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mp24894 step-down wled-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 1 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. the future of analog ic technology description the mp24894 is a high-efficiency step-down controller. it is designed to operate in continuous current mode (ccm) to power leds of high-brightness with a wide input voltage range of 6v to 60v. the mp24894 employs a hysteretic control architecture that accurately regulates led current with a feedback coming from an external high-side current-sense resistor. this control scheme optimizes circuit stabilization and fast response time without loop compensation. its low 200mv average feedback voltage reduces power loss and improves the converter?s efficiency. the mp24894 implements pwm and analog dimming together through the en/dim pin. the mp24894 includes thermal overload protection in case of output overload. the mp24894 is available in tsot6 package. features ? wide 6v to 60v input range ? able to drive >1a led load ? hysteresis control ? high efficiency (>95%) ? 2500:1 pwm dimming ratio ? open led protection ? short led protection ? thermal shutdown applications ? low voltage halogen replacement ? low voltage general illumination ? automotive/decorative led lighting ? signs/emergency lighting ? led backlighting 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 6v-60v v in c in r sense mp24894 in rs dr gnd vcc en/dim d1 l1
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 2 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. ordering information part number* package top marking MP24894GJ tsot6 acg * for tape & reel, add suffix ?z (e.g. MP24894GJ?z); package reference 2 1 34 5 6 in rs en/dim gnd dr vcc tsot6 absolute maxi mum ratings (1) v in .................................................-0.3v to +65v v rs ..............................................(v in - 5v) to v in all other pins ...............................-0.3v to +6.5v continuous power dissipation (t a = 25c) (2) tsot6 ..................................................... 1.25w junction temperature ...............................150c lead temperature ....................................260c storage temperature............... -65c to +150c recommended operating conditions (3) supply voltage v in ..............................6v to 60v operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc tsot6 ..................................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 powe r 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 circ uitry 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.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 3 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. electrical characteristics v in = 24v, t a = 25c, unless otherwise noted. parameter symbol condition min typ max units input voltage v in 6 60 v shutdown supply current i sd 80 108 a quiescent supply current i q no switching 0.3 0.5 ma vcc voltage vcc v en/dim = 3.5v 5.5 6 v feedback average voltage (with respect to v in ) v in -v rs v en/dim = 3.5v 194 200 206 mv feedback reference voltage hysterisis v fb_hys 30 mv en/dim enable high voltage v en_high v en rising 0.29 0.34 v en/dim enable hysterisis v en_hys 20 50 80 mv en/dim pull-up current pull up to 5v 2.8 a en/dim pull-down current pull down to gnd 25 a min recommended pwm dimming frequency f pwmmin 0.1 khz max recommended pwm dimming frequency f pwmmax 20 khz gate driver source resistor r_ source v gs = 5.5v 6 ? gate driver sink resistor r_ sink 2 ? gate driver output-voltage high v oh i drv = 10ma 5.5 v gate driver output-voltage low v ol i drv = 10ma 0.5 v minimum on time t on_min guarantee by designer 100 ns minimum off time t off_min guarantee by designer 100 ns recommended maximum operating frequency f max 1 mhz uvlo threshold voltage(vcc) v uvloth vcc rising 5.6 v uvlo hysteresis v uvlohys 0.4 v thermal shutdown threshold temp rising 150 c thermal shutdown hysteresis guarantee by designer 20 c
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 4 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical characteristics vcc uvlo vs. temperature en uvlo vs. temperature vcc voltage vs. temperature feedback reference voltage peak feedback reference voltage valley vcc voltage (v) feedback reference voltage valley (v) feedback reference voltage peak (v) vcc uvlo (v) en uvlo (v) 6 6.05 6.1 6.15 6.2 6.25 6.3 6.35 6.4 6.45 -50 0 50 100 150 5.64 5.65 5.66 5.67 5.68 5.69 5.7 5.71 -50 0 50 100 150 0.278 0.279 0.28 0.281 0.282 0.283 0.284 0.285 0.286 0.287 0.288 -50 0 50 100 150 168.4 168.6 168.8 169.0 169.2 169.4 169.6 -50 0 50 100 150 226.0 226.2 226.4 226.6 226.8 227.0 227.2 -50 0 50 100 150
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 5 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics performance waveforms are tested on the evaluation board of the design example section. v in = 24v, 3leds, i out = 1a, t a = 25c, unless otherwise noted. steady state input power on input power off en power on en power off short led+ to led- protection 60 65 70 75 80 85 90 95 100 10 20 30 40 50 60 efficiency v sw 20v/div. v gate 5v/div. i l 500ma/div. v sw 20v/div. v in 10v/div. i led 1a/div. v en 5v/div. v sw 20v/div. v in 10v/div. v en 5v/div. i led 1a/div. v sw 20v/div. v gate 5v/div. v en 5v/div. i led 1a/div. v sw 20v/div. v gate 5v/div. v en 5v/div. i led 1a/div. v sw 20v/div. v gate 5v/div. v en 5v/div. i led 1a/div. v sw 20v/div. v gate 5v/div. v en 5v/div. i led 1a/div. v sw 20v/div. v gate 5v/div. v led- 10v/div. i l 1a/div.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 6 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. typical performanc e characteristics (continued) performance waveforms are tested on the evaluation board of the design example section. v in = 24v, 3leds, i out = 1a, t a = 25c, unless otherwise noted. open led load protection open led load recovery v sw 20v/div. v gate 5v/div. v en 5v/div. i l 1a/div. v sw 20v/div. v gate 5v/div. i l 1a/div. short led+ to led- recovery v sw 20v/div. v gate 5v/div. v led- 10v/div. i l 1a/div.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 7 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. pin functions tsot6 pin# name description 1 in input supply pin. connect a decoupling capacitor from in pin to gnd. 2 rs led current sense input. connect a current-sen se resistor that programs led average current to the in pin. 3 en/dim enable/dimming command input. a voltage great er than 0.3v turns on the chip. to use pwm dimming, apply a square wave signal to this pin. if diming-off time is larger than 20ms, the ic shuts down. for analog dimming, the en/dim pin voltage rises from 0.3v to 2.7v and led current will change from 20% to 100% of the maximum led current. 4 gnd ground. 5 dr gate-driver output. connect this pin to the gate of the external mosfet. 6 vcc internal regulator output. connect a 1 f decoupling cap from this pin to ground.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 8 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. functional block diagram c vcc uvlo regulator in 1.18v reference en/dim 0.29v buffer 1.18v thermal shutdown rs pwm driver vcc enable dr c in in rsense d l r1 r2 figure 1?mp24894 functional block diagram
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 9 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. operation steady state the mp24894 is a step-down led-current controller with hysteresis control that is easily configured for a wide input that ranges from 6v to 60v input. the mp24894 uses a high-side current-sense resistor to detect and regulate led current. the voltage across the current- sense resistor is measured and regulated in the 200mv30mv range. the internal 1.18v reference voltage provides a 0.3v reference to enable the part. when v en >0.3v, the output of the comparator goes high and enables the other blocks. the mp24894 also provides a 5v pull-up voltage as current reference voltage when en/dim pin is float. the inductor current is sensed through the high-side resistor, r sense . when the switch is on, r2 (see figure 1) is shorted and inductor current upper-threshold is fixed by r1. when the switch is off, inductor current lower-threshold is fixed by r1 and r2. the ratio of r1 and r2 determines the current hysteresis. system soft start the voltage on the en/dim pin provides the inductor current reference. an external capacitor from the en/dim pin to ground provides a soft-start delay. when v in starts, internal voltage source charges the capacitor from 0v to 5v to fulfill soft-start function. dimming control the mp24894 allows the en/dim pin to control both analog and pwm dimming. whenever the voltage on dim is less than 0.25v, the chip turns off. for analog dimming, when the voltage on dim is from 0.3v to 2.7v, the led current will change from 20% to 100% of the maximum led current. if the voltage on en pin is higher than 2.9v, output led current will equal the maximum led current. for pwm dimming, the signal amplitude must exceed 3v. choose a pwm frequency in range of 100hz to 20khz for good dimming linearity.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 10 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. application information setting the led current the led current is identical and set by the current sense resistor between the in pin and rs pin. r sense =200mv/i led for r sense =0.2 ? , the led current is set to 1a selecting the inductor lower value of inductance can result in a higher switching frequency, which causes a larger switching loss. choose a switch frequency between 100khz to 600khz for most application. according to switching frequency, inductor value can be estimated as: out out in led sw v (1- ) v v l 0.3 i f = for higher efficiency, choose an inductor with a dc resistance 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. choose a capacitor value between 10f and 22f for most applications. the voltage rating should be greater than the input voltage. use a low esr capacitor for input decoupling. selecting the output capacitor for most applications, the output capacitor is not necessary. for applications that require that the peak-to-peak led ripple current falls below 30% of the average current, add a capacitor across the leds. higher capacitor values will result in proportionally lower ripple. a value of 2.2f will meet most requirements. selecting soft-start capacitor when selecting a soft-start capacitor, the delay time can be estimated as 0.2ms/nf. for pwm dimming, select c < 2.2nf to eliminate its effect on the average led current. dimming control mp24894 provides 1:2500 high-ratio pwm dimming. apply a 100hz to 20khz square waveform to the en/dim pin. the average led current is proportional to pwm duty cycle. layout consideration pay careful attention to the pcb layout and component placement. r sense should be placed close to the in pin and rs pin in order to minimize current sense error. the input loop?including input capacitor, schottky diode, and mosfet ?should be as short as possible. design example below is a design example following the application guidelines for the specifications: table 1: design example v in 24v v out 10v iout 1a the detailed application schematic is shown in figure 2. the typical performance and circuit waveforms have been shown in the typical performance characteristics section. for more device applications, please refer to the related evaluation board datasheets.
mp24894 ? step-down led-current controller with wide 6v to 60v input voltage mp24894 rev 1.01 www.monolithicpower.com 11 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. en/dim vin+ 0 r3 100v c2 100v ns r2 l1 50v c4 vcc vin- mp24894 0.2 r1 10v c3 ns c5 c1 am4499n q1 b290 d1 led+ i n 1 r s 2 gn d 4 vcc 6 dr 5 en/dim 3 u1 led- dim dr led- led+ sw vcc vin 0 r4 figure 2: application circuit
mp24894 ? step-down led-current controller with wide 6v to 60v 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. mp24894 rev 1.01 www.monolithicpower.com 12 12/20/2012 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2012 mps. all rights reserved. package information tsot6 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 1 3 4 6 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 (botto m of leads after forming) shall be 0.10 millimeters max. 5) drawing conforms to jedec mo-193, variation ab. 6) drawing is not to scale. 7) pin 1 is lower left pin when reading top mark from left to right, (see example top mark) 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 aaaa pin 1 see note 7 example top mark

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