max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds evaluation kit available general description the max1553/max1554 drive white leds in series with a constant current to provide efficient display backlight- ing in cellular phones, pdas, and other hand-held devices. the step-up converter includes an internal 40v, low r dson , n-channel mosfet switch for high efficiency and maximum battery life. the max1553 has a current limit of 480ma for driving two to six white leds, while the max1554 has a current limit of 970ma for driving up to 10 white leds. a single analog/pwm dual mode? input provides two simple means of brightness adjustment. a separate enable input provides on/off control. soft-start mini- mizes inrush current during startup. the max1553/max1554 are available in space-saving 8-pin tdfn 3mm x 3mm packages. applications cellular phones pda, palmtop, and wireless handhelds color display backlight benefits and features highly integrated and flexible solution for wide range of backlighting applications ? constant-current regulation for even led illumination ? internal 40v mosfet switch capable of driving 10 leds ? 2.7v to 5.5v input voltage range ? analog or pwm control of led intensity ? optimized for low input ripple soft-start minimizes inrush current high effici ency improves battery life ? up to 88% efficiency driving 6 leds ? up to 82% efficiency driving 9 leds (20ma, v cc = 3.6v) tiny 8-pin, 3mm x 3mm tdfn package saves space ? small, low-profile external components top view ss brt 6 7 8 0v lx 3 2 1 en v cc gnd 5 fb 4 tdfn 3mm x 3mm max1553 max1554 pin configuration ordering information lx ss v cc fb on off brt gnd 2.7v to 5.5v input ov en pwm or dc control max1553 max1554 white leds typical operating circuit part temp range pin-package top mark m a x1 5 5 3 e ta -40? to +85? 8 td fn 3m m x 3m m agx m a x1 5 5 4 e ta -40? to +85? 8 td fn 3m m x 3m m agy dual mode is a trademark of maxim integrated products, inc. 19-2875; rev 2; 5/15
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 2 www.maximintegrated.com absolute maximum ratings v cc , fb, ov to gnd..............................................-0.3v to +6.0v lx to gnd ..............................................................-0.3v to +45v en, brt, ss to gnd...................................-0.3v to (v cc + 0.3v) i lx ...................................................................................0.9a rms continuous power dissipation (t a = +70?) 8-pin 3mm x 3mm 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? electrical characteristics (v cc = 3.3v, v ov = 0v, c out = 1?, r sense = 10 , t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25 c.) 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. parameter conditions min typ max units max1553 2.7 5.5 supply voltage max1554 3.15 5.50 v undervoltage lockout threshold v cc rising or falling, 35mv hysteresis typical 2.35 2.5 2.65 v not switching 0.33 0.65 quiescent current switching 0.44 0.9 ma t a = +25? 0.1 1 shutdown supply current v en = 0v t a = +85? 1 ? ov threshold rising edge 1.18 1.25 1.33 v t a = +25? 1 200 ov input bias current v ov = 1v t a = +85? 10 na brt input resistance 0 < v brt < 1.5v, en = v cc 200 400 600 k timing control maximum on-time v cc = 3.3v 2.0 3.4 4.8 ? on-time constant (k) t on = k / v cc 6.3 ?-v minimum off-time 150 250 350 ns error amplifier v brt = 1.25v 192 203 212 fb threshold v brt = 3.3v 280 mv t a = +25? 15 200 fb input bias current v fb = 1.0v t a = +85? 100 na n-channel switch lx on-resistance 0.8 1.4
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 3 www.maximintegrated.com parameter conditions min max units max1553 2.7 5.5 supply voltage max1554 3.15 5.50 v undervoltage lockout threshold v cc rising or falling, 35mv hysteresis typical 2.35 2.65 v not switching 0.65 quiescent current switching 0.9 ma ov threshold rising edge 1.18 1.33 v brt input resistance 0 < v brt < 1.5v, en = v cc 200 600 k timing control maximum on-time v cc = 3.3v 2.0 4.8 ? minimum off-time 150 350 ns error amplifier fb threshold v brt = 1.25v 192 217 mv n-channel switch lx on-resistance 1.4 max1553 300 600 lx current limit max1554, v cc = 4.2v 600 1200 ma shutdown control en logic-level high 1.8 v en logic-level low 0.4 v electrical characteristics (continued) (v cc = 3.3v, v ov = 0v, c out = 1?, r sense = 10 , t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25 c.) parameter conditions min typ max units max1553 300 480 600 lx current limit max1554, v cc = 4.2v 600 970 1200 ma t a = +25? 0.1 5 lx leakage current v lx = 38v, v en = 0v t a = +85? 1 ? shutdown control en logic-level high 1.8 v en logic-level low 0.4 v t a = +25? 0.01 1 en input current v en = 0v or 5.5v t a = +85? 0.1 ? electrical characteristics (v cc = 3.3v, v ov = 0v, c out = 1?, r sense = 10 , t a = -40? to +85? , unless otherwise noted.) (note 1) note 1: specifications to -40? are guaranteed by design, not production tested.
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 4 www.maximintegrated.com efficiency vs. load current driving 6 white leds max1553/54 toc01 load current (ma) efficiency (%) 15 10 5 60 70 80 90 100 50 020 v cc = 5v v cc = 4v v cc = 3.6v v cc = 3v l1 = 22 h no capacitor across leds efficiency vs. load current driving 6 white leds max1553/54 toc02 load current (ma) efficiency (%) 15 10 5 60 70 80 90 100 50 020 v cc = 5v v cc = 4v v cc = 3.6v v cc = 3v l1 = 33 h 4700pf across leds efficiency vs. load current driving 6 white leds max1553/54 toc03 load current (ma) efficiency (%) 15 10 5 60 70 80 90 100 50 020 v cc = 5v v cc = 4v v cc = 3.6v v cc = 3v l1 = 47 h 4700pf across leds efficiency vs. load current with max1554 driving 9 white leds max1553/54 toc04 load current (ma) efficiency (%) 15 10 5 60 70 80 90 100 50 020 v cc = 5v v cc = 4v v cc = 3.6v circuit of figure 3 led current vs. input voltage max1553/54 toc05 input voltage (v) led current (ma) 5.0 4.5 4.0 3.5 3.0 14 17 20 23 26 11 2.5 5.5 l1 = 22 h, no capacitor across leds l1 = 47 h, 4700pf across leds l1 = 33 h, 4700pf across leds r1 = 10 , v brt = 1.25v led current vs. input voltage max1553/54 toc06 input voltage (v) led current (ma) 5.0 4.5 4.0 3.5 3.0 14 17 20 23 26 11 2.5 5.5 l1 = 22 h, no capacitor across leds l1 = 47 h, 4700pf across leds l1 = 33 h, 4700pf across leds r1 = 14 , v brt = 3.3v led current vs. input voltage with max1554 driving 9 leds max1553/54 toc07 input voltage (v) led current (ma) 5.0 4.5 4.0 3.5 14 17 20 23 26 11 3.0 5.5 circuit of figure 3 led current vs. brt voltage max1553/54 toc08 brt voltage (v) led current (ma) 3.0 2.4 1.8 1.2 0.6 5 10 15 20 25 30 35 0 0 3.6 led current vs. brt duty cycle max1553/54 toc09 brt duty cycle (%) led current (ma) 80 60 40 20 5 10 15 20 25 30 0 0100 typical operating characteristics (max1553 driving six white leds, v cc = v en = 3.6v, circuit of figure 1, t a = +25?, unless otherwise noted.)
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 5 www.maximintegrated.com switching waveforms (continuous operation, 3.75v li+ battery, 18ma output) max1553/54 toc10 2 s/div v lx v out i l 10v/div 200mv/div 200ma/div l1 = 47 h, 4700pf capacitor across leds switching waveforms (discontinuous operation, 3.75v li+ battery, 10ma output) max1553/54 toc11 2 s/div v lx v out i l 10v/div 200mv/div 200ma/div l1 = 47 h, 4700pf capacitor across leds startup/shutdown waveforms max1553/54 toc12 40ms/div v en v fb v out 5v/div 200mv/div 10v/div l1 = 22 h brt step response max1553/54 toc13 20ms/div v brt v fb v out 1v/div 200mv/div 2v/div l1 = 22 h, v brt = 0.5v to 1.25v to o.5v typical operating characteristics (continued) (max1553 driving six white leds, v cc = v en = 3.6v, circuit of figure 1, t a = +25?, unless otherwise noted.)
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 6 www.maximintegrated.com pin name function 1 gnd ground 2v cc voltage-supply input. 2.7v to 5.5v. the ic is powered from v cc . 3 en enable input. drive high or connect to v cc to enable the ic. drive en low for shutdown. 4 brt brightness-control input. either an analog or pwm control signal can be used. the led current can be controlled over a 10 to 1 range. the pwm signal must be between 100hz and 10khz, and must have an amplitude greater than 1.72v. 5fb feedback input. connect to the cathode of the led string and connect a resistor from fb to gnd to set the led current. 6ss soft-start timing-control input. connect a capacitor from ss to gnd to control soft-start timing. see the soft- start section for information on selecting the soft-start capacitor. ss is pulled to ground with an internal 200 switch when en is low. 7ov overvoltage sense. connect to a resistor-divider from the anode of the led string to set the overvoltage threshold. see figures 1, 2, and 3. 8 lx inductor connection. connect to the inductor and diode. lx is high impedance when en is low. ep exposed pad. connect to gnd. pin description detailed description control scheme the max1553/max1554 utilize a minimum off-time, cur- rent-limited control scheme. if the voltage at fb drops below the regulation threshold, the internal low-side mosfet turns on and the inductor current ramps up to the current limit. once the current-limit comparator trips, the low-side mosfet turns off for the minimum off-time (250ns). after 250ns, if the voltage at fb is above the regulation threshold, the low-side mosfet stays off. if the voltage at fb is below the regulation point, the low-side mosfet turns back on and the cycle repeats. by using a regulation control scheme that is not fixed frequency and that can skip pulses, the max1553/max1554 operate with very high efficiency. soft-start soft-start is provided on the max1553/max1554 to min- imize inrush current. the soft-start time is set with an external capacitor, c3 (figures 1, 2, and 3). use the fol- lowing equation to solve for c3: where t ss is the soft-start time. a value of 0.1? pro- vides a soft-start time of 20ms. shutdown the max1553/max1554 feature a low-current shut- down feature. when en is low, the ic turns off, reduc- ing its supply current to approximately 0.1?. for normal operation, drive en high or connect to v cc . overvoltage protection the max1553/max1554 have an adjustable overvolt- age- protection circuit. when the voltage at ov reaches the overvoltage threshold (1.25v typ), the protection cir- cuitry prevents the internal mosfet from switching, allowing the output voltage to decay. the peak output voltage in an overvoltage-protection event is set with a resistor-divider from the output con- nected to ov (r2 and r3 in figures 1, 2, and 3). select a value for r3 (10k is recommended), then solve for r2 using the following equation: where v ov is the overvoltage threshold (1.25v typ), and v out(peak) is the desired peak output voltage. rrx v v out peak ov 23 1 =? ? ? ? ? ? ? () c x t ss 3 210 5 =
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 7 www.maximintegrated.com max1553 max1554 enable control circuitry control logic en v cc lx driver gnd ov comparator ref ov uvlo 1.25v bandgap reference bias generator current limit v lim ref 67k 128k 96k 110k fb brt ss 1.25v minimum t off one-shot minimum t on one-shot error comparator lx ss r1 10 r3 10k r2 200k v cc fb on off brt gnd 2.7v to 5.5v input c1 4.7 f c3 0.1 f c2 0.47 f 25v l1 47 h toko a920cy-470m d1 cmdsh2-3 ov en d2?d7 white leds pwm or dc control max1553 c4 4700pf lx ss r1 10 r3 10k r2 330k v cc fb on off brt gnd 2.7v to 5.5v input c1 10 f c3 0.1 f c2 0.47 f 50v l1 4.7 h murata lqh32c d1 cmdsh1-60m ov en d2?d10 white leds pwm or dc control max1553 c4 3300pf figure 1. circuit with the max1553 driving six white leds figure 2. circuit with the max1553 driving nine white leds at up to 15ma functional diagram
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 8 www.maximintegrated.com adjusting the led current adjusting the output current changes the brightness of the leds. the led current is set by the voltage at brt (v brt ) and the sense resistor (r1) at fb. the v brt range for adjusting output current is 0 to 1.25v. over this range, the led current is found from the following equation: brt can be overdriven; however, applying a v brt greater than 1.72v does not increase the output current above the level at 1.72v. see the led current vs. brt voltage graph in the typical operating characteristics section. to set the maximum led current, calculate r1 when v brt is at its maximum, as follows: where v brt(max) is 1.72v if brt is connected to any value greater than 1.72v, such as v cc . otherwise, v brt(max) is the maximum applied brt control volt- age. power dissipation in r1 is typically less than 5mw; therefore, power dissipation in a standard chip resistor is not a concern. pwm dimming control the brt input is also used as a digital input allowing led brightness control with a logic-level pwm signal applied directly to brt. the frequency range is from 100hz to 10khz, and the duty cycle range is 0 to 100%. a 0% duty cycle corresponds to the minimum current, and a 100% duty cycle corresponds to full current. see the led current vs. brt duty cycle graph in the typical operating characteristics section. the brt resistor and ss capacitor form a lowpass filter, so pwm dimming results in dc current to the leds without the need for additional rc filters. capacitor selection a 0.47? ceramic output capacitor (c2) is recommend- ed for most applications. for circuits driving six or fewer leds, use a 4.7? ceramic input capacitor (c1). for circuits driving more than six leds, use a 10? input capacitor (c1). for best stability over a wide tem- perature range, use capacitors with an x5r, x7r, or better dielectric. inductor selection the max1553 has a 480ma inductor current limit and can drive up to six leds at 20ma or nine leds at 15ma. inductor values from 4.7? to 47? work satis- factorily. larger values provide the best efficiency while small inductor values allow the smallest inductor size. a good choice for best efficiency is the toko d62 or d62l series at 47?. for smallest size, the murata lqh32c at 4.7? works well. the max1554 has a 970ma inductor current limit and can drive up to 10 leds at 20ma. inductor values from 4.7? to 22? work satisfactorily. a good choice for high efficiency and small size when driving 9 or 10 leds is the toko d62 series at 22?. when large inductor values are used to optimize effi- ciency, the max1553/max1554 operate with continuous inductor current. with large inductor values (typically greater than 10?), stability, input, and output ripple are improved by connecting a capacitor in parallel with the leds (c4 in figures 1, 2, and 3). to prevent saturation, use an inductor with a current rating that matches the device? lx current limit. however, if size is particularly important, it is some- times acceptable to operate the inductor 10% into satu- ration. for best efficiency, the inductor? dc resistance should also be as low as possible. diode selection the max1553/max1554s?high switching frequency demands a high-speed rectification diode (d1) for opti- mum efficiency. a schottky diode is recommended due to its fast recovery time and low forward-voltage drop. ensure the diode? average and peak current ratings exceed the average output current and peak inductor current. in addition, the diode? reverse breakdown voltage must exceed v out . r v xi brt max led max 1 017 667 = + () () . . i v xr led brt = + 017 667 1 . . lx ss r1 10 r3 10k r2 330k v cc fb on off brt gnd 3.15v to 5.5v input c1 10 f c3 0.1 f c2 0.47 f 50v l1 22 h a915by-220m d1 cmdsh1-60m ov en d2?d11 white leds pwm or dc control max1554 c4 3300pf figure 3. circuit with the max1554 driving 10 white leds
max1553/max1554 high-efficiency, 40v step-up converters for 2 to 10 white leds maxim integrated | 9 www.maximintegrated.com supplier phone website central semiconductor 631-435-1110 www.centralsemi.com kamaya 260-489-1533 www.kamaya.com murata 814-237-1431 www.murata.com nichia 248-352-6575 www.nichia.com panasonic 714-373-7939 www.panasonic.com sumida 847-956-0666 www.sumida.com taiyo yuden 408-573-4150 www.t-yuden.com tdk 847-803-6100 www.component.tdk.com toko 847-297-0070 www.toko.com table 1. component suppliers lx ss v cc fb on off brt gnd battery input c1 4.7 f c3 0.1 f c2 0.47 f ov en white leds c4 0.1 f 3.3v logic max1553 max1554 l1 d1 r2 r3 r1 applications information low input-voltage applications the max1553/max1554 have minimum input voltages of 2.7v (max1553) and 3.15v (max1554). however, lower battery voltages can still be boosted for led drive as long as v cc remains within the operating range. since most systems have a 3.3v system supply active when the display is active and backlit, that logic supply can be used to supply v cc , while the battery power connects directly to the boost inductor. no bat- tery current is drawn when en is low (figure 4). pc board layout due to fast-switching waveforms and high-current paths, careful pc board layout is required. an evalua- tion kit (max1553evkit) is available as an example of a proper layout. when laying out a board, minimize trace lengths between the ic and the inductor, diode, input capaci- tor, output capacitor, and r1. keep traces short, direct, and wide. keep noisy traces, such as the lx node trace, away from fb. place the v cc bypass capacitor (c1) as close to the ic as possible. the ground con- nections of c1 and c2 should be as close together as possible. star connect the grounds for r1, r3, c3, and the brt voltage supply as close to the ic as possible. the traces from v cc to c1, from c2 to the leds, and from the leds to r1 can be longer if required. chip information transistor count: 740 process: bicmos figure 4. the max1553/max1554 can drive leds from battery voltages that are lower than the device operating voltage range by powering v cc from a logic supply and connecting the boost inductor to the battery. package information for the latest package outline information and land patterns (foot- prints), go to www.maximintegrated.com/packages . note that a ?? ?? or ??in the package code indicates rohs status only. package drawings may show a different suffix character, but the drawing pertains to the package regardless of rohs status. package type package code outline no. land pattern no. tdfn-ep t833-2 21-0137 90-0059
for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim integrateds web site at www.maximintegrated.com. maxim integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim integr ated product. no circuit patent licenses are implied. maxim integrated reserves the right to change the circuitry and specifications without notice at any time . the parametric values (min and max limits) shown in the electrical characteristics table are guaranteed. other parametric values quoted in this data sheet are provided for guidance. maxim integrated and the maxim integrated logo are trademarks of maxim integrated products, inc. 2015 maxim integrated products , inc. | 10 high-efficiency, 40v step-up converters for 2 to 10 white leds max1553/max1554 revision history revision number revision date description pages changed 2 5/15 revised benefits and features section 1
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