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general description the MAX9708 mono/stereo, class d audio power ampli- fier delivers up to 2 x 21w into an 8 ? stereo mode and 1 x 42w into a 4 ? load in mono mode while offering up to 87% efficiency. the MAX9708 provides class ab amplifier performance with the benefits of class d effi- ciency, eliminating the need for a bulky heatsink and conserving power. the MAX9708 operates from a single +10v to +18v supply, driving the load in a btl configu- ration. the MAX9708 offers two modulation schemes: a fixed- frequency modulation (ffm) mode, and a spread-spec- trum modulation (ssm) mode that reduces emi-radiated emissions. the MAX9708 can be synchro- nized to an external clock from 600khz to 1.2mhz. a synchronized output allows multiple units to be cascad- ed in the system. features include fully differential inputs, comprehensive click-and-pop suppression, and four selectable-gain set- tings (22db, 25db, 29.5db, and 36db). a pin-program- mable thermal flag provides seven different thermal warning thresholds. short-circuit and thermal-overload protection prevent the device from being damaged during a fault condition. the MAX9708 is available in 56-pin tqfn (8mm x 8mm x 0.8mm) and 64-pin tqfp (10mm x 10mm x 1.4mm) packages, and is specified over the extended -40? to +85? temperature range. applications lcd tvs pdp tvs automotive pc/hifi audio solutions features ? 2 x 21w output power in stereo mode (8 ? , thd = 10%) ? 1 x 42w output power in mono mode (4 ? , thd = 10%) ? high efficiency: up to 87% ? filterless class d amplifier ? unique patented spread-spectrum mode ? programmable gain (+22db, +25db, +29.5db, +36db) ? high psrr (90db at 1khz) ? differential inputs suppress common-mode noise ? shutdown and mute control ? integrated click-and-pop suppression ? low 0.1% thd+n ? current limit and thermal protection ? programmable thermal flag ? sync input/output ? available in thermally efficient, space-saving packages: 56-pin tqfn and 64-pin tqfp MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ________________________________________________________________ maxim integrated products 1 class d modulator syncout temp output protection gain control fs1, fs2 MAX9708 stereo mode g1, g2 2 sync right channel left channel mono 2 th0, th1, th2 3 part temp range pin-package pkg code MAX9708etn -40? to +85? 56 tqfn-ep** t5688-3 MAX9708ecb* -40? to +85? 64 tqfp-ep** c64e-6 simplified block diagram ordering information 19-3678; rev 0; 7/05 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. * future product?ontact factory for availability. ** ep = exposed paddle. pin configurations appear at end of data sheet. evaluation kit available class d modulator syncout temp output protection gain control fs1, fs2 MAX9708 mono mode g1, g2 2 sync audio input v digital mono 2 th0, th1, th2 3
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , mono = low (stereo mode), shdn = mute = high, g1 = low, g2 = high (a v = 22db), fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are connected between out_+ and out_-, unless otherwise stated. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. pv dd , v dd to pgnd, gnd .......................................-0.3 to +30v pv dd to v dd ..........................................................-0.3v to +0.3v outr+, outr-, outl+, outl- to pgnd, gnd...........................-0.3v to (pv dd + 0.3v) c1n to gnd .............................................-0.3v to (pv dd + 0.3v) c1p to gnd..............................(pv dd - 0.3v) to (cpv dd + 0.3v) cpv dd to gnd ..........................................(pv dd - 0.3v) to +40v all other pins to gnd.............................................-0.3v to +12v continuous input current (except pv dd , v dd , outr+, outr-, outl+, and outl-) ...........................................20ma continuous power dissipation (t a = +70?) 56-pin thin qfn (derate 47.6mw/? above +70?) ......3.81w 64-pin tqfp (derate 43.5mw/? above +70?).............3.48w operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? junction temperature ......................................................+150? thermal resistance ( jc ) 56-pin thin qfn .......................................................0.6?/w 64-pin tqfp?................................................................2?/w lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units supply voltage range v dd inferred from psrr test 10 18 v shutdown current i shdn shdn = low 0.1 1 a shutdown to full operation t son 100 ms mute to full operation t mute 100 ms g1 = 0, g2 = 1 50 85 125 g1 = 1, g2 = 1 40 63 90 g1 = 1, g2 = 0 25 43 60 input impedance r in g1= 0, g2 = 0 12 21 30 k ? output pulldown resistance shdn = gnd 600 k ? output offset voltage v os ac-coupled input, measured between out_+ and out_- ?0 mv pv dd = 10v to 18v 68 90 f ripple = 1khz 90 power-supply rejection ratio psrr 200mv p-p ripple (note 2) f ripple = 20khz 50 db dc, input referred 50 70 common-mode rejection ratio cmrr f = 20hz to 20khz, input referred 70 db switch on-resistance r ds one power switch 0.3 0.75 ? fs1 fs2 00 180 200 220 11 (ssm) 200 10 160 switching frequency f sw 01 250 khz oscillator spread bandwidth fs1 = fs2 = high (ssm) ? % syncin lock range equal to f sw x 4 600 1200 khz
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier _______________________________________________________________________________________ 3 electrical characteristics (continued) (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , mono = low (stereo mode), shdn = mute = high, g1 = low, g2 = high (a v = 22db), fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are connected between out_+ and out_-, unless otherwise stated. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units g1 = 0, g2 = 1 21.6 22.0 22.3 g1 = 1, g2 = 1 24.9 25.0 25.6 g1 = 1, g2 = 0 29.2 29.5 29.9 gain a v g1 = 0, g2 = 0 35.9 36.0 36.6 db th2 th1 th0 000 +80 001 +90 010 +100 011 +110 100 +120 101 +129 110 +139 temp flag threshold t flag 111 +150 ? temp flag accuracy from +80? to +140? ? ? temp flag hysteresis 2c stereo mode (r load = 8 ? ) mute = 1, r load = 20 30 quiescent current mute = 0 5 11 ma output power p out f = 1khz, thd = 10%, t a = +25?, r load = 8 ? , pv dd = 18v 20 21 w total harmonic distortion plus noise thd+n f = 1khz, bw = 22hz to 22khz, r load = 8 ? , p out = 8w 0.1 % 22hz to 22khz 91 signal-to-noise ratio snr r load = 8 ? , p out = 10w a-weighted 96 db efficiency = ? , l > 60h , p ou t = 15w + 15w , f = 1khz 87 % left-right channel gain matching p out = 10w 0.02 db
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 4 _______________________________________________________________________________________ electrical characteristics (continued) (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , mono = low (stereo mode), shdn = mute = high, g1 = low, g2 = high (a v = 22db), fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are connected between out_+ and out_-, unless otherwise stated. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units output short-circuit current threshold i sc r load = 0 ? 2.4 a into shutdown -63 click-and-pop level k cp peak voltage, 32 samples/second, a-weighted (notes 2, 4) out of shutdown -55 dbv mono mode (r load = 4 ? , mono = high) mute = 1, r load = 20 quiescent current mute = 0 5 ma r load = 8 ? 23 output power p out f = 1khz, thd = 10% r load = 4 ? 42 w total harmonic distortion plus noise f = 1khz, bw = 22hz to 22khz, r load = 4 ? , p out = 17w 0.12 % 20hz to 20khz 91 signal-to-noise ratio snr r load = 4 ? , p out = 10w a-weighted 95 db efficiency r load = 4 ? , l > 40?, p out = 42w, f = 1khz 85 % output short-circuit current threshold i sc r load = 0 ? 4.8 a into shutdown -60 click-and-pop level k cp peak voltage, 32 samples/second, a-weighted (notes 2, 4) out of shutdown -63 dbv digital inputs ( shdn , mute , g1, g2, fs1, fs2, th0, th1, th2, syncin, mono) logic-input current i in 0 to 12v 1 a logic-input high voltage v ih 2.5 v logic-input low voltage v il 0.8 v open-drain outputs ( temp , syncout) open-drain output low voltage v ol i sink = 3ma 0.4 v leakage current i leak v pullup = 5.5v 0.2 ? note 1: all devices are 100% production tested at +25?. all temperature limits are guaranteed by design. note 2: inputs ac-coupled to gnd. note 3: the device is current limited. the maximum output power is obtained with an 8 ? load. note 4: testing performed with an 8 ? resistive load in series with a 68? inductive load connected across btl outputs. mode tran- sitions are controlled by shdn .
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier _______________________________________________________________________________________ 5 total harmonic distortion plus noise vs. output power MAX9708 toc01 output power per channel (w) thd+n (%) 25 20 15 10 5 0.1 1 10 100 0.01 030 pv dd = 18v, 8 ? stereo mode, 1khz total harmonic distortion plus noise vs. output power MAX9708 toc02 output power per channel (w) thd+n (%) 10 5 0.1 1 10 100 0.01 015 pv dd = 12v, stereo mode, f in = 1khz r l = 8 ? r l = 4 ? total harmonic distortion plus noise vs. frequency MAX9708 toc03 frequency (hz) thd+n (%) 10k 1k 100 0.1 10 100k 1 0.01 pv dd = 18v, 8 ? stereo mode, p out = 8.3w per channel efficiency vs. output power MAX9708 toc04 output power per channel (w) efficiency (%) 25 20 15 10 5 20 30 40 50 60 70 80 90 100 10 030 pv dd = 18v, 8 ? stereo mode output power vs. supply voltage MAX9708 toc05 supply voltage (v) output power per channel (w) 16 14 12 5 10 15 20 25 30 0 10 18 r l = 8 ? stereo mode 10% thd+n 1% thd+n no-load supply current vs. supply voltage MAX9708 toc06 supply voltage (v) supply current (ma) 20 18 16 14 12 12 14 16 18 20 22 24 10 10 22 stereo mode t a = +25 c t a = +85 c t a = -40 c t ypical operating characteristics (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , shdn = high, mono = low, mute = high, g1 = low, g2 = high, fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are between out_+ and out_-, t a = +25?, unless otherwise stated.) shutdown supply current vs. supply voltage MAX9708 toc07 supply voltage (v) supply current (na) 20 18 12 14 16 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 10 22 shdn = 0 total harmonic distortion plus noise vs. output power MAX9708 toc08 output power (w) thd+n (%) 50 40 30 20 10 0.1 1 10 100 0.01 060 pv dd = 18v, 4 ? mono mode, 1khz
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 6 _______________________________________________________________________________________ total harmonic distortion plus noise vs. frequency MAX9708 toc10 frequency (hz) thd+n (%) 10k 1k 100 0.1 10 100k 1 0.01 pv dd = 18v, 4 ? mono mode, p out = 18w wideband output spectrum (ssm mode) MAX9708 toc11 frequency (hz) output amplitude (dbv) 10m 1m -60 -50 -40 -30 -20 -10 0 10 20 30 -70 100k 100m 10khz rbw wideband output spectrum (ffm mode) MAX9708 toc12 frequency (hz) output amplitude (dbv) 10m 1m 100k 100m 10khz rbw -60 -50 -40 -30 -20 -10 0 10 20 30 -70 output frequency spectrum (ssm mode) MAX9708 toc13 frequency (khz) output amplitude (dbv) 20 16 12 8 4 -100 -80 -60 -40 -20 0 -120 024 output frequency spectrum (ffm mode) MAX9708 toc14 frequency (khz) output amplitude (dbv) 20 16 12 8 4 -100 -80 -60 -40 -20 0 -120 024 t ypical operating characteristics (continued) (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , shdn = high, mono = low, mute = high, g1 = low, g2 = high, fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are between out_+ and out_-, t a = +25?, unless otherwise stated.) total harmonic distortion plus noise vs. output power MAX9708 toc09 output power (w) thd+n (%) 20 15 10 5 0.1 1 10 100 0.01 025 pv dd = 12v, mono mode, f in = 1khz r l = 4 ?
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier _______________________________________________________________________________________ 7 efficiency vs. output power MAX9708 toc15 output power (w) efficiency (%) 50 40 30 20 10 20 30 40 50 60 70 80 90 100 10 060 pv dd = 18v, 4 ? mono mode output power vs. supply voltage MAX9708 toc16 supply voltage (v) output power (w) 16 14 12 10 20 30 40 50 60 0 10 18 r l = 4 ?, mono mode, 10% thd+n output power vs. load resistance MAX9708 toc17 load resistance ( ? ) output power (w) 10 8 6 10 20 30 40 50 60 0 412 mono mode, 10% thd+n, pv dd = 18v output power vs. load resistance MAX9708 toc18 load resistance ( ? ) output power per channel (w) 11 10 9 8 5 10 15 20 25 30 0 712 stereo mode, 10% thd+n, pv dd = 18v mute response MAX9708 toc19 40ms/div mute 5v/div output 50mv/div shutdown response MAX9708 toc20 40ms/div shdn 5v/div output 50mv/div t ypical operating characteristics (continued) (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , shdn = high, mono = low, mute = high, g1 = low, g2 = high, fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are between out_+ and out_-, t a = +25?, unless otherwise stated.)
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 8 _______________________________________________________________________________________ common-mode rejection ratio vs. frequency MAX9708 toc21 frequency (hz) cmrr (db) 10k 1k 100 -105 -100 -95 -90 -85 -80 -75 -70 -65 -60 -110 10 100k input referred power-supply rejection ratio vs. frequency MAX9708 toc22 frequency (hz) psrr (db) 10k 1k 100 -100 -90 -80 -70 -60 -50 -40 -30 -110 10 100k crosstalk vs. frequency MAX9708 toc23 frequency (hz) crosstalk (db) 10k 1k 100 -110 -100 -90 -80 -70 -60 -50 -40 -120 10 100k maximum steady-state output power vs. temperature MAX9708 toc24 ambient temperature ( c) output power per channel (w) 60 40 50 5 15 10 25 20 30 35 40 0 30 70 pv dd = 18v, 8 ? stereo mode, 1khz, fs1 = fs2 = 1 th0 = th1 = 1 th2 = 0 measured with the ev kit (tqfn package), junction temperature maintained at +110 c maximum steady-state output power vs. temperature MAX9708 toc25 ambient temperature ( c) output power (w) 60 40 50 10 20 40 30 50 60 70 0 30 70 pv dd = 18v, 4 ? mono mode, 1khz, fs1 = fs2 = 1 th0 = th1 = 1 th2 = 0 measured with the ev kit (tqfn package), junction temperature maintained at +110 c t ypical operating characteristics (continued) (pv dd = v dd = +18v, pgnd = gnd = 0v, c ss = 0.47?, c reg = 0.01?, c1 = 0.1?, c2 = 1?, r load = , shdn = high, mono = low, mute = high, g1 = low, g2 = high, fs1 = fs2 = high (ssm), syncin = low. all load resistors (r l ) are between out_+ and out_-, t a = +25?, unless otherwise stated.) pin description pin tqfp tqfn name function 1, 8, 13, 16, 17, 32, 33, 41, 48, 49, 50, 55, 58, 63, 64 1, 12, 42, 43, 44, 55, 56 n.c. no connection. not internally connected. 2, 3, 4, 45, 46, 47, 56, 57 2, 3, 4, 39, 40, 41, 49, 50 pgnd power ground 5, 6, 7, 42, 43, 44 5, 6, 7, 36, 37, 38 pv dd positive power supply. bypass to pgnd with a 0.1? and a 47? capacitor with the smallest capacitor placed as close to pins as possible.
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier _______________________________________________________________________________________ 9 pin description (continued) pin tqfp tqfn name function 98 c1n charge-pump flying capacitor c1, negative terminal 10 9 c1p charge-pump flying capacitor c1, positive terminal 11 10 cpv dd charge-pump power supply. bypass to pv dd with a 1? capacitor as close to the pin as possible. 12 11 syncout open-drain, slew-rate limited clock output. pullup with a 10k ? resistor to reg. 14 13 syncin clock synchronization input. allows for synchronization of the internal oscillator with an external clock. syncin is internally pulled up to v reg with a 100k ? resistor. 15 14 fs2 frequency select 2 18 15 fs1 frequency select 1 19 16 inl- left-channel negative input (stereo mode only) 20 17 inl+ left-channel positive input (stereo mode only) 21 18 mono mono/stereo mode input. drive logic-high for mono mode. drive logic-low for stereo mode. 22, 23, 24 19, 20, 21 reg internal regulator output voltage (6v). bypass with a 0.01? capacitor to gnd. 25, 26 22, 23 gnd analog ground 27 24 ss soft-start. connect a 0.47? capacitor to gnd to utilize soft-start power-up sequence. 28 25 v dd analog power supply. bypass to gnd with a 0.1? capacitor as close to pin as possible. 29 26 inr- right-channel positive input. in mono mode, inr+ is the positive input. 30 27 inr+ right-channel negative input. in mono mode, inr- is the negative input. 31 28 g1 gain select input 1 34 29 g2 gain select input 2 35 30 shdn active-low shutdown input. drive shdn high for normal operation. drive shdn low to place the device in shutdown mode. 36 31 mute active-low mute input. drive logic-low to place the device in mute. in mute mode, class d output stage is no longer switching. drive high for normal operation. mute is internally pulled up to v reg with a 100k ? resistor. 37 32 temp thermal flag output, open drain. pull up with a 10k ? resistor to reg. 38 33 th2 temperature flag threshold select input 2 39 34 th1 temperature flag threshold select input 1 40 35 th0 temperature flag threshold select input 0 51, 52 45, 46 outr- right-channel negative output 53, 54 47, 48 outr+ right-channel positive output 59, 60 51, 52 outl- left-channel negative output 61, 62 53, 54 outl+ left-channel positive output ep ep ep exposed paddle. connect to gnd with multiple vias for best heat dissipation.
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 10 ______________________________________________________________________________________ t ypical application circuits/functional diagrams outr+ outr- outl- outl+ syncin inl+ inl- inr+ inr- shdn g2 g1 syncout pgnd r in r in r in r in v bias v bias th0 th1 th2 temp cpv dd pv dd pv dd pv dd pv dd pv dd v dd v dd c1p c1n reg + - left channel + - right channel v digital c2 1 f c1 0.1 f 0.1 f 47 f* 1 f 1 f 1 f 1 f c reg 0.01 f c ss 0.47 f v digital v digital v digital v digital gnd mono fs1 fs2 r f r f r f r f 10k ? 10k ? 14 (15) 13 (14) 17 (20) 16 (19) 27 (30) 26 (29) 30 (35) 28 (31) 29 (34) 18 (21) 35 (40) 34 (39) 33 (38) 32 (37) 19, 20, 21 (22, 23, 24) 8 (9) 9 (10) 10 (11) 51, 52 (59, 60) 53, 54 (61, 62) 45, 46 (51, 52) 47, 48 (53, 54) 11 (12) 22, 23 (25, 26) 2?, 39?1 49?0 (2?, 45?7, 56?7) 5?, 36?8 (5?, 42-44) 25 (28) 15 (18) ss 24 (27) mute 31 (36) ( ) tqfp package *additional bulk capacitance configuration: tqfn stereo mode, ssm, internal oscillator, gain = 22db, thermal setting = +120 c MAX9708 gain control control charge pump regulator thermal sensor mux class d modulator and h-bridge class d modulator and h-bridge figure 1. typical application and functional diagram in stereo mode
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 11 t ypical application circuits/functional diagrams (continued) outr+ outr- outl- outl+ syncin inr+ inr- shdn g1 g2 syncout pgnd r in r in v bias th0 th1 th2 temp cpv dd pv dd pv dd pv dd pv dd pv dd v dd v dd c1p c1n reg + - audio input v digital c2 1 f 0.1 f 0.1 f 47 f* 1 f 1 f c reg 0.01 f c1 0.1 f c ss 0.47 f v digital v digital v digital v digital gnd mono fs1 fs2 r f r f 10k ? 10k ? 14 (15) 13 (14) 17 (20) 16 (19) 30 (35) 28 (31) 29 (34) 18 (21) 35 (40) 34 (39) 33 (38) 32 (37) 19, 20, 21 (22, 23, 24) 8 (9) 9 (10) 10 (11) 51, 52 (59, 60) 53, 54 (61, 62) 45, 46 (51, 52) 47, 48 (53, 54) 11 (12) 22, 23 (25, 26) 2?, 39?1 49?0 (2?, 45?7, 56?7) 5?, 36?8 (5?, 42?4) 25 (28) 15 (18) ss 24 (27) mute 31 (36) v digital MAX9708 gain control charge pump regulator thermal sensor mux control class d modulator and h-bridge class d modulator and h-bridge ( ) tqfp package *additional bulk capacitance configuration: tqfn mono mode, ssm, internal oscillator, gain = 22db, thermal setting = +120 c figure 2. typical application and functional diagram in mono mode
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 12 ______________________________________________________________________________________ detailed description the MAX9708 filterless, class d audio power amplifier features several improvements to switch-mode amplifi- er technology. the MAX9708 is a two-channel, stereo amplifier with 21w output power on each channel. the amplifier can be configured to output 42w output power in mono mode. the device offers class ab per- formance with class d efficiency, while occupying min- imal board space. a unique filterless modulation scheme 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 device can also be con- figured as a single-ended input amplifier. mono/stereo configuration the MAX9708 features a mono mode that allows the right and left channels to operate in parallel, achieving up to 42w of output power. the mono mode is enabled by applying logic-high to mono. in this mode, an audio signal applied to the right channel (inr+/inr-) is routed to the h-bridge of both channels, while a signal applied to the left channel (inl+/inl-) is ignored. outl+ must be connected to outr+ and outl- must be connected to outr- using heavy pc board traces as close to the device as possible (see figure 2). when the device is placed in mono mode on a pc board with outputs wired together, ensure that the mono pin can never be driven low when the device is enabled. driving the mono pin low (stereo mode) while the outputs are wired together in mono mode may trigger the short circuit or thermal protection or both, and may even damage the device. efficiency efficiency of a class d amplifier is attributed to the region of operation of the output stage transistors. in a class d amplifier, the output transistors act as current- steering switches and consume negligible additional power. any power loss associated with the class d out- put stage is mostly due to the i 2 r loss of the mosfet on-resistance and quiescent current overhead. the theoretical best efficiency of a linear amplifier is 78%; however, that efficiency is only exhibited at peak output powers. under normal operating levels (typical music reproduction levels), efficiency falls below 30%, where- as the MAX9708 still exhibits 87% efficiency under the same conditions. shutdown the MAX9708 features a shutdown mode that reduces power consumption and extends battery life. driving shdn low places the device in low-power (0.1?) shut- down mode. connect shdn to digital high for normal operation. mute function the MAX9708 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 MAX9708, drive mute to logic-low. driving mute low during the power-up/down or shutdown/turn-on cycle optimizes click-and-pop suppression. click-and-pop suppression the MAX9708 features comprehensive click-and-pop suppression that eliminates audible transients on start- up and shutdown. while in shutdown, the h-bridge is pulled to gnd through a 330k ? resistor. 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. following startup, a soft-start function gradually un-mutes the input ampli- fiers. the value of the soft-start capacitor has an impact on the click-and-pop levels as well as startup time. thermal sensor the MAX9708 features an on-chip temperature sensor that monitors the die temperature. when the junction temperature exceeds a programmed level, temp is pulled low. this flags the user to reduce power or shut down the device. temp may be connected to ss or mute for automatic shutdown during overheating. if temp is connected to mute , during thermal-protection mode, the audio is muted and the device is in mute mode. if temp is connected to ss, during thermal-pro- tection mode, the device is shut down but the thermal sensor is still active.
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 13 temp returns high once the junction temperature cools below the set threshold minus the thermal hysteresis. if temp is connected to either mute or ss, the audio output resumes. the temperature threshold is set by the th0, th1, and th2 inputs as shown in table 1. an rc filter may be used to eliminate any transient at the temp output as shown in figure 3. gain selection the MAX9708 features four pin-selectable gain settings; see table 2. operating modes fixed-frequency modulation (ffm) mode the MAX9708 features three switching frequencies in the ffm mode (table 3). in this mode, the frequency spectrum of the class d output consists of the funda- mental switching frequency and its associated harmon- ics (see the wideband output spectrum graph in the typical operating characteristics ). select one of the three fixed switching frequencies such that the harmon- ics do not fall in a sensitive band. the switching fre- quency can be changed at any time without affecting audio reproduction. spread-spectrum modulation (ssm) mode the MAX9708 features a unique, patented spread- spectrum (ssm) mode that flattens the wideband spec- tral components, improving emi emissions that may be radiated by the speaker and cables. this mode is enabled by setting fs1 = fs2 = high. in ssm mode, the switching frequency varies randomly by ?% around the center frequency (200khz). the modulation scheme remains the same, but the period of the triangle wave- form 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. ssm mode reduces emi com- pared to fixed-frequency mode. this can also help to randomize visual artifacts caused by radiated or sup- ply-borne interference in displays. synchronous switching mode the MAX9708 syncin input allows the class d amplifi- er to switch at a frequency defined by an external clock frequency. synchronizing the amplifier with an external clock source may confine the switching frequency to a less sensitive band. the external clock frequency range is from 600khz to 1.2mhz and can have any duty cycle, but the minimum pulse must be greater than 100ns. syncout is an open-drain clock output for synchro- nizing external circuitry. its frequency is four times the amplifier? switching frequency, and it is active in either internal or external oscillator mode. figure 3. an rc filter eliminates transient during switching table 1. MAX9708 junction temperature threshold setting temp 0.1 f 10k ? 10k ? v digital to digital input junction temperature (?) th2 th1 th0 80 low low low 90 low low high 100 low high low 110 low high high 120 high low low 129 high low high 139 high high low 150 high high high table 2. MAX9708 gain setting g1 g2 gain (db) low high 22 high high 25 high low 29.5 low low 36 table 3. switching frequencies fs1 fs2 syncout frequency (khz) modulation 00 200 fixed-frequency 01 250 fixed-frequency 10 160 fixed-frequency 11 200 ? spread-spectrum
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 14 ______________________________________________________________________________________ linear regulator (reg) the supply voltage range for the MAX9708 is from 10v to 18v to achieve high-output power. an internal linear regulator reduces this voltage to 6.3v for use with small-signal and digital circuitry that does not require a high-voltage supply. bypass a 0.01? capacitor from reg to gnd. applications information logic inputs all of the digital logic inputs and output have an absolute maximum rating of +12v. if the MAX9708 is operating with a supply voltage between 10v and 12v, digital inputs can be connected to pv dd or v dd . if pv dd and v dd are greater than 12v, digital inputs and outputs must connected to a digital system supply lower than 12v. input amplifier differential input the MAX9708 features 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 flat-panel displays, noisy digital signals can be picked up by the amplifier? inputs. these signals appear at the amplifiers?inputs as common-mode noise. a differential input amplifier amplifies only the difference of the two inputs, while any signal common to both inputs is attenuated. single-ended input the MAX9708 can be configured as a single-ended input amplifier by capacitively coupling either input to gnd and driving the other input (figure 4). component selection input filter an input capacitor, c in , in conjunction with the input impedance of the MAX9708, 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 zero-source imped- ance, the -3db point of the highpass filter is given by: choose c in so that f -3db is well below the lowest fre- quency of interest. setting f -3db too high affects the low-frequency response of the amplifier. use capaci- tors with dielectrics that 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. output filter the MAX9708 does not require an output filter. however, output filtering can be used if a design is fail- ing radiated emissions due to board layout or cable length, or the circuit is near emi-sensitive devices. refer to the MAX9708 evaluation kit for suggested filter topologies. the tuning and component selection of the filter should be optimized for the load. a purely resistor load (8 ? ) used for lab testing will require different com- ponents than a real, complex load-speaker load. charge-pump capacitor selection the MAX9708 has an internal charge-pump converter that produces a voltage level for internal circuitry. it requires a flying capacitor (c1) and a holding capacitor (c2). 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. the capacitors?voltage rating must be greater than 36v. f rc db in in ? = 3 1 2 figure 4. single-ended input connections inr+ inr- MAX9708 1 f 1 f
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 15 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 dis- torting the input signal. mute the MAX9708 by driving mute low. driving mute low turns off the class d out- put stage, but does not affect the input bias levels of the MAX9708. frequency synchronization the MAX9708 outputs up to 21w on each channel in stereo mode. if higher output power or a 2.1 solution is needed, two MAX9708s can be used. each MAX9708 is synchronized by connecting syncout from the first MAX9708 to syncin of the second MAX9708 (see figure 5). supply bypassing/layout proper power-supply bypassing ensures low-distortion operation. for optimum performance, bypass pv dd to pgnd with a 0.1? capacitor as close to each pv dd pin as possible. a low-impedance, high-current power- supply connection to pv dd is assumed. additional bulk capacitance should be added as required depending on the application and power-supply characteristics. gnd and pgnd should be star-connected to system ground. for the tqfn package, solder the exposed paddle (ep) to the ground plane using multiple-plated through-hole vias. the exposed paddle must be sol- dered to the ground plane for rated power dissipation and good ground return. use wider pc board traces to lower the parasitic resistance for the high-power output pins (outr+, outr-, outl+, outl-). refer to the MAX9708 evaluation kit for layout guidance. thermal considerations class d amplifiers provide much better efficiency and thermal performance than a comparable class ab amplifier. however, the system? thermal performance must be considered with realistic expectations along with its many parameters. 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 maxi- mum output power with a continuous sine wave. the pc board must be optimized for best dissipation (see the pc board thermal considerations section). audio content, both music and voice, has a much lower rms value relative to its peak output power. 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 per- formance 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 perfor- mance will be less than the system? actual capability for real music or voice. pc board thermal considerations the exposed pad is the primary route for conducting 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 copper polygon. add as much copper as pos- sible from this polygon to any adjacent pin on the class d amplifier as well as to any adjacent components, pro- vided 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 capa- bilities 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? constraints for signal routing. 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 out of the package, they do provide a small amount. the total improvement would not exceed approximately 10%, but it could make the difference between accept- able performance and thermal problems.
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 16 ______________________________________________________________________________________ auxiliary heatsinking 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 resis- tance 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 cost- effective location for a heatsink. if an lc filter is used in the design, placing the inductor in close proximity to the ic can help draw heat away from the MAX9708. thermal calculations the die temperature of a class d amplifier can be esti- mated with some basic calculations. for example, the die temperature is calculated for the below conditions: ? a = +40? ? out = 16w efficiency ( ) = 87% ja = 21?/w first, the class d amplifier? power dissipation must be calculated: then the power dissipation is used to calculate the die temperature, t c , as follows: load impedance the on-resistance of the mosfet output stage in class d amplifiers affects both the efficiency and the peak-cur- rent capability. reducing the peak current into the load reduces the i 2 r losses in the mosfets, which increases efficiency. to keep the peak currents lower, choose the highest impedance speaker that can still deliver the desired output power within the voltage swing limits of the class d amplifier and its supply voltage. although most loudspeakers fall either 4 ? or 8 ? , there are other impedances available that can provide a more thermally efficient solution. another consideration is the load impedance across the audio frequency band. a loudspeaker is a complex electro-mechanical system with a variety of resonance. in other words, an 8 ? speaker usually has 8 ? imped- ance within a very narrow range. this 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 multidriver audio system. systems application circuit the MAX9708 can be configured into multiple amplifier systems. one concept is a 2.1 audio system (figure 5) where a stereo audio source is split into three channels. the left- and right-channel inputs are highpass filtered to remove the bass content, and then amplified by the MAX9708 in stereo mode. also, the left- and right-chan- nel inputs are summed together and lowpass filtered to remove the high-frequency content, then amplified by a second MAX9708 in mono mode. the conceptual drawing of figure 5 can be applied to either single-ended or differential systems. figure 6 illustrates the circuitry required to implement a fully differential filtering system. by maintaining a fully differ- ential path, the signal-to-noise ratio remains uncompro- mised and noise pickup is kept very low. however, keeping a fully differential signal path results in almost twice the component count, and therefore performance must be weighed against cost and size. the highpass and lowpass filters should have different cutoff frequencies to ensure an equal power response at the crossover frequency. the filters should be at -6db amplitude at the crossover frequency, which is known as a linkwitz-riley alignment. in the example circuit of figure 6, the -3db cutoff frequency for the highpass filters is 250hz, and the -3db cutoff frequency for the lowpass filter is 160hz. both the highpass filters and the lowpass filters are at a -6db amplitude at approximately 200hz. if the filters were to have the same -3db cutoff frequency, a measurement of sound pressure level (spl) vs. frequency would have a peak at the crossover frequency. the circuit in figure 6 uses inverting amplifiers for their ease in biasing. note the phase labeling at the outputs has been reversed. the resistors should be 1% or better in tolerance and the capacitors 5% tolerance or better. ttp c w cw c ca diss ja =+ =+ = 40 24 21 90 4 /. p p p w ww diss out out === ?? . . 16 087 16 2 4
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 17 mismatch in the components can cause discrepancies between the nominal transfer function and actual perfor- mance. also, the mismatch of the input resistors (r15, r17, r19, and r21 in figure 6) of the summing amplifier and lowpass filter will cause some high-frequency sound to be sent to the subwoofer. the circuit in figure 6 drives a pair of MAX9708 devices similar to the circuit in figure 5. the inputs to the MAX9708 still require ac-coupling to prevent compro- mising the click-and-pop performance of the MAX9708. the left and right drivers should be at an 8 ? to 12 ? impedance, whereas the subwoofer can be 4 ? to 12 ? depending on the desired output power, the available power-supply voltage, and the sensitivity of the individ- ual speakers in the system. the four gain settings of the MAX9708 allow gain adjustments to match the sen- sitivity of the speakers. figure 5. multiple amplifiers implement a 2.1 audio system MAX9708 MAX9708 highpass filter 8 ? full- range speaker 8 ? full- range speaker 4 ? or 8 ? woofer right audio left audio highpass filter lowpass filter v digital outr+ outr- outl+ outl- outr+ outr- outl+ outl- inr+ inr- mono inl+ inl- inr+ syncin syncout inr- mono inl+ inl-
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 18 ______________________________________________________________________________________ figure 6. fully differential crossover filters bias 2 3 1 c1 47nf r3 28k ? r2, 56.2k ? r1 56.2k ? c2 47nf max4478 u1a bias 6 5 7 c3 47nf r7 28k ? r6, 56.2k ? right audio output right audio input r5 56.2k ? r4 28k ? c4 47nf max4478 u1b bias 9 10 8 c5 47nf r10 28k ? r9, 56.2k ? r8 56.2k ? c6 47nf max4478 u1c bias 13 12 14 c7 47nf r14 28k ? r13, 56.2k ? left audio output subwoofer output is ac-coupled to a MAX9708 configured as a mono amplifier note: op-amp power pins omitted for clarity. all resistors are 1% or better. all capacitors are 5% or better. right and left outputs are ac-coupled to a MAX9708 configured as a stereo amplifier subwoofer audio output left audio input r12 56.2k ? r11 28k ? c8 47nf max4478 u1d bias 2 3 1 r17 26.1k ? r15 26.1k ? max4478 u2a r16 13k ? c9, 47nf c10 47nf r18 7.5k ? bias 6 5 7 r21 28k ? r19 26.1k ? max4478 u2b r20 13k ? c11, 47nf r22 7.5k ?
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 19 pin configurations top view pgnd pgnd pgnd pv dd pv dd pv dd th0 th1 th2 g2 temp mute shdn n.c. 36 37 38 39 40 32 33 34 35 41 18 19 20 21 22 23 24 25 26 27 outl+ thin qfn 30 31 29 inr+ inr- v dd ss gnd gnd reg reg reg fs1 15 16 17 mono inl+ inl- outl- outl- pgnd pgnd outr+ n.c. n.c. outl+ outr+ outr- outr- n.c. 28 g1 n.c. syncout cpv dd c1p c1n pv dd pv dd fs2 syncin n.c. pv dd pgnd pgnd pgnd n.c. 42 7 6 5 4 311 10 9 8 213 12 14 1 53 52 51 50 49 48 47 46 45 44 56 55 54 43 MAX9708
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 20 ______________________________________________________________________________________ chip information process: bicmos pin configurations (continued) 58 59 60 61 62 54 55 56 57 63 38 39 40 41 42 43 44 45 46 47 cpv dd inl- n.c. tqfp top view outl+ outl+ outl- outl- n.c. pgnd pgnd n.c. outr+ 52 53 49 50 51 outr+ outr- outr- n.c. n.c. fs1 mono inl+ reg reg gnd reg ss gnd inr- v dd g1 inr+ n.c. pgnd pgnd pgnd pv dd pv dd pv dd n.c. th0 th1 th2 33 34 35 36 37 temp mute shdn g2 n.c. c1p c1n n.c. pv dd pv dd n.c. fs2 syncin n.c. syncout pv dd pgnd pgnd pgnd 48 n.c. n.c. 64 n.c. n.c. 23 22 21 20 19 27 26 25 24 18 29 28 32 31 30 17 11 10 9 8 7 6 5 4 3 2 16 15 14 13 12 1 MAX9708
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 21 package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) 56l thin qfn.eps
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier 22 ______________________________________________________________________________________ package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .)
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier ______________________________________________________________________________________ 23 package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) 64l tqfp.eps b 1 2 21-0083 package outline, 64l tqfp, 10x10x1.4mm
MAX9708 20w/40w, filterless, spread-spectrum, mono/stereo, class d amplifier maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 24 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation go to www.maxim-ic.com/packages .) b 2 2 21-0083 package outline, 64l tqfp, 10x10x1.4mm freed

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