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YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 1 description the YB1518 is a st ep-up dc-dc converter ; operates as current source to drive up to 6 white leds(vin at 3.0v) or 8 leds(vin at 3.4v) or 9 leds(vin at 3.4v) in series . series connecting of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors. the li ght intensity of these leds is proportional to the current passing through them . the YB1518 switches at a fixed frequency of ~1mhz, 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 YB1518 can drive up to 9 white leds from a single li-ion battery. 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 1khz to the ctrl pin. YB1518 has integrated latched 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 ? 2.7v to 16v input range ? <1ua shutdown current ? high efficiency ? internal soft start ? drives up to 9 white leds(vin at 3.4v) ? over voltage protection 36v ? small 5-lead sot-23 package ? 100mv low reference voltage applications ? lcd display module ? white led backlighting ? pdas, gps terminals ? digital cameras ? cellular phone ? electronic books ? portable applications figure 1: typical application circuit
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 2 pin configuration pin description table 1 ordering information table 2 pin name description 1 sw switching pin. this is the colle ctor of the inte rnal 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 100mv. 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 YB1518st25 3000 units tape & reel y58m figure 2: YB1518 pin configuration
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 3 absolute maximum ratings vin .........................................................................20v sw voltage ............................................................36v fb voltage ...............................................................5v ctrl voltage...........................................................5v maximum juncti on temp,tj .............................150 c lead temperature (slo kering 10 sec) ................300 c thermal resi stance............................................195 c electricity characteristics recommended operating conditions operating tem perature ............................ -40 c~85 c supply voltage ............................................ 2.7 v~16v sw voltage ............................................................32v 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 90 100 110 mv 100% duty cycle 400 450 ma icl switch current limit 40% duty cycle 350 ma ib fb pin bias current vfb=100mv 1 ua frsw switching frequency 900 930 960 khz dtmx maximum duty cycle 85 % dtmn minimum duty cycle 20 25 % vsat switch vcesat at isw = 200ma 180 mv ilkg switch leakage current ctrl = 0.3v 1 a full on 1.7 v vctl vctrl for full led current full off 0.3 v ictl ctrl pin bias current ctrl = 2v 40 a ovp over voltage protection 34 v ja thermal resistance 220 c/w note: absolute maximum ratings are limits beyond which damage to the device may occur. the maximum allowable power dissipation is a functi on 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 temperature is calculated using: pd(max)= [tj(max)-ta]/ ja . exceeding the maximum allowable power dissipation will cause excessive die temperat ure. all limits at temperature extremes are guaranteed via correlation using standard statistical methods ( t a =25c, vin=3.3v, cin=1uf cout=10uf unless otherwise noted ) table 3
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 4 condition : vin 2.8v ; 4.4v / vcrtl : 3v vout ; 2pcs white leds condition : vin 2.8v ; 4.4v / vctrl: 3v vout ; 3pcs white leds t yp ical performance characteristics efficiency vs vin (2wleds) 78 79 80 81 82 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%) efficiency vs vin (3wleds) 81.0 81.5 82.0 82.5 83.0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%)
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 5 condition : vin 2.8v ; 4.4v / vctrl : 3v vout ; 4pcs white leds condition : vin 2.8v ; 4.4v / vctrl : 3v vout ; 5pcs white leds efficiency vs vin (4wleds) 79 80 81 82 83 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%) efficiency vs vin (5wleds) 75 77 79 81 83 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%)
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 6 condition : vin 2.8v ; 4.4v / vctrl : 3v vout ; 6pcs white leds condition : vin 3.0v ;4.4v / vctrl : 3v vout ; 7pcs white leds efficiency vs vin (6wleds) 72 74 76 78 80 82 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%) efficiency vs vin (7wleds) 70 72 74 76 78 80 2.73.03.33.63.94.24.5 vin(v) efficiency(%)
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 7 condition : vin 3.0v ; 4.4v / vctrl : 3v vout ; 8pcs white leds condition : vin 3.4v ; 6.0v / vctrl : 3v vout ; 9pcs white leds efficiency vs vin (8wleds) 70 72 74 76 78 80 2.7 3.0 3.3 3.6 3.9 4.2 4.5 vin(v) efficiency(%) efficiency vs vin (9wleds) 69 72 75 78 81 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 vin(v) efficiency(%)
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 8 t yp ical performance characteristics supply current (vctrl = 0v) 0 0.2 0.4 0.6 0.8 1 23456789 v ua switching frequency 930.8 931 931.2 931.4 931.6 931.8 932 932.2 23456789 vin(v) khz supply current (vctrl = vin) 0 1 2 3 4 5 6 23456789 v m a ctrl pin bias current 0 10 20 30 40 50 60 23456789 vin(v) ua vcesat 0 50 100 150 200 250 50 100 150 200 250 300 350 400 switching current ( ma) vcesat ( mv) switch leakage current 0 0.1 0.2 0.3 0.4 0.5 23456789 vin (v) ua
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 9 functional block operation the YB1518 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 (comparator-1). when this voltage exceeds the level of the comp arator negative input, the peak current has been reached, and the sr latch (in control logic) is reset and turns off the power switch. the voltage at the negative input of t he comparator comes from the output of t he error amplifier. the error 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 soft start and current limit the internal soft start circuit minimizes the inrush current during turning on YB1518. the maximum switch current is limited to about 450 ma by the chip. 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 signal or a filtered pwm signal can be used to control the led current as illustrated in figure 4 and figure figure 3: YB1518 block diagram led led r mv i 100 =
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 10 5 respectively. using the above different scheme, the led current can be controlled from 0% to 100% to its maximum value. over voltage protection the YB1518 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 YB1518 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 YB1518 will shutdown automatically until input condition changes to bring it out of the shutdown mode. inductor selection a 22uh inductor is recommended for most applications to drive more than 5 leds. figure 4. dimming control using a dc voltage duty iout ( ma) 0% 20 20% 17.4 30% 15 40% 12.4 50% 10 60% 8 70% 6.4 80% 4.07 100% 0 pwm : 2v ; 1khz ; vin=3.6v v dc(v) v fb iout(ma) 2 0 0 1.8 2.2 0.43 1.6 9.2 1.8 1.4 19.6 3.6 1.2 31.1 6 1 43.4 8.5 0.8 63 12.3 0.6 74 14.5 0.4 86.4 16.9 0.2 96.9 19 0 102 20 figure 5. dimming control using a filtered pwm signal
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 11 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. 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 1uf capacitor is sufficient for 2~6 leds, 2.2uf is for 7~8 leds and 4.7uf is for 9 leds 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 connec t 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.
YB1518 step-up dc-dc converter white led driver YB1518 mrev.1.2 www.yobon.com.tw 12 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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