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1 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. 18v, 3 a, 340khz synchronous step - down dc/dc converter pin assignment s sp package (sop - 8 expose d p ad ) fig ure 1. pin assignment of FR9884 ordering information de s cription the FR9884 is a synchronous step - down dc/dc convert er that provides wide 4.5v to 18 v input voltage range and 3a continuous load current capability. fault 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 cu rrent mode control scheme that provides fast transient response. in shutdown mode, the supply current is about 10 a . the FR9884 is available in an 8 - pin soic package, which provides a very compact system solution and good thermal conductance. feature s wi de input voltage from 4.5v to 18 v 3 a output current adjustable output voltage from 0.925v to 1 4 v low rds(on) i ntegrated power mosfet high efficiency u p to 9 3 % fixed 340khz switching frequency current mode operation adjustable soft - start c ycle - by - cycle c urrent l imit input under voltage lockout over - temperature protection with auto recovery 10 a shutdown current thermal enhanced sop - 8 (exposed pad) package rohs compliant application s set - top - box dvd,lcd display olpc, netbook distributed power system datacom, xdsl FR9884 g : green tr: tape / re e l package type s p : sop - 8 (exposed pad) s w s s v i n b s f b c o m p e n g n d 2 3 4 6 5 7 8 1
2 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. typical application circuit figure 2. output 3.3v application circuit figure 3 . low input voltage application circuit figure 4 . high input voltage application circuit f r 9 8 8 4 s s g n d c o m p v i n e n b s f b s w v i n 5 v t o 1 2 v v o u t 3 . 3 v 1 0 f / 2 5 v c e r a m i c x 1 2 2 f / 6 . 3 v c e r a m i c x 2 l 1 1 0 h c 3 0 . 1 f c 4 1 0 n f c 5 1 0 n f r 2 1 0 k ? / 1 % r 1 2 6 . 1 k ? / 1 % r 3 1 0 0 k ? r 4 5 . 6 k ? 1 2 3 4 5 6 7 8 c 7 ( o p t i o n a l ) c 8 ( o p t i o n a l ) 1 0 0 f / 2 5 v e c x 1 c 6 c 1 c 2 f r 9 8 8 4 s s g n d c o m p v i n e n b s f b s w v i n 4 . 5 v t o 5 v v o u t 1 . 8 v 1 0 f / 2 5 v c e r a m i c x 2 2 2 f / 6 . 3 v c e r a m i c x 2 l 1 1 0 h c 3 0 . 1 f c 4 1 0 n f r 2 1 0 k ? / 1 % r 1 9 . 5 3 k ? / 1 % r 3 1 0 0 k ? 1 2 3 4 5 6 7 8 d 1 1 n 4 1 4 8 c 8 ( o p t i o n a l ) c 1 c 7 ( o p t i o n a l ) c 5 1 0 n f r 4 5 . 6 k ? c 2 f r 9 8 8 4 s s g n d c o m p v i n e n b s f b s w v i n 1 2 v t o 1 8 v v o u t 3 . 3 v 1 0 u f / 2 5 v c e r a m i c x 1 2 2 u f / 6 . 3 v c e r a m i c x 2 l 1 1 0 u h c 3 0 . 1 u f c 4 1 0 n f c 5 1 0 n f r 2 1 0 k ? / 1 % r 1 2 6 . 1 k ? / 1 % r 3 1 0 0 k ? r 4 5 . 6 k ? 1 2 3 4 5 6 7 8 c 7 ( o p t i o n a l ) c 8 ( o p t i o n a l ) 3 3 0 u f / 2 5 v e c x 1 c 6 c 1 c 2
3 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. functional pin description pin name pin function bs high side gate drive boost input. a 10nf or greater capacitor must be connected from this pin to sw. it can boost the gate drive to fully turn on the internal high side nmos. v in power supply input pin. drive 4.5v to 18 v voltage to this pin to power on this chip. sw power switching output. it is the output pin of internal high side nmos which is the switch t o supply power. gnd ground pin. connect this pin to exposed pad. fb voltage feedback input pin. connect fb and vout with a resistive voltage divider. this ic senses feedback voltage via fb and regulate s it at 0.925v. comp compensation pin. this pin is used to compensate the regulation control loop. connect a series rc network from comp pin to gnd. en enable input pin. this pin provides a digital control to turn the converter on or off. connect to vin with a 100k? resistor for self - startup. ss soft - start input pin. this pin controls the soft - start period. connect a capacitor from ss to gnd to set the soft start period. block diagram figure 5 . block diagram of FR9884 + + - + - o s c i l l a t o r + r e g u l a t o r c o m p v i n b s s w g n d o v p 5 v c u r r e n t s e n s e a m p l i f i e 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 1 . 4 v 2 . 5 v 1 a 0 . 9 2 5 v 1 . 3 v e r r o r a m p l i f i e r c u r r e n t c o m p a r a t o r + - c l k s l o p e c o m p e n s a t i o n + - + - c o m p o v p v i n u v l o o t p 6 a s r q q f b s s e n
4 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. absolute maximum ratings input supply voltage v in - - ---------------- -- --------- -- --------------- --------------------------- -- ----- - - 0.3v to + 21 v sw voltage v sw - --- -------------------- -- ------------------------------------------------------------------ - 1v to v in + 0.3v boost trap voltage v bs ------- -- ---------------------- -- -------------------------------------------------- v sw - 0.3v to v sw +6v all other pins voltage --------- --- ------------------------------------------------------------------------ - 0.3v to +6v maximum junction temperature (t j ) ------------------- - --------------------------------------------- + 150 c storage temperature (t s ) -------- - ---------------------------------------------------------------------- - 65 c to + 150 c lead temperature (soldering, 10sec.) ----- -- -------------------------------------------------------- +260c power dissipation @t a =25 c , (p d ) sop - 8 (exposed pad ) - --- -------------------------------------------------------------------- 1.25w package thermal resistance, ( ja ): sop - 8 (exposed pad) ---- --- ----------------------------------------------------------------- 50 c/w package thermal resistance, ( jc ): sop - 8 (exposed pad) - -- --------------------------------------------------------------------- 1 5 c/w note 1 stresses beyond those listed under absolute maximum ratings" may cause permanent damage to the device. recommended operating conditions input supply voltage (v in ) - -- -- ------------------------------------------------------ ------------------ -- + 4.5 v to + 18 v output voltage (v out ) --------- --- ------------------------------------------------------------------------- + 0.925v to + 14 v operation temperature range - -- ---------------------------------------- --------------------------- - - - - 40c to +85c
5 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. electrical characteristics (v in = 12 v, t a =25 c , unless otherwise specified.) parameter conditions min typ max unit v in input supply voltage (note 2) 4.5 18 v v in supply current v en = 1.8v 1.1 ma v in shutdown supply current v en = 0v 10 15 a Q Q m m en = 0v, v sw = 0v 10 a 3 a current sense to comp transc onductance (note 3 ) 3.5 a/v error am plifier transconductance (note 3 ) i comp = 10a a/v fb = 0v 110 khz maximum duty cycle v fb = 0.8v 90 % minimum on time (note 3 ) 20 0 ns input uvlo threshold v in rising 4.4 v under voltage lockout threshold hysteresis 400 mv soft - start current 6 a ss = 0.1 f when v in = 4.5v, v out = 3.3v, maximum load current is about 2 a. note 3 not production tested.
6 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. typical performance curves v in = 12v, v out = 3.3v, c1 =10 f x 1, c6=100 f x 1, c2 = 22 f x 2, l1 = 10 h , ta = +25 c , unless otherwise noted. figure 6 . efficiency vs. loading figure 7 . efficiency vs. loading figure 8 . efficiency vs. loading figure 9 . feedback voltage vs. temperature figure 10 . frequency vs. temperature v out = 5 v v out = 3.3 v v out = 1.2 v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 load current (a) efficiency vin=12v vin=5v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 load current (a) efficiency vin=12v vin=18v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 load current (a) efficiency vin=12v vin=18v 0.9 0.905 0.91 0.915 0.92 0.925 0.93 0.935 0.94 0.945 0.95 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 temperature ( ) v fb (v) vin 12v / vout 3.3v 280 290 300 310 320 330 340 350 360 370 380 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 temperature ( ) frequency (khz) vin 12v / vout 3.3v
7 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. typical performance curves (continued) v in = 12v, v out = 3.3v, c1 =10 f x 1, c6=100 f x 1, c2 = 22 f x 2, l1 = 10 h , ta = +25 c , unless otherwise noted . i out =0a i out =3a figure 1 1 . dc ripple waveform figure 1 2 . dc ripple waveform i out =0.1a i out =3 a figure 1 3 . startup through enable waveform figure 14 . startup through enable waveform i out =0.1a i out =3 a figure 15 . s hutdown through enable waveform figure 16 . s hutdown through enable waveform v in 50mv/div. v out 20 mv/div. i l 1 a/div. v sw 5v/div. 4s/div. v in 50 0 mv/div. v out 20 mv/div. i l 1 a/div. v sw 5v/div. 4s/div. v en, 5 v/div. v out 1 v/div. i l 2 a/div. v sw 5v/div. 4 m s/div. v en, 5 v/div. v out 1 v/div. i l 2 a/div. v sw 5v/div. 2m s/div. v en, 5 v/div. v out 1 v/div. i l 2 a/div. v sw 5v/div. 2m s/div. v en, 5 v/div. v out 1 v/div. i l 2 a/div. v sw 5v/div. 4 m s/div.
8 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. typical performance curves (continued) v in = 12v, v out = 3.3v, c1 =10 f x 1, c6=100 f x 1, c2 = 22 f x 2, l1 = 10 h , ta = +25 c , unless otherwise noted . i out = 100ma to 3 a step figure 1 7 . short circuit test waveform figure 1 8 . load transient waveform v out ,, 1 v/div. i l 2 a/div. 40s/div. v out , 5 00mv/div. 400s/div. i l 2 a/div.
9 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. function description the fr9984 is a constant frequency current mode step - down synchronous dc/dc converter. it regulat es input voltage from 4.5v to 18 v, down to an output voltage as low as 0.925v, and provide s 3 a of continuous load current. control loop during normal operation, the output voltage is sensed at fb pin by a resistive voltage divider and amplified through the error amplifier. the voltage of error amplifier output pin -- comp is compared to the swit ch current to controls the rs latch. at each cycle, the high side nmos will be turned on when the oscillator sets the rs latch and turned off when current comparator resets the rs latch. when the load current increases, the fb pin voltage will drop below 0.925v, and it will cause the comp voltage increas ing until average inductor current arrive s at new load current. enable the FR9884 en pin provides digital control to turn on/ off the regulator. when the voltage of en exceeds the threshold voltage, the r egulator will start the soft start function. if the en pin voltage is be low the threshold voltage, only the bandgap voltage will be alive. if the en pin voltage is below the shutdown threshold voltage, the regulator will be disable d and turn into the shu tdown mode. maximum load current the maximum load current decreases at lower input voltage because of large ir drop on the high side switch and low side switch. the slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub - harmonic oscillations when duty cycles are greater than 50% . output over voltage protection when the fb pin voltage exceeds 1.3v, the output over voltage protection function will discharge the comp pin and the ss pin to gnd to turn the high side mosfet off. input under voltage lockout when the FR9884 is power on, the internal circuits will be held inactive until v in exceeds the input uvlo threshold voltage. and the regulator will be disabled when v in is below the input uvlo threshold voltage. the hystereti c of the uvlo comparator is 400 mv. short circuit protection the FR9884 provides short circuit protection function to prevent the device damage d from short condition. when the output is short to ground, the oscillator frequency will be reduced to prevent the inductor current increasing beyond the current limit. in the meantime, the current limit will also be reduced to lower the short current. o nce the short condition is removed, the frequency and current limit will return to normal. over temperature protection the FR9884 incorporates an over temperature protection circuit to protect itself from overheating. when the junction temperature exceeds the thermal shutdown threshold temperature, the regulator will be shut down and re - enable d when the ic junction temperature drops 30 c (typ). compensation the stability of the feedback circuit is controlled by comp pin. the compensation value of the application circuit is optimized for particular requirements. if different conversions are require d , some of the components may need to be change d to ensure stability.
10 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. application information output voltage setting the output voltage v out is set by using a resistive divider from the output to fb. the fb pin regulated voltage is 0.925v. thus the output voltage is: r2 recommended value is 10k?, so r1 is determined by: table 1 lists recommended values of r1 and r2 for most used output voltage. table 1 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? 1.2v 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 controlling the input voltage ripple and the mosfets switching 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 greater than the maximum input voltage. the input capacitor ripple current rms value is calculated as: where d is the duty cycle of the power mosfet. 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. when using tantalum o r electrolytic capacitors, a 10 f ceramic capacitor should be placed as close to the ic as possible. it is recommended that the input ec capacitor could be added for applications if the fr988 4 suffer s high spike input voltage (ex. hot plug test). it can eliminate the spike voltage induced the ic damage d from high input voltage stress (see note 1). table 2 lists recommended values of c1 and c6 for most used in put voltage. table 2 recommended capacitor values v in c1 c6 5v 10 f x2 --- 12 v 10 f x1 100 f x1 1 5v 10 f x1 330 f x1 18v 10 f x1 330 f x1 output capacitor selection the output capacitor is used to keep the dc output voltage and supply the load transient current. low esr capacitors are preferred. ceramic, tantalum or low esr electrolytic capacitors can be used depend ing on the output ripple requirement. add a 100 f or 470 f low esr electrolytic capacitor when operat ing in high input voltage range. it can improve the devices stability . the output ripple voltage v out is described as: where i 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, and the c out is the output capacitor. when using the ceramic capacitors, the resr can be ignored and the output ripple voltage v out is shown as: out r1 v 0.925 1 v r2 ?? ? ? ? ?? ?? ? ? out r1 10.81 v 0.925 k ? ? ? ? ? in(rms) out i i d 1 d ? ? ? ? f r 9 8 8 4 c 6 1 0 0 f / 2 5 v e c x 1 v i n v i n 1 2 v c 1 1 0 f / 2 5 v m l c c x 1 out out osc in vv i1 f l v ?? ? ? ? ? ?? ? ?? out esr osc out 1 v i r 8 f c ?? ? ? ? ? ? ?? ?? ?? out osc out i v 8 f c ? ?? ??
11 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. application information (continued) output inductor selection the output inductor is used for stor ing energy and filter ing output ripple current. but the trade - off condition often happens between maximum energy storage and the physical size of the inductor. the first consideration for selecting the output inductor is to make sure that the inductance is large enough to keep the converter in the cont inuous current mode. that will lower ripple current and result in lower output ripple voltage. a good rule for determining the inductance is set ting the peak - to - peak inductor ripple current i almost equal to 30% of the maximum load current. then the min imum inductance can be calculated with the following equation: where v in is the maximum input voltage. compensation components selection select the appropriate compensation value by following procedure: 1. calculate the r4 value with the following equation: where g ea is the error amplifier voltage gain, and g cs is the current sense gain. 2. calculate the c5 value with the following equation: 3. if the c out esr zero is less than half of the switching frequency, use c7 to cancel the esr zero: external boost diode selection for 5v input applications, it is recommended that an external boost diode could be added. this helps improv ing the efficiency. the boost diode can be a low cost one such as 1n4148. this diode is also recommended for high duty cycle operation (when duty cycle > 65%, v in < 15v). pcb layout recommendation the devices performance and stability are dramatically affected by pcb layout. it is recommended to follow these general guidelines show n as below: 1. place the input capacitors and output capacitors as close to the device as possible. t he t race s which connect to these capacitors should be as short and wide as possible to minimize parasitic inductance and resistance. 2 . place v in capacitors close to the v in pin. 3 . place feedback resistors close to the fb pin. 4 . place compensation components close to the comp pin. 5 . keep the sensitive signal (fb, comp ) away fro m the switching signal (sw ). 6 . 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 pla ne area which connects to the exposed pad should be maximized to improve thermal performance. 7. multi - layer pcb design is recommended. out(max) i 0.3 i ? ? ? ? ? out in out osc in v l v v f i v ?? ? ? ? ?? ? ? ? ?? f r 9 8 8 4 c o m p c 5 r 4 c 7 ( o p t i o n a l ) out osc out ea cs ref 2 c 0.1 f v r4 g g v ? ? ? ? ? ? ?? osc 4 c5 2 r4 0.1 f ? ? ? ? ? out esr cr c7 r4 ? ? f r 9 8 8 4 v i n b s v i n s w d 1 1 n 4 1 4 8 5 v c 4
12 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. application information (continued) figure 1 9 . FR9884 recommended layout diagram 1 2 3 4 5 6 7 8 c 4 l 1 s w g n d c 2 v o u t v i n c 1 r 2 r 1 c 3 r 3 c 5 r 4 c 7 c 6 + C e x p o s e d p a d g n d
13 FR9884 - 1.7 - dec - 2011 FR9884 85t fitipower integrated technology lnc. outline information sop - 8 (exposed pad) package (unit: mm) symbols unit dimension in millimeter min max a 1.25 1.70 a1 0.00 0.15 a2 1.25 1.55 b 0.31 0.51 d 4.80 5.00 d1 3.04 3. 50 e 3.80 4.00 e1 2.15 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 policy fitipowers products are not authorized for use as critical components in life support devices or other medical systems .

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