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general description the max1910/max1912 power leds with a regulated output voltage or current (up to 120ma) from an unreg- ulated input supply (2.7v to 5.3v). these are complete dc-dc converters requiring only four small ceramic capacitors and no inductors. input ripple is minimized by a unique regulation scheme that maintains a fixed 750khz switching frequency over a wide load range. also included are logic-level shutdown and soft-start to reduce input current surges at startup. the max1910 has two automatically selected operating modes: 1.5x and 2x. 1.5x mode improves efficiency at higher input voltages, while 2x mode maintains regula- tion at lower input voltages. the max1912 operates only in 1.5x mode. the max1910 and the max1912 are available in a space-saving 10-pin ?ax package. applications white led backlighting cellular phones pdas digital still cameras mp3 players backup-battery boost converters features ? high-efficiency 1.5x/2x charge pumps ? low input ripple with 750khz operation ? 200mv current-sense threshold reduces power loss ? current- or voltage-regulated charge pump ? up to 120ma output current ? no inductors required ? small ceramic capacitors ? regulated 5% led current ? load disconnected in shutdown ? 1a shutdown current ? small 10-pin max package max1910/max1912 1.5x/2x high-efficiency white led charge pumps ________________________________________________________________ maxim integrated products 1 ordering information 1 2 3 4 5 10 9 8 7 6 set c1- in2 c2+ c1+ c2- in1 gnd max1910 max1912 max top view out shdn pin configuration 19-2290; rev 2; 3/04 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. part temp range pin-package max1910 eub -40 c to +85 c 10 ?ax max1912 eub -40 c to +85 c 10 ?ax v in c in c1 c2 c out in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 t ypical operating circuit
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (v in = 3.6v, gnd = 0, shdn = set = in, c in = 2.2?, c1 = c2 = 0.47?, c out = 2.2?, t a = 0c to +85c . typical values are at t a = +25?, unless otherwise noted.) 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. in1, in2, out, shdn , set to gnd ?0.3v to +6v c1-, c2-, to gnd..................................................-0.3v, v in + 1v c1+, c2+ to gnd..........-0.3v, greater of v out + 1v or v in + 1v out short-circuit to gnd ..........................................continuous continuous power dissipation (t a = +70?) 10-pin ?ax (derate 5.6 mw/? above +70?) ..........444mw operating temperature range ...........................-40? to +85? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) ................................ +300? parameter conditions min typ max units input voltage operating range 2.7 5.3 v undervoltage lockout threshold both rising and falling edges 2.2 2.5 v undervoltage lockout hysteresis 35 mv set regulation point 0.19 0.2 0.21 v max1910 current regulation output current change for 2.7v < v out < 5v 0.5 %/v max1912 current regulation output current change for 3v < v out < 5v 0.5 %/v max1910 v in = 2.7v 80 maximum output current max1912 v in = 3.6v 120 ma no load input current v in = 3.6v 1.5 2.5 ma supply current in shutdown v in = 5.3v, v out = 0, shdn = 0 0.1 10 ? output leakage current in shutdown v in = 3.6v, shdn = 0 0.1 10 ? switching frequency v in = 3.6v 625 750 875 khz switching frequency temperature coefficient f = 750khz 250 ppm/ c set input current 1 100 na shdn input current shdn = 0 or 5.5v 1 a shdn input voltage low 2.7v < v in < 5.3v 0.4 v shdn input voltage high 2.7v < v in < 5.3v 1.6 v thermal-shutdown threshold rising temperature, 15? hysteresis typical 160 ? electrical characteristics (v in = 3.6v, gnd = 0, shdn = set = in, c in = 2.2?, c1 = c2 = 0.47?, c out = 2.2?, t a = -40c to +85c , unless otherwise noted.) (note 1) parameter conditions min max units input voltage operating range 2.7 5.3 v undervoltage lockout threshold both rising and falling edges 2.2 2.5 v max1910 v in = 2.7v 80 maximum output current max1910 v in = 3.6v 120 ma supply current in shutdown v in = 5.3v, v out = 0, shdn = 0 10 a
max1910/max1912 1.5x/2x high-efficiency white led charge pumps _______________________________________________________________________________________ 3 electrical characteristics (continued) (v in = 3.6v, gnd = 0, shdn = set = in, c in = 2.2?, c1 = c2 = 0.47?, c out = 2.2?, t a = -40c to +85c , unless otherwise noted.) (note 1) parameter conditions min max units output leakage current in shutdown v in = 3.6v, shdn = 0 10 a set regulation point 0.19 0.21 v set input current 100 na shdn input current shdn = 0 or 5.5v 1 a shdn input voltage low 2.7v < v in < 5.3v 0.4 v shdn input voltage high 2.7v < v in < 5.3v 1.6 v note 1: limits to -40? are guaranteed by design, not production tested. t ypical operating characteristics (circuit of figure 2, v in = 3.3v, t a = +25?, unless otherwise noted.) input and output voltage ripple max1910/12 toc01 1 s/div v in v out 20mv/div i out = 60ma input and output voltage ripple max1910/12 toc02 1 s/div v in v out 20mv/div circuit of figure 7 driving 4 leds (60ma) start-up input current and output voltage max1910/12 toc03 i in 1ms/div v out 2v/div 50ma/div 5v/div v shdn quiescent current vs. input voltage max1910/12 toc04 input voltage (v) quiescent current (ma) 4.0 3.5 0.5 1.0 1.5 2.5 2.0 3.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0 0 4.5 led current vs. input voltage max1910/12 toc05 input voltage (v) led current (ma) 4.2 3.9 3.6 3.3 3.0 20 40 60 80 100 120 140 0 2.7 4.5 intensity change step response max1910/12 toc06 40 s/div v logic i out v set 2v/div 100mv/div 60ma 20ma circuit of figure 9
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 4 _______________________________________________________________________________________ detailed description the max1910/max1912 are complete charge-pump boost converters requiring only four small ceramic capacitors. they employ a 750khz fixed-frequency 50% duty-cycle clock. the max1910 has two modes of operation: 1.5x and 2x. each mode has two phases: charge and transfer (see figure 1). in 1.5x mode charge phase, transfer capacitors c1 and c2 charge in series from the input voltage. in transfer phase, c1 and c2 are configured in parallel and connected from out to in, transferring charge to c out . if this system were allowed to operate unregulated and unloaded, it would generate an output voltage 1.5 times the input voltage (hence the terms ?ractional charge pump?and ?.5x mode?. when the input voltage drops sufficiently, the operating mode shifts from a 1.5x fractional charge pump to a 2x dou- bler. c2 is not used in doubler mode. the device transi- tions out of doubler mode when v in is greater than ~75% of v out for more than 32 clock cycles (at full load). the max1912 operates only in 1.5x charge- pump mode. output regulation the output is regulated by controlling the rate at which the transfer capacitors are charged. the switching fre- quency and duty cycle are constant, so the output noise spectrum is predictable. input and output ripple are much smaller in value than with other regulating t ypical operating characteristics (continued) (circuit of figure 2, v in = 3.3v, t a = +25?, unless otherwise noted.) efficiency vs. input voltage max1910/12 toc07 input voltage (v) efficiency (%) 4.2 3.9 3.6 3.3 3.0 10 20 30 40 50 60 70 80 90 100 0 2.7 4.5 circuit of figure 2 max1910 4 white leds i out = 60ma input current vs. input voltage driving 4 leds max1910/12 toc08 input voltage (v) current (ma) 4.2 3.9 3.6 3.3 3.0 20 40 60 80 100 120 140 0 2.7 4.5 circuit of figure 2 max1910 i load = 60ma pin description pin name function 1 gnd ground 2 in1 supply voltage input. connect to in2. bypass to gnd with a 2.2? ceramic capacitor. 3 c2- transfer capacitor 2 connection, negative side 4 c1+ transfer capacitor 1 connection, positive side 5 out output. bypass to gnd with a 2.2? ceramic capacitor. 6 shdn shutdown input. drive low to turn off the device and disconnect the load from the input. out is high impedance in shutdown. drive high or connect to in for normal operation. 7 c2+ transfer capacitor 2 connection, positive side 8 in2 supply voltage input. connect to in1. 9 c1- transfer capacitor 1 connection, negative side 10 set set programs the output current with a resistor from set to gnd. set can also program the output voltage with a resistor-divider between out and gnd.
max1910/max1912 1.5x/2x high-efficiency white led charge pumps _______________________________________________________________________________________ 5 charge-pump topologies because the charge trans- ferred per cycle is only the amount required to supply the output load. soft-start the max1910/max1912 include soft-start circuitry to limit inrush current at turn-on. when starting up with the output voltage at zero, the output capacitor charges through a ramped current source, directly from the input with no charge-pump action until the output volt- age is near the input voltage. if the output is shorted to ground, the part remains in this mode without damage until the short is removed. once the output capacitor charges to the input voltage, the charge-pumping action begins. startup surge cur- rent is minimized by ramping up charge on the transfer capacitors. as soon as regulation is reached, soft-start ends and the part operates normally. if the set voltage reaches regulation within 2048 clock cycles (typically 2.7ms), the part begins to run in normal mode. if the set voltage is not reached by 2048 cycles, the soft- start sequence is repeated. the devices continue to repeat the soft-start sequence until the set voltage reaches the regulation point. shutdown mode when driven low, shdn turns off the charge pump. this reduces the quiescent current to approximately 0.1?. the output is high impedance in shutdown. drive shdn high or connect to in for normal operation. thermal shutdown the max1910/max1912 shut down when their die tem- perature reaches +160?. normal operation continues after the die cools by 15?. this prevents damage if an excessive load is applied or the output is shorted to ground. design procedure setting output current the max1910/max1912 have a set voltage threshold of 0.2v, used for led current regulation (figure 2). the current through the resistor and led is: i led = 0.2/r set if additional matching leds with ballast resistors are connected to the output as in figure 2, the current through each additional led is the same as that in the regulated led. in figure 2, total led current depends somewhat on led matching. figure 3 shows a connection that regu- lates the average of all the led currents to reduce the impact of mismatched leds. figure 4? circuit improves led current matching by raising the ballast resistance while maintaining a 200mv v set . the increased ballast resistance tolerates wider led mismatch, but reduces efficiency and raises the minimum input voltage required for regulation. yet another method of biasing leds is shown in figure 5. in this case, the current through the complete paral- lel combination of leds is set by r5. r1?4 are only used to compensate for led variations. this method of biasing is useful for parallel led arrays that do not allow connection to individual leds. setting output voltage the max1910 has a set voltage threshold of 0.2v. output voltage can be set by connecting a resistor volt- age-divider as shown in figure 6. the output voltage is adjustable from v in to 5v. to set the output voltage, select a value for r2 that is less than 20k ? , then solve for r1 using the following equation: capacitor selection use low-esr ceramic capacitors. recommended values are 0.47? for the transfer capacitors, 2.2? to 10? for the input capacitor, and 2.2? to 4.7? for the output capacitor. to ensure stability over a wide temperature range, ceramic capacitors with an x7r dielectric are rec- ommended. place these capacitors as close to the ic as possible. increasing the value of the input and output capacitors further reduces input and output ripple. with a 10? input capacitor and a 4.7? output capacitor, input ripple is less than 5mv peak-to-peak and output ripple is less than 15mv peak-to-peak for 60ma of output current. a constant 750khz switching frequency and fixed 50% duty cycle create input and output ripple with a predictable frequency spectrum. decoupling the input with a 1 ? resistor (as shown in figures 2?) improves stability when operating from low- impedance sources such as high-current laboratory bench power supplies. this resistor can be omitted when operating from higher impedance sources such as lithium or alkaline batteries. for some designs, such as an led driver, input ripple is more important than output ripple. input ripple depends on the source supply? impedance. adding a lowpass fil- ter to the input further reduces ripple. figure 7 shows a c- r-c filter used to reduce input ripple. with 10?-1 ? -10?, input ripple is less than 1mv when driving a 60ma load. rr v out 12 02 1 = ? ? ? ? ? ? . -
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 6 _______________________________________________________________________________________ applications information adjusting led intensity figure 8 shows a circuit using a dac to set the led intensity. maximum intensity occurs when the output of the dac is zero. r l can be initially estimated from the maximum load current: r l 0.2/i l(max) use this as a starting point to calculate r a and r b from the formula below. the total led current, i l , at different dac output voltages is determined by: figure 9 uses a digital input for two-level dimming control. the leds are brightest when a logic-low input (v logic = 0) is applied, and dimmed with a logic-high input. the total led current is determined by: pc board layout the max1910/max1912 are high-frequency switched- capacitor voltage regulators. for best circuit perfor- mance, use a ground plane and keep c in , c out , c1, c2, and feedback resistors (if used) close to the device. if using external feedback, keep the feedback node as small as possible by positioning the feedback resistors very close to set. chip information transistor count: 2497 process: bicmos i r vr rr l l logic b la = 02 02 .( .) - - i r vr rr l l dac b la = 02 02 .( .) - - in gnd sw1 sw7 (regulating switch) sw6 sw5 sw4 sw2 sw3 out c1- c1+ c2- c2+ mode phase sw1 sw2 sw3 sw4 sw5 sw6 sw7 1.5x charging off on off off on off on 1.5x transfer on off on on off on off 2x charging off off on on on off on 2x transfer on off on on off on off figure 1. functional charge-pump switch diagram (switches shown for 1.5x charging phase)
max1910/max1912 1.5x/2x high-efficiency white led charge pumps _______________________________________________________________________________________ 7 1 ? v in 2.2 f 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 10 ? 10 ? 10 ? 1k ? 1k ? 1k ? figure 3. the max1912 regulating average current through leds v in 2.2 f 1 ? 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 15 ? 15 ? 15 ? 15 ? figure 2. led biasing with the max1912
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 8 _______________________________________________________________________________________ 1 ? v in 2.2 f 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set 2-pin connector out shdn max1910 max1912 r1 15 ? r5 3.3 ? r2 15 ? r3 15 ? r4 15 ? figure 5. alternate method of biasing leds controls total current; suitable when the led array must be biased with only two connections v in 2.2 f 1 ? 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 15 ? 15 ? 30 ? 30 ? 30 ? figure 4. alternate method of biasing to improve led-to-led matching
max1910/max1912 1.5x/2x high-efficiency white led charge pumps _______________________________________________________________________________________ 9 v in 2.2 f 2.2 f 1 ? 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 10 ? 10 ? 10 ? figure 7. c-r-c filter reduces ripple on the input v in 1 ? 2.2 f 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 r2 r1 v out figure 6. output voltage set with a resistor-divider
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 10 ______________________________________________________________________________________ v in 2.2 f 0.47 f 0.47 f 2.2 f in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 r l r b r a dimming input (0v or v logic ) 1 ? figure 9. using digital logic input for intensity control v in 1 ? 2.2 f 0.47 f 0.47 f 2.2 f 15 ? 15 ? 15 ? 15 ? in1 in2 c1+ c1- c2+ c2- gnd set out shdn max1910 max1912 r l 4.7 ? r b 1.58k ? r a 22.1k ? 3.3v v dd gnd out serial input max5380 (2-wire input) max5383 (3-wire input) high dac output (2v) = 15ma led current low dac output (0v) = 45ma led current figure 8. circuit with sot dac for intensity control
max1910/max1912 1.5x/2x high-efficiency white led charge pumps 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 ____________________ 11 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. 10lumax.eps package outline, 10l umax/usop 1 1 21-0061 i rev. document control no. approval proprietary information title: top view front view 1 0.498 ref 0.0196 ref s 6 side view bottom view 0 0 6 0.037 ref 0.0078 max 0.006 0.043 0.118 0.120 0.199 0.0275 0.118 0.0106 0.120 0.0197 bsc inches 1 10 l1 0.0035 0.007 e c b 0.187 0.0157 0.114 h l e2 dim 0.116 0.114 0.116 0.002 d2 e1 a1 d1 min - a 0.940 ref 0.500 bsc 0.090 0.177 4.75 2.89 0.40 0.200 0.270 5.05 0.70 3.00 millimeters 0.05 2.89 2.95 2.95 - min 3.00 3.05 0.15 3.05 max 1.10 10 0.60.1 0.60.1 ? 0.500.1 h 4x s e d2 d1 b a2 a e2 e1 l l1 c gage plane a2 0.030 0.037 0.75 0.95 a1 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 .)

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