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R1218X series step-up dc/dc converter for whilte led backlight no.ea-006-1025 1 outline the R1218X series are pwm control type step-up dc/dc converter ics with low supply current. the R1218X is fully dedicated to drive white led with constant current. each of these ics consists of an nmos fet, an oscillator, a pwm comparator, a voltage reference unit, an error amplifier, an under voltage lockout circuit (uvlo), an over-voltage protection circuit (ovp), and so on. the R1218X can drive white leds with high efficiency with low supply current. a diode is built-in the R1218Xxx1a, therefore it is possible to drive up to 4leds without an external diode. the R1218Xxx2a, an external diode is necessary, however, up to 6 serial leds can be driven with the R1218Xxx2a. constant current can be set with an external resistance value. dimming control is possible by pwm signal for ce pin. feedback voltage is 0.2v, therefore power loss by current setting resistance is small and efficiency is good. maximum duty cycle is internally fixed, typ. 91%. leds can be driven from low voltage. protection circuits are the current limit of lx peak current, the over voltage limit of output, and the under voltage lockout function. packages are standard sot23-6 and very tiny plp1820-6. features ? operating voltage ............................................. 1.8v to 5.5v ? built-in 400ma, 1.5 ? , 20v nch mosfet (R1218Xxx1a) ? built-in 400ma, 1.5 ? , 29v nch mosfet (R1218Xxx2a) ? high frequency pwm control .......................... oscillator frequency 1.2mhz ? maximum duty cycle ....................................... typ. 91% ? low feedback voltage ..................................... typ. 0.2v ? uvlo threshold voltage.................................. typ. 1.6v (hysteresis typ. 0.1v) ? lx current limit protection ................................ typ. 700ma ? over voltage protection (ovp) threshold ....... typ. 9.5v(R1218X02xa) .......................................................................... typ. 14.0v(R1218X03xa) .......................................................................... typ. 18.5v(R1218X04xa) .......................................................................... typ. 23.0v(R1218X052a) .......................................................................... typ. 27.5v(R1218X062a) ? led dimming control .....................................by external pwm signal (frequency 500hz to 5khz) to ce pin .......................................................................by feedback voltage and filtered pwm signal (high frequ ency) ? packages.......................................................... sot23-6 or plp1820-6 application ? white led backlight for portable equipment
R1218X 2 block diagrams ? R1218Xxx1a ? R1218Xxx2a slope slope slope slope com com com compensation pensation pensation pensation l x v v v v fb fb fb fb gnd v v v v in in in in ce ce v v v vref ref ref ref oscillator + ? + ? uvlo current current current current sense sense sense sense current current current current protect protect protect protect switch switch switch switch control control control control s r q err. amp pwm comp v out ovp shu tdown delay slope slope slope slope com com com compensation pensation pensation pensation l x v v v v fb fb fb fb gnd v v v v in in in in ce ce vref vref vref vref oscillator + ? + ? uvlo current current current current s s s sense ense ense ense current current current current protect protect protect protect switch switch switch switch control control control control s r q err. amp pwm comp v out ovp shutdown delay
R1218X 3 selection guide the ovp threshold voltage and the package for the ics can be selected at the user's request. the selection can be available by designating the part number as shown below; R1218Xxxxx -xx part number a b c code descriptions a designation of the package n: sot23-6 k: plp1820-6 b designation of ovp threshold and with/without of built-in diode 021a: 9.5v with built-in diode 031a: 14.0v with built-in diode 041a: 18.5v with built-in diode 052a: 23.0v without built-in diode 062a: 27.5v without built-in diode c taping type (sot23-6: tr-f, plp1820-6: tr) pin configurations sot23-6 ? plp1820-6 pin description ? sot23-6 pin no symbol pin description 1 ce chip enable pin 2 v out output voltage 3 v in power supply input pin 4 lx switching pin (open drain output) 5 gnd ground pin 6 v fb feedback pin ce ce ce ce v v v v out out out out v v v v in in in in v v v v fb fb fb fb l x lx l x lx gnd gnd gnd gnd 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6 ce ce ce ce v v v v fb fb fb fb l x lx l x lx v v v v out out out out gnd gnd gnd gnd v v v v in in in in 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 5 6 6 6 6
R1218X 4 ? plp1820-6 pin no symbol pin description 1 ce chip enable pin 2 v fb feedback pin 3 lx switching pin (open drain output) 4 gnd ground pin 5 v in power supply input pin 6 v out output voltage absolute maximum ratings symbol item rating unit v in v in pin voltage 6.5 v v ce ce pin voltage -0.3 to v in +0.3 v v fb v fb pin voltage -0.3 to v in +0.3 v R1218Xxx1a -0.3 to 22.0 v out v out pin voltage R1218Xxx2a -0.3 to 32.0 v R1218Xxx1a -0.3 to 22.0 v lx lx pin voltage R1218Xxx2a -0.3 to 32.0 v i lx lx pin current 1000 ma r1218nxxxa suspended in air 250 p d power dissipation r1218kxxxa*note1 880 mw topt operating temperature range -40 to +85 c tstg storage temperature range -55 to 125 c (*note 1) mounted on board. conditions: board material: fr4 board dimensions: 40*40*1.6(mm), double layer, wiring ratio=50%(both sides), thermal via: 0.54mm*30pcs, wind velocity: 0m/s electrical characteristics ? common (topt=25 c) symbol item conditions min. typ. max. unit v in operating input voltage 1.8 5.5 v i in supply current v in =5.5v, v fb =0v, lx at no load 0.5 1.0 ma i stb standby current v in =5.5v, v ce =0v 0.0 3.0 a v uvlo1 uvlo detector threshold v in falling 1.5 1.6 1.7 v v uvlo2 uvlo released voltage v in rising v uvlo1 +0.1 1.8 v v ceh ce ?h? input voltage v in =5.5v 1.5 v v cel ce ?l? input voltage v in =1.8v 0.5 v r ce ce pull down resistance v in =3.6v 600 1200 1600 k ? tshudn ce shutdown delay v in =3.6v 10 ms
R1218X 5 symbol item conditions min. typ. max. unit v fb v fb voltage tolerance v in =3.6v 0.19 0.20 0.21 v ? v fb / ? t v fb voltage temperature coefficient v in =3.6v, -40 c topt 85 c 150 ppm / c i fb v fb input current v in =5.5v, v fb =0v or 5.5v -0.1 0.1 a r on switch on resistance v in =3.6v, i sw =100ma 1.5 ? R1218Xxx1a v lx =20v 0.0 3.0 ? i off switch leakage current R1218Xxx2a v lx =29v 0.0 3.0 ? i lim switch current limit v in =3.6v 400 700 1000 ma f osc oscillator frequency v in =3.6v, v out =v fb =0v 1000 1200 1400 khz maxduty maximum duty cycle v in =3.6v, v out =v fb =0v 86 91 % R1218X021a 8.5 9.5 10.5 v R1218X031a 13.0 14.0 15.0 v R1218X041a 17.0 18.5 20.0 v R1218X052a 21.5 23.0 24.5 v v ovp1 ovp detector threshold v in =3.6v v out rising R1218X062a 26.0 27.5 29.0 v R1218X021a v ovp1 -0.5 v R1218X031a v ovp1 -0.75 v R1218X041a v ovp1 -1.0 v R1218X052a v ovp1 -1.25 v v ovp2 ovp released voltage v in =3.6v v out falling R1218X062a v ovp1 -1.5 v ? R1218Xxx1a symbol item conditions min. typ. max. unit v f diode forward voltage i diode =100ma 0.8 v i r diode leakage current v out =20v, v lx =0v 10 a test circuits supply current test circuit uvlo detector threshold/ uvlo released voltage v v v v in in in in ce ce ce ce gnd gnd gnd gnd v v v v fb fb fb fb v v v v in in in in l l l l x x x x ce ce ce ce gnd gnd gnd gnd v v v v fb fb fb fb
R1218X 6 vfb voltage, oscillator frequency, maximum duty test circuit ovp detector threshold, ovp released voltage test circuit typical applications R1218X041a R1218X062a ? led current setting led current can be set with feedback resister(r1) i led =v fb /r1 ? led dimming control, softstart (1) led dimming control by pwm signal to ce pin led dimming control is possible by forcing pwm signal to ce pin. when the power-on or start up with ce pin, softstart function works, however, after that, if the ce pin is set as "l" and set ce pin "h" again during the shutdown delay time, softstart function is disabled and starts up fast to normal mode, therefore 200hz to 5khz pwm signal is standard. by the ce pin input, led turns on and off. average led current varies depending on the duty cycle of ce input. too high frequency pwm signal is not effective because of its delay. (2)dimming control by dc voltage led dimming control is also possible by using the dc voltage to v fb pin. led current is adjustable by dc voltage and resisters, r1 and r2 in the figure 4. i led =(dc-0.2)/r2-0.2/r1 (3)dimming control by feedback voltage and filtered pwm signal led dimming control is also possible by using the feedback voltage and filtered pwm signal. led current is adjustable according to the "h" level (vh) and "l" level(vl) of pwm signal and resisters, r1, r2, r3, and r4 in the figure5.duty v v v v in in in in l l l l x x x x v v v v fb fb fb fb v v v v out out out out gnd gnd gnd gnd ce ce ce ce c2 0.22uf c1 1uf r1 10 ? l1 22uh v v v v in in in in l l l l x x x x ce gnd gnd gnd gnd v v v v fb fb fb fb v v v v in in in in l l l l x x x x ce ce ce ce v v v v out out out out gnd gnd gnd gnd v v v v fb fb fb fb v v v v in in in in l l l l x x x x v v v v fb fb fb fb v v v v out out out out gnd gnd gnd gnd ce ce ce ce c2 0.22uf c1 1uf r1 10 ? l1 22 uh
R1218X 7 =0% to 100% pwm signal duty cycle can be used up to the maximum led current and minimum led current as in the next formulas. i ledmin =(0.2-r2*(vh-0.2)/(r3+r4))/r1 i ledmax =(0.2-r2*(vl-0.2)/(r3+r4))/r1 for example, supposed that the pwm signal level is set as 2.5v/0v, to adjust the led current range from 0ma to 20ma by the duty cycle, our recommendation external components values are, r1=10 ? , r2=5.1k ? , r3=51k ? , r4=5.1k ? or around. c3 should be set large enough to regard the pwm signal as adjustable dc voltage by the filter. in this method, higher frequency control than the frequency against the ce pin can be used for dimming control. for example, if the frequency is 40khz, 0.1uf or more capacitor is our recommendation value as c3. figure 3. dimming controle by ce pin input figure 4. dimming control by dc voltage figure 5. dimming controle by filtered pwm signal ? selection of inductors the peak current of the inductor at normal mode can be calculated as next formula: ilxpeak=1.25 i led v out /v in +0.5 v in (v out -v in )/(l v out f osc ) when the start-up or dimming control by ce pin, transient current flows, the peak current must be equal or less than the current limit of the ic. the peak current should not beyond the rating current of the inductor. for example, for 4 serial led drive from v in =3.6v, recommendation value of the inductor is 10uh or more. ? selection of capacitors set 1 f or more value bypass capacitor between vin pin and the gnd like c1 as in the figure above as close as posible to the ic. set 0.22 f or more capacitor between v out and the gnd like c2 as in the figure above. v fb ce r1 v fb r1 r2 dc v fb r1 r2 r3 r4 c3 vh vl
R1218X 8 typical characteristics 1) efficiency vs. i led ( 2led) l:lqh32cn220 topt=25 c 2. efficiency vs. i led (3led) l: lqh32cn220, topt=25 c 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =1.8v R1218X021a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =3.6v R1218X021a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =4.2v R1218X021 a 0 10 20 30 40 50 60 70 80 90 100 048121620 led current i led (ma) efficiency (%) v in =2.7v R1218X031a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency ( %) v in =3.6v R1218X031a
R1218X 9 3. efficiency vs. iled (4 led ) l: lqh32cn220, topt=25 c 0 10 20 30 40 50 60 70 80 90 100 0 4 8 121620 led i led (ma) efficiency v in =4.2v R1218X031a 0 10 20 30 40 50 60 70 80 90 100 048121620 led current i led (ma) efficiency (%) v in =2.7v R1218X041a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =3.6v R1218X041a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =4.2v R1218X041a
R1218X 10 4. efficiency vs. i led (6led) l: lqh32cn220, diode: crs02 5. pwm dimming control (2 led) v in =3.6v, r1=10 ? ? ? ? ? 5-1. duty vs. led current l lqh32cn220 diode crs02 l lqh32cn220 diode crs02 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =2.7v R1218X062a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) v in =3.6v R1218X062a 0 10 20 30 40 50 60 70 80 90 100 0 4 8 12 16 20 led current i led (ma) efficiency (%) 25 v in =4.2v R1218X062a 0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 0 20406080100 duty (%) led current i led (ma) 5khz 1khz 200hz R1218X021a topt=25
R1218X 11 5-2. output voltage waveform (topt=25 c) 6. pwm dimming control (4 led) v in =3.6v, r1=10 ? 6-1. duty vs. led current (topt=25 c) 6-2. output voltage waveform R1218X021a 0 5 10 15 20 25 0 0.8 1.6 2.4 3.2 4 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=200hz output voltage R1218X021a 0 5 10 15 20 25 0 0.04 0.08 0.12 0.16 0.2 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=5khz output voltage 0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 0 20406080100 duty (%) led current i led (ma) 5khz 1khz 200hz R1218X041a R1218X041a 0 10 20 30 40 50 0 0.8 1.6 2.4 3.2 4 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=200hz output voltage R1218X041a 0 10 20 30 40 50 0 0.04 0.08 0.12 0.16 0.2 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=5kh out p ut volta g e
R1218X 12 7. pwm dimming control (6 led) vin=3.6v,r1=10 ? 7-1. duty vs. led current (topt=25 c) 7-2. output voltage waveform (topt=25 c) 8. vfb voltage vs. temperature 9. uvlo detector threshold/released voltage vs. temperature 0 2.5 5 7.5 10 12.5 15 17.5 20 22.5 25 0 20406080100 duty (%) led current i led (ma) 5khz 1khz 200hz R1218X062a R1218X062a 0 10 20 30 40 50 0 0.04 0.08 0.12 0.16 0.2 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=5khz out p ut volta g e R1218X062a 0 10 20 30 40 50 0 0.8 1.6 2.4 3.2 4 time (ms) output voltage v out (v) 0 5 10 ce input voltage v ce (v) ce input voltage fosc=200hz out p ut volta g e 0.185 0.19 0.195 0.2 0.205 0.21 0.215 -50 -25 0 25 50 75 100 temperature topt (c) vfb voltage v fb (v) R1218X041a v in =3.6v 1.5 1.54 1.58 1.62 1.66 1.7 -50 -25 0 25 50 75 100 temperature topt ( c) uvlo detector threshold uvlo1(v) R1218X041a v in =3.6v uvlo detecto r uvlo released
R1218X 13 10. oscillator frequency vs. temperature 11. maximum duty cycle vs. temperature 12. ovp detector threshold/released voltage vs. temperature 13. supply current vs. temperature 14. lx current limit vs. temperature 1000 1050 1100 1150 1200 1250 1300 1350 1400 -50 -25 0 25 50 75 100 temperature topt (c) oscillator frequency1 f osc1 (khz) vin=3.6v R1218X041a 85 87 89 91 93 95 97 99 -50 -25 0 25 50 75 100 temperature topt ( c) maxduty maxduty (%) R1218X041a vin=3.6v 16.5 17 17.5 18 18.5 19 19.5 20 20.5 -50 -25 0 25 50 75 100 temperature topt ( c) ovp detector threshold ovp1(v) R1218X041a vin=3.6v ovp detector threshold ovp released voltage 0 40 80 120 160 200 240 280 320 360 -50 -25 0 25 50 75 100 temperature topt ( c) supply current1 i cc1 (ua) R1218X041a vin=3.6v 300 400 500 600 700 800 900 1000 -50 -25 0 25 50 75 100 temperature topt ( c) lx current limit i lim (ma) R1218X041a vin=3.6v
R1218X 14 15. ovp transient response (topt=25 c) 16. efficiency dependence on inductors R1218X041a [internal diode type] 50 55 60 65 70 75 80 85 90 0 5 10 15 20 led current i led [m a] efficiency [%] lqh32cn220k53 lqh32cn100k53 glf2012t220k glf2012t100k v in =3.6v R1218X021a 0 2.5 5 7.5 10 12.5 15 0 20406080100 time (ms) ovp voltage v ovp (v) ovp voltage R1218X041a 0 5 10 15 20 25 0 20406080100 time (ms) ovp voltage v ovp (v) ovp voltage R1218X062a 0 5 10 15 20 25 30 35 0 20406080100 time (ms) ovp voltage v ovp (v) ovp voltage

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