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_______________________________________________________________ maxim integrated products 1 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com. MAX98500 boosted 2.2w class d amplifier with automatic level control 19-5189; rev 0; 5/10 simplified block diagram general description the MAX98500 is a high-efficiency, class d audio ampli - fier that features an integrated boost converter to deliver a constant output power over a wide range of battery supply voltages. the boost converter operates at 2mhz, requiring only a small (2.2 f h) external inductor and capacitor. the automatic level control has a battery tracking func - tion that reduces the output swing as the supply voltage drops, preventing collapse of battery voltage. the amplifier has differential inputs and an internal fully differential design. the MAX98500 also features three gain settings (6db, 15.5db, and 20db) that are select - able with a logic input. the MAX98500 is available in a small, 0.5mm pitch 16-bump wlp package (2.1mm x 2.1mm). it is specified over the extended -40 n c to +85n c temperature range. applications cell phones smartphones gps devices mobile internet devices active speaker accessories features s boosted class d output s integrated automatic level control s output power 2.2w into 8 i , 10% thd+n 1.7w into 8 i , 1% thd+n s wide 2.5v to 5.5v supply voltage range s undervoltage lockout protection s high total efficiency of 87% s high step-up switching frequency (2mhz) s active emission limiting for low emi + denotes a lead(pb)-free/rohs-compliant package. ordering information typical application circuit appears at end of data sheet. part temp range pin-package MAX98500ewe+ -40nc to +85nc 16 wlp control differential input boost converter gain output stage battery spkp spkn pvdd v ccout lx v bat agnd spkpgnd bstpgnd c4 a4 d1, c2 d3 rknee b3 gain b2 sdspk c3 sdbst d4 b4 a3 a2 a1 b1 c1 inp d2 inn MAX98500
2 ______________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v bat to agnd ......................................................... -0.3v to +6v v ccout to bstpgnd, agnd ................................. -0.3v to +6v pvdd to spkpgnd ................................................. -0.3v to +6v bstpgnd, spkpgnd to agnd ......................... -0.3v to +0.3v gain to agnd ........................................ -0.3v to (v bat + 0.3v) sdbst, sdspk to agnd ...................................... -0.3v to v bat all other pins (excluding lx) to agnd .................. -0.3v to +6v current into/out of lx, v ccout , bstpgnd ..................... q3.9a continuous current into/out of spk_, pvdd, spkpgnd .................................................................. q800ma continuous input current (all other pins) ........................ q20ma duration of short circuit between v ccout and bstpgnd ...................................................... continuous duration of spk_ short circuit to pvdd or spkpgnd .............................................................. continuous duration of short circuit between spkp and spkn .............................................................. continuous continuous power dissipation, multilayer board (t a = +70 nc) wlp (derate 20.4mw/ n c above +70nc) ........................ 1.33w ja (note 1) ................................................................. 49nc/w junction temperature ..................................................... +150nc operating temperature range .......................... -40n c to +85nc storage temperature range ............................ -65n c to +150nc soldering temperature (reflow) ...................................... +260nc electrical characteristics (v bat = 3.6v, r l = j between spkp and spkn, a v = +6db, c in = 1 f f, 20hz to 22khz ac measurement bandwidth, t a = t min to t max , unless otherwise noted. typical values are at t a = +25 n c.) (note 2) absolute maximum ratings note 1: package thermal resistances were obtained using the method described in jedec specification jesd51-7, using a four- layer board. for detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. parameter symbol conditions min typ max units power-supply rejection ratio (note 3) psrr t a = +25nc, v bat = 2.5v to 5.5v 95 db quiescent current i vbat t a = +25nc, sdspk = sdbst = v bat 3.05 ma t a = +25nc, v sdspk = 0v, sdbst = v bat 0.09 0.15 i pvdd t a = +25nc, pvdd = 5.55v, sdspk = sdbst = v bat 1.7 2.7 combined efficiency e p out = 1.7w, f = 1khz, z spk = 8i + 68fh 87 % shutdown current i shdn v sdspk = v sdbst = 0v, t a = +25nc 0.04 1.5 fa turn-on time t on time from power-on to full operation 10 12 ms boost converter battery supply voltage range v bat 2.5 5.5 v soft-start interval t on 5.6 ms undervoltage lockout uvlo v bat falling 2.1 2.2 2.3 v boost converter output voltage v vccout i load = 0ma 5.45 5.5 5.65 v output current limit i max v bat r = 3.6v 1.5 a input current limit i limit startup, v ccout = 0v 0.3 0.5 a nmos current limit i lx,max 3.3 a pmos turn-off current limit 10 ma switching frequency f s 1.8 2.0 2.2 mhz efficiency e 0.1a p i out p 0.75a 93 % startup short-circuit time converter latch off 50 ms thermal shutdown 165 nc lx leakage current v lx = 0v or 5.5v, v ccout = 5.5v t a = +25nc -1.0 +0.1 +1.0 fa -40nc p t a p +85nc 0.1
_______________________________________________________________________________________ 3 MAX98500 boosted 2.2w class d amplifier with automatic level control electrical characteristics (continued) (v bat = 3.6v, r l = j between spkp and spkn, a v = +6db, c in = 1 f f, 20hz to 22khz ac measurement bandwidth, t a = t min to t max , unless otherwise noted. typical values are at t a = +25 n c.) (note 2) parameter symbol conditions min typ max units speaker amplifier output offset voltage v os t a = +25nc 1 3 mv click-and-pop level k cp peak voltage, t a = +25nc, a-weighted, 32 samples per second, z spk = 8i + 68fh, (notes 3, 4) into shutdown -56 dbv out of shutdown -56 output power (note 5) p out z spk = 8i + 68fh thd+n p 1% 1.7 w thd+n p 10% 2.2 total harmonic distortion plus noise thd+n f = 1khz, p out = 850mw, t a = +25nc, z spk = 8i + 68fh 0.05 % output switching frequency 300 khz gain a v gain = agnd 5.5 6 6.5 db gain = unconnected 15 15.5 16 gain = v bat 19.5 20 20.5 output current limit 2 a efficiency e p out = 1.7w, f = 1khz, z spk = 8i + 68fh 92 % output noise a-weighted 43 fv rms input resistance r in sdbst = sdspk = v bat a v = 6db (gain = agnd) 36 54 72 ki a v = 15.5db (gain = unconnected) 12 18 26 a v = 20db (gain = v bat ) 6.5 11 16 v sdbst = v sdspk = 0v all gain settings 110 common-mode rejection ratio cmrr f = 1khz 60 db bias voltage v bias 1.3 1.4 1.5 v alc attack time 20 fs/db release time 1.6 s/db maximum attenuation 8 db attenuation resolution 0.5 db knee voltage v knee t a = +25nc r knee = 154ki 2.19 2.3 2.42 v r knee = 40.5ki 3.14 3.3 3.47 r knee = 13ki 3.71 3.9 4.10
4 ______________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control electrical characteristics (continued) (v bat = 3.6v, r l = j between spkp and spkn, a v = +6db, c in = 1 f f, 20hz to 22khz ac measurement bandwidth, t a = t min to t max , unless otherwise noted. typical values are at t a = +25 n c.) (note 2) note 2: 100% production tested at t a = +25 n c. specifications over temperature limits are guaranteed by design. note 3: amplifier inputs are ac-coupled to agnd. note 4: mode transitions are controlled by sdspk. parameter symbol conditions min typ max units knee resistor r knee t a = +25nc, a v = 15.5db v knee = 3.25v 43.2 ki v knee = 3.35v 37.4 v knee = 3.45v 32.4 v knee = 3.55v 27.4 v knee = 3.65v 23.2 v knee = 3.75v 18.7 v knee = 3.85v 15.0 digital inputs (sdbst, sdspk) input voltage high v ih 1.4 v input voltage low v il 0.4 v input capacitance c in 10 pf input leakage current i in t a = +25nc -1.0 +1.0 fa
_______________________________________________________________________________________ 5 MAX98500 boosted 2.2w class d amplifier with automatic level control typical operating characteristics (v bat = 3.6v, r l = between spkp and spkn, a v = +15.5db, rknee = v bat , 20hz to 22khz ac measurement bandwidth, unless otherwise noted.) general battery current vs. battery voltage MAX98500 toc01 battery voltage (v) battery current (ma) 5.0 4.5 4.0 3.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 2.5 5.5 inputs ac-coupled to agnd sdspk = sdbst = v bat battery current vs. battery voltage MAX98500 toc02 battery voltage (v) battery current (a) 5.0 4.5 4.0 3.5 3.0 80 100 120 140 60 2.5 5.5 inputs ac-coupled to agnd sdspk = gnd, sdbst = v bat battery current vs. battery voltage MAX98500 toc03 battery voltage (v) battery current (a) 5.0 4.5 4.0 3.5 3.0 1 2 3 4 5 6 7 8 9 10 0 2.5 5.5 inputs ac-coupled to agnd sdspk = v bat , sdbst = agnd turn-on response MAX98500 toc04 v ccout 2v/div spkr output 1v/div sdbst 2v/div ov ov ov 2ms/div efficiency vs. output power MAX98500 toc05 p out (w) efficiency (%) 2.0 1.5 1.0 0.5 10 20 30 40 50 60 70 80 90 100 0 0 2.5 v bat = 4.2v v bat = 3.6v v bat = 3.0v z load = 8i + 68h f in = 1khz
6 ______________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control typical operating characteristics (continued) (v bat = 3.6v, r l = between spkp and spkn, a v = +15.5db, rknee = v bat , 20hz to 22khz ac measurement bandwidth, unless otherwise noted.) speaker thd+n vs. frequency MAX98500 toc06 frequency (khz) thd+n (%) 10 1 0.1 0.01 0.1 1 10 0.001 0.01 100 z load = 8 i + 68h p out = 1.4w p out = 400mw thd+n vs. output power MAX98500 toc07 output power (w) thd+n (%) 2.0 1.6 1.2 0.8 0.4 0.01 0.1 1 10 100 0.001 0 2.4 z load = 8 i + 68h f = 6khz f = 1khz f = 100hz output power vs. load resistance MAX98500 toc08 load resistance (i) output power (w) 100 10 1.5 1.0 0.5 2.0 2.5 3.0 0 1 1000 f in = 1khz z sprk = load + 68f thd+n = 10% thd+n = 1% output power vs. battery voltage MAX98500 toc09 battery voltage (v) output power (w) 5.0 4.5 4.0 3.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0 0 2.5 5.5 f in = 1khz z sprk = 8 i + 68h thd+n = 1% thd+n = 10% gain vs. frequency MAX98500 toc10 frequency (khz) gain (db) 100 10 1 -30 -20 -10 0 10 20 30 -40 0.1 1000 z load = 8 i + 68h a v = 20db a v = 6db a v = 15.5db
_______________________________________________________________________________________ 7 MAX98500 boosted 2.2w class d amplifier with automatic level control typical operating characteristics (continued) (v bat = 3.6v, r l = between spkp and spkn, a v = +15.5db, rknee = v bat , 20hz to 22khz ac measurement bandwidth, unless otherwise noted.) speaker power-supply rejection ratio vs. frequency MAX98500 toc11 frequency (khz) psrr (db) 10 1 0.1 -80 -60 -40 -20 0 -100 0.01 100 v ripple at pvdd = 200m v p-p inputs ac-coupled agnd common-mode rejection ratio vs. frequency MAX98500 toc12 frequency (khz) cmrr (db) 10 1 0.1 -80 -60 -40 -20 0 -100 0.01 100 a v = 6db a v = 20db a v = 15.5db z load = 8 i + 68h shutdown response MAX98500 toc13 spkr output 1v/div 0v 0v 40s/div sdspk 2v/div turn-on response MAX98500 toc14 spkr output 1v/div 0v 0v 1ms/div sdspk 2v/div sdbst = v bat clipping response MAX98500 toc15 spkr output 500mv/div 0v 200s/div thd+n = 10% wideband output spectrum MAX98500 toc16 frequency (mhz) amplitude (dbv) 100 10 1 -80 -60 -40 -20 0 20 -100 0.1 1000 rbw = 100hz audio inputs ac-grounded inband output spectrum MAX98500 toc17 frequency (khz) amplitude (dbv) 15 10 5 -100 -80 -60 -40 -20 0 -120 0 20 f in = 1khz output = -60dbv
8 ______________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control typical operating characteristics (continued) (v bat = 3.6v, r l = between spkp and spkn, a v = +15.5db, rknee = v bat , 20hz to 22khz ac measurement bandwidth, unless otherwise noted.) boost converter efficiency vs. output current MAX98500 toc18 i out (ma) efficiency (%) 1400 1200 800 1000 400 600 200 82 84 86 88 90 92 94 96 98 100 80 0 1600 v bat = 5v v bat = 4.2v v bat = 4v v bat = 3.6v v bat = 3v v bat = 3.3v load regulation vs. output current MAX98500 toc19 i out (ma) load regulation (%) 1400 1200 1000 800 600 400 200 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 -1.2 0 1600 v bat = 5v v bat = 4.2v v bat = 4v v bat = 3v v bat = 3.3v v bat = 3.6v output voltage vs. output current MAX98500 toc20 i out (a) output voltage (v) 1400 1200 200 400 600 800 1000 5.45 5.46 5.47 5.48 5.49 5.50 5.51 5.52 5.44 0 1600 v bat = 3v v bat = 3.3v v bat = 3.6v v bat = 4.2v v bat = 5v switching frequency vs. battery voltage MAX98500 toc21 battery voltage (v) switching frequency (mhz) 4.3 4.1 3.9 3.7 3.5 3.3 3.1 2.9 2.7 1.98 i out = 100ma 2.00 2.02 2.04 1.96 2.5 4.5 i out = 500ma soft-start MAX98500 toc22 v ccout 2v/div 0v 0v 1ms/div sdbst 2v/div
_______________________________________________________________________________________ 9 MAX98500 boosted 2.2w class d amplifier with automatic level control pin description pin configuration MAX98500 v ccout lx bstpgnd pvdd 2 3 4 1 a gain rkne e v bat spkp b spkpgnd top view (bump side down) wlp agnd spkn c inp inn spkpgnd d + sdbs t sdspk bump name function a1 pvdd speaker amplifier power supply. bypass to spkpgnd with a 0.1mf capacitor. a2 v ccout boost converter output. connect a 22mf (0805) capacitor between v ccout and bstpgnd. a3 lx boost switch input a4 bstpgnd boost power ground b1 spkp positive speaker output b2 gain gain select input. connect gain to ground to set the speaker gain to 6db. leave gain unconnected to set the speaker gain to 15.5db. connect gain to v bat to set the speaker gain to 20db. b3 rknee alc knee voltage set input. set the alc knee voltage with a resistor to agnd. b4 v bat battery voltage input. connect a 10mf (0805) capacitor between v bat and bstpgnd. include at least 22mf of system bulk capacitance. c1 spkn negative speaker output c2, d1 spkpgnd speaker ground c3 sdspk speaker output shutdown. drive sdspk low to shutdown the speaker output. c4 agnd analog ground d2 inp positive audio input d3 inn negative audio input d4 sdbst boost converter shutdown. drive sdbst low to shutdown the boost converter and the speaker output.
10 _____________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control detailed description the MAX98500 is a high-efficiency class d audio ampli - fier that features an integrated boost converter to deliver a constant output power over a large range of battery supply voltages. the boost converter operates at 2mhz, requiring only a small (2.2 f h) external inductor and output capaci - tor. the amplifier has differential inputs and an internal fully differential design with three gain settings (6db, 15.5db, and 20db) that are selectable with a logic input. the MAX98500 also features automatic level control. the automatic level control reduces the output swing when the battery voltage decreases to prevent the collapse of battery voltage. class d speaker amplifier the MAX98500 filterless class d amplifier offers much higher efficiency than class ab amplifiers. the high efficiency of a class d amplifier is due to the switching operation of the output stage transistors. any power loss associated with the class d output stage is mostly due to the i 2 r loss of the mosfet on-resistance and quiescent current overhead. low-emi filterless output stage traditional class d amplifiers require the use of external lc filters, or shielding, to meet en55022b electromag - netic-interference (emi) regulation standards. maxims patented active emissions limiting edge-rate control circuitry reduces emi emissions, while maintaining up to 92% efficiency (speaker only). above 10mhz, the wide - band spectrum looks like noise for emi purposes. automatic level control the MAX98500 features an automatic level control circuit that limits the maximum speaker output swing. this helps: u avoid clipping u save the battery from collapsing, which could cause a reset of the system the limiter keeps the peak voltage below a value that is a function of battery voltage, as shown in figure 1. the full output swing of 5.2v is maintained for battery voltages down to the knee voltage, while for lower battery voltages the maximum v peak -swing is reduced by 3v/v. the knee voltage can be changed by applying different resistors between rknee and agnd. the typical track - ing function is shifted horizontally with different r knee resistor values (figure 2). the preamplifier gain reduces as the automatic level control activates. the maximum gain reduction is 8db with a resolution of 0.5db steps. the attack (gain reduction) happens immediately (20 fs/ db), while the release is set to 1.6s/db. gain select the MAX98500 features three internal gain settings that are selectable with the gain input. table 1 shows the gain settings. figure 1. typical tracking function table 1. gain settings figure 2. the relationship of r knee and v knee peak amplifier output voltage vs. battery voltage battery voltage (v) peak amplifier output voltage (v peak ) 5 2 3 4 1 1 2 4 3 5 6 0 0 6 knee voltage slope gain amplifier gain (db) agnd 6 unconnected 15.5 v bat 20 v knee vs. r knee r knee (ki) v knee (v) 60 50 40 30 20 3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 2.9 10 70
______________________________________________________________________________________ 11 MAX98500 boosted 2.2w class d amplifier with automatic level control shutdown the MAX98500 features two active-low shutdown inputs (sdspk and sdbst ). table 2 shows the different shut- down configurations. click-and-pop suppression the MAX98500 speaker amplifier features maxims com - prehensive click-and-pop suppression. during startup, the click-and-pop suppression circuitry reduces any audible transient sources internal to the device. when entering shutdown, the differential speaker outputs ramp down to spkpgnd quickly and simultaneously. current-limit and thermal protection the ic features overcurrent and thermal protection. the ic shuts down when the v ccout output decreases to about 80% of the expected output. the ic also enters into shutdown when the die temperature exceeds +165n c. the device remains in shutdown until power is reset or sdbst is toggled low and back high after the fault condition has been removed. the ic speaker amplifier also features a 2a (typ) short-circuit protection scheme. boost converter soft-start the MAX98500 features a two-stage, soft-start, power- up sequence. when sdbst is taken high and v bat is above uvlo the soft-start first ramps v ccout quickly to v bat voltage with a battery current of 300ma (typ). once the v ccout reaches the v bat voltage, the internal switching turns on and ramps the v ccout to 5.5v in 5ms (typ), see the soft-start graph in the typical operating characteristics . the maximum load current is available after the soft-start is completed. undervoltage lockout (uvlo) the undervoltage lockout (uvlo) circuit compares the voltage at v bat with the uvlo threshold (2.2v typ) to ensure that the input voltage is high enough for reliable operation. once the v bat voltage exceeds the uvlo threshold, the soft-start begins. when the input voltage falls below the uvlo threshold, the boost converter and speaker amplifier turn off. applications information filterless class d operation traditional class d amplifiers require an output filter to recover the audio signal from the amplifiers output. the filter adds cost, increases the solution size of the ampli - fier, and can decrease efficiency and thd+n perfor - mance. the traditional pwm scheme uses large differen - tial output swings (2 x supply voltage peak-to-peak) and causes large ripple currents. any parasitic resistance in the filter components results in a loss of power and low - ers the efficiency. the MAX98500 does not require an output filter. the device relies on the inherent inductance of the speaker coil and the natural filtering of both the speaker and the human ear to recover the audio component of the square-wave output. eliminating the output filter results in a smaller, less costly, and more efficient solution. because the frequency of the MAX98500 output is well beyond the bandwidth of most speakers, voice coil movement due to the square-wave frequency is very small. although this movement is small, a speaker not designed to handle the additional power can be dam - aged. for optimum results, use a speaker with a series inductance > 10 f h. typical 8i speakers exhibit series inductances in the 20 f h to 100f h range. rf susceptibility gsm radios transmit using time-division multiple access (tdma) with 217hz intervals. the result is an rf signal with strong amplitude modulation at 217hz and its har - monics that is easily demodulated by audio amplifiers. the MAX98500 is designed specifically to reject rf signals; however, pcb layout has a large impact on the susceptibility of the end product. in rf applications, improvements to both layout and component selection decrease the MAX98500s suscep - tibility to rf noise and prevent rf signals from being demodulated into audible noise. trace lengths should be kept below 1/4 of the wavelength of the rf frequency of interest. minimizing the trace lengths prevents them from functioning as antennas and coupling rf signals into the MAX98500. the wavelength ( l ) in meters is given by: l = c/f where c = 3 x 10 8 m/s, and f = the rf frequency of interest. table 2. shutdown configurations sdbst sdspk boost status speaker status low low off off low high off off high low on off high high on on
12 _____________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control route audio signals on the middle layers of the pcb to allow the ground planes above and below to shield them from rf interference. ideally the top and bottom layers of the pcb should primarily be ground planes to create effective shielding. additional rf immunity can also be obtained from rely - ing on the self-resonant frequency of capacitors as it exhibits the frequency response similar to a notch filter. depending on the manufacturer, 10pf to 20pf capacitors typically exhibit self resonance at rf frequencies. these capacitors, when placed at the input pins, can effectively shunt the rf noise at the inputs of the MAX98500. for these capacitors to be effective, they must have a low- impedance, low-inductance path to the ground plane. do not use microvias to connect to the ground plane as these vias do not conduct well at rf frequencies. speaker component selection optional ferrite bead filter additional emi suppression can be achieved using a filter constructed from a ferrite bead and a capacitor to ground (figure 3). use a ferrite bead with low dc resis - tance, high-frequency (> 100mhz) impedance between 100i and 600i , and rated for at least 1a. the capacitor value varies based on the ferrite bead chosen and the actual speaker lead length. select a capacitor less than 1nf based on emi performance. input capacitor (c in ) an input capacitor, c in , in conjunction with the input impedance of the MAX98500 speaker inputs forms a highpass filter that removes the dc bias from an incom - ing analog signal. the ac-coupling capacitor allows the amplifier to automatically bias the signal to an optimum dc level. assuming zero-source impedance, the -3db point of the highpass filter is given by: -3db in in 1 f 2 r c = choose c in such that f -3db is well below the lowest fre - quency of interest. for best audio quality, use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. capacitors with high- voltage coefficients, such as ceramics, could result in increased distortion at low frequencies. boost converter component selection inductor selection in most step-up converter designs, a reasonable induc - tor value can be derived from the following equation. this equation sets peak-to-peak inductor current at 1/2 the dc inductor current: l = (2 x v batt x d x (1-d))/(i out(max ) x f sw ) where f sw is the switching frequency, and d is the duty factor given by d = 1 - (v bat /v out ). using l from the equation above results in a peak-to-peak inductor cur - rent ripple of 0.5 x i out /(1 - d), and a peak inductor current of 1.25 x i out /(1 - d). ensure the peak (satura - tion) current rating of the inductor meets or exceeds this requirement. the recommended nominal inductance for the MAX98500 is 2.2 f h. nominal inductance decreases as the inductor current increases. if the decrease from the nominal inductance is severe, the boost converter may become unstable or shut down at lower output power levels than expected. ensure the minimum inductance at the peak inductor current is 1.0 fh. output capacitor (c vccout ) an output capacitor, c vccout , is required to keep the output voltage ripple small and to ensure regulation loop stability. the output capacitor must have low imped - ance at the switching frequency. ceramic capacitors are highly recommended due to their small size and low esr. ceramic capacitors with x5r or x7r temperature characteristics generally perform well. the recommend - ed nominal capacitance for the MAX98500 is 22 f f (0805 case size or larger). ensure the minimum capacitance at 5.5v is 6.8 ff. input capacitor (c vbat ) an input capacitor, c vbat , reduces the current peaks drawn from the battery or input power source and reduc - es switching noise in the ic. the impedance of the input capacitor at the switching frequency should be kept very low. ceramic capacitors are highly recommended due to their small size and low esr. ceramic capacitors with x5r or x7r temperature characteristics generally per - form well. one 10 f f ceramic capacitor is recommended with a system bulk capacitance of 22 f f or larger. figure 3. optional class d ferrite bead filter MAX98500 spkp spkn
______________________________________________________________________________________ 13 MAX98500 boosted 2.2w class d amplifier with automatic level control supply bypassing, layout, and grounding proper layout and grounding are essential for optimum performance. use a large continuous ground plane on a dedicated layer of the pcb to minimize loop areas. connect agnd and bstpgnd/spkpgnd directly to the ground plane using the shortest traces length possible. proper grounding improves audio performance, and prevents any digital noise from coupling into the analog audio signals. bypass v bat with a 10 f f capacitor and a system bulk capacitance of 22 f f or larger. bypass pvdd to spkpgnd with a 0.1 f f capacitor and with as minimal a loop area as possible. connect spkp and spkn to the speaker using the shortest and widest traces possible. reducing trace length minimizes radiated emi. route spkp/spkn as a differential pair on the pcb to minimize loop area, thereby, the inductance of the circuit. if filter components are used on the speaker outputs, be sure to locate them as close as possible to the MAX98500 to ensure maximum effectiveness. minimize the trace length from any ground-tied passive components to spkpgnd to further minimize radiated emi. an evaluation kit (MAX98500 evaluation kit) is available to provide an example layout for the MAX98500. wlp applications information for the latest application details on wlp construction, dimensions, tape carrier information, pcb techniques, bump-pad layout, and recommended reflow tempera - ture profile, as well as the latest information on reliability testing results, refer to the application note 1891: wafer- level packaging (wlp) and its applications on maxims website at www.maxim-ic.com/ucsp. see figure 4 for the recommended pcb footprint for the MAX98500. figure 4. recommended pcb footprint typical application circuit 0.25mm 0.22mm control differential input boost converter gain output stage battery spkp spkn pvdd 8i v ccout lx v bat 22f* 27.4ki 1% c in 1f c in 1f *system level requirement agnd spkpgnd bstpgnd c4 a4 d1, c2 d3 rknee b3 gain b2 sdspk c3 sdbst d4 b4 a3 a2 a1 b1 c1 c vbat 10f 0805 10% 2.2h 20% inp d2 inn MAX98500 c vccout 22f 0805 10% 0.1f 10%
14 _____________________________________________________________________________________ MAX98500 boosted 2.2w class d amplifier with automatic level control package type package code document no. 16 wlp w162b2+1 21-0200 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages. note that a +, #, or - in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status.
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 15 ? 2010 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. MAX98500 boosted 2.2w class d amplifier with automatic level control revision history revision number revision date description pages changed 0 5/10 initial release

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