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mp1593 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 1 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. the future of analog ic technology tm tm description the mp1593 is a step-down regulator with an internal power mosfet. it achieves 3a of 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. an adjustable soft-start reduces the stress on the input source at startup. in shutdown mode the regulator draws 20a of supply current. the mp1593 requires a minimum number of readily available external components, providing a compact solution. evaluation board reference board number dimensions ev1593dn-00a 2.1?x x 1.3?y x 0.4?z features ? 3a output current ? programmable soft-start ? 100m ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? up to 95% efficiency ? 20 a shutdown mode ? fixed 385khz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.75v to 28v operating input range ? output adjustable from 1.22v ? under-voltage lockout ? available in 8-pin soic package applications ? distributed power systems ? battery chargers ? pre-regulator for linear regulators ? flat panel tvs ? set-top boxes ? cigarette lighter powered devices ? dvd/pvr devices ?mps? and ?the future of analog ic technology? are trademarks of monolithic power systems, inc. typical application input 4.75v to 28v output 3.3v 3a c3 8.2nf d1 b340a c5 10nf mp1593 bs in fb sw ss gnd comp en c6 (optional) 1 3 5 6 4 8 7 2 off on efficiency (%) 100 95 90 85 80 75 70 65 60 55 50 load current (a) efficiency vs load current 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 v in = 9v v in = 12v v in = 24v
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 2 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. package reference part number* package temperature MP1593DN soic8e (exposed pad) ?40 c to +85 c * for tape & reel, add suffix ?z (eg. MP1593DN?z) for rohs compliant packaging, add suffix ?lf (eg. MP1593DN?lf?z) absolute maxi mum ratings (1) supply voltage v in ....................... ?0.3v to +30v switch voltage v sw .............. ?0.5v to v in + 0.3v boost voltage v bs ..........v sw ? 0.3v to v sw + 6v all other pins................................. ?0.3v to +6v junction temperature...............................150 c lead temperature ....................................260 c storage temperature .............?65c to +150 c recommended operating conditions (2) input voltage v in ............................ 4.75v to 28v ambient operating temp............. ?40 c to +85 c thermal resistance (3) ja jc soic8e (exposed pad).......... 50 ...... 10... c/w notes: 1) exceeding these ratings may damage the device. 2) the device is not guaranteed to function outside of its operating conditions. 3) measured on approximately 1? square of 1 oz copper. electrical characteristics v in = 12v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units shutdown supply current v en = 0v 20 30 a supply current v en = 2.6v, v fb = 1.4v 1.0 1.2 ma feedback voltage v fb 4.75v v in 28v v comp < 2v 1.194 1.222 1.250 v error amplifier voltage gain a ea 400 v/v error amplifier transconductance g ea ? i comp = 10 a 500 800 1120 a/v high-side switch on-resistance r ds(on)1 100 140 m ? low-side switch on-resistance r ds(on)2 10 ? high-side switch leakage current v en = 0v, v sw = 0v 0 10 a current limit 4.8 6.2 7.6 a current sense to comp transconductance g cs 5.4 a/v oscillation frequency f osc1 335 385 435 khz short circuit oscillation frequency f osc2 v fb = 0v 25 45 60 khz maximum duty cycle d max v fb = 1.0v 90 % minimum duty cycle d min v fb = 1.5v 0 % bs in sw gnd ss en comp fb 1 2 3 4 8 7 6 5 top view exposed pad on backside connect to pin 4
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 3 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. electrical characteristics (continued) v in = 12v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units en threshold voltage 0.9 1.2 1.5 v enable pull up current v en = 0v 1.0 1.7 2.5 a under-voltage lockout threshold v in rising 2.3 2.6 2.9 v under-voltage lockout threshold hysteresis 210 mv soft-start period c ss = 0.1 f 10 ms thermal shutdown 160 c typical performanc e characteristics refer to typical application schematic on page 1 420 410 400 390 380 370 360 350 340 oscillation frequency (khz) temperature ( c) oscillation frequency vs temperature 5.0 4.9 4.8 4.7 4.6 4.5 4.4 4.3 4.2 4.1 4.0 peak current limit (a) temperature ( c) peak current limit vs temperature 1.245 1.235 1.225 1.215 1.205 1.195 feedback voltage (v) -60 -40 -20 0 20 40 60 80 100 120 140 temperature ( c) feedback voltage vs temperature -50 -25 -0 25 50 75 100 125 150 -60 -40 -20 0 20 40 60 80 100 120 140 soft-start waveforms v out 1v/div. i l 1a/div. 4ms/div. v out 1v/div. i l 1a/div. turn off waveforms v out 100mv/div. i l 1a/div. v in = 12v, v out = 3.3v, 1a - 2a step load transient waveforms
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 4 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. typical performanc e characteristics (continued) refer to typical application schematic on page 1 efficiency (%) 100 95 90 85 80 75 70 65 60 55 50 load current (ma) efficiency vs load current 0 500 1000 1500 2000 2500 3000 3500 v in = 9v v in = 12v v in = 24v 100 95 90 85 80 75 70 65 60 55 50 efficiency (%) 0 500 1000 1500 2000 2500 3000 3500 load current (ma) efficiency vs load current v in = 5v v in = 24v v in = 12v i l 1a/div. v out 10mv/div. v sw 10v/div. v in 100mv/div. switching waveforms pin functions pin # name description 1 bs high-side gate drive boost input. bs supplies the drive for the high-side n-channel mosfet switch. connect a 10nf or greater capacitor fr om sw to bs to power the high-side switch. 2 in power input. in supplies power to the ic. drive in with a 4.75v to 28v power source. bypass in to gnd with a suitably large capacitor to eliminate noise on the input to the ic. see input capacitor. 3 sw power switching output. sw is the switching node that supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switch. 4 gnd ground. note: connect the exposed pad to pin 4. 5 fb feedback input. fb senses the output voltage and re gulates it. drive fb with a resistive voltage divider from the output voltage to ground . the feedback threshold is 1.222v. see setting the output voltage. 6 comp compensation node. comp is used to compensate the regulation control loop. connect a series rc network from comp to gnd. in some cases, an additional capacitor from comp to gnd is required. see compensation. 7 en enable input. en is a digital input that turns the regulator on or o ff. drive en high to turn on the regulator; low to turn it off. an under-volt age lockout (uvlo) function can be implemented by the addition of a resistor divider from v in to gnd. for complete low current shutdown the en pin voltage needs to be less than 0.7v. for aut omatic startup leave en disconnected. 8 ss soft-start control input. ss contro ls the soft-start peri od. connect a capacitor from ss to gnd to set the soft-start period. a 0.1 f capacitor sets the soft-start period to 10ms. to disable the soft-start feature, leave ss disconnected.
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 5 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. operation lockout comparator error amplifier frequency foldback comparator internal regulators 1.8v slope comp clk current comparator current sense amplifier shutdown comparator ss 8 comp 6 in 2 en 7 gnd 4 oscillator 45/385khz s r q sw 3 bs m1 m2 1 5v + q 1.2v + + 2.60v/ 2.39v + 1.22v 0.7v + + fb 5 -- -- -- -- -- -- figure 1?functional block diagram the mp1593 is a current-mode step-down regulator. it regulates input voltages from 4.75v to 28v down to an output voltage as low as 1.22v, and is able to supply up to 3a of continuous load current. the mp1593 uses current-mode control to regulate the output voltage. the output voltage is measured at fb through a resistive voltage divider and amplified through the internal error amplifier. the output current of the transconductance error amplifier is presented at comp where a network compensates the regulation control system. the voltage at comp is compared to the internally measured switch current to control the output voltage. the converter uses an internal n-channel mosfet switch to step-down the input voltage to the regulated output voltage. since the mosfet requires a gate voltage greater than the input voltage, a boost capacitor connected between sw and bs drives the gate. the capacitor is internally charged when sw is low. an internal 10 ? switch from sw to gnd is used to insure that sw is pulled to gnd when it is low to fully charge the bs capacitor.
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 6 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. application information component selection setting the output voltage the output voltage is set using a resistive voltage divider from the output voltage to the fb pin. the voltage divider divides the output voltage down to the feedback voltage by the ratio: 2 r 1 r 2 r v v out fb + = where v fb is the feedback voltage and v out is the output voltage. thus the output voltage is: 2 r 2 r 1 r 22 . 1 v out + = r2 can be as high as 100k ? , but a typical value is 10k ? . using that value, r1 is determined by: ) k )( 22 . 1 v ( 18 . 8 1 r out ? ? = for a 3.3v output voltage, r2 is 10k ? and r1 is 17k ? . inductor the inductor is required to supply constant current to the output load while being driven by the switched input voltage. a larger value inductor will result in less ripple current that will result in lower output ripple voltage. however, larger value inductors will have larger physical size, higher series resistance and/or lower saturation current. a good standard for determining the inductance to use is to allow the inductor peak-to-peak ripple current to be approximately 30% of the maximum switch current limit. also, make sure that the peak inductor current is below the maximum switch current limit. the inductance value can be calculated by: ? ? ? ? ? ? ? ? ? = in out l s out v v 1 ? i f v l where v in is the input voltage, f s is the switching frequency and ? i l is the peak-to-peak inductor ripple current. choose an inductor that will not saturate under the maximum inductor peak current. the peak inductor current can be calculated by: ? ? ? ? ? ? ? ? ? + = in out s out load lp v v 1 l f 2 v i i where i load is the load current. table 1 lists a number of suitable inductors from various manufacturers. the choice of which inductor to use mainly depends on the price vs. size requirements and any emi requirement. table 1?inductor selection guide package dimensions (mm) vendor/ model core type core material w l h sumida cr75 open ferrite 7.0 7.8 5.5 cdh74 open ferrite 7.3 8.0 5.2 cdrh5d28 shielded ferrite 5.5 5.7 5.5 cdrh5d28 shielded ferrite 5.5 5.7 5.5 cdrh6d28 shielded ferrite 6.7 6.7 3.0 cdrh104r shielded ferrite 10.1 10.0 3.0 toko d53lc type a shielded ferrite 5.0 5.0 3.0 d75c shielded ferrite 7.6 7.6 5.1 d104c shielded ferrite 10.0 10.0 4.3 d10fl open ferrite 9.7 1.5 4.0 coilcraft do3308 open ferrite 9.4 13.0 3.0 do3316 open ferrite 9.4 13.0 5.1
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 7 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. output rectifier diode the output rectifier diode supplies current to the inductor when the high-side switch is off. use a schottky diode to reduce losses due to diode forward voltage and recovery times. choose a diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating is greater than the maximum load current. table 2 lists example schottky diodes and manufacturers. table 2?diode selection guide diode v oltage/current rating manufacture sk33 30v, 3a diodes inc. sk34 40v, 3a diodes inc. b330 30v, 3a diodes inc. b340 40v, 3a diodes inc. mbrs330 30v, 3a on semiconductor mbrs340 40v, 3a on semiconductor input capacitor the input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the ac current to the step-down converter while maintaining the dc input voltage. use low esr capacitors for the best performance. ceramic capacitors are preferred, but tantalum or low-esr electrolytic capacitors will also suffice. since the input capacitor (c1) absorbs the input switching current it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: ? ? ? ? ? ? ? ? ? = in out in out load 1 c v v 1 v v i i the worst-case condition occurs at v in = 2v out , where: 2 i i load 1 c = for simplification, choose the input capacitor whose rms current rating is greater than half of the maximum load current. the input capacitor can be electrolytic, tantalum or ceramic. when using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor (i.e. 0.1 f) should be placed as close to the ic as possible. when using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at the input. the input voltage ripple caused by the capacitance can be estimated by: ? ? ? ? ? ? ? ? ? = ? in out in out s load in v v 1 v v 1 c f i v output capacitor the output capacitor is required to maintain the dc output voltage. ceramic, tantalum or low esr electrolytic capacitors are recommended. low esr capacitors are preferred to keep the output voltage ripple low. the output voltage ripple can be estimated by: ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? = ? 2 c f 8 1 r v v 1 l f v v s esr in out s out out where l is the inductor value, c2 is the output capacitance value and r esr is the equivalent series resistance (esr) value of the output capacitor. in the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, which is the main cause of the output voltage ripple. for simplification, the output voltage ripple can be estimated by: ? ? ? ? ? ? ? ? ? = in out 2 s out out v v 1 2 c l f 8 v ? v in the case of tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: esr in out s out out r v v 1 l f v ? v ? ? ? ? ? ? ? ? ? = the characteristics of the output capacitor also affect the stability of the regulation system. the mp1593 can be optimized for a wide range of capacitance and esr values.
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 8 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. compensation components the mp1593 employs current mode control for easy compensation and fast transient response. the system stability and transient response are controlled through the comp pin. comp is the output of the internal transconductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. the dc gain of the voltage feedback loop is given by: out fb vea cs load vdc v v a g r a = where a vea is the error amplifier voltage gain, g cs is the current sense transconductance and r load is the load resistor value. the system has two poles of importance. one is due to the compensation capacitor (c3) and the output resistor of error amplifier, while the other is due to the output capacitor and the load resistor. these poles are located at: vea ea 1 p a 3 c 2 g f = load 2 p r 2 c 2 1 f = where g ea is the error amplifier transconductance. the system has one zero of importance, due to the compensation capacitor (c3) and the compensation resistor (r3). this zero is located at: 3 r 3 c 2 1 f 1 z = the system may have another zero of importance, if the output capacitor has a large capacitance and/or a high esr value. the zero, due to the esr and capacitance of the output capacitor, is located at: esr esr r 2 c 2 1 f = in this case (as shown in figure 3), a third pole set by the compensation capacitor (c6) and the compensation resistor (r3) is used to compensate the effect of the esr zero on the loop gain. this pole is located at: 3 r 6 c 2 1 f 3 p = the goal of compensation design is to shape the converter transfer function to get a desired loop gain. the system crossover frequency (where the feedback loop has unity gain) is important. lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system instability. a good standard is to set the crossover frequency to approximately one-tenth of the switching frequency. the switching frequency for the mp1593 is 385khz, so the desired crossover frequency is around 38khz. table 3 lists the typical values of compensation components for some standard output voltages with various output capacitors and inductors. the values of the compensation components have been optimized for fast transient responses and good stability at given conditions.
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 9 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. table 3?compensation values for typical output voltage/capacitor combinations v out l c2 r3 c3 c6 1.8v 4.7 h 100 f ceramic 5.6k ? 3.3nf none 2.5v 4.7- 6.8 h 47 f ceramic 3.9k ? 5.6nf none 3.3v 6.8- 10 h 22 fx2 ceramic 5.6k ? 8.2nf none 5v 10- 15 h 22 fx2 ceramic 7.5k ? 10nf none 12v 15- 22 h 22 fx2 ceramic 10k ? 3.3nf none 1.8 4.7 h 100 f sp-cap 5.6k ? 3.3nf 100pf 2.5v 4.7- 6.8 h 47 f sp-cap 4.7k ? 5.6nf none 3.3v 6.8- 10 h 47 f sp-cap 6.8k ? 10nf none 5v 10- 15 h 47 f sp cap 10k ? 10nf none 2.5v 4.7- 6.8 h 560 f al. 30m ? esr 10k ? 5.6nf 1.5nf 3.3v 6.8- 10 h 560 f al 30m ? esr 10k ? 8.2nf 1.5nf 5v 10- 15 h 470 f al. 30m ? esr 15k ? 5.6nf 1nf 12v 15- 22 h 220 f al. 30m ? esr 15k ? 4.7nf 390pf to optimize the compensation components for conditions not listed in table 3, the following procedure can be used. 1. choose the compensation resistor (r3) to set the desired crossover frequency. determine r3 by the following equation: fb out cs ea c v v g g f 2 c 2 3 r = where f c is the desired crossover frequency (which typically has a value no higher than 38khz). 2. choose the compensation capacitor (c3) to achieve the desired phase margin. for applications with typical inductor values, setting the compensation zero, f z1 , below one forth of the crossover frequency provides sufficient phase margin. determine c3 by the following equation: c f 3 r 2 4 3 c > where r3 is the compensation resistor value. 3. determine if the second compensation capacitor (c6) is required. it is required if the esr zero of the output capacitor is located at less than half of the 385khz switching frequency, or the following relationship is valid: 2 f r 2 c 2 1 s esr < where c2 is the output capacitance value, r esr is the esr value of the output capacitor and f s is the switching frequency. if this is the case, then add the second compensation capacitor (c6) to set the pole f p3 at the location of the esr zero. determine c6 by the equation: 3 r r 2 c 6 c esr = where c2 is the output capacitance value, r esr is the esr value of the output capacitor and r3 is the compensation resistor. 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. mp1593 sw bs 3 1 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.
mp1593 ? 3a, 28v, 385khz step-down converter mp1593 rev. 1.9 www.monolithicpower.com 10 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. typical application circuits input 4.75v to 28v output 2.5v 3a c3 3.3nf c6 (optional) d1 b340a c5 10nf mp1593 bs in fb sw ss gnd comp en 1 3 5 6 4 8 7 2 off on figure 3?mp1593 with avx 47f, 6.3v ceramic output capacitor input 4.75v to 28v output 2.5v 3a c3 3.3nf c6 (optional) d1 b340a c5 10nf mp1593 bs in fb sw ss gnd comp en 1 3 5 6 4 8 7 2 off on figure 4?mp1593 with panasonic 47f, 6.3v special polymer output capacitor
mp1593 ? 3a, 28v, 385khz step-down converter notice: the information in this document is subject to change without notice. users should warrant 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. mp1593 rev. 1.9 www.monolithicpower.com 11 9/14/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 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

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