F capacitor as close to each VDD pin as possible. A low-impedance, high-current power-supply connection to V DD is assumed. Additional bulk capacitance should be added as required depending on the application and power-supply characteristics. AGND and PGND should be star connected to system ground. Refer to the MAX9704 Evaluation Kit for layout guidance. Audio content, both music and voice, has a much lower RMS value relative to its peak output power. Figure 5 shows a sine wave and an audio signal in the time domain. Both are measured for RMS value by the oscilloscope. Although the audio signal has a slightly higher peak value than the sine wave, its RMS value is almost half that of the sine wave. Therefore, while an audio signal may reach similar peaks as a continuous sine wave, the actual thermal impact on the Class D amplifier is highly reduced. If the thermal performance of a system is being evaluated, it is important to use actual audio signals instead of sine waves for testing. If sine waves must be used, the thermal performance will be less than the system's actual capability. PC Board Thermal Considerations The exposed pad is the primary route of keeping heat away from the IC. With a bottom-side exposed pad, the PC board and its copper becomes the primary heatsink for the Class D amplifier. Solder the exposed pad to a large copper polygon. Add as much copper as possible from this polygon to any adjacent pin on the Class D amplifier as well as to any adjacent components, provided these connections are at the same potential. These copper paths must be as wide as possible. Each of these paths contributes to the overall thermal capabilities of the system. The copper polygon to which the exposed pad is attached should have multiple vias to the opposite side of the PC board, where they connect to another copper polygon. Make this polygon as large as possible within the system's constraints for signal routing. Class D Amplifier Thermal Considerations Class D amplifiers provide much better efficiency and thermal performance than a comparable Class AB amplifier. However, the system's thermal performance must be considered with realistic expectations and include consideration of many parameters. This section examines Class D amplifiers using general examples to illustrate good design practices. Continuous Sine Wave vs. Music When a Class D amplifier is evaluated in the lab, often a continuous sine wave is used as the signal source. While this is convenient for measurement purposes, it represents a worst-case scenario for thermal loading on the amplifier. It is not uncommon for a Class D amplifier to enter thermal shutdown if driven near maximum output power with a continuous sine wave. 12 20ms/div Figure 5. RMS Comparison of Sine Wave vs. Audio Signal ______________________________________________________________________________________ 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers Decreasing the ambient temperature or reducing JA will improve the die temperature of the MAX9704. JA can be reduced by increasing the copper size/weight of the ground plane connected to the exposed paddle of the MAX9704 TQFN package. Additionally, JA can be reduced by attaching a heatsink, adding a fan, or mounting a vertical PC board. Auxiliary Heatsinking Load Impedance If operating in higher ambient temperatures, it is possible to improve the thermal performance of a PC board with the addition of an external heatsink. The thermal resistance to this heatsink must be kept as low as possible to maximize its performance. With a bottom-side exposed pad, the lowest resistance thermal path is on the bottom of the PC board. The topside of the IC is not a significant thermal path for the device, and therefore is not a costeffective location for a heatsink. The on-resistance of the MOSFET output stage in Class D amplifiers affects both the efficiency and the peak-current capability. Reducing the peak current into the load reduces the I2R losses in the MOSFETs, thereby increasing efficiency. To keep the peak currents lower, choose the highest impedance speaker which can still deliver the desired output power within the voltage swing limits of the Class D amplifier and its supply voltage. Thermal Calculations The die temperature of a Class D amplifier can be estimated with some basic calculations. For example, the die temperature is calculated for the below conditions: * TA = +40C * POUT = 2x8W = 16W * RL = 16 * Efficiency () = 87% * JA = 27C/W First, the Class D amplifier's power dissipation must be calculated. PDISS = POUT 16W - POUT = - 16W = 2.4 W 0.87 Then the power dissipation is used to calculate the die temperature, TC, as follows: TC = TA + PDISS x JA = 40C + 2.4W x 27C/W = 104.8C Although most loudspeakers are either 4 or 8, there are other impedances available which can provide a more thermally efficient solution. Another consideration is the load impedance across the audio frequency band. A loudspeaker is a complex electromechanical system with a variety of resonances. In other words, an 8 speaker is usually only 8 impedance within a very narrow range, and often extends well below 8, reducing the thermal efficiency below what is expected. This lower-than-expected impedance can be further reduced when a crossover network is used in a multi-driver audio system. Optimize MAX9703/MAX9704 Efficiency with Load Impedance and Supply Voltage To optimize the efficiency of the MAX9703/MAX9704, load the output stage with 12 to 16 speakers. The MAX9703/MAX9704 exhibits highest efficiency performance when driving higher load impedance (see the Typical Operating Characteristics). If a 12 to 16 load is not available, select a lower supply voltage when driving 6 to 10 loads. ______________________________________________________________________________________ 13 MAX9703/MAX9704 Additional improvements are possible if all the traces from the device are made as wide as possible. Although the IC pins are not the primary thermal path of the package, they do provide a small amount. The total improvement would not exceed about 10%, but it could make the difference between acceptable performance and thermal problems. 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers MAX9703/MAX9704 Functional Diagrams 10V TO 25V 100F* 25V 0.1F 25V 1 2 PGND 0.47F 0.1F 25V 3 4 21 22 VDD VDD 23 24 PGND 12 IN+ OUT+ 30 MODULATOR 0.47F 11 IN- OUT+ 29 OUT- 28 H-BRIDGE OUT- 27 VREG VREG VREG VREG 18 FS1 19 FS2 14 SHDN 15 G1 16 G2 13 SS 0.18F 10V VREG 0.01F 10V 9 REG OSCILLATOR GAIN CONTROL SHUTDOWN CONTROL MAX9703 C1P 6 CHARGE PUMP 5 C1 0.1F 25V C1N 10 AGND CHOLD 7 C2 1F 25V LOGIC INPUTS SHOWN FOR AV = 16dB (SSM). VIN = LOGIC HIGH > 2.5V. CHOOSE CAPACITOR VOLTAGE RATING V . DD *SYSTEM-LEVEL REQUIREMENT. 14 VDD ______________________________________________________________________________________ 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 10V TO 25V 100F* 25V 0.1F 25V 1 2 PGND 0.47F 0.47F 0.1F 25V 3 4 21 22 VDD VDD 23 24 PGND 10 INL+ OUTL+ 32 MODULATOR 9 INL- OUTL+ 31 OUTL- 30 H-BRIDGE OUTL- 29 VREG VREG 0.47F 19 FS1 20 FS2 OSCILLATOR 16 INR+ OUTR+ 28 MODULATOR 0.47F 15 INR- OUTR+ 27 OUTR- 26 H-BRIDGE OUTR- 25 VREG VREG 11 SHDN 17 G1 18 G2 12 SS 0.18F 10V VREG 0.01F 10V 14 REG MAX9704 GAIN CONTROL SHUTDOWN CONTROL C1P 6 CHARGE PUMP 5 C1 0.1F 25V C1N 13 AGND CHOLD 7 VDD C2 1F 25V LOGIC INPUTS SHOWN FOR AV = 16dB (SSM). VIN = LOGIC HIGH > 2.5V. CHOOSE CAPACITOR VOLTAGE RATING V . DD *SYSTEM-LEVEL REQUIREMENT. ______________________________________________________________________________________ 15 MAX9703/MAX9704 Functional Diagrams (continued) 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers MAX9703/MAX9704 System Diagram VDD 100F* 1F 0.47F OUTL- VDD SHDN INL- OUTL- INL+ OUTL+ 0.47F OUTL+ CODEC MAX9704 0.47F OUTR+ INR+ OUTR+ INR- OUTR- 0.47F OUTR- 5V SS 100k 0.18F SHDN 1F VDD INL1F 1F 15k MAX9722B INL+ OUTL INR+ OUTR INR- PVSS SVSS 15k 1F 30k 30k C1P CIN 1F 1F LOGIC INPUTS SHOWN FOR AV = 16dB (SSM). *BULK CAPACITANCE, IF NEEDED. 16 ______________________________________________________________________________________ 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers PGND VDD VDD N.C. FS2 FS1 N.C. PGND PGND VDD VDD FS2 FS1 G2 24 23 22 21 20 19 18 17 24 23 22 21 20 19 18 17 N.C. 25 16 G2 G1 PGND TOP VIEW OUTR- 25 16 INR+ N.C. 26 15 G1 OUTR- 26 15 INR- OUT- 27 14 SHDN OUTR+ 27 14 REG. OUT- 28 13 SS OUTR+ 28 13 AGND MAX9703 MAX9704 10 INL+ N.C. 32 9 REG. OUTL+ 32 9 INL- PGND 1 2 3 4 5 6 7 8 1 2 TQFN (5mm x 5mm) 3 4 5 6 7 8 N.C. 31 CHOLD OUTL+ C1P AGND C1N 10 VDD 31 VDD N.C. PGND SHDN PGND SS 11 N.C. 12 30 C1P 29 OUTL- CHOLD OUTL- IN- C1N IN+ 11 VDD 12 30 VDD 29 OUT+ PGND OUT+ TQFN (7mm x 7mm) Chip Information MAX9703 TRANSISTOR COUNT: 3093 MAX9704 TRANSISTOR COUNT: 4630 PROCESS: BiCMOS ______________________________________________________________________________________ 17 MAX9703/MAX9704 Pin Configurations 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.) E DETAIL A 32, 44, 48L QFN.EPS MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers (NE-1) X e E/2 k e D/2 C L (ND-1) X e D D2 D2/2 b L E2/2 C L k E2 C L C L L L e A1 A2 e A PACKAGE OUTLINE 32, 44, 48, 56L THIN QFN, 7x7x0.8mm 21-0144 18 ______________________________________________________________________________________ F 1 2 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers PACKAGE OUTLINE 32, 44, 48, 56L THIN QFN, 7x7x0.8mm 21-0144 F 2 ______________________________________________________________________________________ 2 19 MAX9703/MAX9704 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.) QFN THIN.EPS MAX9703/MAX9704 10W Stereo/15W Mono, Filterless, Spread-Spectrum, Class D Amplifiers 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. 20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2006 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.