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AIC3643 built-in ovp white led step-up converter analog integrations corporation si-soft research center ds-3643g-01 20090820 3a1, no.1, li-hsin rd. i, science park, hsinchu 300, taiwan, r.o.c. tel: 886-3-5772500 fax: 886-3-5772510 www.analog.com.tw 1 features built-in open circuit protection over voltage protection efficiency up to 83% at v in =4.2v, 3leds, i led =20ma 1.2mhz fixed switching frequency drives up to 5leds in series 2.5v to 5.5v input voltage low supply current: 150 a matches led current requires tiny inductor and capacitors tsot-23-6, and sot-23-6 packages applications cellular phones pdas dscs handheld devices white led display backlighting description AIC3643 is a current-mode pulse-width- modulation (pwm), st ep-up dc/dc converter designed to drive white leds with a constant current to provide backlight in hand-held devices. series connection of leds provides identical led currents resulting in uniform brightness. this configuration eliminates the need of ballast resistors. the built-in open load protection prevents the damage resulting from an open circuit condition. also low 100mv feedback voltage minimizes power loss in the current setting resistor for better efficiency. AIC3643 is a step-up pwm converter, which includes an internal n-channel mosfet switch for high efficiency. the high switching frequency, 1.2mhz, allows the use of tiny external components. AIC3643 is available in a space-saving tsot- 23-6, and sot-23-6 packages. typical application circuit l 6.8 h d1 sw vin ovp shdn fb gnd AIC3643 3.0~4.2v r fb 5 f c2 3.3 f 20ma l1: gtsd31-6r8m, gotrend d1: ss0540, pan jit c1: jmk107bj105ka, taiyo yuden c2: grm21br61c335k, murata 0 5 10 15 20 25 30 60 65 70 75 80 85 90 3 leds, 6.8 h l1: gtsd31-6r8m, gotrend d1: ss0540, pan jit test circuit refer to fig.1 v in =3v v in =3.6v v in =4.2v efficiency (%) led current (ma) fig. 1 li-ion powered driver for three white leds
AIC3643 2 ordering information example: AIC3643gg6tr in sot-23-6 green package & tape & reel packing type packing type tr: tape & reel bg: bag package type g6: sot-23-6 k6: tsot-23-6 g: green package a ic3643xxx xx pin configuration gnd sw 3 2 1 4 vin 6 fb shdn ovp 5 sot-23-6 tsot-23-6 front view note: pin1 is determined by orienting the package marking as shown. 3643g/3643k marking part no. marking AIC3643gg6 3643g AIC3643gk6 3643k
AIC3643 3 absolute maximum ratings input voltage (vin) 6v sw voltage 33v fb voltage 6v shdn voltage 6v ovp voltage 34v operating temperature range ?40 c to 85 c storage temperature range ?65 c to 150 c maximum junction temperature 150 c lead temperature (soldering, 10 sec) 260 c thermal resistance junction to case sot-23-6 115 c/w tsot-23-6 115 c/w thermal resistance junction to ambient sot-23-6 250 c/w tsot-23-6 250 c/w absolute maximum ratings are those values beyond which the life of a device may be impaired.
AIC3643 4 electrical characteristics (v shdn =1.5v, v in =3v, t a =25 c, unless otherwise specified.) (note 1) parameter symbol test conditions min typ max unit operating voltage v in 2.5 5.5 v supply current i in switching 1 3 ma non switching 150 270 a v shdn = 0v 0.1 1.0 error amplifier feedback voltage v fb 90 100 110 mv fb input bias current i fb v fb =100mv 1 na oscillator switching frequency f osc 0.8 1.2 1.6 mhz maximum duty cycle d 91 94 % power switch sw on resistance r ds(on) 1.4 2.5 ? switch leakage current i sw(off) v sw =33v 0.1 1 a switch current limit i il 0.65 1 a control input shdn voltage high v ih on 1.5 v shdn voltage low v il off 0.3 v over voltage protection ovp input resistance r ovp 0.8 1.2 1.6 m ? ovp threshold v ovp 1v hysteresis typical 22 28 32 v note 1: specifications are production tested at t a =25 c. specifications over the -40 c to 85 c operating temperature range are assured by design, characterization and correlation with statistical quality controls (sqc).
AIC3643 5 typical performance characteristics 2.5 3.0 3.5 4.0 4.5 5.0 5.5 100 110 120 130 140 150 160 170 180 190 200 non-switching fb=v in supply current ( a) supply voltage (v) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 800 1000 1200 1400 1600 switching fb=gnd supply current ( a) supply voltage (v) fig. 2 supply current vs. supply voltage fig. 3 supply current vs. supply voltage 2.53.03.54.04.55.05.5 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 r ds-on ( ) supply voltage (v) 0 102030405060708090100 0 20 40 60 80 100 2khz 1khz 500hz 200hz 100hz v in =3.6v; l=6.8 h c in =1 f; c out =3.3 f 3leds i led_duty /i ledmax (%) shdn pin pwm duty (%) fig. 4 r ds_on vs. supply voltage fig. 5 dimming control by shutdown pin -40-20 0 20406080 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 switching frequency (mhz) temperature ( o c) -40-20 0 20406080 96 98 100 102 104 106 108 110 feedback voltage (mv) temperature ( o c) fig. 6 switching frequency vs. temperature fig. 7 feedback voltage vs. temperature
AIC3643 6 typical performance characteristics (continued) -40-20 0 20406080 20 21 22 23 24 v in =5.5v v in =4.2v v in =3.6v v in =3v v in =2.5v led current (ma) temperature ( o c) fig. 8 led current vs. temperatur e fig. 9 start up from shutdown 0 5 10 15 20 25 30 60 65 70 75 80 85 90 3 leds, 6.8 h l1: gtsd31-6r8m, gotrend d1: ss0540, pan jit test circuit refer to fig.1 v in =3v v in =3.6v v in =4.2v efficiency (%) led current (ma) fig. 10 operation waveform fig. 11 3leds efficiency vs. led current 0 5 10 15 20 25 30 60 65 70 75 80 85 90 4 leds, 6.8 h l1: gtsd31-6r8m, gotrend d1: ss0540, pan jit test circuit refer to fig.1 v in =4.2v v in =3.6v v in =3v efficiency (%) led current (ma) 0 5 10 15 20 25 30 60 65 70 75 80 85 90 5 leds, 6.8 h l1: gtsd31-6r8m, gotrend d1: ss0540, pan jit test circuit refer to fig.1 v in =4.2v v in =3.6v v in =3v efficiency (%) led current (ma) fig. 12 4leds efficiency vs. led current fig. 13 5leds efficiency vs. led current v in =3v; 3leds; l=6.8 f; c out =3.3 f; i led =20ma v shdn , 2v/div v out , 2v/div i inductor , 200ma/div output ripple, 50mv/div i inductor , 200ma/div v sw , 5v/div v in =3.6v; 3leds; l=6.8 f; c out =3.3 f; i led =20ma
AIC3643 7 block diagram cc rc rs m1 - + pwm comparator 28v ovp over voltage comparator - + 100mv vin fb vref + - error amp gnd sw pwm/pfm control shdn driver + - current amp. control logic 1.2mhz oscillator slope compensation pin descriptions pin 1: sw - switch pin. connect inductor/diode here. minimize trace area at this pin to reduce emi. pin 2: gnd - ground pin. tie directly to local ground plane. pin 3: fb - feedback pin. reference voltage is 100mv. connect cathode of lowest led and resistor here. calculate resistor value to obtain led current according to the formula: r fb = 100mv/i led pin 4: shdn - shutdown pin. tie to higher than 1.5v to enable device, 0.3v or less to disable device. pin 5: ovp - overvoltage protection. when vout is greater than 28v, the internal mosfet turns off. pin 6: vin - power input pin. bypass vin to gnd with a capacitor sitting as close to vin as possible.
AIC3643 8 application information inductor selection a 6.8 h inductor is recommended for most AIC3643 applications. although small size and high efficiency are major concerns, the inductor should have low core losses at 1.2mhz and low dcr (copper wire resistance). it is important to ensure the inductor saturation current exceeding the peak inductor current in application to prevent core saturation. for ccm (continuous conduction mode) operation, the peak inductor current can be calculated from: () l f 2 d v i i osc ) max ( ) min ( in max in peak ? ? + = l f 2 d v v v i osc ) max ( ) min ( in ) min ( in out ) max ( led ? ? + ? ? = capacitor selection the small size of ceramic capacitors makes them ideal for AIC3643 applications. x5r and x7r types are recommended because they retain their capacitance over wider ranges of voltage and temperature than other types, such as y5v or z5u. 1 f input capacitor with 3.3 f output capacitor are sufficient for most AIC3643 applications. diode selection schottky diodes, with their low forward voltage drop and fast reverse recovery, are the ideal choices for AIC3643 applications. the forward voltage drop of an schottky diode represents the conduction losses in the diode, while the diode capacitance (c t or c d ) represents the switching losses. for diode selection, both forward voltage drop and diode capacitance need to be considered. in addition, the rating of selected schottky diode should be able to handle the output voltage and the maximum peak diode current. led current control led current is controlled by feedback resistor (r fb in figure 1). the feedback reference voltage is 100mv. the led current is 100mv/r fb . in order to have accurate led current, precision resistors are preferred (1% recommended). the formula for r fb selection is shown below. led fb i mv 100 r = open-circuit protection in the cases of output open circuit, when the leds are disconnected from the circuit or the leds fail, the feedback voltage will be zero. AIC3643 will then switch to a high duty cycle resulting in a high output voltage, which may cause sw pin voltage to exceed its maximum 33v rating. connect built- in ovp (over voltage protection) pin to output terminal to prevent the damage resulting from an open circuit condition. dimming control there are three different ways of dimming control circuits as follows: 1. using a pwm signal pwm brightness control provides the widest dimming range by pulsing the leds on and off at full and zero current, respectively. the change of average led current depends on the duty cycle of the pwm signal. typically, a 0.1khz to 2khz pwm signal is used. two applications of pwm dimming with AIC3643 are shown in figure 14 and figure 15. one, as figure 14, uses pwm signal to drive shdn pin directly for dimming control. the other, as figure 15, employs pwm signal going through a resistor to drive fb pin. if the shdn pin is used, the increase of duty cycle results in led brightness enhancement. if the fb pin is used, on the contrary, the increase of duty cycle will decrease its brightness. in this application, leds are dimmed by fb pin and turned off completely by shdn . 2. using a dc voltage for some applications, the preferred method of a dimming control uses a variable dc voltage to adjust led current. the dimming control using a dc voltage is shown in figure 16. with a v dc
AIC3643 9 ranging from 0v to 5v, the selection of resistors in figure 16 results in dimming control of led current from 20ma to 0ma, respectively. 3. using a filtered pwm signal filtered pwm signal can be considered as an adjustable dc voltage. it can be used to replace the variable dc voltage source in dimming control. the circuit is shown in figure 17. layout consideration in order to ensure a proper operation of AIC3643, the following points should be managed comprehensively. 1. the input capacitor and v in should be placed as close as possible to each other to reduce the input ripple voltage. 2. the output loop, which is consisted of the inductor, the internal power switch, the schottky diode and the output capacitor, should be kept as small as possible. 3. the routes with large current should be kept short and wide. 4. logically the large current on the converter should flow at the same direction. 5. the fb pin should be connected to the feedback resistors directly and the route should be away from the noise sources. l 6.8 h d1 sw vin ovp shdn fb gnd AIC3643 vin r fb 5 c1 1 f c2 3.3 f pwm ss0540 fig. 14 dimming control with a pwm signal l 6.8 f c2 3.3 f pwm r2 49k r1 1k fig. 15 dimming control using a pwm signal
AIC3643 10 l 6.8 f c2 3.3 fig. 16 dimming control using a dc voltage l 6.8 h d1 ss0540 sw vin ovp shdn fb gnd AIC3643 vin c1 1 f pwm r2 49k c3 0.1 f r3 5.1k r fb 5 c2 3.3 f r1 1k fig. 17dimming control using a filter pwm signal application example l 6.8 h d1 ss0540 sw vin ovp shdn fb gnd AIC3643 3.0~4.2v c1 1 f 20ma r fb 5 fig. 18 six white leds application in li-ion battery
AIC3643 11 physical dimensions (unit: mm) sot-23-6 package outline drawing c a a2 b with plating view b l1 l seating plane gauge plane 0.25 a1 section a-a base metal e1 d e aa e1 see view b e 0 0.90 0.30 1.50 2.60 2.80 0.08 0.30 0.05 e l1 l e1 c e e1 d b a2 a1 0.95 bsc 8 0.60 1.90 bsc 0.42 ref 1.30 1.70 3.00 3.00 0.22 0.50 0.15 0.95 min. s y m b o l a 1.45 max. sot-23-6 millimeters note : 1. refer to jedec mo-178ab. 2. dimension "d" does not include mold flash, protru sions or gate burrs. mold flash, protrusion or gate bu rrs shall not exceed 10 mil per side. 3. dimension "e1" does not include inter-lead flash or protrusions. 4. controlling dimensio n is millimeter, converted in ch dimensions are not necessarily exact.
AIC3643 12 tsot-23-6 package outline drawing 0 0.70 0.30 1.50 2.60 2.80 0.08 0.30 0 e l1 l e1 c e e1 d b a2 a1 0.95 bsc 8 0.60 1.90 bsc 0.60 ref 0.90 1.70 3.00 3.00 0.22 0.50 0.10 - min. s y m b o l a 1.00 max. tsot-23-6 millimeters note : 1. refer to jedec mo-193aa. 2. dimension "d" does not include mold flash, protru sions or gate burrs. mold flash, protrusion or gate bu rrs shall not exceed 6 mil per side. 3. dimension "e1" does not include inter-lead flash or protrusions. 4. controlling dimension is millimeter, converted in ch dimensions are not necessarily exact. c a a2 b with plating view b l1 l seating plane gauge plane 0.25 a1 section a-a base metal e1 d e aa e1 see view b e
AIC3643 13 note: information provided by aic is believed to be accurate and reli able. however, we cannot assume responsibility for use of any circuitry other than circuitry entirely em bodied in an aic product; nor for any infringement of patents or other rights of thir d parties that may result from its use. we reserve the right to change the circuitry and spec ifications without notice. life support policy: aic does not authorize any aic product for use in life support devices and/or systems. life support device s or systems are devices or systems which, (i) are intended for surgic al implant into the body or (ii) support or sustain life, and whose failure to perform, when properly used in accordance with inst ructions for use provided in the labeling, can be reasonably expe cted to result in a significant injury to the user.

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