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BM2596 (msp1250g) 150khz 3a step-down voltage converter general description the BM2596(=msp1250g) series of regulators are integrated circuits that provide all active functions for a step-d o wn ( b u ck) swit ching regul ator, capable of d r iving a 3a loa d with excellen t line and loa d regul ation. these dev ic es are avail- able in fixed output voltag es of 3.3v, 5v, 12v, and an ad ju st-able o u tput version . requiri ng a minimum number of external compon ents, these regulators ar e simple to use and include i n ternal frequency compensat ion?, and a fixed-frequency oscillator. the msp1250g series operates at a switching frequency of 150 khz thus allowing smaller sized filter components than what would be need ed with lower freq uency switchin g regulato r s. available in a standard 5-l ead to-2 2 0 package with 5 pins lead in one line options, and a 5-lead to-263 surf ace mount package. a standard series of inductors are availa ble from several different manufacture rs optimized for use wi th the msp1250g series. this feature greatly simplifies the design of switch- m ode pow er supplies. other featur es include a guar anteed 2% toler ance on output voltage und er specified input voltage and output load conditi ons, and 1 0 % on the oscillator frequency. external shutdown is included, featuri ng typically 80 a standb y curren t. self-protection features include a two stage freque ncy reducing current lim it for the outpu t switch and an ove r tem peratur e shu t down for complete prote c tion under fault conditions. features 3.3v, 5v, 12v, and adjus table outp u t versions (adj) adjustable version out put voltage r ange, 1.25v to 37v2% max over line and load conditions available in to-220 an d to-263 pa ckages guarante ed 3a output load current input voltage ra nge u p to 40v requires only 4 exte rn al componen ts excellent line and load r egulation spec ifications 150 khz fixed frequency internal oscillator ttl shutdown capa bil i ty low pow er standby m ode, i q typically 80 a g means pb free in msp1250g uses readily availa ble standard ind u ctors ? thermal shutdown and current limit protection applications simple high-efficien cy step-dow n (buck) reg u lator , car dvd electronic on-card switching regulators , lcd-tv , lcd-monitor , adsl positive to negative conve r ter www.bookly.com 1
BM2596 (msp1250g) 150khz 3a step-down voltage converter 5-lead to-220 (t) 5-lead to-263 (s) +vin ?this is the positive inp u t sup p ly for the i c switching regulato r . a suitable inpu t bypass capacitor must b e pres ent at this pin to minimize voltage transients and to supply the switching currents needed by the r e gulator . ground ?circuit ground . output ?internal switch. the voltage at this pin switches between (+vin - vsat) and appr oximatel y -0.5v, with a duty cycle of appr ox ima t ely vout/vin. to minimize coupling to sensitive cir c uitry, the pc boa rd cop per ar ea co nnected to this pin shou ld be kept to a minimum . feedbac k ?senses th e regulate d o u tput volt age to complete the feedback loop . ?allows the switching r egulator circuit to be shut down using logic level signals thus dropping the total in put supply current to approximately 80 a. pulling this pin below a threshold voltage of approximately 1.3v tu rns the regulator on, and pulling this pin abov e 1.3v (up to a maximum of 25v) shu t s the r egulat or dow n. if this s hutdown feature is not need ed, the pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the on co ndition. marking information: BM2596 -xx or msp1250g -xx on the chip, both two numbers are pb-free; www.bookly.com 2 xx means output voltage 12 3 v in 45 v out gnd fb
BM2596 (msp1250g) 150khz 3a step-down voltage converter block diagram absolute maximum ratings (note 1) p a r a m e t e r r a t i n g u n i t maximum supply voltage 45 v pin input voltage -0.3 25 v feedb ack pin voltage -0.3 25 v output voltage to groun d (steady state) -1 v power dissipation internally limited -- storage tem peratur e ran ge -65 1 50
esd susceptibility (human body model) (note 2) kv maximum junction temperature 150
temperatur e range -40 1 25
conditions supply volta ge 4.5 40 v note 1: absolute maximum ratings indicate li mi ts beyond which dama ge to the de vice may occur. operating ratings indicate c onditions for which the device is intended to be functional, but do not guarante e s pecific performance limits. fo r guara n tee d specificatio ns and test con d itions, see the el ectrical char acteristics. note 2: the human bo dy model is a 1 00 pf capacit or discharge d through a 1.5k resistor into each pin. www.bookly.com 3
BM2596 (msp1250g) 150khz 3a step-down voltage converter electrical characteristics ? condition :t j = 25
? v o =3.3v msp1250g-- v o =3.3v s y mbol parameter conditions min (note 4) ty p (note 3) max (note4 ) units system pa rameters (note 5) test circuit figure 1 v out output voltage 4.75v ? v in ? 40v 0.2a ? i load ? 3a 3.18 3.3 3.42 v ? effi ciency v in =12v d i load =3a - - 75 -- % v o =5v msp1250g-- v o =5.0v s y mbol parameter conditions min (note 4) ty p (note 3) max (note4 ) units system pa rameters (note 5) test circuit figure 1 v out output voltage 7v ? v in ? 40 v 0.2a ? i load ? 3a 4.80 5.0 5.250 v ? effi ciency v in =12v d - - 84 -- % v o =12v msp1250g-- v o =12.0v s y mbol parameter conditions min (note 4) ty p (note 3) max (note4 ) units system pa rameters (note 5) test circuit figure 1 v out output voltage 15v ? v in ? 40v 0.2a ? i load ? 3a 11 . 4 0 1 2 . 0 12.60 v ? effi ciency v in =25v d i load =3a - - 88 --- % v out is adju st able msp1250g?adj s y mbol parameter conditions min (note 4) ty p (note 3) max (note4 ) units system pa rameters (note 5) test circuit figure 1 v fb feedb ack voltage 4.5v ? v in ? 40v 0.2a ? i load ? 3a vout prog rammed for 3v. circuit of figure 1 1.21 1.25 1.29 v ? effi ciency v in =12v d v out =3v d i load =3a - - 75 -- % www.bookly.com 4
BM2596 (msp1250g) 150khz 3a step-down voltage converter all output voltage versions electrical characteristics ? condition :t j = 25
? msp1250g?xx s y mbol parameter conditions min (note 4) ty p (note 3) max (note4 units device pa rameters i b f eedb ack bias current adjusta b le versio n only , vfb = 1.3v - - 1 0 100 na f o oscillator f r eque nc y (note 6) 125 150 173 khz v sa t vsat saturation voltag e i out = 3 a(notes 7, 8) - - 1 . 1 6 1.5 v ma x du ty cy cl e (on) (note 8) -- 100 -- % dc min dut y cy c l e ? off ? (note 9) -- 0 -- % i cl current limit peak curr ent (notes 7, 8) 4.2 4.8 5.5 a output = 0v (notes 7, 9) - - - - 5 0 ? a i l output leak ag e current output = - 1v (notes 10) - - 2 3 0 m a i q quiesce nt curr ent (note 9) -- 7 10 ma i st b y standb y qui e s c ent current on/of f pin = 5v (of f ) (note 10) - - 8 0 250 ? a jc t o -220 or t o -263 junction to case - - 2 - -
/w ja t o -220 packag e ,juncti on to ambie n t(note 11) - - 5 0 - -
/w ja t o -263 packa ge, junction to ambient (note 12) - - 5 0 - -
/w ja t o -263 packag e ,juncti on to ambie n t(note 13) - - 3 0 - -
/w ja t hermal resistance t o -263 packa ge, junction to ambie n t(note 14) - - 2 0 - -
/w control test circuit figure 1 on /of f pin logic input - - 1 . 3 - - v v ih lo w (r egu lator on) -- -- 0.6 v v il t h reshold volt age high( re gul ator off) -- -- 2.0 v i h v logic =2.5v (regulator off) - - 5 1 5 ? a i l on /off pin input current v logic =0 .5 v (reg ulator on) - - 0 . 0 2 5 ? a www.bookly.com 5
BM2596 (msp1250g) 150khz 3a step-down voltage converter note 3: typi cal numbers are at 25
and re prese n t the most likely norm. note 4: all limits guarant eed at room temperature (standard type face) and at temperature extremes (b old type fac e ). all room temper ature limits are 100% production tested. all limits at temperatur e ext r emes are guara n teed vi a correlation using standard statistical quality co ntrol (sqc) m e thods. all limits ar e used to calculate aver age o u tgoing q ual ity level (aoq l ) . note5: exter nal compone nts such as the catch di ode, inductor, input and output capacitor s, and volta ge prog rammin g resistors can affect switching regulat or system performance. note 6: the switching freque ncy is reduced when the second stage curre nt limit is activated. note 7: no d i ode, inductor or capacit or connected to output pin. note 8: feedback pin removed fro m output and connecte d to 0v to force the output transistor swi t ch on. note 9: fee dback pin removed from output and connec ted to 12v for the 3 . 3v, 5v, and the adj. version, and 15v for the 12v ver s ion, to force the output transistor switch off. note 10: v in = 40v. note 11: ju nction to ambient thermal resistance (no exter nal heat sink) for the to-220 package mounted ve rtically, with t he leads soldere d to a printed circuit board with (1 oz.) copper area of app roximately 1 in 2 . note 12: jun c tion to ambient thermal resistance wi th the to-26 3 package tab soldered to a single printe d circuit board with 0.5 in 2 of (1 oz.) copper ar ea. note 13: jun c tion to ambient thermal resistance wi th the to-26 3 package tab soldered to a single sided printed circuit board with 2.5 in 2 of (1 oz.) copper area. note 14: jun c tion to ambient thermal resistance wi th the to-26 3 package tab soldered to a double side d printed circuit board with 3 in 2 of (1 oz.) copper ar e a on the ms p1250g side of the board, a nd app roxim a tely 16 in 2 o f copper on the other side of the p-c bo ard. www.bookly.com 6
BM2596 (msp1250g) 150khz 3a step-down voltage converter external components input capacitor c in ? a low esr aluminum or tantal um bypass capacitor is need ed betwee n the input pin a n d gro und pin . it must be located ne ar the r egula t or using sh ort leads. this capacitor prevents large voltage tran sients from appe aring at the input, an d provi des the inst an t aneo us current neede d each time the switch turns on. selecting an input cap a citor requir e s consulting the manuf acturers dat a sheet for maximum allowabl e rms ripple current. for a maximu m ambient temperatu r e of 40c, a g ener al guid e lin e would be to select a cap a citor with a ripple cu rr en t rating of ap proximatel y 50% of the dc load current. for ambient temperatures up to 70c, a current rating of 75% of the dc load current woul d be a good choice for a conservati ve design. the cap a citor volt age rating m u st be at least 1.25 times greater than th e maxi mum input volt age , and of ten a much high er volt age cap a citor is needed to satisfy the rms cur r ent requi re ment s. feedforward capa c itor (adjustable output voltage version) c ff ----a fee d forwar d cap a citor c ff , shown across r2 in figure1 is used when the ou tput voltage is greater th an 10v or w hen c out has a very lo w esr. this capac itor ad ds lead compensation to the feedback loop and i n creases the phas e margi n for better loop stability. output capacitor c out ?an o u tput capacitor is required to filter the output an d provi de regulator loop stability. low impedance or low esr electrolytic or solid tantalum capacitors designed for switchi ng regulator a ppli c ations mu st be used. w hen selecting an output capacitor, the im portant capa citor parameters are; the 100 khz equivale nt series resistance ( esr), the r m s ripple cu rrent rati ng, voltage ratin g , and c apacitance value. fo r the output capacitor, the esr va lue is the most important par ameter. the output capacitor requir e s an esr value th at has an up per an d lo w e r limit. for lo w output rip p l e voltage, a l o w esr value is needed. this value is determi ned by the maxi mum allowa ble output rippl e voltage, typi cally 1% to 2% of the output voltag e. but if t he selected ca pacitor?s esr is extremel y low, there is a possibility of an uns table feedback loo p , resulting in an oscilla tion at the output. catch dio d e d ----buck regulators require a diode to provide a return path for th e inductor current when the swit ch turns off. thi s must be a fast diode and must be located close to the msp1250g using shor t leads and short printed circui t traces. because of their ver y fast switching speed and low forwa r d volta ge drop, sch o ttky diodes provi de the best performa n ce, especially in low output volt age applications (5v and lo wer). ultra fast recove ry, or high-efficiency rectifiers are also a go od choice, but some types with an abrupt turnoff characteristic may caus e instability or emi problems. inductor selection l ----all switching reg u lato rs have two basic modes of operation; continuous and discontin uous . the difference between the two types relates to the inductor current, whether it is flowing continuously, or if it drops to zer o for a perio d of time in th e normal switching cycle. each mode has distin ctively differen t operat ing characteristics, which can affect the regulator s perfor m ance and r equirem ents. mo st switch er designs w ill oper ate in the discontinuous m ode w hen the loa d current is low. the msp1250g (or any of the simple switcher family) can bemu s ed fo r both continuous a nd di scontinuous modes of oper ation. www.bookly.com 7
BM2596 (msp1250g) 150khz 3a step-down voltage converter ty pical application 1. fixed output voltage versions , BM2596 (msp1250g) 2. inverting regula t o r the circuit in figure follo wing convert s a posit ive input voltag e to a negative output volta g e with a common grou nd. the ci rcuit operates by b ootstrapping the regulator? s ground pin to the negative output volt age, and then groun ding the feedback pi n, the msp12 50g generate a negative output volt age. si nce this re gulator topol ogy can prod uce an output volt age that is either gr eate r than o r le ss than the input vo lt ag e, the maxi mum output current gr e a tly depe nds on both the inpu t and output volt age. the maximum vo lt age appea ring across the regulato r is the absolute sum of the input an d out put volt age, and this must be limited to a maximum of 40v .additional diodes are required in this regulator confi guration. diode d1 is used to solate input volt age ripple or noise from coupling thro ugh the c in cap a citor to the output, unde r light or no load conditio n s. wit hout diode d3, w hen the inpu t voltage is first applied, the charging cur r ent of c in can pull the o u tput positive by several v o lts for a short period of time. adding d 3 pre v ents the output fr om going p o s itive by more than a di ode voltage. www.bookly.com 8
BM2596 (msp1250g) 150khz 3a step-down voltage converter test circuit and lay o ut guidelines c in --4 70 ? f, 50v, aluminum electrolyt ic nichicon ?pl series? c out --22 0 ? f, 25v alu m inum electr olytic, nichicon ?pl serie s ? d 1 --5a, 40v schottky re ctifier, 1n58 25 l 1 --68 ? h, l 38 wher e vref = 1.23v select r 1 to be app roxim a tely 1 k c , u s e a 1% resi stor for best stability. c in --470 ? f, 50v, aluminum electrolyt ic nichicon ?pl series? c out --22 0 ? f, 35v aluminum electrolyt ic, nichico n ?pl series? d 1 --5a, 40v schottky re ctifier, 1n58 25 l 1 --68 ? h, l38 r 1 --1 k c , 1 % c ff -- see application information section www.bookly.com 9
BM2596 msp1250g 3a dc/dc w w w w w w . . b b o o o o k k l l y y . . c c o o m m 10 package dimension to-220 (n220) r s j k n a c b d f g 1 23 t s c t j r b a f 45 d g n k to-263 (n263) a d c b i e l f g k

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