View MP2108_3339178.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

MP2108 2a, 6v, 740khz synchronous buck converter MP2108 rev 1.1 www.monolithicpower.com 1 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. the future of analog ic technology description the MP2108 is a 2a, 740khz 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 740khz switching frequency allows for small filtering components, further reducing the solution size. the MP2108 includes cycle-by-cycle current limiting and under voltage lockout. internal power switches, combined with the tiny 10-pin msop or 3mm x 3mm qfn packages, provide a solution requiring a minimum of board space. qfn package is recommended if output current is higher than 1.5a. evaluation board reference board number dimensions ev2108dq/dk-00a 2.5?x x 2.0?y x 0.5?z features ? 2a output current ? synchronous rectification ? internal 160m ? and 190m ? power switches ? input range of 2.6v to 6v ? over 95% efficiency ? under voltage lockout protection ? soft-start operation ? thermal shutdown ? internal current limit (source & sink) ? tiny 10-pin msop and 3x3 qfn packages applications ? soho routers, pcmcia cards, mini pci ? handheld computers, pdas ? cell phones, digital still and video cameras ? small lcd displays ?mps? and ?the future of analog ic technology? are registered trademarks of monolithic power systems, inc. typical application MP2108 lx vin bst 1 3 7 4 5 9 8 6 10 2 fb comp ss pgnd sgnd vref run output 2.5v / 2a input 2.6v to 6v off on 10nf 10nf 2.2nf 10nf 100 90 80 70 60 50 40 30 20 10 0 efficiency (%) 0.01 0.1 1 10 load current (a) v out =2.5v v out =1.2v v in =3.3v
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 2 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. package reference bst vin lx pgnd sgnd 1 2 3 4 5 10 9 8 7 6 run vref comp fb ss top view part number* package temperature MP2108dk msop10 ?40 c to +85 c * for tape & reel, add suffix ?z (eg. MP2108dk?z) for rohs compliant packaging, add suffix ?lf (eg. MP2108dk?lf?z) top view bst vin lx pgnd sgnd 1 2 3 4 5 run vref comp fb ss 10 9 8 7 6 exposed pad on backside part number** package*** temperature MP2108dq qfn10 (3mm x 3mm) ?40 c to +85 c ** *** for tape & reel, add suffix ?z (eg. MP2108dq?z) for rohs compliant packaging, add suffix ?lf (eg. MP2108dq?lf?z) recommended for output currents higher than 1.5a absolute maxi mum ratings (1) input supply voltage v in ............................. 6.5v 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 6 output voltage v out ...........................0.9v to 5v operating temperature.............. ? 40 c to +85 c thermal resistance (3) ja jc msop10 ................................ 150 ..... 65... c/w qfn10 (3mm x 3mm) ............. 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 6 v input undervoltage lockout 2.2 v input undervoltage 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 6v 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
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 3 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. electrical characteristics (continued) v in = 5.0v, t a = +25 c, unless otherwise noted. parameter symbol condition min typ max units oscillator switching frequency f sw 620 740 920 khz maximum duty cycle d max v fb = 0.7v 85 % minimum on time t on 200 ns error amplifier voltage gain a vea 400 v/v transconductance g ea 450 a/v comp maximum output current 40 a fb regulation voltage v fb 875 895 915 mv fb input bias current i fb v fb = 0.9v ?100 na soft-start soft-start current i ss 2 a output switch on-resistance v in = 5v 190 m ? switch on resistance v in = 3v 280 m ? v in = 5v 160 m ? synchronous rectifier on resistance v in = 3v 230 m ? switch current limit (source) 2.5 3.5 a synchronous rectifier current limit (sink) 350 ma thermal shutdown 160 c pin functions pin # name description 1 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. 2 vin internal power input. vin supplies the powe r to the MP2108 through the internal ldo regulator. bypass vin to pgnd with a 10f or greater capacitor. connect vin to the input source voltage. 3 lx output switching node. lx is the source of the 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. 4 pgnd power ground. pgnd is the source of the n-channel mosfet synchronous rectifier. connect pgnd to sgnd as close to the MP2108 as possible. 5 sgnd signal ground. 6 ss soft-start input. place a capacitor from ss to sgnd to set the soft-start period. the MP2108 sources 2a from ss to the soft-start c apacitor at start-up. as the voltage at ss rises, the feedback threshold voltage increases to limit inrush current at startup. 7 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. 8 comp compensation node. comp is the output of the error amplifier. connect a series rc network to compensate the regulation control loop. 9 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. 10 run on/off control input. drive run high to turn on the MP2108, drive run low to turn the MP2108 off. for automatic startup, connect run to vin via a 100k ? pull-up resistor.
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 4 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. typical performanc e characteristics circuit of figure 2, v in = 5v, v out = 2.5v, l1 = 5h, c1 = 10f, c2 = 22f, t a = +25 c, unless otherwise noted. 100 90 80 70 60 50 40 30 20 10 0 efficiency (%) 0.01 0.1 1 10 load current (a) efficiency vs load current v out =3.3v v out =1.2v v out =2.5v v in =5v 0.904 0.902 0.900 0.898 0.896 0.894 0.892 0.890 0.888 0.886 0.884 feedback votlage (v) -50 -25 0 25 50 100 75 150 125 die temperature ( o c) feedback voltage vs die temperature 830 810 790 770 750 730 710 690 670 650 630 switching frequency (khz) die temperature ( o c) switching frequency vs die temperature -50 -25 0 25 50 100 75 125 5.0 4.5 4.0 3.5 3.0 2.5 2.0 peak current (a) 020 60 40 80 100 duty cycle (%) peak current vs duty cycle
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 5 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. typical performanc e characteristics (continued) circuit of figure 2, v in = 5v, v out = 2.5v, l1 = 5h, c1 = 10f, c2 = 22f, t a = +25 c, unless otherwise noted. v en 2v/div. v out 2v/div. 1ms/div. start-up through enable no load v en 2v/div. v out 2v/div. 400ms/div. shut-down through enable no load v en 5v/div. v out 1v/div. 100ms/div. start-up through enable full load v en 2v/div. v out 2v/div. 200ms/div. shut-down through enable full load v sw 5v/div. v out ac coupled 10mv/div. i l 1a/div. 400ns/div. steady state operation no load v sw 5v/div. v out ac coupled 10mv/div. i l 2a/div. 400ns/div. steady state operation full load v out ac coupled 200mv/div. i l 1a/div. load transient 0.5a-1a step resistive load
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 6 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. operation run v in 2 1 3 4 7 8 5 6 9 10 fb r2 r1 pgnd c7 c2 c1 lx l1 v ref 2.4v v bp v in 2.6v to 6v sgnd v out off on 720khz oscillator ramp pwm comparator enable ckt & ldo regulator gate drive regulator uvlo & thermal shutdown current limit comparator control logic -- + vdr vdr ss c5 c6 v fb 0.9v gm error amplifier current limit threshold -- -- + comp r3 c3 c4 -- -- + + current sense amplifier -- + bst figure 1?functional block diagram
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 7 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. the MP2108 measures the output voltage through an external resistive voltage divider and compares it to the internal 0.9v reference 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 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 voltage 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. voltage is maintained 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 MP2108 lx vin bst fb comp ss pgnd sgnd vref run output 2.5v / 2a input 2.6v to 6v c5 10nf c6 10nf c3 2.2nf c7 10nf c4 open 1 3 7 4 5 9 8 6 10 2 figure 2?typical application circuit internal low-dropout regulator the internal power to the MP2108 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 MP2108. therefore, do not apply any external load to vref. soft-start the MP2108 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 MP2108, 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 MP2108 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
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 8 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. rate as the voltage at ss, forcing a linear output voltage ramp 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 for c5 between 10nf and 22nf 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 0.9v 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 9 . 0 v 2 r out ? ? ? ? ? ? ? ? ? = where r2 is the high-side resistor, r1 is the low-side resistor and v out is the output voltage. selecting the 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 are also an option. 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 ic. 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 and r esr is the equivalent series resistance of the output capacitors. 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 in turn results 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 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.
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 9 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. 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, 0.9v, a vea is the transconductance error amplifier voltage gain, 400 v/v and g cs is the current sense transconductance, (roughly the output current divided by the voltage at comp), 4.5a/v. 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 (450a/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 1db or 0db) is important. set the crossover frequency 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 listed in table 1 yields 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.
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 10 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. 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 = where g ea is the ea transconductance (450 a/v) and 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 > where r esr is the equivalent series resistance of the output capacitor. the second compensation capcacitor is determined 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 it is recommended that an external boost diode be added to help improve the regulator efficiency. the diode can be a low cost diode such as an in4148 or bat54. MP2108 lx bst 5v boost diode 10nf 1 3 figure 3?external boost diode this diode is also recommended for high duty cycle operation (when in out v v >65%).
MP2108 ? 2a, 6v, 740khz syn chronous buck converter MP2108 rev 1.1 www.monolithicpower.com 11 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. package information msop10
MP2108 ? 2a, 6v, 740khz syn chronous buck 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. MP2108 rev. 1.1 www.monolithicpower.com 12 10/2/2006 mps proprietary information. unaut horized photocopy and duplication prohibited. ? 2006 mps. all rights reserved. qfn10 (3mm x 3mm)

▲Up To Search▲

Price & Availability of MP2108

	To Download MP2108 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .