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mp2106 1.5a, 15v, 800khz synchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 1 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. the future of analog ic technology tm tm description the mp2106 is a 1.5a, 800khz synchronous buck converter designed for low voltage applications requiring high efficiency. it is capable of providing output voltages as low as 0.9v, and integrates top and bottom switches to minimize power loss and component count. the 800khz switching frequency reduces the size of filtering components, further reducing the solution size. the mp2106 includes cycle-by-cycle current limiting and under voltage lockout. the internal power switches, combined with the tiny 10-pin msop and qfn packages, provide a solution requiring a minimum of surface area. evaluation board reference board number dimensions ev2106dq/dk-00a 2.5?x x 2.0?y x 0.5?z features ? 1.5a output current ? synchronous rectification ? internal 210m ? and 255m ? power switches ? input range of 2.6v to 15v ? >90% efficiency ? zero current shutdown mode ? under voltage lockout protection ? soft-start operation ? thermal shutdown ? internal current limit (source & sink) ? tiny 10-pin msop or qfn package applications ? dc/dc regulation from wall adapters ? portable entertainment systems ? set top boxes ? digital video cameras, dect ? networking equipment ? wireless modems ?mps? and ?the future of analog ic technology? are trademarks of monolithic power systems, inc. typical application mp2106 lx vin bst fb 6 7 8 2 9 10 4 3 1 5 comp ss pgnd sgnd vref run output 1.8v / 1.5a input 2.6v to 15v mp2106_tac_s01 off on 10nf 10nf c7 c1 c2 c5 c3 c6 3.3nf 10nf r4 r3 r2 l1 r1 100 90 80 70 60 50 40 30 20 10 0 efficiency (%) 0.01 0.1 1 10 load current (a) mp2106_tac_ec02 efficiency vs. load current v in =5v v in =3.3v
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 2 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm package reference ss fb comp vref run 1 2 3 4 5 10 9 8 7 6 sgnd pgnd lx vin bst top view mp2106_pd01-msop10 part number* package temperature mp2106dk msop10 ?40 c to +85 c * for tape & reel, add suffix ?z (eg. mp2106dk?z) for lead free, add suffix ?lf (eg. mp2106dk?lf?z) mp2106_pd02-qfn10 top view ss fb comp vref run 1 2 3 4 5 sgnd pgnd lx vin bst 10 9 8 7 6 exposed pad on backside part number** package temperature mp2106dq qfn10 (3mm x 3mm) ?40 c to +85 c ** for tape & reel, add suffix ?z (eg. mp2106dq?z) for lead free, add suffix ?lf (eg. mp2106dq?lf?z) absolute maxi mum ratings (1) input supply voltage v in .............................. 16v lx voltage v lx ..................... ? 0.3v to v in + 0.3v bst to lx voltage ......................... ? 0.3v to +6v voltage on all other pins............... ? 0.3v to +6v storage temperature............... ? 55 c to +150 c recommended operating conditions (2) input supply voltage v in ..................2.6v to 15v output voltage v out ........................0.9v to 5.5v operating temperature.............. ? 40 c to +85 c thermal resistance (3) ja jc msop10 ................................ 150 ..... 65... c/w qfn10 .................................... 50 ...... 12... 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 = 5.0v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units input voltage range v in 2.6 15 v input under voltage lockout 2.2 v input under voltage lockout hysteresis 100 mv shutdown supply current v run 0.3v 0.5 1.0 a operating supply current v run > 2v, v fb = 1.1v 1.2 1.8 ma vref voltage v ref v in = 2.6v to 15v 2.4 v run input low voltage v il 0.4 v run input high voltage v hl 1.5 v run hysteresis 100 mv run input bias current 1 a oscillator switching frequency f sw 700 800 900 khz maximum duty cycle d max v fb = 0.7v 85 % minimum on time t on 200 ns
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 3 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm electrical characteristics (continued) v in = 5.0v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units error amplifier voltage gain a vea 400 v/v transconductance g ea 300 a/v comp maximum output current 30 a fb regulation voltage v fb 875 895 915 mv fb input bias current i fb v fb = 0.895v ?100 na soft-start soft-start current i ss 2 a output switch on-resistance v in = 5v 255 m ? switch on resistance v in = 3v 315 m ? v in = 5v 210 m ? synchronous rectifier on resistance v in = 3v 255 m ? switch current limit (source) 2.5 a synchronous rectifier current limit (sink) 350 ma thermal shutdown 160 c pin functions pin # name description 1 ss soft-start input. place a capacitor from ss to sgnd to set the soft-start period. the mp2106 sources 2a from ss to the soft-start capacito r at startup. as the ss voltage rises, the feedback threshold voltage increases to limit inrush current during startup. 2 fb feedback input. fb is the inverting input of the internal error amplifier. connect a resistive voltage divider from the output voltage to fb to set the output voltage value. 3 comp compensation node. comp is the output of the error amplifier. connect a series rc network to compensate the regulation control loop. 4 vref internal 2.4v regulator bypass. connect a 10nf capacitor between vref and sgnd to bypass the internal regulator. do not apply any load to vref. 5 run on/off control input. drive run high to turn on the mp2106; low to turn it off. for automatic startup, connect run to vin via a pullup resistor. 6 bst power switch boost. bst powers the gate of the high-side n-channel power mosfet switch. connect a 10nf or greater capacitor between bst and lx. 7 vin internal power input. vin supplies the powe r to the mp2106 through the internal ldo regulator. bypass vin to pgnd with a 10f or greater capacitor. connect vin to the input source voltage. 8 lx output switching node. lx is the source of t he high-side n-channel switch and the drain of the low-side n-channel switch. connect the output lc filter between lx and the output. 9 pgnd power ground. pgnd is the source of the n-ch annel mosfet synchronous rectifier. connect pgnd to sgnd as close to the mp2106 as possible. 10 sgnd signal ground.
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 4 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm typical performanc e characteristics circuit of figure 2, v in = 5v, v out = 1.8v, l1 = 5h, c1 = 10f, c2 = 22f, t a = +25 c, unless otherwise noted. v out 1v/div. i l 1a/div. mp2106-tpc06 short circuit protection v out 1v/div. i l 1a/div. short circuit recovery mp2106-tpc07 v sw 5v/div. v o ac coupled 10mv/div. v in ac coupled 200mv/div. i l 1a/div. mp2106-tpc01 steady state operation 1.5a load v sw 5v/div. v o ac coupled 10mv/div. v in ac coupled 20mv/div. i l 1a/div. steady state operation no load mp2106-tpc02 v en 2v/div. v out 1v/div. v sw 5v/div. i l 1a/div. 1ms/div. mp2106-tpc04 startup from shutdown 1.5a resistive load v en 2v/div. v out 1v/div. v sw 5v/div. i l 1a/div. 1ms/div. startup from shutdown no load mp2106-tpc05 v out ac coupled 200mv/div. i load 1a/div. i l 1a/div. mp2106-tpc03 load transient
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 5 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm operation mp2106_bd01 run v in 7 6 8 9 2 3 10 1 4 5 fb r2 r1 pgnd c7 c2 c1 lx l1 v ref v bp 2.4v v bp v in 2.6v to 15v sgnd v out off on 800khz oscillator ramp pwm comparator enable ckt & ldo regulator gate drive regulator uvlo & thermal shutdown current limit comparator control logic -- + vdr vdr vdr ss c5 c6 v fb 0.895v gm error amplifier current limit threshold -- -- + comp r3 c3 c4 -- -- + + current sense amplifier -- + bst figure 1?functional block diagram
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 6 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm the mp2106 measures the output voltage through an external resistive voltage divider and compares that voltage to the internal 0.9v reference in order to generate the error voltage at comp. the current-mode regulator uses the voltage at comp and compares it to the inductor current to regulate the output voltage. the use of current-mode regulation improves transient response and improves control loop stability. at the beginning of each cycle, the high-side n-channel mosfet is turned on, forcing the inductor current to rise. the current at the drain of the high-side mosfet is internally measured and converted to a voltage by the current sense amplifier. that voltage is compared to the error voltage at comp. when the inductor current rises sufficiently, the pwm comparator turns off the high-side switch and turns on the low-side switch, forcing the inductor current to decrease. the average inductor current is controlled by the voltage at comp, which in turn is controlled by the output voltage. thus the output voltage controls the inductor current to satisfy the load. since the high-side n-channel mosfet requires voltages above v in to drive its gate, a bootstrap capacitor from lx to bst is required to drive the high-side mosfet gate. when lx is driven low (through the low-side mosfet), the bst capacitor is internally charged. the voltage at bst is applied to the high-side mosfet gate to turn it on, and maintains that voltage until the high-side mosfet is turned off and the low-side mosfet is turned on, and the cycle repeats. connect a 10nf or greater capacitor from bst to sw to drive the high-side mosfet gate. application information mp2106 lx vin bst fb comp ss pgnd sgnd vref run output 1.8v / 1.5a input 2.6v to 15v mp2106_tac_f02 c5 10nf c6 10nf c3 3.3nf c7 10nf c4 open 6 7 8 2 9 10 4 3 1 5 figure 2?typical application circuit internal low-dropout regulator the internal power to the mp2106 is supplied from the input voltage (vin) through an internal 2.4v low-dropout linear regulator, whose output is vref. bypass vref to sgnd with a 10nf or greater capacitor for proper operation. the internal regulator can not supply more current than is required to operate the mp2106. therefore, do not apply any external load to vref. soft-start the mp2106 includes a soft-start timer that slowly ramps the output voltage at startup to prevent excessive current at the input. when power is applied to the mp2106, and run is asserted, a 2a internal current source charges the external capacitor at ss. as the capacitor charges, the voltage at ss rises. the mp2106 internally limits the feedback threshold voltage at fb to that of the voltage at ss. this forces the output voltage to rise at the same rate as the voltage at ss, forcing the output
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 7 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm voltage to ramp linearly from 0v to the desired regulation voltage during soft-start. the soft-start period is determined by the equation: 5 c 45 . 0 t ss = where c5 (in nf) is the soft-start capacitor from ss to gnd, and t ss (in ms) is the soft-start period. determine the capacitor required for a given soft-start period by the equation: ss t 22 . 2 5 c = use values between 10nf and 22nf for c5 to set the soft-start period (between 4ms and 10ms). setting the output voltage (see figure 2) set the output voltage by selecting the resistive voltage divider ratio. the voltage divider drops the output voltage to the 0.895v feedback voltage. use 10k ? for the low-side resistor of the voltage divider. determine the high-side resistor by the equation: 1 r 1 v 895 . 0 v 2 r out ? ? ? ? ? ? ? ? ? = where r2 is the high-side resistor, v out is the output voltage and r1 is the low-side resistor. selecting the input capacitor the input current to the step-down converter is discontinuous, and 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 may also suffice. the capacitor can be electrolytic, tantalum or ceramic. because it absorbs the input switching current it must have an adequate ripple current rating. use a capacitor with rms current rating greater than 1/2 of the dc load current. for stable operation, place the input capacitor as close to the ic as possible. a smaller high quality 0.1f ceramic capacitor may be placed closer to the ic with the larger capacitor placed further away. if using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. all ceramic capacitors should be placed close to the mp2106. for most applications, a 10 f ceramic capacitor will work. selecting the output capacitor the output capacitor (c2) is required to maintain the dc output voltage. low esr capacitors are preferred to keep the output voltage ripple to a minimum. the characteristics of the output capacitor also affect the stability of the regulation control system. ceramic, tantalum, or low esr electrolytic capacitors are recommended. the output voltage ripple is: ? ? ? ? ? ? ? ? + ? ? ? ? ? ? ? ? ? = 2 c f 8 1 r v v 1 l f v v sw esr in out sw out ripple where v ripple is the output voltage ripple, f sw is the switching frequency, v in is the input voltage, r esr is the equivalent series resistance of the output capacitors and f sw is the switching frequency. choose an output capacitor to satisfy the output ripple requirements of the design. a 22f ceramic capacitor is suitable for most applications. selecting the 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 will result in lower output ripple voltage. however, the larger value inductor is likely to have a larger physical size and higher series resistance. 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 to be approximately 30% to 40% of the maximum load current. make sure that the peak inductor current (the load current plus half the peak-to- peak inductor ripple current) is below 2.5a to prevent loss of regulation due to the current limit.
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 8 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm calculate the required inductance value by the equation: () i f v v v v l sw in out in out ? ? = where ? i is the peak-to-peak inductor ripple current. it is recommended to choose ? i to be 30%~40% of the maximum load current. 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: load cs vea out fb vdc r g a v v a ? ? ? ? ? ? ? ? = where v fb is the feedback voltage, a vea is the transconductance error amplifier voltage gain, g cs is the current sense transconductance (roughly the output current divided by the voltage at comp) and r load is the load resistance: out out load i v r = 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 load resistance and the output capacitor (c2), where: 3 c a 2 g f vea ea 1 p = p1 is the first pole, and g ea is the error amplifier transconductance (300a/v) and 2 c r 2 1 f load 2 p = the system has one zero of importance, due to the compensation capacitor (c3) and the compensation resistor (r3). the zero is: 3 c 3 r 2 1 f 1 z = if large value capacitors with relatively high equivalent-series-resistance (esr) are used, the zero due to the capacitance and esr of the output capacitor can be compensated by a third pole set by r3 and c4. the pole is: 4 c 3 r 2 1 f 3 p = the system crossover frequency (the frequency where the loop gain drops to 1, or 0db, is important. set the crossover frequency to below one tenth of the switching frequency to insure stable operation. lower crossover frequencies result in slower response and worse transient load recovery. higher crossover frequencies degrade the phase and/or gain margins and can result in instability. table 1?compensation values for typical output voltage/capacitor combinations v out c2 r3 c3 c4 1.8v 22f ceramic 6.8k ? 3.3nf none 2.5v 22f ceramic 9.1k ? 2.2nf none 3.3v 22f ceramic 12k ? 1.8nf none 1.8v 47f tantalum (300m ? ) 13k ? 2nf 1nf 2.5v 47f tantalum (300m ? ) 18k ? 1.2nf 750pf 3.3v 47f tantalum (300m ? ) 24k ? 1nf 560pf choosing the compensation components the values of the compensation components given in table 1 yield a stable control loop for the given output voltage and capacitor. to optimize the compensation components for conditions not listed in table 1, use the following procedure.
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 9 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm choose the compensation resistor to set the desired crossover frequency. determine the value by the following equation: fb cs ea c out v g g f v 2 c 2 3 r = where f c is the desired crossover frequency (preferably 33khz). choose the compensation capacitor to set the zero below one fourth of the crossover frequency. determine the value by the following equation: c f 3 r 2 3 c > determine if the second compensation capacitor, c4 is required. it is required if the esr zero of the output capacitor happens at less than half of the switching frequency. or: 1 f r 2 c sw esr > if this is the case, then add the second compensation capacitor. determine the value by the equation: 3 r r 2 c 4 c (max) esr = where r esr(max) is the maximum esr of the output capacitor. external boost diode for input voltages less than or equal to 5v, it is recommended that an external boost diode be added. this will help improve the regulator efficiency. the diode can be a low cost diode such as an in4148 or bat54. mp2106 lx bst 5v 8 6 boost diode 10nf mp2106_f03 figure 3?external boost 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. however, do not exceed the absolute maximum voltage for these pins.
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter mp2106 rev. 1.6 www.monolithicpower.com 10 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm package information msop10
mp2106 ? 1.5a, 15v, 800khz sy nchronous buck converter notice: the information in this document is subject to change wi thout notice. please contact mps for current specifications. users should warrant and guarantee that th ird party intellectual property rights are not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp2106 rev. 1.6 www.monolithicpower.com 11 2/22/2006 mps proprietary information. unauthorized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. tm qfn10 (3mm x 3mm)

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