general description the MAX1575 charge pump drives up to four white leds in the main display and up to two white leds in the sub-display with regulated constant current for uni- form intensity. by utilizing adaptive 1x/1.5x charge- pump modes and very-low-dropout current regulators, it achieves high efficiency over the full 1-cell lithium- battery input voltage range. a 1mhz fixed-frequency switching allows for tiny external components, and the regulation scheme is optimized to ensure low emi and low input ripple. the MAX1575 uses an external resistor to set the full- scale 100% led current. two enable inputs, enm and ens, are used for simple on/off controls for the main and sub-displays, respectively. by repeatedly pulsing either enable input, the leds can be dimmed in multiple steps down to 5%. once the desired brightness is set, the MAX1575 maintains that brightness setting as long as the enable input is kept high. if an enable input is kept low for more than 2ms, the led current for the respec- tive display is set to zero. if both enable inputs are kept low for more than 2ms, the MAX1575 enters shutdown. the MAX1575 is available in a 16-pin 4mm x 4mm thin qfn package (0.8mm max height). applications cell phones with main and sub-displays pdas/smart phones with up to six white leds features ? powers main and sub-display leds ? 85% average efficiency (p led / p batt ) over li+ battery discharge ? 2% led current matching ? up to 30ma/led drive capability ? adaptive 1x/1.5x mode switchover ? low input ripple and emi ? individual 5% to 100% dimming through single-wire serial pulse interface ? low 0.1a shutdown current ? 2.7v to 5.5v supply voltage range ? soft-start limits inrush current ? output-overvoltage protection ? thermal-shutdown protection ? 16-pin thin qfn 4mm x 4mm package MAX1575 white led 1x/1.5x charge pump for main and sub-displays ________________________________________________________________ maxim integrated products 1 ordering information 19-3097; rev 0; 12/03 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. evaluation kit available part temp range pin-package MAX1575ete -40 c to +85 c 16 thin qfn 4mm x 4mm c2p 1 out 2 set 3 ens 4 enm 5 led6 6 led5 7 led4 8 led3 9 led2 10 led1 11 gnd 12 c1n 13 in 14 c2n 15 c1p 16 MAX1575 thin qfn 4mm x 4mm top view pin configuration enm ens in gnd led1 led2 led3 led4 out c1p c1n c2p c2n 2.7v to 5.5v 1 f 1 f 1 f 1 f led5 led6 main sub set enable main on/off and dimming enable sub on/off and dimming r set MAX1575 typical operating circuit
MAX1575 white led 1x/1.5x charge pump for main and sub-displays 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = 3.6v, v gnd = 0v, enm = ens = in, r set = 6.81k ? , c in = c1 = c2 = c out = 1?, t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25 c.) (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, enm, ens to gnd..................................-0.3v to +6.0v set, led_, c1n, c2n to gnd.....................-0.3v to (v in + 0.3v) c1p, c2p to gnd.............................................................-0.3v to the greater of (v out + 1v) or (v in + 1v) out short circuit to gnd ..........................................continuous continuous power dissipation (t a = +70 c) 16-pin thin qfn 4mm x 4mm (derate 16.9 mw/ c above +70 c) ............................1349mw junction temperature ......................................................+150 c storage temperature range .............................-65 c to +150 c lead temperature (soldering, 10s) .................................+300 c parameter conditions min typ max units in operating voltage 2.7 5.5 v undervoltage-lockout threshold v in falling 2.25 2.45 2.60 v undervoltage-lockout hysteresis 35 mv out overvoltage-protection threshold v out rising 5 v 1mhz switching in 1.5x mode 2 no-load supply current no switching in 1x mode,10% setting 0.5 ma shutdown supply current enm = ens = out = gnd 0.1 2 a soft-start time 2ms set bias voltage 0.6 v set leakage in shutdown enm = ens = gnd 0.01 1 a t a = 0 c to +85 c10 130 set current range t a = -40 c to +85 c30 130 ? set-to-led_ current ratio (i led_ / i set ) 100% setting 234 a/a t a = +25 c to +85 c-8 2+8 led current accuracy t a = -40 c to +85 c -9.5 +9.5 % t a = +25 c to +85 c-5 1.5 +5 led-to-led current matching (note 2) t a = -40 c to +85 c -6.5 +6.5 % maximum led_ sink current r set = 4.53k ? = = = 3.4v, v out = 3.9v, 100% setting 120 ma 1x mode (v in - v out ) / i out 1 2.5 open-loop out resistance 1.5x mode (1.5 x v in - v out ) / i out 4.2 10 ? switching frequency 1 mhz out pulldown resistance enm = ens = gnd 5 k ? enm, ens high voltage v in = 2.7v to 5.5v 1.6 v enm, ens low voltage v in = 2.7v to 5.5v 0.4 v enm, ens input current v en_ = 0v or 5.5v 0.01 1 a shutdown delay from falling edge of enm and ens 1.0 2 3.3 ms
MAX1575 white led 1x/1.5x charge pump for main and sub-displays _______________________________________________________________________________________ 3 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 current into the led drops 10% from the led current at v led_ = 0.2v. electrical characteristics (continued) (v in = 3.6v, v gnd = 0v, enm = ens = in, r set = 6.81k ? , c in = c1 = c2 = c out = 1?, t a = -40? to +85?, unless otherwise noted. typical values are at t a = +25 c.) (note 1) parameter conditions min typ max units t lo (enm, ens) (figure 1) 0.5 500 ? t hi (enm, ens) (figure 1) 0.5 ? initial t hi (enm, ens) (figure 1) only required for first en_ pulse 50 ? thermal-shutdown threshold +160 c thermal-shutdown hysteresis 20 c typical operating characteristics (v in = 3.6v, enm = ens = in, circuit of figure 2, t a = +25 c, unless otherwise noted.) efficiency vs. supply voltage driving six white leds MAX1575 toc01 supply voltage (v) efficiency (%) 3.9 3.6 3.3 3.0 20 30 40 50 60 70 80 90 100 2.7 4.2 supply voltage falling 20ma/led 8ma/led 2ma/led input current vs. supply voltage driving six white leds MAX1575 toc02 supply voltage (v) input current (ma) 3.9 3.6 3.3 3.0 20 40 60 80 100 120 140 160 180 200 0 2.7 4.2 20ma/led 8ma/led 2ma/led supply voltage falling input current vs. supply voltage driving four white leds MAX1575 toc03 supply voltage (v) input current (ma) 3.9 3.6 3.3 3.0 20 40 60 80 100 120 140 160 180 200 0 2.7 4.2 20ma/led 8ma/led 2ma/led supply voltage falling input current vs. supply voltage driving two white leds MAX1575 toc04 supply voltage (v) input current (ma) 3.9 3.6 3.3 3.0 20 40 60 80 100 120 140 160 180 200 0 2.7 4.2 20ma/led 8ma/led 2ma/led supply voltage falling input ripple vs. supply voltage driving six white leds MAX1575 toc05 supply voltage (v) input ripple (mv p-p ) 5.1 4.7 4.3 3.9 3.5 3.1 10 20 30 40 50 60 70 0 2.7 5.5 20ma/led 8ma/led 2ma/led led current matching vs. supply voltage MAX1575 toc06 supply voltage (v) led current (ma) 5.1 4.7 4.3 3.9 3.5 3.1 18 19 20 21 22 17 2.7 5.5
MAX1575 white led 1x/1.5x charge pump for main and sub-displays 4 _______________________________________________________________________________________ output current vs. supply voltage driving six leds at 20ma each MAX1575 toc07 supply voltage (v) output current (ma) 5.1 4.7 4.3 3.9 3.5 3.1 118 119 120 121 122 123 117 2.7 5.5 led current vs. r set MAX1575 toc08 r set (k ? ) led current (ma) 10 10 100 1 100 1 100% brightness setting operating waveforms (1x) MAX1575 toc09 400ns/div v out v in i in 200mv/div ac-coupled 50mv/div ac-coupled 50ma/div 0ma operating waveforms (1.5x) MAX1575 toc10 400ns/div v out v in i in 200mv/div ac-coupled 50mv/div ac-coupled 50ma/div 0 startup waveforms MAX1575 toc11 1ms/div v out v enm and v ens i in 5v/div 100ma/div 2v/div 0 0 main startup with sub-display on MAX1575 toc12 1ms/div v out v enm i in 5v/div 500mv/div 100ma/div 0 dimming response MAX1575 toc13 10ms/div v out v enm and v ens i out 2v/div 2v/div 50ma/div 0 line transient 3.8v to 3.3v to 3.8v MAX1575 toc14 40 s/div v out v in i out 1v/div 50ma/div 0ma 1v/div ac-coupled typical operating characteristics (continued) (v in = 3.6v, enm = ens = in, circuit of figure 2, t a = +25 c, unless otherwise noted.)
detailed description the MAX1575 charge pump drives up to four white leds in the main display and up to two white leds in the sub-display with regulated constant current for uniform intensity. by utilizing adaptive 1x/1.5x charge- pump modes and very-low-dropout current regulators, it achieves high efficiency over the 1-cell lithium-battery input voltage range. 1mhz fixed-frequency switching allows for tiny external components and low input ripple. 1x to 1.5x switchover when v in is higher than v out , the MAX1575 operates in 1x mode and v out is pulled up to v in . the internal cur- rent regulators regulate the led current. as v in drops, v led_ eventually falls below the switchover threshold of 100mv and the MAX1575 starts switching in 1.5x mode. when the input voltage rises above v out by about 50mv, the MAX1575 switches back to 1x mode. soft-start the MAX1575 includes soft-start circuitry to limit inrush current at turn-on. when starting up, the output capacitor is charged directly from the input with a ramped current source (with no charge-pump action) until the output volt- age approaches 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. during the soft-start time, the output current is set to 5% of the maximum set by r set . in the case of 1.5x mode, soft-start operates until the low- est of led1?ed6 reaches regulation. if an overload con- dition occurs, soft-start repeats every 2ms. if the output is shorted to ground (or <1.25v), the part reverts to soft- start and the ramped current source. MAX1575 white led 1x/1.5x charge pump for main and sub-displays _______________________________________________________________________________________ 5 pin name function 1 c2p transfer-capacitor 2 positive connection. connect a 1? ceramic capacitor from c2p to c2n. 2 out output. connect a 1? ceramic capacitor from out to gnd. connect out to the anodes of all the leds. out is internally pulled down with 5k ? during shutdown. 3 set current-set input. connect a resistor (r set ) from set to gnd to set the maximum led current. i led(max) = 228 0.6v / r set . set is internally biased to 0.6v. set is high impedance during shutdown. 4 ens enable and dimming control for led5 and led6 (sub-display). the first time ens goes high (50? min), led5 and led6 turn on at 100% brightness. p ul si ng e n s l ow d i m s the le d s i n m ul ti p l e step s. if ens is held low for more than 2ms (typ), led5 and led6 turn off. when enm and ens are both held low for more than 2ms (typ), the ic goes into shutdown mode. see figure 1. 5 enm e nab l e and d i m m i ng c ontr ol for le d 1 le d 4 ( m ai n d i sp l ay) . the fi r st ti m e e n m g oes hi g h ( 50? m i n) , le d 1 le d 4 tur n on at 100% b r i g htness. p ul si ng e n m l ow d i m s the le d s i n m ul ti p l e step s. if e n m i s hel d l ow for m or e than 2m s ( typ ) , le d 1 le d 4 tur n off. w hen e n m and e n s ar e b oth hel d l ow for m or e than 2m s ( typ ) , the ic g oes i nto shutd ow n m od e. s ee fi g ur e 1. 6 led6 7 led5 sub-display leds cathode connection. current flowing into led_ is described in the ens and set descriptions above. the charge pump regulates the lowest-enabled led_ voltage to 180mv. connect led_ to in if the led is not populated. led_ is high impedance during shutdown. 8 led4 9 led3 10 led2 11 led1 main-display leds cathode connection. current flowing into led_ is described in the enm and set descriptions above. the charge pump regulates the lowest-enabled led_ voltage to 180mv. connect led_ to in if the led is not populated. led_ is high impedance during shutdown. 12 gnd ground. connect gnd as close as possible to system ground and to the ground of the input bypass capacitor. 13 c1n transfer-capacitor 1 negative connection. connect a 1? ceramic capacitor from c1p to c1n. 14 in supply voltage input. connect a 1? ceramic capacitor from in to gnd. the input voltage range is 2.7v to 5.5v. in is high impedance during shutdown. 15 c2n transfer-capacitor 2 negative connection. connect a 1? ceramic capacitor from c2p to c2n. 16 c1p transfer-capacitor 1 positive connection. connect a 1? ceramic capacitor from c1p to c1n. ep exposed paddle. connect the exposed paddle to gnd. pin description
MAX1575 setting the output current the led current at full (100%) brightness is set (up to 30ma) by a resistor, r set , as follows: enm and ens dimming controls when the leds are enabled by driving enm or ens high, the led current initially goes to i led_ . dimming for the main display is done by pulsing enm low (500ns to 500? pulse width). dimming for the sub- display is done by pulsing ens low (500ns to 500? pulse width). each pulse reduces the led current by 10%, so after one pulse the led current is 0.9 x i led . the 10th pulse reduces the current by 5% so the led current reduces from 0.1 x i led_ to 0.05 x i led . the 11th pulse sets the led current back to i led_ . figure 1 shows a timing diagram for en_. because soft-start is longer than intitial t hi , apply dim- ming pulses quickly upon startup (after initial t hi ) to avoid led_ current transitioning through full brightness. if dimming control is not required, en_ work as simple on/off controls. drive enm high to enable the main leds, or drive enm low to turn off the main leds. drive ens high to enable the sub-leds, or drive ens low to turn off the sub-leds. drive both enm and ens low to put the ic in low-power shutdown mode. shutdown mode when both enm and ens are held low for 2ms or longer, the MAX1575 is shut down and put in a low-current mode. out is internally pulled to gnd with 5k ? during shutdown. overvoltage protection if any led fails as an open circuit, the output voltage is limited to approximately 5v by gating on/off the charge pump. in case any led_ is floating or grounded, the MAX1575 operates in the same overvoltage-protection mode. to avoid overvoltage-protection mode when using fewer than six leds, connect any unused led_ to in. thermal shutdown the MAX1575 includes a thermal-limit circuit that shuts down the ic at approximately +160 c. the part turns on after the ic cools by approximately 20 c. applications information driving fewer than six leds when driving fewer than six leds, connect any unused led_ directly to in ( figure 3). when connected in this manner, the corresponding led driver is disabled. input ripple for led drivers, input ripple is more important than out- put ripple. input ripple depends on the source supply? impedance. adding a lowpass filter to the input further reduces input ripple. alternately, increasing c in to 2.2? cuts input ripple in half with only a small increase in foot- print. the 1x mode always has very low input ripple. r v i set led = 0 6 228 . _ white led 1x/1.5x charge pump for main and sub-displays 6 _______________________________________________________________________________________ enm or ens i led_ shdn 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 5% 100% 90% shdn 1 11 10 9 8 7 6 5 4 3 2 t lo t shdn 2ms (typ) 0 t soft-start initial t hi 50 s t hi 500ns to 500 s 500ns figure 1. en_ timing diagram
MAX1575 white led 1x/1.5x charge pump for main and sub-displays _______________________________________________________________________________________ 7 1x/1.5x regulating charge pump error amp1 control and reference 0.6v enm ens gnd in set led1 led2 led3 led4 out c1p c1n c2p c2n 2.7v to 5.5v c1 1 f c2 1 f c out 1 f r set 0.18v error amp2 ovd 1.25v selmin c in 1 f d1 d2 d3 d4 d5 d6 led5 led6 main control sub control controlled current mirror main enable and dimming sub enable and dimming figure 2. functional diagram and typical application circuit
MAX1575 component selection use only ceramic capacitors with an x5r, x7r, or better dielectric. see table 1 for a list of recommended parts. pc board layout and routing the MAX1575 is a high-frequency switched-capacitor voltage regulator. for best circuit performance, use a solid ground plane and place c in , c out , c1, and c2 as close to the MAX1575 as possible. connect gnd to the exposed paddle directly under the ic. refer to the MAX1575 evaluation kit for an example. chip information transistor count: 5738 process: bicmos white led 1x/1.5x charge pump for main and sub-displays 8 _______________________________________________________________________________________ enm ens in gnd led1 led2 led3 led4 out c1p c1n c2p c2n 2.7v to 5.5v 1 f 1 f 1 f 1 f led5 led6 main sub set enable main on/off and dimming enable sub on/off and dimming r set MAX1575 figure 3. driving fewer than six white leds designation value manufacturer part description murata grm155r60j105k 1? 10%, 6.3v x5r ceramic capacitors (0402) taiyo yuden jmk107bj105ka 1? 10%, 6.3v x5r ceramic capacitors (0603) c in , c out , c1, c2 1? tdk c1005x5r0j105m 1? 20%, 6.3v x5r ceramic capacitors (0402) d1?6 nichia nscw215t white leds kamaya r set as required panasonic 1% resistor table 1. recommended components
MAX1575 white led 1x/1.5x charge pump for main and sub-displays 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 _____________________ 9 2003 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 .) 24l qfn thin.eps b 1 2 21-0139 package outline 12,16,20,24l qfn thin, 4x4x0.8 mm b 2 2 21-0139 package outline 12,16,20,24l qfn thin, 4x4x0.8 mm
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