general description the MAX1947 is a compact, high-efficiency, step-up dc- dc converter that regulates output voltages from 1.8v to 3.3v to power ?/dsp cores, memory, and i/o rails in 1- and 2-cell alkaline/nimh/nicd battery-powered systems. it features an internal 800ma switch and synchronous rectifier to achieve up to 94% efficiency and to eliminate the need for an external schottky diode. high-frequency switching (up to 2mhz) results in low ripple and small external components, while automatic pulse skipping at light loads reduces supply current to just 70? for extended battery life. maxim? proprietary true shutdown reduces supply current to just 2? and fully discharges the output to ground. the convert- er is offered in fixed-output voltages of 1.8v, 2.5v, 3.0v, and 3.3v, requiring no feedback or compensation net- work. a 75ms reset output flag provides for power-on reset (por) and undervoltage detection. the MAX1947 is available in a space-saving 8-pin tdfn package. applications mp3 players, pagers, and cd players pdas and organizers digital still cameras cordless phones wireless mice/keyboards portable medical equipment other battery-powered systems features ? low input (0.7v) and output (1.8v) voltage capability ? internal synchronous rectifier ? high 94% efficiency ? fixed output voltages: 1.8v, 2.5v, 3v, and 3.3v ? up to 2mhz switching allows small external components and low output ripple ? automatic pulse skipping at light loads for extended battery life ? low 70a (typ) operating supply current (measured at out) ? low 2a logic-controlled shutdown ? true shutdown fully discharges output to ground ? uses only small ceramic capacitors ? 75ms reset output flag MAX1947 low input/output voltage step-up dc-dc converter with reset ________________________________________________________________ maxim integrated products 1 lx pgnd shdn 8 7 batt out gnd gnd reset tdfn 3mm x 3mm top view 1 2 3 4 6 5 MAX1947 pin configuration ordering information MAX1947 lx gnd batt out pgnd 10 f 2.2 f 4.7 h v out +1.8v, +2.5v, +3.0v, +3.3v v in +0.7v to +v out reset shdn t ypical application circuit 19-3086; rev 0; 5/04 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. * xy represents the output voltage code (e.g., 18 =1.8v). standard output voltages include 3.3v (33), 3.0v (30), 2.5v (25), and 1.8v (18). contact the factory for other output voltages in 100mv increments between 1.8v and 3.3v; the minimum order quantity is 25,000 units. evaluation kit available part temp range pin-package MAX1947etaxy* -40 c to +85 c8 tdfn 3mm x 3mm true shutdown is a trademark of maxim integrated products, inc.
MAX1947 low input/output voltage step-up dc-dc converter with reset 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v batt = 1.5v, t a = -40 c to +85 c, unless otherwise noted. typical values are at t a = +25 c.) (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. note 1: lx has internal clamp diodes to pgnd and out. applications that forward bias these diodes should take care not to exceed the ic? package power-dissipation limits. batt, out, shdn to gnd ...................................-0.3v to +4.0v reset to gnd..........................................-0.3v to (v out + 0.3v) pgnd to gnd .......................................................-0.3v to +0.3v switch current (i lx , i out , i pgnd ) (note 1) .................-1a to +1a continuous power dissipation (t a = +70 c) 8-pin tdfn (derate 24.4mw/ c above +70 c)..........................................................1951.2mw 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 minimum startup voltage r load = 1k ? , t a = +25 c 0.8 0.95 v startup-voltage temperature coefficient -2.1 mv/ c maximum input operating voltage (note 3) 3.6 v minimum input operating voltage 0.7 v MAX1947eta18, i load = 40ma 1.74 1.8 1.86 MAX1947eta25, i load = 32ma 2.42 2.5 2.58 MAX1947eta30, i load = 25ma 2.9 3.0 3.1 output voltage MAX1947eta33, i load = 25ma 3.2 3.3 3.4 v load regulation no load to full load 1.2 % MAX1947eta18 160 273 MAX1947eta25 130 214 MAX1947eta30 100 185 v batt = 1v MAX1947eta33 100 169 MAX1947eta25 240 380 MAX1947eta30 200 361 full-load output current v batt = 1.8v MAX1947eta33 200 329 ma supply current into batt no switching 2 4 ? supply current into out no switching 70 110 ? lx switch maximum on-time 0.7 1 1.3 ? lx switch minimum off-time 0.2 0.25 0.3 ? maximum on-time to minimum off-time ratio 3.6 4 4.6 frequency in startup 650 khz
MAX1947 low input/output voltage step-up dc-dc converter with reset _______________________________________________________________________________________ 3 note 2: limits are 100% production tested at t a = +25 c. limits over the operating temperature range are guaranteed by design. note 3: when batt is greater than the output-voltage set point, the part is in track mode (see the track mode section). electrical characteristics (continued) (v batt = 1.5v, t a = -40 c to +85 c, unless otherwise noted. typical values are at t a = +25 c.) (note 2) parameter conditions min typ max units startup to normal-mode output transition voltage 50mv hysteresis, rising edge 1.40 1.62 1.73 v t a = 0? to +85? 600 800 1000 nfet current limit t a = -40? to +85? 580 800 1000 ma t a = 0? to +85? 15 75 150 pfet turn-off current t a = -40? to +85? 10 75 150 ma MAX1947eta18 0.3 0.6 MAX1947eta25 0.22 0.44 MAX1947eta30 0.17 0.34 internal nfet on-resistance i lx = 100ma MAX1947eta33 0.15 0.3 ? MAX1947eta18 0.5 1.0 MAX1947eta25 0.35 0.7 MAX1947eta30 0.28 0.56 internal pfet on-resistance i lx = 100ma MAX1947eta33 0.25 0.5 ? t a = +25? 0.1 1 lx leakage current shdn = gnd, v out = 0v, v lx = 3.6v t a = +85? 1 ? shutdown mode shutdown supply current shdn = gnd 2 4 ? v ih 0.8 x v batt shdn input voltage v il 0.18 x v batt v shdn = out or gnd, t a = +25 c1 100 shdn input bias current shdn = out or gnd, t a = +85 c5 na out discharge resistance in shutdown shdn = gnd 500 1000 ? reset output reset out voltage trip level v out falling, 1% hysteresis 87 90 93 % minimum v out for valid reset 0.9 v reset timeout 65 140 235 ms i sink = 200? 0.3 reset output voltage i source = 200? 0.8 x v out v
MAX1947 low input/output voltage step-up dc-dc converter with reset 4 _______________________________________________________________________________________ t ypical operating characteristics (v in = 1.5v, circuit of typical application circuit, t a = +25?, unless otherwise noted.) 0.1 10 1 100 1000 MAX1947eta18 efficiency vs. load current MAX1947toc01 load current (ma) efficiency (%) 100 60 70 80 90 65 75 85 95 v in = 1.6v v in = 1.25v v in = 1v 0.1 10 1 100 1000 MAX1947eta33 efficiency vs. load current MAX1947toc04 load current (ma) efficiency (%) 100 60 70 80 90 65 75 85 95 v in = 1.8v v in = 1.25v v in = 1v v in = 2.5v 0.6 1.0 0.8 1.4 1.2 1.6 1.8 2.0 startup voltage vs. load current MAX1947toc07 load current (ma) startup voltage (v) 04060 20 100 140 80 120 v out = 1.8v v out = 2.5v v out = 3.0v v out = 3.3v 0.1 10 1 100 1000 MAX1947eta25 efficiency vs. load current MAX1947toc02 load current (ma) efficiency (%) 100 60 70 80 90 65 75 85 95 v in = 1.6v v in = 1.25v v in = 1v 0 400 200 800 600 1000 1200 maximum output current vs. input voltage MAX1947toc05 input voltage (v) maximum output current (ma) 0.7 1.7 2.2 1.2 2.7 3.2 3.7 v out = 1.8v v out = 2.5v v out = 3.0v v out = 3.3v 0 0.3 0.2 0.1 0.4 0.5 0.6 0.7 0.8 0.9 1.0 -40 10 -15 35 60 85 startup voltage vs. temperature MAX1947toc08 temperature ( c) startup voltage (v) r load = 1k ? r load = 0 ? 0.1 10 1 100 1000 MAX1947eta30 efficiency vs. load current MAX1947toc03 load current (ma) efficiency (%) 100 60 70 80 90 65 75 85 95 v in = 1.8v v in = 1.25v v in = 1v v in = 2.5v 0 200 100 400 300 500 600 no-load input current vs. input voltage MAX1947toc06 input voltage (v) input current ( a) 0.7 1.7 2.2 1.2 2.7 3.2 3.7 v out = 1.8v v out = 2.5v v out = 3.3v 0 0.6 0.4 0.2 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.7 1.7 1.2 2.2 2.7 3.2 3.7 shutdown threshold vs. input voltage MAX1947toc09 input voltage (v) shutdown threshold (v)
MAX1947 low input/output voltage step-up dc-dc converter with reset _______________________________________________________________________________________ 5 t ypical operating characteristics (continued) (v in = 1.5v, circuit of typical application circuit, t a = +25?, unless otherwise noted.) 1.74 1.76 1.80 1.78 1.82 1.84 0 100 50 150 200 250 300 350 output voltage vs. load current MAX1947toc10 load current (ma) output voltage (v) heavy-load switching waveforms MAX1947toc13 v out (ac-coupled) i l v lx v in (ac-coupled) 50mv/div 50mv/div 2v/div 500ma/div 2 s/div line-transient waveforms MAX1947toc15 v in v out (ac-coupled) 1.5v 1v 50mv/div 10 s/div 1.74 1.76 1.80 1.78 1.82 1.84 0.7 0.9 0.8 1.0 1.1 1.3 1.5 1.2 1.4 1.6 1.7 no-load output voltage vs. input voltage MAX1947toc11 input voltage (v) output voltage (v) light-load switching waveforms MAX1947toc14 v out (ac-coupled) i l v lx v in (ac-coupled) 50mv/div 50mv/div 2v/div 500ma/div 2 s/div load-transient waveforms MAX1947toc16 i load v out (ac-coupled) 200ma/div 50mv/div 10 s/div 1.74 1.76 1.80 1.78 1.82 1.84 -40 10 -15 35 60 85 output voltage vs. temperature MAX1947toc12 temperature ( c) output voltage (v) i load = 40ma
MAX1947 detailed description the MAX1947 compact step-up dc-dc converter starts up with voltages as low as 0.8v and operates with input voltages down to 0.7v. an internal synchronous rectifier reduces cost by eliminating the need for an external schottky diode and improves overall efficiency by reducing losses in the circuit. the efficiency is further increased with the low 70? quiescent current and low on-resistance of the internal n-channel mosfet power switch. the MAX1947 uses maxim? proprietary true shutdown circuitry, which disconnects the output from the input in shutdown and actively discharges the output to ground. low input/output voltage step-up dc-dc converter with reset 6 _______________________________________________________________________________________ pin description pin name function 1 reset active-low push-pull reset output. reset goes high 75ms (min) after the output voltage has exceeded 90% of its final value. the reset output is valid for output voltages as low as 0.9v. reset is driven low in shutdown. 2 gnd ground. connect to exposed paddle. 3 gnd ground. connect to exposed paddle. 4 shdn shutdown input. connect to batt or logic 1 for normal operation. connect to gnd or logic 0 for a low quiescent-current shutdown mode. 5 pgnd power ground. connect to exposed paddle. 6lx inductor connection to the drains of the internal n-channel switch and p-channel synchronous rectifier 7 out regulator output. bypass with 10? ceramic capacitor to gnd for full-load capability. for less than 50% of full load, a 4.7? capacitor can be used. 8 batt batter y c onnecti on. v b a tt i s us ed for t he star tup osci l l ator and to p ow er the chi p w hen v ou t < v b a tt . ? p exposed paddle. connect to gnd and pgnd. power-on reset waveforms MAX1947toc17 v in v out v reset 1v/div 1v/div 1v/div 20ms/div exiting and entering shutdown waveforms MAX1947toc18 v out v shdn v reset 1v/div 1v/div 1v/div 20ms/div t ypical operating characteristics (continued) (v in = 1.5v, circuit of typical application circuit, t a = +25?, unless otherwise noted.)
control scheme the MAX1947 is a bootstrapped design. upon turn-on, a startup oscillator brings the output voltage high enough to allow the main dc-dc circuitry to run. once the output voltage reaches 1.62v (typ) the main dc-dc circuitry turns on and boosts the output voltage to the final regulation point. the unique minimum off-time, current-limited control scheme is the key to the MAX1947? low operating cur- rent and high efficiency over a wide load range. the architecture combines the high output power and effi- ciency of a pulse-width modulation (pwm) device with the ultra-low quiescent current of a traditional pulse- skipping controller. the switching frequency can be as high as 2mhz and depends upon the load current and input voltage. the MAX1947 is designed to operate using low-esr ceramic capacitors, so output voltage ripple due to esr is very small (approximately 10mv p-p ). track mode the MAX1947 enters track mode when batt is greater than the output-voltage regulation point. track mode can only be entered under the following conditions: v batt > v out , v out > v out regulation point, and the minimum off-time expires. during track mode, the syn- chronous rectifier is turned on 100% of the time and the output voltage tracks the battery voltage. track mode is exited by v out falling below the v out regulation point. synchronous rectification the internal synchronous rectifier eliminates the need for an external schottky diode, reducing cost and board space. during the cycle off-time, the p-channel mosfet turns on and shunts the mosfet body diode. as a result, the synchronous rectifier significantly improves efficiency without the addition of an external compo- nent. conversion efficiency can be as high as 94%. reset the MAX1947 features an active-low push-pull reset output for use with a microcontroller (?). it signals the ? when the MAX1947 output voltage is within operat- ing limits. during startup, reset is held low. when the reset threshold (90% of the output regulation voltage) is reached, a 75ms (min) timer begins counting. reset is switched high once the timer expires. MAX1947 low input/output voltage step-up dc-dc converter with reset _______________________________________________________________________________________ 7 functional diagram startup oscillator shutdown circuitry t on max timer control logic and gate drivers batt shdn 0.9 x ref ref error amplifier zero-crossing amplifier current-limit amplifier p* n lx pgnd out reset 75ms timer t off min timer 1.25v reference (ref) gnd MAX1947 ref *body diode control
MAX1947 shutdown the MAX1947 enters shutdown mode when shdn is driven low. during shutdown, the synchronous rectifier disconnects the output from the input, eliminating the dc conduction path that normally exists with traditional boost converters in shutdown mode. the output is actively dis- charged to ground through an internal 500 ? resistor. the quiescent current is reduced to 2? while in shutdown mode. drive shdn high for normal operation. the output reaches regulation approximately 650? after shdn goes high. applications information inductor selection an inductor value of 4.7? performs well in most appli- cations. the MAX1947 also works with inductors in the 2.2? to 6.8? range. smaller inductance values typi- cally offer a smaller physical size for a given series resistance, allowing the smallest overall circuit dimen- sions but with lower output-current capability. circuits using larger inductance values exhibit higher output- current capability, but are larger for the same series resistance and current rating. the inductor? incremental saturation current rating should be greater than the peak switch-current limit. however, it is generally acceptable to bias the inductor into saturation by as much as 20%, although this slightly reduces efficiency (see the electrical characteristics for the MAX1947 nfet current limit). table 1 lists the suggested components for several typ- ical applications. also, the inductor? dc resistance sig- nificantly affects efficiency. low input/output voltage step-up dc-dc converter with reset 8 _______________________________________________________________________________________ application load input capacitor (f) output capacitor (f) inductor (h) 50% full load 2.2 4.7 3.3 1-cell input, output < 2.7v >50% full load 2.2 10 3.3 50% full load 2.2 4.7 4.7 1-cell input, output > 2.7v >50% full load 2.2 10 4.7 50% full load 2.2 4.7 6.8 2-cell input >50% full load 2.2 10 6.8 table 1. suggested component values manufacturer part part number phone website sumida inductor cdrh3d16 series 81-3-3667-3381 www.sumida.com output capacitors 4.7? jmk212bj475mg, 10? jmk212bj106mg taiyo yuden input capacitors 2.2? lmk107bj225ma 408-573-4150 www.t-yuden.com output capacitors 4.7? c2012x5r0j475k, 10? c2012x5r0j106k tdk input capacitors 2.2? c1608x5r03225m 888-835-6646 www.tdk.com table 2. suggested component manufacturers
calculate the maximum output current (i outmax ) using inductor ripple current (i ripple ) and duty cycle (d) as follows: here, i lim is the nfet current limit (800ma typ), t off is the lx switch? off-time (0.25? typ), and r l is the series resistance of the inductor. capacitor selection the MAX1947 is specifically designed for using small, inexpensive, low-esr ceramic capacitors. x5r and x7r dielectrics are recommended when operating over wide temperature ranges. bypass the output of the MAX1947 with 10? when using maximum load cur- rents. when using less than half the maximum load cur- rent capability, the output capacitor can be reduced to 4.7?. bypass the input with a 2.2? or larger ceramic capacitor. table 1 lists the suggested values for the input and output capacitors for typical applications. pc board layout and grounding careful printed circuit-board layout is important for min- imizing ground bounce and noise. keep the ic? gnd pins and the ground leads of the input and output filter capacitors very close together. connect gnd and pgnd directly to the exposed paddle. in addition, keep all connections to the out and lx pins as short as pos- sible. to maximize output power and efficiency and minimize output ripple voltage, use short, wide traces from the input and output. a sample layout is available in the MAX1947 evaluation kit. chip information transistor count: 5156 process: bicmos MAX1947 low input/output voltage step-up dc-dc converter with reset _______________________________________________________________________________________ 9 i vir rv lt rr d vi lim i ripple r ds on pfet rv vi lim i ripple r ds on pfet rr ripple out lim ds on pfet l batt off ds on pfet l out l batt out ds on nfet l = + + ? + + = + ? + ? ? ? ? ? ? ? ? ? ? ? ? ? + ? ? + ? ? ? ? () / () () ( () ) () ( () ) () () () 2 2 2 ? ? ? ? ? ? ? ? ? = ? ? ii lim i ripple d outmax ()() 2 1
MAX1947 low input/output voltage step-up dc-dc 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. 10 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. 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 .) 6, 8, &10l, dfn thin.eps l c l c pin 1 index area d e l e l a e number of leads shown are for reference only e2 detail a n f 1 2 21-0137 package outline, 6, 8, 10 & 14l, tdfn, exposed pad, 3x3x0.80 mm common dimensions symbol min. max. a0.700 .80 d2.903 .10 e2.903 .10 a1 0.00 0.05 l 0.20 0.40 pkg. code n d2 e2 e jedec spec b [(n/2)-1] x e package variations 0.25 min. k a2 0.20 ref. 2.300.10 1.500.10 6 t633-1 0.95 bsc mo229 / weea 1.90 ref f 2 2 21-0137 package outline, 6, 8, 10 & 14l, tdfn, exposed pad, 3x3x0.80 mm 0.400.05 1.95 ref 0.300.05 0.65 bsc 2.300.10 8 t833-1 2.00 ref 0.250.05 0.50 bsc 2.300.10 10 t1033-1 2.40 ref 0.200.03 - - - - 0.40 bsc 1.700.10 2.300.10 14 t1433-1 1.500.10 1.500.10 mo229 / weec mo229 / weed-3 0.40 bsc - - - - 0.200.03 2.40 ref t1433-2 14 2.300.10 1.700.10
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