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general description the MAX9705 3rd-generation, ultra-low emi, mono, class d audio power amplifier provides class ab performance with class d efficiency. the MAX9705 delivers 2.3w into a 4 ? load and offers efficiencies above 85%. active emissions limiting (ael) circuitry greatly reduces emi by actively controlling the output fet gate transitions under all possible transient output-voltage conditions. ael pre- vents high-frequency emissions resulting from conven- tional class d free-wheeling behavior in the presence of an inductive load. zero dead time (zdt) technology maintains state-of-the-art efficiency and thd+n perfor- mance by allowing the output fets to switch simultane- ously without cross-conduction. a patented spread- spectrum modulation scheme eliminates the need for out- put filtering found in traditional class d devices. these design concepts reduce an application? component count and extend battery life. the MAX9705 offers two modulation schemes: a fixed- frequency (ffm) mode and a spread-spectrum (ssm) mode that further reduces emi-radiated emissions due to the modulation frequency. the MAX9705 oscillator can be synchronized to an external clock through the sync input, allowing the switching frequency to be externally defined. the sync input also allows multiple MAX9705s to be cascaded and frequency locked, minimizing inter- ference due to clock intermodulation. the device utilizes a fully differential architecture, a full-bridged output, and comprehensive click-and-pop suppression. the gain of the MAX9705 is set internally (MAX9705a: 6db, MAX9705b: 12db, MAX9705c: 15.6db, MAX9705d: 20db), further reducing external component count. the MAX9705 is available in 10-pin tdfn (3mm x 3mm x 0.8mm), and 12-bump ucsp (1.5mm x 2mm x 0.6mm) packages. the MAX9705 is specified over the extended -40? to +85? temperature range. applications features filterless amplifier passes fcc-radiated emissions standards with 24in of cable unique spread-spectrum mode and active emissions limiting (ael) achieves better than 20db margin under fcc limits zero dead time (zdt) h-bridge maintains state- of-the-art efficiency and thd+n simple master-slave setup for stereo operation up to 90% efficiency 2.3w into 4? (1% thd+n) low 0.02% thd+n (p out = 1w, v dd = 5.0v) high psrr (75db at 217hz) integrated click-and-pop suppression low quiescent current (5.4ma) low-power shutdown mode (0.3 a) short-circuit and thermal-overload protection available in thermally efficient, space-saving packages 10-pin tdfn (3mm x 3mm x 0.8mm) 12-bump ucsp (1.5mm x 2mm x 0.6mm) pin-for-pin compatible with the max9700 and max9712 MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier ________________________________________________________________ maxim integrated products 1 ordering information 19-3405; rev 3; 5/09 evaluation kit available cellular phones pdas mp3 players portable audio part temp range pin- package top mark MAX9705aetb+t -40 o c to +85 o c 10 tdfn acy MAX9705aebc+t -40 o c to +85 o c 12 ucsp ach MAX9705betb+t -40 o c to +85 o c 10 tdfn acx MAX9705bebc+t -40 o c to +85 o c 12 ucsp acg ordering information continued at end of data sheet. ucsp is a trademark of maxim integrated products, inc. + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel. selector guide appears at end of data sheet. 30.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 frequency (mhz) amplitude (db v/m) fcc emi limit maxim's new ultra-low output spectrum emi spectrum diagram for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim's website at www.maxim-ic.com.
2.3w, ultra-low-emi, filterless, class d audio amplifier 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics ( v dd = pv dd = v shdn = 3.3v , v gnd = v pgnd = 0, sync = gnd (ffm), r l = , r l connected between out+ and out-, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (notes 1, 2) 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 pv dd to v dd ..........................................................-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_........?00ma continuous input current (all other pins) .........................?0ma duration of out_ short circuit to gnd or pv dd ........continuous duration of short circuit between out+ and out-.....continuous continuous power dissipation (t a = +70?) 10-pin tdfn (derate 24.4mw/? above +70?) .....1951.2mw 12-bump ucsp (derate 6.1mw/? above +70?)........484mw junction temperature ......................................................+150? operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? bump temperature (soldering) reflow ..........................................................................+235? MAX9705 parameter symbol conditions min typ max units general supply voltage range v dd inferred from psrr test 2.5 5.5 v quiescent current i dd 5.4 7 ma shutdown current i shdn 0.3 10 ? turn-on time t on 30 ms input resistance r in t a = +25? 12 20 k ? MAX9705a 0.88 1.0 1.12 MAX9705b 0.73 0.83 0.93 MAX9705c 0.61 0.71 0.81 input bias voltage v bias either input MAX9705d 0.48 0.56 0.64 v MAX9705a 1.9 2.0 2.1 MAX9705b 3.8 4.0 4.2 MAX9705c 5.7 6.0 6.3 voltage gain a v MAX9705d 9.5 10 10.5 v/v output offset voltage v os t a = +25? 10 ?9 mv common-mode rejection ratio cmrr f in = 1khz, input referred 56 db v dd = 2.5v to 5.5v, t a = +25? 50 75 f ripple = 217hz 75 power-supply rejection ratio (note 3) psrr 200mv p-p ripple f ripple = 20khz 60 db r l = 8 ? 600 output power p out thd+n = 1%, f in = 1khz r l = 4 ? MAX9705_etb+t and MAX9705_eub+ only 950 mw r l = 8 ? , p out = 450mw 0.02 total harmonic distortion plus noise thd+n f in = 1khz, either ffm or ssm r l = 4 ? , p out = 375mw 0.025 % into shutdown -68 click/pop level k cp peak voltage, a-weighted (notes 3, 4) out of shutdown -60.5 db output slew rate sr 176 v/?
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 3 electrical characteristics (continued) ( v dd = pv dd = v shdn = 3.3v , v gnd = v pgnd = 0, sync = gnd (ffm), r l = , r l connected between out+ and out-, t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (notes 1, 2) 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?. for r l = 16 ? , l = 136?. note 3: inputs ac-coupled to gnd. note 4: testing performed with 8 ? resistive load in series with 68? inductive load connected across btl output. mode transitions are controlled by shdn pin. k cp level is calculated as 20 x log[(peak voltage under normal operation at rated power level)/(peak voltage during mode transition, no input signal)]. units are expressed in db. note 5: sync has a 1m ? resistor to v ref = 1.25v. parameter symbol conditions min typ max units rise/fall time t rise , t fall 10% to 90% 15 ns ffm 91 bw = 22hz to 22khz ssm 89 ffm 93 signal-to-noise ratio snr v out = 2v rms a-weighted ssm 91 db sync = gnd 980 1100 1220 oscillator frequency f osc sync = v dd (ssm mode) 1220 120 khz sync frequency lock range 800 2000 khz efficiency p out = 800mw, f in = 1khz, r l = 8 ? 89 % digital inputs ( shdn , sync) v ih 2 input thresholds v il 0.8 v shdn input leakage current 0.1 10 ? sync input current (note 5) -1.25 10 ? electrical characteristics ( v dd = pv dd = v shdn = 5v , v gnd = v pgnd = 0, sync = gnd (ffm), r l = , r l connected between out+ and out-, 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 7ma shutdown current i shdn 0.55 ? f = 217hz 75 power-supply rejection ratio psrr 200mv p-p ripple f = 20khz 60 db r l = 16 ? 750 r l = 8 ? 1400 output power p out thd+n = 1%, f = 1khz r l = 4 ? MAX9705_etb+t and MAX9705_eub+ only 2300 mw r l = 8 ? , p out = 1.0w 0.02 total harmonic distortion plus noise thd+n f = 1khz, either ffm or ssm r l = 4 ? , p out = 1.75w 0.05 % ffm 94 bw = 22hz to 22khz ssm 91 ffm 97 signal-to-noise ratio snr v out = 3v rms a-weighted ssm 93 db
100 0 0.5 1.0 1.5 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power MAX9705toc04 output power (w) thd+n (%) v dd = 3.3v r l = 4 ? f in = 1khz 100 01.0 0.5 2.0 1.5 2.5 3.0 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power MAX9705toc05 output power (w) thd+n (%) f in = 1khz v dd = 5.0v r l = 4 ? 100 0 0.4 0.2 0.8 0.6 1.0 1.2 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power MAX9705toc06 output power (w) thd+n (%) v dd = 3.3v r l = 8 ? f in = 1khz ffm ssm 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc07 frequency (hz) thd+n (%) 1k v dd = 3.3v r l = 8 ? p out = 100mw p out = 450mw 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc08 frequency (hz) thd+n (%) 1k v dd = 5.0v r l = 8 ? p out = 250mw p out = 1w 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc09 frequency (hz) thd+n (%) 1k v dd = 2.5v r l = 4 ? p out = 50mw p out = 300mw MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 4 _______________________________________________________________________________________ typical operating characteristics (v dd = 3.3v, sync = v dd (ssm), differential input, t a = +25?, unless otherwise noted. typical operating characteristics for 4 ? load condition apply to the MAX9705_etb+t only.) 100 0 0.4 0.8 1.0 0.2 0.6 1.2 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power MAX9705toc01 output power (w) thd+n (%) f in = 1khz v dd = 3.3v r l = 8 ? 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 MAX9705toc02 output power (w) thd+n (%) f in = 1khz v dd = 5.0v r l = 8 ? 100 0 0.2 0.4 0.6 0.8 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power MAX9705toc03 output power (w) thd+n (%) f in = 1khz v dd = 2.5v r l = 4 ?
MAX9705 typical operating characteristics (continued) (v dd = 3.3v, sync = v dd (ssm), differential input, t a = +25?, unless otherwise noted. typical operating characteristics for 4 ? load condition apply to the MAX9705_etb+t only.) 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc10 frequency (hz) thd+n (%) 1k v dd = 3.3v r l = 4 ? p out = 100mw p out = 800mw 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc11 frequency (hz) thd+n (%) 1k v dd = 5.0v r l = 4 ? p out = 250mw p out = 1.75w 100 0.01 10 100 10k 100k total harmonic distortion plus noise vs. frequency 0.1 1 10 MAX9705toc12 frequency (hz) thd+n (%) 1k v dd = 3.3v r l = 8 ? p out = 450mw ffm ssm 2.3w, ultra-low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 5 100 0 0.5 1.5 1.0 2.0 2.5 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. common-mode voltage MAX9705toc13 common-mode voltage (v) thd+n (%) v dd = 3.3v to 5v f in = 1khz p out = 500mw gain = 6db r l = 8 ? 0 30 20 10 40 50 60 70 80 90 100 0 0.4 0.2 0.6 0.8 1.0 efficiency vs. output power MAX9705toc14 output power (w) efficiency (%) v dd = 3.3v f in = 1khz r l = 8 ? r l = 4 ? 0 30 20 10 40 50 60 70 80 90 100 0 1.0 0.5 1.5 2.0 2.5 3.0 efficiency vs. output power MAX9705toc15 output power (w) efficiency (%) v dd = 5.0v f in = 1khz r l = 8 ? r l = 4 ? 0 30 20 10 40 50 60 70 80 90 100 2.5 3.5 3.0 4.0 4.5 5.0 5.5 efficiency vs. supply voltage MAX9705toc16 supply voltage (v) efficiency (%) f in = 1khz thd+n = 1% r l = 8 ? r l = 4 ? 0 30 20 10 40 50 60 70 80 90 100 800 1200 1000 1400 1600 1800 2000 efficiency vs. sync frequency MAX9705toc17 sync frequency (khz) efficiency (%) v dd = 3.3v f in = 1khz thd+n = 1% r l = 8 ? r l = 4 ? 0 30 20 10 40 50 60 70 80 90 100 800 1200 1000 1400 1600 1800 2000 efficiency vs. sync frequency MAX9705toc18 sync frequency (khz) efficiency (%) v dd = 5.0v f in = 1khz thd+n = 1% r l = 8 ? r l = 4 ?
-140 -120 -100 -80 -60 -40 -20 0 20 0 5 10 15 20 spread-spectrum-mode output spectrum vs. frequency MAX9705 toc25 frequency (khz) amplitude (dbv) r l = 8 ? v dd = 5.0v f in = 1khz a-weighted MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 6 _______________________________________________________________________________________ 0 0.6 0.4 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.5 3.5 3.0 4.0 4.5 5.0 5.5 output power vs. supply voltage MAX9705toc19 supply voltage (v) output power (w) f in = 1khz r l = 8 ? thd+n = 1% thd+n = 10% 0 1.5 1.0 0.5 2.0 2.5 3.0 3.5 2.5 3.5 3.0 4.0 4.5 5.0 5.5 output power vs. supply voltage MAX9705toc20 supply voltage (v) output power (w) f in = 1khz r l = 4 ? thd+n = 1% thd+n = 10% 4.0 0 1 100 1000 output power vs. load resistance 1.5 1.0 3.0 2.0 3.5 0.5 2.5 MAX9705 toc21 load resistance ( ? ) output power (w) 10 f in = 1khz z load = 33 h in series with r l thd+n = 1% 3.3v 5.0v 0 -10 -100 10 100 10k 100k power-supply rejection ratio vs. frequency -90 -50 -70 -80 -40 -60 -20 -30 MAX9705 toc22 frequency (hz) psrr (db) 1k v dd = 3.3v v in = 200mv p-p r l = 8 ? -140 -120 -100 -80 -60 -40 -20 0 20 0 5 10 15 20 fixed-frequency-mode output spectrum vs. frequency MAX9705 toc23 frequency (khz) amplitude (dbv) r l = 8 ? v dd = 5.0v f in = 1khz bw = 22hz to 22khz -140 -120 -100 -80 -60 -40 -20 0 20 0 5 10 15 20 spread-spectrum-mode output spectrum vs. frequency MAX9705 toc24 frequency (khz) amplitude (dbv) r l = 8 ? v dd = 5.0v f in = 1khz bw = 22hz to 22khz typical operating characteristics (continued) (v dd = 3.3v, sync = v dd (ssm), differential input, t a = +25?, unless otherwise noted. typical operating characteristics for 4 ? load condition apply to the MAX9705_etb+t only.)
MAX9705 0 -140 0 100 1000 wideband output spectrum fixed-frequency mode -80 -100 -20 -60 -120 -40 MAX9705 toc26 frequency (mhz) amplitude (dbv) 10 r l = 8 ? v dd = 5.0v inputs ac grounded 0 -140 0 100 1000 wideband output spectrum spread-spectrum mode -80 -100 -20 -60 -120 -40 MAX9705 toc27 frequency (mhz) amplitude (dbv) 10 r l = 8 ? v dd = 5.0v inputs ac grounded 2.3w, ultra-low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 7 4 5 6 7 8 9 10 2.5 3.5 4.5 5.5 supply current vs. supply voltage MAX9705 toc28 supply voltage (v) supply current (ma) sync = v dd (ssm) sync = gnd (ffm) no load inputs ac grounded 5.00 5.25 5.50 5.75 6.25 6.00 6.50 6.75 7.00 -40 -15 10 35 60 85 supply current vs. temperature MAX9705 toc29 temperature ( c) supply current (ma) sync = v dd (ssm) sync = gnd (ffm)) v dd = 3.3v no load inputs ac grounded 0 0.10 0.20 0.30 0.50 0.40 0.60 0.80 0.70 0.90 1.00 2.5 3.0 3.5 4.0 4.5 5.0 5.5 shutdown current vs. supply voltage MAX9705 toc30 supply voltage (v) shutdown current ( a) t a = +25 c t a = +85 c t a = -40 c no load inputs ac grounded shdn = gnd turn-on/turn-off response MAX9705 toc31 MAX9705 output shdn 0v 250mv/div 3v 10ms/div f = 1khz r l = 8 ? typical operating characteristics (continued) (v dd = 3.3v, sync = v dd (ssm), differential input, t a = +25?, unless otherwise noted. typical operating characteristics for 4 ? load condition apply to the MAX9705_etb+t only.)
functional diagram MAX9705 2 (b1) 5 (b2) 3 (c1) 7 (b3) ( ) ucsp bump. figure shows MAX9705 configured for spread-spectrum operation. 1 f pgnd out+ out- pv dd pgnd pgnd pv dd 4 (c2) gnd in+ v dd 2.5v to 5.5v 1 (a1) shdn in- uvlo/power management class d modulator pv dd sync 10 (b4) 6 (a3) 8 (a4) 9 (c4) click-and-pop suppression oscillator 1 f 1 f low-emi driver low-emi driver MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 8 _______________________________________________________________________________________
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier _______________________________________________________________________________________ 9 detailed description the MAX9705 ultra-low-emi, filterless, class d audio power amplifier features several improvements to switch- mode amplifier technology. the MAX9705 features output driver active emissions limiting circuitry to reduce emi. zero dead time technology maintains state-of-the-art effi- ciency and thd+n performance by allowing the output fets to switch simultaneously without cross-conduction. a unique filterless modulation scheme, synchronizable switching frequency, and spread-spectrum mode create a compact, flexible, low-noise, efficient audio power amplifier while occupying minimal board space. the dif- ferential input architecture reduces common-mode noise pickup with or without the use of input-coupling capaci- tors. the MAX9705 can also be configured as a single- ended input amplifier without performance degradation. thermal-overload and short-circuit protection prevent the MAX9705 from being damaged during a fault condition. the amplifier is disabled if the die temperature reaches +125?. the die must cool by 10? before normal opera- tion can continue. the output of the MAX9705 shuts down if the output current reaches approximately 2a. each out- put fet has its own short-circuit protection. this protec- tion scheme allows the amplifier to survive shorts to either supply rail. after a thermal overload or short circuit, the device remains disabled for a minimum of 50? before attempting to return to normal operation. the amplifier will shut down immediately and wait another 50? before turn- ing on if the fault condition is still present. this operation will cause the output to pulse during a persistent fault. comparators monitor the MAX9705 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. operating modes fixed-frequency modulation (ffm) mode the ffm mode is selected by setting sync = gnd for a 1.1mhz switching frequency. in ffm mode, the frequen- cy spectrum of the class d output consists of the funda- mental switching frequency and its associated harmonics (see the wideband output spectrum fixed- frequency mode graph in the typical operating characteristics ). pin description pin bump tdfn ucsp name function 1a1v dd analog power supply 2 b1 in+ noninverting audio input 3 c1 in- inverting audio input 4 c2 gnd analog ground 5b2 shdn active-low shutdown input. connect to v dd for normal operation. 6 a3 sync frequency select and external clock input. sync = gnd: fixed-frequency mode with f s = 1100khz. sync = v dd : spread-spectrum mode with f s = 1220khz 120khz. sync = clocked: fixed-frequency mode with f s = external clock frequency. 7 b3 pgnd power ground 8 a4 out+ amplifier-output positive phase 9 c4 out- amplifier-output negative phase 10 b4 pv dd h-bridge power supply ep exposed pad. internally connected to ground. connect to a large ground plane to maximize thermal performance. not intended as an electrical connection point (tdfn only).
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 10 ______________________________________________________________________________________ spread-spectrum modulation (ssm) mode the MAX9705 features a unique, patented spread-spec- trum mode that flattens the wideband spectral components, improving emi emissions 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 switch- ing frequency varies randomly by ?20khz around the center frequency (1.22mhz). the modulation scheme remains the same, but the period of the sawtooth wave- form changes from cycle to cycle (figure 2). instead of a large amount of spectral energy present at multiples of the switching frequency, the energy is now spread over a bandwidth that increases with frequency. above a few megahertz, the wideband spectrum looks like white noise for emi purposes (see the emi spectrum diagram ). external clock mode the sync input allows the MAX9705 to be synchronized to a system clock moving the spectral components of the switching harmonics to insensitive frequency bands. applying an external ttl clock of 800khz to 2mhz to sync synchronizes the switching frequency of the MAX9705. the period of the sync clock can be ran- domized, enabling the MAX9705 to be synchronized to another MAX9705 operating in ssm mode. figure 1. MAX9705 outputs with an input signal applied out+ out- v in- v in+ v out+ - v out- t on(min) t sw sync input mode gnd ffm with f s = 1100khz v dd ssm with f s = 1220khz 120khz clocked ffm with f s = external clock frequency table 1. operating modes
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 11 filterless modulation/common-mode idle the MAX9705 uses maxim? unique, patented modula- tion scheme that eliminates the lc filter required by traditional 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 a finite load cur- rent, increasing power consumption. when no signal is present at the input of the MAX9705, the outputs switch as shown in figure 3. because the MAX9705 drives the speaker differentially, the two outputs cancel each other, resulting in no net idle-mode voltage across the speak- er, minimizing power consumption. 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 supply current. 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 MAX9705 still exhibits >70% efficiencies under the same conditions (figure 4). shutdown the MAX9705 has a shutdown mode that reduces power consumption and extends battery life. driving shdn low places the MAX9705 in a low-power (0.3?) shutdown mode. connect shdn to v dd for normal operation. figure 2. MAX9705 output with an input signal applied (ssm mode) v out+ - v out- t sw t sw t sw t sw v in- v in+ out+ out- t on(min)
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 12 ______________________________________________________________________________________ click-and-pop suppression the MAX9705 features comprehensive click-and-pop suppression that eliminates audible transients on start- up 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, pre- venting clicks and pops when the h-bridge is subse- quently enabled. for 30ms following startup, a soft-start function gradually unmutes the input amplifiers. 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 and thd+n perfor- mance. 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, lower- ing the efficiency. the MAX9705 does not require an output filter. the device relies on the inherent inductance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component of the square-wave output. eliminating the output filter results in a smaller, less costly, more efficient solution. because the frequency of the MAX9705 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 dam- aged. for optimum results, use a speaker with a series inductance >10?. typical 8 ? speakers exhibit series inductances in the 20? to 100? range. power-conversion efficiency unlike a class ab amplifier, the output offset voltage of a class d amplifier does not noticeably increase quies- cent-current draw when a load is applied. this is due to the power conversion of the class d amplifier. for exam- ple, 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 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 8?/(v dd /100 ), which is on the order of a few microamps. input amplifier differential input the MAX9705 features a differential input structure, making it compatible with many codecs, and offering improved noise immunity over a single-ended input amplifier. in devices such as cellular phones, high-fre- quency signals from the rf transmitter can be picked up by the amplifier? input traces. the signals appear at the amplifier? inputs as common-mode noise. a differ- ential input amplifier amplifies the difference of the two inputs; any signal common to both inputs is canceled. single-ended input the MAX9705 can be configured as a single-ended input amplifier by capacitively coupling either input to gnd and driving the other input (figure 5). figure 3. MAX9705 outputs with no input signal v in = 0v out- out+ v out+ - v out- = 0v figure 4. MAX9705 efficiency vs. class ab efficiency efficiency vs. output power output power (w) efficiency (%) 0.8 0.6 0.4 0.2 10 20 30 40 50 60 70 80 90 100 0 01.0 v dd = 3.3v f in = 1khz r l = 8 ? class ab MAX9705
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 13 note that the single-ended voltage range of the MAX9705a is 3v p-p . this limits the achievable output power for this device. use higher gain versions (MAX9705b, MAX9705c, MAX9705d) if higher output power is desired in a single-ended application. 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 cou- pling eliminates the input-coupling capacitors, reduc- ing component count to potentially one external component (see the system diagram ). however, the low-frequency rejection of the capacitors is lost, allow- ing low-frequency signals to feed through to the load. component selection input filter an input capacitor, c in , in conjunction with the input resistance of the MAX9705 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: choose c in so f -3db is well below the lowest frequency of interest. setting f -3db too high affects the low- frequency response of the amplifier. use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies. if a ceramic capacitor is selected due to size constraints, use the largest package possible to minimize voltage coeffi- cient effects. in addition, use x7r dielectrics as opposed to y5v or z5u. other considerations when designing the input filter include the constraints of the overall system and the actual frequency band of interest. although high-fidelity audio calls for a flat gain response between 20hz and 20khz, portable voice-reproduction devices such as cellular phones and two-way radios need only concen- trate on the frequency range of the spoken human voice (typically 300hz to 3.5khz). in addition, speakers used in portable devices typically have a poor response below 150hz. taking these two factors into considera- tion, the input filter may not need to be designed for a 20hz to 20khz response, saving both board space and cost due to the use of smaller capacitors. output filter the MAX9705 does not require an output filter. the device passes fcc emissions standards with 24in of unshielded twisted-pair speaker cables. however, an output filter can be used if a design is failing radiated emissions due to board layout or excessive cable length, or the circuit is near emi-sensitive devices. supply bypassing/layout proper power-supply bypassing ensures low-distortion operation. for optimum performance, bypass v dd to gnd and pv dd to pgnd with separate 1? capacitors as close to each 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. refer to the MAX9705 evaluation kit for layout guidance. stereo configuration two MAX9705s can be configured as a stereo amplifier (figure 6). device u1 is the master amplifier; its unfil- tered output drives the sync input of the slave device (u2), synchronizing the switching frequencies of the two devices. synchronizing two MAX9705s ensures that no beat frequencies occur within the audio spectrum. this configuration works when the master device is in either ffm or ssm mode. there is excellent thd+n perfor- mance and minimal crosstalk between devices due to the sync connection (figures 7 and 8). u2 locks onto only the frequency present at sync, not the pulse width. the internal feedback loop of device u2 ensures that the audio component of u1? output is rejected. f rc db in in ? = 3 1 2 figure 5. single-ended input 1 f in+ in- 1 f single-ended audio input MAX9705
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier figure 6. master-slave stereo configuration in+ in- out+ out- sync 1 f right-channel differential audio input MAX9705 v dd v dd pv dd in+ in- out+ out- sync 1 f left-channel differential audio input MAX9705 v dd pv dd figure 7. master-slave thd+n total harmonic distortion plus noise vs. output power output power (w) thd+n (%) 0.6 0.4 0.2 0.01 0.1 1 10 100 0.001 00.8 v dd = 3.3v slave device f in = 1khz sync = gnd (ffm) r l = 8 ? crosstalk vs. frequency frequency (hz) crosstalk (db) 10k 1k 100 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -110 10 100k v dd = 3.3v v in = 500mv p-p f in = 1khz sync = gnd (ffm) r l = 8 ? master to slave slave to master figure 8. master-slave crosstalk 14 ______________________________________________________________________________________
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 15 figure 9a. single-ended drive of MAX9705 plus volume in+ 1 f 1 f MAX9705 in- cw 50k ? in+ MAX9705 in- 1 f 1 f cw 22k ? 50k ? 22k ? figure 9b. improved single-ended drive of MAX9705 plus volume ordering information (continued) part temp range pin- package top mark MAX9705cetb+t -40 o c to +85 o c 10 tdfn acz MAX9705cebc+t -40 o c to +85 o c 12 ucsp aci MAX9705detb+t -40 o c to +85 o c 10 tdfn ada MAX9705debc+t -40 o c to +85 o c 12 ucsp acj selector guide part pin-package gain (db) MAX9705aetb+t 10 tdfn 6 MAX9705aebc+t 12 ucsp 6 MAX9705betb+t 10 tdfn 12 MAX9705bebc+t 12 ucsp 12 MAX9705cetb+t 10 tdfn 15.6 MAX9705cebc+t 12 ucsp 15.6 MAX9705detb+t 10 tdfn 20 MAX9705debc+t 12 ucsp 20 + MAX9705 top view top view (bump side down) ucsp sync out+ v dd 1 a b c 234 in- out- gnd in+ shdn pv dd pgnd 1234 5 10987 6 pv dd out+ pgnd v dd in- gnd MAX9705 out- in+ sync shdn tdfn pin configurations + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel.
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier 16 ______________________________________________________________________________________ max4063 MAX9705 max9722 codec/ baseband processor aux_in bias in+ in- out in+ v dd out+ out- inl inr c1p cin sv ss pv ss outr outl v dd v dd 0.1 f 0.1 f 0.1 f 2.2k ? 2.2k ? v dd v dd controller in- pv dd sync out 1 f 1 f 1 f 1 f 1 f 1 f shdn shdn system diagram
MAX9705 2.3w, ultra-low-emi, filterless, class d audio amplifier ______________________________________________________________________________________ 17 chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a "+", "#", or "-" in the package code indicates rohs status only. package draw- ings may show a different suffix character, but the drawing per- tains to the package regardless of rohs status. package type package code document no. 10 tdfn t1033-1 21-0137 12 ucsp b12-11 21-0104
MAX9705 2.3w, ultra-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. 18 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 2 8/08 removed ?ax package option 1?, 9, 10, 15 3 5/09 removed sync unconnected mode 3, 7, 9, 10, 14

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