innovative power tm - 1 - www.active-semi.com copyright ? 2011 active-semi, inc. act6311 white led/oled step-up converter efficiency vs. output current efficiency (%) output current (ma) vin = 3.6v vin = 3v act6311-0001 features ? adjustable output voltage ? drives oleds or white leds ? 30v high voltage switch ? 1mhz switching frequency ? tiny inductors and capacitors ? tiny sot23-5 package applications ? oled applications ? cell phones ? digital cameras ? pdas, laptops ? mp3 players ? gps general description the act6311 step-up dc/dc converter is optimized for driving oleds or white leds. it can provide an output voltage up to 24v. the device is capable of driving up to seven leds in series from a lithium-ion battery, with inherent current matching and uniform brightness. the act6311 incorporates a 30v high voltage switch. the device operates at 1mhz and allows the use of few external components. the act6311 is available in the tiny sot23-5 package. 0 20 40 60 80 100 0 5 10 15 20 25 30 35 v in = 3v v in = 3.6v figure 1. typical application circuit rev 3, 22-feb-11
act6311 innovative power tm - 2 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 ordering information pin configuration part number temperature range package pins to p mark packing ACT6311UC-T -40c to 85c sot23-5 5 ycxb tape & reel pin description pin number pin name pin description 1 sw switch output. connect this pin to the inductor and the schottky diode. to reduce emi, minimize the pcb trace path between this pin and the input bypass capacitor. 2 g ground. 3 fb feedback input. this pin is referenced to 1.24v 4 shdn shutdown control. connect to a logic high to enable the device. connect to a logic low to disable the device. never leave the pin unconnected. 5 in supply input. bypass to g with a capacitor 1f capacitor or higher. figure 2: application as white led drive 1 2 3 5 4 i n shdn s w g fb sot23-5 a ct6311 uc g
act6311 innovative power tm - 3 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 absolute maximum ratings parameter value unit in, shdn voltage -0.3 to 6 v sw voltage -0.3 to 30 v fb voltage -0.3 to v in + 0.3 v maximum power dissipation (derate 5mw/c above t a = 50c) 0.4 w junction to ambient thermal resistance ( ja ) 190 c/w operating junction temperature -40 to 150 c lead temperature (soldering, 10 sec) 300 c parameter symbol test cond itions min typ max unit input voltage range 2.5 5.5 v feedback voltage v fb v in = 3v 1.18 1.24 1.30 v fb input current 50 na supply current shdn = in 0.7 1.5 ma supply current in shutdown shdn = g 0 1 a switching frequency f sw 0.8 1 1.2 mhz maximum duty cycle d max 80 85 % switch current limit i lim 75% duty cycle 320 ma switch on voltage i sw = 200ma 350 mv switch leakage current v sw = 20v, shdn = g 10 a shdn logic high threshold 1.6 v shdn logic low threshold 0.4 v shdn input current 0 1 a (note: exceeding these limits may damage the device. exposure to absolute maximum rating conditi ons for long periods may affect device reliability.) electrical characteristics (v in = v shdn = 3v, t a = 25c, unless otherwise specified.)
act6311 innovative power tm - 4 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 functional description the act6311 is a high efficiency step-up dc/dc converter that employs a current-mode, fixed frequency pulse-width modulation (pwm) architecture with excellent line and load regulation. figure 3 shows the functional block diagram of the ic. the flip-flop is set at the start of each oscillator cycle, and turns on the power switch. during this on time, the switch current level is sensed and added to a ramp signal, and the resulting sum is compared with the output of the error amplifier. if the error comparator output is high, the flip-flop is reset and the power switch turns off. thus, the peak inductor current level is controlled by the error amplifier output, which is integrated from the difference between fb input and the 1.24v reference point. the act6311 operates at a constant switching frequency for output current higher than 4ma. if the output current decreases fu rther, the ic will enter frequency modulation mode, resulting in some low frequency ripple. figure 3. functional block diagram error amplifier
act6311 innovative power tm - 5 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 part number current rating (ma) dcr ( ? ) supplier cdrh3d16-220 350 0.5 sumida eljpc220kf 160 4.0 panasonic lqh3c220 250 0.7 murata lem2520-220 125 5.5 taiyo yuden part number if(ma) vrrm (v) supplier cmdsh-3 100 30 central cmdsh2-3 200 30 central bat54 200 30 zetex i led (ma) r1 ( ? ) 5 246 10 124 12 103.3 15 82.7 20 62 application information inductor selection table 1: recommended inductors a 22h inductor is typically used for the act6311. the inductor should have low dc resistance (dcr) and losses at 1mhz. see table 1 for examples of small size inductors. capacitor selection the act6311 only requires a 1f input capcitor and a 1f output capacitor for most applications. ceramic capacitors are ideal for these applications. for best performance, use x5r and x7r type ceramic capacitors, which possess less degradation in capacitance over voltage and temperature ranges. diode selection the act6311 requires a fast recovery schottky diode as the rectifier. select a low forward voltage drop schottky diode with a forward current (if) rating of 100ma to 200ma and a sufficient peak repetitive reverse voltage (vrrm). some suitable schottkky diodes are listed in table 2. table 2: recommended schottky diodes oled application figure 1 shows the feedback network necessary to set the output voltage. select the proper ratio of the two feedback resistors r1 and r2 based on the desired output voltage. typically choose r1 = 20k ? and determine r2 from the output voltage: white led application the led current is determi ned by the value of the feedback resistor r1. bec ause the fb input of the ic is regulated to 1.24v, the led current is determined by i led = 1.24v/r1. the value of r1 for different led currents is shown in table 3. table 3: r1 resistor value selection to improve efficiency, resistors r2 and r3 can be connected as shown in figure 4 to lower the effective feedback voltage. the following are dimming control methods for the act6311 series white led application. 1) pwm signal driving shdn when a pwm signal is connected to the shdn pin, the act6311 is turned on and off alternately under the control of the pwm signal. the current through the leds is either zero or full scale. by changing the duty cycle of the pwm signal (typically 1khz to 10khz), a controlled avera ge current is obtained. 2) dc voltage control figure 5 shows an application in which a dc voltage is used to adjust the led current. the led current increases when v dc is lower than v fb and decreases when v dc is higher than v fb . in figure 5, the led current range of 15ma to 0ma is controlled by v dc = 0v to 2v. 3) filtered pwm control figure 6 shows an application using a filtered pwm signal to control dimming. 4) logic control a logic signal can be used to adjust the led current in a discrete step, as shown in figure 7. ? ? ? ? ? ? ? = 1 v 24 . 1 v 1 r 2 r out (1)
act6311 innovative power tm - 6 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 start-up and inrush current in order to facilitate quick st artup, a soft-start circuit is not incorporated into the act6311. when the ic is first turned on with no external soft-start circuit, the peak inrush current is about 400ma. figure 8 shows an implementation for soft-start. when soft-start and dimming controls are used simultaneously, a low frequency pwm signal (less than 10khz) or the methods in figures 5, 6 and 7 should be used. open-circuit protection (white leds) if one of the leds is di sconnected, the fb voltage drops to zero and the ic switches at maximum duty cycle. this results in a high voltage that may exceed the sw voltage rating. to limit this voltage, use a zener diode as shown in figure 9. the zener voltage must be large than the total forward voltage of the leds and the curren t rating should be higher than 0.1ma. board layout to reduce emi, minimize the area and path length of all traces connected to sw. use a ground plane under the switching regulator and connect r1 directly to the g pin of the ic. act6311 fb r2 56k led1 led2 led3 r1 62 ? r3 33.4k vdc act6311 fb r2 56k led1 led2 led3 r1 62 ? r3 33.4k c1 0.1f r4 10k pwm figure 4. current setting for white led application figure 5. dc voltage controlled dimming figure 6. filtered pwm controlled dimming figure 7. logic controlled dimming act6311 fb led1 led2 led3 r1 r2 logic
act6311 innovative power tm - 7 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 figure 8: soft-start circuit figure 9: open-circuit protection act6311 d1 c1 100nf r2 200k d2 r3 56k r1 20k fb output
act6311 innovative power tm - 8 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 typical performanc e characteristics (circuit of figure 1, unless otherwise specified.) 1.30 1.25 1.20 line regulation 1.15 1.10 -40 -15 10 35 60 85 temperature (c) fb voltage vs. temperature fb voltage (v) 14.0 13.5 13.0 12.5 12.0 3.0 3.5 4.0 4.5 5.0 5.5 input voltage (v) output voltage (v) 12.0 12.5 13.0 13.5 14.0 0 5 10 15 20 25 30 35 load (ma) load regulation output voltage (v) 1.10 1.05 1.00 0.95 0.90 -40 -15 10 35 60 85 temperature (c) switching frequency vs. temperature switching frequency (mhz) 250 300 250 400 450 current limit (ma) duty cycle (%) current limit vs. duty cycle 20 30 40 50 60 70 80 efficiency (%) efficiency vs. output voltage output current (ma) 0 10 20 30 40 50 60 70 80 90 100 0 5 10 15 20 25 30 35 v in = 3.6v i out = 20ma act6311-0001 act6311-0002 act6311-0003 act6311-0004 act6311-0005 act6311-0006 v in = 3.6v v in = 3v v in = 3v
act6311 innovative power tm - 9 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 act6311-0007 act6311-0008 act6311-0009 act6311-0010 act6311-0011 switching waveform in discontinuous mode sw 5v/div inductor current 100ma/div v in = 3v no load v in = 3.6v i load = 20ma v in = 3.6v v out = 13.6v v out = 13.6v i out = 10ma v in = 3.6v i load = 20ma test circuit figure 8 startup without soft start circuit load step response startup with soft start circuit line step response 1s/div shdn typical performance ch aracteristics cont?d (circuit of figure 1, unless otherwise specified.) 20s/div vout 200mv/div inductor current 200ma/div vout 5v/div 4ms/div shdn inductor current 50ma/div vout 5v/div 100s/div vout 1v/div 20ma load step 2ma 100s/div vout 500mv/div vin 3v 5.5v
act6311 innovative power tm - 10 - www.active-semi.com copyright ? 2011 active-semi, inc. rev 3, 22-feb-11 package outline sot23-5 package outline and dimensions symbol dimension in millimeters dimension in inches min max min max a - 1.450 - 0.057 a1 0.000 0.150 0.000 0.006 a2 0.900 1.300 0.035 0.051 b 0.300 0.500 0.012 0.020 c 0.080 0.220 0.003 0.009 d 2.900 bsc 0.114 bsc e 1.600 bsc 0.063 bsc e1 2.800 bsc 0.110 bsc e 0.950 bsc 0.037 bsc e1 1.900 bsc 0.075 bsc l 0.60ref l1 0.300 0.600 0.012 0.024 0 8 0 8 0.024ref active-semi, inc. reserves the right to modify the circuitry or specifications without notice. user s should evaluate each product to make sure that it is suitable for their applicat ions. active-semi products are not intended or authorized for use as critical components in life-support dev ices or systems. active-semi, inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. active-semi and its logo are trademarks of active-semi, inc. for more information on this and other products, contact sales@active-semi.com or visit http://www.active-semi.com . ? is a registered trademark of active-semi.
|
