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e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 1 of 16 2007/1 1 /21 description the ect 340 9 is a dual cha nnel cur- rent mode pwm dc-dc step -do w n conv erte r o p e r ati ng at 1.5 m hz con s tant fre quen cy. the device is i deal for p o rtable equipm ent re quirin g two sep a rate po wer su pplie s that need hi gh current up to 60 0ma. the de vice ope rate s from singl e-cell lit h ium-i on batt e ries whil e st ill achieving over 96% efficien cy. the ECT3409 al so ca n run at 100% duty cycle fo r low dropo ut ope ration, exten d ing battery l i fe in portabl e sy stems while li g h t load o pera t ion provid es very low outp u t rip p le for noi se sen s itive appl ication s . the device h a s a uniq ue adaptive slo p e comp en sat i on scheme th at make s it po ssible to o perate with a lo we r rang e of ind u ctor valu es to optimize size an d provide efficient ope ration. th e 1.5mhz swit chin g freq ue ncy minimizes th e size of external comp one nts whil e kee p ing swit chin g losse s low. the ect340 9 ca n operate fro m a 2.5v to 5.5v input voltage and can sup p ly up to 600ma output cu rren t for each cha nnel. the ect 340 9 is availabl e in a pb-free 3x3mm tdf n -1 0 packa ge an d operate s over the -40c to +85 c temperature range. features z v in range: 2.5v to 5.5v z up to 600ma output cu rre n t z high effic i ency: up to 96% z 1.5mhz co nstant frequ en cy ope r ation z 100% duty cycle dropo ut operation z low r ds (on) internal s w itches: 0.35 ? z curre n t mode operatio n for excellent line and load t r an sie nt respon se z adaptive slope com pen sation z soft start z short-circuit and the r mal fault prote c tion z <1a shutdo wn current z powe r-o n re set output z available is the lea d fre e packag e applications z cellula r tele phon es z digital still cameras z pdas z portable me d i a players z wirel e s s an d dsl block diagram http://
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 2 of 16 2007/1 1 /21 pin# symbol functio n 1 fb1 f eedb ack in pu t for channel 1. conn ect f b 1 to the center p o int of an e x tern al r e sistor div i der. the feedback threshold voltage is 0.6v. 2 en1 channel 1 enable pin. active high. in shutdown, all functions are disabled drawing <1a supply current. do not leave en1 floating. 3 in po w e r su pp l y i nput p i n. must be clos el y d e c oup led to gn d w i t h a 2.2 f or greater cer a mi c cap a c i tor . 4 lx1 cha nne l 1 s w it chin g no de pi n . connect the output in ductor to this pin. 5 gnd ground 6 n/c no connection 7 lx2 cha nne l 2 s w it chin g no de p i n . conn ect the output i nduct o r to this pin. 8 por po w e r- on res e t, active lo w . open drai n. exte rnal res i stor (10 0 k ? ) i s requ i r ed . 9 en2 channel 2 enable pin. active high. in shutdown, all functions are disabled drawing <1a supply current. do not leave en2 floating. 10 fb2 f eedb ack i npu t for chan nel 2. con nect f b 2 t o the c enter p o i nt of an e x tern al r e sistor div i d e r . the feedback threshold voltage is 0.6v. ? ep exposed paddle. the exposed paddle should be connected to board ground plane and gnd. the ground plane should include a large exposed copper pad under the package for thermal dissipation (see package outline). packag e v out v o lt a g e part numb er marking marking info rmation tdfn-10 adj ECT3409-adj-ff 3409x yy ww x is the output volt age of p r oduct i on. example: blank adjust able. y y is the year o f production. 07 means the p r odu ct is manufactured in y e a r of 2007. ww is the w eek of production. 25 means the product is manufactured in the 25 th w eek. pin descriptions ordering information marking in formation tdfn -10 (to p vie w ) pin assignment ECT3409 - xxx - xx f o u t p ut v o l t ag e: v ou t = ad j : ad j u s t a b l e p a c k a g e : f = td fn - 1 0 f: lead-free circuit type
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 3 of 16 2007/1 1 /21 absolute maximum rating (1) parameter sy mbol v a lue units input sup p l y v o ltag es v in -0.3 to 6.0 v en1, en2 volt ages v en 1, v en 2 -0.3 to v in + 0.3 v f b 1, f b 2 voltages v fb1 , v fb2 -0.3 to v in + 0.3 v lx1,l x 2 v o lta ges v lx 1, v lx 2 -0.3 to v in + 0.3 v por voltages v por -0.3 to 6.0 v operatin g t e mperatur e ra ng e (2 ) t a -40 to + 85 c junctio n t e mperature r a n g e (2) t j + 125 c storage t e mperature r a n g e t st g -65 to 150 c lea d t e mperature (sol deri ng, 10s) t lead + 300 c recommended operating conditions parameter sy mbol v a lue unit s t hermal resist ance (3 ) ja 45 c/w maximum po w e r dissipation at t a = 25c p d 2.2 w note : (1). absolute ma ximum ratings a r e those values be y ond w h ich th e life of a device ma y be imp a ired . (2). t j is calculat ed from t he ambi ent tempe r ature t a a nd po wer di ssip a tion p d according to th e follow i ng formula: t j = t a + p d x ja . (3). the r mal resi st ance is specifie d w i th app roxima tely 1 squa re inch of 1 oz coppe r .
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 4 of 16 2007/1 1 /21 electrical characteristics v in = v en = 3.6v , t a = 25 unless other w i se note d. des c ription sy mbol te s t conditions min ty p max unit s step-down converter input voltage range v in ? 2.5 ? 5.5 v active mode, v fb = 0.5v ? 500 800 inpu t dc supply cu rren t i q shutdown mode, en1 = en2 = 0v, v in = 4.2v ? 0.3 2.0 a t a = 25c, channel 1 or 2 0.5880 0.6000 0.6120 t a = 0c t a +85c, channel 1 or 2 0.5865 0.6000 0.6135 regu lated f eedba ck vo l t a g e v fb t = - 4 0 c t +85c , cha nne l 1 o r 2 ( s e e n o t e :2 ) 0. 5 8 50 0 . 600 0 0. 6 1 50 v fb input bias current i fb ? -30 ? 30 na ou tpu t v o l t age lin e regu lation v ou t / v ou t / v in v in = 2.5v to 5.5v, i out = 10ma ? 0.11 0.40 %/v ou tpu t v o l t age loa d regu lation v ou t / v ou t / i ou t i ou t = 10 ma to 600 ma ? 0 . 001 5 ? %/m a maximum output current i lim v in = 3.0v 600 ? ? ma startup time t s f r om enabl e to output reg u lati on ? 100 ? s over-t emperature shut d o w n t h reshol d t sd ? ? 140 ? c over-t emperature shut d o w n h y steresis t hy s ? ? 15 ? c oscillator frequency f osc v fb = 0.6v 1.2 1.5 1.8 mhz p-channel mosfet i lx = 300ma ? 0.35 0.45 n - channe l mosfet r ds ( o n) i lx = 300 ma ? 0. 28 0. 45 peak inductor current ? v in = 3v, v fb = 0.5v; duty cycle <35% ? 1.20 ? a enable threshold low v en(l) ? ? ? 0.3 v enable threshold high v en(h) ? 1.5 ? ? v en input current i en ? -1.0 ? 1.0 a v fb ramping up ? 8.5 ? % v fb ramping down ? -8.5 ? % power-on reset delay ? 175 ? ms po w e r - o n res e t t h reshol d (por ) ? p o w e r- on rese t on -re s is t anc e ? 10 0 ? ? note : 1 . s p e c i f i c a t i o n s o v er the temp erat ure ran ge a r e gu aranteed b y design and cha r acter i zation. 2. the regulated feedback voltage is test in an internal test mode that connects v fb to the output of the error amplifier.
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 5 of 16 2007/1 1 /21 t y pical performance characteristics
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 6 of 16 2007/1 1 /21 t y pical performance characteristics (continued)
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 7 of 16 2007/1 1 /21 functional description the ECT3409 is a dual high performance 600ma, 1 . 5 m h z f i x e d f r e q u e n c y m o n o l i t h i c s w i t c h - m o d e s t e p - d o w n conve r t e r whi c h use s cu rre nt mode a r c h i t e c t u r e w i t h a n adaptive slope compensation scheme . it min imizes external component size and optimizes ef ficiency over the complete load range. the ad aptive slope c o mpensation allows the device to remain st able over a wider ra nge of inductor values so that smaller values (1h to 4.7h) with associated lower dcr ca n be used to achieve highe r ef ficiency . apart from th e small byp a ss input cap a citor , only a small l-c filter is required at each output. the a d j ust able output s can be programmed with external feed back to any volt age, rangin g from ver y lo w output volt a ges to the inp u t vo lt a g e and by using an internal re ference of 0.6 v . the p a rt uses internal mosfet s for each channel to achieve high ef ficiency . at dropou t, th e converter d u ty c y cle incr eases to 100% and the output vo lt ag es track the input vo lt age minus the low r ds (on) drop of the p-channel high-side mosfet s . the converter ef ficiency ha s been optimized for all loa d conditio n s, r anging from n o load to 600 ma at v in = 3v wi th a n input volt age range from 2 . 5v to 5.5 v . t h e internal er ror amplifier a n d c o m p e n s a t i o n p r o v i d e s e x c e l l e n t t r a n s i e n t response, load, and l i ne regulation . in ternal sof t st art elimina t es an y output vol t a g e overshoot when the ena ble or th e input volt age is applied. current mode pwm control slope compe n sated curre nt mode pwm control p r ovides st ab l e swit ching a n d cy cle- by -c y c le cur - re n t limit f o r excellent load and line re sponse and protection of the internal m a in switch (p-c hannel m o sfet) and synchrono u s rectifier (n-ch annel mosfet). during normal ope ration, the in tern al p- channel mosfet is turned o n for a spe c ified time to ramp the inductor curre nt at ea ch rising edg e of the inter nal oscillator , and is switched of f when the peak inductor cu rre nt is above th e error volt ag e. the curren t comp arator , i comp , l i m i t s th e p e a k i n d u ctor curre nt. when the main switch i s of f, the syn c hrono us re ctifier turns on imm ediately a n d st ays on until either the inductor curre n t st art s to reverse, a s indicated b y the current reversal co mp arator , i zero , or the be ginning of the next clock cycle. the ovdet comp arator control s output transient overshoo t by turning th e main switch of f and keeping it of f until the fau l t is no lon ger p r esent. control loop the ECT3409 is a peak current mod e s t e p -down conve r ter. the current through th e p-channel mosfet (hig h side) is sensed for current loop control, as well a s short circuit and o v erload protection . an adap tive slop e compensation signal is added to the sensed cu rrent to main tain stab ility for duty cycle s greater tha n 50%. the peak current mode loop appears as a voltage-programmed curre nt source in p a rallel with th e output capa citor. the ou tput o f the voltage error amplifier prog rams the curr ent mode loo p for the nece ssary peak switch current to force a cons tant ou tpu t voltage for a l l load and line conditions. internal loop co mpensation termi nates the tran conduc tance voltage error amplifier outpu t. for fixed volta ge versions , the error amplifier re ference volt age is in te rnally set to pr ogram the co nverter outpu t vo ltage . for the adjus table ou tput, the error amplifier re ference is fixed a t 0 . 6 v . enable the enab le pins are active high. when p u lled low, the enable input force the ECT3409 in to a lo w power, non -switching state . the total inpu t current dur ing shu t down is less than 2a.
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 8 of 16 2007/1 1 /21 current limit and over-temperature protection for over load conditions, th e peak input current is limited. to minimize power d i ssipation and stresses under current limi t and shor t-circuit condi tions, switchin g is termina t e d after enterin g current lim it for a series o f pulses. swi t ching is termina t ed for seven conse c utive clock cycles a fter a curr ent limit h as been sensed for a serie s of four con s ecutive clock cycles. thermal protection completely disables sw itching w hen interna l dissipation b e comes excessive. the junction o v er- t emperature threshold is 140c with 15 c of hys t eresis. once an o v er- tempera t ure or over-current fau l t conditions is r e moved , the output voltag e auto m atically recovers. dropout operation when the inp u t volt age de creases towa rd the value of the ou tp ut vo lt a ge, the ect340 9 a llo ws the ma in switch to remain on f o r more than one swit ching cycle and increases t h e dut y c y cle until it r e aches 100%. t h e d u t y c y c l e d o f a s t e p - d o w n c o n v e r t e r i s d e f i n e d a s : whe r e t on is the main switch on time an d f osc is the oscillator frequency (1.5m h z). the output voltage then is the input volt age minu s the voltage drop acro ss the main swit ch and the induct o r. at low input su pply voltage, the r ds (on) of the p-ch ann el m o sfet incre ase s an d t he efficien cy of the co nverte r d e c re a s e s . cautio n mu st be exe r ci sed to ensure th e heat di ssip ated do es not excee d the maximum jun c tion temp era t ure of the ic. maximum load current the ect340 9 will o perate with a n in put su pply voltage a s lo w a s 2.5v; however, the maximum lo ad curren t decrea s e s at lowe r inp u t due to the large i r d r o p on t he m a in switch an d syn c hrono us rectifie r. the sl op e comp en satio n sign al red u c e s the pea k inducto r cu rrent a s a fun c tion of the duty cycle to prevent sub - ha rmoni c oscillation s at duty cycles g r eate r t han 5 0 %. conversely, the curre n t limit increa se s as the d u t y cycle decre ase s . % 100 * % 100 * * in out osc on v v f t d =
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 9 of 16 2007/1 1 /21 applications inform ation
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 10 of 16 2007/1 1 /21 setting th e output v o ltage figure 1 shows the basic application circuit for the ECT3409. resistors r1 and r3 and r2 and r4 program the ou tpu t to regula t e at a vo ltage high er than 0.6 v . to limit the b i as current req u ired for the e x terna l feedb ack resistor string while mainta ining g ood no ise immunity, the minimum sugg ested va lue for r1 and r3 is 59k ? . alth ough a larger value will further reduce quiescent cu rrent, it will also increase the impedance o f the feedb ack node, ma king it more s ensitive to externa l noise and in terfere n ce. table 1 summarizes the resistor va lues for var i ou s output vo lta ges with r1 a nd r3 set to e i ther 59k ? for good no is e immun i ty or 316k ? for red u ced no load input current. the ad justable feedback re sistors, comb ined with an e x terna l feed forward capacitors (c4 and c5 in f i gure 1); deliver enhanced tra n sient respon se for e x treme pulsed load applica t ions . the addition of the feed forward capacito r typically requires a lar ger outpu t ca pacitor c2 an d c3 for stability. the e x ter nal resistor se ts the ou tput voltage according to the following equ ation : table1. resistor selection for output voltag e se tting; standar d 1% resistor v a lues substituted closest to the calculated values v out (v) r1 =59 k r2 (k ? ) r1 =31 6 k r2 (k ? ) 0.8 19.6 105 0.9 29.4 158 1.0 39.2 210 1.1 49.9 261 1.2 59.0 316 1.3 68.1 365 1.4 78.7 422 1.5 88.7 475 1.8 118 634 1.85 124 655 2.0 137 732 2.5 187 1000 3.3 267 1430 ? ? ? ? ? ? + = 1 2 1 * 6 . 0 r r v v out 1 * 1 2 r v v r ref out ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = or
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 1 1 of 16 2007/1 1 /21 inductor selection for mo st desi gns, the ect 3409 op erate s with indu cto r values of 1h to 4.7h. low indu ctan ce values are physi cally smalle r, but require faster swit chin g, wh ich re sults in some efficie n c y loss. the indu ctor value can be deriv ed from the followin g equatio n: whe r e i l is indu ctor ri ppl e cu rre nt. large value in du ctors lo we r ri pple current and small val ue indu cto r s result in high rip p le cu rre nts. ch oo se indu ctor ri p p le cu rrent ap proximately 3 5 % of the maximum load current 600ma , or i l = 210ma. for outpu t vo ltages abo ve 2.0v, when light-load e f ficiency is impor tant, the min imum recommended inductor size is 2.2h. for op timum voltag e position i ng load transients, choose an inductor with dc series res i stance in the 50m ? to 150m ? range . for higher e f ficiency a t h eavy loads (a bove 200m a), or min imal load regulatio n (with some transient over- shoo t), the resistance should be kep t b e low100m ? . the dc cu rrent ra ting o f the inductor s hould be a t le ast equa l to the ma ximum load cur- rent p l us ha lf the ripple current to pre v ent core sa turation (600ma + 105ma). tab l e 2 lis ts some typical surface moun t inductors tha t mee t targe t applications for the ECT3409 . manufa c turer' s spe c ificatio ns list both the inducto r dc cu rr ent rating, which is a thermal limit a tion, and the pe a k curre n t rating , which i s d e t e r m i n e d by the saturation char a c te risti cs. th e indu ctor shoul d no t show any ap pre c iabl e saturation u n der n o rm al lo ad co ndition s. some induct o rs m a y meet the peak a n d averag e cu rrent rating s ye t result in exce ssive lo sse s du e to a high dcr. always co nsid e r the lo sses a s soci ated with the dcr an d its effect on the total conve r ter efficien cy when sele cting a n i ndu ctor. fo r example, the 2.2h cr4 3 seri es i ndu ct or sele cted from sumida has a 71.2m ? dcr an d a 1.75adccurrent rating. at full load, the indu ctor dc lo ss i s 25m w which give s a 2 . 8% loss in efficien cy for a 600 ma, 1.5v output. t able2. t y pic a l surface mount inductors part l( h) max dc r( m ? ) r at ed d c cu rrent ( a ) size wxl x h (m m ) 1.5 80 1.35 2.2 120 1.10 3.3 173 0.9 cdrh 2d1 1 /h p 4.7 238 0.75 3.2 x 3.2 x 1. 2 1.0 45 1.72 2.2 75 1.32 3.3 110 1.04 sumida cdrh 4d1 8 4.7 162 0.84 4.7 x 4.7 x 2. 0 1.5 120 1.29 2.2 140 1.14 3.3 180 0.98 t o ko d31 2 c 4.7 240 0.79 3.6 x3.6 x1.2 osc l in out in out f i v v v v l * * ) ( * '
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 12 of 16 2007/1 1 /21 slope compensation the ect34 0 9 step-d o wn conve r ter u s es pea k cu rrent mode co ntrol with a unique ada ptive slope co m pen sation scheme to m a intain sta b ility with lowe r value ind u cto r s fo r duty cy cl es g r eate r th an 50%. usin g lowe r value inducto rs provide s bett e r overall effi cien cy and al so ma ke s it easie r to stand ardi ze on on e inducto r for different req u ired o u t- put voltage le vels. in order to do this an d ke ep the st ep-d o wn con v erter stable whe n the d u ty cycle i s g r e a ter tha n 50%, the ect34 09 sep a rate s the sl ope co mpe n s ation into 2 phase s . th e requi red slope co mpe n s ation is automatically detecte d by a n internal circuit usin g the f eedb ack volt age v fb befo r e the e rro r a m p compa r i s on to v ref . whe n belo w 50% duty cycle, the sl op e com pen sati on is 0.2 84a /s; but whe n above 50 % duty cycle , the slope comp en satio n is set to 1.136a/s. th e output indu ctor val ue mu st be sele cte d so the i ndu ctor cu rre nt d own slop e meets the int e rnal slop e compen satio n requi rem ents. below 50% d u ty cycle, the slop e com p e n satio n req u irement is: therefore: above 50% d u ty cycle, therefore: with these ad aptive setting s, a 2.2h in ducto r ca n be used fo r all output voltage s from 0.6v to 5v. s a l m / 284 . 0 * 2 25 . 1 = = h m l 2 . 2 625 . 0 = = s a l m / 136 . 1 * 2 5 = = h m l 2 . 2 5 . 2 = =
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 13 of 16 2007/1 1 /21 input capacitor selection the input cap a citor reduces the surge current drawn from the inpu t and switching noise from the device. th e input cap acitor impedance at the switching frequency shoul d be l ess than the inpu t source impedance to prevent high frequency switching current p a ssing to th e input. t h e c a lc u l a t e d v a l u e v a r i e s w i th i nput voltage and i s a maximum whe n v in is double the o u tput voltage. a low esr input cap a citor size d for ma ximum rms curre n t must be use d . ceramic cap a cit o rs with x5r or x7r diele c trics a r e highly re co mmend ed be cau s e of their low esr an d small temp eratu r e coef fi cient s. a 22f ceramic cap a citor for most appli c ati ons i s suf f i c ie nt. a large va lue may be u s ed for im pro v ed input volt age filtering. the maximu m input cap a citor rms cu rrent is: the inpu t capacitor rms r i pple current varies with the input and output voltage a nd will a l ways be less than or equal to half of the to tal dc load cu rrent to minimi ze stray ind u ct a n ce, the cap a citor sho u ld b e pla c ed as closely a s p o ssible to th e ic. thi s keep s the high freque ncy co ntent of the input cu r- rent locali zed, mi nimizin g emi and inp u t volt age rip p le. a laboratory t e st set-u p typically con s ist s of two l ong wire s ru nnin g from the be n c h po we r sup p ly to the evaluation board i nput v o lt age pi ns. t he in du ct ance of these wires, alon g with the low-es r cerami c input cap a citor , ca n create a high q net - wo rk that may af fect converte r p e rf orma nce. this proble m of ten be com e s app arent in t he form of exce ssive rin g ing in the o u tput volt age durin g loa d trans i ent s. errors in the loo p phase and gain mea s u r e m ent s can als o result. since the in d u ct ance of a sho r t pcb tra c e feedi ng the input volt ag e is significa n t ly lower than the power le ads from the bench po wer supply , most appli c atio ns do not exh i bit this pro b l e m. in applications wh ere the input p o wer sou r ce lead ind u ct an ce cann ot be redu ced to a level that does not af fe ct the co nverte r perfo rman ce, a high esr t a n t a l u m or alumi num electrolytic sh ould be pla c e d in p a rallel with the low esr, esl byp a ss cerami c. this da mpe n s the high q netwo rk a nd stabili ze s the system. s o pp in o in o in f esr i v v v v v c * 1 * ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? = s o pp min in f esr i v c * 4 * 1 ) ( ? ? ? ? ? ? ? ? ? = 2 ) ( o max rmx i i = o in in o in o v forv v v v v * 2 4 1 1 * = = ? ? ? ? ? ? ? ? ?
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 14 of 16 2007/1 1 /21 output ca pacitor selection the fun c tion of output ca p a citan c e i s to store ene rgy to atte mpt to maintain a co nstant voltag e. the ene rg y is store d in the cap a cit o r?s el ect r ic fi eld due to the voltage appli ed. the value of output capa citan c e is ge nerally sel e ct ed to limit o u tput voltage ripple to the level require d by the spe c ification. since the ri pple current i n the output indu ctor i s u s ually dete r m i ned by l, v out and v in , the s e ries impeda nce of the ca pa citor prima r ily det ermin e s th e output vo ltag e rippl e. the three eleme n t s of the cap a citor that contri bute to its impedan ce (and outpu t voltage ripple) are equi v alent seri es resi stan ce (e sr), equival ent serie s indu ctan ce (e sl), and cap a citan c e (c). the output voltage dro op due to a load transie nt is dominated by the cap a cita n c e of the ceramic out- put capa citor. duri ng a step increa se in l oad current, the ce rami c o u tput cap a cit o r alo ne sup p lies the lo ad current u n til the loop respon ds. wi thin two swit chin g cycle s , the loop respond s and th e inducto r cu rre nt incre a ses to match the load curre n t demand. the relation ship o f the output voltage droo p during the two switchi ng cycle s to the output cap a cita nce can be e s timated by: in many practical desi g n s , to get the required esr, a cap a cito r with much more capa citan c e than is neede d must be sele cted.fo r both continuo us a nd di sco n tinuou s ind u c tor cu rre nt mode o perati on, the esr of the c out n eede d to limit the rippl e to v o , v p eak-to-pea k i s : rippl e curre n t flowing thro ugh a cap a cit o r?s esr cau s e s pow er di ssi pation in the cap a cito r. this po we r dissi pation cau s e s a tem peratu r e in crease intern al to the cap a citor . exce ssive te mp er a t u r e can seri ou sly sho r ten the expecte d life of a cap a citor . cap a cit o rs have rip p l ed curre n t ra ti ngs th at are depen dent o n ambie n t temperature an d sho u ld not be excee ded. the o u tput cap a citor ripple curre n t is the inducto r current, i l , minus the outpu t curre nt, i o . the rms value of the ripple current flowin g in th e output cap a cit ance (conti nuou s indu ct or cu rrent mo de op eratio n) is give n by: esl can be a problem by causi ng rin g in g in the low megah ert z re gion but can be co ntroll ed by choo sin g low esl cap a citors, limiting lead l ength (p cb and cap a cito r), and repla c ing one larg e device with several sm a ller one s connected in p a rallel. in con c lu sio n , in orde r to meet the requi rem ent of output volt age ripple small and re g u lation loop st ab i l i t y , c e r a m i c c a p a c i t o r s w i t h x 5 r o r x 7 r diele c trics are recomme n ded due to their lo w esr and high rip p le current rating s. the output rippl e v out is dete r mined by: a 10f cera mic cap a cito r can sati sfy most appli c atio ns. s droop load out f v i c * * 3 = 289 . 0 * 6 3 ) ( l max rms i i = = l i v esr 0 () ? ? ? ? ? ? ? ? + ? out osc osc in out in pp out c f esr l f v v v v v * * 8 1 * * * *
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 15 of 16 2007/1 1 /21 thermal calculation s there are three types o f lo sses associated with the ECT3409 step- down conver ter: switching losses, conduction losses , and qu iescent current losses. conductio n losses are associated with the r ds (o n) characteristics of the powe r ou tpu t switching de vices. switchin g losses are dominated by the gate charge of the po wer output switching. at full load, assuming continuous condu ction mode (c cm), a s implified form o f th e losses is g i ven by i q is the ste p - down converter quiescent current. the term t sw is us ed to estima te the fu ll loa d step-down converter swit ching loss es. for the condition where the step-down converter is in dropout a t 10 0% du ty cycle , the tota l de vice dissipatio n reduces to: since r ds (on ) , quiescent current and switc hing losses all vary w i th in p u t vo lta ge, the tota l losses should be in ve stigated over the complete inpu t voltage range. g i ven the to tal lo sses, the maximum junction temperatur e can be der ived from the ja for the tdfn-10 pa ckage which is 45c/w. [ ] () in q o sw in o in ls dson o hs dson o total v i i f t v v v r v r i p * ) * * ( * * * ) ( ) ( 2 + + ? + = in q hs dson o total v i r i p * * ) ( 2 + = amb ja total max j t p t + = * ) (
e c t3409 dual channel 600ma, 1.5m hz step-down converter e-cmos corp. ( www .ecmos.com.tw ) page 16 of 16 2007/1 1 /21 mechanical dimensions outli ne d r a wing t d f n -1 0 dimensio n s inches mm dimn min max min max a 0.1 16 0.1 19 2.95 3.05 b 0.1 16 0.1 19 2.95 3.05 c 0.065 0.069 1.65 1.75 d 0.093 0.096 2.35 2.45 b 0.007 0.01 1 0.18 0.28 e 0.020 0.500 bsc l 0.014 0.018 0.35 0.45 a1 0.028 0.031 0.70 0.80 a2 0.000 0.004 0.00 0.10 a3 0.008 0.203ref

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