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mp3308 step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 1 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the mp3308 is a monolithic step-up converter designed to drive arrays of white leds from a 3.3v input or a single-cell lithium-ion battery. the mp3308 uses fixed-frequency current- mode 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 mp3308 features dual pwm-dimming input control and true pwm dimming?this control allows for a wide luminescent range that makes the display readable under a variety of ambient light conditions with minimal pwm dimming noise. the mp3308 includes over-voltage protection, short-circuit protection, under-voltage lockout, current limiting, and thermal overload protection. the mp3308 is available in small 3mmx4mm 14-pin qfn package. features ? internal power mosfet ? drives up to 10 white leds in series ? 2.2mhz fixed switching frequency ? up to 88% efficiency ? dual pwm-dimming input control ? internal 1.3a current limit ? 3% true pwm dimming duty accuracy ? adjustable over-voltage protection threshold ? low 200mv feedback voltage ? under-voltage lockout, short-circuit protection, thermal shutdown ? available in 3mmx4mm qfn14 package applications ? small lcd panels ? digital picture frames ? smartphones ? portable media players ? digital cameras all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under products, quality assurance page. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application v in mp3308 iset led en pwmoa gnd pwmia ovp enable ld c in r iset c fset in c out c oa sw r ovp 1 r ovp2 pwmib pwmob fset c ob v out
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 2 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number* package top marking MP3308DL qfn14 (3x4mm) 3308 for tape & reel, add suffix ?z (e.g. MP3308DL-z). for rohs, compliant packaging, add suffix ?lf (e.g. MP3308DL?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............... -55c to +150c continuous power dissipation (t a = 25c) (2) ??????????????????....2.6w recommended operating conditions (3) supply voltage (v in )..............................3v to 6v sw pin ................................................v in to 36v operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc qfn14 (3x4mm) .....................48 ...... 10 ... 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. pin 1 id 14 13 12 11 10 9 8 1 2 3 4 5 6 7 top view exposed pad on backside connect to gnd qfn14 (3x4mm)
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 3 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in = v en = 5v, t a = 25c, 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 25 30 a supply current (quiescent) i in_qs v iset = 0.3v 860 a switching frequency f sw 1.7 2.2 2.7 mhz maximum duty cycle d max v iset = 0v 90 % under voltage lockout v in under voltage lockout v uvlo v in rising 2.1 2.3 v under voltage lockout hysteresis 30 mv over-voltage protection threshold v ovp v out rising 0.9 v enable and dimming en/pwmix off threshold v logic_low v en falling 0.4 v en/pwmix on threshold v logic_high v en rising 1.8 v true pwm dimming duty accuracy ? d dpwm d_pwmia=d_pwmib=70% 3 % 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 on-resistance (m2 in the functional block diagram) 0.8 ?
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 4 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions pin # name description 1 sw power switch output. drain of the internal mosfet switch. connect to the power inductor and the output rectifier. sw can swing between gnd and 40v. 2 pgnd, exposed pad power ground. connect exposed pad to gnd plane for proper thermal performance. 3 in input supply pin. locally bypassed. 4 pwmia pwm input a. a pply one pwm signal on this pin for brightness control. this signal is uniform and filtered at pwmoa pin. 5 pwmib pwm input b. a pply the other pwm signal on this pin for brightness control. this signal is uniform and filtered at pwmob pin. 6 en on/off control. hold en pin low to turn off part, high to turn of part. 7 fset pwm dimming frequency programmer. connect a capacitor from this pin to gnd to set the pwm-dimming frequency as the formula, f pwm (hz) = 16176 / c fset (nf) 8 pwmob pwm filtered output b. connect a capacitor from this pin to gnd. 9 pwmoa pwm filtered output a. connect a capacitor from this pin to gnd. 10,14 gnd ground. 11 ovp over-voltage protection. connect a resistor di vider from output to this pin to adjust the ovp threshold. when this pin voltage reache s the shutdown threshold 0.9v, the switch turns off. 12 led led current input. open-drain output of an internal dimming control switch. connect the led cathode to this pin. 13 iset led current set. this pin is the source output of an internal dimming control switch. the mp3308 regulates the voltage across the current setting resistor. tie a current-setting resistor from this pin to ground. regulates the voltage to 200mv.
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 5 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics operation frequency vs. temperature quiescent current vs. temperature v(iset) vs. temperature v(ovp) vs. temperature 198.000 199.000 200.000 201.000 202.000 203.000 204.000 -50 0 50 100 150 0.875 0.878 0.881 0.884 0.887 0.890 0.893 -50 0 50 100 150 800 810 820 830 840 850 860 870 880 890 900 -50 0 50 100 150 2 2.05 2.1 2.15 2.2 2.25 2.3 2.35 2.4 2.45 2.5 -50 0 50 100 150
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 6 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics v in =5v, 3 leds in series, 9 strings parallel, 120ma/string, unless otherwise noted. v sw 5v/div. v out 5v/div. v in 5v/div. i l 500ma/div. v sw 5v/div. v out 5v/div. v en 5v/div. wled current 100ma/div. steady state operation en power on v sw 5v/div. v out 5v/div. v in 5v/div. wled current 100ma/div. v sw 5v/div. v out 5v/div. v en 5v/div. wled current 100ma/div. v in power on en shut down 3 3.5 4 4.5 5 5.5 6 6.5 20 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180 20 40 60 80 100 120 140 160 180 efficiency led current (ma) led current (ma) v in (v) pwmia/b duty cycle pwmia duty cycle pwmib duty cycle efficiency vs. v in pwmia dimming duty vs. wled current pwmib dimming duty vs. wled current pwmia*dpwmib vs. wled current v sw 5v/div. v out 5v/div. v in 5v/div. wled current 100ma/div. v in shut down
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 7 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics (continued) v sw 10v/div. v out 5v/div. v led 5v/div. i out 1a/div. wled current 100ma/div. short protection v sw 5v/div. pwmib 5v/div. pwmia 5v/div. v sw 5v/div. v out 5v/div. wled current 200ma/div. open load protection
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 8 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. functional block diagram control logic enable& dimming generator iset led pwmia pwmib sw gnd osc iset current sense amplifier pwm comparator error amplifier pwmoa pwmob fset en enable for blocks ovp 0.9v regulator in dual pwm dimming control m2 m1 ovp comparator power for blocks figure 1?functional block diagram
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 9 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation the mp3308 uses a constant-frequency peak- current?mode boost-regulator architecture to regulate multiple strings of white leds connected in series. at the start of each oscillator cycle, the control circuitry turns on the mosfet. a stabilizing ramp at the output of the current sense amplifier prevents sub-harmonic oscillations at duty cycles greater than 50 percent?this output feeds into the positive input of the pwm comparator. when this voltage equals the output voltage of the error amplifier the power mosfet turns off. the error amplifier compares the difference between the 200mv reference voltage and the feedback voltage. if the feedback voltage drops, the output of the error amplifier increases, resulting in more current flowing through the power mosfet and increasing the power delivered to the output, thus regulating the output. dual pwm dimming can adjust led brightness. true pwm dimming allows for flexible control of the backlighting luminance to improve visibility for a wide range of ambient brightness. a capacitor on the fset pin sets the pwm dimming frequency with a duty cycle of: pwmia pwmib dd where d pwmia is the duty cycle on the pwmia pin, and d pwmib is the duty cycle on the pwmib pin. external capacitors on the pwmoa and the pwmob pins smooth the pwm signals to provide dc signals by selecting the proper time constant. mp3308 provides over-voltage protection, which will shut off the mp3308 if the output voltage goes too high. ovp pin senses the output voltage through the tap of a resistor divider between v out and gnd. in the case of an led failure, the feedback voltage goes to zero and the part will run at maximum duty cycle. the output voltage then rises and triggers ovp if the ovp pin exceeds 1.23v. mp3308 also provides short-circuit protection in cases where individual leds on a string or a whole led string shorts: this condition causes the iset pin to pull high. if the voltage exceeds 0.4v for more than 240s, mp3308 will shutdown.
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 10 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information vin en pwmb c1 c2 l1 b0530 d1 c3 160k r3 10k r4 ns c6 led+ led- nc c5 100k r11 0.1 c4 100 r5 jp1 1 r1 ns r2 68nf c8 68nf c9 10nf c7 100k r10 100k r9 pwma bias 10k r6 10k r7 10k r8 pwmob 8 pgnd 2 led 12 fset 7 pwmia 4 sw 1 gnd 10 iset 13 in 3 en 6 gnd 14 ovp 11 pwmoa 9 pwmib 5 u1 mp3308 33nf c10 figure 2?typical application driving 9 strings of 3 wleds figure 2 shows a typical application circuit that can drive up to nine strings of three white leds with an output of 9v/180ma. a 4.7f output capacitor is sufficient for most applications. a 3.3h inductor with low dc inductor resistance (dcr) will improve efficiency. two 4.7 f ceramic capacitors provide sufficient input decoupling. use schottky diodes with fast recovery for high frequencies, and rated for a 500ma peak inductor current. an internal soft-start limits i in at startup and i out overshoot. the ramped voltage added to the current sense amplifier reduces the maximum output current as the duty cycle increases. as more leds are added, the output voltage rises but the maximum current delivered to the load falls as well. setting the led current the resistor r1 sets the led current, where the current value is given by: led 200mv i r1 = table 1 pairs resistor values with an 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 pwm dimming requires the application of square waves to both the pwmia and the pwmib pins. a capacitor on the fset pin sets the pwm dimming frequency according to the equation: f pwm (hz) = 16176 / c fset ( n f) , for c fset =10nf, the f pwm is set to 1.6khz. the recommended f pwm range is 50hz to 50khz. the minimum recommended amplitude of the pwm signal is 2v. external capacitors on both pwmoa and pwmob, together with internal 100k ? resistors filter the square waveform to provide a dc value. the time constant should be ten times greater than a pwm waveform cycle: pwm rc 10 t >?
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 11 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. selecting the inductor the inductor forces a higher output voltage driven from a lower input voltage. a larger inductor value results in less ripple current, a lower peak inductor current, and reduces stress on the internal n-channel mosfet. however, larger-value inductor has a larger physical footprint, higher series resistance, and lower saturation current. choose an inductor that does not saturate under the worst-case load conditions. calculate the required inductance value using the following equations: 2 out sw load v d(1d) l 2 f i ? in out v d1 v =? where v in and v out are the input and output voltages, f sw is the switching frequency, i load is the led load current, and is the efficiency. over-voltage protection open load protection will shut off the mp3308 if the output voltage reaches over-voltage protection (ovp) threshold. led failures will result in the feedback voltage falling to zero, which will cause the part to run at maximum duty cycle and boost the output voltage. if the output voltage exceeds the adjusted ovp threshold: + ov r2 v=0.9v(1 ) r3 , the mp3308 will shut down and will not remain off until the power cycles. layout considerations layout requires special consideration to avoid electromagnetic interference from the high- frequency switching path. the high-frequency ripper current in the loop from the sw pin, through the output diode, and output capacitor to gnd requires a connection loop that is as short as possible. the in pin must be locally bypassed, with a highly-recommended rc filter to eliminate noise. see figure 3 for an example of this circuit. vin c1 c2 l1 b0530 d1 0.1 c4 100 r5 jp1 bias pgnd 2 led 12 sw 1 iset 13 in 3 gnd 14 u1 mp3308 figure 3?input bias filtering
mp3308 ? step-up white led driver with dual pwm dimming input control mp3308 rev. 1.02 www.monolithicpower.com 12 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical application circuits vin en pwmb c1 c2 l1 b0530 d1 c3 160k r3 10k r4 ns c6 led+ led- nc c5 100k r11 c4 100 r5 jp1 1 r1 ns r2 68nf c8 68nf v in bias circuit c9 10nf c7 100k r10 100k r9 pwma bias 10k r6 10k r7 10k r8 pwmob 8 pgnd 2 led 12 fset 7 pwmia 4 sw 1 gnd 10 iset 13 in 3 en 6 gnd 14 ovp 11 pwmoa 9 pwmib 5 u1 mp3308 33nf c10 led+ 900 r12 d2 bias led+ bias figure 4? driving 27 wleds (9 wleds in series and 3 strings paralleled) with 3v-3.3v input voltage 1 (1) use additional bias circuit for low input voltage compatibility.
mp3308 ? step-up white led driver with dual pwm dimming input control 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. mp3308 rev. 1.02 www.monolithicpower.com 13 7/19/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information qfn14 (3x4mm) side view top view 1 14 87 bottom view 2.90 3.10 1.60 1.80 3.90 4.10 3.20 3.40 0.50 bsc 0.18 0.30 0.80 1.00 0.00 0.05 0.20 ref 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) jedec reference is mo-229, variation vged-4. 5) drawing is not to scale . pin 1 id see detail a 3.30 0.70 pin 1 id option b r0.20 typ. pin 1 id option a 0.30x45 o typ. detail a 0.30 0.50 pin 1 id index area

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