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YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 1 description the YB1520 is a step-up dc-dc converter ; operates as current source to drive up to 9 white leds in series or 30 white leds in parallel/series configuration. series connecting of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors. the light intensity of these leds is proportional to the current passing through them . the YB1520 switches at a fixed frequency of 700khz, allowing the use of tiny, low profile inductors and capacitors to minimize footprint and cost in space consideration applications for cellular phone backlighting or other hand held equipment. the YB1520 can drive up to 9 white leds from a single li-ion battery and drive up to 30 white leds from a 5v. the wide input voltage range from 2.7v to 16v is ideal for portable and automotive (5v/12v) applications with higher conversion efficiency. to control led brightness, the led current can be pulsed by applying a pwm (pulse width modulated) signal with a frequency range of 100hz to 50khz to the ctrl pin. YB1520 has integrated over voltage protection that prevents damage to the device in case of a high impedance output due to faulty led or open circuit caused by abnormal conditions. typical application circuit features ? built-in internal switch ? adjustable output voltage up to 35v ? 2.7v to 16v input range ? <1ua shutdown current ? high efficiency ? drives up to 30 white leds in ? parallel/series ? over voltage protection ? small 5-lead sot-23 package applications ? lcd display module ? white led backlighting ? pdas, gps terminals ? digital cameras ? cellular phone ? electronic books ? portable applications figure 1: typical application circuit
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 2 pin configuration pin description table 1 ordering information pin name description 1 sw switching pin. this is the colle ctor of the internal npn power switch. connect to inductor and diode. minimize the metal trace area connected to this pin to reduce emi. 2 gnd ground pin. connect direct ly to local ground plane. 3 fb feedback pin. reference voltage is 200mv. connect leds and a resistor at this pin. led current is determined by the resistance and ctrl voltage. 4 ctrl shutdown pin and dimming control pin. vctrl > 1.8v generates full-scale led current vctrl < 0.4v chip is off switching from 0.4v to 2.0v, pwm duty cycle controls the led current 5 vin input supply pin. bypass this pin with a capacitor as close to the device as possible order number supplied as package marking YB1520st25 3000 units tape & reel y52m
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 3 absolute maximum ratings vin..........................................................................20v sw voltage ............................................................36v fb voltage ...............................................................5v ctrl voltage...........................................................5v maximum junction temp , tj (not 2)...................150 c lead temperature (sol dering 10 sec) ................300 c thermal resi stance............................................195 c electricity characteristics recommended operating conditions operating temperature (note 3) ................ C 40 c~85 c supply voltage ............................................. 2.5v~16v sw voltage ............................................................30v (ta=25c, vin=3.3v, cin=1uf c out=10uf unless otherwise noted) note: absolute maximum ratings are limits beyond which damage to the dev ice may occur. the maximum allowable power dissipation is a function of maximum function temperature, tj(max ), the junction to ambient thermal resistance, ja , and the ambient temperature. the maximum allowable, power dissipation at any ambient te mperature is calculated us ing: pd(max)= [tj(max)-ta]/ ja . exceeding the maximum allowable power dissipation will cause excessive die te mperature. all limits at temperature extremes are guaranteed via co rr e l a ti o n us in g s t a n da r d s t a ti s ti ca l m e th ods symbol function parameter test conditions min typ max units vin input voltage range 2.7 16 v not switching vfb = 0.3v 1.2 1.5 1.7 ma iq (quiescent current) shutdown ctrl = 0v 0.3 1 ua vfb feedback voltage iout=20ma,vout=12.5v circuit of figure 1 180 200 220 mv icl 100% duty cycle 850 900 950 ma ilim switch current limit 40% duty cycle 600 ma ib fb pin bias current vfb=200mv 2 10 20 ua frsw switching frequency 680 700 720 khz dtmx maximum duty cycle 85 % dtmn minimum duty cycle 20 25 % vsat switch vcesat at isw = 200ma 120 mv ilkg switch leakage current ctrl = 0.3v 1 a full on 1.7 1.8 v vctl vctrl for full led current full off 0.2 0.3 v ictl ctrl pin bias current ctrl = 2v 20 a ovp over voltage protection 34 v ja thermal resistance 220 c/w
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 4 efficiency 3s5p output ripple t yp ical performance characteristics 84% 85% 86% 87% 88% 89% 4 4.5 5 5.5 6 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 5 efficiency 3s6p output ripple 82% 84% 86% 88% 90% 4 4.5 5 5.5 6 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 6 efficiency 3s7p output ripple 80% 82% 84% 86% 88% 90% 44.555.56 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 7 efficiency 3s8p output ripple 80% 82% 84% 86% 88% 90% 4 4.5 5 5.5 6 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 8 efficiency 3s9p output ripple 80% 82% 84% 86% 88% 4 4.5 5 5.5 6 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 9 efficiency 3s10p output ripple 80% 82% 84% 86% 88% 44.555.56 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 10 efficiency 9s output ripple 76% 78% 80% 82% 84% 3 3.5 4 4.5 5 5.5 6 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 11 efficiency 8s3p output ripple 79% 80% 81% 82% 83% 84% 85% 44.555.56 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 12 efficiency 9s3p output ripple 78% 80% 82% 84% 86% 44.555.566.57 vin(v) efficiency(% )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 13 typical performance characteristics drive switch saturation voltage(vcesat) 60 80 100 120 140 160 0 50 100 150 200 250 300 switch current(ma) saturation voltage(mv) switching frequency 695 700 705 710 715 720 725 730 0 20406080100120 temperature (c) switching frequency (khz ) switch leakage current 0.5 0.6 0.7 0.8 0.9 1 2 4 6 8 10 12 14 16 vin(v) i(ua ) supply current test 0.5 1 1.5 2 2.5 2 4 6 8 10 12 14 16 vin (v) iin ( ma )
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 14 switching waveform
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 15 functional block operation the YB1520 uses a constant frequency, current mode control scheme to regulate the output led current. its operation can be understood by referring to the block diagram in figure 3. at the start of each oscillator cycle, a voltage proportional to the switch current is added to a ramp output and the resulting sum is fed into the positive terminal of the pwm comparator. when this voltage exceeds the level of the comparator negative in put, the peak current has been reached, and the sr latch is reset and turns off th e power switch. the voltage at the negativ e input of the comparator comes from the output of the error amplifier. the er ror amplifier sets the correct peak current level to keep the output in regulation. if the error amplifier?s output increases, more current is delivered to the output; if it decreases, less current is delivered. application information inrush current the maximum switch current is limited to about 900 ma by the chip typically, a larger cout will increase the duration of high current. however, when vin is first connected, an even larger current can flow into cout. this occurs when the sw pin is open circuit and the cout voltage changes from 0v to vin in a few microseconds. because the duration of this large current is short, it will usually not cause problems. if this current is not desirable, an external soft-start circuit can be added to significantly reduce this inrush current. figure 3: YB1520 block diagram
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 16 led current and dimming control the led?s current is set by a resistor connected at fb pin to gnd using: the maximum led current set initially can be reduced by pulse width modulating the ctrl. a better approach is to adjust the feedback voltage for dimming control. either a dc level sig nal or a filtered pwm signal can be used to control the led current as illustrat ed in figure 4 and figure 5 respectively. using the above different scheme, the led current can be controlled from 20% to 80% to its maximum value. figure 4. dimming control using a dc voltage figure 5. dimming control using a filtered pwm signa l(1khz , 2vp-p , duty 20%~80%) over voltage protection the YB1520 has an internal over voltage protection circuit which also acts as an open-circuit protection. in the cases of open circuit or the leds failure, the leds are disconnected from the circuit, and the feedback voltage will be zero. the YB1520 will then switch to a high duty cycle resulting in a high output voltage, which may cause sw pin voltage to exceed its maximum 34v rating. the YB1520 will shutdown automatically until input condition changes to bring it out of the shutdown mode. inductor selection a 47uh inductor is recommended for most applications to drive more than 9 leds in serials and 33uh inductor is recommended for drive 30 leds in serials/parallel. although small size a nd high efficiency are major concerns, the inductor should have low core losses at 1mhz and low dcr (copper wire resistance). diode selection to maintain high efficiency, the average current rating of the schottky diode should be large than the peak inductor current, ipk. schottky diode with a low forward drop and fast switching speeds are ideal for increase efficiency in portable application. choose a reverse breakdown of the schottky diode large than the output voltage. led led r mv i 200 =
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 17 capacitor selection choose low esr capaci tors for the output to minimize output voltage ripple. multilayer capacitors are a good choice for this as well. a 47uf capacitor is sufficient for most applications. for additional bypassing, a 100nf ceramic capacitor can be used to shunt high frequency ripple on the input. the input bypass capacitor cin, as shown in figure 1, must be placed close to the ic. this will reduce cop per trace resistance which affects input voltage ripple of the ic. for additional input voltage filtering, a 100nf bypass capacitor can be placed in parallel with cin to shunt any high frequency noise to ground. the output capacitor, cout, should also be placed close to the ic. any copper trace connections for the cout capacitor can increase the series resistance, which directly effect output voltage ripple. the feedback network, resister r2 should be kept close to the fb pin to minimize copper trace connections that can inject noise into the system. the ground connection for the feedback resistor network should connect directly to an analog ground plane. the analog ground plane should tie directly to the gnd pin. if no analog ground plane is available, the ground connection for the feedback network should tie directly to the gnd pin. trace connections made to the inductor and schottky diode should be minimized to reduce power dissipation and increase overall efficiency.
YB1520 high power step-up dc-dc converter, white led driver YB1520 mrev.1.2 www.yobon.com.tw 18 package description all the contains in this datasheet are not assuming any responsibility for use of any circuitry described no circuit patent license ar e implied and yobon reserves the right at any time without notice to change said circuitry and specifications. yobon inc. would like to receive your f eedback with your recommends and suggestions that is always welcome and with our appreciations.

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