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| mp3384 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 1 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. the future of analog ic technology description the mp3384 is a step-up converter with 4-channel current sources designed for driving the white led arrays for large size lcd panel backlighting applications. the mp3384 uses current mode, fixed frequency architecture. the switching frequency can be selected at 1.25mhz or 625khz. it generates an output voltage up to 50v from a 4.5v to 25v input supply. the mp3384 independently r egulates the current in each led string to the user programmed value set by an external current setting resistor. the mp3384 applies 4 internal current sources to achieve a current balance of 2.5% regulation accuracy between strings. its low 600mv regulation voltage on led current sources reduces power loss and improves efficiency. the mp3384 includes under voltage lockout, current limiting, over voltage, short led, open led and thermal shut-down protection. the mp3384 is available in small qfn16 (3mmx 3mm) package. features ? high efficiency and small size ? 4.5v to 25v input voltage range ? 50v maximum step-up voltage ? balanced driver for 4 strings of wled ? 2.5% current matching accuracy between strings ? selectable switching frequency: 1.25mhz or 625khz ? pwm dimming ? programmable over-voltage protection ? under voltage lockout ? open and short led protection ? thermal shutdown ? small 16-pin qfn (3mm x 3mm) applications ? notebook pc ? netbook pc ? digital picture frames ? handy terminals display ? automotive system and tablet computer all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under quality assurance. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithi c power systems, inc. typical application
mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 2 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. ordering information part number* package top marking MP3384EQ qfn16 (3mm x 3mm) 5s * for tape & reel, add suffix ?z (e.g. MP3384EQ?z). for rohs compliant packaging, add suffix ?lf (e.g. MP3384EQ?lf?z) package reference top view exposed pad connect to pin 12 pin 1 id en osc iset gnd pgnd nc ovp led4 1 2 3 4 13 14 15 16 8 7 6 5 led3 led2 led1 pwm sw comp vcc vin 12 11 10 9 absolute maxi mum ratings (1) v in .................................................-0.3v to +30v v sw , v led1 to v led4 ............................-1v to +50v all other pins ..................................-0.3v to +6v continuous power dissipation (t a = +25c) (2) ??????????????????....2.1w junction temperature ...............................150 c lead temperature ....................................260 c storage temperature............... -65 c to +150 c recommended operating conditions (3) supply voltage v in ...........................4.5v to 25v max led current/string............................ 40ma operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc qfn16 (3mm x 3mm) ...........60 ...... 12 ... 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 power 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 operation conditions. 4) measured on jesd51-7, 4-layer pcb. mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 3 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. electrical characteristics v in =12v, v en = 5v, t a = +25 c, unless otherwise noted. parameters symbol condition min typ max units operating input voltage v in 4.5 25 v supply current (quiescent) i q v in =12v, v en =5v, no load. 1.8 ma supply current (shutdown) i st v en =0v, v in =12v 2 a ldo output voltage v cc v en =5v, 6v mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 5 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. pin functions pin # name description 1 en enable control input. do not let this pin floating. 2 osc switching frequency selection input. when float this pin or connect this pin to vcc, the step-up converter switching frequency is 1.25 mhz. when connect this pin to gnd, the step-up converter switching frequency is 625khz. 3 iset led current setting. tie a current setting resistor from this pin to ground to program the current in each led string. i led = 1000 x 1.21v / r set 4 gnd analog ground. 5 pwm pwm signal input. the logic signal on this pin controls the pwm burst mode dimming frequency and duty cycle. 6 led1 led string 1 current input. this pin is the ope n-drain output of an internal dimming control switch. connect the led string 1 cathode to this pi n. if this string is not used, connect vout to this pin. 7 led2 led string 2 current input. this pin is the ope n-drain output of an internal dimming control switch. connect the led string 2 cathode to this pi n. if this string is not used, connect vout to this pin. 8 led3 led string 3 current input. this pin is the ope n-drain output of an internal dimming control switch. connect the led string 3 cathode to this pi n. if this string is not used, connect vout to this pin. 9 led4 led string 4 current input. this pin is the ope n-drain output of an internal dimming control switch. connect the led string 4 cathode to this pi n. if this string is not used, connect vout to this pin. 10 ovp over-voltage protection input. connect a resistor divider from output to this pin to program the ovp threshold. when this pin voltage reac hes 1.23v, the mp3384 triggers ov protection mode. 11 nc no connect. 12 pgnd step-up converter power ground. connect exposed pad to pgnd. 13 sw step-up converter power switch output. sw is the drain of the internal mosfet switch. connect the power inductor and output rectifier to sw. sw can swing between gnd and 50v. 14 comp step-up converter compensation pin. this pin is used to compensate the regulation control loop. connect a capacitor or a series rc network from comp to gnd. 15 vcc the internal 5v linear regulator output. vcc provides power supply for the internal mosfet switch gate driver and the internal co ntrol circuitry. bypass vcc to gnd with a ceramic capacitor. if vin is less than 5.5v, apply an external 5v supply directly on vcc. 16 vin supply input. vin supplies the power to the mp3384 chip. drive vin with a 4.5v to 25v power source. must be locally bypassed. mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 6 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical performanc e characteristics v in =12v, 10 leds in series, 4 strings parallel, 20ma/string, unless otherwise noted. v sw 20v/div. v led1 500mv/div. v out /ac 500mv/div. i led 50ma/div. v sw 20v/div. v in 5v/div. v out 20v/div. i led 50ma/div. v sw 20v/div. v pwm 5v/div. v out 20v/div. i led 50ma/div. v sw 20v/div. v out 20v/div. i led 50ma/div. v sw 20v/div. v out 20v/div. i led 50ma/div. v sw 20v/div. v led1 20v/div. v out 20v/div. i led 50ma/div. v sw 20v/div. v en 5v/div. v out 20v/div. i led 50ma/div. steady state v in startup v en startup pwm dimming f pwm =200hz, d pwm =50% open led protection open all led strings at working short led protecton short v out to led1 at working efficiency (%) efficiency vs. input voltage 50 60 70 80 90 100 0 5 10 15 20 25 30 input voltage (v) mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 7 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. function diagram figure 1?mp3384 function diagram mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 8 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. operation the mp3384 employs a constant frequency, peak current mode step-up converter and 4-channels regulated current sources to regulate the array of 4 strings white leds. the operation of the mp3384 can be understood by referring to the block diagram of figure 1. internal 5v regulator the mp3384 includes an internal linear regulator (vcc). when vin is greater than 5.5v, this regulator offers a 5v power supply for the internal mosfet switch gate driver and the internal control circuitry. the vcc voltage drops to 0v when the chip shuts down. in the application of vin lower than 5.5v, tie vcc and vin together. the mp3384 features under voltage lockout. the chip is disabled until vcc exceeds the uvlo threshold. and the hysteresis of uvlo is approximately 200mv. system startup when the mp3384 is enabled, the chip checks the topology connection first. the chip monitors the ovp pin to see if the schottky diode is not connected. if the ovp voltage is lower than 70mv, the chip will be disabled. the mp3384 will also check other safety limits, including uvlo and otp after the ovp test is passed. if they are all in function, it then starts boosting the step-up converter with an internal soft-start. it is recommended on the start up sequence that the enable signal comes after input voltage and pwm dimming signal established. step-up converter the converter operation frequency is selectable (1.25mhz or 625khz), which is helpful for optimizing the external components sizes and improving the efficiency. at the beginning of each cycle, the power fet is turned on with the internal clock. 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 pwm comparator. when this result voltage reaches the output voltage of the error amplifier (v comp ) the power fet is turned off. the voltage at the output of the internal error amplifier is an amplified signal of the difference between the 600mv reference voltage and the feedback voltage. the converter automatically chooses the lowest active ledx pin voltage for providing enough bus voltage to power all the led arrays. if the feedback voltage drops below the 600mv reference, the output of the error amplifier increases. it results in more current flowing through the power fet, thus increasing the power delivered to the output. in this way it forms a close loop to make the output voltage in regulation. at light-load or vout near to vin operation, the converter runs into the pulse-skipping mode, the fet is turned on for a minimum on-time of approximately 100ns, and then the converter discharges the power to the output in the remnant period. the fet will keep off until the output voltage needs to be boosted again. dimming control the mp3384 provides pwm dimming mode with external pwm signal on pwm pin. the method results in pwm chopping of the current in the leds for all 4 channels to provide led control. the brightness of the led array is proportional to the duty cycle of the pwm signal. open string protection the open string protection is achieved through the over voltage protection. if one or more strings are open, the respective ledx pins are pulled to ground and the ic keeps charging the output voltage until it reach ovp threshold. then the part will mark off the open strings whose ledx pin voltage are less than 180mv. once the mark-off operation completes, the remaining led strings will force the output voltage back into tight regulation. the string with the highest voltage drop is the ruling string during output regulation. the mp3384 always tries to light at least one string and if all strings in use are open, the mp3384 shuts down the step-up converter. the mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 9 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. part will maintain mark-off information until the part shuts down. short string protection the mp3384 monitors the ledx pin voltage to judge if the short string condition occurs. if one or more strings are short, the respective ledx pins will be pulled up to the boost output and tolerate high voltage stress. if the ledx pin voltage is higher than 5.5v, the short string condition is detected on the respective string. when the short string fault (ledx over-voltage fault) continues for greater than 1.6ms, the string is marked off and disabled. once a string is marked off, its current regulation is forced to disconnect from the output voltage loop regulation. the marked-off led strings will be shut off totally until the part restarts. if all strings in use are short, the mp3384 will shut down the step-up converter. mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 10 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. application information selecting the switching frequency the switching frequency of the step-up converter can be selected to 1.25mhz or 625khz. a bi-level switching frequency selection (osc) input sets the internal oscillator frequency for the step-up converter. when connects osc pin to gnd, the switching frequency is set to 625khz, when floats the osc pin or connects it to vcc, the frequency is set to 1.25mhz. setting the led current the led string currents are identical and set through the current setting resistor on the iset pin. i led = 1000 x 1.21v / r set for r set =60.4k ? , the led current is set to 20ma. the iset pin can not be open. setting the over voltage protection the open string protection is achieved through the over voltage protection (ovp). in some cases, an led string failure results in the feedback voltage always zero. the part then keeps boosting the output voltage higher and higher. if the output voltage reaches the programmed ovp threshold, the protection will be triggered. to make sure the chip functions properly, the ovp setting resistor divider must be set to a proper value. the recommended ovp point is about 1.3 times of the output voltage for normal operation. v ovp =1.23v*(r 1 +r 2 )/r 2 pwm dimming mode the mp3384 provides pwm dimming mode with external pwm signal on pwm pin. an external pwm dimming signal is directly employed to achieve pwm dimming control. apply the 100hz to 2khz pwm dimming signal to pwm pin. the minimum recommended amplitude of the pwm signal is 1.5v (see figure 2). vcc c1 pwm mp3384 pwm dimming 100hz~2khz figure 2? pwm dimming selecting the inductor a 22 h (for 1.25mhz switching frequency) /47uh (for 625khz switching frequency) inductor with a dc current rating of at least 40% higher than the maximum input current is recommended for most applications. for highest efficiency, the inductor?s dc resistance should be as small as possible. selecting the input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. the input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from passing through the input. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. for most applications, a 4.7 f capacitor is sufficient. selecting the output capacitor the output capacitor keeps the output voltage ripple small and ensures feedback loop stability. the output capacitor impedance should be low at the switching frequency. ceramic capacitors with x7r dielectrics are recommended for their low esr characteristics. for most applications, a 2.2 f ceramic capacitor is sufficient. mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 11 1/29/2013 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 mp3384 sw to pgnd pin (u1), output diode (d1), and output capacitor (c3) is flowing with high frequency pulse current, therefore, it must be as short as possible (see figure 3). figure 3?layout consideration the ic exposed pad is internally connected to gnd pin, and all logic signals are referred to gnd. the pgnd should be externally connected to gnd and is recommended to keep away from the logic signals. mp3384- 50v, 4-string white led driver mp3384 rev. 1.01 www.monolithicpower.com 12 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. typical application circuit vin f1 gnd en pwm dim r14 10k c6 nc r4 nc r3 0k c9 0.47uf r7 20k c2 nc r8 nc r15 20k 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 4.5v-25v r5 60.4k d1 dfls160 led+ 10 leds in series 4 strings 20ma/string led4 led3 led2 led1 r2 10k c7 nc r9 nc r1 324k c4 nc r13 0k r12 0k r11 0k r10 0k en osc iset gnd u1 mp3384 pwm led1 led2 led3 led4 ovp nc pgnd sw comp vcc vin figure 4?driving 10 led in series and 4 string led application circuit mp3384- 50v, 4-string white led driver 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. mp3384 rev. 1.01 www.monolithicpower.com 13 1/29/2013 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2013 mps. all rights reserved. package information side view top view 1 16 13 12 9 8 5 4 bottom view 2.90 3.10 1.50 1.80 2.90 3.10 1.50 1.80 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 sh all be 0.10 millimeter max. 4) drawing conforms to jedec mo-220, variation veed-4. 5) drawing is not to scale. pin 1 id see detail a pin 1 id option a 0.30x45 o typ. pin 1 id option b r0.20 typ. detail a pin 1 id index area 0.70 0.30 0.50 |
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