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MP3305 36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 1 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. the future of analog ic technology description the MP3305 is a monolithic step-up converter designed for driving arrays of wleds from 5v input or a single cell lithium ion battery. the MP3305 uses current mode, fixed frequency architecture to regulate the led current, which is measured through an external current sense resistor. its low 200mv feedback voltage reduces power loss and improves efficiency. the MP3305 features up to 50khz true pwm dimming, which allows the flexible control of the backlighting luminance under wide range of the ambient brightness, and also avoids the possibility of pwm dimming audible noise. the MP3305 is turned off if an over-voltage condition is present due to an open circuit condition. use one external resistor voltage divider to adjust ovp threshold. MP3305 also includes under-voltage lockout, current limiting and thermal overload protection preventing damage in the event of an output overload. the MP3305 is available in small 8-pin qfn 2x3mm package. features ? internal power mosfet ? drives up to 10 series white leds ? up to 88% efficiency ? pwm dimming frequency from 250hz to 50khz ? 2.2mhz fixed switching frequency ? adjustable open load shutdown threshold (ovp) ? low 200mv feedback voltage ? uvlo, thermal shutdown ? internal 1.3a current limit ? available in 2mm x 3mm qfn8 package applications ? lcd panels ? digital picture frames ? handheld computers and pdas ? digital still cameras ? small lcd displays all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website unde r quality assurance. ?monolithic powe r systems?, ?mps?, and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application MP3305 v in 5v enable/ dimming control led1 led2 led3 r2 r1 r set l d c1 c2 led28 led29 led30 in en gnd led iset ovp sw string 1 string 10 ... v in vs. efficiency 50 60 70 80 90 100 3 3.5 4 4.5 5 5.5 6 6.5 v in (v) efficiency (%)
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 2 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. ordering information part number* package top marking free air temperature (t a ) MP3305dd qfn8 (2mm x 3mm) 6e -40 c to +85 c * for tape & reel, add suffix ?z (e.g. MP3305dd?z). for rohs compliant packaging, add suffix ?lf (e.g. MP3305dd?lf?z) package reference absolute maxi mum ratings (1) sw pin, led pin...........................-0.5v to +40v all other pins ...............................-0.3v to +6.5v storage temperature............... -55 c to +150 c continuous power dissipation (t a = +25c) (2) ??????????????????....1.9w recommended operating conditions (3) in supply voltage .................................3v to 6v sw pin ................................................v in to 36v operating junct. temp (t j )...... -40 c to +125 c thermal resistance (4) ja jc qfn8 (2mm x 3mm) ...............65 ...... 13 ... c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature t j (max), the junction-to- ambient thermal resistance ja , and the ambient temperature t a . the maximum allowable continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)-t a )/ ja . exceeding the maximum allowable powe r dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7, 4-layer pcb. top view sw pgnd vin ovp 1 2 3 4 gnd iset led en 8 7 6 5 exposed pad connect to gnd
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 3 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. electrical characteristics v in = v en = 5v, t a = +25 c, unless otherwise noted. parameters symbol condition min typ max units operating input voltage v in 2.5 6 v supply current (shutdown) i in_sd v en = 0v 1 2 a supply current (quiescent) i in_qs v iset = 0.3v 690 850 a switching frequency f sw 1.7 2.2 2.7 mhz maximum duty cycle d max v iset = 0v 90 % under voltage lockout in under voltage lockout v uvlo v in rising 2.25 2.45 v under voltage lockout hysteresis 92 mv open lamp shutdown threshold v ovp v ov rising 0.9 v enable en off threshold v en_low v en falling 0.4 v en on threshold v en_high v en rising 1.8 v disable timer 5 ms minimum en on pulse 5 s feedback iset voltage v iset v en > 2v 185 200 215 mv iset input bias current v iset = 0.2v -600 -300 na output switch sw on-resistance r on 0.4 ? sw current limit duty cycle = 60% 1.33 a thermal shutdown 150 c led switch (m2, refer block diagram) on resistance 0.8 ?
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 4 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. pin functions qfn8 pin # name pin function 1 sw power switch output. sw is the drain of t he internal mosfet switch. connect the power inductor and output rectifier to sw . sw can swing between gnd and 36v. 2,8 gnd, exposed pad ground. connect exposed pad to gnd plane for proper thermal performance. 3 in input supply pin. must be locally bypassed. 4 ovp open load protection adjusting pin. connect a resistor divider from output to this pin to adjust the ovp threshold. when this pin voltage reaches the shutdown threshold 0.9v, the switch will be turned off 5 en on/off control and dimming command input. holding en pin low for more than 5ms will turn the part off. to use pwm dimming, add a 250hz to 50khz square wave signal to this pin. 6 led led current input. this pin is the open-drain output of an internal dimming control switch. connect the led cathode to this pin. 7 iset led current set. this pin is the source output of an internal dimming control switch. the MP3305 regulates the voltage across the curr ent setting resistor. tie a current setting resistor from this pin to ground. the regulation voltage is 200mv.
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 5 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical performanc e characteristics v in = 5v, i led = 200ma, 3wleds 10strings, unless otherwise noted. open load protection pwm dimming f pwm =50khz, dpwm=50% steady state operation enable startup enable shutdown i inductor 500ma/div fb 50mv/div v out (ac) 100mv/div sw 5v/div i led 200ma/div en 5v/div v out 5v/div sw 10v/div i led 100ma/div v out 5v/div sw 10v/div i led 100ma/div en 5v/div v out 5v/div sw 10v/div i led 200ma/div pwm 2v/div v out 10v/div sw 10v/div 400ns/div v in vs. efficiency 50 60 70 80 90 100 3 3.5 4 4.5 5 5.5 6 6.5 v in (v) efficiency (%) pwm dimming duty vs. wled current 0 20 40 60 80 100 120 140 160 180 200 020406080100 pwm dimming duty (%) wled current (ma) 50khz 20khz 250hz 1khz
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 6 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. operation the MP3305 uses a constant frequency, peak current mode boost regulator architecture to regulate the series string of white leds. the operation of the MP3305 can be understood by referring to the block diagram of figure 1. at the start of each oscillator cycle the fet is turned on through the control circuitry. to prevent sub-harmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the output of the current sense amplifier and the result is fed into the positive input of the pwm comparator. when this voltage equals the output voltage of the error amplifier the power fet is turned off. the voltage at the output of the error amplifier is an amplified version of the difference between the 200mv reference voltage and the feedback voltage. in this way the peak current level keeps the output in regulation. if the feedback voltage starts to drop, the output of the error amplifier increases. this results in more current flowing through the power fet, thus increasing the power delivered to the output. pwm comparator amplifier enable control logic current sense amplifier sw m1 m2 pgnd ovp 0.9v - + led iset iset en gnd 2.2mhz osc enable & dimming control - + - + + - + figure 1?functional block diagram
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 7 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. application information enable/ dimming control MP3305 v in 5v mbr0520 c2 c1 in en gnd led iset ovp sw figure 2?circuit for driving 10 strings of 3 wleds a typical application circuit can be seen in figure 2. the 10 strings of 3 white leds can be driven from a 5v at an output current of 200ma. a 2.2f output capacitor is sufficient for most applications. a 2.2h inductor with low dcr (inductor dc resistance) is recommended to improve efficiency. a 10f ceramic capacitor is recommended for the input capacitance in the real system. schottky diodes have fast recovery and a low forward voltage are recommended. schottky diodes rated with 500ma are sufficient for the MP3305. the MP3305 has internal soft- start to limit the amount of current through vin at startup and to also limit the amount of overshoot on the output. the ramped voltage that is added to the current sense amplifier reduces the current output as the duty cycle increases. as more leds are added, the output voltage rises but the current that can be delivered to the load is reduced as well. setting the led current the led current is controlled by the current setting resistor, r1. the current through the leds is given by: i led =200mv/r1. table 1 shows the selection of resistors for a given led current. table 1?i led vs. r1 i led (ma) r1 ( ? ) 1 200 5 40 10 20 20 10 60 3.33 180 1.11 200 1 pwm dimming apply a 250hz to 50khz square waveform to the en pin to implement pwm dimming of the leds. the minimum recommended amplitude of the pwm signal is 2v. open load protection open load protection will shut off the MP3305 if the output voltage goes too high. in some cases an led may fail, this will result in the feedback voltage always being zero. the part will run at maximum duty cycle boosting the output voltage higher and higher. if the output voltage ever exceeds the adjusted ovp threshold ( + ov r2 v =0.9v(1 ) r3 ), the MP3305 will shut down. the part will not switch again until the power is recycled.
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 8 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. layout considerations careful attention must be paid to the pcb board layout and components placement. proper layout of the high frequency switching path is critical to prevent noise and electromagnetic interference problems. the loop of MP3305 sw to gnd pin, output diode, and output capacitor is flowing with high frequency ripple current, it must be as short as possible. and connect the gnd (2 pin) and pgnd (8 pin) together thru thermal pad, as showed in figure 3. figure 3?layout consideration the in pin of the ic must be locally bypassed. a rc filter is highly recommended for eliminating the noise on in pin. it could be implemented as shown in figure 4. MP3305 sw gnd in input figure 4?input bias filtering
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 9 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical application circuits MP3305 sw ovp in iset led pgnd gnd en led+ led- c2 330nf 50v d2 5.6v 7.5 zener d1 b0540 l1 10uh optional bias circuit gnd en vin 3.3v -18v c1 r3 r4 10uf 25v c3 0.1uf 50v 2 31 6 7 5 8 4 figure 5 ? driving 27 wleds (9 wleds in series and 3 strings paralleled) with 3.3v-18v input voltage in order to improve the mosfet on-resistance at low input voltage and make the chip compatible for high input voltage, the additional bias circuit should be used. MP3305 sw ovp led in iset pgnd gnd en gnd en led+ led- vin 4.5v-18v c1 10uf 25v c4 330nf 50v c3 0.1uf 25v q2 2n3904 d2 5.6v zener required bias circuit for high input voltage l1 d1 10uh b0540 7 8 2 3 4 1 6 5 figure 6 ? wide input voltage step-up converter for 27 wleds ( 9 wleds in series and 3 strings paralleled )
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp MP3305 rev. 1.0 www.monolithicpower.com 10 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical application circuits (continued) MP3305 sw ovp in led gnd iset pgnd en c3 330nf r1 r2 d1 b0540 l1 led1 led2 led3 led4 led5 led6 led7 led8 led9 led10 gnd en vin 5v c1 16v c2 16v 1 27 5 8 6 4 3 1% r3 r4 figure 7 ? driving 10 wleds in series with 5v input voltage
MP3305 ?36v, 1.3a, step-up white led driver with high frequency true pwm dimming & adjust ovp notice: the information in this document is subject to change wi thout notice. users should warra nt and guarantee that third party intellectual property rights are not infringed upon w hen integrating mps products into any application. mps will not assume any legal responsibility for any said applications. MP3305 rev. 1.0 www.monolithicpower.com 11 4/10/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. package information qfn8 (2mm x 3mm) side view top view bottom view 2.90 3.10 1.90 2.10 0.00 0.05 pin 1 id marking 1.70 0.50 0.25 recommended land pattern 2.90 note: 1) all dimensions are in millimeters. 2) exposed paddle size does not include mold flash. 3) lead coplanarity shall be 0.10 millimeter max. 4) drawing conforms to jedec mo-229, variation vced-2. 5) drawing is not to scale. 1.60 0.70 pin 1 id option b r0.20 typ. detail a pin 1 id index area 1 8 5 4 1.65 1.85 1.50 1.70 0.50 bsc 0.18 0.30 pin 1 id see detail a 0.30 0.50 0.80 1.00 0.20 ref pin 1 id option a 0.30x45? typ.

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