mp2370 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 1 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. the future of analog ic technology description the mp2370 is a monolithic step-down white led driver with a built-in power mosfet. it achieves 1.2a peak output current over a wide input supply range with excellent load and line regulation. current mode operation provides fast transient response and eases loop stabilization. fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. the mp2370 requires a minimum number of readily available standard external components. the mp2370 is available in a tsot23-6 package. features ? 1.2a peak output current ? 0.35 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? also work with cap-less configuration ? up to 87% efficiency ? 0.1 a shutdown mode ? fixed 1.4mhz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.5v to 24v operating input range ? 0.15v sense voltage ? available in a tsot23-6 package applications ? wled drivers ? distributed power systems ? battery charger ? pre-regulator for linear regulators ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application sw fb bst gnd in en 1 6 3 2 4 5 off on efficiency (%) 0.1 60 70 80 90 100 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 output current (a) efficiency vs output current circuit as figure 1 v in =12v v in =20v v in =8v
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 2 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. package reference bst gnd fb 1 2 3 6 5 4 sw in en top view part number* package temperature mp2370dj tsot23-6 ?40 c to +85 c * for tape & reel, add suffix ?z (eg. mp2370dj?z) for rohs compliant packaging, add suffix ?lf (eg. mp2370dj?lf?z) absolute maxi mum ratings (1) supply voltage v in ....................................... 26v v sw ....................................... ?0.3v to v in + 0.3v v bs ....................................................... v sw + 6v all other pins................................. ?0.3v to +6v junction temperature...............................150 c lead temperature ....................................260 c storage temperature ..............?65 c to +150 c recommended operating conditions (2) supply voltage v in ........................... 4.5v to 24v output voltage v out ...................... 0.15v to 15v ambient temperature ................?40 c to +85 c thermal resistance (3) ja jc tsot23-6.............................. 220 .... 110.. c/w notes: 1) exceeding these ratings may damage the device. 2) the device function is not guaranteed outside of the recommended operating conditions. 3) measured on approximately 1? square of 1 oz copper. electrical characteristics v in = 12v, t a = +25 c, unless otherwise noted. parameters symbol condition min typ max units feedback voltage v fb 4.5v v in 24v 0.145 0.155 0.165 v feedback current i fb v fb = 0.15v 0.1 a switch-on resistance (4) r ds(on) 0.35 ? switch leakage v en = 0v, v sw = 0v 10 a current limit (4) 1.8 a oscillator frequency f sw v fb = 0.13v 1.2 1.4 1.7 mhz fold-back frequency v fb = 0v 700 khz maximum duty cycle v fb = 0.13v 87 % minimum on-time (4) t on 100 ns under voltage lockout threshold rising 2.5 2.8 3.1 v under voltage lockout threshold hysteresis 150 mv en input low voltage 0.4 v en input high voltage 1.2 v v en = 2v 2.1 en input current v en = 0v 0.1 a supply current (shutdown) i s v en = 0v 0.1 1.0 a supply current (quiescent) i q v en = 2v, v fb = 0.2v 0.8 1.0 ma thermal shutdown (4) 150 c note: 4) guaranteed by design.
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 3 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. pin functions pin # name description 1 bst bootstrap. a capacitor is connected between sw and bs pins to form a floating supply across the power switch driver. this capacitor is needed to drive the power switch?s gate above the supply voltage. 2 gnd ground. this pin is the voltage reference for t he regulated output voltage. for this reason care must be taken in its layout. this node should be pl aced outside of the d1 to c1 ground path to prevent switching current spikes from inducing voltage noise into the part. 3 fb current sense feedback voltage. its internal threshold is 0.15v. 4 en on/off control input. pull en above 1.2v to turn the device on. 5 in supply voltage. the mp2370 operates from a +4.5 v to +24v unregulated input. input capacitor is needed to prevent large voltage spikes from appearing at the input. 6 sw switch output.
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 4 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. typical performace characteristics circuit as figure 1, v in = 12v, load: one 3 watt white led, unless otherwise noted. enable start up enable turn off steady state operation 40us/div 40us/div 400ns/div v sw 10v/div v en 5v/div i led 0.5a/div v sw 10v/div v en 5v/div i led 0.5a/div v sw 10v/div v out (ac) 20mv/div i inductor 0.5a/div 80 70 90 output short output short entry output short recovery 1us/div 4us/div 4us/div v sw 10v/div v sw 10v/div v sw 10v/div v out 2v/div v out 2v/div i led 0.5a/div i led 0.5a/div i inductor 0.5a/div line regulation v out = 3.3v 400us/div v en 5v/div line regulation v out = 3.3v current limit vs 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.8 1.6 2.0 10 20 40 60 30 50 inductor peak current(a) duty(%) v out 2v/div v sw 10v/div 0.5a/div i led pwm dimming duty(%) 0 20 40 60 80 100 output current(a) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.8 0.7 0.9 i duty cycle
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 5 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. operation the mp2370 is a current mode buck regulator. that is, the ea output voltage is proportional to the peak inductor current. at the beginning of a cycle, m1 is off. the ea output voltage is higher than the current sense amplifier output, and the current comparator?s output is low. the rising edge of the 1.4mhz clk signal sets the rs flip-flop. its output turns on m1 thus connecting the sw pin and inductor to the input supply. the increasing inductor current is sensed and amplified by the current sense amplifier. ramp compensation is summed to the current sense amplifier output and compared to the error amplifier output by the pwm comparator. when the sum of the current sense amplifier output and the slope compensation signal exceeds the ea output voltage, the rs flip- flop is reset and m1 is turned off. the external schottky rectifier diode (d1) conducts the inductor current. if the sum of the current sense amplifier output and the slope compensation signal does not exceed the ea output for a whole cycle, then the falling edge of the clk resets the flip-flop. the output of the error amplifier integrates the voltage difference between the feedback and the 0.15v bandgap reference. the polarity is such that a fb pin voltage lower than 0.15v increases the ea output voltage. since the ea output voltage is proportional to the peak inductor current, an increase in its voltage also increases current delivered to the output. 5 in en fb gnd sw bst 4 3 2 1 6 regulator oscillator 1.4mhz/700khz ramp generator driver current sense amplifier error amplifier current limit comparator pwm comparator d x20 m1 regulator reference ea -- + -- + -- + s r r q -- + 27pf 0.15v 1pf figure 1?functional block diagram
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 6 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. application information setting led current the current sense resistor is inserted between the anode of wled and gnd. the current sense resistor value is calculated as: led i v 15 . 0 1 r = for 1a wled current, choose r1 = 150m ? selecting the inductor a 1h to 10h inductor with a dc current rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor?s dc resistance should be less than 200m ? . refer to table 2 for suggested surface mount inductors. for most designs, the required inductance value can be derived from the following equation. sw l in out in out f i v ) v v ( v l ? = where i l is the inductor ripple current. choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current is calculated from: 2 i i i l load ) max ( l + = under light load conditions below 100ma, a larger inductance is recommended to improve efficiency. see table 2 for suggested inductors. also note that the maximum recommended load current is 1a if the duty cycle exceeds 35%. 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 output impedance of the input source 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 4.7f capacitor is sufficient. selecting the output capacitor the output capacitor keeps the output current ripple small and ensures feedback loop stability. the output capacitor impedance should be low at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended for their low esr characteristics. for most applications, a 2.2f ceramic capacitor will be sufficient. the mp2370 can also work properly without output capacitor by adding a small capacitor in the feedback loop (see figure 2). the small capacitor is recommended 680pf. pc board layout the high current paths (gnd, in and sw) should be placed very close to the device with short, direct and wide traces. the input capacitor needs to be as close as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin. keep the switch node traces short and away from the feedback network.
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 mp2370 rev. 0.96 www.monolithicpower.com 7 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. table 2?suggested surface mount inductors manufacturer part number inductance(h) max dcr( ? ) current rating (a) dimensions l x w x h (mm 3 ) toko a921cy-4r7m 4.7 0.027 1.66 6 x 6.3 x 3 sumida cdrh4d28c/ld 4.7 0.036 1.5 5.1 x 5.1 x 3 wurth electronics 7440530047 4. 7 0.038 2.0 5.8 x 5.8 x 2.8 typical application circuits mp2370 in en gnd fb sw bs l1 0.75a vin 1 6 3 2 4 5 figure 2?white led driver without output capacitor mp2370 sw fb bst gnd in en 1 6 3 2 4 5 u1 v in 6v-23v off on l1 1a figure 3?white led driver with over-voltage clamp output mp2370 sw fb bst gnd in en 1 6 3 2 4 5 cb 10nf c1 4.7uf 25v c2 2.2uf 25v led1 led2 led3 d1 b130a v in 16v-23v off on l1 4.7uh/1.5a figure 4?driving 3 white leds in series from 16v- 23v input voltage
mp2370 ? 1.2a, 24v, 1.4mhz step-down white led driver in a tsot23-6 notice: the information in this document is subject to change wi thout notice. please contact m ps for current specifications. users should warrant and guarantee that third party intellectual property rights ar e not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp2370 rev. 0.96 www.monolithicpower.com 8 9/21/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. package information tsot23-6 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 (bottom 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 detail aaaa pin 1 see note 7 example top mark
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