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general description the MAX9759 mono class d, audio power amplifier provides class ab amplifier audio performance with the benefits of class d efficiency, eliminating the need for a heatsink and extending battery life. the MAX9759 deliv- ers up to 3.2w of continuous power into a 4 ? load while offering greater than 90% efficiency. maxim? next-gen- eration, low-emi modulation scheme allows the amplifi- er to operate without an external lc filter while still meeting fcc emi-radiated emission levels. the MAX9759 offers two modulation schemes: a fixed- frequency modulation (ffm) mode and a spread-spec- trum modulation (ssm) mode. the ssm mode flattens the wideband spectral components, reducing emi-radi- ated emissions due to the modulation frequency. furthermore, the MAX9759 oscillator can be synchro- nized to an external clock through the sync input, allowing the switching frequency to range from 1000khz to 1600khz. the sync input and sync_out output of the MAX9759 allow multiple maxim class d amplifiers to be cascaded and frequency locked, mini- mizing interference due to clock intermodulation. the MAX9759 utilizes fully differential input amplifiers, a full- bridged output, comprehensive click-and-pop suppres- sion, and features four selectable gain settings (6db, 12db, 18db, 24db). the MAX9759 features high 81db psrr, low 0.02% thd+n, and snr in excess of 90db. short-circuit and thermal-overload protection prevents damage to the device during a fault condition. the MAX9759 operates from a single 5v supply, consumes 8.4ma of supply current, and is available in a 16-pin thin qfn package (4mm x 4mm x 0.8mm) and a 16-pin tssop package. the MAX9759 is fully specified over the extended -40? to +85? temperature range. applications cell phones/pdas notebook pcs portable dvd players flat-panel pc monitors lcd tvs lcd projectors features ? 3.2w into 4 ? load (thd+n = 10%) ? filterless amplifier passes fcc radiated emissions standards with 7.6cm of cable ? 92% efficiency ? high psrr (81db at 1khz) ? low 0.02% thd+n ? external clock synchronization for multiple, cascaded maxim class d amplifiers ? 3.0v to 5.5v single-supply operation ? pin-selectable gain (6db, 12db, 18db, 24db) ? integrated click-and-pop suppression ? low quiescent current (8.4ma) ? low-power shutdown mode (10a) ? mute function ? short-circuit and thermal-overload protection ? available in thermally efficient packages 16-pin tqfn (4mm x 4mm x 0.8mm) 16-pin tssop MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier ________________________________________________________________ maxim integrated products 1 MAX9759 differential audio input sync input sync output v dd oscillator modulator and h-bridge mono speaker output gain control mute control shdn control g1 g2 shdn mute simplified block diagram ordering information 19-3691; rev 0; 5/05 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. part temp range pin-package MAX9759ete+ -40 c to +85 c 16 tqfn-ep* MAX9759eue+ -40 c to +85 c 16 tssop pin configurations appear at end of data sheet. + denotes lead-free package. * ep = exposed paddle.
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 2 _______________________________________________________________________________________ absolute maximum ratings 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. v dd to gnd..............................................................................6v pv dd to pgnd .........................................................................6v gnd to pgnd .......................................................-0.3v to +0.3v all other pins to gnd.................................-0.3v to (v dd + 0.3v) continuous current into/out of pv dd /pgnd/out+/out-....1.7a duration of out+ or out- short circuit to v dd /gnd/pv dd /pgnd............................................continuous duration of short circuit between out+ and out- ..continuous continuous power dissipation (t a = +70?) 16-pin tqfn (derate 16.9mw/? above +70?) .....1349.1mw 16-pin tssop (derate 9.4mw/? above +70?) .......754.7mw junction temperature ......................................................+150? operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? esd protection (+ibm).........................................................?kv electrical characteristics (v dd = 5.0v) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = 0v (ffm). gain = 12db (g1 = 0, g2 = 1). speaker load resistor (r l ) connected between out+ and out-, unless otherwise noted, r l = , t a = t min to t max , unless otherwise noted. typical val- ues are at t a = +25?.) (notes 1, 2) parameter symbol conditions min typ max units general supply voltage range v dd inferred from psrr test 3.0 5.5 v quiescent current i dd no load 8.4 12 ma mute current i mute v mute = 0v 5.5 8 ma shutdown current i dd ( shdn ) v shdn = 0v 0.1 10 ? shutdown to full operation t son 40 ms mute to full operation t mute 40 ms common-mode rejection ratio cmrr f = 1khz, input referred, v in = 200mv p-p 67 db input dc bias voltage v cm 1.3 1.5 1.7 v gain = +24db 14 20 26 gain = +18db 25 36 47 gain = +12db 40 60 80 input resistance r in gain = +6db 60 90 120 k ? g1 = 0, g2 = 0 +22 +24 +26 g1 = 1, g2 = 0 +16 +18 +20 g1 = 0, g2 = 1 +10 +12 +14 voltage gain a v g1 = 1, g2 = 1 +4 +6 +8 db output offset voltage v os t a = +25 c 10 50 mv v dd = 4.5v to 5.5v 62 90 f ripple = 217hz 79 f ripple = 1khz 81 power-supply rejection ratio (note 3) psrr 200mv p-p ripple f ripple = 20khz 70 db
MAX9759 3.2w, high efficiency, low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 3 electrical characteristics (v dd = 5.0v) (continued) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = 0v (ffm). gain = 12db (g1 = 0, g2 = 1). speaker load resistor (r l ) connected between out+ and out-, unless otherwise noted, r l = , t a = t min to t max , unless otherwise noted. typical val- ues are at t a = +25?.) (notes 1, 2) parameter symbol conditions min typ max units r l = 3 ? 3.4 r l = 4 ? 2.6 thd+n = 1% r l = 8 ? 1.4 r l = 3 ? 4.3 r l = 4 ? 3.2 output power p out thd+n = 10% r l = 8 ? 1.8 w r l = 3 ? 0.08 r l = 4 ? ? ? a-weighted ssm 92 db sync = gnd (ffm mode) 1000 1100 1200 sync = float (ffm mode) 1102 1500 1837 oscillator frequency f osc sync = v dd (ssm mode) 1200 70 khz sync frequency lock range ttl-compatible clock input 1000 1600 khz into shutdown -50 click-and-pop level k cp peak voltage, a-weighted, 32 samples per second (notes 3, 4) out of shutdown -57 db efficiency p out = 1w, f in = 1khz, r l = 8 ? in series with 68? 92 % digital inputs ( shdn , mute , g1, g2, sync) sync, g1, g2 input voltage high v inh v dd x 0.9 v sync, g1, g2 input voltage low v inl v dd x 0.1 v shdn , mute voltage high v inh 2v shdn , mute voltage low v inl 0.8 v sync input resistance 200 k ? sync input current 35 ? shdn , mute, g1, g2 input current 1a sync capacitance 10 pf digital outputs (sync_out) output voltage high v oh i oh = 3ma 2.4 v output voltage low v ol i ol = 3ma 0.4 v sync_out capacitive drive ttl-compatible clock output 100 pf
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 4 _______________________________________________________________________________________ electrical characteristics (v dd = 3.3v) (v dd = pv dd = shdn = mute = 3.3v, gnd = pgnd = 0v, sync = gnd (ffm). gain = 12db (g1 = 0, g2 = 1). speaker load resis- tor (r l ) connected between out+ and out-, unless otherwise noted. r l = , t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (notes 1, 2) parameter symbol conditions min typ max units quiescent current i dd 6ma mute current i mute v mute = 0v 5 a shutdown current i shdn v shdn = 0v 0.1 ? common-mode rejection ratio cmrr f = 1khz, input referred 67 db v dd = 3.0v to 5.5v 50 72 db f ripple = 217hz 79 f ripple = 1khz 81 power-supply rejection ratio psrr 200mv p-p ripple f ripple = 20khz 70 db r l = 3 ? 1.5 r l = 4 ? 1.1 thd+n = 1% r l = 8 ? 0.65 r l = 3 ? 1.8 r l = 4 ? 1.3 output power p out thd+n = 10% r l = 8 ? ? ? ? ? note 1: all devices are 100% production tested at +25?. 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 r l = 4 ? , l = 33?. for r l = 8 ? , l = 68?. note 3: inputs ac-coupled to gnd. note 4: testing performed with 8 ? resistive load in series with a 68? inductive load across btl outputs. mode transitions are con- trolled by the shdn pin.
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 5 t ypical operating characteristics (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = v dd (ssm), unless otherwise noted. gain = 12db (g1 = 0, g2 = 1). thd+n measurement bandwidth: 22hz to 22khz. typical values are at t a = +25?.) (see typical operating circuit ) total harmonic distortion plus noise vs. frequency MAX9759 toc01 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 5v r l = 3 ? p out = 1w p out = 2.6w total harmonic distortion plus noise vs. frequency MAX9759 toc02 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 3.3v r l = 3 ? p out = 500mw p out = 1.3w total harmonic distortion plus noise vs. frequency MAX9759 toc03 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 5v r l = 4 ? p out = 1w p out = 2.2w total harmonic distortion plus noise vs. frequency MAX9759 toc04 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 3.3v r l = 4 ? p out = 500mw p out = 700mw total harmonic distortion plus noise vs. frequency MAX9759 toc05 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 5v r l = 8 ? p out = 600mw p out = 1.2w total harmonic distortion plus noise vs. frequency MAX9759 toc06 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.001 0.1 1 10 10 100k v dd = 3.3v r l = 8 ? p out = 300mw p out = 500mw total harmonic distortion plus noise vs. frequency MAX9759 toc07 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 10 0.001 10 100k v dd = 5v r l = 8 ? p out = 1.2w ssm ffm total harmonic distortion plus noise vs. output power MAX9759 toc08 output power (w) thd+n (%) 4 3 2 1 0.01 0.1 1 10 100 0.001 0 v dd = 5v r l = 3 ? f in = 200hz, 1khz f in = 10khz total harmonic distortion plus noise vs. output power MAX9759 toc09 output power (w) thd+n (%) 1.5 1.0 0.5 0.01 0.1 1 10 100 0.001 0 2.0 v dd = 3.3v r l = 3 ? f in = 200hz, 1khz f in = 10khz
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 6 _______________________________________________________________________________________ total harmonic distortion plus noise vs. output power MAX9759 toc12 output power (w) thd+n (%) 1.5 1.0 0.5 0.01 0.1 1 10 100 0.001 0 2.0 v dd = 5v r l = 8 ? f in = 200hz, 1khz f in = 10khz total harmonic distortion plus noise vs. output power MAX9759 toc13 output power (w) thd+n (%) 0.6 0.4 0.2 0.01 0.1 1 10 100 0.001 0 0.8 v dd = 3.3v r l = 8 ? f in = 200hz, 1khz f in = 10khz total harmonic distortion plus noise vs. output power MAX9759 toc14 output power (w) thd+n (%) 1.5 1.0 0.5 0.01 0.1 1 10 100 0.001 0 2.0 v dd = 5v f in = 1khz r l = 8 ? f = 1180khz, ffm f = 1400khz, ffm efficiency vs. output power MAX9759 toc15 output power (w) efficiency (%) 4 3 2 1 10 20 30 40 50 60 70 80 90 100 0 05 r l = 8 ? r l = 4 ? r l = 3 ? v dd = 5v f in = 1khz efficiency vs. output power MAX9759 toc16 output power (w) efficiency (%) 1.5 1.0 0.5 10 20 30 40 50 60 70 80 90 100 0 0 2.0 r l = 8 ? r l = 4 ? r l = 3 ? v dd = 3.3v f in = 1khz efficiency vs. supply voltage MAX9759 toc17 supply voltage (v) efficiency (%) 5.5 5.0 4.5 4.0 3.5 40 50 60 70 80 90 100 30 3.0 r l = 8 ? r l = 4 ? f in = 1khz thd+n = 1% output power vs. supply voltage MAX9759 toc18 supply voltage (v) output power (w) 5.5 5.0 4.5 4.0 3.5 1 2 3 4 5 6 0 3.0 r l = 3 ? f in = 1khz thd+n = 1% thd+n = 10% t ypical operating characteristics (continued) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = v dd (ssm), unless otherwise noted. gain = 12db (g1 = 0, g2 = 1). thd+n measurement bandwidth: 22hz to 22khz. typical values are at t a = +25?.) (see typical operating circuit ) total harmonic distortion plus noise vs. output power MAX9759 toc10 output power (w) thd+n (%) 3 2 1 0.01 0.1 1 10 100 0.001 0 v dd = 5v r l = 4 ? f in = 200hz, 1khz f in = 10khz total harmonic distortion plus noise vs. output power MAX9759 toc11 output power (w) thd+n (%) 1.0 0.5 0.01 0.1 1 10 100 0.001 0 1.5 v dd = 3.3v r l = 4 ? f in = 200hz, 1khz f in = 10khz
MAX9759 3.2w, high efficiency, low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 7 total harmonic distortion plus noise vs. common-mode voltage MAX9759 toc24 common-mode voltage (v) thd+n (%) 3 2 1 0.01 0.1 1 10 100 0.001 04 v dd = 5v r l = 8 ? f in = 1khz p out = 300mw diff input v dd = 5v r l = 8 ? f in = 1khz p out = 300mw diff input v dd = 3.3v r l = 8 ? f in = 1khz p out = 300mw diff input t ypical operating characteristics (continued) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = v dd (ssm), unless otherwise noted. gain = 12db (g1 = 0, g2 = 1). thd+n measurement bandwidth: 22hz to 22khz. typical values are at t a = +25?.) (see typical operating circuit ) output power vs. supply voltage MAX9759 toc19 supply voltage (v) output power (w) 5.5 5.0 3.5 4.0 4.5 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 3.0 r l = 4 ? f in = 1khz thd+n = 10% thd+n = 1% output power vs. supply voltage MAX9759 toc20 supply voltage (v) output power (w) 5.5 5.0 4.5 4.0 3.5 0.5 1.0 1.5 2.0 2.5 0 3.0 r l = 8 ? f in = 1khz thd+n = 10% thd+n = 1% output power vs. load resistance MAX9759 toc21 load resistance ( ? ) output power (w) 10 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 1 100 v dd = 5v f in = 1khz 10% thd+n 1% thd+n output power vs. load resistance MAX9759 toc22 load resistance ( ? ) output power (w) 10 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 1 100 v dd = 3.3v f in = 1khz 10% thd+n 1% thd+n total harmonic distortion plus noise vs. common-mode voltage MAX9759 toc23 common-mode voltage (v) thd+n (%) 3 2 1 0.01 0.1 1 10 100 0.001 04 v dd = 5v r l = 8 ? f in = 1khz p out = 300mw diff input
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 8 _______________________________________________________________________________________ common-mode rejection ratio vs. frequency MAX9759 toc25 frequency (hz) cmrr (db) 10k 1k 100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -100 10 100k input referred v in = 200mv p-p power-supply rejection ratio vs. frequency MAX9759 toc26 frequency (hz) psrr (db) 10k 1k 100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -100 10 100k output referred inputs ac grounded t ypical operating characteristics (continued) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = v dd (ssm), unless otherwise noted. gain = 12db (g1 = 0, g2 = 1). thd+n measurement bandwidth: 22hz to 22khz. typical values are at t a = +25?.) (see typical operating circuit ) mute response MAX9759 toc32 20ms/div 5v 0v 500mv/div MAX9759 output mute f = 1khz r l = 8 ? shutdown response MAX9759 toc31 20ms/div 5v 0v 500mv/div MAX9759 output shdn f = 1khz r l = 8 ? output frequency spectrum MAX9759 toc28 frequency (hz) output magnitude (dbv) 15k 10k 5k -120 -100 -80 -60 -40 -20 0 -140 0 20k ssm mode v out = -60dbv f in = 1khz r l = 8 ? unweighted wideband output spectrum (ffm mode) MAX9759 toc29 frequency (hz) output amplitude (dbv) 100m 10m -50 -40 -30 -20 -10 0 10 20 30 40 -60 1m 1000m rbw = 10khz output frequency spectrum MAX9759 toc27 frequency (hz) output magnitude (dbv) 15k 10k 5k -120 -100 -80 -60 -40 -20 0 -140 0 20k ffm mode v out = -60dbv f in = 1khz r l = 8 ? unweighted wideband output spectrum (ssm mode) MAX9759 toc30 frequency (hz) output amplitude (dbv) 100m 10m -50 -40 -30 -20 -10 0 10 20 30 40 -60 1m 1000m rbw = 10khz
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 9 MAX9759 2 (8) 16 (6) 3 (9) 15 (5) 7 (13) 6, 14 (4, 12) 4 (10) ( ) tssop 1 f pgnd out+ out- pv dd pv dd gnd in+ v dd v dd 1 (7) 8 (14) in- sync uvlo/power management class d modulator pv dd 9, 12 (2, 15) 11 (1) 10 (16) click-and-pop suppression oscillator 10 f * 1 f 1 f mute 5 (11) shdn control v dd gnd r in r in g1 g2 bias note: typical operating circuit depicts MAX9759 in ffm mode with f s = 1400khz and +18db of gain. * bulk capacitance, if needed. sync_out 13 (3) r f r f t ypical operating circuit/functional diagram t ypical operating characteristics (continued) (v dd = pv dd = shdn = mute = 5v, gnd = pgnd = 0v, sync = v dd (ssm), unless otherwise noted. gain = 12db (g1 = 0, g2 = 1). thd+n measurement bandwidth: 22hz to 22khz. typical values are at t a = +25?.) (see typical operating circuit ) supply current vs. supply voltage MAX9759 toc33 supply voltage (v) supply current (ma) 5.5 5.0 4.5 4.0 3.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 4.5 3.0 ffm t a = +85 c t a = -40 c t a = +25 c shutdown supply current vs. supply voltage MAX9759 toc34 supply voltage (v) supply current ( a) 5.3 5.1 4.9 4.7 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20 0 4.5 5.5 t a = +85 c t a = +25 c t a = -40 c ffm package temperature vs. time MAX9759 toc35 time (s) package temperature ( c) 250 200 150 100 50 10 20 30 40 50 60 0 0 300 r l = 8 ? at 10% thd+n r l = 4 ? at 10% thd+n r l = 3 ? at 10% thd+n MAX9759evkit free air t a = +25 c f in = 1khz sine wave
detailed description operating modes the MAX9759 filterless, class d audio power amplifier features several improvements to switch-mode amplifier technology. the MAX9759 offers class ab performance with class d efficiency, while occupying minimal board space. a unique modulation scheme, synchronizable switching frequency, and ssm mode create a compact, flexible, low-noise, efficient audio power amplifier. the differential input architecture reduces common-mode noise pickup, and can be used without input-coupling capacitors. the device can also be configured as a sin- gle-ended input amplifier. comparators monitor the MAX9759 inputs and com- pare the complementary input voltages to the sawtooth waveform. the comparators trip when the input magni- tude 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, gener- ating a minimum-width pulse t on(min) at the output of the second comparator (figure 1). as the input voltage increases or decreases, the duration of the pulse at one output increases (the first comparator to trip) while the other output pulse duration remains at t on(min) . this causes the net voltage across the speaker (v out+ - v out- ) to change. fixed-frequency modulation (ffm) mode the MAX9759 features two ffm modes. the ffm modes are selected by setting sync = gnd for a 1.1mhz switching frequency, and sync = float for a 1.5mhz switching frequency. in ffm mode, the fre- quency spectrum of the class d output consists of the fundamental switching frequency and its associated harmonics (see the wideband fft graph in the typical operating characteristics ). the MAX9759 allows the switching frequency to be changed, should the fre- quency of one or more of the harmonics fall in a sensi- tive band. this can be done at any time and does not affect audio reproduction. MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 10 ______________________________________________________________________________________ pin description pin tqfn tssop name function 17v dd analog power supply. bypass to gnd with a 1? ceramic capacitor. 28 in+ noninverting audio input 39 in- inverting audio input 41 0 gnd analog ground 511 shdn active-low shutdown input. drive shdn low to shut down the MAX9759. connect to v dd for normal operation. 6, 14 4, 12 pgnd power ground 71 3 sync frequency select and external clock input: sync = gnd: fixed-frequency mode with f s = 1100khz. sync = float: fixed-frequency mode with f s = 1500khz. sync = v dd : spread-spectrum mode with f s = 1200khz 70khz. sync = clocked: fixed-frequency mode with f s = external clock frequency. 814 mute active-low mute function. drive mute low to disable the h-bridge outputs. connect to v dd for normal operation. 9, 12 2, 15 pv dd h-bridge power supply. bypass to pgnd with a 10? ceramic capacitor. 10 16 out- negative speaker output 11 1 out+ positive speaker output 13 3 sync_out internal clock output. connect sync_out to the clock input of cascaded maxim class d amplifiers. float sync_out if unused. 15 5 g2 gain control 2 (see the gain selection section) 16 6 g1 gain control 1 (see the gain selection section) ep ep ep exposed paddle. can be left floating or tied to gnd.
MAX9759 3.2w, high efficiency, low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 11 spread-spectrum modulation (ssm) mode the MAX9759 features a unique, patented spread-spec- trum mode that reduces peak component energy in the wideband spectrum, improving emi emissions that may be radiated by the speaker and cables by 5db. proprietary techniques ensure that the cycle-to-cycle variation of the switching period does not degrade audio reproduction or efficiency (see the typical operating characteristics ). select ssm mode by setting sync = v dd . in ssm mode, the switching frequency varies by ?0khz 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 ener- gy is now spread over a bandwidth that increases with frequency. above a few megahertz, the wideband spec- trum looks like white noise for emi purposes (figure 3). out+ out- v in- v in+ v out+ - v out- t on(min) t sw figure 1. MAX9759 outputs with an input signal applied sync input mode gnd ffm with f s = 1100khz float ffm with f s = 1500khz v dd ssm with f s = 1200khz 70khz clocked ffm with f s = external clock frequency table 1. operating modes
external synchronization the sync function allows the MAX9759 to allocate spectral components of the switching harmonics to insensitive frequency bands and facilitates synchroniza- tion to a system clock (allowing for a fully synchronous system). applying an external ttl clock of 1000khz to 1600khz to sync synchronizes the switching frequency of the MAX9759. the period of the sync clock can be randomized, enabling the MAX9759 to be synchronized to another MAX9759 operating in ssm mode. cascading amplifiers the sync_out function of the MAX9759 allows for multiple maxim class d amplifiers to be cascaded and frequency locked. synchronizing multiple class d amplifiers ensures that no beat frequencies within the audio spectrum occur on the power-supply rails. any intermodulation distortion due to the interference of several modulation frequencies is minimized as a result. leave the sync_out pin of the MAX9759 float- ing if the sync_out function is not applicable. filterless modulation/common-mode idle the MAX9759 uses maxim? unique, patented modula- tion scheme that eliminates the lc filter required by tra- ditional class d amplifiers, improving efficiency, reducing component count, and conserving board space and system cost. conventional class d amplifiers output a 50% duty-cycle square wave when no signal is present. with no filter, the square wave appears across the load as a dc voltage, resulting in finite load current, increasing power consumption. when no signal is pre- MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 12 ______________________________________________________________________________________ v out+ - v out- t sw t sw t sw t sw v in- v in+ out+ out- t on(min) figure 2. MAX9759 outputs with an input signal applied (ssm mode)
MAX9759 3.2w, high efficiency, low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 13 sent at the input of the MAX9759, the outputs switch as shown in figure 4. because the MAX9759 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle mode voltage across the speaker and minimal power consumption. efficiency efficiency of a class d amplifier is mostly associated with the region of operation of the output stage transis- tors. in a class d amplifier, the output transistors act as current-steering switches and consume negligible addi- tional power. any power loss associated with the class d output stage is mostly due to the i x 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 (i.e., typi- cal music reproduction levels), efficiency of a linear amplifier can fall below 30%. the MAX9759 class d amplifier still exhibits >90% efficiencies under the same conditions (figure 5). gain selection the MAX9759 features an internally set, logic-selec- table gain. the g1 and g2 logic inputs set the gain of the MAX9759 speaker amplifier (table 2). shutdown the MAX9759 features a shutdown mode that reduces power consumption and extends battery life. driving shdn low places the MAX9759 in a low-power (0.1?) shutdown mode. drive shdn high for normal operation. 30 60 80 100 120 140 160 180 280 300 220 200 240 260 15 20 25 30 35 40 45 50 amplitude (db v/m) frequency (mhz) MAX9759 output spectrum fcc limit figure 3. MAX9759 emi spectrum v in = 0v out- out+ v out+ - v out- = 0v figure 4. MAX9759 outputs with no input signal 0 30 20 10 50 40 90 80 70 60 100 0 0.2 0.4 0.8 1.2 0.6 1.0 efficiency vs. output power output power (w) efficiency (%) v dd = 5v f = 1khz r l = 8 ? class ab MAX9759 figure 5. MAX9759 efficiency vs. output power g2 g1 gain (db) 00 +24 01 +18 10 +12 11 +6 table 2. gain selection idle mode is a trademark of maxim integrated products, inc.
mute the MAX9759 features a mute function that disables the h-bridge outputs of the switching amplifier. the mute function only affects the power amplifiers of the MAX9759; it does not shut down the device. driving mute low places the MAX9759 in a disabled output mode. drive mute high for normal operation. click-and-pop suppression the MAX9759 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. for improved click-and-pop performance, sequence the digital inputs of the shdn and mute pins of the MAX9759 during power-up and power-down of the device such that transients are eliminated from each power cycle. apply power to the MAX9759 with both shdn and mute held low. release shdn before mute such that minimal transients occur during startup of the device. the mute function allows the MAX9759 to be powered up with the h-bridge outputs of the switching amplifier disabled. for power-down, sequence the power cycle such that the amplifier is muted first and subse- quently shut down before power is disconnected from the ic. this power cycle eliminates any audible transients on power-up and power-down of the MAX9759. applications information filterless operation traditional class d amplifiers require an output filter to recover the audio signal from the amplifier? output. the filters add cost, increase the solution size of the amplifi- er, and can decrease efficiency. the traditional pwm scheme uses large differential output swings (2 x v dd 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 MAX9759 does not require an output filter for the short speaker cable. the device relies on the inherent induc- tance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio com- ponent of the square-wave output. eliminating the output filter results in a smaller, less costly, more efficient solution. because the frequency of the MAX9759 output is well beyond the bandwidth of most speakers, voice coil movement due to the switching frequency is very small. although this movement is small, a speaker not designed to handle the additional power can be dam- aged. for optimum results, use a speaker with a series inductance > 10? to 100? range. power-conversion efficiency unlike a class ab amplifier, the output offset voltage of a class d amplifier does not noticeably increase quiescent current draw when a load is applied. this is due to the power conversion of the class d amplifier. for example, an 8mv dc offset across an 8 ? load results in 1ma extra current consumption in a class ab device. in the class d case, an 8mv offset into an 8 ? load equates to an addi- tional power drain of 8?. due to the high efficiency of the class d amplifier, this represents an additional quies- cent current draw of 8w/(v dd /100 ), which is on the order of a few microamps. input amplifier differential input the MAX9759 features a differential input structure, making it compatible with many codecs, and offers improved noise immunity over a single-ended input amplifier. high-frequency signals can be picked up by the amplifier? input traces and can appear at the amplifier? inputs as common-mode noise. a differential input amplifier amplifies the difference of the two inputs; any signal common to both inputs is cancelled. single-ended input the MAX9759 can be configured as a single-ended input amplifier by capacitively coupling one input to gnd while simultaneously driving the other input (figure 6). dc-coupled input the input amplifier can accept dc-coupled inputs that are biased within the amplifier? common-mode range (see the typical operating characteristics ). dc coupling eliminates the input-coupling capacitors, reducing com- ponent count to potentially one external component (see the system diagram ). however, the low-frequency rejec- tion of the capacitors is lost, allowing low-frequency sig- nals to feedthrough to the load. MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 14 ______________________________________________________________________________________ 1 f in+ in- 1 f single-ended audio input MAX9759 figure 6. single-ended input
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 15 component selection input filter an input capacitor, c in , in conjunction with the input impedance of the MAX9759 forms a highpass filter that removes the dc bias from an incoming signal. the ac- coupling capacitor allows the amplifier to bias the sig- nal to an optimum dc level. assuming zero source impedance, the -3db point of the highpass filter is given by: f -3db = 1/(2 r in c in ) choose c in such 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 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. in+ in- out+ out- sync_out right-channel differential audio input MAX9759 v dd v dd pv dd in+ in- out+ sync_out sync left-channel differential audio input MAX9759 v dd pv dd in+ in- out+ sync_out sync differential audio input MAX9759 v dd pv dd sync u1 u2 figure 7. master-slave configuration 100 0 0.5 1.0 1.5 2.0 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power output power (w) thd+n (%) v dd = 5.0v f = 1khz r l = 8 ? slave device figure 8. total harmonic distortion plus noise vs. output voltage -150 10 100 1k 100k crosstalk vs. frequency -130 -110 -90 -30 frequency (hz) crosstalk (db) -70 -50 10k v dd = 5v r l = 8 ? f = 1khz master to slave slave to master figure 9. crosstalk vs. frequency
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 16 ______________________________________________________________________________________ output filter the MAX9759 does not require an output filter for the short speaker cable. the device passes fcc emissions standards with 7.6cm of unshielded speaker cables. however, output filtering can be used if a design is fail- ing radiated emissions due to board layout, cable length, or the circuit? close proximity to emi-sensitive devices. use an lc filter when radiated emissions are a concern, or when long leads are used to connect the amplifier to the speaker. supply bypassing, layout, and grounding proper power-supply bypassing ensures low-distortion operation. for optimum performance, bypass v dd to gnd and pv dd to pgnd with separate 0.1? capaci- tors as close to each pin as possible. a low-imped- ance, 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. use wide, low-resistance output traces. as load imped- ance decreases, the current drawn from the device out- puts increase. at higher current, the resistance of the output traces decrease the power delivered to the load. wide output, supply, and gnd traces also improve the power dissipation of the device. the MAX9759 thin qfn package features an exposed thermal pad on its underside. this pad lowers the package? thermal resistance by providing a direct heat conduction path. due to the high efficiency of the MAX9759? class d amplifier, additional heatsinking is not required. if additional heatsinking is required, con- nect the exposed paddle to gnd. stereo configuration two MAX9759s can be configured as a stereo amplifier (figure 7). device u1 is the master amplifier; its oscilla- tor output, sync_out, drives the sync input of the slave device (u2), synchronizing the switching frequen- cies of the two devices. synchronizing two MAX9759s ensures that no beat frequencies within the audio spec- trum occur on the power-supply rails. this stereo con- figuration works when the master device is in either ffm or ssm mode. there is excellent thd+n perfor- mance and minimal crosstalk between devices due to the sync and sync_out connection (figures 8, 9). multiple MAX9759s can be cascaded and frequency locked in a similar fashion (figure 7). repeat the stereo configuration outlined in figure 7 for multiple cascading amplifier applications. volume control if volume control is required, connect a potentiometer between the differential inputs of the MAX9759, as seen in figure 10. in this configuration, each input ?ees identical rc paths when the device is powered up. the variable resistive element appears between the two inputs, meaning the setting affects both inputs the same way. this configuration significantly improves transient performance on power-up or release from shdn . MAX9759 in+ MAX9759 in- 1 f 1 f cw 22k ? 50k ? 22k ? figure 10. single-ended drive of MAX9759 plus volume control
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 17 system diagram MAX9759 v dd v dd v dd av dd 1 f out-r 8 ? speaker 1 f 1 f av ss in+ in- g2 g1 mute shdn pgnd av ss gnd pv dd v dd out+ out- sync sync_out MAX9759 v dd v dd 1 f center out 4 ? speaker 1 f 1 f av ss in+ in- g2 g1 mute shdn pgnd gnd pv dd v dd out+ out- sync sync sync_out MAX9759 v dd v dd 1 f out-l 8 ? speaker 1 f 1 f av ss in+ in- g2 g1 mute shdn pgnd gnd pv dd v dd out+ out- sync_out out-r eapd center out out-l 2.1 audio codec note: system diagram depicts MAX9759 in ssm mode with f s = 1200 70khz and +12db of gain.
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier 18 ______________________________________________________________________________________ MAX9759 1 out+ 2 pv dd 3 sync_out 4 pgnd 5 g2 6 g1 7 v dd 8 in+ 16 out- 15 pv dd 14 13 sync 12 pgnd 11 10 gnd 9 in- thin qfn tssop shdn mute top view MAX9759 13 14 15 12 34 5 6 16 12 11 10 9 8 7 pgnd sync_out g2 v dd in+ in- gnd out+ out- pv dd g1 sync mute pgnd shdn pv dd pin configurations chip information transistor count: 4219 process: bicmos
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 19 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 .) 24l qfn thin.eps package outline, 21-0139 2 1 d 12, 16, 20, 24, 28l thin qfn, 4x4x0.8mm package outline, 21-0139 2 2 d 12, 16, 20, 24, 28l thin qfn, 4x4x0.8mm
MAX9759 3.2w, high-efficiency, low-emi, filterless, class d audio 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. 20 ____________________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. MAX9759 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 .) tssop4.40mm.eps package outline, tssop 4.40mm body 21-0066 1 1 g

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