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general description the max9726 stereo, directdrive, headphone amplifier with bassmax and volume control is ideal for portable audio applications where space is at a premium and per- formance is essential. the max9726 operates from a sin- gle 2.7v to 5.5v power supply and includes features that reduce external component count, system cost, board space, and offer improved audio reproduction. high 85db psrr makes the max9726 ideal for direct connec- tion to a battery-powered supply and eliminates the need for a dedicated ldo. the max9726 features maxim? industry-leading click-and-pop suppression circuitry, which reduces/eliminates audible transients during power-up and power-down. the headphone amplifier uses maxim? directdrive archi- tecture that produces a ground-referenced output from a single supply, eliminating the need for large dc-blocking capacitors. the headphone amplifiers deliver 105mw into a 32 load and feature low 0.02% thd+n. the bassmax feature boosts the bass response of the amplifier, improving audio reproduction when using inex- pensive headphones. the integrated volume control fea- tures 64 discrete volume levels, eliminating the need for an external potentiometer. external resistors set the max9726? overall gain allowing for custom gain settings. bassmax and the volume control are enabled through the i 2 c/smbus -compatible interface. shutdown can be con- trolled through the hardware or software interface. the max9726 consumes only 5.5ma of supply current, provides short-circuit and thermal-overload protection, and is specified over the -40? to +85? extended tem- perature range. the max9726 is available in a tiny (2mm x 2.5mm x 0.62mm) 20-bump chip-scale pack- age (ucsp) and a 20-pin tqfn package (4mm x 4mm x 0.75mm). applications features ? 105mw directdrive headphone amplifier eliminates bulky dc-blocking capacitors ? 2.7v to 5.5v single-supply operation ? integrated 64-level volume control ? high 85db psrr at 1khz ? software-enabled bass boost (bassmax) ? industry-leading click-and-pop suppression ? 7.5kv hbm esd-protected headphone outputs ? short-circuit and thermal-overload protection ? low-power shutdown mode (8a) ? low 0.02% thd+n ? i 2 c/smbus-compatible interface ? available in space-saving, thermally efficient packages 20-bump ucsp (2mm x 2.5mm x 0.62mm) 20-pin tqfn (4mm x 4mm x 0.75mm) max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control ________________________________________________________________ maxim integrated products 1 ordering information i 2 c interface volume control bassmax bassmax 2.7v to 5.5v supply scl bml outl bmr outr sda inl inr fbr fbl max9726 simplified block diagram 19-0627; rev 1; 3/08 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. pin configurations appear at end of data sheet. note: all devices specified over the -40? to +85? operating range. + denotes lead-free package. * ep = exposed pad. t = tape and reel. part pin-package slave address max9726aebp+t 20 ucsp-20 1001100 MAX9726AETP+ 20 tqfn-ep* 1001100 max9726bebp+t 20 ucsp-20 1001101 max9726betp+ 20 tqfn-ep* 1001101 smbus is a trademark of intel corp. ucsp is a trademark of maxim integrated products, inc. evaluation kit available
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 2 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ absolute maximum ratings electrical characteristics (5v supply) (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v dd to pgnd............................................................-0.3v to +6v pv ss to sv ss .........................................................-0.3v to +0.3v sgnd to pgnd .....................................................-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 pv ss , sv ss to pgnd ................................................+0.3v to -6v in_ to sgnd...................................(sv ss - 0.3v) to (v dd + 0.3v) fb_ to sgnd..................................(sv ss - 0.3v) to (v dd + 0.3v) sda, scl to pgnd ....................................-0.3v to (v dd + 0.3v) shdn to pgnd ..........................................-0.3v to (v dd + 0.3v) out_ to sgnd ............................................................-3v to +3v bm_ to sgnd ..............................................................-3v to +3v duration of out_ short circuit to pgnd....................continuous continuous current into/out of: v dd , c1p, pgnd, c1n, pv ss , sv ss , or out_ ...........?50ma any other pin................................................................?0ma continuous power dissipation (t a = +70?, multilayer board) 20-bump ucsp (derate 10mw/? above +70?) .......800mw 20-pin tqfn (derate 25.6mw/? above +70?) .......2051mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? outl and outr esd protecti on (human body model )....?.5kv bump temperature (soldering) reflow............................+230? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units general supply voltage range v dd 2.7 5.5 v quiescent supply current i dd no load 5.5 10 ma shutdown supply current i dd_shdn shdn = 0v 8 15 a turn-on time t on 440 ? turn-off time t off 1s thermal-shutdown threshold t thres +150 ? thermal-shutdown hysteresis t hyst 12 ? headphone amplifier output offset voltage v oshp measured between out_ and sgnd, gain = 0db, r in = r f = 10k , t a = +25 c (note 2) ?.6 10 mv input offset voltage of input amplifier v os referenced to sgnd, measured between fbr, fbl, and sgnd 3mv input bias current i b ?0 ?00 na bmr, bml input bias current i bias_bb ?0 ?00 na dc, v dd = 2.7v to 5.5v 80 97 f = 1khz, 100mv p-p ripple 85 power-supply rejection ratio (note 2) psrr f = 20khz, 100mv p-p ripple 74 db r l = 16 124 output power p out thd+n = 1%, f in = 1khz r l = 32 104 mw r l = 16 , p out = 15mw, f in = 1khz 0.04 total harmonic distortion plus noise thd+n r l = 32 , p out = 30mw, f in = 1khz 0.02 %
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 electrical characteristics (5v supply) (continued) (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units bw = 22hz to 22khz 102 signal-to-noise ratio snr r l = 32 , v out = 1.77v rms a-weighted 105 db slew rate sr 1 v/? capacitive drive no sustained oscillations 200 pf output resistance in shutdown r out_shdn v shdn = 0v, measured from out_ to sgnd 50 k into shutdown 59 click-and-pop level k cp peak voltage, a-weighted, 32 samples per second (notes 2, 4) out of shutdown 61 dbv charge-pump switching frequency f cp 515 610 705 khz crosstalk l to r, or r to l, f = 10khz, v out = 1v p-p , r l = 32 , both channels loaded 85 db volume control 0 to 64db ?.1 68db to 96db ?.5 attenuator step accuracy 100db to 120db ? db digital inputs ( shdn , sda, scl) input high voltage v ih 0.7 x v dd v input low voltage v il 0.3 x v dd v input leakage current ? ? digital outputs (sda) output low voltage v ol i ol = 3ma 0.06 v output high current i oh v sda = v dd 1a parameter symbol conditions min typ max units r l = 16 80 output power p out thd+n = 1%, f in = 1khz r l = 32 70 mw r l = 16 , p out = 15mw, f in = 1khz 0.05 total harmonic distortion plus noise thd+n r l = 32 , p out = 30mw, f in = 1khz 0.03 % electrical characteristics (3.3v supply) (v dd = shdn = 3.3v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum volume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1)
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 4 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ parameter symbol conditions min typ max units f = 1khz, 100mv p-p ripple 85 power-supply rejection ratio (note 2) psrr f = 20khz, 100mv p-p ripple 73 db bw = 22hz to 22khz 101 signal-to-noise ratio snr r l = 32 , v out = 1.5v rms a-weighted 104 db into shutdown 62 click-and-pop level k cp peak voltage, a-weighted, 32 samples per second (notes 2, 4) out of shutdown 67 dbv electrical characteristics (3.3v supply) (continued) (v dd = shdn = 3.3v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum volume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units serial clock frequency f scl 0 400 khz bus free time between a stop and a start condition t buf 1.3 ? hold time repeated for a start condition t hd:sta 0.6 ? low period of the scl clock t low 1.3 ? high period of the scl clock t high 0.6 ? setup time for a repeated start condition t su:sta 0.6 ? data hold time t hd:dat 0 0.9 ? data setup time t su:dat 100 ns rise time of both sda and scl signals t r 300 ns fall time of both sda and scl signals t f 300 ns setup time for stop condition t su:sto 0.6 ? pulse width of suppressed spike t sp 50 ns capacitive load for each bus line c l_bus 400 pf timing characteristics (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. t a = t min to t max , unless otherwise noted. typical values are at t a = +25?.) (notes 1, 3) note 1: all specifications are 100% tested at t a = +25?. temperature limits are guaranteed by design. note 2: inputs ac-coupled to sgnd. note 3: guaranteed by design. note 4: headphone testing performed with a 32 resistive load connected to pgnd. mode transitions are controlled by shdn . k cp level is calculated as 20log[(peak voltage during mode transition, no input signal)/1v rms ]. units are expressed in dbv.
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control total harmonic distortion plus noise vs. output power output power (mw) thd+n (%) max9726 toc01 0 20 40 60 80 100 120 140 160 0.001 0.01 0.1 1 10 100 f in = 10khz f in = 1khz v dd = 3.3v r l = 16 f in = 20hz total harmonic distortion plus noise vs. output power output power (mw) thd+n (%) max9726 toc02 0 20406080100120140160 0.001 0.01 0.1 1 10 100 f in = 10khz f in = 1khz v dd = 3.3v r l = 32 f in = 20hz total harmonic distortion plus noise vs. output power output power (mw) thd+n (%) max9726 toc03 0 20 40 60 80 100 120 140 160 180 200 0.001 0.01 0.1 1 10 100 v dd = 5v r l = 16 f in = 1khz f in = 10khz f in = 20hz total harmonic distortion plus noise vs. output power output power (mw) thd+n (%) max9726 toc04 0 20 40 60 80 100 120 140 160 0.001 0.01 0.1 1 10 100 v dd = 5v r l = 32 f in = 1khz f in = 10khz f in = 20hz total harmonic distortion plus noise vs. frequency frequency (hz) thd+n (%) max9726 toc05 10 100 1k 10k 100k 0.001 0.01 0.1 1 10 v dd = 3.3v r l = 16 output power = 60mw output power = 20mw total harmonic distortion plus noise vs. frequency frequency (hz) thd+n (%) max9726 toc06 10 100 1k 10k 100k 0.001 0.01 0.1 1 10 v dd = 3.3v r l = 32 output power = 60mw output power = 20mw total harmonic distortion plus noise vs. frequency frequency (hz) thd+n (%) max9726 toc07 10 100 1k 10k 100k 0.001 0.01 0.1 1 10 v dd = 5v r l = 16 output power = 80mw output power = 40mw typical operating characteristics (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. outputs in phase, both channels loaded. t a = +25?, unless otherwise noted.) (see the functional diagram/typical operating circuit ) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 6 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ typical operating characteristics (continued) (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. outputs in phase, both channels loaded. t a = +25?, unless otherwise noted.) (see the functional diagram/typical operating circuit ) total harmonic distortion plus noise vs. frequency frequency (hz) thd+n (%) max9726 toc08 10 100 1k 10k 100k 0.001 0.01 0.1 1 10 v cc = 5v r l = 32 output power = 80mw output power = 40mw power dissipation vs. output power max9726 toc09 total output power (mw) power dissipation (mw) 160 120 80 40 100 200 300 400 500 600 0 0200 v dd = 3.3v f in = 1khz p out = p outr + p outl r l = 32 r l = 16 power dissipation vs. output power max9726 toc10 total output power (mw) power dissipation (mw) 200 160 120 80 40 100 200 300 400 500 600 700 800 900 1000 0 0240 v dd = 5v f in = 1khz p out = p outr + p outl r l = 16 r l = 32 output power vs. load resistance max9726 toc11 load resistance ( ) output power (mw) 100 20 40 60 80 100 120 0 10 1000 v dd = 3.3v, f in = 1khz thd+n = 10% thd+n = 1% output power vs. load resistance max9726 toc12 load resistance ( ) output power (mw) 100 30 60 90 120 150 180 210 0 10 1000 v dd = 5v, f in = 1khz thd+n = 10% thd+n = 1% output power vs. supply voltage max9726 toc13 supply voltage (v) output power (mw) 5.0 4.5 4.0 3.5 3.0 20 40 60 80 100 120 140 160 180 0 2.5 5.5 r l = 16 f in = 1khz thd+n = 10% thd+n = 1% output power vs. supply voltage max9726 toc14 supply voltage (v) output power (mw) 20 40 60 80 100 120 140 160 0 5.0 4.5 4.0 3.5 3.0 2.5 5.5 thd+n = 10% thd+n = 1% r l = 32 f in = 1khz
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7 power-supply rejection ratio vs. frequency max9726 toc15 frequency (hz) psrr (db) 10k 1k 100 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -110 10 100k v dd = 5v + 100mv p-p r in = r f = 10k power-supply rejection ratio vs. frequency max9726 toc16 frequency (hz) psrr (db) 10k 1k 100 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 -110 10 100k v dd = 3.3v + 100mv p-p r in = r f = 10k crosstalk vs. frequency frequency (hz) crosstalk (db) max9726 toc17 -120 -110 -100 -90 -80 -70 -60 10 100 1k 10k 100k v in = 1v p-p r l = 32 g = 0db right to left left to right typical operating characteristics (continued) (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. outputs in phase, both channels loaded. t a = +25?, unless otherwise noted.) (see the functional diagram/typical operating circuit ) crosstalk vs. frequency frequency (hz) crosstalk (db) max9726 toc18 -100 -90 -80 -70 -60 -50 -40 10 100 1k 10k 100k v in = 1v p-p r l = 32 g = -10db left to right right to left bassmax frequency response max9726 toc19 frequency (hz) gain (db) 10k 1k 100 10 15 20 25 30 35 40 10 1 100k r2 = 36k c3 = 0.068 f r2 = 22k c3 = 0.1 f r2 = 10k c3 = 0.22 f r1 = 47k r l = 32 bassmax disabled output fft max9726 toc20 frequency (khz) amplitude (dbv) 15 10 5 -120 -100 -80 -60 -40 -20 0 -140 020 v in = 100mv rms atten = 60db v out = -60dbv r l = 320 f in = 1khz v dd = 5v output power vs. charge-pump capacitance and load resistance max9726 toc21 load resistance ( ) output power (mw) 45 40 30 35 20 25 15 70 80 90 100 110 120 130 140 150 160 60 10 50 v dd = 5v f in = 1khz thd+n = 1% c1 = c2 = 2.2 f c1 = c2 = 1 f c1 = c2 = 0.68 f
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 8 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ output power vs. charge-pump capacitance and load resistance max9726 toc22 load resistance ( ) output power (mw) 45 40 35 30 25 20 15 65 70 75 80 85 90 60 10 50 v dd = 3.3v f in = 1khz thd+n = 1% c1 = c2 = 2.2 f c1 = c2 = 1 f c1 = c2 = 0.68 f power-up/power-down max9726 toc23 20ms/div v dd 2v/div v out_ 10mv/div r l = 32 exiting shutdown max9726 toc24 100 s/div v shdn 5v/div v in_ 200mv/div v out_ 2v/div entering shutdown max9726 toc25 20 s/div v shdn 5v/div v in_ 200mv/div v out_ 2v/div supply current vs. supply voltage max9726 toc26 supply voltage (v) supply current (ma) 6 5 3 4 4.9 5.0 5.1 5.2 5.3 5.4 5.5 5.6 4.8 2 no load inputs ac grounded shutdown current vs. supply voltage max9726 toc27 supply voltage (v) shutdown current ( a) 5 4 3 5 6 7 8 9 10 4 26 no load inputs ac grounded typical operating characteristics (continued) (v dd = shdn = 5v, pgnd = sgnd = 0v, c1 = c2 = 1?, c preg = c nreg = 1?, bm_ = 0v, r in = 10k , r f = 10k , maximum vol- ume (overall gain = 0db), bassmax disabled. load connected between out_ and pgnd where specified. outputs in phase, both channels loaded. t a = +25?, unless otherwise noted.) (see the functional diagram/typical operating circuit )
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 9 pin description pin bump tqfn ucsp name function 1a1 v dd power-supply input. bypass v dd to pgnd with a 1? capacitor. 2 a2 c1p charge-pump flying capacitor positive terminal. connect a 1? capacitor between c1p and c1n. 3 a3 pgnd power ground. connect to sgnd. 4 a4 c1n charge-pump flying capacitor negative terminal. connect a 1? capacitor between c1p and c1n. 5a5pv ss charge-pump output. connect to sv ss and bypass with a 1? capacitor to pgnd. 6 b3 sda serial data input. connect a pullup resistor greater than 500 from sda to v dd . 7 c3 scl serial clock input. connect a pullup resistor greater than 500 from scl to v dd . 8c2 shdn active-low shutdown input. drive shdn low to disable the max9726. connect shdn to v dd while bit 7 is high for normal operation (see the command register section). 9 b4 fbl left-channel feedback output. connect a feedback resistor between fbl and inl. see the gain-setting components section. 10 b5 inl left-channel input. connect an input resistor to inl. see the gain-setting components section. 11 c5 inr right-channel input. connect an input resistor to inr. see the gain-setting components section. 12 c4 fbr right-channel feedback output. connect a feedback resistor between fbr and inr. see the gain-setting components section. 13 d5 sgnd signal ground. connect to pgnd. 14 d2 nreg negative supply regulator voltage. bypass nreg to pgnd with a 1? capacitor. 15 d4 bmr right bassmax input. connect an external passive network between outr and bmr to apply bass boost to the right-channel output. see the gain-setting components section. connect bmr to sgnd if bassmax is not used. 16 d1 sv ss headphone amplifier negative power-supply input. connect to pv ss and bypass with a 1? capacitor to pgnd. 17 c1 outr right headphone output 18 b1 outl left headphone output 19 d3 bml left bassmax input. connect an external passive network between outl and bml to apply bass boost to the right-channel output. see the gain-setting components section. connect bml to sgnd if bassmax is not used. 20 b2 preg positive supply regulator voltage. bypass preg to pgnd with a 1? capacitor. ep ep exposed pad. connect ep to sv ss or leave unconnected.
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 10 ______________________________________________________________________________________ detailed description the max9726 stereo headphone amplifier features maxim? directdrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply headphone amplifiers. the max9726 con- sists of two 105mw class ab headphone amplifiers, two adjustable gain preamplifiers, hardware/software shut- down control, inverting charge pump, integrated 64- level volume control, bassmax feature, comprehensive click-and-pop suppression circuitry, and an i 2 c- /smbus-compatible interface (see the functional diagram/typical operating circuit ). a negative power supply (pv ss ) is created internally by inverting the posi- tive supply (v dd ). powering the amplifiers from v dd and pv ss increases the dynamic range of the amplifiers to almost twice that of other single-supply amplifiers, increasing the total available output power. high psrr topologies eliminate the need for an external voltage regulator. an i 2 c-/smbus-compatible interface allows serial com- munication between the max9726 and a microcon- troller. the internal command register controls the shutdown status of the max9726, enables the bassmax circuitry, and sets the volume level (see the volume control section). the max9726? bassmax circuitry improves audio reproduction by boosting the bass response of the amplifier, compensating for any low- frequency attenuation introduced by the headphone. external components set the max9726? overall gain allowing for custom gain settings (see the gain-setting components section). amplifier volume is digitally pro- grammable to any one of 64 levels. directdrive traditional single-supply headphone amplifiers have their outputs biased about a nominal dc voltage, typi- cally half the supply, for maximum dynamic range. large coupling capacitors are needed to block this dc bias from the headphone. without these capacitors, a significant amount of dc current flows to the head- phone, resulting in unnecessary power dissipation and possible damage to both the headphone and head- phone amplifier. in addition to the cost and size disad- vantages, the dc-blocking capacitors required by conventional headphone amplifiers limit low-frequency response and can distort the audio signal. maxim? directdrive architecture uses a charge pump to create an internal negative supply voltage. this allows the max9726 headphone amplifier outputs to be biased about ground, almost doubling the dynamic range while operating from a single supply (see figure 1). with no dc component, there is no need for the large dc-blocking capacitors. instead of two large (up to 220?) tantalum capacitors, the max9726 charge pump requires only two small 1? ceramic capacitors, 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 graphs in the typical operating characteristics for details of the possible capacitor sizes. v dd * * v dd is internally limited to 2.5v due to absolute maximum ratings and to limit power dissipation. -v dd * gnd v out conventional driver-biasing scheme directdrive biasing scheme v dd /2 v dd v dd gnd v out 2v dd * figure 1. traditional amplifier output vs. max9726 directdrive output
charge pump the max9726 features a low-noise charge pump. the 610khz switching frequency is well beyond the audio range, and does not interfere with the audio signals. this enables the max9726 to achieve an snr of 102db. the switch drivers feature a controlled switch- ing speed that minimizes noise generated by turn-on and turn-off transients. limiting the switching speed of the charge pump also minimizes di/dt noise caused by the parasitic bond wire and trace inductance. click-and-pop suppression in conventional single-supply headphone amplifiers, the output coupling capacitor is a major contributor of audible clicks and pops. the amplifier charges the coupling capacitor to its output bias voltage at startup. during shutdown, the capacitor is discharged. this charging and discharging results in a dc shift across the capacitor, which appears as an audible transient at the headphone speaker. since the max9726 head- phone amplifier does not require output-coupling capacitors, no audible transients occur. additionally, the max9726 features extensive click-and- pop suppression that eliminates any audible transient sources internal to the device. the power-up/power- down graph in the typical operating characteristics shows that there are minimal transients at the output upon startup or shutdown. in most applications, the preamplifier driving the max9726 has a dc bias of typically half the supply. the input-coupling capacitor is charged to the pream- plifier? bias voltage through the max9726? input resis- tor (r in ) during startup. the resulting voltage shift across the capacitor creates an audible click-and-pop. delay the rise of shdn by at least four time constants (4 x r in x c in ) relative to the start of the preamplifier to avoid clicks/pops caused by the input filter. shutdown the max9726 features a 8?, low-power shutdown mode that reduces quiescent current consumption and extends battery life. shutdown is controlled by a hard- ware and software interface. driving the shdn input low disables the drive amplifiers, bias circuitry, charge pump, and sets the headphone amplifier output resis- tance to 50k . similarly, the max9726 enters shutdown when bit seven (b7) in the control register is set to 0 (see the command register section). shdn and b7 must be high to enable the max9726. the i 2 c/smbus interface is active and the contents of the command register are not affected when in shutdown. this allows the master to write to the max9726 while in shutdown. bassmax (bass boost) typical headphones do not have a flat-frequency response. the small physical size of the diaphragm does not allow the headphone speaker to efficiently reproduce low frequencies. this physical limitation results in attenuated bass response. the max9726 includes a bass-boost feature that compensates for the headphone? poor bass response by increasing the amplifier gain at low frequencies. the directdrive output of the max9726 has more head- room than typical single-supply headphone amplifiers. this additional headroom allows boosting the bass fre- quencies without the output signal clipping. program the bassmax gain and cutoff frequency with external components connected between out_ and bm_ (see the gain-setting components section and the functional diagram/typical operating circuit ). use the i 2 c-compatible interface to program the command reg- ister to enable/disable the bassmax circuit. bm_ is connected to the noninverting input of the out- put amplifier when bassmax is enabled. bm_ is pulled to sgnd when bassmax is disabled. the typical appli- cation of the bassmax circuit involves feeding a low- pass version of the output signal back to the amplifier. this is realized using positive feedback from out_ to bm_. figure 2 shows the connections needed to imple- ment bassmax. max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11 c3 r2 r1 to headphone speaker r r out_ bm_ from attenuator stage max9726 bassmax enable figure 2. bassmax external connections
max9726 volume control the max9726 includes a 64-level volume control that adjusts the gain of the output amplifiers according to the code contained in the command register. volume is programmed through the command register bits [5:0]. table 5 shows all possible attenuation settings of the max9726 with respect to the overall gain set by the external gain-setting resistors (r in and r f ). mute atten- uation is typically better than 120db when driving a 32 load. to perform smooth-sounding volume changes, step through all intermediate volume settings at a rate of approximately 2ms per step when a volume change occurs. serial interface the max9726 features an i 2 c-/smbus-compatible, 2-wire serial interface consisting of a serial data line (sda) and a serial clock line (scl). sda and scl facili- tate communication between the max9726 and the master at clock rates up to 400khz. figure 3 shows the 2-wire interface timing diagram. the max9726 is a receive-only slave device relying on the master to gen- erate the scl signal. the max9726 cannot write to the sda bus except to acknowledge the receipt of data from the master. the master, typically a microcontroller, generates scl and initiates data transfer on the bus. a master device communicates to the max9726 by transmitting the slave address with the read/ write (r/ w ) bit followed by the data word. each transmit sequence is framed by a start (s) or repeated start (sr) condition and a stop (p) condition. each word trans- mitted over the bus is 8 bits long and is always followed by an acknowledge clock pulse. the max9726 sda line operates as both an input and an open-drain output. a pullup resistor, greater than 500 , is required on the sda bus. the max9726 scl line operates as an input only. a pullup resistor, greater than 500 , is required on scl if there are multiple mas- ters on the bus, or if the master in a single-master sys- tem has an open-drain scl output. series resistors in line with sda and scl are optional. series resistors protect the digital inputs of the max9726 from high- voltage spikes on the bus lines, and minimize crosstalk and undershoot of the bus signals. directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 12 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ scl sda start condition stop condition repeated start condition start condition t hd, sta t su, sta t hd, sta t sp t buf t su, sto t low t su, dat t hd, dat t high t r t f figure 3. 2-wire serial-interface timing diagram
bit transfer one data bit is transferred during each scl cycle. the data on sda must remain stable during the high period of the scl pulse since changes in sda while scl is high are control signals (see the start and stop conditions section). sda and scl idle high when the i 2 c bus is not busy. start and stop conditions sda and scl idle high when the bus is not in use. a master device initiates communication by issuing a start condition. a start condition is a high-to-low transition on sda with scl high. a stop condition is a low-to-high transition on sda while scl is high (figure 5). a start condition from the master signals the beginning of a transmission to the max9726. the mas- ter terminates transmission, and frees the bus, by issu- ing a stop condition. the bus remains active if a repeated start condition is generated instead of a stop condition. early stop conditions the max9726 recognizes a stop condition at any point during data transmission except if the stop condition occurs in the same high pulse as a start condition. slave address the slave address is defined as the seven most signifi- cant bits (msbs) of the serial data transmission. the first byte of information sent to the max9726 after the start condition must contain the slave address and r/ w bit (see table 1). the max9726 is a slave device only capable of being written to. the sent r/ w bit must always be set to zero when configuring the max9726. the max9726 acknowledges the receipt of its address even if r/ w is set to 1. however, the max9726 does not drive sda. addressing the max9726 with r/ w set to 1 causes the master to receive all ones regardless of the contents of the command register. acknowledge the acknowledge bit (ack) is a clocked 9th bit that the max9726 uses to handshake receipt each byte of data (see figure 6). the max9726 pulls down sda during the master generated 9th clock pulse. the sda line must remain stable and low during the high period of the acknowledge clock pulse. monitoring ack allows for detection of unsuccessful data transfers. an unsuc- cessful data transfer occurs if a receiving device is busy or if a system fault has occurred. in the event of an unsuccessful data transfer, the bus master may reattempt communication. max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 13 scl sda ssrp figure 4. start, stop, and repeated start conditions 1 scl start condition sda 289 clock pulse for acknowledgment acknowledge not acknowledge figure 5. acknowledge bit table 1. max9726 slave address with read/ write bit part a6 (msb) a5 a4 a3 a2 a1 a0 r/ w max9726a 1 0011000 max9726b 1 0011010
max9726 write data format a write to the max9726 includes transmission of a start condition, the slave address with the r/ w bit set to 0 (see table 1), one byte of data to configure the command register, and a stop condition. figure 6 illustrates the proper format for one frame. the max9726 only accepts write data, but it acknowl- edges the receipt of its address byte with the r/ w bit set to 1. the max9726 does not write to the sda bus in the event that the r/ w bit is set to 1. subsequently, the master reads all 1? from the max9726. always set the r/ w bit to zero to avoid this situation. command register the max9726 has one command register that is used to enable/disable shutdown, enable/disable bassmax, and set the volume. table 2 describes the function of the bits contained in the command register. set b7 to 0 to shutdown the max9726. the max9726 wakes up from shutdown when b7 is set to 1 provided shdn is high. shdn must be high and b7 must be set to 1 for the max9726 to operate normally (see table 3). set b6 to 1 to enable bassmax (see table 4). the out- put signal? low-frequency response is boosted accord- ing to the external components connected between out_ and bm_. see the gain-setting components sec- tion for details on choosing the external components. adjust the max9726? volume with control bits [5:0]. the volume is adjustable to one of 64 steps ranging from full mute to the maximum gain set by the external components. table 5 lists all the possible volume set- tings for the max9726. figure 7 shows the volume-con- trol transfer function for the max9726. directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 14 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ s a 0 acknowledge from max9726 r/w start condition acknowledge from max9726 b7 b6 b5 b4 b3 b2 command byte is stored on receipt of stop condition a p b1 b0 slave address command byte stop condition figure 6. write data format example max9726 fig07 code (decimal) attenuation of max. gain setting (db) 48 32 16 100 80 60 40 20 0 120 064 figure 7. volume-control transfer function table 2. command register b7 b6 b5 b4 b3 b2 b1 b0 shutdown bassmax enable volume (see table 5) table 3. shutdown control, shdn = v dd mode b7 disabled 0 enabled 1 table 4. bassmax control mode b6 bassmax disabled 0 bassmax enabled 1
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 15 table 5. max9726 volume-control settings b5 b4 b3 b2 b1 b0 (lsb) attenuation of maximum gain setting (db) 000000 120 000001 116 000010 112 000011 108 000100 104 000101 100 000110 96 000111 92 001000 88 001001 84 001010 80 001011 76 001100 72 001101 68 001110 64 001111 62 010000 60 010001 58 010010 56 010011 54 010100 52 010101 50 010110 48 010111 46 011000 44 011001 42 011010 40 011011 38 011100 36 011101 34 011110 32 011111 30 100000 28
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 16 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ table 5. max9726 volume-control settings (continued) b5 b4 b3 b2 b1 b0 (lsb) attenuation of maximum gain setting (db) 100001 27 100010 26 100011 25 100100 24 100101 23 100110 22 100111 21 101000 20 101001 19 101010 18 101011 17 101100 16 101101 15 101110 14 101111 13 110000 12 110001 11 110010 10 110011 9 110100 8 110101 7 110110 6 110111 5 111000 4 111001 3 111010 2.5 111011 2 111100 1.5 111101 1 111110 0.5 111111 0
power-on reset the contents of the max9726? command register at power-on are as shown in table 6. applications information power dissipation and heatsinking 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?, t a is the ambient tempera- ture, and ja is the reciprocal of the derating factor in ?/w as specified in the absolute maximum ratings section. for example, ja for the tqfn package is +39?/w. if the power dissipation exceeds the rated package dissipation, reduce v dd , increase load impedance, decrease the ambient temperature, or add heatsinking. large output, supply, and ground traces decrease ja , allowing more heat to be transferred from the package to surrounding air. output dynamic range dynamic range is the difference between the noise floor of the system and the output level at 1% thd+n. it is essential that a system? dynamic range be known before setting the maximum output gain. output clip- ping occurs if the output signal is greater than the dynamic range of the system. the directdrive architec- ture of the max9726 has increased dynamic range (for a given v dd ) compared to other single-supply ampli- fiers. due to the absolute maximum ratings of the max9726 and to limit power dissipation, the max9726 includes internal circuitry that limits the output voltage to approximately ?.5v. use the thd+n vs. output power graphs in the typical operating characteristics section to identify the sys- tem? dynamic range. find the output power that caus- es 1% thd+n for a given load. this point indicates the output power that causes the output to begin to clip. use the following equation to determine the peak-to- peak output voltage that causes 1% thd+n for a given load. where p out_1% is the output power that causes 1% thd+n, r l is the load resistance, and v out(p-p) is the peak-to-peak output voltage. determine the voltage gain (a v ) necessary to attain this output voltage based on the maximum peak-to-peak input voltage (v in(p-p) ): the maximum voltage gain setting is determined by external components (see the gain-setting components section). uvlo the max9726 features an undervoltage lockout (uvlo) function that prevents the device from operating if the supply voltage is less than 2.7v. this feature ensures proper operation during brownout conditions and pre- vents deep battery discharge. once the supply voltage exceeds the uvlo threshold, the max9726 charge pump is turned on and the amplifiers are powered, pro- vided that shdn is high and b7 in the command regis- ter is set to 1. component selection charge-pump capacitor selection use ceramic capacitors with a low esr for optimum performance. for optimal performance over the extend- ed temperature range, select capacitors with an x7r dielectric. charge-pump flying capacitor (c1) the charge-pump flying capacitor connected between c1n and c1p affects the charge pump? load regula- tion and output impedance. choosing a flying capacitor that is too small degrades the max9726? ability to pro- vide sufficient current drive and leads to a loss of out- put voltage. increasing the value of the flying capacitor improves load regulation and reduces the charge- pump output impedance. see the output power vs. charge-pump capacitance and load resistance graphs in the typical operating characteristics . a v v v out p p in p p = ? ? () () vpr out p p out l () _% ( ? = 22 1 p tt d max j max a ja () () = ? max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 17 table 6. initial power-up command register status mode b7b6b5b4b3b2b1b0 power-on reset 1 1 1 1 1 1 1 1
max9726 charge-pump hold capacitor (c2) the hold capacitor? value and esr directly affect the ripple at pv ss . ripple is reduced by increasing the value of the hold capacitor. choosing a capacitor with lower esr reduces ripple 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 graphs in the typical operating characteristics . c2 should be greater than or equal to the value of c1. input-coupling capacitor the ac-coupling capacitor (c in ) and input resistor (r in ) form a highpass filter that removes any dc bias from an input signal. see the functional diagram/ typical operating circuit . c in prevents any dc compo- nents from the input signal source from appearing in the amplifier outputs. the -3db point of the highpass fil- ter, assuming zero-source impedance due to the input signal source, is given by: choose c in such that f -3db is well below the lowest fre- quency of interest. setting f -3db too high affects the amplifier? low-frequency response. use capacitors with low-voltage coefficient dielectrics. aluminum electrolytic, tantalum, or film dielectric capacitors are good choices for ac-coupling capacitors. capacitors with high-voltage coefficients, such as ceramics (non-c0g dielectrics), can result in increased distortion at low frequencies. gain-setting components with bassmax disabled, the maximum gain of the max9726 is set by the values of the external resistors r in and r f (see the functional diagram/typical operating circuit ). when bassmax is disabled, the maximum gain of the max9726 is: where a v is the maximum voltage gain in db. the over- all voltage gain of the max9726 with bassmax disabled is equal to: where atten db_vol is the attenuation due to the vol- ume setting in db and a total is the overall voltage gain of the max9726 in db. when bassmax is enabled, the bass-boost low-fre- quency response is set by the ratio of r1 to r2, by the following equation (see figure 2): where a boost is the voltage gain boost at low frequen- cies in db. a boost is added to the gain realized by the volume setting and the gain set by resistors r in and r f (a v ). the overall voltage gain of the max9726 at low frequencies with bassmax enabled is equal to: where a total_bb is the overall gain of the max9726 at low frequencies in db. to maintain circuit stability, the ratio must not exceed one-half. a ratio equal to or less than one-third is recommended. the switch that shorts bm_ to sgnd, when bassmax is disabled, can have an on-resistance as high as 300 . choose a value for r1 that is greater than 40k to ensure that positive feedback is negligible when bassmax is dis- abled. table 7 contains a list of r2 values, with r1 = 47k , and the corresponding low-frequency gain boost. a a a atten db total bb v boost db vol __ () =+ ? a rr rr db boost = + ? ? ? ? ? ? ? 20 12 12 log ( ) a a atten db total v db vol = ? _ () a r r db v f in = ? ? ? ? ? ? 20 log ( ) f rc hz db in in ? = 3 1 2 () directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 18 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ table 7. bassmax gain examples (r1 = 47k ) r2 (k ) low-frequency gain boost (db) 39 20.6 33 15.1 27 11.3 22 8.8 15 5.7 10 3.7 r rr 2 12 +
the low-frequency boost attained by the bassmax cir- cuit is added to the gain realized by the maximum gain and volume settings. select the bassmax gain so that the output signal remains within the dynamic range of the max9726. output signal clipping occurs at low fre- quencies if the bassmax gain boost is excessively large. see the output dynamic range section. capacitor c3 forms a pole and a zero according to the following equations: f pole is the frequency at which the gain boost begins to roll off. f zero is the frequency at which the bass- boost gain no longer effects the transfer function. at frequencies greater than or equal to f zero , the gain set by resistors r in and r f and the volume control attenua- tion dominate. table 8 contains a list of capacitor val- ues and the corresponding poles and zeros for a given dc gain. see figure 8 for an example of a gain profile using bassmax. single-pole active lowpass filter (lpf) to configure the max9726 as an active single-pole low- pass filter (figure 9), connect a single feedback capac- itor (c f ) in parallel with the feedback resistor (r f ). the -3db point (below passband) of the active lowpass filter is equal to: the passband gain of the active filter is determined by the external component values described in the gain- setting components section. to minimize distortion, use capacitors with low-voltage coefficient dielectrics when selecting c f . film or c0g dielectric capacitors are good choices for feedback capacitors. capacitors with high-voltage coefficients, such as ceramics (non-c0g dielectrics), can result in increased distortion. f rc hz db ff ? = 3 1 2 () f rr crr hz f rr crr hz pole zero = = + ? 12 2312 12 2312 () () max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 19 table 8. bassmax pole and zero examples for a gain boost of 8.8db (r1 = 47k , r2 = 22k ) c3 (nf) f pole (hz) f zero (hz) 100 38 106 82 47 130 68 56 156 56 68 190 47 81 230 22 174 490 10 384 1060 max9726 fig08 frequency (hz) gain (db) 1k 100 -8 -6 -4 -2 0 2 4 6 8 10 -10 10 10k bassmax frequency response bassmax enabled f zero f pole r1 = 47k r2 = 22k c3 = 0.1 f r l = 32 bassmax disabled figure 8. bassmax gain profile example c f r f r in fb_ in_ to attenuator stage f -3db = 1 2 r f c f max9726 figure 9. single-pole active lowpass filter
max9726 summing amplifier (audio mixer) figure 10 shows the max9726 configured as a sum- ming amplifier, which allows multiple audio sources to be linearly mixed together. using this configuration, the output of the max9726 is equal to the weighted sum of the input signals: as shown in the above equation, the weighting or amount of gain applied to each input signal source is determined by the ratio of r f and the respective input resistor (r in1 , r in2 , r in3 ) connected to each signal source. when bassmax is enabled, the low-frequency gain (a boost ) set by r1, r2, and c3 (see the gain- setting components section) adds to the gain deter- mined by r f and r in_ . select r f and r in_ such that the dynamic range of the max9726 is not exceeded when bassmax is enabled and/or when the input signals are at their maximum values and in phase with each other. layout and grounding proper layout and grounding are essential for optimum performance. connect pgnd and sgnd together at a single point (star ground point) on the pc board. connect pv ss to sv ss at the device and bypass this connection with a 1? capacitor to pgnd. bypass v dd , preg, and nreg to pgnd with a 1? capacitor. place the power-supply bypass capacitor and the charge- pump hold capacitor as close as possible to the max9726. route pgnd, and all traces that carry switching transients, away from sgnd and the audio signal path. route digital signal traces away from the audio signal path. make traces perpendicular to each other when routing digital signals over or under audio signals. the tqfn package features an exposed pad that improves thermal efficiency. ensure that the exposed pad is electrically isolated from pgnd, sgnd, and v dd . connect the exposed pad to pv ss when the board layout dictates that the exposed pad cannot be left unconnected. ucsp applications information for the latest application details on ucsp construction, dimensions, tape carrier information, pc board tech- niques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results, go to maxim? website at www.maxim-ic.com/ucsp and look up the application note: ucsp? wafer-level chip-scale package . vv r r v r r v r r out in f in in f in in f in _ =++ ? ? ? ? ? ? ? 1 1 2 2 3 3 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 20 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ diagram shown with bassmax disabled. r f r in2 fb_ in_ to attenuator stage v fb_ = + v in1 r f -( ) r in1 max9726 + v in2 r f r in2 v in3 r f r in3 c in v in2 r in1 c in v in1 r in3 c in v in3 figure 10. summing amplifier
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 21 functional diagram/typical operating circuit positive regulator preg v cc v dd inl fbl outl bml bmr outr v ee 1 f r in 10k 10 (e2) 1 (a1) 20 (b2) 6 (c2) 7 (c3) 14 (b4) 2 (b1) 4 (d1) 13 (e4) 3 (c1) 5 (e1) c preg 1 f c in 1 f c in 1 f c nreg 1 f c1 1 f 9 (d2) 8 (b3) 18 (a2) 19 (c4) 15 (d4) 17 (a3) r f 10k left audio input right audio input 2.7v to 5.5v r1 47k r2 22k c3 0.1 f c3 0.1 f r2 22k r1 47k 10k to i 2 c master r f and r in are chosen for a gain of 20db. bassmax circuit tuned for +8.8db at 106hz. ( ) ucsp package 10k sda negative regulator nreg sgnd pv ss 16 (a4) 11 (e3) sv ss inr 12 (d3) fbr i 2 c interface scl charge pump c1p c1n v cc v ee r r 0 to 120db attenuator v cc v ee v cc v ee 0 to 120db attenuator r r shdn off on c2 1 f pgnd r in 10k v ee v cc r f 10k max9726
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control 22 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ system diagrams outl outr bml bmr c nreg 1 f c1 1 f 10k 10k controller pgnd pv ss sv ss sgnd 2.7v to 5.5v fm radio ic sda v dd preg nreg scl shdn fbl inl c in 1 f r in 10k r f 100k max9726 c preg 1 f 1 f fbr inr c1p c1n c in 1 f r in 10k r f 100k c3 0.1 f r1 47k r2 22k r2 22k c3 0.1 f c3 0.1 f r1 47k outl outr bml bmr c nreg 1 f c1 1 f 10k 10k controller pgnd pv ss sv ss sgnd 2.7v to 5.5v fm radio ic sda v dd preg nreg scl shdn fbl inl c in 1 f r in 10k r f 100k max9726 c preg 1 f 1 f fbr inr c1p c1n c in 1 f r in 10k r f 100k c2 0.1 f r1 47k r2 22k r2 22k c3 0.1 f c3 0.1 f r1 47k audio dac c in 0.1 f r in 100k c in 0.1 f r in 100k
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 pin configurations 19 + 20 18 17 7 6 8 c1p c1in pv ss 9 v dd nreg fbr inr bmr 12 outl 45 15 14 12 11 bml preg fbl shdn scl sda max9726 pgnd sgnd 3 13 outr 16 10 inl sv ss tqfn (4mm x 4mm) top view ucsp outl outr sv ss v dd 1 a b c 234 5 pv ss inl inr sgnd d c1n fbl fbr bmr pgnd sda scl bml c1p preg shdn nreg top view (bump side down) chip information process: bicmos package information for the latest package outline information, go to www.maxim-ic.com/packages . package type package code document no. 20 ucsp b20-1 21-0095 20 tqfn-ep t2044-3 21-0139
max9726 directdrive, headphone amplifier with bassmax, i 2 c, volume and gain control maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 24 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2008 maxim integrated products is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 9/06 initial release 1 3/08 released ucsp packaging. removed future product reference. 1

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