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al9902 document number: ds 37878 rev. 1 - 2 1 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 linear and pwm dimming high voltage led driver description the al9902 high - voltage pwm led driver provides an e fficient solution for offline high - brightness led lamps from rectified line voltages ranging from 85v ac up to 2 77 v ac . the al9902 has an internal mosfet that allows switching frequencies up to 300khz, with the switching frequency determined by an ext ernal single resistor. the al9902 topology creates a constant current through the leds providing constant light output. the output current is programmed by one external resistor. the led brightness can be varied by both l inear and pwm dimming usin g the al9902 s ld and pwm pins respectively. the pwm input operates with duty ratio of 0 - 100% and frequency of up to several khz. the al9902 is available in the thermally enhanced u - dfn6040 - 12 and so - 16 packages. features ? >90% efficiency ? universal r ectified 85 to 277v ac input r ange ? internal mosfet u p to 650v, 2 a ? high switching frequency u p to 300khz ? internal voltage regulator removes start - up r esistor ? 7.5 v regulated output ? tighter current sense t oleranc e better t han 5% ? led brightness c ontrol with linear and pwm d imming ? internal over - temperature protection (otp) ? u - dfn6040 - 12 and so - 16 packages ? totally lead - free & fully rohs compliant (notes 1 & 2 ) ? halogen and antimony free. green device (note 3) pin assignments u - dfn6040 - 12 so - 16 applications ? led o ffline l amps ? high voltage dc - dc led driver ? signage and decorative led lighting ? back lighting of flat panel displays ? general purpose constant current s ource note s: 1 . no purposely added lead. fully eu directive 2002/95/ec (rohs) & 2011/65/eu (rohs 2) compliant. 2. see http://w ww.diodes.com/quality/lead_free.html for more information about diodes incorporateds definitions of hal ogen - and antimony - free, "green" and lead - f ree . 3. halogen - and antimony - free "green products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds. typi cal applications circuit 7 1 2 6 6 1 1 6 2 3 4 5 6 1 8 9 1 0 1 1 7 1 2 n c n c p w m v d d l d r o s c s w n c s o g n d c s v i n e p 1 e p 2 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 n c n c s w n c p w m v d d l d r o s c n c v i n c s g n d n c n c s o n c a c + a c - c 1 c 2 c 3 r s e n s e r o s c d 1 g n d a l 9 9 0 2 p w m l d v d d c s r o s c s o s w v i n l 1 3 h d 0 6 1 2 4 z 1 6 0 2 v
al9902 document number: ds 37878 rev. 1 - 2 2 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 pin description s pin name u - dfn5040 - 10 so - 16 functions nc 1 14 no connection nc 2 1, 2, 4, 10,16 no connection pw m 3 5 low frequency pwm dimming pin, also enable input. internal 200k pull - down to gnd v dd 4 6 internally regulated supply voltage. ? 7.5 v nominal . can supply up to 1 ma for external circuitry. a sufficient storage capacitor is used to provide storag e when the rectified ac input is near the zero crossing. ld 5 7 linear dimming input. changes the current limit threshold at current sense comparator and changes the average led current. r osc 6 8 oscillator control. a resistor connected between this pin and ground puts the al9902 into fixed frequency mode and sets the switching frequency. v in 7 9 input voltage cs 8 1 1 senses led string and internal mosfet switch current gnd 9 12 device ground nc 1 1 13 no connection so 1 0 15 source of the inter nal mosfet switch sw 12 3 drain of the internal mosfet switch. ep1 ep1 na exposed pad 1(bottom). drain connection of internal power mosfet. ep2 ep2 na exposed pad 2 (bottom). substrate connection of control ic. connect to gnd directly underneath the pa ckage and large pcb area to minimi z e junction to ambient thermal impedance. functional block diagram & typical application v d d l d o o s c o t p s r 2 5 0 m v 2 0 0 k r s e n s e 7 . 5 v g n d v d d l d p w m c s s o a l 9 9 0 2 r o s c s w r o s c v i n d 1 v i n
al9902 document number: ds 37878 rev. 1 - 2 3 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 absolute maximum ratings ( note 4) ( @ t a = +25c, unless otherwise specified.) symbol parameter ratings unit v in(max) maximum input v oltage, v in , to gnd - 0.5 to +520 v v cs maximum cs input pin voltage r elative to gnd - 0.3 to + 0.45 v v ld maximum ld input pin voltage r elative to gnd - 0.3 to (v dd + 0.3) v v pwm maximum pwm input pin voltage r elative to gnd - 0.3 to (v dd + 0.3) v v sw maximum mosfet drain pin voltage r elative to gnd - 0.5 to +650 v v so maximum mosfet source pin voltage r elative to gnd - 0.5 to (v dd + 0.3) v v gate maximum mosfet gate pin voltage r elative to gnd - 0.5 to (v dd + 0.3) v v dd ( max ) maximum v dd pin v oltage r elative to gnd 8.1 v - continuous power dissipation (t a = + 25 ? c) - - - u - dfn6040 - 12 (derate 10mw/ ? c above +25 ? c ) 1 , 000 mw t j junction temperature range +150 c t s t storage temperature range - 65 to + 150 c esd hbm human body model esd protection (note 5) 2 , 000 v note s: 4 . stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. all voltages are with respect to ground. currents are positive into, negative out of the specified termina l. 5 . semiconductor devices are esd sensitive and may be damaged by exposure to esd events. suitable esd precautions should be take n when handli ng and transporting these devices . maximum ratings of internal mosfet (@ t a = +25c, unless otherwise specified.) characteristic symbol value units drain - source voltage v dss 650 v gate - source voltage v gss 30 v continuous drain current (note 5 ) v gs = 10 v steady state t c = +25c i d 1.6 1 a t c = + 100 c pulsed drain current (note 6 ) i dm 3 a avalanche current (note 7 ) v dd = 100v, v gs = 10v, l = 60mh i ar 0.8 a repetitive a valanche e nergy (note 7 ) v dd = 100v, v gs = 10v, l = 60mh e ar 22 mj peak d iode r ecovery dv/dt 5 v/ns recommended operating conditions (@ t a = +25c, unless otherwise specified.) symbol parameter min max unit v indc input dc supply voltage r ange 20 500 v t a ambient temperature r ange - 40 + 1 0 5 c i sw switch pin output c urrent - 0.4 a v dd maximum recommended voltage a pplied to v dd p in (note 6) - 8.1 v v p wm ( lo ) pin pwm input low v oltage 0 1 v v pwm (hi) pin pwm input high v oltage 2.4 v dd note : 6 . when using the al9902 in isolated led lamps an auxiliary winding might be used.
al9902 document number: ds 37878 rev. 1 - 2 4 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 electrical characteristics (@ t a = +25c, unless otherwise specified.) specifications apply to al9902 unless otherwise specified symbol parameter conditions min typ max unit i s h d n shut - down mode supply c urrent pin pwm to gnd, v in = 20v - 0.5 1 ma v dd internally regulated v oltage v in = v in (min) ~ 500v , (note 8) l dd(ext) = 0, gate pin open 7.2 7.5 8.1 v i dd(ext) v dd current available for external c ircuitry v in = 20 to 100v (note 7) - - 1.0 ma uvlo v dd under voltage lockout t hreshold v dd rising 6.4 6.7 7.2 v ?uvlo v dd under voltage lockout h ysteresis v dd falling - 500 - mv r pwm pwm pull - down r esistance v pwm = 5v 1 50 2 00 2 50 k v t mosfet threshold v oltage i sw = 0.5a - 4 - v v fd mosfet diodes forward v oltage i d = 0.5a - 0.85 - v v cs(hi) current sense threshold v oltage t a = - 40c to +125c 237.5 250 262.5 mv f osc oscillator f requency r osc = 1m 20 25 30 khz r osc = 226k 80 100 120 d maxhf maximum oscillator pwm duty cycle f pwmhf = 25khz, at gate, cs to gnd. - - 100 % v ld linear dimming pin voltage r ange t a = <125c, v in = 20v 0 - 2 50 mv t sd thermal shut - d own (junction) use dfn ? ja when i sw =0.4a, v ds =1v - 141 - c t sdh thermal shut - down h ysteresis - - 25 - ? ja thermal resistance junction - to - ambient u - dfn6040 - 12 (note 8) - 65 - ? c/w ? jc thermal resistance junction - to - case - 5 - ? c/w ? ja thermal resistance junction - to - ambient so - 16 - 100 - ? c/w ? jc thermal resistance junction - to - case - 15 - ? c/w no tes: 7 . a lso limited by package power dissipation limit, whichever is lower. 8. device mounted on fr - 4 pcb ( 2 5mm x 2 5mm 1 oz copper, minimum recommended pad layout on top. for better thermal performance , larger copper pad for heat - sink is needed. internal mosfet characteristic symbol min typ max unit test condition off characteristics (note 9 ) drain - source breakdown voltage bv dss 65 0 gs = 0v, i d = 250a dss ds = 650 v, v gs = 0v gate - source leakage i gss gs = 30 v, v ds = 0v on characteristics (note 9 ) gate threshold voltage v gs(th) 3 ds = v gs , i d = 250 a ds (on) gs = 10 v, i d = 1 a diode forward voltage v sd gs = 0v, i s = 1 a dynamic characteristics (note 10 ) input capacitance c iss ds = 25 v, v gs = 0v , f = 1 mhz output capacitance c oss rss g ds = 0 v, v gs = 0v , f = 1mhz total gate charge q g ds = 520 v, v gs = 10 v, i d = 2 a gate - source charge q gs gd d(on) ds = 325 v , v gs = 10 v , r g = 25 d = 2.5 a turn - on rise time t r d(off) f body diode reverse recovery time t rr ds = 100v , i f = 2 a , di/dt = 100a/ body diode reverse recovery charge q rr n otes : 9 . short duration pulse test used to minimize self - heating effect. 10 . guaranteed by design. not subject to production testing.
al9902 document number: ds 37878 rev. 1 - 2 5 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 typical characteristics iout vs. v ld dimming control iout vs. pwm dimming control at 1khz -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 -40 -15 10 35 60 85 ambient temperature (c) change in current sense threshold vs. ambient temperature current sense threshold (mv) 280 300 320 340 360 380 400 420 440 460 -40 -15 10 35 60 85 ambient temperature ( c) input current vs. ambient temperature v = 15v in v = 400v in input current (a) ? -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 -40 -15 10 35 60 85 ambient temperature (c) change in oscillation frequency vs. ambient temperature change in frequency (%) r = 1m osc ? r = 226k osc ? 150 200 250 300 350 400 450 85 105 125 145 165 185 205 225 245 265 input voltage (v ) 180ma led driver short circuit output current vs. input voltage rms short circuit output current (ma) i = 180ma led(nom)
al9902 document number: ds 37878 rev. 1 - 2 6 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 typical chara cteristics (cont inued ) 180ma led driver output current vs. input voltage 180ma led driver efficiency vs. input voltage 180ma led driver power factor vs. input voltage 180ma led driver input power dissipation vs. input voltage
al9902 document number: ds 37878 rev. 1 - 2 7 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 typical characteristics (cont.) typical output characteristics typical transfer characteristics typical on - resistance vs. drain current and gate voltage typical transfer characteristics v , drain-source voltage (v) figure 1 typical output characteristics ds i , d r a i n c u r r e n t ( a ) d 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0 1 2 3 4 5 6 v = 5.0v gs 7 8 9 10 v = 5.5v gs v = 6.0v gs v = 20v gs v = 10v gs v = 8.0v gs v , gate-source voltage (v) gs figure 2 typical transfer characteristics i , d r a i n c u r r e n t ( a ) d 0.001 0.01 0.1 1 10 0 1 2 3 4 5 6 7 8 v = 20v ds t = 85c a t = 125c a t = 150c a t = 25c a t = -55c a i , drain-source current (a) d figure 3 typical on-resistance vs. drain current and gate voltage r , d r a i n - s o u r c e o n - r e s i s t a n c e ( ) d s ( o n ) ? 3 3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8 5 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v = 10v gs v , gate-source voltage (v) gs figure 4 typical transfer characteristics r , d r a i n - s o u r c e o n - r e s i s t a n c e ( ) d s ( o n ) ? 0 2 4 6 8 10 12 14 16 18 20 4 6 8 10 12 14 16 18 20 i = 1.0a d
al9902 document number: ds 37878 rev. 1 - 2 8 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 typical characte ristics (cont.) internal mosfet typical on - resistance vs. drain current and temperature on - resistance variation with temperature on - resistance variation with temperature gate threshold variation vs. ambient temperature i , drain current (a) d figure 5 typical on-resistance vs. drain current and temperature r , d r a i n - s o u r c e o n - r e s i s t a n c e ( ) d s ( o n ) ? 0 3 6 9 12 15 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 t = -55c a t = 25c a t = 85c a t = 125c a t = 150c a v = 10v gs t , junction temperature ( c) figure 6 on-resistance variation with temperature j ? r , d r a i n - s o u r c e o n - r e s i s t a n c e ( n o r m a l i z e d ) d s ( o n ) 0 0.5 1 1.5 2 2.5 3 -50 -25 0 25 50 75 100 125 150 v = v i = 1a gs d 10 v = v i = 2a gs d 20 t , junction temperature ( c) figure 7 on-resistance variation with temperature j ? r , d r a i n - s o u r c e o n - r e s i s t a n c e ( ) d s ( o n ) ? 0 3 6 9 12 15 -50 -25 0 25 50 75 100 125 150 v = v i = 2a gs d 20 v = v i = 1a gs d 10 t , junction temperature ( c) figure 8 gate threshold variation vs. ambient temperature j ? v , g a t e t h r e s h o l d v o l t a g e ( v ) g s ( t h ) 2 2.5 3 3.5 4 4.5 5 -50 -25 0 25 50 75 100 125 150 i = 1ma d i = 250a d
al9902 document number: ds 37878 rev. 1 - 2 9 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 t ypical characteristics (cont.) i nternal mosfet diode forward voltage vs. current typical junction capacitance gate charge soa, safe operation area v , source-drain voltage (v) sd figure 9 diode forward voltage vs. current i , s o u r c e c u r r e n t ( a ) s 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 0 0.3 0.6 0.9 1.2 1.5 t = 150c a t = 125c a t = 85c a t = -55c a t = 25c a v , drain-source voltage (v) ds figure 10typical junction capacitance c , j u n c t i o n c a p a c i t a n c e ( p f ) t 1 10 100 1000 0 5 10 15 20 25 30 35 40 f = 1mhz c iss c oss c rss q (nc) g , total gate charge figure 11 gate charge v g a t e t h r e s h o l d v o l t a g e ( v ) g s 0 2 4 6 8 10 0 2 4 6 8 10 12 14 16 v = 520v i = a ds d 2 v , drain-source voltage (v) figure 12 soa, safe operation area ds i , d r a i n c u r r e n t ( a ) d 0.001 0.01 0.1 1 10 1 10 100 1000 r limited ds(on) t = 150c t = 25c v = 10v single pulse j(max) a gs dut on 1 * mrp board dc p = 10s w p = 1s w p = 100ms w p = 10ms w p = 1ms w p = 100s w
al9902 document number: ds 37878 rev. 1 - 2 10 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 applications inform ation d c - dc and off l ine led d river the al9902 is a cost - effective off line buck led driver - converter specifically designed for d riving led strings. it is suitable for being used with either rectified ac line or any dc voltage between 5 - 500v. see f igure 1 for typical circuit. figure 1 typical application circuit (without pfc) buck d esign e quation s: where i led x 0.3 = i ripple design example for an ac line voltage of 120v , the nominal rectified input voltage v in = 120v x 1.41 = 169v. from this and the led chain voltage the duty cycle can be determined: d = v leds /v in = 30/169 = 0.177 from the switc hing frequency, for example f osc = 50 khz , the required on - time of the internal mosfet can be calculated: t on = d/f osc = 3.5 s the value of the inductor is determined as follows: l = (v in - v leds ) * t on / ( 0.3 * i led ) = 4.6mh c 1 c 2 c 3 r s e n s e r o s c d 1 a l 9 9 0 2 l 1 3 h d 0 6 1 2 4 z 1 6 0 2 v a c + a c - g n d v i n p w m v d d l d c s s w s o r o s c ? d in leds v v osc on f d t ? ? l led on leds in i 3 . 0 t ) v v ( ? ? ? ? sense r )) 3 . 0 i ( 5 . 0 ( i 25 . 0 led led ? ? ?
al9902 document number: ds 37878 rev. 1 - 2 11 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 ap plications information (cont inued ) input bulk capacitor for o ffline lamps , an input bulk capacitor is required to ensure that the rectified ac voltage is held above twice the led string voltage throug hout the ac line cycle. the value can be calculated fr om : where : capacity charge work period, generally about 0.2~0.25 : input frequency for full range (85~265v rms ) should be set 10~15% of if the capacitor has a 15% voltage ripple then a simplified formula for the minimum value of the bulk input capacitor approxi mates to : c min = power factor correction if power factor improvement is required then for the input power less than 25w, a simple method for improving the power factor can be implemented by potential dividing down the rectified mains voltage (resistors r1 and r2 in figure 2 ) and feeding it into the ld pin. the current drawn from the supply voltage will follow an approximate half sine wave. a filter across the leds reduces the potential for flicker. this circuit a lso significantly reduces the size of input capacitors. figure 2 typical applica tion circuit with simple pfc passive power factor correction using 3 high voltage diodes and 2 identical capacitors can be implemented. for further design information please see an75 from the diodes website. dc - dc buck led driver the design procedure f or an ac input buck led driver outlined in the previous chapters equally applies to dc input led drivers. l f max _ dc v ? min _ line v 2 2 in leds led v 0.06 v i ? ? h d 0 6 1 2 4 z 1 6 0 2 v c 4 r s e n s e r o s c d 4 g n d a l 9 9 0 2 p w m v d d l d c s r o s c s o s w v i n l 2 r 2 r 1 c 1 c 2 c 3 l 1 a c + a c - l e d + l e d - ? in c max _ dc l min _ line ch in v f 2 v 2 ) d 1 ( p ? ? ? ? ? ? ch d
al9902 document number: ds 37878 rev. 1 - 2 12 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 applications information (cont.) dc - dc boost led driver due to the topology of the al9902 led driver - con verter , it is capable of being used in boost configurations as shown in figure 3 C at reduced accuracy. the accuracy can be improved by measuring the led current with an op amp and use the op amps output to drive the l d pin. a boost led driver is used wh en the forward voltage drop of the led string is higher than the input supply voltage. for example, the boost topology can be appropriate when input voltage is supplied by a 48v power supply and the led string consists of twenty hb led s, as the case may be for a street light. fig ure 3 boost led driver in a boost converter, when the internal mosfet is on , the energy is stored in the inductor which is then delivered to the output when the internal mosfet switches of f. if the energy stored in the inductor is not fully depleted by the next switching cycle (continuous conduction mode) the dc conversion between input and output voltage is given by: , from the switching fr equency, f osc , the on - time of the mosfet can be calculated: from this the required inductor value can be determined by: the boost topology led driver requires an output capacitor to deliver current to the le d string during the time that the internal mosfet is on. in boost led driver topologies , if the leds should become open circuit damage may occur to the power switch and so some form of detection should be present to provide o ver v oltage detection/protec tion. v i n c 3 r s e n s e r o s c l 1 g n d a l 9 9 0 2 l d p w m v d d c s r o s c s o s w v i n d 1 c 1 c 2 d 1 v v in out ? ? out in out v v v d ? ? osc on f d t ? led on in i 3 . 0 t v l ? ? ?
al9902 document number: ds 37878 rev. 1 - 2 13 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 applications information (cont.) g eneral application the al9902 is capable of operating in isolated or non - isolated topologies. it can also be made to operate in continuous as well as discontinuous conduction mode. fig ure 4 typical application circuit the al9902 contains a high - voltage ldo (see figure 4 ) , the output of the ldo provides a power rail to the internal circuitry including the gate driver. a uvlo on the output of the ldo prev ents incorrect operation at low input voltage to the v in pin. in a non - isolated buck led driver when the gate pin goes high , the internal power mosfet (q1) is turned on causing current to flow through the leds, inductor (l1) and current sense resistor (r s ense ). when the voltage across r sense exceeds the current sense pin threshold , the internal mosfet q1 is turned off. the energy stored in the inductor causes the current to continue to flow through the leds via diode d1. the al9902 s ldo provides all pow er to the rest of the ic including g ate drive and this removes the need for large high power start - up resistors. this means that to during normal operation the al9902 requires around 0.5ma from the high voltage power rail. the ldo can also be used to supp ly up to 1ma to external circuits. the al9902 operates and regulates by limiting the peak current of the internal mosfet; the peak current sense threshold is nominally set at 250mv. the al9902 is capable of operating in a fixed frequency (pwm) mode and al so variable frequency (fixed off - time) mode to regulate the led current. the same basic operation is true for isolated topologies; however in these the energy stored in the transformer delivers ener gy to leds during the off - cycle of the internal mosfet. the on - resistance of the al9902 s internal power mosfet means that it can drive up to 2a . design p arameters setting the led c urrent in the non - isolated b uck converter topology, figure 4 , the average led current is not the peak current divided by 2 - howe ver, there is a certain error due to the difference between the peak and the average current in the inductor. the following equation accounts for thi s error: . ? ? )) i * 5 . 0 ( i mv 250 r ripple led sense ? ? v d d l d o o s c o t p s r 2 5 0 m v 2 0 0 k r s e n s e 7 . 5 v g n d v d d l d p w m c s s o a l 9 9 0 2 r o s c s w r o s c v i n d 1 v i n
al9902 document number: ds 37878 rev. 1 - 2 14 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 applicatio ns information (cont.) setting operating frequency the al9902 is capable of operating between 25 and 450 khz switching frequency range. the switching frequency is programmed by connecting an external resistor between r osc pin and ground. the corresponding oscillator period is: t osc = s with r o sc in k ? the switching frequency is the reciprocal of the oscillator period. typical values for r osc vary from 75k ? to 1m ?. in buck mode the duty cycle, d, is ; so when driving small numbers of leds from high - input voltages , the duty cycle will be reduced and care should be taken to ensure that t on > t blank . the simplest way to do this is to reduce/limit the switching frequency by increasing the r osc value. reducing the switching frequency will also improve the efficiency. when o perating in buck mode , the designer must keep in mind that the input voltage must be maintained higher than two times the forward voltage drop across the leds. this limitation is related to the output current instability that may develop when the al9902 o perates at a duty cycle greater than 0.5. this instability reveals itself as an oscillation of the output current at a sub - harmonic (sbo) of the switching frequency. inductor selection the non - isolated buck circuit, figure 4 , is usually selected and ha s two operation modes: continuous and discontinuous conduction modes . a buck power stage can be designed to operate in continuous mode for load current above a certain level usually 15% to 30% of f ull load. usually the input voltage range, the output volt age and load current are defined by the power stage specification. this leaves the inductor value as the only design parameter to maintain continuous conduction mode. the minimum value of inductor to maintain continuous conduction mode can be determined by the following example. the required inductor value is determined from the desired peak - to - peak led ripple current in the inductor; typically around 30% of the nominal led current. l = , w here d is duty cycle the next step is de termining the total voltage drop across the led string. for example, when the string consists of 10 high - brightness leds and each diode has a forward voltage drop of 3.0v at its nominal current; the total led voltage v leds is 30v. dimming the led brightne ss can be dimmed either linearly (using the ld pin) or via pulse width modulation (using the pwm - d pin); or a combination of both - depending on the application. pulling the pwm pin to ground will turn off the al9902 . when disabled, the al9902 s quiescent current is typically 0.5ma . reducing the ld voltage will reduce the led current but it will not entirely turn off the external power transistor and hence the led current C this is due to the finite blanking period. only the pwm pin will turn off the powe r transistor. linear dimming is accomplished by applying a 45 to 250mv analog signal to the ld pin. this overrides the default 250mv thresh old level of the cs pin and reduces the output current. if an input voltage greater than 250mv is applied to the ld then the output current will not change. the ld pin also provides a simple cost - effective solution to soft start; by connecting a capacitor to the ld pin down to ground at initial power up , the ld pin will be held low causing the sense threshold to be low. as the capacitor charges up the current sense threshold will increase thereby causing the average led current to increase. pwm dimming is achieved by applying an external pwm signal to the pwm pin. the led current is proportional to the pwm duty cycl e and the light output can be adjusted between 0 and 100%. the pwm signal enables and disables the al9902 - modulating the led current. the ultimate accuracy of the pwm dimming method is limited only by the minimum gate pulse width, which is a fractio n of a percentage of the low frequency duty cycle. pwm dimming of the led light can be achieved by turning on and off the converter with low frequency 50hz to 1000h z ttl logic level signal. with both modes of dimming it is not possible to achieve average brightness levels higher than the one set by the current sense threshold level of the al9902 . i f a greater led current is required then a smaller sense resisto r should be used . output open circuit protection the non - isolated buck led driver topology prov ides inherent protection against an open circuit condition in the led string due to the leds being connected in series with the inductor. should the led string become open circuit then no switching occurs and the circuit can be permanently left in this sta te with damage to the rest of the circuit. 25 22 r osc ? ? ? ? ? osc led leds in f i 3 . 0 d v v ? ? ? ? in leds v v
al9902 document number: ds 37878 rev. 1 - 2 15 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 ordering information part number v cs t olerance package code packaging 13 tape and reel quantity part number suffix al9902 fdf - 13 5 % fdf u - dfn6040 - 12 3 , 000/tape & reel - 13 al9902 s16 - 13 5 % s16 so - 16 3 , 000/tape & reel - 13 marking information p a c k a g e a l 9 9 0 2 x x x - 1 3 p a c k i n g 1 3 : t a p e & r e e l f d f : u - d f n 6 0 4 0 - 1 2 s 1 6 : s o - 1 6 ( t o p v i e w ) a l 9 9 0 2 y y w w x x l o g o p a r t n u m b e r w w : w e e k : 0 1 ~ 5 2 ; 5 2 y y : y e a r : 1 5 , 1 6 , 1 7 ~ x x : i n t e r n a l c o d e r e p r e s e n t s 5 2 a n d 5 3 w e e k
al9902 document number: ds 37878 rev. 1 - 2 16 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 package outline dimensions (all d imensions in mm . ) please see ap02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version. u - dfn6040 - 12 so - 16 u - dfn6040 - 12 dim min max typ a 0.55 0.65 0.60 a1 0 0.05 0.02 a3 - - 0.15 b 0.35 0.45 0.40 d 5.95 6.05 6.00 d1 1.95 2.15 2.05 d2 2.35 2.55 2.45 e - - 1.00 e 3.95 4.05 4.00 e1 2.10 2.30 2.20 e2 1.80 2.00 1.90 l 0.35 0.45 0.40 z - - 0.30 all dimensions in mm so - 16 dim min max a 1.40 1.75 a1 0.10 0.25 a2 1.30 1.50 b 0.33 0.51 c 0.19 0.25 d 9.80 10.00 e 3.80 4.00 e 1.27 typ h 5.80 6.20 l 0.38 1.27 ? ? ? ? ? all dimensions in mm a 3 a 1 seating plane d e e l b z a d1 e 1 d2 e 2 d e h l a2 b e a1 a c detail a detail a gauge plane ?
al9902 document number: ds 37878 rev. 1 - 2 17 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 suggested pad layout please see ap02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. u - dfn6040 - 12 so - 16 dimensions value (in mm) c 0.500 g 0.650 g1 0.350 x 0.250 x1 1.075 x2 1.275 x3 2.750 y 0.400 y1 1.150 y2 1.000 y3 2.300 dimensions value (in mm) c 1.270 x 0.670 x1 9.560 y 1.450 y1 6.400 x 3 x 1 y 2 y 3 y c x pin1 x 2 y 1 g 1 g x 1 x c y y 1 pin 1
al9902 document number: ds 37878 rev. 1 - 2 18 of 18 www.diodes.com july 2015 ? diodes incorporated al990 2 important notice diode incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merc hantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes witho ut further notice to this document and any product described herein. diodes incorporated does not assume any liability arisin g out of the application or use of this document or any product described herein; neither does diodes incorporated convey any licen se under its patent or trademark rights, nor the rights of others. any customer or user of this document or products described herein in such appli cations shall assume all risks of such use and will agree to hold diodes incorporated and all the companies whose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthor ized sales channel. should customers purchase or use diodes incorporated products for any unintended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees a rising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. pro duct names and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this document is written in english but may be translated into multiple languages for reference. only the english version of this document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical components in life support devices or system s without the express written approv al of the chief executive officer of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when prope rly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. b. a critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support d evice s or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety - related requirements concerning their products and any use of diodes incorporated products in such safety - critical, life support devices or system s, notwithstanding any devices - or systems - related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorpora ted and its representatives against any damages arising out of the use of diodes incorporated products in such safety - critical, life support devices or systems. copyright ? 201 5 , diodes incorporated www.diodes.com

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