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1 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. 23v, 3a, 340khz synchronous step- down dc/dc converter pin assignments sp package (sop- 8 expose pad ) fig ure 1. pin assignment of FR9888 ordering information description the FR9888 is a synchronous step-down dc/dc converter that provides wide 4.5v to 23v input voltage range and 3a continuous load current capability. fault protection includes cycle-by-cycle current li mit, 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 scheme that provides fast transient response. in shutdown mode, the supply current is about 1ua. the FR9888 is available in an 8-pin soic package, provides a very compact system solution and good thermal conductance. features wide input voltage from 4.5v to 23v 3a output current adjustable output voltage from 0.925v to 14v low rds(on) integrated power mosfet high efficiency up to 93% fixed 340khz switching frequency current mode operation adjustable soft-start cycle-by-cycle current limit input under voltage lockout over-temperature protection with auto recovery 1ua shutdown current internal compensation function sop-8 and thermal enhanced sop-8p packages rohs compliant applications set-top-box dvd,lcd displays olpc, netbook datacom, xdsl g: green tr: tape / reel FR9888 package type sp: sop-8(exposed pad) free datasheet http://www..net/
2 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. typical application circuit FR9888 ss gnd nc vin en bs fb sw vin 5v to 12v vout 3.3v 10uf/25v ceramic x 1 22uf/6.3v ceramic x 2 l1 10uh c3 0.1uf c4 10nf r2 10k/1% r1 26.1k/1% r3 100k 1 2 3 4 5 6 7 8 c8 (optional) 100uf/25v ec x1 c6 c1 c2 figure 2. output 3.3v application circuit figure 3. low input voltage application circuit FR9888 ss gnd nc vin en bs fb sw vin 12v to 21v vout 3.3v 10uf/25v ceramic x 1 22uf/6.3v ceramic x 2 l1 10uh c3 0.1uf c4 10nf r2 10k/1% r1 26.1k/1% r3 100k 1 2 3 4 5 6 7 8 c8 (optional) 330uf/25v ec x1 c6 c1 c2 figure 4. high input voltage application circuit free datasheet http://www..net/
3 FR9888-0.1-oct-2010 fr988 8 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. i t can boost the gate drive to fully turn on the internal high s ide nmos. vin power supply input pin. drive 4.5v to 23v voltage t o this pin to power on this chip. sw power switching output. it is the output pin that i nternal high side nmos switching to supply power. gnd ground pin. connecting this pin to exposed pad. fb voltage feedback input pin. connecting fb and vout with a resistive voltage divider. this ic senses feedback voltage via fb and regulate it at 0.925v. nc no connection. keeping this pin floating. en enable input pin. this pin provides a digital contr ol 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-st art period. connect a capacitor from ss to gnd to s et the soft start period. block diagram figure 5. block diagram of FR9888 free datasheet http://www..net/
4 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. absolute maximum ratings supply voltage v in --------------------------------------------------- ------------------------------------- - 0.3v to + 26v 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 storage temperature (t s )-------------------------------------------------- ----------------------------- - 65 to + 150 lead temperature (soldering, 10sec.) -------------- ------------------------------------------------ +260c power dissipation @t a =25 , (p d ) sop-8 (exposed pad )------------------------------ ---------------------------------------- 1.25w package thermal resistance, ( ja ): sop-8 exposed pad--------------------------------- ---------------------------------------- 50 c/w esd susceptibility hbm(human body mode)----------------------------- ------------------------------------------------- 2kv note1 stresses beyond those listed under absolute maximum ratings" may cause permanent damage to the device. recommended operating conditions supply voltage (v in )-------------------------------------------------- ----------------------------------- 4.5v ~ 23v output voltage (v out ) ------------------------------------------------- ---------------------------------- 0.925v ~ 16v operation temperature range----------------------- ------------------------------------------------- - 40c to + 85c free datasheet http://www..net/
5 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. electrical characteristics (v in =12v, t a =25 , unless otherwise specified.) parameter conditions min typ max unit v in input supply voltage (note2) 4.5 23 v v in supply current v en = 1.8v 1.1 ma v in shutdown supply current v en = 0v 1 a feedback voltage 4.5v Q v in Q 18v 0.9 0.925 0.95 v feedback ovp threshold voltage 1.5 v high-side mosfet r ds (on) (note3) 130 m low-side mosfet r ds (on) (note3) 100 m high-side mosfet leakage current v en = 0v, v sw = 0v 10 ua high-side mosfet current limit (note3) minimum duty 4 5 a low-side mosfet current limit (note3) 3 a error amplifier voltage gain (note3) 400 v/v oscillation frequency 280 340 380 khz short circuit oscillation frequency v fb = 0v 110 khz maximum duty cycle v fb = 0.8v 90 % minimum on time (note3) 220 ns input uvlo threshold v in rising 4.4 v under voltage lockout threshold hysteresis 300 mv soft-start current 6 ua soft-start period c ss = 0.1uf 15 ms en input low voltage 0.4 v en input high voltage 2 v en input current ven = 2v 2 ua thermal shutdown threshold (note3) 160 note2 when v in = 4.5v, v out = 3.3v, maximum load current is about 1a. note3 not production tested. function description free datasheet http://www..net/
6 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. the FR9888 is a constant frequency current mode step-down synchronous dc/dc converter. it regulates input voltage from 4.5v to 18v, down to a n output voltage as low as 0.925v, and can provide 3a of continuous load current. control loop during normal operation, the output voltage is sensed at fb pin through a resistive voltage divide r and amplified through the error amplifier. the volt age of error amplifier output is compared to the switch current to controls the rs latch. at each cycle, th e high side nmos would be turned on when the oscillator sets the rs latch and would be turned of f when current comparator resets the rs latch. when the load current increases, the fb pin voltage drop s below 0.925v, it causes the error amplifier output voltage increase until average inductor current arr ive at new load current. enable the FR9888 en pin provides digital control to turn on/turn off the regulator. when the voltage of en exceeds the threshold voltage, the regulator starts the soft start function. if the en pin voltage is b elow than the threshold voltage, only the bandgap voltag e is alive. if the en pin voltage is below than the shutdown threshold voltage, the regulator will be disable and into the shutdown 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 funct ion of the duty cycle to prevent sub-harmonic oscillati ons at duty cycles greater than 50%. output over voltage protection when the fb pin voltage exceeds 1.5v, the output over voltage protection function will discharge the error amplifier output and the ss pin to gnd, turning the high side mosfet off. input under voltage lockout when the FR9888 power on, the internal circuits are held inactive until v in exceeds the input uvlo threshold voltage. and the regulator will be disabled when v in below the input uvlo threshold voltage. the hysteretic of the uvlo comparator is 300 mv. short circuit protection the FR9888 provides short circuit protection function to prevent the device damage from short condition. when the output short to ground, the oscillator frequency is reduced to prevent the inductor current increasing beyond the current limit. in the meantime, the current limit is also reduced to lower the short current. once the short condition is removed, the frequency and current limit will return to normal. over temperature protection the FR9888 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 shutdown, and re-enables when the ic junction temperature drops by 30 (typ). internal compensation function the stability of the feedback circuit is controlled through internal compensation circuits. this internal compensation function is optimized for most applications and this function can reduce external r, c components. free datasheet http://www..net/
7 FR9888-0.1-oct-2010 fr988 8 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: v out = 1 0.925 1 2 r r ? ? + ? ? ? ? v r2 recommended value is 10k , so r1 is determined by: r1 = 10.81 x (v out C 0.925 ) k 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 1.2 v 3 k 10 k place resistors r1 and r2 close to fb pin to preven t stray pickup. input capacitor selection the use of the input capacitor is controlling the i nput 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 times to 1.5 times greater th an the maximum input voltage. the input capacitor ripp le current rms value is calculated as: i in (rms) = i out x ( ) 1 d d ? 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 als o suffice. when using tantalum or electrolytic capacitors, a 10uf ceramic capacitor should be placed as close to the ic as possible. it is recommended that the input ec capacitor be added for applications if the FR9888 will suffer high spike input voltage (ex. hot plug test). it can eliminate the spike voltage induced the ic damage from high input voltage stress (see note1). table 2 lists recommended values of c1 and c6 for most used input voltage. table 2 recommended capacitor values v in c1 c6 5v 10uf x2 --- 12v 10uf x1 100uf x1 15v 10uf x1 330uf x1 18v 10uf x1 330uf 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, depends on the output ripple requirement. add a 100uf or 470uf low esr electrolytic capacitor when operated in high input voltage range. it can improve the devices stability. the output ripple voltage v out is described as: 1 out out osc in v v i f l v ? ? ? = ? ? ? ? ? 1 8 out esr osc out v i r f c ? ? ? = ? + ? ? ? ? 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: 8 out osc out i v f c ? ? = free datasheet http://www..net/
8 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. application information (continued) when using tantalum or electrolytic capacitors, typically 90% of the output voltage ripple is contributed by the esr of output capacitors. the output ripple voltage v out can be estimated as: out esr v i r ? = ? output inductor selection the output inductor is used for store energy and fi lter output ripple current. but the trade-off condition often happens between maximum energy storage and the physical size of the inductor. the first considerat ion for selecting the output inductor is to make sure t hat the inductance is large enough to keep the converte r in the continuous current mode. that will lower rip ple current and results in lower output ripple voltage. a good rule for determining the inductance is set the peak-to-peak inductor ripple current i almost equal to 30% of the maximum load current. then the minimum inductance can be calculated with the following equation: ( ) 0.3 out max i i ? = ( ) out in out osc in v l v v f i v ? ? ? ? ? ? ? ? where v in is the maximum input voltage. external boost diode selection for 5v input applications, it is recommended that a n external boost diode be added. this helps improve the efficiency. the boost diode can be a low cost o ne 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 is dramatically affected by pcb layout. it is recommended to follow these general guidelines show below: 1. place the input capacitors, output capacitors as close to the device as possible. trace 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. keep the sensitive signal (fb) away from the switching signal (sw). 5. 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 connects to the exposed pad should be maximized to improve thermal performance. 6. multi-layer pcb design is recommended. free datasheet http://www..net/
9 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. application information (continued) figure19. FR9888 recommended layout diagram free datasheet http://www..net/
10 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. outline information sop- 8 package (unit: mm) . note followed from jedec mo-012-e dimension in millimeter symbols unit min max a 1.35 1.75 a1 0.05 0.25 a2 1.30 1.50 b 0.31 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 free datasheet http://www..net/
11 FR9888-0.1-oct-2010 fr988 8 fitipower integrated technology lnc. outline information (continued) sop- 8 (exposed pad) package (unit: mm) dimension in millimeter symbols unit 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 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. life support policy fitipowers products are not authorized for use as critical components in life support devices or othe r medical systems . free datasheet http://www..net/

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