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1 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. 23 v, 2 .5 a, 3 4 0khz synchronous step - down dc/dc converter pin assignment s so package ( sop - 8 ) s p package (sop - 8 exposed pad ) fig ure 1. pin assignment of fr 9886 ordering information de s cription the fr 9886 is a synchronous step - down dc/dc converter that provides wide 4.5v to 23 v input voltage range and 2.5a continuous load current capability. the FR9886 f ault protection includes cycle - by - cycle current limit, input uvlo, output over voltage protection and thermal shutdown. besides, adjustable soft - start function prevents inrush current at turn - on. this device uses current mode control schem e which provides fast transient response. internal c ompensation function reduces external compe nsation components and simplifies the design process. in shutd own mode, the supply current is less than 1ua. the fr 9886 is available in an 8 - pin soic package, provides a very compact system solution and good thermal conductance. feature s high efficiency up to 9 6% low rds(on) integrated power mosfet internal compensation function wide input voltage range: 4.5v to 23 v adjustable output voltage range : 0.925 v to 20v 2.5a output current fixed 3 4 0khz switching frequency current mode operation ad justable soft - start cycle - by - cycle current limit input under voltage lockout over - temperature protection with auto recovery < 1ua shutdown current sop - 8 and sop - 8 exposed pad package application s set - top - box (stb) televisions distributed po wer systems xdsl modems g : green tr: tape / re e l FR9886 package type so: sop - 8 s p : sop - 8 (exposed pad) s s v i n f b n c g n d 2 3 4 6 5 7 8 1 b o o s t l x s h d n s s v i n f b n c g n d 2 3 4 6 5 7 8 1 b o o s t l x s h d n free datasheet http:///
2 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. typical application circu it figure 2. c in /c out use ceramic capacitor s application circuit figure 3 . c in /c out use electrolytic capacitor s application circuit v out r1 r2 c6 l1 c out 1.2v 3k ? 10k ? 200pf~1nf 4.7uh 2 2uf mlcc x2 1.8v 9.53k ? 10k ? 200pf~1nf 4.7uh 22uf mlcc x2 2.5v 16.9k ? 10k ? 200pf~1nf 10uh 22uf mlcc x2 3.3v 26.1k ? 10k ? 200pf~1nf 10uh 22uf mlcc x2 5v 44.2k ? 10k ? 200pf~ 1nf 10uh 22uf mlcc x2 1.2v 3k ? 10k ? -- 4.7uh 100uf ec x1 1.8v 9.53k ? 10k ? -- 4 . 7
h 100uf ec x1 2.5v 16.9k ? 10k ? -- 10uh 100uf ec x1 3.3v 26.1k ? 10k ? -- 10uh 100uf ec x1 5v 44.2k ? 10k ? -- 10uh 100uf ec x1 table 1. reco mmended component values f r 9 8 8 6 s s g n d n c v i n b o o s t f b l x v i n 4 . 5 v t o 2 3 v v o u t 1 0 u f / 2 5 v c e r a m i c x 2 2 2 u f / 6 . 3 v c e r a m i c x 2 l 1 4 . 7 u h ~ 1 5 u h c 3 1 0 n f ~ 0 . 1 u f r 2 r 1 r 3 1 0 k ? ~ 1 0 0 k ? 1 2 3 4 5 6 7 8 c 6 ( o p t i o n a l ) c 1 c 2 c 4 1 0 n f ~ 0 . 1 u f s h d n 3 . 3 v 1 0 k ? 2 6 . 1 k ? f r 9 8 8 6 s s g n d n c v i n b o o s t f b l x v i n 4 . 5 v t o 2 3 v v o u t 0 . 1 u f / 2 5 v c e r a m i c x 1 1 0 0 u f / 6 . 3 v e c x 1 r 2 r 1 1 2 3 4 5 6 7 8 c 6 ( o p t i o n a l ) c 1 c 2 1 0 0 u f / 2 5 v e c x 1 c 5 l 1 4 . 7 u h ~ 1 5 u h c 4 1 0 n f ~ 0 . 1 u f r 3 1 0 k ? ~ 1 0 0 k ? c 3 1 0 n f ~ 0 . 1 u f s h d n 3 . 3 v 2 6 . 1 k ? 1 0 k ? free datasheet http:///
3 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. functional pin description i/o pin name pin no. pin function i fb 5 voltage feedback inpu t pin. connect fb and v out with a resistive voltage divider. this ic senses feedback voltage via fb and regulate s it at 0.925v. i vin 2 power supply input pin. drive this pin by 4.5v to 23v voltage to power on the chip . i 7 enable input pin. this pin provides a digital control to turn the converter on or off. connect vin with a 100k? resistor for self - startup. i gnd 4 ground pin. connect this pin to exposed pad. o lx 3 power switching output. it is the output pin of internal high side nmos which is the switching t o supply power. o ss 8 soft - start pin. this pin c ontrols the soft - start period. connect a capacitor from ss to gnd to set the soft start period. o boost 1 high side gate drive boost pin . a 10nf or greater capacitor must be connected from this pin to lx. it can boost the gate drive to fully turn on th e internal high side nmos. o nc 6 no connection. keep s this pin floating. block diagram figure 4 . block diagram of fr 9886 s h d n p w m c o n t r o l d r i v e r l o g i c b o o s t l x r o t p o v p u v l o c u r r e n t c o m p s o s c i l l a t o r h i g h - s i d e m o s f e t l o w - s i d e m o s f e t i s e n s s f b 0 . 9 2 5 v u v l o & p o r v i n v c c g n d c u r r e n t l i m i t o t p i n t e r n a l r e g u l a t o r v c c o v p 6 a 1 m s h d n free datasheet http:///
4 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. absolute maximum ratings ( note 1) supply voltage v in -- ------------------- ------------- --- ------------------ ------------------------------ - - 0.3v to + 2 5 v enable voltage v ---------------------------------- --- ------------------ ------------------------- - - 0.3v to + 2 5 v lx voltage v lx (50 ns) --- ------ - -------------------------------- ---- - - -------------- - ----------------- -- - 1v to v in + 0.3v boost trap voltage v b oost -------------- - ---------- - --------------- ------------------------------- - --- v lx - 0.3v to v lx + 6v all other pins voltage ----- ---------- - ---- - --------------------------- ------------------------------ - - -- - 0.3 v to +6v maximum junction temperature (t j ) --------------------------------- ----------------------- --- --- +150 storage temperature (t s ) -- --------------------------------------- ----------------------------- - - - ---- - 65 to +150 lead temperature (soldering, 10sec.) ------------------------------------------ ---------- ------- + 260c power dissipation @ t a = 25 , (p d ) ( note 2) sop - 8 - -- ---- ------------ ---------------------- --------------- --------- ----- -- -- ------ --- - ----- 1.39 w sop - 8 (exposed pad ) --- ---- ------ --------- - --- -- ------ ---------------------------------- 2.08 w package thermal resistance, ( ja ) : sop - 8 ---------------------- -------------- -------------------- ------------------------------ ---- 9 0 c/w sop - 8 (exposed pad ) --- ---- ------ --------- - --- -- ------ ---------------------------------- 60 c/w package thermal resistance, ( j c ) : sop - 8 ------------------------------------ -------------------- ------------------------------ ---- 39 c/w s op - 8 (exposed pad ) ----------------------------- ----- ----------------------------- ----- 15 c/w note 1 stresses beyond this list ed under absolute maximum ratings" may cause permanent damage to the device. note 2 pcb heat sink copper area = 10mm 2 . recommended operating conditions supply voltage v in ----------------------------- -- ------------------------------ - ---------------------- + 4.5v to + 23v enable voltage v --- ----------------------- -- ------------------------ -- - ----------------- -- - ---- 0v to v in operation temperature range ------------------------------------- ----------------------------- - - - - 40c to + 85c s h d n free datasheet http:///
5 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. electrical characteristics (v in = 12 v, t a =25 , unle ss otherwise specified.) parameter symbol conditions min typ max unit v in input supply voltage v in 4.5 23 v v in quiescent current i ddq v = 1.8v , v fb = 1. 0 v 2.5 ma v in shutdown supply current i sd v = 0v 1 a fb 4.5v Q in Q ovp 1. 5 v high - side mosfet r ds (on) (note 3 ) r ds(on) 1 2 0 m ds (on) (note 3 ) r ds(on) 100 m lx (leak) v = 0v, v lx = 0v 10 ua high - side mosfet current limit (note 3 ) i limit(hs) minimum duty 3.5 4.5 a low - side mosfet current limit (note 3 ) i limit(ls) from drain to source 1.5 a error amp lifier voltage gain (note 3 ) 400 v/v osci llation frequency f osc 290 3 4 0 42 0 k hz short circuit oscillation frequency f osc(short) v fb = 0v 1 1 0 khz maximum duty cycle d max v fb = 0.8v 90 % minimum on time (note 3 ) t min 10 0 ns input uvlo threshold v uvlo(vth) v in rising 4. 3 v under voltage l ockout threshold hysteresis v uvlo(hys) 25 0 mv soft - start current i ss v ss =0v 6 ua soft - start period t ss c ss = 0.1uf 15 ms input low voltage v (l) 0.4 v inpu t high voltage v ( h ) 2 v input current i v =2v 2 ua therma l shutdown threshold (note 3 ) t sd 1 70 not production tested. s h d n s h d n free datasheet http:///
6 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. typical performance curves v in = 12v, v out = 3.3v, c1 =10uf x 2 , c2 = 22uf x 2, l1 = 10uh, ta = +25 , unless otherwise noted. figure 5 . efficiency vs. load current figure 6 . efficiency vs. load current figure 7 . efficiency vs. load current figure 8 . current limit vs. temperature figure 9 . feedback voltage vs. temperature figure 1 0 . switching frequency vs. temperature v out = 1.2v v out = 3.3v v out = 5v free datasheet http:///
7 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. typical performance curves v in = 12v, v out = 3.3v, c1 = 10uf x 2 , c2 = 22uf x 2, l1 = 10uh, ta = +25 , unless otherwise noted. i out =0a i out = 2.5a figure 1 1 . steady state waveform figure 1 2 . steady state waveform i out =0 a i out = 2.5a figure 1 3 . power on through vin waveform figure 1 4 . power on through vin waveform i out =0 a i out = 2.5a figure 1 5 . power off through vin waveform figure 1 6 . power off throug h vin waveform v in 10m v/div. (ac) v out 20m v/div. (ac) i l 1 a/div. v lx 5v/div. 2u s/div. v in 5 v/div. i l 1 a/div. v lx 5v/div. 20m s/div. v in 5 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. 20m s/div. v out 1 v/div. 20m s/div. 2 0 m s/div. 2u s/div. v in 100m v/div. (ac) v out 20m v/div. (ac) i l 1 a/div. v lx 5v/div. v in 10 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. v in 10 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. free datasheet http:///
8 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. typical performance curves v in = 12v, v out = 3.3v, c1 = 10uf x 2 , c2 = 22uf x 2, l1 = 10uh, ta = +25 , unless otherwise noted. i out =0a i out = 2.5a figure 1 7 . power o n through waveform figure 1 8 . power o n through waveform i ou t =0a i out = 2.5a figure 19 . power off t hrough waveform figure 2 0 . power off t hrough waveform figure 2 1 . load transient waveform figure 2 2 . short circuit test v 5 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. 4m s/div. v 5 v/div. i l 1 a/div. v lx 5v/div. 4m s/div. v 5 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. 80u s/div. v out 1 v/div. 400u s/div. 40 u s/div. 4m s/div. v out 200m v/div. i l 1 a/div. v out 1 v/div. i l 1 a/div. v 5 v/div. v out 1 v/div. i l 1 a/div. v lx 5v/div. s h d n s h d n free datasheet http:///
9 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. function description the fr 9886 is a high efficiency, internal compensation, and constant frequency current mode step - down synchronous dc/dc converter . it has integrated high - side (120m , typ) and low - side (100m , typ) power switches , and provides 2.5a continuous load current . it regulates input voltage from 4.5v to 23 v, and down to an output voltage as low as 0.925v. control loop under normal operation, the output voltage is sens ed by fb pin through a resistive voltage divider and amplified through the error amplifier. the voltage of error amplifier output is compared to the switch current to control the rs latch. at the beginning of each clock cycle, the high - side nmos turn s on when the oscillator sets the rs latch, a n d turns off w hen current comparator resets the rs latch. then the low - side nmos turns on until the clock period ends. enable the fr 9886 pin provides digital control to turn on / turn of f the regulator. when the voltage of exceeds the threshold voltage, the regulator starts the soft start function. i f the pin voltage is below than the shutdown threshold voltage, the regulator w ill turn into the shutdown mode and the shutdown current will be smaller than 1ua . for auto start - up operation, connect en to vin through a 100k resistor. soft start the FR9886 employs adjustable soft start function to reduce input inrush current during start up . when the device turns on, a 6ua current begins charging the capacitor which is connected from ss pin to gnd. the equation for the s oft start time is shown as below: the v fb voltage is 0.925v and the i ss current is 6ua. if a 0.1uf capacitor is connected from ss pin to gnd, the soft start time will be 15ms. output over voltage protection when the fb pin voltage exceeds 1. 5 v, the output over voltage protection function will be triggered and turn off the high - side/low - side mosfet . input under voltage lockout when the FR9886 is power on, the internal circuits are held inactive until v in voltage exceeds the input uvlo threshold voltage. and the regulator will be disabled when v in is below the input uvlo threshold voltage. the hysteretic of the uvlo comparator is 250 mv (typ). short circuit protection the fr 9886 provides short circuit protection function to prevent the device damage from short condition. when the short condition occurs and the feedback voltage drops lower than 0.4v, the oscillator frequency will be reduced to 110khz to prevent the inductor current increasing beyond the current limit. i n the meantime , the current limit will also be reduced to lower the short current. once the short condition is removed, the frequency and current limit will return to normal. over current protection the FR9886 over current protection function is implemente d using cycle - by - cycle current limit architecture. the inductor current is monitored by measuring the high - side mosfet series sense resistor voltage. when the load current increases , the inductor current also increases. when the peak inductor current rea ches the current limit threshold, the output voltage start s to drop. when the over current condition is removed, the output voltage returns to the regulated value. over temperature protection the fr 9886 incorporates an over temperature protection ci rcuit to protect itself from overheating. when the junction temperature exceeds the thermal shutdown threshold temperature, the regulator will be shutdown . a nd t he hysteretic of the over temperature protection is 60 (typ). internal compensation function the stability of the feedback circuit is controlled through internal compensation circuits . th is internal compensation function is optimized for most applications and this function can reduce external r, c component s . s h d n ? ? ? ? ? ? ss fb ss ss c nf v t ms = i ua ? free datasheet http:///
10 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. application information output voltage setting the output voltage v out is set using a resistive divider from the output to fb. the fb pin regulated voltage is 0.925v. thus the output voltage is: table 2 lists rec ommend ed values of r1 and r2 for most used output voltage. table 2 recommended resistance values v out r1 r2 5v 44.2 k ? 10 k ? 3.3v 26.1 k ? 10 k ? 2.5v 16.9 k ? 10 k ? 1.8v 9.53 k ? 10 k ? 1. 2 v 3 k ? 10 k ? place resistors r1 and r2 close to fb pin to prevent stray pickup. input capacitor selection the use of the input capacitor is filtering the input voltage ripple and the mosfets s witching spike voltage. because the input current to the step - down converter is discontinuous, the input capacitor is required to supply the current to the converter to keep the dc input voltage. the capacitor voltage rating should be 1.25 to 1.5 times g reater than the maximum input voltage. t he input capacitor ripple current rms value is calculated as: where d is the duty cycle of the power mosfet. this function reaches the maximum value at d=0.5 and the equivalent rms current is equal to i out /2. the following diagram is the graphical representation of above equation . a low esr capacitor is required to keep the noise minimum. ceramic capacitors are better, but tantalum or low esr electrolytic capacitors may also suffice. w hen using tantalum o r electrolytic capacitors, a 0.1 uf ceramic capacitor should be placed as close to the ic as possible. output capacitor selection the output capacitor is used to keep the dc output voltage and supply the load transient current. when operating in constant current mode, the output ripple is determ ined by four compon ents: the following figures show the form of the ripple contributions. v ripple(esr) (t) + v ripple(esl) (t) + v ripple(c) (t) + v noise = v ripple (t) 1a 1.5a 2a 2.5a (t) (t) (t) (t ) out r1 v =0.925v 1+ r2 ?? ? ?? ?? ? ? ? ? in rms out i =i d 1-d ?? ? ? ? ? ? ? ? ? ripple ripple(c) ripple(esr) ripple(esl) noise v t v t v t v t v ?? ?? free datasheet http:///
11 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. application information w here i l is the peak - to - peak inductor ripple current, f osc is the switching frequency, l is the inductance value, v in is the input voltage, v out is the output voltage, r ( esr ) is the equivalent series resistance value of the output capacitor, l ( es l) is the equival ent series inductance value of the output capacitor and the c out is the output capacitor. the following diagram is a n example to graphical represent i l equation. low esr capacitors are preferred. ceramic, tantalum or low esr electrolytic capacito rs can be used depend ing o n the output ripple requirement . when using the ceramic capacitors , the esl component is usually negligible. it is important to use the proper method to eliminate high frequency noise when measuring the output ripple. the figure shows how to locate the probe across the capacitor when measuring output ripple. removing the scope probe plastic jacket in order to expose the ground at the tip of the probe. it gives a very short connection from the probe ground to the capacitor and el iminating noise. output inductor selection the ou tput inductor is used for stor ing energy and filtering output ripple current. but the trade - off condition often happens between maximum energy storage and the physical size of the inductor. t he first consideration for selecting the output inductor is to m ake sure that the inductance is large enough to keep the converter in the continuous current mode. t hat will lower ripple current and result in lower output ripple voltage. the inductance value should be determin ed to set the peak - to - peak inductor ripple current i l around 2 0% to 50% of the maximum load current. then the inductance can be calculated with the following equation: to guarantee sufficient output current, peak inductor current must be lo wer than the FR9886 high - side mosfet current limit. the peak inductor current is as below : ceramic capacitor vout gnd l=10uh l=6.8uh l=4.7uh v out =3.3v, f osc =340khz probe ground ripple(esr) l (esr) v = i r ?? ? ? ripple(esl) l (esl) osc 1 v = i l f d1 ? ? ? ? ? d ripple(c) l out osc 1 v = i 8 c f ?? ?? out out l osc in vv i1 f l v ?? ? ? ? ? ?? ? ?? ? ? l out(max) i = 0.2~0.5 i ?? ? ? out in out osc l in v l v -v f iv ?? ?? ?? ?? ?? l peak out(max) i i =i + 2 free datasheet http:///
12 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. application information feedforward capacitor selection internal compensation function allows users saving time in desig n and saving cost by reducing the number of external components. the use of a feedforward capacitor c6 in the feedback network is recommended to improve the transient response or higher phase margin . for optimizing the feedf orward capacitor, knowing the cross frequency is the first thing . the cross frequency (or the converter bandwidth) can be determined by using a network analyzer. when getting the cross frequency with no feedforward capacitor identified, the value of feed forward capacitor c6 can be calculated with the following equation : w here f cross is the cross frequency. to reduce transient ripple, the feedforward capacitor value can be increased to push the cross frequency to higher region. although this can improve transient response, it also decrease phase margin and cause more ringing. in the other hand, if more phase margin is desired, the feedforward capacitor value can be decreased to push the cross frequency to lower region. external boost diode selection for 5v input applications, it is recommended to add an external boost diode . this helps improving the efficiency. the boost diode can be a low cost one such as 1n4148. pcb layout recommendation the de vice s performance and stability is dramatically affected by pcb layout. it is recommended to follow these general guidelines show as below: 1. place the input capacitors and output capacitors as c lose to the device as possible. trace to these capacitors sh ould be as short and wide as possible to minimize parasitic inductance and resistance. 2. place feedback resistors close to the fb pin. 3. keep the sensitive signal (fb ) away from the switching signal ( lx ). 4 . the exposed pad of the package should be soldered to an equivalent area of metal on the pcb. this area should connect to the gnd plane and have multiple via connections to the back of the pcb as well as connections to intermediate pcb layers. the gnd plane area connecting to the exposed pad should be maxim ized to improve thermal performance. 5 . multi - layer pcb design is recommended. figure 2 3 . FR9886 sop - 8 (exposed pad) package c in / cout with ec capacitors recommended pcb layout diagram f r 9 8 8 6 v o u t f b r 1 r 2 c 6 cross 1 1 1 1 c6 - 2 f r1 r1 r2 ? ? ? ? ? f r 9 8 8 6 v i n b o o s t v i n l x d 1 1 n 4 1 4 8 5 v c 4 1 2 3 4 5 6 7 8 l 1 l x g n d v o u t v i n e x p o s e d p a d g n d c 4 c 5 r 1 r 2 r 3 c 3 c 6 c 2 + C c 1 + C free datasheet http:///
13 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. outline information sop - 8 package (uni t: mm) . note followe d f rom jedec mo - 012 - e symbols unit dimension in millimeter min max a 1.4 0 1.75 a1 0. 10 0.25 a2 1. 30 1.50 b 0.3 1 0.51 d 4.80 5.00 e 3.80 4.00 e 1.20 1.34 h 5.80 6.20 l 0.40 1.27 carrier dimensions free datasheet http:///
14 FR9886 - 1.0 - apr - 2011 FR9886 85t fitipower integrated technology lnc. outline information sop - 8 (exposed pad ) package (unit: mm) symbols unit dimension in millimete r min max a 1.25 1.7 0 a1 0. 0 0 0. 15 a2 1.25 1.55 b 0.3 1 0.51 d 4.80 5.00 d1 1.82 3.35 e 3.80 4.00 e1 1.82 2.41 e 1.20 1.34 h 5.80 6.20 l 0.40 1.27 note followed from jedec mo - 012 - e . carrier dimensions life support poli cy fitipower s products are not authorized for use as critical components in life support devices or other medical systems . free datasheet http:///

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