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directdrive outputs eliminate dc-blocking capacitors. c1n c1p outl single 1.5v cell aa or aaa battery outr sgnd pgnd max9725a?ax9725d inverting charge pump inr inl v dd pv ss c2 v ss c3 general description the max9725a?ax9725d fixed-gain, stereo head- phone amplifiers are ideal for portable equipment where board space is at a premium. the max9725e offers the flexibility to adjust the gain with external input and feed- back resistors. the max9725a?ax9725e use a unique directdrive architecture to produce a ground-referenced output from a single supply, eliminating the need for large dc-blocking capacitors, saving cost, board space, and component height. fixed gains of -2v/v (max9725a), -1.5v/v (max9725b), -1v/v (max9725c), and -4v/v (max9725d) further reduce external component count. the adjustable gain of the max9725e directdrive head- phone amplifier allows for any gain down to -1v/v using external resistors. the max9725 delivers up to 20mw per channel into a 32 load and achieves 0.006% thd+n. an 80db at 1khz power-supply rejection ratio (psrr) allows the max9725 to operate from noisy digital supplies without an additional linear regulator. the max9725 includes 8kv esd protec- tion on the headphone output. comprehensive click-and- pop circuitry suppresses audible clicks and pops at startup and shutdown. a low-power shutdown mode reduces supply current to 0.6? (typ). the max9725 operates from a single 0.9v to 1.8v supply, allowing the device to be powered directly from a single aa or aaa battery. the max9725 consumes only 2.1ma of supply current, provides short-circuit protection, and is specified over the extended -40c to +85? tem- perature range. the max9725 is available in a tiny (1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale package (ucsp) and a 12-pin thin qfn package (4mm x 4mm x 0.8mm). applications features ? low quiescent current 2.1ma (max9725a?ax9725d) 2.3ma (max9725e) ? single-cell, 0.9v to 1.8v single-supply operation ? fixed gain eliminates external feedback network max9725a: -2v/v max9725b: -1.5v/v max9725c: -1v/v max9725d: -4v/v ? adjustable gain with external input and feedback resistors max9725e: minimum stable gain of -1v/v ? ground-referenced outputs eliminate dc bias ? no degradation of low-frequency response due to output capacitors ? 20mw per channel into 32 ? low 0.006% thd+n ? high psrr (80db at 1khz) ? integrated click-and-pop suppression ? low-power shutdown control ? short-circuit protection ? 8kv esd-protected amplifier outputs ? available in space-saving packages 12-bump ucsp (1.54mm x 2.02mm x 0.6mm) 12-pin thin qfn (4mm x 4mm x 0.8mm) max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown ________________________________________________________________ maxim integrated products 1 19-3465; rev 4; 3/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available ordering information pa rt pin- pa ck a g e t o p m a rk g a in ( v/v) max9725aebc +tg45 12 u c s p+ ack - 2 m ax9725ae tc+ 12 tqfn- ep* + aae w - 2 max9725bebc +tg45 12 u c s p+ acl - 1.5 ucsp is a trademark of maxim integrated products, inc. ordering information continued at end of data sheet. note: all devices are specified over the -40? to +85? operating temperature range. + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel. * ep = exposed pad. pin configurations appear at end of data sheet. block diagrams continued at end of data sheet. mp3 players cellular phones pdas smart phones portable audio equipment block diagrams
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 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. sgnd to pgnd .....................................................-0.3v to +0.3v v dd to sgnd or pgnd ............................................-0.3v to +2v v ss to pv ss ...........................................................-0.3v to +0.3v c1p to pgnd..............................................-0.3v to (v dd + 0.3v) c1n to pgnd............................................(pv ss - 0.3v) to +0.3v v ss , pv ss to gnd ....................................................+0.3v to -2v outr, outl, inr, inl to sgnd (max9725a?ax9725d)..............(v ss - 0.3v) to (v dd + 0.3v) outr, outl to sgnd (max9725e) ..................................(v ss - 0.3v) to (v dd + 0.3v) inr, inl to sgnd (max9725e)...................................-4v to +4v shdn to sgnd or pgnd .........................................-0.3v to +4v output short-circuit current ......................................continuous continuous power dissipation (t a = +70 c) 12-bump ucsp (derate 6.5mw/ c above +70 c)....518.8mw 12-pin thin qfn (derate 16.9mw/ c above +70 c) ..1349.1mw junction temperature ......................................................+150 c operating temperature range ...........................-40 c to +85 c storage temperature range .............................-65 c to +150 c bump temperature (soldering) reflow............................+230 c lead temperature (soldering, 10s) .................................+300 c electrical characteristics (max9725aCmax9725d) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss , c1 = c2 = 1?, c in = 1?, r l = , t a = t min to t max, unless other- wise noted. typical values are at t a = +25 c.) (see the functional diagrams. ) (note 1) parameter symbol conditions min typ max units supply voltage range v dd guaranteed by psrr test 0.9 1.8 v quiescent supply current i dd both channels active 2.1 3.3 ma t a = +25 c 0.6 10 shutdown current i shdn v shdn = 0v t a = -40 c to +85 c30 ? shutdown to full operation t on 180 ? v ih v dd = 0.9v to 1.8v 0.7 x v dd shdn thresholds v il v dd = 0.9v to 1.8v 0.3 x v dd v shdn input leakage current i leak v dd = 0.9v to 1.8v (note 2) 1a charge pump oscillator frequency f osc 493 580 667 khz amplifiers max9725a -2.04 -2.00 -1.96 max9725b -1.53 -1.5 -1.47 max9725c -1.02 -1.00 -0.98 voltage gain a v max9725d -4.08 -4.00 -3.92 v/v gain match a v ?.5 % max9725a/max9725d ?.3 ?.05 max9725b ?.45 ?.58 total output offset voltage v os input ac-coupled, r l = 32 to gnd, t a = +25 c max9725c ?.6 ?.1 mv input resistance r in 15 25 35 k v dd = 0.9v to 1.8v, t a = +25 c6080 f in = 1khz 70 power-supply rejection ratio psrr 100mv p-p ripple f in = 20khz 62 db r l = 32 10 20 v dd = 1.5v r l = 16 25 v dd = 1.0v, r l = 32 7 output power (note 3) p out v dd = 0.9v, r l = 32 6 mw
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown _______________________________________________________________________________________ 3 electrical characteristics (max9725aCmax9725d) (continued) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss , c1 = c2 = 1?, c in = 1?, r l = , t a = t min to t max, unless other- wise noted. typical values are at t a = +25 c.) (see the functional diagrams. ) (note 1) parameter symbol conditions min typ max units r l = 32 , p out = 12mw, f = 1khz 0.006 total harmonic distortion plus noise thd+n r l = 16 , p out = 15mw, f = 1khz 0.015 % bw = 22hz to 22khz 89 signal-to-noise ratio snr r l = 32 , p out = 12mw a-weighted filter 92 db slew rate sr 0.2 v/? maximum capacitive load c l no sustained oscillations 150 pf crosstalk xtalk f in = 1.0khz, r l = 32 , p out = 5mw 100 db into shutdown 72.8 click-and-pop level k cp r l = 32 , peak voltage, a-weighted, 32 samples per second (note 4) out of shutdown 72.8 dbv esd protection v esd human body model (outr, outl) ? kv electrical characteristics (max9725e) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss , c1 = c2 = 1?, c in = 1?, r l = 32 , r f = 60k , r in = 10k , t a = t min to t max, unless otherwise noted. typical values are at t a = +25 c.) (see the functional diagrams. ) (note 1) parameter symbol conditions min typ max units supply voltage range v dd guaranteed by psrr test 0.9 1.8 v quiescent supply current i dd both channels active 2.3 3.7 ma t a = +25 c 0.6 1 shutdown current i shdn v shdn = 0v t a = -40 c to +85 c10 ? shutdown to full operation t on 180 ? v ih v dd = 0.9v to 1.8v 0.7 x v dd shdn thresholds v il v dd = 0.9v to 1.8v 0.3 x v dd v shdn input leakage current i leak v dd = 0.9v to 1.8v (note 2) 1a charge pump oscillator frequency f osc 483 592 687 khz amplifiers voltage gain a v (note 5) -6.11 -6.07 -6.00 v/v minimum stable gain a v -1.0 v/v total output offset voltage v os input ac-coupled, r l = 32 to gnd, t a = +25 c (note 6) ?.63 ?.1 mv input resistance r in 6.3 9.78 14 k inr, inl input leakage current i lk ?00 na maximum input parasitic capacitance c par 5pf v dd = 0.9v to 1.8v, t a = +25 c 52.9 67.8 f in = 1khz 70 power-supply rejection ratio psrr 100mv p-p ripple (note 5) f in = 20khz 62 db
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 4 _______________________________________________________________________________________ note 1: all specifications are 100% tested at t a = +25?; temperature limits are guaranteed by design. note 2: input leakage current measurements limited by automated test equipment. note 3: f in = 1khz, t a = +25?, thd+n < 1%, both channels driven in-phase. note 4: testing performed with 32 resistive load connected to outputs. mode transitions controlled by shdn . k cp level calculated as 20 log [peak voltage under normal operation at rated power level / peak voltage during mode transition]. inputs are ac- grounded. note 5: using existing resistors with 1% precision. note 6: r in = 10 , r f =10k . typical operating characteristics (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss, c1 = c2 = 1?, c in = 1?, thd+n measurement bandwidth = 22hz to 22khz, t a = +25 c, unless otherwise noted.) ( see the functional diagrams. ) 10 10k 1k 100 100k total harmonic distortion plus noise vs. frequency max9725 toc01 frequency (hz) thd+n (%) 1 0.1 0.001 0.01 v dd = 1.5v r l = 16 a v = -2v/v p out = 15mw p out = 2mw 10 10k 1k 100 100k total harmonic distortion plus noise vs. frequency max9725 toc02 frequency (hz) thd+n (%) 1 0.1 0.001 0.01 v dd = 1.5v r l = 32 a v = -2v/v p out = 12mw p out = 2mw 10 10k 1k 100 100k total harmonic distortion plus noise vs. frequency max9725 toc03 frequency (hz) thd+n (%) 1 0.1 0.001 0.01 v dd = 1v r l = 16 a v = -2v/v p out = 0.7mw p out = 4mw electrical characteristics (max9725e) (continued) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss , c1 = c2 = 1?, c in = 1?, r l = 32 , r f = 60k , r in = 10k , t a = t min to t max, unless otherwise noted. typical values are at t a = +25 c.) (see the functional diagrams. ) (note 1) parameter symbol conditions min typ max units r l = 32 10 24 v dd = 1.5v r l = 16 25 v dd = 1.0v, r l = 32 7 output power (note 3) p out v dd = 0.9v, r l = 32 6 mw r l = 32 , p out = 12mw, f = 1khz 0.006 total harmonic distortion plus noise (note 5) thd+n r l = 16 , p out = 15mw, f = 1khz 0.015 % bw = 22hz to 22khz 89 signal-to-noise ratio snr r l = 32 , p out = 12mw a-weighted filter 92 db slew rate sr 0.3 v/? maximum capacitive load c l no sustained oscillations 150 pf crosstalk xtalk f in = 1.0khz, r l = 32 , p out = 5mw 100 db into shutdown 72.8 click-and-pop level k cp r l = 32 , peak voltage, a-weighted, 32 samples per second (note 4) out of shutdown 72.8 dbv esd protection v esd human body model (outr, outl) ? kv r l = 32 -120 attenuation in shutdown a tt ( sd ) v shdn = 0v r l = 10k -75 db
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown _______________________________________________________________________________________ 5 typical operating characteristics (continued) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss, c1 = c2 = 1?, c in = 1?, thd+n measurement bandwidth = 22hz to 22khz, t a = +25 c, unless otherwise noted.) ( see the functional diagrams. ) 100 0 5 10 15 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power max9725 toc07 output power (mw) thd+n (%) v dd = 1v r l = 16 a v = -2v/v f in = 20hz f in = 1khz f in = 10khz 100 0 5 10 15 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power max9725 toc08 output power (mw) thd+n (%) v dd = 1v r l = 32 a v = -2v/v f in = 20hz f in = 1khz f in = 10khz 10 100 10k 1k 100k power-supply rejection ratio vs. frequency max9725 toc09 frequency (hz) psrr (db) -10 -110 -60 -50 -40 -30 -20 -70 -80 -90 -100 v dd = 1.5v r l = 32 10 100 10k 1k 100k power-supply rejection ratio vs. frequency max9725 toc10 frequency (hz) psrr (db) 0 -100 -50 -40 -30 -20 -10 -60 -70 -80 -90 v dd = 1v r l = 32 10 100 10k 1k 100k crosstalk vs. frequency max9725 toc11 frequency (hz) psrr (db) 0 -20 -40 -60 -80 -100 -120 v dd = 1.5v p out = 5mw r l = 32 right to left left to right 0 10 20 30 40 50 60 70 80 0.9 1.1 1.3 1.5 output power vs. supply voltage max9725 toc12 supply voltage (v) output power (mw) f in = 1khz r l = 16 both inputs driven in-phase thd+n = 10% thd+n = 1% 10 10k 1k 100 100k total harmonic distortion plus noise vs. frequency max9725 toc04 frequency (hz) thd+n (%) 1 0.1 0.001 0.01 p out = 0.7mw p out = 4mw v dd = 1v r l = 32 a v = -2v/v 100 010203040 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power max9725 toc05 output power (mw) thd+n (%) v dd = 1.5v r l = 16 a v = -2v/v f in = 20hz f in = 1khz f in = 10khz 100 010203040 10 1 0.1 0.01 0.001 total harmonic distortion plus noise vs. output power max9725 toc06 output power (mw) thd+n (%) v dd = 1.5v r l = 32 a v = -2v/v f in = 20hz f in = 1khz f in = 10khz
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 6 _______________________________________________________________________________________ 0 10 20 30 40 50 60 70 80 0 1020304050 power dissipation vs. output power max9725 toc16 output power (mw) power dissipation (mw) v dd = 1.5v f in = 1khz p out = p outl + p outr outputs in-phase r l = 16 r l = 32 0 5 10 15 20 25 30 35 0 5 10 15 20 power dissipation vs. output power max9725 toc17 output power (mw) power dissipation (mw) v dd = 1v f in = 1khz p out = p outl + p outr outputs in-phase r l = 16 r l = 32 10 100 10k 1k 100k gain flatness vs. frequency frequency (hz) amplitude (db) 2 1 0 -1 -2 -3 -4 -5 -7 -6 -8 -9 -10 max9725 toc18 0 5 10 15 20 25 30 35 40 10 20 30 40 50 output power vs. charge-pump capacitance and load resistance max9725 toc19 load resistance ( ) output power (mw) v dd = 1.5v f in = 1khz thd+n = 1% c1 = c2 = 2.2 f c1 = c2 = 1 f c1 = c2 = 0.47 f c1 = c2 = 0.68 f -160 -140 -120 -100 -80 -60 -40 -20 0 0 5 10 15 20 output spectrum vs. frequency max9725 toc20 frequency (khz) amplitude (db) f in = 1khz r l = 32 v out = -60dbv v dd = 1.5v 0 1.5 1.0 0.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.9 1.1 1.0 1.2 1.3 1.4 1.5 supply current vs. supply voltage max9725 toc21 supply voltage (v) supply current (ma) no load typical operating characteristics (continued) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss, c1 = c2 = 1?, c in = 1?, thd+n measurement bandwidth = 22hz to 22khz, t a = +25 c, unless otherwise noted.) ( see the functional diagrams. ) 0 15 10 5 20 25 30 35 40 45 50 0.9 1.1 1.3 1.5 output power vs. supply voltage max9725 toc13 supply voltage (v) output power (mw) f in = 1khz r l = 32 both inputs driven in-phase thd+n = 10% thd+n = 1% 80 70 0 10 100 1k output power vs. load resistance 20 max9725 toc14 load resistance ( ) output power (mw) 40 60 10 30 50 v dd = 1.5v f in = 1khz both inputs driven in-phase thd+n = 10% thd+n = 1% 80 70 0 10 100 1k output power vs. load resistance 20 max9725 toc15 load resistance ( ) output power (mw) 40 60 10 30 50 v dd = 1v f in = 1khz both inputs driven in-phase thd+n = 10% thd+n = 1%
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown _______________________________________________________________________________________ 7 pin bump thin qfn ucsp name function 1 a1 c1n flying capacitor negative terminal. connect a 1? capacitor from c1p to c1n. 2a2pv ss inverting charge-pump output. bypass with 1? from pv ss to pgnd. pv ss must be connected to v ss . 3 a3 inl left-amplifier inverting input. connect input resistor r in from input capacitor c1n to inl (max9725e only). 4 a4 inr right-amplifier inverting input. connect input resistor r in from input capacitor c1n to inr (max9725e only). 5b4v ss amplifier negative power supply. must be connected to pv ss . 6 b3 sgnd signal ground. sgnd must be connected to pgnd. sgnd is the ground reference for the input and output signal. 7 c4 outr right-channel output. connect feedback resistor r fb between outr and inr (max9725e only). 8 c3 outl left-channel output. connect feedback resistor r fb between outl and inl (max9725e only). 9c2v dd positive power-supply input. bypass with a 1? capacitor to pgnd. 10 c1 c1p flying capacitor positive terminal. connect a 1? capacitor from c1p to c1n. 11 b1 pgnd power ground. ground reference for the internal charge pump. pgnd must be connected to sgnd. 12 b2 shdn active-low shutdown. connect to v dd for normal operation. pull low to disable the amplifier and charge pump. ep ep exposed paddle. internally connected to v ss . leave paddle unconnected or solder to v ss . pin description shutdown current vs. supply voltage max9725 toc22 supply voltage (v) shutdown current ( a) 1.3 1.1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.9 1.5 exiting shutdown max9725 toc23 200 s/div out_ 1v/div shdn 500mv/div power-up/-down waveform max9725toc24 200ms/div out_ 10mv/div v dd 1v/div typical operating characteristics (continued) (v dd = 1.5v, v pgnd = v sgnd = 0v, v shdn = 1.5v, v ss = v pvss, c1 = c2 = 1?, c in = 1?, thd+n measurement bandwidth = 22hz to 22khz, t a = +25 c, unless otherwise noted.) ( see the functional diagrams. )
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 8 _______________________________________________________________________________________ detailed description the max9725 stereo headphone driver features maxim? directdrive architecture, eliminating the large output-cou- pling capacitors required by conventional single-supply headphone drivers. the max9725 consists of two 20mw class ab headphone drivers, shutdown control, inverting charge pump, internal gain-setting resistors, and compre- hensive click-and-pop suppression circuitry (see the functional diagrams ). a negative power supply (pv ss ) is created by inverting the positive supply (v dd ). powering the drivers from v dd and pv ss increases the dynamic range of the drivers to almost twice that of other 1v sin- gle-supply drivers. this increase in dynamic range allows for higher output power. the outputs of the max9725 are biased about gnd (figure 1). the benefit of this gnd bias is that the driver outputs do not have a dc component, thus large dc- blocking capacitors are unnecessary. eliminating the dc-blocking capacitors on the output saves board space, system cost, and improves frequency response. directdrive conventional single-supply headphone drivers have their outputs biased about a nominal dc voltage (typically half the supply) for maximum dynamic range. large coupling capacitors are needed to block the dc bias from the headphones. without these capacitors, a significant amount of dc current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both headphone and headphone driver. maxim? directdrive architecture uses a charge pump to create an internal negative supply voltage. this allows the max9725 outputs to be biased about gnd, increasing the dynamic range while operating from a single supply. a conventional amplifier powered from 1.5v ideally provides 18mw to a 16 load. the max9725 provides 25mw to a 16 load. the directdrive architecture eliminates the need for two large (220?, typ) dc-blocking capacitors on the out- put. the max9725 charge pump requires two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone driver. see the output power vs. charge- pump capacitance and load resistance graph in the typical operating characteristics for details of the possi- ble capacitor sizes. previous attempts to eliminate the output-coupling capacitors involved biasing the headphone return (sleeve) to the dc-bias voltage of the headphone amplifiers. this method raises some issues: the sleeve is typically grounded to the chassis. using this biasing approach, the sleeve must be isolated from system ground, complicating product design. during an esd strike, the driver? esd structures are the only path to system ground. the driver must be able to withstand the full esd strike. when using the headphone jack as a line out to other equipment, the bias voltage on the sleeve may conflict with the ground potential from other equip- ment, resulting in possible damage to the drivers. figure 1. traditional driver output waveform vs. max9725 output waveform (ideal case) v dd -v dd gnd v out conventional driver-biasing scheme directdrive biasing scheme v dd / 2 v dd gnd v out
max9725 low-frequency response large dc-blocking capacitors limit the amplifier? low- frequency response and can distort the audio signal: 1) the impedance of the headphone load and the dc- blocking capacitor forms a highpass filter with the -3db point set by: where r l is the impedance of the headphone and c out is the value of the dc-blocking capacitor. the highpass filter is required by conventional single- ended, single power-supply headphone drivers to block the midrail dc-bias component of the audio signal from the headphones. the drawback to the filter is that it can attenuate low-frequency signals. larger values of c out reduce this effect but result in physically larger, more expensive capacitors. figure 2 shows the relationship between the size of c out and the resulting low-frequency attenuation. note that the -3db point for a 16 headphone with a 100? blocking capacitor is 100hz, well within the normal audio band, resulting in low-frequency attenuation of the reproduced signal. 2) the voltage coefficient of the dc-blocking capacitor contributes distortion to the reproduced audio signal as the capacitance value varies when the function of the voltage across the capacitor changes. at low frequencies, the reactance of the capacitor domi- nates at frequencies below the -3db point and the voltage coefficient appears as frequency-dependent distortion. figure 3 shows the thd+n introduced by two different capacitor dielectric types. note that below 100hz, thd+n increases rapidly. the combination of low-frequency attenuation and fre- quency-dependent distortion compromises audio reproduction in portable audio equipment that empha- sizes low-frequency effects such as multimedia lap- tops, as well as mp3, cd, and dvd players. these low-frequency, capacitor-related deficiencies are elimi- nated by using directdrive technology. charge pump the max9725 features a low-noise charge pump. the 580khz switching frequency is well beyond the audio range, and does not interfere with the audio signals. the switch drivers feature a controlled switching speed that minimizes noise generated by turn-on and turn-off transients. the di/dt noise caused by the parasitic bond wire and trace inductance is minimized by limiting the turn-on/off speed of the charge pump. additional high- frequency noise attenuation can be achieved by increasing the size of c2 (see the functional diagrams ). extra noise attenuation is not typically required. shutdown the max9725? low-power shutdown mode reduces supply current to 0.6?. driving shdn low disables the amplifiers and charge pump. the driver? output imped- ance is typically 50k (max9725a), 37.5k (max9725b), 25k (max9725c), 100k (max9725d), or r f (max9725e) when in shutdown mode. f 2rc -3db l out = 1 figure 2. low-frequency attenuation for common dc-blocking capacitor values lf rolloff (16 load) frequency (hz) attenuation (db) 100 -30 -25 -20 -10 -3db corner for 100 f is 100hz -15 -5 -3 0 -35 10 1k 33 f 330 f 220 f 100 f figure 3. distortion contributed by dc-blocking capacitors additional thd+n due to dc-blocking capacitors frequency (hz) thd+n (%) 10k 1k 100 0.001 0.01 0.1 1 10 0.0001 10 100k tantalum alum/elec 1v, low-power, directdrive, stereo headphone amplifier with shutdown _______________________________________________________________________________________ 9
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 10 ______________________________________________________________________________________ click-and-pop suppression in conventional single-supply audio drivers, the output- coupling capacitor is a major contributor of audible clicks and pops. upon startup, the driver charges the coupling capacitor to its bias voltage, typically half the supply. likewise, on shutdown, the capacitor is dis- charged to gnd. this results in a dc shift across the capacitor that appears as an audible transient at the speaker. the max9725? directdrive technology elimi- nates the need for output-coupling capacitors. the max9725 also features extensive click-and-pop suppression that eliminates any audible transient sources internal to the device. the power-up/-down waveform in the typical operating characteristics shows minimal dc shift and no spurious transients at the output upon startup or shutdown. in most applications, the output of the preamplifier dri- ving the max9725 has a dc bias of typically half the supply. at startup, the input-coupling capacitor is charged to the preamplifier? dc bias voltage through the internal input resistor (25k for max9725a- max9725d, minimum 10k for max9725e) causing an audible click and pop. delaying the rise of shdn 4 or 5 time constants, based on r in x c in , relative to the start- up of the preamplifier eliminates any click and pop caused by the input filter (see the functional diagrams ). applications information power dissipation linear power amplifiers can dissipate a significant amount of power under normal operating conditions. the maximum power dissipation for each package is given in the absolute maximum ratings section under continuous power dissipation or can be calculated by the following equation: where t j(max) is +150 c, t a is the ambient tempera- ture, and ja is the reciprocal of the derating factor in c/w as specified in the absolute maximum ratings section. for example, ja for the thin qfn package is +59.3 c/w. the max9725 has two power dissipation sources, the charge pump and the two amplifiers. if the power dissi- pation exceeds the rated package dissipation, reduce v dd , increase load impedance, decrease the ambient temperature, or add heatsinking to the device. large output, supply, and ground traces decrease ja , allow- ing more heat to be transferred from the package to surrounding air. output power the max9725? output power increases when the left and right audio signals differ in magnitude and/or phase. figure 4 shows the two extreme cases for in- and out-of-phase input signals. the output power of a typical stereo application lies between the two extremes shown in figure 4. the max9725 is specified to output 20mw per channel when both inputs are in-phase. powering other circuits from the negative supply the max9725 internally generates a negative supply voltage (pv ss ) to provide the ground-referenced output signal. other devices can be powered from pv ss pro- vided the current drawn from the charge pump does not exceed 1ma. headphone driver output power and thd+n will be adversely affected if more than 1ma is drawn from pv ss . using pv ss as an lcd bias is a typi- cal application for the negative supply. pv ss is unregulated and proportional to v dd . connect a 1? capacitor from c1p to c1n for best charge-pump operation. p t-t disspkg(max) j(max) a ja = figure 4. output power vs. supply voltage with inputs in-/out- of-phase 0 15 10 5 20 25 30 35 40 45 50 0.9 1.1 1.3 1.5 output power vs. supply voltage with inputs in- and out-of-phase supply voltage (v) output power (mw) f in = 1khz r l = 16 thd+n = 1% inputs 180 out-of-phase inputs in-phase
max9725 component selection input filtering the ac-coupling capacitor (c in ) and an internal gain- setting resistor form a highpass filter that removes any dc bias from an input signal (see the functional diagrams ). c in allows the max9725a?ax9725d to bias the signal to an optimum dc level. the -3db point of the highpass filter, assuming zero source imped- ance, is given by: choose c in so f -3db is well below the lowest frequency of interest. r in for the max9725a?ax9725d is 25k and a minimum of 10k for the max9725e. setting f -3db too high affects the amplifier? low-frequency response. use capacitors with low-voltage coefficient dielectrics. film or c0g dielectric capacitors are good choices for ac-cou- pling capacitors. capacitors with high-voltage coeffi- cients, such as ceramics, can result in increased distortion at low frequencies. charge-pump capacitor selection use capacitors with less than 100m of esr. low-esr ceramic capacitors minimize the output impedance of the charge pump. capacitors with an x7r dielectric provide the best performance over the extended temperature range. table 1 lists suggested capacitor manufacturers. flying capacitor (c1) the value of c1 affects the charge pump? load regula- tion and output impedance. choosing c1 too small degrades the max9725? ability to provide sufficient current drive and leads to a loss of output voltage. increasing the value of c1 improves load regulation and reduces the charge-pump output impedance. see the output power vs. charge-pump capacitance and load resistance graph in the typical operating characteristics . hold capacitor (c2) the hold capacitor? value and esr directly affect the ripple at pv ss . increasing the value of c2 reduces rip- ple. choosing a capacitor with lower esr reduces rip- ple and output impedance. lower capacitance values can be used in systems with low maximum output power levels. see the output power vs. charge-pump capacitance and load resistance graph in the typical operating characteristics . power-supply bypass capacitor (c3) the power-supply bypass capacitor (c3) lowers the output impedance of the power supply and reduces the impact of the max9725? charge-pump switching tran- sients. bypass v dd to pgnd with the same value as c1. place c3 as close to v dd as possible. layout and grounding proper layout and grounding are essential for optimum performance. connect pgnd and sgnd together at a single point on the pc board. connect pv ss to sv ss and bypass with c2 to pgnd. bypass v dd to pgnd with c3. place capacitors c2 and c3 as close to the max9725 as possible. route pgnd, and all traces that carry switching transients, away from sgnd and the audio signal path. the max9725 does not require additional heatsinking. the thin qfn package features an exposed paddle that improves thermal efficiency of the package. ensure the exposed paddle is electrically isolated from gnd and v dd . connect the exposed paddle to v ss if necessary. ucsp applications information for the latest application details on ucsp construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout , and recommend- ed reflow temperature profile, as well as the latest infor- mation on reliability testing results, go to maxim? website at www.maxim-ic.com/ucsp for the application note 1891: wafer-level packaging (wlp) and its applications . f 2c -3db in = 1 r in table 1. suggested capacitor manufacturers supplier phone fax website murata 770-436-1300 www.murata.com taiyo yuden 800-348-2496 847-925-0899 www.t-yuden.com tdk 847-803-6100 847-390-4405 www.component.tdk.com 1v, low-power, directdrive, stereo headphone amplifier with shutdown ______________________________________________________________________________________ 11
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 12 ______________________________________________________________________________________ outr 0.9v to 1.8v outl sgnd pgnd v dd inr inl c1p c1n v ss pv ss mp3 decoder 1 f 1 f 1 f 1 f shdn 1 f max9725a max9725d stereo dac max9725e 1 f r in r f sgnd pgnd charge pump r f inl c1n din outl 1 f r in inr outr p vss v ss 1 f 1 f v dd shdn 1 f system diagrams
max9725 charge pump uvlo/ shutdown control click-and-pop suppression c1n c1p pv ss v ss pgnd sgnd *max9725a = 50k . max9725b = 37.5k . max9725c = 25k . max9725d = 100k . ( ) denote bumps for ucsp. inr v dd v ss v dd sgnd outr headphone jack 12 (b2) 9 (c2) 10 (c1) 11 (b1) 1 (a1) 2 (a2) 5 (b4) 8 (c3) 7 (c4) 6 (b3) c1 1 f c2 1 f 0.9v to 1.8v c3 1 f c in 0.47 f r in 25k left- channel audio in v ss v dd r f * outl shdn 3 (a3) inl 4 (a4) sgnd max9725a max9725d c in 0.47 f r f * left- channel audio in r in 25k functional diagrams 1v, low-power, directdrive, stereo headphone amplifier with shutdown ______________________________________________________________________________________ 13
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 14 ______________________________________________________________________________________ charge pump uvlo/ shutdown control click-and-pop suppression c1n c1p pv ss v ss pgnd sgnd ( ) denote bumps for ucsp. inr v dd v dd v ss sgnd outr headphone jack 12 (b2) 9 (c2) 10 (c1) 11 (b1) 1 (a1) 2 (a2) 5 (b4) 8 (c3) 7 (c4) r f r in c in 1 f c in 1 f r f 6 (b3) c1 1 f c2 1 f 0.9v to 1.8v c3 1 f v ss v dd outl shdn 3 (a3) inl 4 (a4) sgnd max9725e right- channel audio in left-channel audio in r in functional diagrams (continued)
max9725 c1n c1p outl single 1.5v cell aa or aaa battery outr sgnd r fb pgnd max9725e inverting charge pump inr inl v dd pv ss c2 v ss c3 r fb directdrive outputs eliminate dc-blocking capacitors. block diagrams (continued) ordering information (continued) pa rt pin- pa ck a g e t o p m a rk g a in ( v/v) m ax9725be tc+ 12 tqfn- ep* + aae x - 1.5 max9725cebc+tg45 12 u c s p+ acm - 1 m ax9725c e tc+ 12 tqfn- ep* + aae y - 1 max9725d ebc +tg45 12 u c s p+ acn - 4 m ax9725d e tc+ 12 tqfn- ep* + aae z - 4 max9725e ebc +tg45 12 u c s p+ aef ad j m ax9725e e tc+ ** 12 tqfn- ep* + aagh ad j note: all devices are specified over the -40? to +85? operating temperature range. + denotes a lead(pb)-free/rohs-compliant package. t = tape and reel. * ep = exposed pad. ** future product?ontact factory for availability. 12 3 c b a ucsp top view (bump-side down) 4 c1n pv ss inl inr v ss sgnd c1p v dd outl outr pgnd shdn top view thin qfn max9725 12 *ep *ep = exposed pad. 11 + 10 4 5 pv ss inl 6 c1n outl outr v dd 12 pgnd 3 987 shdn sgnd v ss inr max9725 c1p pin configurations 1v, low-power, directdrive, stereo headphone amplifier with shutdown ______________________________________________________________________________________ 15
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 16 ______________________________________________________________________________________ package type package code document no. 12 ucsp b12-1 21-0104 12 tqfn-ep t1244-4 21-0139 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.
max9725 1v, low-power, directdrive, stereo headphone amplifier with shutdown 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 17 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision number revision date description pages changed 0 11/04 initial release 1 5/05 removed future product asterisks for ucsp package, added ec table note 1?, 13, 14 2 11/07 added max9725e packages, max9725e ec table, block diagram, functional diagram, and system diagram. updated package outlines. 1?, 6, 8?9 3 8/08 corrected error in functional diagrams 14 4 3/09 updated ordering information , style changes 1, 15 revision history

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