mp1580 2a, 380 khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 1 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. the future of analog ic technology tm tm description the mp1580 is a monolithic step-down switch mode converter with a built in internal power mosfet. it achieves 2a 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. in shutdown mode the regulator draws 23 a of supply current. the mp1580 requires a minimum number of readily available standard external components. a synchronization pin allows the part to be driven to 600khz. evaluation board reference board number dimensions ev0007 2.3?x x 1.5?y x 0.5?z features ? 2a output current ? 0.18 ? internal power mosfet switch ? stable with low esr output ceramic capacitors ? up to 95% efficiency ? 23 a shutdown mode ? fixed 380khz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? wide 4.75 to 25v operating input range ? output adjustable from 1.22v to 21v ? programmable under voltage lockout ? frequency synchronization input ? available in an 8-pin so package applications ? distributed power systems ? battery chargers ? pre-regulator for linear regulators ?mps? and ?the future of analog ic technology? are trademarks of monolithic power systems, inc. typical application mp1580_tac_s01 mp1580 sw in bs fb sync comp gnd en output 2.5v / 2a input 4.75v to 25v open not used off on c6 open c3 2.2nf c5 10nf d1 6 5 3 1 2 7 8 4 efficiency (%) 95 90 85 80 75 70 output current (a) mp1580_tac_ec01 efficiency vs output current voltage 0 0.5 1.5 12 v out = 5.0v v out = 3.3v v out = 2.5v v in = 10v
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 2 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm package reference bs in sw gnd sync en comp fb 1 2 3 4 8 7 6 5 top view mp1580_pd01-soic8 part number* package temperature mp1580hs soic8 ?40 c to +125 c * for tape & reel, add suffix ?z (eg. mp1580hs?z) for lead free, add suffix ?lf (eg. mp1580hs ?lf?z) 8 7 6 5 sync en comp fb bs in sw gnd 1 2 3 4 top view mp1580_pd02-pdip8 part number** package temperature mp1580hp pdip8 ?40 c to +125 c ** for tape & reel, add suffix ?z (eg. mp1580hp?z) for lead free, add suffix ?lf (eg. mp1580hp ?lf?z) absolute maxi mum ratings (1) supply voltage (v in )..................................... 27v switch voltage (v sw ).................. ?1v to v in + 1v bootstrap voltage (v bs ) ....................... v sw + 6v feedback voltage (v fb ) .................?0.3v to +6v enable/uvlo voltage (v en )...........?0.3v to +6v comp voltage (v comp ) ...................?0.3v to +6v sync voltage (v sync )......................?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 25v operating temperature...............?40 c to +125 c thermal resistance (3) ja jc soic8.................................... 105 ..... 50... c/w pdip8 ..................................... 95 ...... 55... 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 feedback voltage 4.75v v in 25v v comp < 2v 1.198 1.222 1.246 v upper switch-on resistance 0.18 ? lower switch-on resistance 10 ? upper switch leakage v en = 0v, v sw = 0v 0 10 a current limit (4) 2.4 3.0 3.6 a current limit gain. output current to comp pin voltage 1.95 a/v error amplifier voltage gain 400 v/v error amplifier transconductance i c = 10 a 500 770 1100 a/v oscillator frequency 342 380 418 khz short circuit frequency v fb = 0v 20 35 54 khz sync frequency sync drive 0v to 2.7v 445 600 khz
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 3 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm electrical characteristics (continued) v in = 12v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units maximum duty cycle v fb = 1.0v 90 % minimum duty cycle v fb = 1.5v 0 % en shutdown threshold voltage i cc > 100 a 0.7 1.0 1.3 v enable pull-up current v en = 0v 1.15 1.46 1.8 a en uvlo threshold rising v en rising 2.37 2.495 2.62 v en uvlo threshold hysteresis 210 mv supply current (shutdown) v en 0.4v 23 36 a supply current (quiescent) v en 2.6v, v fb = 1.4v 1.0 1.2 ma thermal shutdown 160 c note: 4) derate current limit 0.011a/c. pin functions pin # name description 1 bs bootstrap (c5). this capacitor is needed to drive the power switch?s gate above the supply voltage. it is connected between sw and bs pins to form a floating supply across the power switch driver. the voltage across c5 is about 5v and is supplied by the internal +5v supply when the sw pin voltage is low. 2 in supply voltage. the mp1580 operates from a +4.75v to +25v unregulated input. c1 is needed to prevent large voltage spikes from appearing at the input. 3 sw switch. this connects the inductor to either in through m1 or to gnd through m2. 4 gnd 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. 5 fb feedback. an external resistor divider from the output to gnd, tapped to the fb pin sets the output voltage. to prevent current limit r un away during a short circuit fault condition the frequency foldback comparator lowers the oscillator frequency when the fb voltage is below 700mv. 6 comp compensation. this node is the output of t he transconductance error amplifier and the input to the current comparator. frequen cy compensation is done at this node by connecting a series r-c to ground. see t he compensation section for exact details. 7 en enable/uvlo. a voltage greater than 2.62v enabl es operation. for complete low current shutdown the en pin voltage needs to be less than 700mv. 8 sync synchronization input. this pin is used to sync hronize the internal os cillator frequency to an external source. there is an internal 11k ? pull down resistor to gnd; therefore leave sync unconnected if unused.
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 4 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm operation the mp1580 is a current mode regulator; the comp pin voltage is proportional to the peak inductor current. at the beginning of a cycle: the upper transistor m1 is off; the lower transistor m2 is on (refer to figure 1); the comp pin voltage is higher than the current sense amplifier output and the current comparator?s output is low. the rising edge of the 380khz clk signal sets the rs flip-flop. its output turns off m2 and 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 current comparator. when the current sense amplifier plus slope compensation signal exceeds the comp pin voltage, the rs flip-flop is reset and the mp1580 reverts to its initial m1 off, m2 on, 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 1.222v bandgap reference. the polarity is such that an fb pin voltage less than 1.222v increases the comp pin voltage. since the comp pin voltage is proportional to the peak inductor current, an increase in its voltage increases the current delivered to the output. the lower 10 ? switch ensures that the bootstrap capacitor voltage is charged during light load conditions. an external schottky diode d1 carries the inductor current when m1 is off (see figure 1). mp1580_bd01 lockout comparator error amplifier frequency foldback comparator internal regulators 1.8v slope comp clk current comparator current sense amplifier shutdown comparator comp 6 in 2 en 7 sync 8 gnd 4 oscillator 40/380khz s r q sw 3 bs 1 5v + q 0.7v + + 2.285v/ 2.495v + 1.222v 0.7v + + fb 5 -- -- -- -- -- -- figure 1?functional block diagram
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 5 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm application information component selection sync pin operation the sync pin driving waveform should be a square wave with a rise time less than 20ns. the minimum high voltage level is 2.7v and the low level is less than 0.8v. the frequency of the external sync signal needs to be greater than 445khz. a rising edge on the sync pin forces a reset of the oscillator. the upper transistor m1 is switched off immediately if it is not already off. 250ns later m1 turns on connecting sw to v in . setting the output voltage the output voltage is set using a resistive voltage divider from the output to fb (see figure 3). the voltage divider divides the output voltage down 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 222 . 1 v out + = r2 can be as high as 100k ? , but a typical value is 10k ? . using this value, r1 is determined by: ) 222 . 1 v ( 18 . 8 1 r out ? ? for example, 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 results in less ripple current that in turn results in lower output ripple voltage. however, the larger value inductor has a larger physical size, higher series resistance and/or lower saturation current. choose an inductor that does not saturate under the worst-case load conditions. a good rule for determining the inductance is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum load current. also, make sure that the peak inductor current (the load current plus half the peak-to-peak inductor ripple current) is below the 2.4a minimum current limit. the inductance value can be calculated by the equation: i f v ) v v ( v l in out in out ? = where v in is the input voltage, f is the oscillator frequency and i is the peak-to-peak inductor ripple current. table 1 lists a number of suitable inductors from various manufacturers. 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 11.5 4.0 coilcraft do3308 open ferrite 9.4 13.0 3.0 do3316 open ferrite 9.4 13.0 5.1
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 6 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm input capacitor the input current to the step-down converter is discontinuous, so a capacitor is required to supply the ac current to the step-down converter while maintaining the dc input voltage. a low esr capacitor is required to keep the noise at the ic to a minimum. ceramic capacitors are preferred, but tantalum or low- esr electrolytic capacitors will also suffice. the input capacitor value should be greater than 10 f. the capacitor can be electrolytic, tantalum or ceramic. however, since it absorbs the input switching current it requires an adequate ripple current rating. its rms current rating should be greater than approximately 1/2 of the dc load current. to ensure stable operation, c1 should be placed as close to the in pin as possible. alternately, a smaller high quality ceramic 0.1 f capacitor may be placed closer to the in pin and a larger capacitor placed further away. if using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type capacitor. all ceramic capacitors should be placed close to the mp1580. output capacitor the output capacitor is required to maintain the dc output voltage. low esr capacitors are preferred to keep the output voltage ripple low. the characteristics of the output capacitor also affect the stability of the regulation control system. ceramic, tantalum or low esr electrolytic capacitors are recommended. in the case of ceramic capacitors, the impedance at the oscillator frequency is dominated by the capacitance, so the output voltage ripple is mostly independent of the esr. the output voltage ripple is estimated to be: 2 lc in ripple f f v 4 . 1 v ? ? ? ? ? ? ? ? ? where v ripple is the output ripple voltage, f lc is the resonant frequency of the lc filter and f is the oscillator frequency. in the case of tantalum or low-esr electrolytic capacitors, the esr dominates the impedance at the oscillator frequency, therefore the output ripple is calculated as: esr ripple r i v ? where v ripple is the output voltage ripple and r esr is the equivalent series resistance of the output capacitors. output rectifier diode the output rectifier diode supplies the current to the inductor when the upper transistor m1 is off. to reduce losses due to the diode forward voltage and recovery times, use a schottky rectifier. table 2 provides the schottky rectifier part numbers based on the maximum input voltage and current rating. table 2?schottky rectifier selection guide 2a load current v in (max) part number vendor 15v 30bq015 4 b220 1 sk23 6 20v sr22 6 20bq030 4 b230 1 sk23 6 sr23 3, 6 26v ss23 2, 3 table 3 lists some rectifier manufacturers. table 3?schottky diode manufacturers vendor web site diodes, inc. www.diodes.com fairchild semiconductor www.fairchildsemi.com general semiconductor www.gensemi.com international rectifier www.irf.com on semiconductor www.onsemi.com pan jit international www.panjit.com.tw choose a rectifier that has a maximum reverse voltage rating greater than the maximum input voltage, and a current rating greater than the maximum load current.
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 7 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm compensation the system stability is 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 loop gain is: out fb vea cs load vdc v v a g r a = where a vea is the transconductance error amplifier voltage gain, 400 v/v, g cs is the current sense gain, (roughly the output current divided by the voltage at comp), 1.95 a/v and r load is the load resistance (v out / i out where i out is the output load current). the system has 2 poles of importance, one is due to the compensation capacitor (c3), and the other is due to the output capacitor (c2). these are: vea ea 1 p a 3 c 2 g f = where p1 is the first pole and g ea is the error amplifier transconductance (770a/v). and load 2 p r 2 c 2 1 f = the system has one zero of importance, due to the compensation capacitor (c3) and the compensation resistor (r3). the zero is: 3 r 3 c 2 1 f 1 z = if a large value capacitor (c2) with relatively high equivalent-series-resistance (esr) is used, the zero due to the capacitance and esr of the output capacitor can be compensated by a third pole set by r3 and c6. the pole is: 3 r 6 c 2 1 f 3 p = the system crossover frequency (the frequency where the loop gain drops to 1, or 0db) is important. a good rule of thumb is to set the crossover frequency to approximately 1/10 of the switching frequency. in this case, the switching frequency is 380khz, so use a crossover frequency, f c , of 40khz. lower crossover frequencies result in slower response and worse transient load recovery. higher crossover frequencies can result in instability. choosing the compensation components the values of the compensation components given in table 4 yield a stable control loop for the output voltage and capacitor given. table 4?compensation values for typical output voltage/capacitor combinations v out c2 r3 c3 c6 2.5v 22 f ceramic 7.5k ? 2.2nf none 3.3v 22 f ceramic 10k ? 2nf none 5v 22 f ceramic 15k ? 1.2nf none 12v 22 f ceramic 33k ? 1nf none 2.5v 560 f/6.3v (30m ? esr) 200k ? 1nf 100pf 3.3v 560 f/6.3v (30m ? esr) 200k ? 1nf 82pf 5v 470 f/10v (30m ? esr) 250k ? 1nf 56pf 12v 220 f/25v (30m ? esr) 250k ? 1nf 27pf to optimize the compensation components for conditions not listed in table 4, use the following procedure: choose the compensation resistor to set the desired crossover frequency. determine the value by the following equation: fb out cs ea c v v g g f 2 c 2 3 r = putting in the known constants and setting the crossover frequency to the desired 40khz: out 8 v 2 c 10 37 . 1 3 r choose the compensation capacitor to set the zero below ? of the crossover frequency. determine the value by the following equation: 3 r v 2 c 22 . 0 3 c out >
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 8 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm determine if the second compensation capacitor, c6, is required. it is required if the esr zero of the output capacitor happens at less than four times the crossover frequency. or: 1 f r 2 c 8 c esr or 1 v r 3 r 10 34 . 7 out esr 5 ? if this is the case, add the second compensation capacitor. determine the value by the equation: 3 r r 2 c 6 c ) max ( esr = where r esr(max) is the maximum esr of the output capacitor. for example: v out = 3.3v c2= 22 f ceramic (esr = 10m ? ) = ? k 9 . 9 ) 3 . 3 ( ) 10 22 ( ) 10 37 . 1 ( 3 r 6 8 use the nearest standard value of 10k ? . nf 6 . 1 10 10 3 . 3 ) 10 22 ( 22 . 0 3 c 3 6 = > ? use a standard value of 2nf 014 . 0 f r 2 c 2 c esr = which is less than 1, therefore no second compensation capacitor is required. table 5?recommended components for standard output voltages v out r1 l1 minimum 1.22v 0 ? 6.8 h 1.5v 2.32k ? 6.8 h 1.8v 4.75k ? 10 h 2.5v 10.5k ? 10 h 3.3v 16.9k ? 15 h 5.0v 30.9k ? 22 h negative output voltage the mp1580 can be configured as a buck- boost regulator to supply negative output voltage. because the gnd pin of the ic is now connected to the negative output voltage, the maximum allowable input voltage is the ic input voltage rating (25v) minus the negative output voltage value. a typical application circuit is shown in figure 3. 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. mp1580 sw bs 10nf 5v mp1580_f02 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.
mp1580 ? 2a, 380khz step-down converter mp1580 rev. 3.0 www.monolithicpower.com 9 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm typical application circuits mp1580_f03 mp1580 sw in bs fb sync 6 5 3 1 2 7 8 4 comp gnd en output 2.5v / 2a input 4.75v to 25v open not used off on c6 open c3 2.2nf c5 10nf d1 figure 3?application circuit for -5v supply mp1580_f04 mp1580 sw in bs fb sync comp gnd en output -5v / 0.8a input 4.75v to 20v open not used off on c6 open c3 10nf c5 10nf d1 b230 6 5 3 1 2 7 8 4 figure 4?mp1580 with murata 22f/10v ceramic output capacitor
mp1580 ? 2a, 380khz step-down converter 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. mp1580 rev. 3.0 www.monolithicpower.com 10 10/10/2007 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2007 mps. all rights reserved. tm package information soic8 note: 1) control dimension is in inches. dimension in bracket is m illimeters. 0.016(0.410) 0.050(1.270) 0 o -8 o detail "a" 0.011(0.280) 0.020(0.508) x 45 o see detail "a" 0.0075(0.191) 0.0098(0.249) 0.229(5.820) 0.244(6.200) seating plane 0.001(0.030) 0.004(0.101) 0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524) 0.150(3.810) 0.157(4.000) pin 1 ident. 0.050(1.270)bsc 0.013(0.330) 0.020(0.508) pdip8
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