mp2270 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 1 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. the future of analog ic technology description the mp2270 is a monolithic step-down switch mode converter with a built-in internal power mosfet. it achieves 1.8a continuous 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 mp2270 requires a minimum number of readily available standard external components. the mp2270 is available in a 10-pin exposed pad msop package. features ? 1.8a continuous output current ? 0.3 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? 0.1 a shutdown mode ? fixed 700khz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.5v to 24v operating input range ? output adjustable from 0.81v to 20v ? available in a 10-pin exposed pad msop package applications ? broadband communications equipment ? digital entertainment systems ? 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 mp2270 sw fb bst 5 6 8 10 3 1 gnd in en v out 3.3v cb 10nf d1 b230a v in off on v in i out_max =1.8
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 2 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. ordering information part number* package top marking free air temperature (t a ) MP2270DH msop10w/exposed pad 2270d -40 c to +85 c * for tape & reel, add suffix ?z (e.g. MP2270DH?z). for rohs compliant packaging, add suffix ?lf (e.g. MP2270DH?lf?z) package reference exposed pad on backside connect to gnd bst n/c sw n/c in 1 2 3 4 5 10 9 8 7 6 fb n/c gnd n/c en top view 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 continuous power dissipation (t a = +25c) (2) ??????????????????....2.3w 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 24v operating junct. temp (t j )...... -40 c to +125 c thermal resistance (4) ja jc msop10 w/exposed pad .......55 ...... 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 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.
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 3 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. 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 0.790 0.810 0.830 v feedback current i fb v fb = 0.8v 10 na switch on-resistance (5) r ds(on) 0.3 ? switch leakage v en = 0v, v sw = 0v 0 10 a current limit (5) duty cycle = 40% 2.0 2.5 a oscillator frequency f sw v fb = 0.6v 700 khz fold-back frequency v fb = 0v 230 khz maximum duty cycle v fb = 0.6v 87 % minimum on-time (5) 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 1.5 v v en = 2v 2.1 en input current v en = 0v 0.01 a supply current (shutdown) v en = 0v 0.1 1.0 a supply current (quiescent) v en = 2v, v fb = 1v 0.8 1.0 ma thermal shutdown (5) 150 c note: 5) guaranteed by design.
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 4 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. pin functions pin # name description 2, 4, 9, 7 nc no connect. 3 sw switch output. 5 in supply voltage. the mp2270 operates from a +4.5v to +24v unregulated input. c1 is needed to prevent large voltage spikes from appearing at the input. 6 en on/off control input. pull above 1.2v to turn the device on. 10 fb feedback. an external resistor divider from t he output to gnd, tapped to the fb pin sets the output voltage. to prevent current limit run aw ay during a short circuit fault condition the frequency foldback comparator lowers the osc illator frequency when the fb voltage is below 250mv. 8 gnd, exposed pad ground. this pin is the voltage reference for the regulated output voltage. for this reason care must be taken in its layout. this node should be placed outside of the d1 to c1 ground path to prevent switching current spikes from inducing voltage noise into the part. exposed pad must be connected to a ground plane for proper thermal operation. 1 bst bootstrap. this capacitor is needed to dr ive the power switch?s gate above the supply voltage. it is connected between sw and bst pins to form a floating supply across the power switch driver.
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 5 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. typical performanc e characteristics v in = 12v, v out = 1.8v, l=6.8 h, i load =0.5a ? 1.8a, t a = +20 c, unless otherwise noted. 0 204060 100 80 01 5 700 720 740 760 780 800 820 840 860 880 900 10 15 20 0 20 525 10 15 0 0.5 0 5 10 15 20 25 30 35 40 1.0 1.5 2.0 0 0.5 1.0 1.5 2.5 2.0 3.0 0 510152025 d max limit v out_max minimum on time limit v fb_min v in =12v v in =20v
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 6 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. typical performanc e characteristics (continued) v in = 12v, v out = 1.8v, l=6.8 h, i load =0.5a ? 1.8a, t a = +20 c, unless otherwise noted.
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 7 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. operation the mp2270 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 700khz 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 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 the 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 0.81v bandgap reference. the polarity is such that a fb pin voltage lower than 0.8v 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. in en fb gnd sw bst regulator oscillator 700khz driver current sense amplifier error amplifier current limit comparator pwm comparator d x20 m1 regulator reference ea -- + -- + -- + s r r q -- + 27pf 1pf figure 1?functional block diagram
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 8 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. application information setting output voltage the external resistor divider is used to set the output voltage (see the schematic on front page). the feedback resistor r1 also sets the feedback loop bandwidth with the internal compensation capacitor (see figure 1). r2 can be determined by: 1 v 81 . 0 v 1 r 2 r out ? = table 1?resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) 1.8 80.6 (1%) 64.9 (1%) 2.5 49.9 (1%) 23.7 (1%) 3.3 49.9 (1%) 16.2 (1%) 5 49.9 (1%) 9.53 (1%) 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 ? . for most designs, the required inductance value can be derived from the following equation. osc l in out in out f i v ) v v ( v l ? = where i l is the inductor ripple current. choose an inductor with a rating current of approximately 30% higher than the maximum load current if the maximum load current is 1.8a. 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 for improved efficiency. see table 2 for suggested inductors. selecting the input capacitor the input capacitor reduces the surge current drawn from the input 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 10f capacitor is sufficient. selecting the output capacitor the output capacitor keeps output voltage ripple small and ensures 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 22f ceramic capacitor will be sufficient. 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.
mp2270 ? 1.8a, 24v, 700khz step-down converter mp2270 rev. 1.1 www.monolithicpower.com 9 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. external bootstrap diode an external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external bst diode are: z v out =5v or 3.3v; and z duty cycle is high: d= in out v v >65% in these cases, an external bst diode is recommended from the output of the voltage regulator to bst pin, as shown in fig.2 mp2270 sw bst c l bst c 5v or 3.3v out external bst diode in4148 figure 2?add optional external bootstrap diode to enhance efficiency the recommended external bst diode is in4148, and the bst cap is 0.1~1f. table 2?suggested surface mount inductors manufacturer part number inductance(h) max dcr( ? ) current rating (a) dimensions l x w x h (mm 3 ) wurth electronics 7447785004 4. 7 0.060 2.5 5.9 x 6.2 x 3.3 toko a916cy-4r7m 4.7 0.026 2.5 6.2 x 6.3 x 3.5 coiltronics dr73-4r7 4.7 0.03 3 6.0 x 7.6 x 3.5
mp2270 ? 1.8a, 24v, 700khz step-down converter 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. mp2270 rev. 1.1 www.monolithicpower.com 10 4/16/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. package information msop 10 (exposed pad)
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