general description the max8570 family of lcd step-up converters uses an internal n-channel switch and an internal p-channel output isolation switch. these converters operate from a 2.7v to 5.5v supply voltage and deliver up to 28v at the output. a unique control scheme provides the highest efficien- cy over a wide range of load conditions. the internal mosfet switch reduces external component count and a high switching frequency (up to 800khz) allows for tiny surface-mount components. three current-limit options are available. the max8570 and max8572 use a 110ma current limit to reduce ripple and component size in low-current applications. for high-power require- ments, the max8574 and max8575 use a 500ma cur- rent limit and supply up to 20ma at 20v. the max8571 and max8573 use a 250ma current limit for a compro- mise between ripple and power. built-in safety features protect the internal switch and down-stream compo- nents from fault conditions. additional features include a low quiescent current and a true shutdown ? mode to save power. the max8570/ max8571/max8574 allow the user to set the output voltage between 3v and 28v, and the max8572/ max8573/max8575 have a preset 15v output. these step-up converters are ideal for small lcd panels with low current requirements, but can also be used in other applications. the max8571 evaluation kit is available to help reduce design time. applications lcd bias generators polymer leds (oled) cellular or cordless phones palmtop computers personal digital assistants (pdas) organizers handy terminals features ? 15v or adjustable output voltage up to 28v ? safety features protect against output faults ? 20ma at 20v from a single li+ battery ? true shutdown ? 87% efficiency ? up to 800khz switching frequency ? small 6-pin sot23 package max8570?ax8575 high-efficiency lcd boost with true shutdown ________________________________________________________________ maxim integrated products 1 ordering information 19-3329; rev 1; 10/04 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. evaluation kit available part temp range pin- package top mark max8570 eut-t -40 c to +85 c 6 sot23-6 abtj max8571 eut-t -40 c to +85 c 6 sot23-6 abtk max8572 eut-t -40 c to +85 c 6 sot23-6 abtl max8573 eut-t -40 c to +85 c 6 sot23-6 abtm max8574 eut-t -40 c to +85 c 6 sot23-6 abtn max8575 eut-t -40 c to +85 c 6 sot23-6 abto gnd lx 16v cc 5sw fb max8570 max8571 max8574 sot23-6 top view 2 34 shdn gnd lx 16v cc 5sw out max8572 max8573 max8575 sot23-6 2 34 shdn pin configurations part current limit output voltage max8570 eut 110ma adjustable max8571 eut 250ma adjustable max8572 eut 110ma 15v max8573 eut 250ma 15v max8574 eut 500ma adjustable max8575 eut 500ma 15v selector guide true shutdown is a trademark of maxim integrated products, inc. max8572 max8573 max8575 sw v cc lx out gnd on off v cc = 2.7v to 5.5v v out = v cc to 28v shdn t ypical operating circuit
max8570?ax8575 high-efficiency lcd boost with true shutdown 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v cc = v shdn = 3.6v, sw floating, v fb = 1.3v (max8570/max8571/max8574) or v out = 16v (max8572/max8573/max8575), t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. v cc , shdn to gnd ..................................................-0.3v to +6v sw to gnd .................................................-0.3v to (v cc + 0.3v) fb to gnd (max8570/max8571/ max8574)...............................................-0.3v to (v cc + 0.3v) out to gnd (max8572/max8573/max8575) .......-0.3v to +30v lx to gnd ..............................................................-0.3v to +30v i lx , i cc ..............................................................................600ma continuous power dissipation (t a = +70?) sot23-6 (derate 8.7 mw/? above +70?).............695.7 mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter conditions min typ max units v cc input voltage range 2.70 5.50 v v cc undervoltage lockout v cc rising, 50mv typical hysteresis 2.33 2.5 2.65 v v cc supply current 25 35 ? t a = +25 c 0.05 1 v cc shutdown current shdn = gnd, v cc = 5.5v t a = -40 c to +85 c 0.05 ? line regulation circuit of figure 3, v out = 15v, i load = 5ma, v cc = 2.7v to 5.5v 0.1 %/v load regulation circuit of figure 3, v out = 15v, i load = 0 to 5ma 0.1 %/ma t a = 0 c to +85 c 1.216 1.226 1.236 fb regulation voltage t a = -40 c to +85 c 1.2137 1.2383 v fb input bias current -50 -4 +50 na t a = 0 c to +85 c 14.85 15 15.15 out regulation voltage t a = -40 c to +85 c 14.813 15.187 v out input bias current v out = 15v 2.4 4.4 ? lx voltage range 28 v max8571/max8573 0.217 0.241 0.267 max8570/max8572 0.088 0.101 0.108 lx switch current limit (note 2) max8574/max8575 0.425 0.484 0.540 a max8571/max8573/max8574/max8575, i lx = 100ma 0.9 1.5 lx on-resistance max8570/max8572, i lx = 50ma 1.5 2.4 ? t a = +25 c 0.01 2 lx leakage current v lx = 28v t a = -40 c to +85 c 0.05 ? maximum lx on-time 81114 s v fb > 1v or v out > 12.2v 0.8 1 1.2 minimum lx off-time v fb = 0.25v or v out = 3.4v 4.0 5 6.0 ? current-limit propagation delay 55 ns shdn low level (v il )2. 7v v cc 5.5v 0.7 v 4.2v v cc 5.5v 1.5 shdn high level (v ih ) 2.7v v cc < 4.2v 1.4 v shdn leakage current -1 +1 ?
max8570?ax8575 high-efficiency lcd boost with true shutdown _______________________________________________________________________________________ 3 efficiency vs. supply voltage max8570/71/73/74/75 toc06 supply voltage (v) efficiency (%) 5.1 4.7 4.3 3.9 3.5 3.1 75 80 85 90 95 100 70 2.7 5.5 l1 = toko a914byw-470m 47 h, 1ma load 47 h, 5ma load l1 = murata lqh32cn220k23 22 h, 5ma load 22 h, 1ma load t ypical operating characteristics (max8571, v cc = 3.6v, v out = 18v, circuit of figure 2, t a = +25 c, unless otherwise noted.) output voltage vs. supply voltage (max8571) max8570/71/73/74/75 toc01 supply voltage (v) output voltage (v) 5.1 4.7 3.9 4.3 3.5 3.1 17.6 17.7 17.8 17.9 18.0 18.1 18.2 18.3 18.4 18.5 17.5 2.7 5.5 l1 = murata lqh32cn220k23 r1 = 3.9m ? , r2 = 287k ? 5ma load 1ma load output voltage vs. supply voltage (figure 3, max8573) max8570/71/73/74/75 toc02 supply voltage (v) output voltage (v) 5.1 4.7 3.9 4.3 3.5 3.1 14.6 14.7 14.8 14.9 15.0 15.1 15.2 15.3 15.4 15.5 14.5 2.7 5.5 l1 = murata lqh32cn220k23 5ma load 1ma load output voltage vs. supply voltage (max8574) max8570/71/73/74/75 toc03 supply voltage (v) output voltage (v) 4.6 4.3 4.0 3.7 3.4 17.2 18.2 18.0 17.8 17.6 17.4 18.4 18.6 18.8 19.0 17.0 3.1 4.9 l1 = toko s1024-100m r1 = 1.1m ? , r2 = 75k ? , c4 = 4.7pf 5ma load 20ma load output voltage vs. load current max8570/71/73/74/75 toc04 load current (ma) output voltage (v) 20 15 5 10 17.6 17.8 18.0 18.2 18.4 18.6 18.8 19.0 17.4 025 l1 = murata lqh32cn220k23 r1 = 3.9m ? , r2 = 287k ? , c4 = 10pf max8570 max8571 max8574, r1 = 1.1m ? , r2 = 75k ? , c4 = 4.7pf output voltage vs. temperature max8570/71/73/74/75 toc05 temperature ( c) output voltage (v) 60 35 10 -15 17.7 17.8 17.9 18.0 18.1 18.2 18.3 18.4 17.6 -40 85 1ma load note 1: parameters are production tested at t a = +25?. limits over temperature are guaranteed by design. note 2: specified currents are measured at dc. actual lx current limits are slightly higher in circuit due to current-limit comparator delay. actual currents (with 2?) are 110ma (max8570/max8572), 250ma (max8571/max8573), and 500ma (max8574/max8575). electrical characteristics (continued) (v cc = v shdn = 3.6v, sw floating, v fb = 1.3v (max8570/max8571/max8574) or v out = 16v (max8572/max8573/max8575), t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter conditions min typ max units v cc = 3.6v, v sw = 0v, v fb = 0v, i cc (peak) 0.45 0.75 1.10 sw pmos current limit v cc = 3.6v, v sw = 0v, v fb = 0v, i cc (average) 0.15 0.30 0.60 a sw pmos on-resistance v cc = 2.7v, v fb = 0v, i sw = 100ma 1.5 2.5 ? t a = +25 c 0.01 1 sw pmos leakage current sw = gnd, v cc = 5.5v, v fb = 0v t a = -40 c to +85 c 0.02 ? sw soft-start time v cc = 2.7v, c sw = 4.7? 0.2 1 ms
max8570?ax8575 high-efficiency lcd boost with true shutdown 4 _______________________________________________________________________________________ efficiency vs. battery voltage (figure 4) max8570/71/73/74/75 toc07 battery voltage (v) efficiency (%) 10 8 6 4 2 50 60 70 80 90 100 40 012 l1 = murata lqh32cn220k23 5ma load 1ma load v cc = 3.6v efficiency vs. load current with 22 h inductor max8570/71/73/74/75 toc08 load current (ma) efficiency (%) 10 1 50 60 70 80 90 100 40 0.1 100 max8574, toko a914byw-220m max8571, murata lqh32cn220k23 max8570, murata lqh32cn220k23 efficiency vs. load current with 47 h inductor max8570/71/73/74/75 toc09 load current (ma) efficiency (%) 10 1 50 60 70 80 90 100 40 0.1 100 max8570, l1 = murata lqh32cn470k23 max8571, l1 = toko a914byw-470m peak inductor current limit vs. supply voltage max8570/71/73/74/75 toc10 supply voltage (v) current limit (ma) 5.1 4.7 4.3 3.9 3.5 3.1 100 200 300 400 500 600 700 0 2.7 5.5 max8574 max8571 max8570 supply current vs. load current max8570/71/73/74/75 toc11 load current (ma) supply current (ma) 10 5 20 40 60 80 100 120 0 015 l1 = murata lqh32cn220k23 no-load current vs. supply voltage max8570/71/73/74/75 toc12 supply voltage (v) supply current ( a) 5 4 1 2 3 10 20 30 40 50 60 70 80 0 06 r1 = 3.9m ? r2 = 287k ? r1 = 7.87m ? r2 = 576k ? max8573, figure 3 l1 = murata lqh32cn220k23 no switching line transient 3v to 5.5v (max8571) max8570/71/73/74/75 toc13 100 s/div v cc v out 200mv/div (ac-coupled) 2v/div 0 3.6k ? load, r1 = 3.9m ? , r2 = 287k ? line transient 3v to 5.5v (figure 3, max8573) max8570/71/73/74/75 toc14 100 s/div v cc v out 200mv/div (ac-coupled) 2v/div 0 3k ? load t ypical operating characteristics (continued) (max8571, v cc = 3.6v, v out = 18v, circuit of figure 2, t a = +25 c, unless otherwise noted.)
max8570?ax8575 high-efficiency lcd boost with true shutdown _______________________________________________________________________________________ 5 pin name function fb (max8570/ max8571/ max8574) feedback for setting the output voltage. connect fb to the center of a resistor voltage-divider from the output to gnd to set positive output voltages. 1 out (max8572/ max8573/ max8575) output. the output voltage is preset to 15v. connect a 1? ceramic capacitor from out to gnd. in shutdown, out is pulled to gnd by an internal 7.5m ? resistor. 2 gnd ground 3 shdn shutdown input. a logic low at shdn places the part in low-power shutdown mode. pull shdn high or connect to v cc for normal operation. 4l xi nductor switching connection 5sw isolation switch output. internally connected to the drain of a p-channel mosfet used to isolate the output from the input during shutdown. connect a 4.7? ceramic capacitor from sw to gnd. if true shutdown is not required, sw can be left open with the input supply connected directly to the inductor. 6v cc input voltage supply. connect a 2.7v to 5.5v input supply to v cc . connect a 1? ceramic capacitor from v cc to gnd. pin description load transient max8570/71/73/74/75 toc15 100 s/div v out i out 100mv/div (ac-coupled) 5ma/div 0 startup and shutdown waveforms max8570/71/73/74/75 toc16 400 s/div v out i lx 5v/div 10v/div 200ma/div 1.8 ? load 0 0 v shdn boost soft-start sw turn-on t ypical operating characteristics (continued) (max8571, v cc = 3.6v, v out = 18v, circuit of figure 2, t a = +25 c, unless otherwise noted.)
max8570?ax8575 high-efficiency lcd boost with true shutdown 6 _______________________________________________________________________________________ max8570 max8575 ea ilim thermal shutdown out fb (max8570/max8571/ max8574 only) gnd (max8572/max8573/ max8575 only) lx sw v cc 1.226v control logic shdn figure 1. functional diagram max8570 max8571 max8574 sw v cc lx fb gnd on off v cc = 2.7v to 5.5v v out = v batt to 28v r1 r2 c3 4.7 f l1 22 h c1 1 f shdn c2 1 f c4 10pf v batt = 0.8v to 28v d1 figure 4. using a separate input supply for the inductor max8570 max8571 max8574 sw v cc lx fb gnd on off v cc = 2.7v to 5.5v +v out -v out r1 c3 4.7 f l1 22 h c1 1 f shdn c2 1 f c5 1 f c4 10pf c6 0.1 f d1 d3 d2 r2 figure 5. negative output voltage for lcd bias max8570 max8571 max8574 sw v cc lx fb gnd on off v cc = 2.7v to 5.5v v out = v cc to 28v r1 r2 c3 4.7 f l1 22 h c1 1 f shdn c2 1 f c4 10pf d1 figure 2. typical application circuit with adjustable output voltage max8572 max8573 max8575 sw v cc lx out gnd on off v cc = 2.7v to 5.5v v out = 15v c3 4.7 f l1 22 h c1 1 f shdn c2 1 f d1 figure 3. typical application circuit with 15v preset output voltage
max8570?ax8575 high-efficiency lcd boost with true shutdown _______________________________________________________________________________________ 7 detailed description the max8570 family of compact, step-up dc-dc con- verters operate from a 2.7v to 5.5v supply. consuming only 25? of supply current, these ics include an inter- nal mosfet switch with a low on-resistance. a true- shutdown feature disconnects the battery from the load and reduces the supply current to 0.05? (typ). these dc-dc converters are available with either a fixed 15v output or are adjustable up to 28v. three current-limit options are available: 110ma, 250ma, and 500ma. see the selector guide on page 1. control scheme the max8570 family features a minimum off-time cur- rent-limited control scheme operating in discontinuous mode. an internal p-channel mosfet switch connects v cc to sw to provide power to the inductor when the converter is operating. when the converter is shut down, this switch disconnects the input supply from the inductor (see figure 1). to boost the output voltage, an n-channel mosfet switch turns on and allows current to ramp up in the inductor. once this current reaches the current limit, the switch turns off and the inductor current flows through d1 to supply the output. the switching fre- quency varies depending on the load and input voltage and can be up to 800khz. setting the output voltage the output voltage of the max8570, max8571, and max8574 is adjustable from v cc to 28v by using a resistor voltage-divider (see figure 2). select r2 from 10k ? to 600k ? and calculate r1 with the following equation: where v fb = 1.226v and v out can range from v cc to 28v. for best accuracy, ensure that the bias current through the feedback resistors is at least 2?. the max8572, max8573, and max8575 have a fixed 15v output. when using these parts, connect out directly to the output (see figure 3). shutdown ( shdn ) drive shdn low to enter shutdown. during shutdown the supply current drops to 0.05? (typ), the output is disconnected from the input, and lx enters a high- impedance state. the capacitance and load at the out- put determine the rate at which v out decays. shdn can be pulled as high as 6v regardless of the input and output voltages. with a typical step-up converter circuit, the output remains connected to the input through the inductor and output rectifier, holding the output voltage to one diode drop below v cc when the converter is shut down and allowing the output to draw power from the input. the max8570 family features true-shutdown mode, dis- connecting the output from the input with an internal p- channel mosfet switch when shut down. this eliminates power draw from the input during shutdown. soft-start the max8570 family uses two soft-start mechanisms. when the true-shutdown feature is used (sw is con- nected as in figure 2 and figure 3), the gate of the internal high-side p-channel switch turns on slowly to prevent inrush current. this takes approximately 200?. when sw is fully turned on, the internal n-channel switch begins boosting the input to set the output volt- age. when v fb is less than 0.5v (with or without the use of true shutdown), the minimum off-time of the internal n-channel switch increases from 1 s to 5? to control inrush current. separate power for inductor separate power supplies can be used for the ic and the inductor. this allows power to be used from a bat- tery or supply with a voltage as low as 0.8v, or higher than the v cc operating range of the converter. when using a separate inductor supply, sw is left unconnect- ed and the supply is connected directly to the inductor (see figure 4). note that in this configuration the output is no longer disconnected from the input during shut- down. in shutdown the output voltage goes to a diode drop below the inductor supply voltage. protection features the max8570 family has protection features designed to make it extremely robust to application errors (see table 1). if the output capacitor in the application is missing, the max8570 family protects the internal switch from being damaged. if the top feedback resis- tor or the external diode is disconnected, the converter stops switching and the output is resistively loaded to ground. similarly, if the external diode polarity is reversed, the converter discontinues switching. if the bottom feedback resistor is missing, the output stays at a diode drop less than the inductor supply voltage or 1.226v (whichever is greater). in fact, in response to most fault conditions, the max8570 family protects not only itself, but also the downstream circuitry. rr v v out fb 12 1 = ? ? ? ? ? ? ?
max8570?ax8575 high-efficiency lcd boost with true shutdown 8 _______________________________________________________________________________________ design procedure inductor selection smaller inductance values typically offer smaller physi- cal size for a given series resistance or saturation cur- rent. circuits using larger inductance values may provide more output power. the inductor? saturation current rating should be greater than the peak switch- ing current. recommended inductor values range from 10? to 100?. selecting the current limit the peak lx current limit (i lx(max) ) required for the application is calculated from the following equation: where p out(max) is the maximum output power required by the load and v batt(min) is the minimum supply voltage used to supply the inductor (this is v cc unless a separate supply is used for the inductor). the ic current limit must be greater than this calculated value. see the selector guide on page 1 for selecting the ic with the correct current limit. diode selection the high switching frequency of up to 800khz requires a high-speed rectifier. schottky diodes are recom- mended due to their low forward-voltage drop. to maintain high efficiency, the average current rating of the diode should be greater than the peak switching current. choose a reverse breakdown voltage greater than the output voltage. capacitors small ceramic surface-mount capacitors with x7r or x5r temperature characteristics are recommended due to their small size, low cost, low equivalent series resistance (esr), and low equivalent series inductance (esl). if nonceramic capacitors are used, it is important that they have low esr to reduce the output ripple volt- age and peak-peak load-transient voltage. for most applications, use a 1 f ceramic capacitor for the output and v cc bypass capacitors. for sw or the inductor supply, a 4.7? or greater ceramic capacitor is recommended. i p v p v s p l lx max out max batt min out max batt min out max () () () () () () .. + ? ? ? ? ? ? +? 125 1 25 3 2 common application faults result with competing step-up converters result with max8570 family out to fb resistor missing or disconnected. out voltage rises until the output capacitor is destroyed and/or downstream components are damaged. converter stops switching. output cap missing and fb floating. out voltage rises until the output capacitor is destroyed and/or downstream components are damaged. lx may boost one or two times before the fb voltage exceeds the trip point. in the rare case where the capacitive loading and external loading on out is small enough that the energy in one cycle can slew it more than 50v, the internal mosfet will clamp between 35v and 70v (nondestructively). fb shorted to gnd. out voltage rises until the output capacitor is destroyed and/or downstream components are damaged. converter stops switching and out is resistively loaded to gnd. diode missing or disconnected. diode reverse polarity. inductor energy forces lx node high, possibly damaging the internal switch. out is resistively loaded to gnd and the converter stops switching. fb node floating. unpredictable, possibly boosting output voltage beyond acceptable design range. fb node driven above its regulation point, the converter stops switching, and out is resistively loaded to gnd. out shorted to ground. current ramps up through inductor and diode, generally destroying one of the devices. true off-switch detects short, opens when current reaches pmos current limit, and restarts soft-start. this protects the inductor and diode. table 1. protection features
max8570?ax8575 high-efficiency lcd boost with true shutdown _______________________________________________________________________________________ 9 for the max8570/max8571/max8574 a feed-forward capacitor (c4 in figures 2 and 3) connected from the output to fb improves stability over a wide range of battery voltages. a 10pf capacitor is recommended for the max8571 and max8574. a 10pf to 47pf capacitor is recommended for the max8570. note that increasing c4 degrades line and load regulation. applications information negative output voltage for lcd bias a negative output voltage can be generated by adding a diode/capacitor charge pump as shown in figure 5. in this configuration, the negative output is lower in magni- tude than the positive output by a forward diode drop. if there is little or no load on the positive output, the nega- tive output drifts from its nominal voltage. to prevent this, it may be necessary to preload the positive output with a few hundred microamps, which can be done by selecting lower than normal values of r1 and r2. pc board layout careful printed circuit layout is important for minimizing ground bounce and noise. keep the gnd pin and ground pads for the input and output capacitors as close together as possible. keep the connection to lx as short as possible. locate the feedback resistors as close as possible to the fb pin and keep the feedback traces routed away from noisy areas such as lx. refer to the max8571evkit for a layout example. chip information transistor count: 742 process: bicmos
max8570?ax8575 high-efficiency lcd boost with true shutdown 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 .) 6lsot.eps f 1 1 21-0058 package outline, sot-23, 6l
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