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general description the MAX9720 stereo headphone amplifier combines maxim? patented directdrive architecture and smartsense, an automatic mono/stereo detection fea- ture. conventional headphone amplifiers require a bulky dc-blocking capacitor between the headphone and the amplifier. directdrive produces a ground-referenced out- put from a single supply, eliminating the need for large dc-blocking capacitors, saving cost, board space, and component height. smartsense automatically detects the presence of a short at either the left or right amplifier output. under a fault condition, the shorted output is automatically dis- abled and the stereo input signal is automatically mixed and routed to the remaining active channel. this feature is useful in cell phone and pda applications where a variety of headphone jacks with unknown loads can be inserted into the headphone jack socket. smartsense prevents both damage to the amplifier and eliminates battery drain into a shorted load. the MAX9720 delivers up to 50mw per channel into a 16 ? load and has an ultra-low 0.003% thd+n. a high (92db at 217khz) power-supply rejection ratio (psrr) allows the device to operate from noisy digital supplies without additional power conditioning. the gain of the MAX9720 is set internally, further reducing component count. two gain options are available (-1v/v, MAX9720a and -1.41v/v, MAX9720b). the headphone outputs include a comprehensive click-and-pop circuitry that eliminates audible glitches on startup and shutdown. a shutdown mode provides a fast 250? turn-on time. the MAX9720 operates from a single 1.8v to 3.6v supply and consumes only 5ma of supply current. the MAX9720 also features thermal overload protection, and is specified over the extended -40? to +85? tem- perature range. the MAX9720 is available in a tiny (2mm x 2mm x 0.6mm) 16-bump chip-scale package (ucsp) and a 16-pin tssop package. applications features directdrive eliminates bulky dc-blocking capacitors smartsense automatic short detection low 5ma quiescent current fixed gain eliminates external feedback network MAX9720a: -1v/v MAX9720b: -1.41v/v 50mw per channel output power ultra-low 0.003% thd+n high psrr (92db at 217hz) integrated click-and-pop suppression 1.8v to 3.6v single-supply operation thermal overload protection available in space-saving packages 16-bump ucsp (2mm x 2mm x 0.6mm) 16-pin tssop MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ________________________________________________________________ maxim integrated products 1 ordering information 19-2859; rev 0; 4/03 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. pin configuration and typical application circuit appear at end of data sheet. part temp range pin/bump- package gain (v/v) MAX9720aebe-t -40 o c to +85 o c 16 ucsp-16 -1 MAX9720bebe-t -40 o c to +85 o c 16 ucsp-16 -1.41 MAX9720aeue -40 o c to +85 o c 16 tssop -1 MAX9720beue -40 o c to +85 o c 16 tssop -1.41 pdas cellular phones mp3 players notebook pcs smart phones tablet pcs portable audio equipment smartsense and ucsp are trademarks of maxim integrated products, inc. r in + l in r out hps mode1 mode2 alert 3.6v to 1.8v supply MAX9720 smartsense l out simplified block diagram
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v dd = v mode1 = v mode2 = 3.0v, pgnd = sgnd = 0v, r l = , c1 = c2 = 2.2f. t a = t min to t max, unless otherwise noted. typical values are at t a = +25 c.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. pgnd to sgnd .....................................................-0.3v to +0.3v pv ss to sv ss .........................................................-0.3v to +0.3v v dd to pgnd or sgnd ............................................-0.3v to +4v pv ss and sv ss to pgnd or sgnd ..........................-4v to +0.3v in_, out_, and hps to sgnd .......(sv ss - 0.3v) to (v dd + 0.3v) c1p to pgnd ...............................(pgnd - 0.3v) to (v dd + 0.3v) c1n to pgnd .............................(pv ss - 0.3v) to (pgnd + 0.3v) alert to pgnd .......................................................-0.3v to +4v mode_ to pgnd ........................................-0.3v to (v dd + 0.3v) time to sgnd ............................................-0.3v to (v dd + 0.3v) output short circuit to gnd or v dd ............................... continuous continuous power dissipation (t a = +70 c) 16-bump ucsp (derate 8.2mw/ c above +70 c) .......659mw 16-pin tssop (derate 9.4mw/ c above +70 c) .......754.7mw junction temperature ......................................................+150 c operating temperature range ...........................-40 c to +85 c storage temperature range .............................-65 c to +150 c bump temperature (soldering) reflow ...........................................................................+235 c lead temperature (soldering, 10s) .................................+300 c parameter symbol conditions min typ max units general supply voltage range v dd inferred from psrr test 1.8 3.6 v stereo mode 5 8.4 supply current i dd m ono m od e ( m od e 1 = v d d , m od e 2 = gn d ) 3 ma shutdown supply current i shdn mode1 = mode2 = gnd 6 10 a turn-on/turn-off time t s 250 s charge pump oscillator frequency f osc 272 320 368 khz headphone amplifiers MAX9720a -1.02 -1 -0.98 voltage gain a v MAX9720b -1.443 -1.415 -1.386 v/v gain match ? a v between outl and outr 1% MAX9720a -5 -0.8 +3.6 total output offset voltage (note 3) v os MAX9720b -6.5 -1 +4.5 mv input resistance r in 10 15 20 k ? 1.8v v dd 3.6v (note 3) dc 76 92 f ripple = 217hz 92 f ripple = 1khz 86 power-supply rejection ratio psrr v dd = 3.0v, 200mv p-p ripple (note 3) f ripple = 20khz 61 db r l = 32 ? 50 output power p out thd+n = 1%, f in = 1khz, t a = +25 c r l = 16 ? 32 50 mw
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown _______________________________________________________________________________________ 3 note 1: all specifications are 100% tested at t a = +25 o c; temperature limits are guaranteed by design. note 2: inputs are ac-coupled to ground. note 3: inputs are connected directly to ground. electrical characteristics (continued) (v dd = v mode1 = v mode2 = 3.0v, pgnd = sgnd = 0v, r l = , c1 = c2 = 2.2f. t a = t min to t max, unless otherwise noted. typical values are at t a = +25 c.) (note 1) parameter symbol conditions min typ max units r l = 32 ? , p out = 30mw 0.003 total harmonic distortion plus noise thd+n f in = 1khz r l = 16 ? , p out = 30mw 0.005 % signal-to-noise ratio snr f in = 1khz, v out = 0.5v rms , r l = 16 ? , bw = 22hz to 22khz 97 db slew rate sr 0.8 v/s maximum capacitive load c l no sustained oscillations 150 pf crosstalk r l = 32 ? , p out = 1mw, f in = 10khz 75 db thermal shutdown threshold 140 o c thermal shutdown hysteresis 15 o c smartsense shorted load threshold r sms 2.4 4 5.6 ? pulse duration t sms 3.1 s debounce time (time) time charging current i time 0.7 1.1 1.8 a time discharge switch resistance r time hps = gnd 4 10 k ? time threshold v time 1 1.1 1.2 v headphone sense input (hps) v ih 0.9 x v dd hps threshold v il 0.7 x v dd v input leakage current i il mode1= mode2 = gnd 1a input capacitance c in 10 pf alert output current high i oh v alert = v dd 1a output voltage low v ol i ol = 3ma 0.4 v mode_ input v ih 0.7 x v dd mode_ thresholds v il 0.3 x v dd v mode_ input leakage current 1a
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 4 _______________________________________________________________________________________ typical operating characteristics (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .) total harmonic distortion plus noise vs. frequency MAX9720 toc01 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1v/v r l = 16 ? p out = 10mw p out = 40mw total harmonic distortion plus noise vs. frequency MAX9720 toc02 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1v/v r l = 32 ? p out = 10mw p out = 40mw total harmonic distortion plus noise vs. frequency MAX9720 toc03 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1.41v/v r l = 16 ? p out = 10mw p out = 40mw total harmonic distortion plus noise vs. frequency MAX9720 toc04 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1.41v/v r l = 32 ? p out = 10mw p out = 40mw total harmonic distortion plus noise vs. frequency MAX9720 toc05 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 1.8v a v = -1v/v r l = 16 ? p out = 2mw p out = 9mw frequency (hz) 10k 1k 100 10 100k total harmonic distortion plus noise vs. frequency MAX9720 toc06 thd + n (%) 1 0.1 0.001 0.01 v dd = 1.8v a v = -1v/v r l = 32 ? p out = 2mw p out = 9mw total harmonic distortion plus noise vs. frequency MAX9720 toc07 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1.41v/v r l = 16 ? p out = 2mw p out = 9mw total harmonic distortion plus noise vs. frequency MAX9720 toc08 frequency (hz) thd+n (%) 10k 1k 100 0.01 0.1 1 0.001 10 100k v dd = 3v a v = -1.41v/v r l = 32 ? p out = 2mw p out = 9mw total harmonic distortion plus noise vs. output power MAX9720 toc09 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 20hz r l = 16 ?
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown _______________________________________________________________________________________ 5 total harmonic distortion plus noise vs. output power MAX9720 toc10 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 1khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc11 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 10khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc12 output power (mw) thd+n (%) 80 60 40 20 0.01 0.1 1 10 100 0.001 0 100 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 20hz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc13 output power (mw) thd+n (%) 80 60 40 20 0.01 0.1 1 10 100 0.001 0 100 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 1khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc14 output power (mw) thd+n (%) 80 60 40 20 0.01 0.1 1 10 100 0.001 0 100 outputs in phase outputs out of phase v dd = 3v a v = -1v/v f = 10khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc15 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 20hz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc16 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 1khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc17 output power (mw) thd+n (%) 120 90 60 30 0.01 0.1 1 10 100 0.001 0 150 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 10khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc18 output power (mw) thd+n (%) 0.01 0.1 1 10 100 0.001 0 100 80 60 40 20 120 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 20hz r l = 32 ? typical operating characteristics (continued) (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .)
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 6 _______________________________________________________________________________________ typical operating characteristics (continued) (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .) total harmonic distortion plus noise vs. output power MAX9720 toc19 output power (mw) thd+n (%) 0.01 0.1 1 10 100 0.001 0 120 100 80 60 40 20 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 1khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc20 output power (mw) thd+n (%) 0.01 0.1 1 10 100 0.001 0 120 100 80 60 40 20 outputs in phase outputs out of phase v dd = 3v a v = -1.41v/v f = 10khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc21 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 20hz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc22 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 1khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc23 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 10khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc24 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 035 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 20hz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc25 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 035 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 1khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc26 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 035 outputs in phase outputs out of phase v dd = 1.8v a v = -1v/v f = 10khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc27 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 20hz r l = 16 ?
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown _______________________________________________________________________________________ 7 total harmonic distortion plus noise vs. output power MAX9720 toc28 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 1khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc29 output power (mw) thd+n (%) 40 30 20 10 0.01 0.1 1 10 100 0.001 050 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 10khz r l = 16 ? total harmonic distortion plus noise vs. output power MAX9720 toc30 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 040 35 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 20hz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc31 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 040 35 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 1khz r l = 32 ? total harmonic distortion plus noise vs. output power MAX9720 toc32 output power (mw) thd+n (%) 25 15 530 20 10 0.01 0.1 1 10 100 0.001 040 35 outputs in phase outputs out of phase v dd = 1.8v a v = -1.41v/v f = 10khz r l = 32 ? output power vs. supply voltage MAX9720 toc33 supply voltage (v) output power (mw) 3.3 3.0 2.7 2.4 2.1 20 40 60 80 100 120 140 160 180 200 0 1.8 3.6 f in = 1khz r l = 16 ? thd+n = 1% stereo out of phase stereo in phase output power vs. supply voltage MAX9720 toc34 supply voltage (v) output power (mw) 3.3 3.0 2.7 2.4 2.1 20 40 60 80 100 120 140 160 180 200 0 1.8 3.6 f in = 1khz r l = 16 ? thd+n = 10% stereo out of phase stereo in phase output power vs. supply voltage MAX9720 toc35 supply voltage (v) output power (mw) 3.3 3.0 2.7 2.4 2.1 20 40 60 80 100 120 140 160 0 1.8 3.6 f in = 1khz r l = 32 ? thd+n = 1% stereo out of phase stereo in phase output power vs. supply voltage MAX9720 toc36 supply voltage (v) output power (mw) 3.3 3.0 2.7 2.4 2.1 20 40 60 80 100 120 140 160 0 1.8 3.6 f in = 1khz r l = 32 ? thd+n = 10% stereo out of phase stereo in phase typical operating characteristics (continued) (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .)
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 8 _______________________________________________________________________________________ typical operating characteristics (continued) (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .) output power vs. load resistance MAX9720 toc37 load resistance ( ? ) output power (mw) 20 40 60 80 100 120 140 160 0 10 100 f = 1khz thd+n = 1% inputs out of phase inputs in phase output power vs. load resistance MAX9720 toc38 load resistance ( ? ) output power (mw) 20 40 60 80 100 120 140 160 0 10 100 f = 1khz thd+n = 10% inputs out of phase inputs in phase output power vs. load resistance MAX9720 toc39 load resistance ( ? ) output power (mw) 5 10 15 20 25 30 35 40 0 10 100 v dd = 1.8v f = 1khz thd+n = 1% inputs out of phase inputs in phase output power vs. load resistance MAX9720 toc40 load resistance ( ? ) output power (mw) 5 10 15 20 25 30 35 40 0 10 100 v dd = 1.8v f = 1khz thd+n = 10% inputs out of phase inputs in phase power dissipation vs. output power MAX9720 toc41 output power (mw) power dissipation (mw) 200 150 100 50 50 100 150 200 250 300 350 0 0 250 r l = 16 ? r l = 32 ? v dd = 3v f = 1khz p out = p outl + p outr power dissipation vs. output power MAX9720 toc42 output power (mw) power dissipation (mw) 60 40 20 25 50 75 100 125 0 080 r l = 16 ? r l = 32 ? v dd = 1.8v f = 1khz p out = p outl + p outr power-supply rejection ratio vs. frequency MAX9720 toc43 frequency (hz) psrr (db) 10k 1k 100 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -120 10 100k v dd = 3v v ripple = 200mv p-p power-supply rejection ratio vs. frequency MAX9720 toc44 frequency (hz) psrr (db) 10k 1k 100 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 100k v dd = 1.8v v ripple = 200mv p-p crosstalk vs. frequency MAX9720 toc45 frequency (hz) crosstalk (db) 10k 1k 100 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -120 10 100k v dd = 3v r l = 32 ? v in = 200mv p-p right-to-left channel left-to-right channel
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown _______________________________________________________________________________________ 9 crosstalk vs. frequency MAX9720 toc46 frequency (hz) crosstalk (db) 10k 1k 100 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -120 10 100k v dd = 1.8v r l = 32 ? v in = 200mv p-p right-to-left channel left-to-right channel gain flatness vs. frequency MAX9720 toc47 frequency (hz) gain (db) 1k 100 10 1 0.1 -4 -3 -2 -1 0 1 2 3 4 5 -5 0.01 10k a v = -1v/v charge-pump output impedance vs. supply voltage MAX9720 toc48 supply voltage (v) output impedance ( ? ) 3.3 3.0 2.7 2.4 2.1 2 4 6 8 10 12 14 0 1.8 3.6 i load = 10ma 0.47 f output power vs. load resistance and charge-pump capacitor size MAX9720 toc49 load resistance ( ? ) output power (mw) 40 30 20 10 20 30 40 50 60 0 10 50 2.2 f 1 f f in = 1khz thd+n = 1% outputs in phase output spectrum vs. frequency MAX9720 toc50 frequency (hz) output spectrum (db) 10k 1k -100 -80 -60 -40 -20 0 -120 100 100k v in = 1v p-p r l = 32 ? f in = 1khz supply current vs. supply voltage MAX9720 toc51 supply voltage (v) supply current (ma) 3.3 3.0 2.7 2.4 2.1 1 2 3 4 5 6 0 1.8 3.6 stereo mode mono mode shutdown supply current vs. supply voltage MAX9720 toc52 supply voltage (v) supply current ( a) 3.3 3.0 2.7 2.4 2.1 1 2 3 4 5 6 7 8 9 0 1.8 3.6 exiting shutdown MAX9720 toc53 400 s/div out_ 500mv/div 3v 0v f in = 1khz r l = 32 ? mode1 and mode2 power-up/down waveform MAX9720 toc54 200ms/div fft: 25hz/div out_fft out_ 20db/div 3v 0v 10mv/div v in = gnd r l = 32 ? v dd 100db typical operating characteristics (continued) (v dd = 3v, thd+n bandwidth = 22hz to 22khz, mode1 = mode2 = v dd .)
MAX9720 detailed description the MAX9720 fixed-gain, stereo headphone amplifier includes maxim s patented directdrive architecture and smartsense. directdrive eliminates the large output- coupling capacitors required by conventional single- supply headphone amplifiers. smartsense automatically detects the presence of a short at either output. under a fault condition, the shorted output is automatically disabled and the stereo input signal is automatically mixed and routed to the remaining active channel. this prevents damage to the amplifier and optimizes power savings by eliminating battery drain into a shorted load. the device consists of two 50mw class ab headphone amplifiers, an internal feedback network (MAX9720a: fixed -1v/v gain, MAX9720b: fixed -1.41v/v gain), a mono mixer/attenuator, undervoltage lockout (uvlo)/ shutdown control, smartsense, a charge pump, and comprehensive click-and-pop suppression circuitry (see functional diagram ). the charge pump inverts the positive supply (v dd ), creating a negative supply (pv ss ). the headphone amplifiers operate from these bipolar supplies with their outputs biased about gnd (figure 1). the amplifiers have almost twice the supply range compared to other single-supply amplifiers, nearly quadrupling the available output power. the benefit of the gnd bias is that the amplifier outputs do not have a dc component (typically v dd /2). this elimi- nates the large dc-blocking capacitors required with conventional headphone amplifiers, conserving board space, system cost, and improving frequency response. the noninvasive smartsense feature of the MAX9720 detects a short on either output. the smartsense routine executes when the device is powered up or brought out of shutdown (see the smartsense section). if a fault is detected, the shorted channel is shut down, the output goes high impedance, and the stereo audio input is mixed/attenuated and fed to the remaining active chan- nel. the device also features an alert output that indi- cates to a host c that smartsense has detected a short-circuit condition on either amplifier output. forced stereo and forced mono modes can also be selected through the two mode_ inputs. in forced operation mode, smartsense is disabled and the device operates as specified by the mode_ inputs, regardless of output load conditions. a fast low-power shutdown mode is also selected through the mode_ inputs (see the mode_ selection section). the uvlo prevents operation from an insufficient power supply and click-and-pop suppression, which eliminates audible transients on startup and shutdown. additionally, the MAX9720 features thermal overload protection and can withstand 4kv esd strikes on the output. 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 10 ______________________________________________________________________________________ pin description pin bump tssop ucsp name function 1d2v dd positive power supply 2 c2 mode1 mode select 1 logic input 3 d1 c1p flying capacitor positive terminal 4 c1 pgnd power ground. connect to sgnd. 5 b1 c1n flying capacitor negative terminal 6a1pv ss charge-pump output 7 b2 mode2 mode select 2 logic input 8a2 alert open-drain interrupt logic output 9 a3 inl left-channel audio input 10 b3 time debouncing timer capacitor 11 a4 inr right-channel audio input 12 b4 sgnd signal ground. connect to pgnd. 13 c4 sv ss amplifier negative power supply. connect to pv ss. 14 d4 outr right-channel output 15 c3 hps headphone sense input 16 d3 outl left-channel output
directdrive conventional single-supply headphone amplifiers have their outputs biased about a nominal dc voltage (typical- ly half the supply) for maximum dynamic range. large coupling capacitors are needed to block this dc bias from the headphone. without these capacitors, a signifi- cant amount of dc current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both headphone and headphone amplifier. maxim s patented directdrive architecture uses a charge pump to create an internal negative supply volt- age. this allows the MAX9720 output to be biased about gnd, almost doubling dynamic range while operating from a single supply. with no dc component, there is no need for the large dc-blocking capacitors. instead of two large capacitors (220f typ), the MAX9720 charge pump requires only two, small ceram- ic capacitors (1f typ), conserving board space, reducing cost, and improving the frequency response of the headphone amplifier. see the output power vs. charge-pump capacitance and load resistance graph in the typical operating characteristics for details of the possible 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 raised 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 amplifier s esd structures are the only path to system ground. the amplifier 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 equipment, resulting in large ground-loop current and possible damage to the amplifiers. when using a combination microphone and speak- er headset (in a cell phone or pda application), the microphone typically requires a gnd return. any dc bias on the sleeve conflicts with the microphone requirements (figure 2). low-frequency response in addition to the cost and size disadvantages, the dc- blocking capacitors limit the low-frequency response of the amplifier and distort the audio signal: the impedance of the headphone load and the dc- blocking capacitor form a highpass filter with the -3db point determined 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-supply headphone amplifiers to block the midrail dc component of the audio signal from the headphones. depending on the -3db point, the filter can attenuate low-frequency signals within the audio band. larger values of c out reduce the attenuation, but are physically larger, more expensive capacitors. figure 3 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 100f blocking capacitor is 100hz, well within the audio band. f rc db l out ? = 3 1 2 MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ______________________________________________________________________________________ 11 +v dd -v dd gnd v out conventional driver-biasing scheme directdrive biasing scheme v dd /2 v dd gnd v out figure 1. conventional amplifier output waveform vs. MAX9720 output waveform
MAX9720 the voltage coefficient of the capacitor, the change in capacitance due to a change in the voltage across the capacitor, distorts the audio signal. at frequencies around the -3db point, the reactance of the capacitor dominates, and the voltage coefficient appears as frequency-dependent distortion. figure 4 shows the thd+n introduced by two different capacitor dielectrics. note that around the -3db point, thd+n increases dramatically. the combination of low-frequency attenuation and fre- quency-dependent distortion compromises audio reproduction. directdrive improves low-frequency reproduction in portable audio equipment that empha- sizes low-frequency effects such as multimedia laptops and mp3, cd, and dvd players. charge pump the MAX9720 features a low-noise charge pump. the 320khz 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. limiting the switching speed of the charge pump minimizes the di/dt noise caused by the parasitic bond wire and trace inductance. although not typically required, additional high-frequency ripple attenuation can be achieved by increasing the size of c2 (see typical application circuit ). smartsense the smartsense feature detects a short on either out- put and automatically reconfigures the MAX9720 for optimum power savings. if an output short circuit is detected during the smartsense routine, the shorted channel is disabled, alert is asserted, and the device is set to mono mode (assuming the other channel is not shorted). smartsense works by applying an inaudible 3s test voltage pulse to the load. the resulting current from the test pulse and load is sensed. if the load impedance is less than 4 ? , the output is determined to be a short. 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 12 ______________________________________________________________________________________ headphone driver microphone amplifier microphone amplifier output audio input audio input microphone bias MAX9720 figure 2. earbud speaker/microphone combination headset configuration 0 -30 0.01 0.1 1 10 100 low-frequency rolloff (r l = 16 ? ) -24 -27 -12 -15 -18 -21 -6 -9 -3 frequency (hz) attenuation (db) directdrive 330 f 220 f 100 f 33 f figure 3. low-frequency attenuation of common dc-blocking capacitor values 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 figure 4. distortion contributed by dc-blocking capacitors
mode selection (mode_) smartsense is controlled by the two mode select inputs, mode1 and mode2. table 1 shows the operat- ing modes in relation to the status of the mode_ inputs. when mode1 = mode2 = low, the device is in low- power shutdown mode. when mode1 = high and mode2 = low, the device is in forced mono mode. the right channel is disabled, outr goes high impedance, and the stereo audio input is mixed, and the audio sig- nal is reproduced on outl. smartsense is disabled in this mode. when mode1 = low and mode2 = high, the device is in forced stereo mode, and smartsense is disabled. when the device detects the presence of a short before forced stereo mode is selected, the device remains in mono mode (figure 5). when mode1 = mode2 = high, the device is in automatic detection mode; the operating mode of the device is determined by smartsense. mode1 is also used to execute a host-controlled smartsense routine and reset the alert output. on the rising edge of mode1, the device invokes a smartsense routine. the falling edge of mode1 resets the alert output to its idle state. automatic detection mode a fault condition is defined as a short (under 4 ? ) on either amplifier output to ground. smartsense automati- cally detects and disables the shorted output. the mixer/attenuator combines the two stereo inputs (inl and inr), attenuates the resultant signal by a factor of 2, and redirects the audio playback to the remaining active channel. this allows for full reproduction of a stereo signal through a single headphone while main- taining optimum headroom. the mixed mono signal is output only on the properly loaded channel. if both out- puts are shorted then both outputs go into a high- impedance state and no audio playback occurs. in automatic detection mode (mode1 = mode2 = high), any of the following events trigger a smartsense test sequence: hps rises above 0.8 x v dd, indicating a headphone jack has been inserted into the socket. the 180ma high-side (sourcing) overcurrent thresh- old is approached, and the output is near gnd. the die temperature exceeds the thermal limit (+140 c). power or shutdown is cycled. MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ______________________________________________________________________________________ 13 m1 = l m2 = l ? m1 = h m2 = l ? m1 = l m2 = h ? short detected ? status change ? shdn smartsense forced mono forced stereo mono mode status change ? status change ? status change ? stereo mode status change ? n n n n n n n n n y y y y y y y y y MAX9720 figure 5. smartsense flow diagram mode1 mode2 smartsense operating mode high high enabled automatic detection mode low low disabled shutdown high low disabled forced left mono low high disabled forced stereo high enabled host controlled x reset alert table 1. MAX9720 operating modes
MAX9720 for automatic headphone detection, connect hps to the control pin of a 3-wire headphone jack, as shown in figure 7. with no headphone present, the output imped- ance of the amplifier pulls hps to less than 0.8 x v dd . when a headphone plug is inserted into the jack, the control pin is disconnected from the tip contact, and hps is pulled to v dd through the internal 100k ? pullup. a debounce delay controls the time between hps going high and the initiation of the smartsense test sequence. this time is controlled by an external capacitor on the time pin and allows the user to customize the de- bounce time (see the time capacitor section). shutdown driving mode1 and mode2 to gnd shuts down the MAX9720, disconnects the internal hps pullup resistor, disables the charge pump and amplifiers, sets the amplifier output impedance to 1k ? , and reduces sup- ply current to less than 6a. forced mono mode in forced left mono mode (mode1 = high, mode2 = low), the right channel is disabled and outr goes high impedance. the stereo signal inputs are combined through the mixer/attenuator and output on the left channel. in forced mono mode, the smartsense routine is disabled. forced stereo mode in forced stereo mode (mode1 = low, mode2 = high), the device operates as a stereo headphone amplifier. in forced stereo mode, the smartsense routine is dis- abled. a a l l e e r r t t output the MAX9720 includes an active-low, open-drain alert output that indicates to the master device that smartsense has detected a fault condition. alert trig- gers when an output short circuit is detected through the smartsense routine. during normal operation, alert idles high. if a fault condition is detected, alert pulls the line low. alert remains low until mode1 is toggled from high to low. click-and-pop suppression in conventional single-supply audio amplifiers, the out- put-coupling capacitor is a major contributor of audible clicks and pops. upon startup, the amplifier charges the coupling capacitor to its bias voltage, typically half the supply. likewise, during shutdown, the capacitor is discharged to gnd. a dc shift across the capacitor results, which in turn appears as an audible transient at the speaker. since the MAX9720 does not require out- put-coupling capacitors, no audible transient occurs. additionally, the MAX9720 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 that there are minimal spectral components in the audible range at the output upon startup and shut- down. in most applications, the preamplifier output driving the MAX9720 has a dc bias of typically half the supply. during startup, the input-coupling capacitor is charged to the preamplifier s dc bias voltage through the input resistor of the MAX9720, resulting in a dc shift across the capacitor and an audible click/pop. delaying the startup of the MAX9720 by 4 to 5 time constants (80ms to 100ms) based on r in and c in , relative to the startup of the preamplifier, eliminates this click/pop caused by the input filter. if the smartsense routine occurs during normal opera- tion, a low-level audible transient may be heard. to pre- vent this, a host-controlled smartsense routine should only be executed when alert asserts. 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 14 ______________________________________________________________________________________ tip (signal) sleeve (gnd) figure 6. typical 2-wire (mono) headphone plug outr outl 16 14 15 MAX9720 v dd hps r1 100k ? figure 7. hps configuration
applications information power dissipation under normal operating conditions, linear power ampli- fiers can dissipate a significant amount of power. 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 temperature, and ja is the reciprocal of the derating factor in c/w as specified in the absolute maximum ratings section. for example, ja of the tssop package is +106.38 c/w. the MAX9720 has two power dissipation sources: the charge pump and the two amplifiers. if the power dissipa- tion for a given application exceeds the maximum allowed for a given package, either reduce v dd , increase load impedance, decrease the ambient temperature, or add heat sinking to the device. large output traces improve the maximum power dissipation in the package. thermal overload protection limits total power dissipa- tion in the MAX9720. when the junction temperature exceeds +140 c, the thermal protection circuitry dis- ables the amplifier output stage. the amplifiers are enabled once the junction temperature cools by 15 c, resulting in a pulsing output under continuous thermal overload conditions. output power the MAX9720 is specified for the worst-case condi- tion when both inputs are in phase. under this condi- tion, the amplifiers simultaneously draw current from the charge pump, leading to a slight loss in headroom of v ss . in typical stereo audio applications, the left and right signals present differences in both magnitude and phase, subsequently leading to an increase in the max- imum attainable output power. figure 8 shows the two extreme cases for in- and out-of-phase. in reality, the available power lies between these extremes. powering other circuits from a negative supply an additional benefit of the MAX9720 is the internally generated, negative supply voltage (pv ss ). pv ss is the negative supply for the MAX9720 headphone amplifiers. pv ss can power other devices within a system. limit the current drawn from pv ss to 5ma. exceeding this affects the operation of the headphone amplifiers. a typical application is a negative supply to adjust the contrast of lcd modules. the charge-pump voltage at pv ss is roughly propor- tional to v dd and is not a regulated voltage. consider the charge-pump output impedance when powering other devices from pv ss . see the charge-pump output impedance graph in the typical operating characteristics . use 2.2f charge-pump capacitors for the highest output power; 1f or lower capacitors can also be used for most applications. see the output power vs. load resistance and charge-pump capacitance graph for details of the output power vs. capacitor size. component selection input filtering the input capacitor (c in ), in conjunction with the MAX9720 input impedance, forms a highpass filter that removes the dc bias from an incoming signal (see typical application circuit ). the ac-coupling capacitor allows the amplifier to bias the signal to an optimum dc level. assuming zero-source impedance, the -3db point of the highpass filter is given by: r in is the amplifier s internal input impedance value given in the electrical characteristics . chose c in such that f -3db is well below the lowest frequency of interest. setting f -3db too high affects the amplifier s low-fre- quency response. use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or alu- minum electrolytic. capacitors with high-voltage coeffi- cients, such as ceramics, may result in increased distortion at low frequencies. f rc db in in ? = 3 1 2 p tt disspkg max j max a ja () () = ? MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ______________________________________________________________________________________ 15 100 0.001 040 20 80 120 160 140 total harmonic distortion plus noise vs. output power 0.01 0.1 1 10 output power (mw) thd+n (%) 60 100 v dd = 3v a v = -1v/v f = 1khz r l = 16 ? outputs in phase single- channel outputs out of phase figure 8. thd+n vs. output power with inputs in-/out-of-phase
MAX9720 charge-pump capacitor selection use capacitors with an esr less than 100m ? for opti- mum performance. low-esr ceramic capacitors mini- mize the output resistance of the charge pump. for best performance over the extended temperature range, select capacitors with an x7r dielectric. table 2 lists suggested manufacturers. flying capacitor (c1) the value of the flying capacitor (c1) affects the charge pump s load regulation and output impedance. a c1 value that is too small degrades the device s ability to provide sufficient current drive, which leads to a loss of output voltage. in most applications, 1f for both c1 and c2 provides adequate performance. increasing the value of c1 improves load regulation and reduces the charge-pump output resistance to an extent. see the output power vs. charge pump capacitance and load resistance graph in the typical operating characteristics . above 2.2f, the on-resistance of the switches and the esr of c1 and c2 dominate. hold capacitor (c2) the hold capacitor value and esr directly affect the ripple on pv ss . increasing the value of c2 reduces out- put ripple. likewise, decreasing the esr of c2 reduces both ripple and output impedance. lower capacitance values can be used in systems with low maximum out- put power levels. see the output power vs. charge- pump capacitance and load resistance graph in the typical operating characteristics . power-supply bypass capacitor the power-supply bypass capacitor (c3) lowers the output impedance of the power supply and reduces the impact of the MAX9720 s charge-pump switching tran- sients. bypass v dd with c3, the same value as c1, and place it physically close to the device. time capacitor the time capacitor (c time ) sets the hps debounce time. the debounce time is the delay between hps exceeding 0.8 x v dd and the execution of the smartsense routine. the delay ensures that any exces- sive contact bounce caused by the insertion of a head- phone plug into the jack does not cause hps to register an invalid state (figure 9). the value of the c time in nf equals the nominal delay time in ms, i.e., c time = 10nf = t delay = 10ms. c time values in the 200nf to 600nf range are recommended. adding volume control the addition of a digital potentiometer provides simple, digital volume control. figure 10 shows the MAX9720 with the max5408 dual log taper digital potentiometer used as an input attenuator. connect the high terminal of the max5408 to the audio input, the low terminal to gnd, and the wiper to c in . setting the wiper to the top position passes the audio signal unattenuated. setting the wiper to the lowest position fully attenuates the input. 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 all components associated with the charge pump (c2 and c3) to the pgnd plane. connect pv ss and sv ss together at the device. bypassing of both the positive and negative supplies is accomplished by the charge-pump capaci- tors, c2 and c3 (see typical application circuit ). place capacitors c1 and c3 as close to the device as possi- ble. place capacitor c2 as close to pv ss as possible. route pgnd and all traces that carry switching tran- sients away from sgnd, traces, and components in the audio signal path. 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 16 ______________________________________________________________________________________ supplier phone fax website taiyo yuden 800-348-2498 847-925-0899 www.t-yuden.com tdk 847-803-6100 847-390-4405 www.component.tdk.com table 2. suggested capacitor manufacturers
ucsp applications information for the latest application details on ucsp construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and the recom- mended reflow temperature profile, as well as the latest information on reliability testing results, go to maxim s website at www.maxim-ic.com/ucsp and look up application note: ucsp? wafer-level chip-scale package . MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ______________________________________________________________________________________ 17 t delay 3.1 s 70mv out_ hps headphone inserted figure 9. hps debouncing delay outl MAX9720 inl 9 max5408 h0 l0 5 6 w0a 7 left audio input 11 w1a 10 c in c in right audio input inr outr 14 16 h1 l1 12 11 figure 10. MAX9720 and max5408 volume control circuit chip information transistor count: 4858 process: bicmos 16 15 14 13 12 11 10 9 1 2 3 4 5 6 7 8 v dd outl hps outr sv ss sgnd inr time inl top view top view (bump side down) MAX9720 tssop mode1 c1p pv ss pgnd c1n mode2 alert ucsp a b c d 12 34 pv ss alert inl inr c1n mode2 time sgnd pgnd mode1 hps sv ss c1p v dd outl outr pin configurations
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 18 ______________________________________________________________________________________ max4365 out+ out- in bias v dd shdn 15k ? 15k ? v dd 0.1 f 0.1 f 15k ? 0.1 f 1 f 220nf max4063 MAX9720 outl hps outr c1p cin pv ss sv ss mode1 mode2 1 f 1 f 100k ? 10k ? 1 f inl inr alert time aux_in bias in+ in- 2.2k ? 2.2k ? 0.1 f 0.1 f v dd 0.1 f codec/ baseband processor c out out 1 f 1 f v dd v dd v dd system diagram
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown ______________________________________________________________________________________ 19 charge pump uvlo and shutdown control click-and-pop suppression smartsense and headphone detection mixer attenuator and gain setting mixer attenuator and gain setting c1n c1p pv ss sv ss pgnd sgnd time inr v dd sv ss v dd sgnd inl mode1 mode2 logic control alert r4 10k ? outr left- channel audio input right- channel audio input 1 (d2) 2 (c2) 7 (b2) 8 (a2) 3 (d1) 4 (c1) 5 (b1) 6 (a1) 13 (c4) 16 (d3) 15 (c3) 9 (a3) 14 (d4) 12 (b4) 10 (b3) MAX9720 c1 1 f c2 1 f c4 220nf ( ) ucsp bump. 1.8v to 3.8v c3 1 f c in 1 f sv ss v dd v dd hps outl c in 1 f 11 (a4) sgnd r1 100k ? typical application circuit
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 .) MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown 20 ______________________________________________________________________________________ 16l,ucsp.eps
MAX9720 50mw, directdrive, stereo headphone amplifier with smartsense and shutdown maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 21 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. 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

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