mp24892 step down white led driver with wide 6v ? 45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 1 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. the future of analog ic technology description the mp24892 is a high-efficiency step-down converter that functions in continuous current mode to drive high-brightness led. it can take a wide input voltage range of 6v?45v. the mp24892 employs a hysteretic control architecture to regulate a high-accuracy led current, which is measured through an external high-side current-sensing resistor. moreover, this control scheme provides optimal circuit stabilization and a very quick response time without loop compensation. its low 202mv average feedback voltage reduces power loss and improves the converter efficiency. the mp24892 implements pwm and analog dimming together through the dim pin. the mp24892 includes thermal overload protection that prevents damage in the event of an output overload. the mp24892 is available in a small tsot23-5 package. features ? wide 6v-to-45v input range ? 1a output current ? high efficiency (>95%) ? hysteresis control ? pwm & analog dimming ? 1000:1 pwm dimming resolution ? thermal shutdown ? inherent open led protection ? short led protection ? available in a tsot23-5 package applications ? low-voltage halogen replacement ? low-voltage general illumination ? automotive/decorative led lighting ? signs/emergency lighting ? led backlighting a ll mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under the products, qualit y a ssurance page. ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application v in r 45 sense d1 l1 in c in rs sw en/dim gnd mp24892
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 2 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. ordering information part number package top marking MP24892DJ * tsot23-5 abhy * for tape & reel, add suffix ?z (e.g. MP24892DJ?z); package reference tsot23-5 absolute maxi mum ratings (1) v in , v sw ......................................... -0.3v to +50v v rs .................................................. v in -5v to v in all other pins ............................... -0.3v to +6.3v continuous power dissipation (t a = +25c) (2) tsot23-5 ................................................ 1.25w junction temperature ............................... 150 ? c lead temperature .................................... 260 ? c storage temperature ............... -65 ? c to +150 ? c recommended operating conditions (3) supply voltage v in .............................. 6v to 45v maximum junction temp. (t j ) -40c to +125c thermal resistance (4) ja jc tsot23-5 ............................. 100 ..... 55 ... ? 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.
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 3 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. electrical characteristics v in = 24v, t a = +25 ? c, unless otherwise noted. parameter symbol condition min typ max units input voltage v in 6 45 v shutdown supply current i sd 108 a quiescent supply current i q no switching 1 ma internal reference voltage i ref 1.275 v feedback reference voltage (with respect to v in ) v in -v rs v en/dim = 1.28v 192 202 212 mv feedback reference voltage hysterisis v fb_hys 30 mv en/dim max. dimming voltage v dim max 2.56 v en/dim mim. dimming voltage v dim min 0.3 v en/dim enable high voltage v en high v en rising 0.25 0.3 v en/dim enable hysteresis v en hys 20 50 80 mv en/dim pull-up resistor r en 45 k ? recommended pwm dimming frequency f pwm 0.1 2 khz switch on resistance r ds on 0.5 ? minimum on time t on min 100 ns minimum off time t off min 100 ns recommended maximum operating frequency f max 600 khz recommended duty cycle range at f max d 30 70 % start-up time t ss external capacitor on dim pin is 4.7nf 0.3 ms
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 4 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. pin functions tsot23-5 pin# name description 1 sw internal mosfet drain. connecting the common terminal of inductor and anode of schottky to this pin. 2 gnd ground. 3 en/dim enable/dimming. apply a square wave sign al for pwm dimming (refer to application information). apply a 0.3v ? 2.5v dc voltage for analog dimming. the dc voltage linearly controls the led current range from 25% to 200% . turn off the output current when pulling this pin below 0.2v. connect a 1nf ? 10nf capacitor for normal operation (v en/dim =1.28v). 4 rs led current sense input. connect the current sense resistor to this pin. 5 in input supply. connect an appropriate de coupling capacitor from in pin to gnd.
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 5 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. typical performanc e characteristics v in =30v, 3 led s in series, i out =550ma, unless otherwise noted. efficiency (%) input voltage (v) efficiency vs. input voltage analog dimming curve 0 0.2 0.4 0.6 0.8 1 1.2 0 0.5 1 1.5 2 2.5 3 analog dim (v) output current (a) iled vs. rset 0 0.2 0.4 0.6 0.8 1 1.2 0.1 0.3 0.5 0.7 0.9 1.1 iled(a) v sw 10v/div. i led 200ma/div. steady state v sw 20v/div. v in 20v/div. i led 500ma/div. vin startup v sw 20v/div. v en 1v/div. en signal 2v/div. i led 500ma/div. ven startup v sw 20v/div. pwm signal 2v/div. i led 500ma/div. pwm dimming f pwm = 200hz, d pwm = 50% v sw 20v/div. v led+ 10v/div. i led 200ma/div. open led protection open leds at working v sw 20v/div. v led- 10v/div. i led 200ma/div. short led protection short leds at working 70 75 80 85 90 95 100 10 15 20 25 30 35 40 45 function diagram
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 6 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. figure 1: mp24892 functional block diagram
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 7 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. operation steady state the mp24892 is a hysteretic-controlled step- down led driver that is easily configured for various applications with an input range of 6v? 45v. the converter employs a high-side current sensing resistor to detect and regulate the led current. the voltage across the current sensing resistor is kept measured and regulated in 202mv30mv range. the internal 1.275v reference voltage provides a 0.2v reference to enable the part and a 1.275v pull-up voltage as the current reference. when v en >0.2v, the output of the comparator goes high and the other blocks are enabled. output current is sensed through a high-side resistor, r sense . when the switch turns on, the internal resistor r2 shorts out and r1 determines the output current upper-threshold. when the switch is off, r1 and r2 determine the output current lower-threshold. the ratio of r1 and r2 determines the current hysteresis. enable control once the input voltage is applied, a 2a current is sourced out from en/dim pin. if en/dim is left open, the ic will automatically start up to the maximum brightness. applying a capacitor on this pin programs a soft start time. applying an external voltage in the range of 0.2v to 1.25v to this pin linearly controls the current sensing voltage reference from 0mv to 202mv for analog dimming. applying an external pwm signal with an amplitude of approximately 1.25v to this pin enables pwm dimming. for more on the flexible external pwm dimming method, please refer to the selecting dimming control mode section. system soft-start the voltage on the en/dim pin functions as the inductor current reference. an external capacitor from the en/dim pin to ground provides a soft- start delay. when v in starts, the internal voltage source charges the capacitor from 0v to 1.25v. dimming control mp24892 provides two dimming methods: pwm dimming and dc analog dimming. to use pwm dimming, apply a square wave to the en/dim pin. to use analog dimming, apply a 0.3v?2.5v dc voltage to this pin.
mp24892 ? step down wled driver with wide 6v?45v input voltage mp24892 rev. 1.0 www.monolithicpower.com 8 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. application information setting the led current the led current is set by the current sense resistor between the in pin and rs pin. r sense =202mv/i led for r set =0.36 ? , the led current is set to 550ma selecting the inductor a lower inductance value results in a higher switching frequency, which causes greater switching losses. select a switching frequency between 200khz to 600khz for most application. estimate the inductor value using the equation below, where f sw is the switching frequency: out out in led sw v (1- ) v v l 0.3 i f ? ? ?? for higher efficiency, select an inductor with the lowest dc resistance possible. selecting the diode the output diode supplies current to the inductor when the internal mosfet is off. to reduce losses due to diode forward voltage and recovery time, use a schottky diode rated for a reverse voltage greater than the input voltage. the average current rating must exceed the maximum expected load current, and the peak current rating must exceed the peak inductor current. selecting the input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. use a 10f?22f capacitor with a voltage rating that exceeds the input voltage for most applications. select a capacitor with low esr. selecting the output capacitor an output capacitor is not necessary for most applications, but if the peak-to-peak ripple led current must be less than 30% of the average current, add a capacitor across the leds. the ripple current is inversely proportional to the capacitor value. use a 2.2f capacitor for most applications. selecting soft-start capacitor the delay time can be estimated as 0.2ms/nf with the soft-start capacitor. in pwm dimming, use a capacitor c in <2.2nf to eliminate its effect on the led average current. selecting dimming control mode mp24892 provides two dimming methods: dc analog dimming and pwm dimming. 1. dc analog dimming mode apply a 0.3v-to-2.5v dc voltage to the en/dim pin. this voltage linearly changes the inductor current reference the inductor current range from 25% to 200%. (see figure 2) en/dim vin r6 0 c5 1nf 3 6 5 2 in gnd gnd en/dim mp24892 tp4 figure 2: analog dimming external circuit 2. pwm dimming mode apply a 100hz-to-2khz square waveform to the en/dim pin. the average led current is proportional to pwm duty cycle. because this pin is pulled up by the 1.25v internal source as the inductor current reference, use an npn-transistor on/off circuit to separate the pwm signal from the current reference (see figure 2). the minimum amplitude of the pwm signal is 1.5v. en/dim vin r6 nc r4 10k r7 10k q1 r5 ns c5 1nf 3 6 5 2 in gnd gnd en/dim mp24892 tp4 figure 3: pwm dimming external circuit layout consideration pay close attention to the pcb board layout and component placement. place r sense close to the in and rs pins to minimize the set current error. the input loop?including the input capacitor, the schottky diode, and the internal mosfet? should be as short as possible.
mp24892 ? step down wled driver with wide 6v?45v input voltage notice: the information in this document is subject to change wi thout notice. users should warrant and guarantee that third party intellectual property rights are not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp24892 rev. 1.0 www.monolithicpower.com 9 11/3/2011 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2011 mps. all rights reserved. package information tsot23-5 0.30 0.50 seating plane 0.95 bsc 0.84 0.90 1.00 max 0.00 0.10 top view front view side view recommended land pattern 2.80 3.00 1.50 1.70 2.60 3.00 13 4 5 0.09 0.20 note: 1) all dimensions are in millimeters . 2) package length does not include mold flash , protrusion or gate burr. 3) package width does not include interlead flash or protrusion. 4) lead coplanarity (bottom of leads after forming ) shall be 0.10 millimeters max. 5) drawing conforms to jedec mo-193, variation aa. 6) drawing is not to scale . 0.30 0.50 0 o -8 o 0.25 bsc gauge plane 2.60 typ 1.20 typ 0.95 bsc 0.60 typ see detail "a" detail ?a?
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