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MP2492 2a, 55v, 100khz step -down converter with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 1 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. the future of analog ic technology description the MP2492 is a monolithic step-down switch mode converter with a programmable output current limit. it achieves 2a continuous output current over a wide input supply range with excellent load and line regulation. the maximum output current can be programmed by sensing current through the inductor dc resistance (dcr) or an accurate sense resistor. MP2492 achieves low emi signature with well controlled switching edges. fault condition protection includes cycle-by-cycle current limiting, and thermal shutdown. the MP2492 requires a minimum number of readily available standard external components. the MP2492 is available in qfn10 (3mm x 3mm) and soic8e packages. features ? wide 4.5v to 55v operating input range ? programmable up to 2a output current ? output adjustable from 0.8v to 15v ? programmable output current limit without power loss ? 0.25 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? fixed 100khz frequency ? low emi signature ? thermal shutdown ? cycle-by-cycle over current protection ? available in qfn10 and soic8e packages applications ? usb power supplies ? automotive cigarette lighter adapters ? power supply for linear chargers ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application , v out =5v v in =12v efficiency 20 30 40 50 60 70 80 90 100 0.0 0.4 0.8 1.2 1.6 2.0 i out (a) efficiency ( % )
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 2 12/20/2010 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 ) MP2492dn * soic8e MP2492dn ?40 c to +85 c MP2492dq ** qfn10(3mmx3mm) 3q ?40 c to +85 c * for tape & reel, add suffix ?z (e.g. MP2492dn?z). for rohs compliant packaging, add suffix ?lf (e.g. MP2492dn?lf?z) * * for tape & reel, add suffix ?z (e.g. MP2492dq?z). for rohs compliant packaging, add suffix ?lf (e.g. MP2492dq?lf?z) package reference vin gnd fb ss sw bst isp isn exposed pad on backside connect to gnd vin gnd en fb ss sw bst pgood isp isn exposed pad on backside connect to gnd soic8e qfn10(3mmx3mm) absolute maxi mum ratings (1) input voltage v in .......................................... 60v v sw ....................................... ?0.3v to v in + 0.3v v bst ................................................... v sw + 6.5v v isn, v isp ................................................ 0v to15v | v isn, - v isp | ........................................ 0 to 0.5v v en, ....................................................... 0v to15v all other pins .............................. ?0.3v to +6.5v continuous power dissipation (t a = +25c) (2) soic8e ...................................................... 2.5w qfn10 (3 x 3 mm) ..................................... 2.5w junction temperature ............................... 150 c lead temperature .................................... 260 c storage temperature .............. ?50 c to +150 c recommended operating conditions (3) input voltage v in .............................. 4.5v to 55v output voltage v out (v in >16.5v) ...... 0.8v to 15v output voltage v out (v in <=16.5v) ..................... ........................................ 0.8v to (v in ?1.7) v operating junct. temp. .......... ?40 c to +125 c thermal resistance (4) ja jc soic8e................................... 50...... 10 .. c/w qfn10 (3 x 3 mm)...................50........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.
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 3 12/20/2010 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 55v 0.78 0.8 0.82 v feedback bias current i bias(fb) v fb = 0.8v 10 na switch on resistance r ds(on) 0.25 ? switch leakage (5) v en = 0v, v sw = 0v 0.1 10 a current limit 3.5 a oscillator frequency f sw v fb = 0.6v 80 100 120 khz boot-strap voltage v bst - v sw 4.3 v minimum on time t on v fb = 1v 100 ns sw rising edge trise vin=12v, vo=5v, io=2a 50 ns sw falling edge tfall vin=12v, vo=5v, io=2a 50 ns under voltage lockout threshold rising 3.0 3.3 3.6 v under voltage lockout threshold hysteresis 200 mv supply current (quiescent) v en = 2v, v fb = 1v 500 800 a thermal shutdown 150 c current sense voltage v isp ?v isn v isp , v isn 0.4?15v 90 100 110 mv input bias current (isn, isp) i bias (isn,isp) v isp , v isn 0.4?15v ?1 ?0.5 +1 a en input low voltage (5) 0.4 v en input high voltage (5) 1.8 v en input bias current (5) v en = 0-6v -10 -2 10 a pgood sink voltage dropout sink current 5ma 0.3 v note: 4) guaranteed by design 5) only available for the mp2490dq
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 4 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. pin functions qfn10 pin # soic-8 pin # name description 1 1 vin supply voltage. the MP2492 operates from a +4.5v to +55v unregulated input. c in is needed to prevent large voltage spikes from appearing at the input. put c in as close to the ic as possible. it is the drain of the internal power device and power supply for the whole chip. 2 2 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 c in ground path to prevent switching current spikes from inducing voltage noise into the part, exposed pad must be connected to ground pin. 3 en on/off control input. 4 3 fb a n external resistor divider from the output to gnd, tapped to the fb pin sets the output voltage. 5 4 ss connect to an external capacitor used for soft-start and compensation for current limiting loop. 6 5 isn negative current sense input for load current limiting. 7 6 isp positive current sense 8 pgood power good signal. when fb is less t han 90% of 0.8v, pgood is low. it is an open-drain output. use a high value pull-up resistor externally to pull it up to system power supply. 9 7 bst bootstrap. this capacitor is needed to drive 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. an on-chip regulator is used to charge up the external boot-strap capacitor. if the on- chip regulator is not strong enough, one optional diode can be connected from in or out to charge the external boot-strap capacitor. 10 8 sw switch output. it is the source of power device.
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 5 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. typical performanc e characteristics c 1 =220uf, c 2 =2.2uf, c 3 =39uf, c 4 =22uf, l=39uh, t a =25oc unless otherwise noted. 2.0 2.8 3.6 4.4 5.2 6.0 0 20406080100 duty cycle ( % ) i l current (a) v out (v) v out (v) v out (v) v out (v) i out (a) i out (a) i out (a) load regulation load regulation load regulation maximum i out vs. duty cycle loop gain with phase margin v in =12v, v out =5v, i out =1.8a 4.980 4.984 4.988 4.992 4.996 5.000 5.004 0.0 0.4 0.8 1.2 1.6 2.0 v in =8v v in =12v v in =50v 3.290 3.294 3.298 3.302 3.306 3.310 0.0 0.4 0.8 1.2 1.6 2.0 2.500 2.502 2.504 2.506 2.508 2.510 0.0 0.4 0.8 1.2 1.6 2.0 v in =8v v in =50v v in =12v v in =12v v in =50v 20 30 40 50 60 70 80 90 100 0.0 0.4 0.8 1.2 1.6 2.0 i out (a) v out =5v v out =5v efficiency ( % ) efficiency ( % ) efficiency vs. load current efficiency vs. load current efficien cy vs. load current v in =8v v in =12v v in =50v 20 30 40 50 60 70 80 90 100 0.0 0.4 0.8 1.2 1.6 2.0 v in =8v v in =12v v in =50v i out (a) v out =3.3v v out =3.3v 20 30 40 50 60 70 80 90 100 0.0 0.4 0.8 1.2 1.6 2.0 i out (a) efficiency ( % ) v out =2.5v v out =2.5v v in =4.5v v in =12v v in =50v -50 -40 -30 -20 -10 0 10 20 30 40 50 0.1 1 10 100 1000 frequency (khz) -200 -160 -120 -80 -40 0 40 80 120 160 200 current regulation sense to dcr 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 load current ( a ) gain phase
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 6 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. typical performanc e characteristics (continued) c 1 =220uf, c 2 =2.2uf, c 3 =39uf, c 4 =22uf, l=39uh, t a =25oc unless otherwise noted. v in 100mv/div. v sw 10v/div. v out 10mv/div. v out 5v/div. v out 5v/div. i l 2a/div. 10us/div. 20ms/div. 20ms/div. steady state v in = 12v, v out =5v, i out = 2a electrical load v in 10v/div. v sw 10v/div. i out 2a/div. i out 2a/div. power ramp up v in = 12v, v out = 5v, i out = 2a resistor load v in 10v/div. v sw 10v/div. power ramp down v in = 12v,v out = 5v, i out = 2a resistor load v pg 5v/div. v sw 50v/div. v out 5v/div. i out 2a/div. steady state v in = 50v, v out = 5v, i out = 1.8a electrical load v fb vs. temperature v out 20mv/div. v out 2v/div. v out 2v/div. i out 1a/div. i out 2a/div. i out 2a/div. 4ms/div. load transient response v in = 12v,v out = 5v, i out = 0.1a to 2a 1us/div. 2us/div. short circuit v in = 12v,v out = 5v, i out =0.5a short circuit recovery v in = 12v,v out = 5v 30 0 5 10 15 20 25 30 35 40 45 50 55 60 100 600 800 400 1000 frequency (mhz) 0.790 0.792 0.794 0.796 0.798 0.800 -50 -20 10 40 70 100 v fb voltage(v) e lectric field s trength 3 m q p
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 7 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. operation the MP2492 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 sw 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 100khz clk signal sets the rs flip-flop. its output turns on sw 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 current comparator. when the current sense amplifier plus slope compensation signal exceeds the ea output voltage, the rs flip-flop is reset and the MP2492 reverts to its initial sw off state. if the current sense amplifier plus slope compensation signal does not exceed the comp voltage, 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 0.8v 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 increases current delivered to the output. an external schottky diode (d1) carries the inductor current when sw is off. the output current information is sensed via the isp and isn pins. the sense voltage is set at 100mv. if v sense , the difference of v isp and v isn , is less than 100mv, the output voltage of the power supply will be set by the fb pin. if v sense reaches 100mv, the current limit loop will pull down on ss and regulate the output at a constant current. en pwm comparator current limit comparator 6pf 72.8pf d isp isn enable regulator 4.0v en ss vin ss fb sw oscillator reference x13.5 current sense amplifier - bst ramp generator regulator por regulator 100mv driver rsen 20m m1 6pf 2483k 72.8pf s r r q er gnd 100khz figure 1?function block diagram
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 8 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. application information setting the 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). choose r1 to be around 300k ? for optimal transient response. r2 is then given by: 1 v 8 . 0 v 1 r 2 r out ? = table 1?resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) 1.8 300 (1%) 240 (1%) 2.5 300 (1%) 141.1 (1%) 3.3 300 (1%) 96 (1%) 5 300 (1%) 57.1 (1%) selecting the inductor a 1 h to 10 h 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 dc resistance should be less than 200m ? . for most designs, the 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 inductor current ripple to be approximately 30% of the maximum load current, 2a. the maximum inductor peak current is: 2 i i i l load ) max ( l ? + = under light load conditions below 100ma, larger inductance is recommended for improved efficiency. selecting the input capacitor the input capacitor reduces the surge current drawn from the input and also 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 pass to 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 output voltage small and ensures regulation loop stability. the output capacitor impedance should be low at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended. 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 switching node sw short and away from the feedback network. external bootstrap diode it is recommended that an external bootstrap diode be added when the system has a 5v fixed input or the power supply generates a 5v output. this helps improve the efficiency of the regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. MP2492 sw bst 10nf 5v figure 2?external bootstrap diode this diode is also recommended for high duty cycle operation (when in out v v >65%) and high output voltage (v out >12v) applications.
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 9 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. output current sensing the output current can be sensed through the dc resistance (dcr) of the inductor, as shown in figure 3a. for more accurate sensing, use a more accurate sense resistor. in figure 3a, the output current limit is set as: o u t 1 0 0 m v r b i d c r 2 r a r b = + where dcr is the dc resistance of the inductor winding. in figure 3a, it is desirable to keep s r a r b l 1 c r a r b d c r = + for more accurate sensing, use a more accurate sense resistor. in figure 3b, the output current limit is set as: o u t s e n s e 1 0 0 m v i r = figure 3?current sensing methods
MP2492 ? 2a, 55v, 100khz with programmable output current limit MP2492 rev. 1.0 www.monolithicpower.com 10 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. package information soic8e (exposed pad) see detail "a" 0.0075(0.19) 0.0098(0.25) 0.050(1.27) bsc 0.013(0.33) 0.020(0.51) seating plane 0.000(0.00) 0.006(0.15) 0.051(1.30) 0.067(1.70) top view front view side view bottom view note: 1) control dimension is in inches . dimension in bracket is in millimeters . 2) package length does not include mold flash , protrusions or gate burrs . 3) package width does not include interlead flash or protrusions. 4) lead coplanarity (bottom of leads after forming ) shall be 0.004" inches max. 5) drawing conforms to jedec ms-012, variation ba. 6) drawing is not to scale. 0.089(2.26) 0.101(2.56) 0.124(3.15) 0.136(3.45) recommended land pattern 0.213(5.40) 0.063(1.60) 0.050(1.27) 0.024(0.61) 0.103(2.62) 0.138(3.51) 0.150(3.80) 0.157(4.00) pin 1 id 0.189(4.80) 0.197(5.00) 0.228(5.80) 0.244(6.20) 14 85 0.016(0.41) 0.050(1.27) 0 o -8 o detail "a" 0.010(0.25) 0.020(0.50) x 45 o 0.010(0.25) bsc gauge plane
MP2492 ? 2a, 55v, 100khz with programmable output current limit 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. MP2492 rev. 1.0 www.monolithicpower.com 11 12/20/2010 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2010 mps. all rights reserved. qfn10 (3mm x 3mm) side view top view 1 10 6 5 bottom view 2.90 3.10 1.45 1.75 2.90 3.10 2.25 2.55 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 shall be 0.10 millimeter max. 4) drawing conforms to jedec mo-229, variation veed-5. 5) drawing is not to scale. pin 1 id see detail a 2.50 0.70 pin 1 id option b r0.20 typ. pin 1 id option a r0.20 typ. detail a 0.30 0.50 pin 1 id index area

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