general description the MAX1573 fractional charge pump drives up to four white leds with regulated constant current for uniform intensity. by utilizing proprietary adaptive 1x/1.5x modes and ultra-low-dropout current regulators, it maintains the highest possible efficiency over the full 1-cell li+ battery input voltage range. the 1mhz fixed- frequency switching allows for tiny external compo- nents and the regulation scheme is optimized to ensure low emi and low input ripple. an external resistor sets the full-scale led current, while two digital inputs control on/off and select amongst three levels of brightness. a pulse-width modulation (pwm) signal can also be used to modulate led brightness, requiring no additional components. the MAX1573 is available in the tiny chip-scale ucsp (4 x 4 grid) and 16-pin thin qfn packages. applications cell phones, smart phones pdas, digital cameras, camcorders mp3 players other handhelds with color displays features proprietary adaptive 1x/1.5x modes high efficiency (p leds /p batt ), up to 92% 0.2% led current matching 28ma/led drive capability low input ripple and emi eliminates ballast resistors logic or pwm dimming control low 0.1a shutdown current 2.7v to 5.5v input voltage range soft-start limits inrush current output overvoltage protection thermal shutdown protection no external schottky diode required tiny ucsp (2.1mm x 2.1mm x 0.6mm) and thin qfn (4mm x 4mm) packages MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn ________________________________________________________________ maxim integrated products 1 top view MAX1573 12 13 14 15 16 8 7 6 5 11 10 9 1234 n.c. gnd led3 led4 led1 led2 set en2 in c2n c1p c2p out en1 n.c. cin thin qfn 4mm 4mm pin configurations ordering information MAX1573 v in 2.7v to 5.5v r set on/off and dimming control set gnd c1n c1p c2n c2p out led1 led2 led3 led4 in en1 1 f 1 f 1 f 1 f v out up to 4 leds en2 typical operating circuit 19-2847; rev 1; 8/03 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. part temp range pin-package MAX1573ebe-t -40 c to +85 c 14 ucsp (4 x 4) MAX1573ete -40 c to +85 c 16 thin qfn ucsp is a trademark of maxim integrated products, inc. pin configurations continued at end of data sheet.
MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = v en1 = v en2 = 3.6v, c in = c1 = c2 = c out = 1f, t a = -40 c to +85 c. typical values are at t a = +25 c, unless otherwise noted.) (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. in, out, en1, en2 to gnd ...................................-0.3v to +6.0v set, led1, led2, led3, led4 to gnd ......-0.3v to (v in + 0.3v) c1n, c2n to gnd ..........................................-0.3v to (v in + 1v) c1p, c2p to gnd ............................................-0.3v to greater of ............................................................. (v out + 1v) or (v in + 1v) out short circuit to gnd ..........................................continuous continuous power dissipation (t a = +70 c) 14-bump ucsp (derate 7.36mw/ c above +70 c) ....589mw 16-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 parameter conditions min typ max units in operating voltage 2.7 5.5 v undervoltage lockout threshold v in rising or falling, 35mv hysteresis 2.25 2.45 2.60 v supply current switching, no load, i set = 130a 2 4 ma shutdown supply current en1 = en2 = out = gnd, t a = +25 c 0.1 10 a soft-start completion time 2.1 ms set bias voltage 0.570 0.6 0.630 v set leakage in shutdown en1 = en2 = gnd, t a = +25 c 0.01 1 a set current range 40 130 a en1 = en2 = in 190 219 245 en1 = in, en2 = gnd 58 66 74 set to led_ current ratio (i led /i set )i set = 60a en1 = gnd, en2 = in 19.5 22 25.0 a/a led_ current accuracy e n 1 = en 2 = in , r s e t = 4.64k ? , t a = 0 c to + 85 c 0.6 % led_ current matching i set = 130a, t a = 0 c to +85 c (note 2) 0.2 % maximum led_ sink current i set = 130a, en1 = en2 = in 25.9 28 ma led_ dropout voltage i set = 87a (note 3) 40 80 mv led_ minimum regulation voltage (1.5x mode) en1 = en2 = in, i set = 87a 100 150 200 mv led leakage in shutdown en1 = en2 = gnd, v led = 5.5v, t a = +25 c 0.01 1 a maximum out current v in 3.4v, v out 3.9v, en1 = en2 = in 120 ma 1x mode (1 x v in - v out ) / i out 1.5 open-loop out resistance 1.5x mode (1.5 x v in - v out ) / i out 10 ? switching frequency 1 mhz en1, en2 logic high voltage v in = 2.7v to 5.5v 1.6 v en1, en2 logic low voltage v in = 2.7v to 5.5v 0.4 v en1, en2 input current v en _ = gnd or 5.5v, t a = +25 c 0.01 1 a thermal-shutdown threshold 20 c hysteresis 160 c note 1: specifications to -40 c are guaranteed by design and not production tested. note 2: led_ current matching is defined as: (i led - i avg ) / i avg . note 3: dropout voltage is defined as the led_ to gnd voltage at which the led_ current drops 10% from the value at v led = 200mv.
MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn _______________________________________________________________________________________ 3 50 60 70 80 90 100 4.2 3.8 3.7 3.9 3.6 3.5 3.4 3.0 efficiency (p leds /p batt ) vs. li+ battery discharge MAX1573 toc01 li+ battery voltage, time-weighted (v) efficiency (%) full 3/10 1/10 50 60 80 70 90 100 3.0 3.4 3.2 3.6 3.8 4.0 4.2 efficiency (p leds /p batt ) vs. supply voltage MAX1573 toc02 supply voltage (v) 1/10 3/10 full efficiency (%) 0 40 20 80 60 100 120 3.0 3.4 3.6 3.2 3.8 4.0 4.2 supply current vs. supply voltage MAX1573 toc03 supply voltage (v) battery current (ma) full 1/10 3/10 0 2 1 5 4 3 8 7 6 9 3.0 3.4 3.2 3.6 3.8 4.0 4.2 input ripple vs. supply voltage MAX1573 toc04 supply voltage (v) input ripple (mv rms ) full 3/10 1/10 10 13 12 11 15 14 19 18 17 16 20 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 led current vs. supply voltage MAX1573 toc05 supply voltage (v) led current (ma) led4 led2 led1 led3 17.5 17.4 17.3 17.2 17.1 17.0 16.9 16.8 16.7 16.6 16.5 -40 -20 -10 -30 0 10 20 30 40 50 60 70 80 led current vs. temperature MAX1573 toc06 temperature ( c) led current (ma) 0 15 10 5 20 25 30 59 8 6 7 10 11 12 13 14 15 led current vs. r set MAX1573 toc07 r set (k ? ) led current (ma) full 1/10 3/10 typical operating characteristics (v in = 3.6v, en1 = en2 = in, c in = c1 = c2 = c out = 1f, r set = 7.50k ? , t a = +25 c, unless otherwise noted.) 500ns/div 20mv/ div 10ma/ div 20mv/ div v in i in v out typical operating waveforms in 1x mode MAX1573 toc08 3.6v li+ battery input 500ns/div 20mv/ div 10ma/ div 20mv/ div v in i in v out typical operating waveforms in 1.5x mode MAX1573 toc09 3.4v li+ battery input
MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn 4 _______________________________________________________________________________________ typical operating characteristics (continued) (v in = 3.6v, en1 = en2 = in, c in = c1 = c2 = c out = 1f, r set = 7.50k ? , t a = +25 c, unless otherwise noted.) startup and shutdown response MAX1573 toc10 500 s/div 5v/ div 2v/ div 50ma/ div v en_ v out i in led_ = 4 ? 17ma en1 = en2 dimming response MAX1573 toc11 5 s/div 2v/ div 50ma/ div v eni1 i out en2 = in pin description pin tqfn ucsp name function 1 b2 c2p transfer capacitor 2 positive connection. see the component selection section for capacitor value. 2 a2 out output. bypass to gnd with a 1f ceramic capacitor. connect to the anodes of all the leds. out is high impedance during shutdown. 3 a3 en1 enable, dimming control input 1. en1 and en2 control shutdown and the led current. see table 1. 4 n.c. no connection 5 a4 en2 enable, dimming control input 2. en1 and en2 control shutdown and the led current. see table 1. 6 b4 set bias-current set input. connect a resistor from set to gnd to set the led bias current (i set ). i set = 600mv/r set . 7 c4 led2 led2 cathode connection and charge-pump feedback. the charge pump regulates to the lowest voltage on any of the led_ inputs. connect led2 to the cathode of one output led. connect led2 to in if this led is not populated. 8 d4 led1 led1 cathode connection and charge-pump feedback. the charge pump regulates to the lowest voltage on any of the led_ inputs. connect led1 to the cathode of one output led. connect led1 to in if this led is not populated. 9 c3 led4 led4 cathode connection and charge-pump feedback. the charge pump regulates to the lowest voltage on any of the led_ inputs. connect led4 to the cathode of one output led. connect led4 to in if this led is not populated. 10 d3 led3 led3 cathode connection and charge-pump feedback. the charge pump regulates to the lowest voltage on any of the led_ inputs. connect led3 to the cathode of one output led. connect led3 to in if this led is not populated. 11 d2 gnd ground 12 n.c. no connection
detailed description the MAX1573 is a complete charge-pump buck-boost converter requiring only four small ceramic capacitors. the MAX1573 utilizes a proprietary 1x/1.5x fractional charge-pump topology to drive up to four white leds with regulated constant current for uniform intensity. the MAX1573 operates with a 1mhz fixed frequency. an external resistor (r set ) programs the full-scale led current, while two digital inputs control on/off and pro- vide brightness control. output regulation the MAX1573 operates in 1x mode until just above dropout. then the MAX1573 switches to 1.5x charge- pump mode to regulate the lowest of led1 led4 to 150mv and maintain constant led brightness even at very low battery voltages. using this topology, there is no led brightness change during the 1x/1.5x switchover, which guarantees no flicker on the display. the switchover scheme has low hysteresis, minimizing operation in the less-efficient 1.5x mode. the 1x mode produces almost no ripple, while the 1.5x mode regu- lates the output voltage by controlling the rate at which the transfer capacitors are charged. in this way, the switching frequency remains constant for reduced input ripple and stable noise spectrum. soft-start the MAX1573 includes soft-start circuitry to limit inrush current at turn-on. when starting up with an output voltage that is not near the input voltage, the output capacitor is charged directly from the input with a dac- ramped current source (with no charge-pump action) until the output voltage is near the input voltage. once this occurs, the charge pump determines if 1x or 1.5x mode is required. in the case of 1x mode, the soft-start is terminated and normal operation begins. in the case of 1.5x mode, soft-start operates until the lowest of led1 led4 reaches regulation. if an overload condi- tion occurs, soft-start repeats every 2.1ms. if the output is shorted to ground, the output current is limited by the MAX1573 fractional-switching technique. MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn _______________________________________________________________________________________ 5 pin description (continued) pin tqfn ucsp name function 13 d1 c1n transfer capacitor 1 negative connection. see the component selection section for capacitor value. 14 c1 in supply voltage input. in supplies power for the ic. bypass in to gnd with a 1f ceramic capacitor. 15 b1 c2n transfer capacitor 2 negative connection. see the component selection section for capacitor value. 16 a1 c1p transfer capacitor 1 positive connection. see the component selection section for capacitor value. p p n MAX1573 0.6v set en2 en1 c1p in 0.15v brightness control minimum select 1x/1.5x regulated charge pump c1n c2p c2n 1.25v out led1 led2 led3 led4 gnd ldo current regulator ldo current regulator ldo current regulator ldo current regulator block diagram
true shutdown mode when en1 and en2 are grounded, the MAX1573 is in shutdown, and the charge pump examines whether the input voltage is greater than or less than the output volt- age and shorts the transfer capacitor nodes to either in or out as necessary. the output is high impedance in either case. thermal shutdown the MAX1573 includes a thermal-limit circuit that shuts down the ic at about +160 c. turn-on occurs after the ic cools by approximately 20 c. setting the output current set controls the led bias current. current flowing into led1, led2, led3, and led4 is a multiple of the current flowing out of set. set the output current as follows: where k = 22, 66, or 219 (depending upon en1 and en2, see table 1), and r set is the resistor connected between set and gnd (see the typical operating circuit ). applications information dimming using en1 and en2 use en1 and en2 inputs as a digital 2-bit number to control on/off, 1/10, 3/10, and full current (see table 1). r set programs the full current level (see the setting the output current section). dimming using pwm into en1 use en2 for shutdown and drive en1 with a pwm sig- nal. current can be varied from 1/10 to full. the wave- forms in the typical operating characteristics show the response time of dimming. en2 keeps the part on, elimi- nating any soft-start delay that would impede pwm con- trol, allowing a pwm frequency up to 50khz (figure 1). dimming using a filtered pwm signal use a high-frequency pwm signal to drive an r-c-r fil- ter on the set pin (figure 2). a 0% pwm duty cycle corresponds to 18.7ma/led, while a 100% pwm duty cycle corresponds to 0ma/led. at pwm frequencies above 5khz, c3 may be reduced. input ripple for led drivers, input ripple is more important than out- put ripple. input ripple depends on the source supply s impedance. adding a lowpass filter to the input further reduces input ripple. figure 3 shows a c-r-c filter used to reduce input ripple to less than 2mv p-p when driving a 75ma load. alternately, increasing c in to 2.2f or 4.7f yields input ripple of 17mv p-p or 9mv p-p , respec- tively, with only a small increase in footprint. the 1x mode always has very low input ripple. ikx v r led set _ . = ? ? ? ? ? ? 06 MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn 6 _______________________________________________________________________________________ led1 led2 led3 led4 1 f gnd en1 en2 set in 1 f v in MAX1573 out 0 to 18.7ma/led c3 1 f r1 14.3k ? r2 14.3k ? r set 9.09k ? pwm input 0 to 2.5v c1p c1n 1 f c2p c2n 1 f figure 2. dimming using filtered pwm signal table 1. en1/en2 states en1/en2 states brightness led current en1 = low, en2 = low shutdown i led = 0 en1 = low, en2 = high 1/10 brightness i led = 22 x i set en1 = high, en2 = low 3/10 brightness i led = 66 x i set en1 = high, en2 = high full brightness i led = 219 x i set led1 led2 led3 led4 gnd c1p c1n 1 f c2p c2n 1 f en2 en1 set in r set 1 f1 f v in MAX1573 pwm input out figure 1. dimming using pwm signal into en1 true shutdown is a trademark of maxim integrated products, inc.
pc board layout and routing the MAX1573 is a high-frequency switched-capacitor voltage regulator. for best circuit performance, use a solid ground plane and place c in and c out as close to the MAX1573 as possible. also, place their ground pads close together and as close as possible to gnd. see the MAX1573 ev kit for an example. component selection use ceramic capacitors with an x5r dielectric or better temperature coefficient. the transfer capacitors may be reduced in value if the input voltage does not fall below 3.4v, if only two or three leds are used, or if four leds are used at 10ma or less. some typical external com- ponent values are shown in table 2. under normal operating conditions, power dissipation is low. maximum power dissipation occurs at an input voltage of 4.2v and all four leds (with v f = 4v) are dri- ven with 30ma per led. the power is calculated as: p d = [(1.5 x v in ) - v f ] x 120ma = 276mw at higher input voltages, the MAX1573 switches to 1x mode and power dissipation decreases. MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn _______________________________________________________________________________________ 7 led1 led2 led3 led4 1 f gnd en1 en2 set in r set 2.2 f 2.2 f v in MAX1573 out 1 ? c1p c1n 1 f c2p c2n 1 f figure 3. c-r-c filter reduces input ripple table 2. typical component values component value (f) manufacturer part description input/output capacitors 1 taiyo yuden jmk107bj105ka 1f 10%, 6.3v x5r ceramic capacitor (0603) 1 taiyo yuden jmk107bj105ka 1f 10%, 6.3v x5r ceramic capacitor (0603) 0.47 taiyo yuden lmk107bj474ka 0.47f 10%, 10v x5r ceramic capacitor (0603) transfer capacitors 0.22 taiyo yuden lmk107bj224ka 0.22f 10%, 10v x7r ceramic capacitor (0603) led nichia nscw215t white leds r set as required panasonic 1% resistor (0603) chip information transistor count: 3655 process: bicmos ucsp 4 ? 4 out en1 en2 c1p 1 a b c d 234 c2n c2p set in led4 led2 c1n gnd led3 led1 top view pin configurations (continued)
MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn 8 _______________________________________________________________________________________ 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 21-0139 a package outline 12,16,20,24l qfn thin, 4x4x0.8 mm a 21-0139 package outline 12,16,20,24l qfn thin, 4x4x0.8 mm
MAX1573 white led 1x/1.5x charge pump in ucsp and thin qfn maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circuit 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 _____________________ 9 ? 2003 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 . 16l,ucsp.eps g 1 1 21-0101 package outline, 4x4 ucsp
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