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general description the max1556/max1556a/max1557 are low-operating- current (16?), fixed-frequency step-down regulators. high efficiency, low-quiescent operating current, low dropout, and minimal (27?) quiescent current in dropout make these converters ideal for powering portable devices from 1-cell li-ion or 3-cell alkaline/nimh batteries. the max1556 delivers up to 1.2a; has pin- selectable 1.8v, 2.5v, and 3.3v outputs; and is also adjustable. the max1557 delivers up to 600ma; has pin- selectable 1v, 1.3v, and 1.5v outputs; and is also adjustable. the max1556/max1556a/max1557 contain a low-on- resistance internal mosfet switch and synchronous rectifier to maximize efficiency and dropout perfor- mance while minimizing external component count. a proprietary topology offers the benefits of a high fixed- frequency operation while still providing excellent effi- ciency at both light and full loads. a 1mhz pwm switching frequency keeps components small. both devices also feature an adjustable soft-start to minimize battery transient loading. the max1556/max1556a/max1557 are available in a tiny 10-pin tdfn (3mm x 3mm) package. applications pdas and palmtop computers cell phones and smart phones digital cameras and camcorders portable mp3 and dvd players hand-held instruments features up to 97% efficiency 95% efficiency at 1ma load current low 16 a quiescent current 1mhz pwm switching tiny 3.3 h inductor selectable 3.3v, 2.5v, 1.8v, 1.5v, 1.3v, 1.2v, 1.0v, and adjustable output 1.2a guaranteed output current (max1556/max1556a) voltage positioning optimizes load-transient response low 27 a quiescent current in dropout low 0.1 a shutdown current no external schottky diode required analog soft-start with zero overshoot current small, 10-pin, 3mm x 3mm tdfn package max1556/max1556a/max1557 16a i q , 1.2a pwm step-down dc-dc converters ________________________________________________________________ maxim integrated products 1 top view lx out shdn 6 7 8 9 10 inp d1 3 2 1 ss gnd in 5 pgnd d2 4 tdfn max1556 max1556a max1557 pin configuration ordering information lx ss on off shdn gnd input 2.6v to 5.5v voltage select output 0.75v to v in pgnd out inp in d1 d2 max1556 max1556a max1557 typical operating circuit 19-3336; rev 3; 1/11 evaluation kit available part temp range pin-package top mark max1556 etb+ -40 c to +85 c 10 tdfn-ep* acq max1556etb/v+t -40 c to +85 c 10 tdfn-ep* aws max1556a etb+ -40 c to +85 c 10 tdfn-ep* auj max1557 etb+ -40 c to +85 c 10 tdfn-ep* acr * ep = exposed paddle. + denotes a lead(pb)-free/rohs-compliant package. /v denotes an automotive qualified part. t = tape and reel. for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = v inp = v shdn = 3.6v, t a = -40? to +85?. typical values are at t a = +25?, unless otherwise noted.) (note 2) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in, inp, out, d2, shdn to gnd ..........................-0.3v to +6.0v ss, d1 to gnd .............................................-0.3v to (v in + 0.3v) pgnd to gnd .......................................................-0.3v to +0.3v lx current (note 1)...........................................................?.25a output short-circuit duration.....................................continuous continuous power dissipation (t a = +70?) 10-pin tdfn (derate 24.4mw/? above +70?) .......1951mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? soldering temperature (reflow) .......................................+260? parameter conditions min typ max units input voltage 2.6 5.5 v undervoltage-lockout threshold v in rising and falling, 35mv hysteresis (typ) 2.20 2.35 2.55 v no switching, d1 = d2 = gnd 16 25 quiescent supply current dropout 27 42 ? t a = +25? 0.1 1 shutdown supply current shdn = gnd t a = +85? 0.1 ? output voltage range 0.75 v in v no load -0.25 +0.75 +1.75 300ma load -0.75 0 +0.75 600ma load -1.5 -0.75 0 1200ma load, max1556 -2.75 -2.25 -1.25 t a = 0? to +85? (note 3) 1200ma load, max1556a -2.25 no load -0.75 +2.25 300ma load -1.5 +1.5 600ma load -2.25 +0.50 output accuracy t a = -40? to +85? (note 3) 1200ma load, max1556 -4.0 -1.0 % max1556/max1556a 1200 maximum output current max1557 600 ma t a = +25? 0.01 0.1 d1 = d2 = gnd max1556/max1557 t a = +85? 0.01 out bias current for preset output voltages 3 4.5 ? no load -0.50 +0.75 +1.75 300ma load -1.2 0 +1.2 600ma load -1.75 -0.75 +0.25 d1 = d2 = gnd, v out = 0.75v at 300ma (typ), t a = 0? to +85? max1556/max1557 1200ma load, max1556 only -3.25 -2.25 -1.25 no load -1.25 +2.25 300ma load -1.75 +1.50 600ma load -2.75 +0.25 fb threshold accuracy d1 = d2 = gnd, v out = 0.75v at 300ma (typ), t a = -40? to +85? max1556/max1557 1200ma load, max1556 only -4.25 -1.00 % note 1: lx has internal clamp diodes to gnd and in. applications that forward bias these diodes should take care not to exceed the ic? package power-dissipation limits.
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters _______________________________________________________________________________________ 3 note 2: all units are 100% production tested at t a = +25?. limits over the operating range are guaranteed by design. note 3: for the max1556, 3.3v output accuracy is specified with a 4.2v input. electrical characteristics (continued) (v in = v inp = v shdn = 3.6v, t a = -40? to +85?. typical values are at t a = +25?, unless otherwise noted.) (note 2) parameter conditions min typ max units v in = 2.6v to 3.6v -0.37 max1556, d1 = in, d2 = gnd; max1556a d1 = d2 = in v in = 3.6v to 5.5v 0.33 v in = 2.6v to 3.6v -0.1 line regulation max1557, d1 = in, d2 = gnd v in = 3.6v to 5.5v 0.09 % v in = 3.6v 0.19 0.35 max1556/max1556a v in = 2.6v 0.23 v in = 3.6v 0.35 0.7 p-channel on-resistance max1557 v in = 2.6v 0.42 ? v in = 3.6v 0.27 0.48 n-channel on-resistance v in = 2.6v 0.33 ? max1556/max1556a 1.5 1.8 2.1 p-channel current-limit threshold max1557 0.8 1.0 1.2 a n-channel zero crossing threshold 20 35 45 ma max1556/max1556a 1.8 rms lx output current max1557 1.0 a rms t a = +25? 0.1 10 lx leakage current v in = 5.5v, lx = gnd or in t a = +85? 0.1 ? maximum duty cycle 100 % minimum duty cycle 0% internal oscillator frequency 0.9 1 1.1 mhz ss output impedance ? v ss / i ss for i ss = 2? 130 200 300 k ? ss discharge resistance shdn = gnd, 1ma sink current 90 200 ? thermal-shutdown threshold +160 ? thermal-shutdown hysteresis 15 ? logic inputs (d1, d2, shdn ) input-voltage high 2.6v v in 5.5v 1.4 v input-voltage low 0.4 v t a = +25? 0.1 1 input leakage t a = +85? 0.1 ?
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters 4 _______________________________________________________________________________________ typical operating characteristics (v in = v inp = 3.6v, d1 = d2 = shdn = in, circuits of figures 2 and 3, t a = +25?, unless otherwise noted.) efficiency vs. load current with 3.3v output max1556/7 toc01 load current (ma) efficiency (%) 100 10 1 60 70 80 90 100 50 40 0.1 1000 10,000 v in = 5v v in = 3.6v v in = 4.2v efficiency vs. load current with 2.5v output max1556/7 toc02 load current (ma) efficiency (%) 100 10 1 60 70 80 90 100 50 40 0.1 1000 10,000 v in = 3.6v v in = 3v v in = 2.6v v in = 5v efficiency vs. load current with 1.8v output max1556/7 toc03 load current (ma) efficiency (%) 100 10 1 60 70 80 90 100 50 40 0.1 1000 10,000 v in = 5v v in = 3.6v v in = 3v v in = 2.6v efficiency vs. load current with 1.0v output (max1557) max1556/7 toc04 load current (ma) efficiency (%) 100 10 1 60 70 80 90 100 50 40 0.1 1000 v in = 5v v in = 3.6v v in = 3v v in = 2.6v output voltage vs. load current max1556/7 toc05 load current (ma) output voltage (v) 1000 800 600 400 200 1.75 1.76 1.77 1.78 1.79 1.80 1.81 1.82 1.83 1.84 1.74 0 1200 t a = -45 c t a = +25 c t a = +85 c output voltage vs. input voltage with 600ma load max1556/7 toc06 input voltage (v) output voltage (v) 5.0 4.5 4.0 3.5 3.0 1.780 1.781 1.782 1.783 1.784 1.785 1.786 1.787 1.788 1.789 1.779 2.5 5.5 t a = -40 c t a = +25 c t a = +85 c output voltage vs. input voltage with no load max1556/7 toc07 input voltage (v) output voltage (v) 5.0 4.5 4.0 3.5 3.0 1.804 1.805 1.806 1.807 1.808 1.809 1.810 1.811 1.812 1.803 2.5 5.5 t a = -40 c t a = +25 c t a = +85 c supply current vs. input voltage max1556/7 toc08 input voltage (v) supply current ( a) 5 4 3 2 2 4 6 8 10 12 14 16 18 20 0 16 heavy-load switching waveforms max1556/7 toc09 v out ac-coupled 10mv/div v lx i lx 2v/div 0 0 400ns 500ma/div i load = 750ma
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters _______________________________________________________________________________________ 5 light-load switching waveforms max1556/7 toc10 20mv/div ac-coupled v lx v out i lx 2v/div 0 4 s/div 0 200ma/div external feedback switching waveforms max1556/7 toc10b v lx i lx 2v/div 0 2 s/div 0 200ma/div v in = 5v, v out = 3.3v, i out = 500ma soft-start/shutdown waveforms max1556/7 toc11 5v/div i lx v shdn v out i in 500ma/div 0 0 100 s/div 0 1v/div 0 500ma/div c ss = 470pf r load = 4 ? soft-start ramp time vs. c ss max1556/7 toc12 c ss (pf) soft-start ramp time (ms) 500 1000 1500 2000 10 0.1 0 2500 1 load transient max1556/7 toc13 50mv/div ac-coupled 500ma/div v out i out 20 s/div 0 i outmin = 20ma load transient max1556/7 toc14 50mv/div ac-coupled 500ma/div v out i out 20 s/div 0 i outmin = 180ma line transient max1556/7 toc15 10mv/div ac-coupled v in v out i lx 3.5v 4v 40 s/div 0 200ma/div bode plot max1556/7 toc16 frequency (khz) gain (db) phase (degrees) 100 10 1 -50 -40 -30 -20 -10 0 10 20 30 40 -60 -30 0 30 60 90 120 150 180 210 240 -60 0.1 1000 0db phase margin = 53 c out = 22 f, r load = 4 ? typical operating characteristics (continued) (v in = v inp = 3.6v, d1 = d2 = shdn = in, circuits of figures 2 and 3, t a = +25?, unless otherwise noted.)
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters 6 _______________________________________________________________________________________ detailed description the max1556/max1557 synchronous step-down con- verters deliver a guaranteed 1.2a/600ma at output volt- ages from 0.75v to v in . they use a 1mhz pwm current-mode control scheme with internal compensation, allowing for tiny external components and a fast transient response. at light loads the max1556/max1557 automat- ically switch to pulse-skipping mode to keep the quies- cent supply current as low as 16?. figures 2 and 3 show the typical application circuits. control scheme during pwm operation the converters use a fixed-fre- quency, current-mode control scheme. the heart of the current-mode pwm controller is an open-loop, multiple- input comparator that compares the error-amp voltage feedback signal against the sum of the amplified cur- rent-sense signal and the slope-compensation ramp. at the beginning of each clock cycle, the internal high-side p-channel mosfet turns on until the pwm comparator trips. during this time the current in the inductor ramps up, sourcing current to the output and storing energy in the inductor? magnetic field. when the p-channel turns off, the internal low-side n-channel mosfet turns on. now the inductor releases the stored energy while the current ramps down, still providing current to the output. the output capacitor stores charge when the inductor current exceeds the load and discharges when the inductor current is lower than the load. under overload conditions, when the inductor current exceeds the cur- rent limit, the high-side mosfet is turned off and the low-side mosfet remains on until the next clock cycle. pin description pin name function 1 in supply voltage input. connect to a 2.6v to 5.5v source. 2 gnd ground. connect to pgnd. 3ss soft-start control. connect a 1000pf capacitor (c ss ) from ss to gnd to eliminate input-current overshoot during startup. c ss is required for normal operation of the max1556/max1557. for greater than 22? total output capacitance, increase c ss to c out / 22,000 for soft-start. ss is internally discharged through 200 ? to gnd in shutdown. 4 out output sense input. connect to the output of the regulator. d1 and d2 select the desired output voltage through an internal feedback resistor-divider. the internal feedback resistor-divider remains connected in shutdown. 5 shdn shutdown input. drive shdn low to enable low-power shutdown mode. drive high or connect to in for normal operation. 6 d2 out voltage-select input. see table 1. 7 pgnd power ground. connect to gnd. 8lx inductor connection. connected to the drains of the internal power mosfets. high impedance in shutdown mode. 9 inp supply voltage, high-current input. connect to a 2.6v to 5.5v source. bypass with a 10? ceramic capacitor to pgnd. 10 d1 out voltage-select input. see table 1. ?p exposed paddle. connect to ground plane. ep also functions as a heatsink. solder to circuit-board ground plane to maximize thermal dissipation. d1 d2 max1556 v out max1556a v out max1557 v out 00 adjustable (v fb = 0.75v) from 0.75v to v in 3.3v adjustable (v fb = 0.75v) from 0.75v to v in 0 1 3.3v 1.5v 1.5v 1 0 2.5v 1.2v 1.3v 1 1 1.8v 2.5v 1.0v table 1. output-voltage-select truth table a zero represents d_ being driven low or connected to gnd. a 1 represents d_ being driven high or connected to in.
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters _______________________________________________________________________________________ 7 lx ss on off shdn gnd input 2.6v to 5.5v voltage select output 0.75v to v in pgnd c1 10 f c4 0.47 f r1 100 ? c2 22 f c3 1000pf l1 3.3 h out inp in 1.2a d1 d2 max1556 max1556a figure 2. max1556 typical application circuit figure 1. functional diagram lx ss on off shdn gnd input 2.6v to 5.5v voltage select output 0.75v to v in pgnd c4 10 f c5 22 f c6 1000pf l2 4.7 h out inp in 600ma d1 d2 max1557 figure 3. max1557 typical application circuit pwm comparator error amplifier current-limit comparator 0.675v current sense slope comp clock 1mhz inp lx pgnd ss gnd pwm auto skip control skip-over enter skip/ sr off v cs zero-cross detect short-circuit protection reference 1.25v out d1 d2 shdn in bias output voltage selector max1556 max1556a max1557
as the load current decreases, the converters enter a pulse-skip mode in which the pwm comparator is dis- abled. at light loads, efficency is enhanced by a pulse-skip mode in which switching occurs only as needed to service the load. quiescent current in skip mode is typically 16?. see the light-load switching waveforms and load transient graphs in the typical operating characteristics . load-transient response/ voltage positioning the max1556/max1556a/max1557 match the load regulation to the voltage droop seen during transients. this is sometimes called voltage positioning. the load line used to achieve this behavior is shown in figures 4 and 5. there is minimal overshoot when the load is removed and minimal voltage drop during a transition from light load to full load. additionally, the max1556, max1556a, and max1557 use a wide-bandwidth feed- back loop to respond more quickly to a load transient than regulators using conventional integrating feedback loops (see load transient in the typical operating characteristics ). the max1556/max1556a/max1557 use of a wide-band control loop and voltage positioning allows superior load-transient response by minimizing the amplitude and duration of overshoot and undershoot in response to load transients. other dc-dc converters, with high gain-control loops, use external compensation to main- tain tight dc load regulation but still allow large voltage droops of 5% or greater for several hundreds of microseconds during transients. for example, if the load is a cpu running at 600mhz, then a dip lasting 100? corresponds to 60,000 cpu clock cycles. voltage positioning on the max1556/max1556a/ max1557 allows up to 2.25% (typ) of load-regulation voltage shift but has no further transient droop. thus, during load transients, the voltage delivered to the cpu remains within spec more effectively than with other regulators that might have tighter initial dc accuracy. in summary, a 2.25% load regulation with no transient droop is much better than a converter with 0.5% load regulation and 5% or more of voltage droop during load transients. load-transient variation can be seen only with an oscilloscope (see the typical operating characteristics ), while dc load regulation read by a voltmeter does not show how the power supply reacts to load transients. dropout/100% duty-cycle operation the max1556/max1556a/max1557 function with a low input-to-output voltage difference by operating at 100% duty cycle. in this state, the high-side p-channel mosfet is always on. this is particularly useful in battery-powered applications with a 3.3v output. the sys- tem and load might operate normally down to 3v or less. the max1556/max1556a/max1557 allow the output to follow the input battery voltage as it drops below the regu- lation voltage. the quiescent current in this state rises minimally to only 27? (typ), which aids in extending bat- tery life. this dropout/100% duty-cycle operation achieves long battery life by taking full advantage of the entire bat- tery range. the input voltage required to maintain regulation is a function of the output voltage and the load. the differ- ence between this minimum input voltage and the out- put voltage is called the dropout voltage. the dropout voltage is therefore a function of the on-resistance of the internal p-channel mosfet (r ds(on)p ) and the inductor resistance (dcr). max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters 8 _______________________________________________________________________________________ -2.5 -1.5 -2.0 -0.5 -1.0 0.5 0 1.0 0 200 400 800 600 1000 1200 load current (ma) change in output voltage (%) v in = 3.6v v in = 5.5v v in = 2.6v figure 4. max1556 voltage-positioning load line figure 5. max1557 voltage-positioning load line 0 200 400 600 load current (ma) change in output voltage (%) -1.0 -0.4 -0.6 -0.8 -0.2 0 0.2 0.4 0.6 0.8 1.0 v in = 5.5v v in = 2.6v v in = 3.6v
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters _______________________________________________________________________________________ 9 v dropout = i out x (r ds(on)p + dcr) r ds(on)p is given in the electrical characteristics . dcr for a few recommended inductors is listed in table 2. soft-start the max1556/max1556a/max1557 use soft-start to eliminate inrush current during startup, reducing tran- sients at the input source. soft-start is particularly use- ful for higher-impedance input sources such as li+ and alkaline cells. connect the required soft-start capacitor from ss to gnd. for most applications using a 22? output capacitor, connect a 1000pf capacitor from ss to gnd. if a larger output capacitor is used, then use the following formula to find the value of the soft-start capacitor: soft-start is implemented by exponentially ramping up the output voltage from 0 to v out(nom) with a time con- stant equal to c ss times 200k ? (see the typical operating characteristics ). assuming three time con- stants to full output voltage, use the following formula to calculate the soft-start time: shutdown mode connecting shdn to gnd or logic low places the max1556/max1556a/max1557 in shutdown mode and reduces supply current to 0.1?. in shutdown, the con- trol circuitry and the internal p-channel and n-channel mosfets turn off and lx becomes high impedance. connect shdn to in or logic high for normal operation. thermal shutdown as soon as the junction temperature of the max1556/max1556a/max1557 exceeds +160?, the ics go into thermal shutdown. in this mode the internal p-channel switch and the internal n-channel synchro- nous rectifier are turned off. the device resumes nor- mal operation when the junction temperature falls below +145?. applications information the max1556/max1556a/ max1557 are optimized for use with small external components. the correct selec- tion of inductors and input and output capacitors ensures high efficiency, low output ripple, and fast tran- sient response. adjusting the output voltage the max1556/max1556a/max1557 offer preset output voltages of 1.0v, 1.2v, 1.3v, 1.5v, 1.8v, 2.5v, and 3.3v as well as an adjustable output using external resistors. whenever possible, the preset outputs (set by d1 and d2) should be used. with external resistor feedback, noise coupling to fb can cause alternate lx pulse to terminate early resulting in an inductor current wave- form with alternate large and small current pulses. see the external feedback switching waveforms graph in typical operating characteristics section. note that external feedback and the alternating large-small pulse waveform do not impact loop stability and have no harmful effect on regulation or reliability. the adjustable output is selected when d1 = d2 = 0 and an external resistor-divider is used to set the output voltage (see figure 6). the max1556/max1557 have a defined line- and load-regulation slope. the load regu- lation is for both preset and adjustable outputs and is described in the electrical characteristics table and figures 4 and 5. the impact of the line-regulation slope txxc ss ss = 600 10 3 c c ss out = 22000 table 2. inductor selection manufacturer part value (?) dcr (m ? )i sat (ma) size (mm) shielded taiyo yuden lmnp04sb3r3n 3.3 36 1300 5 x 5 x 2.0 yes taiyo yuden lmnp04sb4r7n 4.7 50 1200 5 x 5 x 2.0 yes toko d52lc 3.5 73 1340 5 x 5 x 2.0 yes toko d52lc 4.7 87 1140 5 x 5 x 2.0 yes sumida cdrh3d16 4.7 50 1200 3.8 x 3.8 x 1.8 yes toko d412f 4.7 100* 1200* 4.8 x 4.8 x 1.2 yes murata lqh32cn 4.7 97 790 2.5 x 3.2 x 2.0 no sumitomo cxl180 4.7 70* 1000* 3.0 x 3.2 x 1.7 no sumitomo cxld140 4.7 100* 800* 2.8 x 3.2 x 1.5 no * estimated based upon similar-valued prototype inductors.
max1556/max1556a/max1557 can be reduced by applying a correction factor to the feedback resistor equation. first, calculate the correction factor, k, by plugging the desired output voltage into the following formula: k represents the shift in the operating point at the feed- back node (out). select the lower feedback resistor, r3, to be 35.7k ? to ensure stability and solve for r2: inductor selection a 4.7? inductor with a saturation current of at least 800ma is recommended for the max1557 full-load (600ma) application. for the max1556/max1556a appli- cation with 1.2a full load, use a 3.3? inductor with at least 1.34a saturation current. for lower full-load cur- rents the inductor current rating can be reduced. for maximum efficiency, the inductor? resistance (dcr) should be as low as possible. please note that the core material differs among different manufacturers and inductor types and has an impact on the efficiency. see table 2 for recommended inductors and manufacturers. capacitor selection ceramic input and output capacitors are recommend- ed for most applications. for best stability over a wide temperature range, use capacitors with an x5r or bet- ter dielectric due to their small size, low esr, and low temperature coefficients. output capacitor the output capacitor, c out , is required to keep the output voltage ripple small and to ensure regulation loop stability. c out must have low impedance at the switching frequency. a 22? ceramic output capacitor is recommended for most applications. if a larger out- put capacitor is used, then paralleling smaller capaci- tors is suggested to keep the effective impedance of the capacitor low at the switching frequency. input capacitor due to the pulsating nature of the input current in a buck converter, a low-esr input capacitor at inp is required for input voltage filtering and to minimize interference with other circuits. the impedance of the input capaci- tor, c inp , should be kept very low at the switching fre- quency. a minimum value of 10? is recommended at inp for most applications. the input capacitor can be increased for better input filtering. in input filter in all max1557 applications, connect inp directly to in and bypass inp as described in the input capacitor section. no additional bypass capacitor is required at in. for applications using the max1556 and max1556a, an rc filter between inp and in keeps power-supply noise from entering the ic. connect a 100 ? resistor between inp and in, and connect a 0.47? capacitor from in to gnd. soft-start capacitor the soft-start capacitor, c ss , is required for proper operation of the max1556/max1556a/max1557. the recommended value of c ss is discussed in the soft- start section. soft-start times for various soft-start capacitors are shown in the typical operating characteristics . pcb layout and routing due to fast-switching waveforms and high-current paths, careful pcb layout is required. an evaluation kit (max1556evkit) is available to speed design. when laying out a board, minimize trace lengths between the ic, the inductor, the input capacitor, and the output capacitor. keep these traces short, direct, and wide. keep noisy traces, such as the lx node trace, away from out. the input bypass capacitors should be placed as close as possible to the ic. connect gnd to the exposed paddle and star pgnd and gnd together at the output capacitor. the ground connections of the input and output capacitors should be as close together as possible. 075 3 32 . vk v r rr output ? ? ? ? ? ? ? = + () kxvx vv v output . . . = ? ? ? ? ? ? ? ? 106 10 075 36 2 16a i q , 1.2a pwm dc-dc step-down converters 10 ______________________________________________________________________________________ output out r2 r3 ss reference 1.25v error amplifier figure 6. adjustable output voltage
chip information process: bicmos max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters ______________________________________________________________________________________ 11 package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package draw- ings may show a different suffix character, but the drawing per- tains to the package regardless of rohs status. package type package code outline no. land pattern no. 10 tdfn t1033-1 21-0137 90-0003
max1556/max1556a/max1557 16a i q , 1.2a pwm dc-dc step-down converters 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. 12 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 7/04 initial release 1 3/08 adding max1556a as a new version 1?2 2 6/10 added soldering temperature, added toc for external feedback switching waveforms, and added paragraph discussing noise coupling when using external feedback resistors 1, 2, 5, 6, 9, 10, 11 3 1/11 added automotive qualified part 1

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