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aic1577 external nmos step-down pwm controller features n-channel mosfet drive operating input voltage from 4.5v to 24v wide ouput range : 0.8v to 20v 1.5% 0.8v reference low dropout operation : 95% duty cycle 500khz fixed constant frequency low standby current, i q typically 720 a logic-control micropower shutdown output overvoltage protection internal diode for bootstrapped gate drive current mode operation for excellent line and load transient response available in an 8-lead so and msop package applications lcd monitor palmtop computers, pdas wireless modems on-card switching regulators dc power distribution systems description the aic1577 is a current mode switching regulator controller that drives external n- channel power mosfet using a fixed fre- quency architecure. it uses external divider to adjust output voltage from 0.8v to 20v with excellent line and load regulation. a maximum high duty cycle limit of 95% provides low dropout operation which extends operating time in battery-operated systems. switching frequency up to 500khz are achievable thus allowing smaller sized filter components. the operating current level is user-programmable via an external current sense resistor. it also provide output overvolt- age protection under fault conditions. a multifunction pin (i th /run) allows ex ternal compensation for optimum load step re- sponse plus shutdown. soft start can also be implemented with this pin to properly se- quence supplies. package available are in sop8 and msop8 for smd. a n alog integrations corporation si-soft research center ds-1577p-02 010405 3a1, no.1, li-hsin rd. i , science park , hsinchu 300, taiw an , r.o.c. te l: 886-3-5772500 fa x : 886-3-5772510 www. anal og.c o m .tw 1
aic1577 typical application circuit v in 6v~ 2 4 v + c in 1 22 f r s 33m m1 fd s669 4 c3 0. 1 f d1 sl43 l1 10 h v ou t 3.3v 3 a c1 1 000 pf c5 330 pf r3 24 k r2 62 k r1 20k vi n 8 i t h/ run 2 fb 3 gn d 4 sw 5 dr i 6 boos t 7 cs 1 ai c1577 + c in 2 22 f c2 0. 1 f c ou t 220 f c4 1n f c6 2. 2 f c in 1 , c in 2 : her- m e i 22 f / 35 v el ect r ol y t i c ca paci t or s m 1 : fai r chi ld fds6694 n- m o sfet d 1 : g s s l 4 3 l1: t d k slf 125 55 t - 100 m 3 r 4 c ou t : her- m e i 220 f / 1 6 v el ect r ol y t i c ca paci t or c6: t a i y o y u d e n lm k2 12 bj 225 kg- t cer a m i c cap a ci t o r ordering information a ic15 77- x x x x pa cking ty pe tb: tube t r : t a p i n g & r eel pa cka g ing ty pe s: sm a l l outline o: m s op 8 c: com m e rc i a l p: l ead f r ee com m er cia l exam p l e: aic1 577 co t r in m s o p packag e & t aping & re el pa ck ing t y pe aic1 577 po t r in m s o p lea d f r e e packag e & t a ping & reel packing t y pe pi n co nfi g ura t io n t o p v i ew dr i vi n boo s t sw fb i th / ru n gnd cs 1 3 4 2 8 6 5 7 2
aic1577 absolute maximum ratings supply voltage (vin) 25v drive supply voltage (boost) 32v switch voltage (sw) 25v differential boost voltage (boost to sw ) 8v i th /run,vfb voltages 7v peak drive output current < 10 p s (dri ) 2a operating temperature range -40 q c ~ 85 q c junction temperatrue 125 q c storage temperature range -65 q c ~ 150 q c lead temperature (soldering. 10 sec) 260 q c thernal resistance ( t ja ) (assume no ambient airflow, no heatsink) dip8 100 q c/w sop8 160 q c/w msop8 180 q c/w absolute maximum ratings are those v a lues bey ond w h ich the life of a dev i ce may be impaired. test circuit refer to typical application circuit. electrical characteristics (t a =25 q c, v in =15v, unless otherw ise noted.) (note1) parameter test conditions min. typ. max. unit input voltage 4.5 24 v normal mode (note 2) 720 900 p a input supply current shutdown mode, v ith/run = 0 v 1 6 2 0 p a feedback v o l t a g e 0 . 7 8 8 0 . 8 0 . 8 1 2 v ? output overvoltage lockout v fb connect to vout, ? v ov l =v ov l - v fb 2 0 5 5 9 0 m v reference voltage line regulation v in = 4.5v to 20 v 0.002 0.015 %/v output voltage load regula- tion i th sinking 5 p a i th sourcing 5 p a 0.7 -0.4 1.1 -0.8 % run threshold 0.6 0.8 0.9 v maximum current sense threshold v fb = 0 . 7 2 v 1 2 5 1 5 0 1 7 5 m v oscillator f r e q u e n c y 4 5 0 5 0 0 5 5 0 khz 3
aic1577 electrical characteristics (continued) parameter test conditions min. typ. max. unit dri rise time c load = 3000 p f 5 0 7 5 n s dri fall time c load = 3000 p f 5 0 7 5 n s boost voltage v in =8v , i b oos t =5ma, s w = 0 v 4 . 9 5 . 3 5 . 7 v maximum duty cycle 90 94 % soft start time 5 7.5 ms run current source v ith/run =0v , v fb = 0 v 1 . 0 2 . 3 4 . 0 a run pullup current v ith/run = 1 v 1 0 0 1 9 0 2 5 0 a note 1: specifications are production tested at ta=25 c. specifications over the -40 c to 85 c operating temperature range are assured by design, characte rization and correlation with statistical quality controls (sqc). note 2: dynamic supply current is higher due to the gat e charge being delivered at the switching frequency. typical performance characteristics 1 10 10 0 100 0 10 00 0 70 75 80 85 90 95 10 0 v in =6v e f ficienc y ( % ) load c u r r ent ( ma) v in =12v v in =19v v out =3. 3 v fi g. 1 ef f i c i enc y vs load cur r ent ( v ou t =3. 3 v ) e f ficienc y ( % ) load c u r r ent ( ma) fi g. 2 ef f i c i enc y vs load cu r r ent ( v ou t =5. 0 v) 1 10 10 0 10 00 100 00 70 75 80 85 90 95 10 0 v out =5 v v in =6 v v in =12v v in =19 v 4
aic1577 typical performance characteristics (continued) efficienc y (%) input voltage (v) fig. 3 e ffic i enc y v s in put v o ltage 0 5 10 15 20 25 30 70 75 80 85 90 95 10 0 v out =3.3v i load =1a i load =0.1 a efficienc y ( % ) input voltage (v) fig. 4 effic i enc y v s input voltage 0 5 10 15 20 25 30 70 75 80 85 90 95 10 0 v out =5v i load =1a i lo a d =0.1a s u pp l y c u r r en t ( a) i nput vol t age ( v ) fi g. 5 suppl y cu r r en t vs i nput vol t age 0 5 10 15 20 25 30 0 20 40 500 600 700 800 900 no r m a l mo de shut do wn b oos t v o lta g e ( v ) boos t load c u r r ent ( ma) fi g. 6 boos t load r egul at i on 0 v cc =5v v cc =15v v ph ase =0v 0 51 0 15 20 1 2 3 4 5 6 7 b oos t v o lta ge (v ) i nput vol t age ( v ) fi g. 7 boos t li ne r egul at i on i bo ost =2ma v ph ase =0v 0 5 10 15 20 25 30 1 3 5 7 0 2 4 6 vc c dow n vcc up r e ferenc e v o lta g e ( v ) temper at ur e ( c) fi g. 8 ref e r enc e vol t age vs temper at ur e -4 0 - 2 0 0 20 40 60 80 10 0 12 0 14 0 0. 7 9 0 0. 7 9 1 0. 7 9 2 0. 7 9 3 0. 7 9 4 0. 7 9 5 0. 7 9 6 0. 7 9 7 0. 7 9 8 0. 7 9 9 0. 8 0 0 0. 8 0 1 0. 8 0 2 0. 8 0 3 0. 8 0 4 0. 8 0 5 5
aic1577 typical performance characteristics (continued) b oos t v o lta ge (v ) temper at ur e ( c) fi g. 9 boos t vol t age vs te mper at ur e -4 0 -2 0 0 20 40 60 80 10 0 120 140 4. 0 4. 5 5. 0 5. 5 6. 0 i boost =1m a v ph ase =0 v fr e q u enc y ( khz ) temper at ur e ( c) fi g. 10 o per at i ng fr equenc y vs temper at ur e - 40 -20 0 20 40 60 80 100 12 0 14 0 40 0 42 0 44 0 46 0 48 0 50 0 c u rren t s ens e t h res hold (m v ) temper at ur e ( c) fi g. 11 max i mum c u r r ent sens e thr e s hol d vs tem per at ur e -40 -20 0 20 40 60 80 10 0 12 0 14 0 12 0 12 5 13 0 13 5 14 0 14 5 15 0 15 5 16 0 6
aic1577 block diagram + m1 * dr op ou t de t os c vin int v c c 1_ s h u t q2 * q1 * q3 q4 ss re f 0. 8v th erm a l dri v e r fl o a t i n g le b bl an k - + ea vint vi n vin t vi n t 0. 8 v 1. 2 v 2. 4v 0.8 v 1. 3 3 v 0 . 85 5v - + lc _c o m p - + bur s t_ m o de - + sd + ov d t r s q 2. 5 a - + b u ffe r _ it h r2 r1 vin cs ith sw dr i fb gnd b oos t - + i co m p vi n vin vin sl o p e sd cl o c k sd it h cl ock it h vint sl o p e fb 40 m v lo gi c s w it c h in g 7
aic1577 8 ? pin descriptions pin 1: cs - current sense comparator invert- ing input, not to exceed v in volt- age. built in offsets between the cs and v in pins in conjunction with r sense set the current trip thresholds. pin 2: i th /run -combination of error amplifier compensation point and run con- trol inputs. the current compara- tor threshold increases with this control voltage. forcing this pin below 0.8v causes the device to be shutdown. pin 3: fb - feedback error amplifier input, to compare the feedback voltage with the internal reference voltage. connecting a resistor r2 to con- verter output node and a resistor r1 to ground yields the output voltage: v out =0.8 x (r1+r2)/ r1 pin4: gnd - singal gnd for ic. all voltage lev- els are measured with respect to this pin. pin 5: sw - switch node connection to induc- tor. in buck converter applications the voltage swing at this pin is from a schottky diode voltage drop below ground to v in pin 6: dri - external high-side n-mosfet gate drive pin. connect dri to gate of the external high-side n- mosfet. pin 7: boost - supply to high-side floating driver. the bootstrap capacitor c3 is returned to this pin. pin 8: vin - the chip power supply pin. it also provides the gate bias charge for all the mosfets controlled by the ic. recommend supply volt- age is 4.5v~24v. ? application information introduction aic1577 is a current mode switching regulator con- troller that drives external n-channel power mosfet with const ant frequency architecture. it uses external divider to adjust output volt age with excellent line regulation and load regulation. a maximum high duty cycle limit of 95% provides low dropout operation, which extends operating time in battery-operated system. wide input volt age ranges from 4.5v to 24v , and switching frequency (500khz) allows smaller sized filter component s. the operating current level is user-programmable via an external current sense resistor and it automatic ally enters pfm operation at low output current to boost circuit ef ficiency . a multifunction pin (i th /run) allows ex ternal compensation plus shut down. a built-in sof t st art can properly provide sequence supplies. a v ailable p a ckages are in sop8 and msop8 for smd. principle of operation aic1577 uses a current mode with a const ant fre- quency architecture. normally high-side mosfet turns on each cycle when oscillator set s rs latch and it turns of f when internal current comp arator re- set s rs latch. v o lt age on i th /run pin, which is the output volt age of volt age error amplifier , will control peak inductor current. the output volt age feeds back t o v fb pin so that the error amplifier receives a volt age through external resistor divider . when load current increases, it causes a slight decrease
aic1577 max i 100mv s r = in the volt age of v fb pin. thus the i th /run volt age remains increasing until the average inductor cur- rent matches new load current. while the high-side mosfet turns of f, the low-side mosfet is turned on to recharge boot strap cap a citor c3. inductor selection with the operating frequency high to 500khz, smaller inductor value is favored. in general, operating in high frequency will cause low ef ficiency because of large mosfet switching loss. thus the ef fect of inductor value on ripple current and low current operation must be considered as well. main control loop is shut down when i th /run goes below 0.8v . when i th /run pulled up to 0.8v or up by error amplifier , main control loop is enabled. low current operation during heavy load current operation, aic1577 op- erates in pwm mode with a frequency of 500khz. decreasing of the current will cause a drop in i th /run below 1.33v so t hat aic1577 enters pfm mode operation for better ef ficiency . if the volt age across r s does not exceed the of fset of current comp arator within a cycle, then the high-side and internal mosfet s will disable until i th /run goes over 1.33v . the inductor value has a direct influence on ripple current ( i l ), which decreases with high induc- t ance and increases with high v in or v out : ? ? ? ? ? ? ? ? + + ? = d v in v d v out v l f out v in v l ? i v d is the drop volt age of the output schottky diode. accepting a large value of i l allows the use of low induct ance, but yields high output ripple volt age and large core loss. the inductor value also has an ef fect on low current operation. low inductor value causes the pfm operation to begin at high load cur- rent. the ef ficiency of the circuit decreases at the beginning of low current operation. generally speaking, low induct ance in pfm mode will cause the ef ficiency to decrease. component selection aic1577 can be used in many switching regulator applic ations , s u c h as s t ep-down, s t ep-up, sepic and positive-to-negative converters. among all, step-down converter is the most common applica- tion. external component selection, beginning with select ing r s , depends on load requirement of the application. once r s is decided, the choice of in- ductor , which is followed by selecting power mosfet and diode, can be easily chosen. finally , c in and c out can be determined. pow e r mosfet selection for an application of aic1577, an external n- channel power mosfet , used as the high-side switch, must be properly selected. t o prevent mosfet from damage during high input volt age operation, attention should be t a ken to the bv dss specification for mosfet . r s selection the choice of r s has subst antial connection with required output current. the threshold volt age of current comp arator decides peak inductor current, which yields a maximum average output current (i max ). and the peak current is less than half of the peak-to-peak ripple current, i l . other import ant selection criteria for the power mosfet include the ?on? resist ance r ds(on) , in- put volt age and maximum output current. allowing a margin for variation of aic1577, external component can be yielded as: 9
aic1577 output diode selection ? ? ? ? ? ? + = 1 r 2 r 1 v 8 . 0 v out in order not to exceed the diode ratings, it is impor- t ant to specify the diode peak current and average power dissip a tion. the feedback reference volt age 0.8v allows low output volt ages from 0.8v to input volt age. a small cap a citor at 1nf in p a rallel to the upper feedback resistor is required for a st able feedback. c in and c out selection t o prevent the high volt age spike resulted from high frequency switching, a low esr input cap a citor for the maximum rms current must be used. usually cap a citors may be p a ralleled to meet size or height requirement s in the design. i th /run function the i th /run pin, also as a dual-purpose pin, pro- vides loop compensation as well as shut down func- tion. an internal current source at 2.5 a charges up the external cap a citor c5. when the volt age on i th /run pin reaches 0.8v , the aic1577 begins to operate. the selection of c out depends on the required ef - fective series resist ance (esr). in general once the esr requirement is met, the cap a cit ance is suit able for filtering. the output ripple volt age ( v out ) is determined by: c5 33 0pf r3 24k d2 ll 4 1 48 c7 1 f r4 1. 2m v in 4. 5 v ~ 2 4 v i th / run ? ? ? ? ? ? ? ? + ? ? out l out fc 4 1 esr i v where f = operating frequency , c out = output ca- p a cit ance and i l = ripple current of the inductor . once the esr requirement for c out has been met, the rms current rating generally far exceeds the i ripple(p-p) requirement. fig. 12 i th /run pin interfacing topside mosfet driv er supply (c3) external boot strap cap a citor c3 connecting to boost pin supplies the gate drive volt age for high- side mosfet . c3 is charged from intv cc when sw pin is low . when the high-side mosfet turns on, the driver places the c3 volt age across the gate to the source of mosfet . it will enhance the mosfet and turn on the high-side switch. then the switch node volt age sw rises to v in and boost pin rises to v in + i n tv cc . in general, 0.1 f is accept able. ov er current protection over current protection occurs when the peak in- ductor current reaches maximum current sense threshold divided by sense resistor. the maximum current under over current protection can be calcu- lated by the following formula. s r threshold) sense current mum 150mv(maxi max i = at the same time, the frequency of oscillator will be reduced to sixteenth of original value, 500khz. this lower frequency allows the inductor current to safely discharge, thereby preventing current run- away. the frequency of oscillator will automatically output voltage programming the typical aic1577 application circuit is shown in figure18. a resistive divider , as in the following for- mula, set s the output volt age. 10
aic1577 return to its designed value when the peak inductor value no longer exceeds over current protection point. 11 ov er voltage protection over voltage protection occurs when the fb pin voltage (the negative input of error amplifier) ex- ceeds 0.855v. the over voltage comparator will force driver to pull low until output over voltage is removed. pcb lay out since operating in a high switching frequency , 500khz, proper pcb layout and component place- ment may enhance the performance of aic 1577 application circuit. for a better ef ficiency , major loop from input terminal to output terminal should be as short as possible. in addition, in the case of a large current loop, the track wid t h of each component in the loop should maint a in as wide as possible. in order to prevent the ef fect from noise, the gnd pin should be placed close to the ground. also keep the ic? s gnd pin and the ground leads in the short- est dist ance. recommended layout diagrams and component placement are as shown as figures 13 to 16. no sensitive component s, which may cause noise interference to the circuit, should be allowed to be close to sw pin. furthermore, aic1577 is a current mode controller . remaining the sense resistor close to both vin and cs pins is recommended for better ef ficiency and output performance. in addition, all filtering and de- coupling cap a citors, such as c1 and c2, should connect to aic1577 as close as possible. fig. 13 top layer fig. 14 bottom layer
aic1577 fig. 15 plac ement (top overlay) fig. 16 plac ement (bottom overlay) application circuit v in 6v~ 2 4 v + c in 1 22 f r s 33m m1 fds6694 c3 0. 1 f d1 sl 43 l1 10 h v out 3. 3v 3 a c1 1 000p f c5 330pf r3 24k r2 62 k r1 20 k vin 8 it h / ru n 2 fb 3 gnd 4 sw 5 dri 6 boos t 7 cs 1 ai c157 7 + c in 2 22 f c2 0. 1 f c out 22 0 f c4 1n f d2 l l414 8 c7 1 f r4 1. 2m v in 6v ~ 2 4v ** c6 2. 2 f fig. 17 3.3v step-down converter with external soft-start circ uit 12
aic1577 13 v in 5v + c in 1 22 f r s 33 m m1 fds6 69 4 c3 ll 41 4 8 d1 sl43 l1 10 h v ou t 3. 3v 3a c1 10 00 pf c5 3 30p f r3 24 k r2 62 k r1 20 k vi n 8 it h / ru n 2 fb 3 gn d 4 sw 5 dri 6 boos t 7 cs 1 ai c1 577 + c in 2 22 f c2 0. 1 f c ou t 22 0 f c4 1n f d2 c6 2. 2 f c7 1n f fig. 18 5v to 3.3v step-down converter physical dimensions (unit: mm) h l d e h e c b a1 0.5 0 0. 25 0. 40 0 1. 27 8 1.2 7 bs c 4. 80 5. 80 3. 80 0. 33 0. 19 0. 10 5.0 0 6. 20 4. 00 0.5 1 0.2 5 0.2 5 s y m b o l a sop-8 mill imet ers 1. 35 mi n . 1. 75 max. a wi th pla t ing a1 b c d e aa h e h x 45 s e e view b 8 lead plastic so
aic1577 14 a a1 a2 0.2 5 with p l atin g b c e d a e a e1 see v i ew b e l c e e1 d a2 b a1 0. 65 b s c 0. 40 0 0. 70 6 4. 90 b s c 0. 13 2.9 0 2.9 0 0. 75 0. 25 0. 05 0. 23 3. 10 3. 10 0. 95 0. 40 0. 15 s y m b o l a ms op - 8 milli mete rs mi n . 1.1 0 ma x . msop 8 note: information provided by aic is believed to be accurate and reliable. how e ver , w e c annot assume responsibility for use of any ci rcui try other than circuitry entirely em bodied in an aic product; nor for any infringement of p a tent s or other right s of third p a rties that may result from it s use. w e reserve the right to change t he circuitry and specificat ions w i thout notice. life support policy : aic does not authorize any aic product for use in life support devic es and/or sy stems. life support device s or sy s- tems are devices or sy stems w h ich, (i) are intended for surgical implant into the body or (ii) support or sust ain life, and w h o se failure to perform, w h en properly used in accordance w i th instructions fo r use provided in the labeling, can be reasonably expected to res ult in a significant injury to the user .

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