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general description the max1572 is a fixed-frequency, synchronous step- down dc-to-dc converter to power low-voltage micro- processor/dsp cores in portable equipment requiring high efficiency in a limited pc board area. the features are optimized for high efficiency over a wide load range, small external component size, low output ripple, and excellent transient response. the input supply voltage range is from 2.6v to 5.5v, while the output is internally fixed from 0.75v to 2.5v in 50mv increments with a guaranteed output current of 800ma. the high 2mhz switching allows tiny low-cost capacitors and a low-pro- file inductor, while the power-saving pulse-group mode reduces quiescent current to 48? (typ) with light l oads. to reduce noise and rf interference, the converter can be configured to provide forced-pwm operation. the max1572 includes a low on-resistance internal mosfet switch and synchronous rectifier to maximize efficiency and minimize external component count. no external diode is needed. other features include soft- start to eliminate inrush current at startup and a 170ms (min) reset output to provide power-on/undervoltage reset. the max1572 is available in a 12-pin, 4mm x 4mm thin qfn package with exposed paddle. applications cell phones and smart phones pdas, palmtops, and notebook computers mp3 and dvd players digital cameras and camcorders pcmcia cards hand-held instruments features ? up to 97% efficiency ? 2mhz pwm switching ? 800ma guaranteed output current ? low 48? quiescent current ? power-saving modes: pulse-group, pulse-skip, forced-pwm mode ? 0.75v to 2.5v preset output range (in 50mv increments) ? voltage-positioning load transients ? 5mv p-p output ripple ? tiny 2.2? inductor ? 10? ceramic output capacitor ? low 0.1? shutdown current ? no external schottky diode required ? soft-start with zero inrush current ? 170ms (min) reset output ? small 12-pin, 4mm x 4mm thin qfn package max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset ________________________________________________________________ maxim integrated products 1 max1572 12 11 10 7 8 9 pgnd lx batt 3 2 1 gnd ss reset 4 5 6 en1 gnd abatt en2 gnd out 4mm x 4mm thin qfn top view pin configuration ordering information lx 2.2 h pgnd out reset gnd abatt en1 batt mode select input 2.6v to 5.5v output 0.75v to 2.5v 800ma en2 ss max1572 t ypical operating circuit 19-2837; rev 1; 11/04 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. * xyz is for the output voltage (e.g., max1572etc165 has a 1.65v output). minimum order quantity is 2500. ** ep = exposed paddle. evaluation kit available part temp range pin-package max1572etc075 -40 c to +85 c 12 thin qfn-ep** max1572etc130 -40 c to +85 c 12 thin qfn-ep** max1572etc150 -40 c to +85 c 12 thin qfn-ep** max1572etc180 -40 c to +85 c 12 thin qfn-ep** max1572etc250 -40 c to +85 c 12 thin qfn-ep** max1572etcxyz* -40 c to +85 c 12 thin qfn-ep** selector guide appears at end of data sheet.
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v batt = 3.6v, t a = +0? to +85? , unless otherwise noted. typical values are at t a = +25?.) 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. abatt, batt, en1, en2, reset , out, ss to gnd ............................................................-0.3v to +6v pgnd to gnd .......................................................-0.3v to +0.3v lx current (note 1) ............................................................. 2.1a output short-circuit duration ............................................infinite continuous power dissipation (t a = +70 c) 12-pin thin qfn (derate 16.9mw/ c above +70 c) ...1349mw operating temperature range ...........................-40 c to +85 c junction temperature ......................................................+150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering, 10s) .................................+300 c parameter conditions min typ max units batt input voltage 2.6 5.5 v undervoltage lockout threshold v batt rising and falling, 1% hysteresis 2.20 2.35 2.55 v en1 = gnd, en2 = batt, no switching 48 80 quiescent supply current en1 = batt, en2 = gnd, no switching 700 ? shutdown supply current en1 = en2 = gnd, t a = +25? 0.1 1 a maximum output current 800 ma out bias current 69a no load, en1 = en2 = batt 1.2 2.7 100ma load -0.4 +0.8 +2.0 300ma load 0 550ma load -1 output-voltage accuracy (voltage positioning) 800ma load -2 % line regulation 0.3 %/v v batt = 3.6v 0.28 0.45 p-channel on-resistance i lx = 180ma v batt = 2.6v 0.33 ? v batt = 3.6v 0.18 0.30 n-channel on-resistance i lx = 180ma v batt = 2.6v 0.20 ? p-channel current-limit threshold 1.00 1.25 1.65 a n-channel current-limit threshold en1 = en2 = batt -0.68 -0.52 -0.37 a n-channel zero-crossing threshold en1 = batt, en2 = gnd 15 40 65 ma lx output current (note 2) 1.4 a rms lx leakage current en1 = en2 = gnd 0.1 10 ? maximum duty cycle 100 % en1 = batt, en2 = gnd or en1 = gnd, en2 = batt 0 minimum duty cycle en1 = en2 = batt 16.7 17.3 % switching frequency 1.8 2 2.2 mhz ss output impedance 65 100 150 k ? note 1: lx has internal clamp diodes to pgnd and batt. applications that forward bias these diodes should take care not to exceed the ic? package power dissipation limits.
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset _______________________________________________________________________________________ 3 electrical characteristics (continued) (v batt = 3.6v, t a = +0? to +85? , unless otherwise noted. typical values are at t a = +25?.) parameter conditions min typ max units ss discharge resistance en1 = en2 = gnd 100 200 ? v abatt > 4.2v 1.6 en_ logic input high v abatt 4.2v 1.4 v en_ logic input low 0.4 v en_ logic input current 0.1 1 a reset threshold percent of nominal, measured at out 87 90 93 % reset timer delay time from v out > 90% to reset = hi 170 200 230 ms reset output low level i sink = 1ma 0.015 0.075 v reset internal pullup resistance to out 9 14 20 k ? thermal-shutdown threshold t j rising 160 c thermal-shutdown hysteresis 20 c electrical characteristics (v batt = 3.6v, t a = -40? to +85? , unless otherwise noted.) (note 3) parameter conditions min typ max units batt input voltage 2.6 5.5 v undervoltage lockout threshold v batt rising and falling, 1% hysteresis 2.20 2.55 v quiescent supply current en1 = gnd, en2 = batt, no switching 80 ? shutdown supply current en1 = en2 = gnd 3 a maximum output current 800 ma out bias current 9a no load, en1 = en2 = batt 3.2 output-voltage accuracy (voltage positioning) 100ma load -1.2 +2.8 % p-channel on-resistance i lx = 180ma 0.45 ? n-channel on-resistance i lx = 180ma 0.3 ? n-channel current-limit threshold en1 = en2 = batt -0.68 -0.22 a n-channel zero-crossing threshold en1 = batt, en2 = gnd 10 65 ma lx output current (note 2) 1.4 a rms lx leakage current en1 = en2 = gnd 10 ? maximum duty cycle 100 % minimum duty cycle en1 = en2 = batt 17.3 % switching frequency 1.8 2.2 mhz ss output impedance 65 150 k ? ss discharge resistance en1 = en2 = gnd 200 ? v abatt > 4.2v 1.6 en_ logic input high v abatt 4.2v 1.4 v
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset 4 _______________________________________________________________________________________ electrical characteristics (continued) (v batt = 3.6v, t a = -40? to +85? , unless otherwise noted.) (note 2) parameter conditions min typ max units en_ logic input low 0.4 v en_ logic input current 1a reset threshold percent of nominal, measured at out 87 93 % reset timer delay time from v out > 90% to reset = hi 170 230 ms reset output low level i sink = 1ma 0.2 v reset internal pullup resistance to out 9 20 k ? note 2: guaranteed by design, not production tested. note 3: specifications to -40? are guaranteed by design and not production tested. 100 90 40 1100 0 efficiency vs. load current with 2.5v output 60 50 80 70 max1572toc01 load current (ma) efficiency (%) 10 100 v in = 2.6v v in = 3.6v v in = 5v 100 90 40 1100 0 efficiency vs. load current with 1.8v output 60 50 80 70 max1572toc02 load current (ma) efficiency (%) 10 100 v in = 2.6v v in = 3.6v v in = 5v 100 90 40 11000 efficiency vs. load current with 1.5v output 60 50 80 70 max1572toc03 load current (ma) efficiency (%) 10 100 v in = 2.6v v in = 3.6v v in = 5v 100 90 40 1100 0 efficiency vs. load current vs. mode 60 50 80 70 max1572toc04 load current (ma) efficiency (%) 10 100 forced- pwm mode pulse- skip mode pulse- group mode 1.58 1.56 1.40 0 800 output voltage vs. load current 1.48 1.46 1.44 1.42 1.54 1.50 1.52 max1572toc05 load current (ma) output voltage (v) 200 400 600 t a = +85 c t a = +25 c t a = -40 c 1.55 1.45 2.5 5.5 output voltage vs. input voltage with 100ma load 1.49 1.47 1.53 1.51 max1572toc06 input voltage (v) output voltage (v) 3.0 3.5 4.5 5.0 4.0 t a = +85 c t a = +25 c t a = -40 c t ypical operating characteristics (v batt = 3.6v, v out = 1.5v, en1 = gnd, en2 = batt, t a = +25?, unless otherwise noted.)
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset _______________________________________________________________________________________ 5 60 0 2.0 5.5 input current vs. input voltage with no load 30 10 20 50 40 max1572toc07 input voltage (v) input current ( a) 2.5 3.0 4.0 4.5 5.0 3.5 heavy-load switching waveforms max1572 toc08 v lx i l v out ripple 10mv/div 500ma/div 2v/div 200ns/div i load = 500ma light-load switching waveforms max1572 toc09 v lx i l v out ripple 20mv/div 500ma/div 2v/div 2 s/div i load = 20ma soft-start/shutdown waveforms max1572 toc10 v en2 i in v out 1v/div 100ma/div 2v/div 200 s/div reset waveform max1572 toc11 v en2 i in v reset v out 1v/div 1v/div 100ma/div 2v/div 100ms/div load transient, forced-pwm mode max1572 toc12 i load v out 500ma/div 100mv/div 4 s/div i load = 20ma to 550ma t ypical operating characteristics (continued) (v batt = 3.6v, v out = 1.5v, en1 = gnd, en2 = batt, t a = +25?, unless otherwise noted.)
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset 6 _______________________________________________________________________________________ load transient, pulse-skip mode max1572 toc13 i load v out 500ma/div 100mv/div 4 s/div i load = 20ma to 550ma load transient, pulse-group mode max1572 toc14 i load v out 500ma/div 100mv/div 4 s/div i load = 20ma to 550ma line transient max1572 toc15 i l v in v out 200ma/div 20mv/div 1v/div 40 s/div v in = 3.5v to 4.0v t ypical operating characteristics (continued) (v batt = 3.6v, v out = 1.5v, en1 = gnd, en2 = batt, t a = +25?, unless otherwise noted.)
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset _______________________________________________________________________________________ 7 detailed description figure 1 is the functional diagram. pwm control scheme the max1572 uses a 2mhz fixed-frequency, pulse- width-modulated (pwm), current-mode control scheme. the heart of the current-mode pwm controller is an open-loop comparator that compares the error amp voltage-feedback signal against the sum of the ampli- fied current-sense signal and the slope compensation ramp. at each rising edge of the internal clock, the internal high-side p-channel mosfet turns on until the pwm comparator trips. during this on-time, current ramps up through the inductor, sourcing current to the pin description pin name function 1 reset active-low reset output. open-drain output with internal 14k ? pullup to out. reset is driven low in shutdown. 2ss soft-start control. connect a capacitor from ss to gnd to set the soft-start time. use a 1000pf or larger capacitor to eliminate inrush current during startup. with greater than 10? total output capacitance, increase c ss to c out /10,000 for soft-start. in shutdown, ss is discharged internally with 100 ? to gnd. 3, 5, 11 gnd ground. connect all ground pins to the exposed paddle. 4 out output sense input. connect to the output of the regulator. in shutdown, out is discharged internally with 14k ? to gnd. 6 en2 enable/mode control input 2. see table 1. 7 pgnd power ground. connect to exposed paddle. 8l xi nductor connection. lx is high impedance in shutdown. 9 batt s up p l y v ol tag e inp ut. c onnect to a 2.6v to 5.5v sour ce. c onnect a 10f cer am i c cap aci tor fr om batt to g n d . 10 en1 enable/mode control input 1. see table 1. 12 abatt anal og s up p l y inp u t. c o nnect to batt thr oug h a 10 ? r esi stor . c onnect a 0.1f cap aci tor fr om abatt to gn d . exposed paddle exposed paddle. connect to gnd and pgnd. table 1. mode select truth table mode en1 en2 shutdown 0 0 pulse group 0 1 pulse skip 1 0 forced pwm 1 1 a zero represents en_ being driven low or connected to gnd. a 1 represents en_ being driven high or connected to batt. batt clock 2mhz pwm control abatt lx 10 ? 0.1 f 10 f 2.2 h c out pgnd gnd out ss ea reset thermal shutdown reference output 0.75v to 2.5v 800ma input 2.6v to 5.5v max1572 1000pf slope comp reset timer 170ms en1 en2 current sense mode select figure 1. functional diagram
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset 8 _______________________________________________________________________________________ manufacturer part value (?) r l (m ? )i sat (ma) size (mm) shielded murata lqh32cn 2.2 97 790 2.5 x 3.2 x 2.0 no cdrh3d16 2.2 50 1200 3.8 x 3.8 x 1.8 yes sumida cdrh2d11 2.2 78 780 3.2 x 3.2 x 1.2 yes d312f 2.2 170 1200 3.6 x 3.6 x 1.2 no toko d412f 2.2 140 1330 4.8 x 4.8 x 1.2 no table 2. recommended inductors output and storing energy in the inductor? magnetic field. the current-mode feedback system regulates the peak inductor current as a function of the output voltage error signal. since the average inductor current is nearly the same as the peak inductor current (assuming that the inductor value is relatively high to minimize ripple current), the circuit acts as a switch-mode transconduc- tance amplifier. this pushes the output lc filter pole, normally found in a voltage-mode pwm, to a higher fre- quency. to preserve inner-loop stability and eliminate inductor staircasing, an internal slope-compensation ramp is summed into the main pwm comparator. during the second half of the switching cycle (off-time), the internal high-side p-channel mosfet turns off and the internal low-side n-channel mosfet turns on. now the inductor releases the stored energy as its current ramps down while still providing current to the output. the output capacitor stores charge when the inductor current exceeds the load current and discharges when the inductor current is lower, smoothing the voltage across the load. under overload conditions, when the inductor current exceeds the current limit, the high-side mosfet is turned off and the low-side mosfet remains on for the remainder of the cycle to let the inductor current ramp down. pulse-group mode pulse-group mode is used to minimize the supply cur- rent with a light load. in pulse-group mode, the ic shuts off most internal circuitry when v out is +0.8% above nominal regulation. when v out drops below +0.8% of the nominal regulation voltage, the ic powers up its cir- cuits and resumes switching. pulse-skip mode pulse-skip mode is also used to minimize the supply current with a light load. the difference between pulse- group and pulse-skip modes is that when v out rises above the +0.8% regulation point, pulse-group mode stops switching and completely turns off a number of circuits. under the same conditions, pulse-skip mode stops switching but leaves all circuits on. the delay coming out of pulse-skip mode is shorter than with pulse-group mode. in pulse-skip mode, the output volt- age ripple is lower, and the load-transient response faster. however, the quiescent current is higher than in pulse-group mode. forced-pwm mode in forced-pwm mode, the max1572 operates at a con- stant 2mhz switching frequency without pulse skipping. this is desirable in noise-sensitive applications, since the output ripple is minimized and has a predictable noise spectrum. forced-pwm mode requires higher supply current with light loads due to constant switching. 100% duty-cycle operation the max1572 can operate at 100% duty cycle. in this state, the high-side p-channel mosfet is turned on (not switching). this occurs when the input voltage is close to the output voltage. the dropout voltage is the voltage drop due to the output current across the on-resistance of the internal p-channel mosfet (r ds(on)p ) and the inductor resistance (r l ): v dropout = i out ( r ds(on)p + r l ) r ds(on)p is given in the electrical characteristics sec- tion. r l , for a few recommended inductors, is given in table 2. load-transient response/ voltage positioning the max1572 uses voltage positioning that matches the load regulation to the voltage droop seen during load transients. in this way, the output voltage does not overshoot when the load is removed, which results in the total output-voltage variation being half as wide as in a conventional design. figure 2 shows an example of a voltage-positioned and a nonvoltage-positioned load transient. additionally, the max1572 uses a wide-band- width feedback loop to respond more quickly to a load transient than regulators using conventional integrating feedback loops. the load line used to achieve voltage positioning is shown in figure 3. this assumes a nominal operating point of 3.6v input at 300ma load.
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset _______________________________________________________________________________________ 9 soft-start soft-start is used to prevent input-current overshoot dur- ing startup. for most applications using a 10? output capacitor, connect a 1000pf capacitor from ss to gnd. if a larger output capacitor is used, then use the follow- ing formula to find the value of the soft-start capacitor needed to prevent input-current overshoot: c ss = c out /10 4 during soft-start, the output voltage rises from 0 to v out(nom) with a time constant equal to c ss times 100k ? (see the typical operating characteristics ). 170ms reset reset is an open-drain output with an internal 14k ? pullup resistor to out. during startup, reset is held low until 200ms (typ) after the output voltage reaches 90% of its nominal regulation voltage. when the output voltage drops below 90% of its nominal regulation voltage, reset pulls low again. see the typical operating characteristics section for reset waveforms during startup and shutdown. applications information inductor selection a 2.2? inductor with a saturation current of at least 1a is recommended for full-load (800ma) applications. for lower load currents, the inductor current rating may be reduced. for most applications, use an inductor with a current rating 1.25 times the maximum required output current. for maximum efficiency, the inductor? dc resistance should be as low as possible. see table 2 for recommended inductors and manufacturers. capacitor selection ceramic 10? input and output capacitors are recom- mended for most applications. for output voltages below 1.5v, output capacitance should be increased to 22?. for best stability over a wide temperature range, use capacitors with an x5r or better dielectric. abatt input filter in normal applications, an rc filter on abatt keeps power-supply noise from entering the ic. connect a 10 ? resistor between batt and abatt and connect a 0.1? capacitor from abatt to gnd. pc board layout and routing due to fast-switching waveforms and high-current paths, careful pc board layout is required. an evalua- tion kit (max1572evkit) 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 to the ic as possible. connect pgnd and gnd directly to the exposed paddle underneath the ic. the ground connections of the input and output capacitors should be as close together as possible. i out v out (conventional) v out (voltage positioning) figure 2. load transient response, with and without voltage positioning change in output voltage (%) normal operation forced-pwm v in = 5.5v v in = 2.6v +1 0 -1 -2 0200 400 600 800 load current (ma) v in = 3.6v figure 3. voltage-positioning load line
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset 10 ______________________________________________________________________________________ chip information transistor count: 3697 process: bicmos part v out (v) top mark max1572etc075 0.75 aabw max1572etc130 1.30 aacw max1572etc150 1.50 aabx max1572etc180 1.80 aaby max1572etc250 2.50 aabz max1572etcxyz * selector guide * xyz is for output voltage (e.g., max1572etc165 has a 1.65v output). package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) 24l qfn thin.eps c 1 2 21-0139 package outline 12, 16, 20, 24l thin qfn, 4x4x0.8mm
max1572 800ma, 2mhz, pwm dc-to-dc step-down converter with reset maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 11 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) c 2 2 21-0139 package outline 12, 16, 20, 24l thin qfn, 4x4x0.8mm

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