View AL8808_6121000.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

AL8808 document number: ds35648 rev. 2 - 2 1 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 cost effective low emi 30v 1a buck led driver description the AL8808 is a step-down dc/dc converter designed to drive leds with a constant current. the device can drive up to 8 leds, depending on the forward voltage of the leds, in series from a voltage source of 6v to 30v. series connection of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors. the AL8808 switches at frequency up to 1mhz with controlled rise and fall times to reduce emi. this allows the use of small size external components, hence minimizing the pcb area needed. maximum output current of AL8808 is set via an external resistor connected between the v in and set input pins. dimming is achieved by applying either an analog dc voltage or a pwm signal at the ctrl input pin. an input voltage of 0.4v or lower at ctrl switches off the output mosfet simplifying pwm dimming. applications ? mr16 lamps ? general illumination lamps pin assignments features ? led driving current up to 1a ? better than 5% accuracy ? high efficiency up to 96% ? fast controlled falling edges 7ns ? operating input voltage from 6v to 30v ? high switching frequency up to 1mhz ? pwm/dc input for dimming control ? built-in output open-circuit protection ? built-in over-temperature protection ? tsot25: available in ?green? molding compound (no br, sb) ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) notes: 1. no purposely added lead. fully eu directiv e 2002/95/ec (rohs) & 2011/6 5/eu (rohs 2) compliant. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen and antimony free, "green " and lead-free. 3. halogen and antimony free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm t otal br + cl) and <1000ppm antimony compounds. typical applications circuit tsot25 (top view) 1 2 3 5 4 v in set sw gnd ctrl
new product AL8808 document numbe r pin descr i pin number 1 2 3 4 5 function a absolute m symbol esd hbm esd mm v in v set v sw v ctrl i sw t j t lead t st caution: stress e functio n affecte semic o and tr a r : ds35648 rev. 2 i ptions pin name sw gnd ctrl set v in a l block di a m aximum human body m machine mod e continuous v i set pin volta g sw voltage r e ctrl pin inp u switch curren t junction tem p lead temper a storage tem p e s greater than th e n al operation of th e d by exposure to a o nductor devices a a nsporting these d e - 2 switch pin. c gnd pin dimming an d ? leave f ( v ? drive t o ? drive w i outno m ? drive w ? a pwm current set nominal input supply section for m a gram ratings (@ m odel esd prot e e l esd protectio n pin voltage rel a g e relative to v in e lative to gnd u t voltage t p erature a ture soldering p erature range e 'absolute maxi m e device at these o bsolute maximum a re esd sensitive a e vices. w c onnect inducto r d on/off control f loating for norm a v ctrl = 5v, giv e o voltage below 0 ith an analog vo l m ith an analog vo l signal (low leve to be adjusted b output current p pin. must be lo c m ore information. figure 1 t a = +25c, unl e parameter e ction n a tive to gnd pin m um ratings' spec o r any other condi t rating conditions f o a nd may be dama g 2 of 20 w ww.diodes.co r /freewheeling di o input. a l operation. e s nominal avera 0 .4v to turn off o u l tage (0.5v < v c t l tage > 2.6v out p l 0.4v and hig h b elow the level s e p in. configure t h c ally decoupled t . AL8808 bloc k e ss otherwise s p ified above, may c t ions exceeding th o o r extended period s g ed by exposure t o m function o de here, minim i ge output curre n u tput current t rl < 2.5v) to a d p ut current will b e h level > 2.6; tra n e t by the resisto r h e output current o gnd with > 2. 2 k diagram p ecified.) c ause permanent d o se indicated in th i s of time. o esd events. sui t i zing track lengt h n t i outnom = 0.1/ r d just output curr e e 100% of i outn o n sition times les s r connected to s of the device. 2 f x7r cerami ratin g 2.5 20 0 -0.3 to -5 to + -0.3 to -0.3 to 1.2 5 15 0 30 0 -55 to + d amage to the de v i s specification is n t able esd precaut h at this pin to re d r s ) e nt from 20% to o m s than 1s) allo w et input pin. c capacitor ? se e g s 0 +33 0.3 +33 +6 5 0 0 + 150 v ice. these are s t n ot implied. devic e ions should be ta k january 201 ? diodes incorporat e a l8808 d uce emi. 100% of w s the output e applications unit kv v v v v v a c c c tr ess ratings only; e reliability may be k en when handling 3 e d
AL8808 document number: ds35648 rev. 2 - 2 3 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 recommended operating conditions (@t a = +25c, unless otherwise specified.) symbol parameter min max unit v in operating input voltage relative to gnd 6.0 30 v v ctrlh voltage high for pwm dimming relative to gnd 2.6 5.5 v v ctrldc voltage range for 20% to 100% dc dimming relative to gnd 0.5 2.5 v v ctrll voltage low for pwm dimming relative to gnd 0 0.4 v i sw continuous switch current (note 4) 1 a f sw maximum switching frequency 1 mhz t j junction temperature range -40 +125 c note: 4. subject to ambient temperature, input voltage and sw itching frequency. see applications section for suggested derating . electrical characteristics (@ t a = +25c, v in = 12v, ctrl pin floating; unless otherwise specified.) symbol parameter conditions min typ max unit v insu internal regulator start up voltage v in rising 5.6 v v insh internal regulator hysteresis threshold v in falling 200 mv i q quiescent current v in = 30v, output not switching 350 a i s input supply current f sw = 250khz 450 a v th set current threshold voltage 95 100 105 mv v th-h set threshold hysteresis 20 mv i set set pin input current v set = v in -0.1 16 a v ctrl open circuit ctrl pin voltage 5 v r ctrl ctrl pin input resistance referred to internal 5v regulator. 50 k ? v ref internal reference voltage 2.5 v r ds(on) on resistance of sw mosfet i sw = 0.35a 0.35 ? i sw_lkg switch leakage current v in = 30v, v ctrl = 0.4v, v sense = 0v 0.5 a t r sw rise time v sense = 100 20mv, f sw = 250khz v sw = 0.1v to 12v to 0.1v, c l = 15pf 7 ns t f sw fall time 5 ns t otp over-temperature shutdown 145 c t otp-hyst over-temperature hysteresis 10 c ja thermal resistance junction-to-ambient tsot25 (note 5) 209 c/w jl thermal resistance junction-to-lead tsot25 (note 5) 57 jt thermal resistance junction-to-top tsot25 (note 5) 13 notes: 5. device mounted on fr-4 pcb (25mm x 25mm 1oz copper, mi nimum recommended pad layout on top layer and thermal vias to m aximum area bottom layer ground plane. for better thermal performance, larger copper pad for heat-sink is needed. ?refer to figure 42 for the device derating curve.
AL8808 document number: ds35648 rev. 2 - 2 4 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 typical performance characteristics (@ t a = +25c, unless otherwise stated.) 0 3 6 9 12 15 18 21 24 27 30 input voltage (v) figure 2. supply current vs. input voltage 400 350 300 250 200 150 100 50 0 in p u t c u r r en t (a) v = 0v v = v t = +25c ctrl set in a l = 33h t = +25c v = 12v r = 150m 1 led a in set l = 68h l = 100h 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 v ctrl (v) figure 3. switching frequency vs. v ctrl 900 800 700 600 500 400 300 100 0 f r e q u e n c y (k h z) 200 t = +25c v= 12v l = 68h a in 1 led r set = 100m r set = 150m r set = 300m 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 v ctrl (v) figure 4. led current vs. v ctrl 1.2 1.0 0.8 0.6 0.4 0.2 0.0 led c u r r en t (a) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 v ctrl (v) figure 5. i vs. v ctrl ctrl 20 0 -20 -40 -60 -80 -100 -120 c t r l p i n c u r r e n t (a) t = +25c, v = 12v l = 68h, r ain set = 150m 1 led 020406080100 pwm duty cycle (%) figure 6. i vs. pwm duty cycle led 6 5 4 3 2 1 0 led c u r r en t e r r o r (%) 0.9 led c u r r ent (a) 0.6 0.3 0.0 t = +25c, v = 12v l = 68h, r ain set pwm = 150m 1 led, f = 500hz 6 9 12 15 18 21 24 27 30 input voltage v ctrl (v) figure 7. duty cycle vs. input voltage 100 90 70 60 40 30 10 0 d u t y c y c le (%) 80 50 20 t = +25c, r = 150m l = 33h, l = 68h, l = 100h a set
new product AL8808 document numbe r typical p e sw m o s f e t r (m ) ds(on) 6 0 5 0 4 0 3 0 2 0 1 0 0.5 0 0.4 5 0.4 0 0.3 5 0.3 0 0.2 5 0.2 0 0.1 5 0.0 0 0.0 5 0.1 0 sw mosfet r ( ) ds(on) r : ds35648 rev. 2 e rformanc e figure 12. s -40 -25 -10 5 ambi figure 8. 0 0 0 0 0 0 0 0 0 0 0 0 0 v = open v = v = 1 2 ctrl set in 0200 0 5 0 5 0 5 0 5 0 5 0 s w figure 10. v = 12v v = v t = +25c ctrl = floating in set in a - 2 e charact e s teady state w a 50 6 5 20 35 ent tempera t sw r vs ds(on) 2 v 400 600 w itch curren t sw r vs. s ds(on) w e ristics (con t a veforms 5 80 95 110 1 t ure (c) . temperature 800 1 t (ma) s witch current 5 of 20 w ww.diodes.co t .) (@ t a = +25 c 25 000 m c , unless other w fig u figu r 69 fig sw m o s f e t r (m ) ds(on) 400 350 300 250 200 0 100 150 50 v = v = v t = 25 ctrl set a w ise stated.) u re 11. sw out p r e 13. sw outp 12 15 1 8 v ure 9. sw r in ds( o = open v c in p ut fall time ut rise time 21 24 8 (v) vs. input volt a o n) january 201 ? diodes incorporat e a l8808 27 30 a ge 3 e d
AL8808 document number: ds35648 rev. 2 - 2 6 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 typical performance characteristics (l = 68h, t a = +25c, unless otherwise stated.) 6 9 12 15 18 21 24 27 30 input voltage (v) figure 14. efficiency vs. input voltage 100 95 90 85 80 75 70 effi c ien c y (%) 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l= 68h r = 150m a set 1 led 2 leds 3 leds 4 leds 5 leds 7 leds 6 9 12 15 18 21 24 27 30 input voltage (v) figure 15. 330ma led current vs. input voltage 0.36 0.35 0.34 0.33 0.32 0.31 0.30 led c u r r e n t (a) t = 25c l= 68h r = 300m a set 6 9 12 15 18 21 24 27 30 input voltage (v) figure 16. switching frequency vs. input voltage 450 400 300 200 100 50 0 swi t c h in g f r e q u en c y (k h z) 350 250 150 1 led 2 leds 3 leds 4 leds 5 leds 7 leds 6 9 12 15 18 21 24 27 30 input voltage (v) figure 17. 670ma led current vs. input voltage 0.74 0.72 0.70 0.66 0.64 0.62 0.60 led c u r r en t (a) 0.68 t = 25c, v l= 68h, r = 150m a set in = 12v 1 led 2 leds 3 leds 4 leds 5 leds 7 leds 6 9 12 15 18 21 24 27 30 input voltage (v) figure 18. duty cycle vs. input voltage 100 90 70 40 20 10 0 d u t y c y c le (%) 80 60 30 50 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l= 68h r = 150m a set 6 9 12 15 18 21 24 27 30 input voltage (v) figure 19. 1a led current vs. input voltage 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l= 68h r = 100m a set 1.10 1.05 0.95 0.90 led c u r r en t (a) 1.00
AL8808 document number: ds35648 rev. 2 - 2 7 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 typical performance characteristics (670ma led current; t a = +25c unless otherwise stated.) 18 6 9 12 15 21 24 27 30 input voltage (v) figure 20. led current deviation vs. input voltage devia t i o n f r o m t a r g e t c u r r en t (%) 5 3 -3 -5 1 -1 4 leds 5 leds 7 leds 1 led 2 leds 3 leds t = 25c, l = 33h r = 150m a set 18 6 9 12 15 21 24 27 30 input voltage (v) figure 21. switching frequency vs. input voltage swi t c h i n g f r e q u e n c y (k h z) 500 400 100 0 300 200 800 700 600 4 leds 5 leds 7 leds 1 led 2 leds 3 leds t = 25c, l = 33h r = 150m a set 18 6 9 12 15 21 24 27 30 input voltage (v) figure 22. led current deviation vs. input voltage devia t i o n f r o m t a r g e t (%) 2 1 -2 -5 0 -1 5 4 3 -4 -3 4 leds 5 leds 7 leds 1 led 2 leds 3 leds t = 25c, l = 68h r = 150m a set 18 6 9 12 15 21 24 27 30 input voltage (v) figure 23. switching frequency vs. input voltage swi t c h i n g f r e q u e n c y (k h z) 300 250 50 0 200 150 450 400 350 100 t = 25c, l = 100h r = 150m a set 4 leds 5 leds 7 leds 1 led 2 leds 3 leds 18 6 9 12 15 21 24 27 30 input voltage (v) figure 24. led current deviation vs. input voltage deviati o n f r o m ta r g et (%) 2 1 -2 -5 0 -1 5 4 3 -4 -3 18 6 9 12 15 21 24 27 30 input voltage (v) figure 25. switching frequency vs. input voltage swi t c h in g f r e q u en c y (k h z) 150 0 100 250 200 50
AL8808 document number: ds35648 rev. 2 - 2 8 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 typical performance characteristics (1a led current) t a = +25c unless otherwise stated.) 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l = 33h r = 100m a set 18 15 12 69 30 27 24 21 input voltage (v) figure 26. led current deviation vs. input voltage 5 4 3 2 -4 -5 0 devi a ti o n f r o m t a r get c u r r ent ( % ) 1 -1 -2 -3 18 15 12 69 30 27 24 21 input voltage (v) figure 27. switching frequency vs. input voltage 600 500 400 300 100 0 200 swit c hin g f r e q uen c y (khz) 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l = 33h r = 100m a set 18 15 12 69 30 27 24 21 input voltage (v) figure 28. led current deviation vs. input voltage 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l = 68h r = 100m a set 5 4 3 2 -4 -5 0 d evi a t i o n f r o m t a r g e t c u r r e n t ( % ) 1 -1 -2 -3 18 15 12 69 30 27 24 21 input voltage (v) figure 29. switching frequency vs. input voltage 300 250 200 150 50 0 100 swi t c h i n g f r e q u e n c y (k h z) 18 15 12 69 30 27 24 21 input voltage (v) figure 30. led current deviation vs. input voltage 1 led 2 leds 3 leds 4 leds 5 leds 7 leds t = 25c l = 100h r = 100m a set 5 4 3 2 -4 -5 0 d evia t i o n f r o m t a r g e t c u r r e n t (%) 1 -1 -2 -3 18 15 12 69 30 27 24 21 input voltage (v) figure 31. switching frequency vs. input voltage 200 180 160 80 20 0 60 swi t c h in g f r e q u en c y (k h z) 140 100 120 40 1 led
new product AL8808 document numbe r applicati o AL8808 oper a in normal oper a inductor l1, an d voltage and the this rising curr e voltage to the in when this volta g l1, the leds a n of the leds an d this decaying c applied at the i n this switch-on- a led current c the led curre n connected from with ctrl left fl o if the ctrl pin i for example for when the ctr l r : ds35648 rev. 2 o n informa t a tion a tion, when volt a d the leds. th e inductor l1. e nt produces a v o put of the intern a g e reaches an i n n d the schottky d d the schottky di o urrent produces n put of the inter n a nd-off cycle con c ontrol n t is controlled b the ctrl pin t o o ating. if the ct i s driven by an e a desired led c l voltage is brou g - 2 t ion a ge is applied at e current ramps o ltage ramp acr o a l comparator. n ternally set up p d iode d1, and b a o de. a falling voltag e al comparator. w tinues to provid e b y the resistor r o an internal 5v r rl pin is left flo a xternal voltage ( c urrent of 660m a g ht below 0.4v, t w +v in , the al88 0 up linearly, an d o ss r1. the inte r p er threshold, th e a ck to the suppl y e at r1, which is w hen this voltag e the average l e figure 32. 1 (in figure 32) r egulator. when a ting or driven a b where higher than 0.5 v i l wher e a and v ctrl =2.5 v = w ww.diodes.co 0 8 internal swit c d the ramp rate r nal circuit of the e internal switch y rail, but it deca y sensed by the a e falls to the int e e d current set b y typical applic a connected bet w the ctrl pin i s b ove 2.5v the n o 1 r v i th led = v th is nominall y v and lower than r v v v t ref ctrl l ed = e v ref is nomin a v or with the ct r = = 66 . 0 1 . 0 i v led th h is turned off wh m c h is turned on. is determined b AL8808 sense s is turned off. t h y s, with the rate a l8808. a volta g e rnally set lowe r y the sense resis t a tion circuit w een v in and s e s left floating it g e o minal average o y 100mv. 2.5v), the aver a 1 r t h a lly 2.5v r l pin left open m 150 ich allows pwm current starts t o b y the input volt a s the voltage acr o h e inductor curr e of decay deter m g e proportional t o r threshold, the i n t or r1. e t pins. the al 8 e ts pulled up to 5 utput current in t a ge led current the resulting res dimming. o flow through s e a ge (+v in ) min u o ss r1 and appl i e nt continues to m ined by the for w o the sense volt n ternal switch is 8 808 has an int e 5 v - increasing i t he led(s) is de f is: istor is: january 201 ? diodes incorporat e a l8808 e nse resistor r1 u s the led chai n i es a proportion a flow th r ough r1 w ard voltage dro p age across r1 i s turned on agai n e rnal 50k resist o i ts noise rejectio f ined as: 3 e d , n a l , p s n . o r n
AL8808 document number: ds35648 rev. 2 - 2 10 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 application information (cont.) analog dimming the ctrl pin can be driven by an external analog voltage (v ctrl ), to adjust the output current to a value below the nominal average value defined by r1. the led current decreases linearly with the ctrl voltage when 0.5v v ctrl 2.5v. note that 100% brightness is achieved when either the ctrl pi n is left floating or pulled above 2.5v by an external voltage sou rce. for 2.6v v ctrl 5.5v the led current will not get overdriven and will be set the current according to the equation v ctrl = 2.5v (the internal reference voltage). see figure 33 below. pwm dimming led current can be adjusted digitally, by applying a low frequency pulse width modulated (pwm) logic signal to the ctrl pin to turn the device on and off. this will produce an average output current proportional to the duty cycle of the control signal. in particular, a pwm signal with a max resolution of 10bit (~0.1% duty cycle) can be applied to t he ctrl pin to change the output current to a value below the nom inal average value set by resistor r set . to achieve this resolution the pwm frequency has to be lower than 500hz, however higher dimming frequencies can be used, at the expense of dimming dynamic range and accuracy. typically, for a pwm frequency of 500hz the accuracy is better than 2% for pwm ranging from 5% to 100%. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 v (v) figure 33. led current dimming ration and typical error vs. control voltage ctrl 110 100 90 80 70 60 50 40 30 20 10 0 dimmed : 100% led c u r r en t r a t i o (%) led current error dimmed led current ratio 2.0 2.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 typi c al e r r o r (%) t = 25c v = 12v l = 68h a in 50 60 010203040 90100 70 80 pwm duty cycle (%) figure 34. pwm dimming at 500hz 0.8 0.7 0.1 0 0.3 0.2 0.6 0.5 0.4 led c u r r e n t (a) v = 12v t = +25c l = 68h r = 150m 1 led in a set v = 12v t = +25c l = 68h r = 150m 1 led in a set 7.5 0.0 2.5 5.0 15.0 10.0 12.5 pwm duty cycle (%) figure 35. low duty cycle pwm dimming at 500hz l o ad c u r r e n t e r r o r (%) 10 9 8 7 6 5 4 3 2 1 10
new product AL8808 document numbe r applicati o pwm dimmi n the ctrl pin i s output stage. the ultimate p w lower switching the accuracy/lin e at the start of e threshold isn?t r e greater pwm d frequency. the three figure from a 12v rail a figure 36. 0 figure 38. 0 as can be obse value. r : ds35648 rev. 2 o n informa t n g (cont.) s designed to b e w m dimming res o frequencies and e arity of the pw m e ach pwm cycl e e ached then the d imming dynami s below show 0. a t +25c for a n o .2% pwm duty 68 h .2% pwm duty 22 h rved from figur e - 2 t ion (cont.) e driven by both o lution is determ /or higher pwm m dimming. e the led curr e accuracy will be c ranges can b e 2% duty cycle p o minal led curr e cycle at 100hz h inductance cycle at 500hz h inductance e 37 greater di m w 3.3v and 5v lo g ined by the num frequencies the e nt needs to re s greatly affected . e achieved by r p wm pulse resol e nt of 670ma . pwm frequen c pwm frequen c m ming accuracy c 11 of 20 w ww.diodes.co g ic levels directl y ber of full led s number of full s w s tart from zero u . r educing the p w ution with differ e c y and fi g c y and c an be achieve d m y from a logic ou s witching cycles t w itching cycles t u p to the uppe r w m dimming fre e nt pwm freque n g ure 37. 0.2% p d by reducing bo tput with either a t hat can be achi e t hat can be achi e r threshold level quency and/or i n cies and differe wm duty cycl e 22h ind u th the pwm di m a n open drain o u e ved during the e ved is reduced (nominally 120 ncreasing the a nt inductor valu e e at 100hz pwm u ctance m ming frequency january 201 ? diodes incorporat e a l8808 u tput or push pu pwm on-time. a thereby reducin g mv/r set ). if thi s a l8808 switchin g e s driving 2 led s frequency an d and the induct o 3 e d ll a t g s g s d o r
new product AL8808 document numbe r applicati o start-up and s on initial power than 0.45v (typi the output start s this will cause s the upper led c the AL8808 do e accuracy. soft start can b e rail on the ctr l the external ca p occurs it is esse this is achieve d the control volta adding this cap a dimming accura reducing ou t peak to peak ri p a value of 1 f capacitor value s note that the c a voltage. by add altering the me a r : ds35648 rev. 2 o n informa t s oft start up the device w cal). this cause s s switching the l e s ome additional i c urrent threshold e s not have in-b u e easily implem e l pin will charge t p acitor slows up ntial that the ca p d by increasing t h ge at the input o f a citor increases cy depending o n figure t put ripple p ple current in th e will reduce the s . a pacitor will not ing this capacit o a n current value. - 2 t ion (cont.) w ill not start swit c s a slight delay ( e d current will b nput current to t h level by slowin g u ilt soft-start act i e nted by adding a t he external cap a the ramp-up of p acitor is large e n h e time taken fo r f the comparato r the time taken f n the delay intro d 39. soft start w e led(s) can be supply ripple c affect operatin g o r the current w a w c hing until the p ( dependent on r a uild up to the up p i led s h at of charging t h g down the rise o i on allowing ver y a n external cap a a citor up to 5v. the ctrl pin v o n ough to keep t h r the ctrl volt a r . f or the output t o d uced. w ith 100nf ca p reduced, if requ urrent significa n g frequency or e a veform through 12 of 20 w ww.diodes.co ower supply ha s a mp rate of inpu p er threshold le v 1 . 0 v 5 . 2 v ctrl s spk = h e input bulk ca p f the ctrl pin v y fast control of t a citor from the c o ltage thereby r e h e ctrl pin volt a a ge to rise to the o reach 90% of i p acitor on ctr l ired, by shuntin g n tly in the typic a e fficiency, but it w the led(s) cha n m s reached appro x t voltage and in p v el: 1 r 2 . 1 1 p acitance. one w v oltage ? implem t he output powe r c trl pin to grou n e ducing the led a ge below 2.5v d upper (turn-off) ts final value, t h l pin (v in = 24 v , g a capacitor c2 a l case. proporti o w ill increase st a n ges from a tria n x imately 5.6v o r p ut bulk capacit a w ay of reducing t enting a soft-sta r mosfet swit c n d. the internal current via ana l d uring the ramp - threshold and b y h is delay is 25 s i led = 667ma, 1 across the led ( o nally lower rip p a rt-up delay, by n gular ramp to a r the ctrl pin v a nce of the al8 8 t his additional c u rt. c h which improv e pull-up resistor t l og dimming. to - up of the input v y slowing down t s /nf, but will im p 1 led) ( s) as shown in f p le can be achi e reducing the ra t a more sinusoid a january 201 ? diodes incorporat e a l8808 v oltage is great e 8 08 circuit). onc e u rrent is to reduc e e s pwm dimmin g t o the internal 5 v ensure soft-sta r v oltage. t he rate of rise o p act on the pw m f igure 32. e ved with high e t e of rise of le d a l version witho u 3 e d e r e e g v r t o f m e r d u t
new product AL8808 document numbe r applicati o inductor sel e recommended data for select e required switchi led current ac c the inductor sh o the chosen coil required mean o suitable coils fo r part mss1038-333 mss1038-683 npis64d330 m the inductor val the following e q switch ?on? ti m v t in on ? = switch ?off? ti m v t l off = where: l is the coil r l is the coil r s is the cu r i avg is the re v in is the s u i is the coi l v led is the t r sw is the s v d is the di o r : ds35648 rev. 2 o n informa t e ction inductor values e d component v a ng frequenc y . l c uracy (due to pr o o uld be mounte d should have a s o utput current. r use with the a l no. m trf ue should be ch o q uations can be u m e: x i v l avg led ? ? m e: i v i l av g d l ed + + inductance (h) resistance ( ? ) r rent sense resi s quired led curr e u pply voltage (v) l peak-peak rippl t otal led forwar d s witch resistance o de forward volt a - 2 t ion (cont.) for the AL8808 a lues. the indu c l ower inductor v o pagation delay s figure 4 d as close to the d s aturation curren t l 8807 are listed i l (h) d ( 33 0. 68 0. 33 0. o sen to maintai n u sed as a guide, ( r r r x i s w l s + + () r r x l s g + s tance ( ? ) e nt (a) e current (a) {in t d voltage (v) ( ? ) {=0.35 ? no m a ge at the requir e w are in the rang e c tance used will alues can be u s s ) and increase p 0. inductor val u d evice as possi b t higher than the i n the table belo w d cr ( v) i sa t (a ) 093 2. 3 213 1. 5 124 1. 1 n operating duty c with reference t ) w t ernally set to 0. 4 m inal} e d load current ( v 13 of 20 w ww.diodes.co e 33h to 100 h depend on a c s ed to increase t p ower dissipatio n u e with input vol t b le with low resi s peak output cu r w : t ) 3 c o 5 1 c ycle and switch o figure 1 - op e 4 x i avg } v ) m h . note that th e c ombination of i n he switching fre q n (due to switchi n t age and numb e s tance/stray indu c r rent and a conti n manufactu o ilcraft www.coi nic www.nicco m 'on'/'off' times o v e rating wavefor m figur e e AL8808 web c n put voltage an d q uency and red u n g losses). e r of leds c tance connecti o n uous current ra t rer lcraft.com m p.com v er the supply v o m s. e 41. typical sw i c alculator provid d led chain vo u ce solution siz e o ns to the sw pi t ing above the o ltage and load c i tching wavefor m january 201 ? diodes incorporat e a l8808 es performance ltage to set the e but may affect n. c urrent range. m 3 e d
AL8808 document number: ds35648 rev. 2 - 2 14 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 application information (cont.) capacitor selection the small size of ceramic capacitors ma kes them ideal for AL8808 applications. x7 r type is recommended because it retains capa citance value over wider voltage and temperature ranges than other types such as y5v or z5u. x5r is a useful compromise over a restricted te mperature range. note that even x7r capacitance reduc es significantly with increased dc bias vo ltage. at 50% of rated voltage, the capa citance loss is between about 10% to 50% of nominal. therefore it is often neces sary to select a voltage rating which is at least twice the op erating voltage. input capacitor in figure 32, the input capacitor c1 is requi red as a reservoir. diode d1 switches at a rate of typically up to 400khz. the p ower supply has a finite impedance, often including a wiring inductance value of the order of 100nh to 1uh or more depending upon the system desi gn. c1 is required to limit the power supply voltage and current ripple both to allow stable regulation of the led current, and also to m eet emc requirements. a 2.2 f input capacitor is sufficient for most dc powered applicat ions of AL8808. this depends upon the operating voltage and curren t and the maximum level of ripple required. additional capacitors may be required in parallel for emc pur poses. this is described below in a separate section. however, if operated from a rectified low voltage ac source, such as mr16, then the input capacitance will need to be significa ntly increased to provide enough reservoir charge when the input voltage falls below the minimum operati ng voltage of the AL8808 or the led chain voltage output capacitor in figure 32, the output capacitor c2 is normally required to limit the load voltage and current ripple, in order to meet emc requirements. a value of 0.1f to 1f is sufficient for many requirements, dependi ng on voltage and current conditions. additional capacitors may be required in parallel for emc purposes. this is described below in a separate section. diode selection for maximum efficiency and performance, the flywheel rectifier (d 1) should be a fast low capacitance schottky diode with low re verse leakage at the maximum operating voltage and temperature. the silicon pn diode is not suitable because of its increased power loss, due t o a combination of lower forward voltage and reduced recovery time. the use of a super-barrier-rectifier (sbr) is not recommended for use as a flywheel diode in this application. (however the sbr pr ovides significant advantages wh en used with an ac power input as a bridge rectifier d riving v in .) it is important to select d1 with a peak current rating above the peak coil current and a continuous current rating higher than the maximum output load current. in particular, it is recommended to have a diode voltage rating at least 15% higher than v in to ensure safe operation during the switching and a mean current rating at least 10% higher than the peak diode current. the power ratin g is verified by calculating the power loss through the diode. in practice, the voltage rating selection is often increased by up to about 50% to obtain a better compromise with loss due to reverse leakage current at higher tem perature. also the current rating is typically selected to pr ovide a margin of up to about 50%. schottky diodes, e.g. dfls240l or dfls140, with their low forwar d voltage drop and fast reverse recovery, are the ideal choice for AL8808 applications. leakage current is suffici ently limited for the application.
AL8808 document number: ds35648 rev. 2 - 2 15 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 application information (cont.) thermal considerations for continuous conduction mode of operation, the absolute maximum junction temper ature must not be exceeded. the maximum power dissipation depends on several factors: the thermal resistance of the ic package ( jc ), pcb layout, airflow surrounding the ic, and difference between junction and ambient temperature. the maximum power dissipation can be ca lculated using the following formula: ja a ) max ( j ) max ( d t t p ? = where t j(max) is the maximum operating junction temperat ure; for the AL8808 this is +125c. t a is the ambient temperature, and ja is the junction to ambient thermal resistance. the major thermal path for the tsot25 package is pin 2 (gnd pin) and it is important for minimizing the ja that a suitable area and thermal mass is associated with pin 2. the thermal impedance fr om the AL8808 junction to pin 2 is approximately 57c/w. the AL8808?s ja on a 25 x 25mm double sided fr4 pcb with minimum recommended pad layout on top layer and thermal vias to maximum area on bottom layer with 1oz copper standing in still air is appr oximately 209c/w. yielding a maximum power dissipation at 25 c of 0.47w the AL8808?s ja on a 25 x 25mm double sided fr4 pcb with maximum area top and bo ttom with vias is approximately 151c/w; which gives a maximum power dissipation at 25c of 0. 66w. figure 42 shows the power derating of the AL8808 on different area pcb with maximum area on bottom of pcb with 1 and 2oz copper standing in still air. figure 42. derating curve for different pcb (50mm) with 2oz cu max area top 2 (50mm) with 1oz cu max area top 2 (25mm) with 2oz cu max area top 2 (25mm) with 1oz cu min area top 2 (25mm) with 2oz cu min area top 2 (25mm) with 1oz cu min area top 2 (50mm) with 1oz cu min area top 2 -10 5 -40 -25 50 65 20 35 110 125 80 95 ambient temperature (c) p o we r dissi p a t i o n (w) 1.0 0.9 0.1 0 0.8 0.7 0.3 0.2 0.6 0.5 0.4
new product AL8808 document numbe r applicati o emi and lay o the AL8808 is decoupling and switching spee d due to switchin g the turn-on ed g and pcb tracks between the sc h the tracks from short as possibl e there is an ind u estimate the pri m and length will d the resonant fr e diode. an exa m summary: 1. use a the g r (emc 2. place less t h the in paras i more g 3. place 4. place 5. place capa c impe d r : ds35648 rev. 2 o n informa t o ut considera t a switching reg layout of the p c d s of the internal g losses and radi a g e (falling edge) . after the sch o h ottky diode cap a the sw pin to t e . u ctance internall y m ary resonant fr d ominate the siz e e quency of any m ple of good lay o figure 43. p c pcb constructi o r ound areas are ) operation and a capacitor c1 as h an about 5mm. put current pas s i tic inductance o f g round via hole s sense resistor r d1 anode, the s capacitor c2 a s c itor and its cop p d ance coupling d - 2 t ion (cont.) t ions ulator with fast c b.to help with power mosfe t a ted emi. dominates the r a o ttky diode rever s a citance and th e t he anode of th e y in the AL8808 t equency. if the t e of the inductan c oscillation is de t ut is shown in fi c b loop reson o n with copper f o tightly connect e a lso to minimize close as possib to ensure the b s es directly thro u f the copper tra c s close to the gr o r 1 as close as p o s w pin and the i n s close as poss p er trace such th a ue to the added w edges and me a these effects th e t . the rise an d a diated emi whi s e recovery time e track inductanc e schottky diod e t his can be assu rack is capable o c e. t ermined by the gure 44 - the str ance o il on top and b o e d together usin g device tempera t le to v in , and as b est possible e m u gh the capacito c e. ensure low i n o und pad. o ssible to v in an d n ductor as close ible to l1 and s a t the input curr e parasitic induct a 16 of 20 w ww.diodes.co a sures small dif f e AL8808 has b d fall times are c ch is due to an i of around 5ns h e, l track , see f e , d1, and then f med to be arou n o f handling 1a i n combined indu c ay track inducta n o ttom. provide m g plated via hol e t ures by spreadi n close as possib m i filtering (great e r mounting pad. n ductance conn e d set. together as pos s s et. to ensur e e nt passes dire c a nce of the copp e m f erential voltage s een developed t c ontrolled to get i nteraction betw e h as occurred; th e f igure 43. f rom d1?s catho d n d 1nh. for pc b n creasing the thi c c tance in the tra n ce should be le figure m aximum covera g e s placed at reg n g the dissipate d le to the cathod e e st attenuation), this minimize s e ction between t h s ible to avoid rin e the best possi b c tly through the c e r trace. s ; as a result o f t o minimise radi a the right compr o e en the schottk y e falling edge of d e to the decou p b tracks a figure c kness will hav e ck and the effe c ss than 5nh. 44. recomme n g e of copper gro ular intervals. t d heat. e of d1. the se p place the capac i s common impe d h e capacitor an d ging. b le emi filtering c apacitor mounti n f this care has a ted emissions b o mise between p y diode (d1), s w the sw pin see s p ling capacitors of 0.5nh per m m e a minor effect o c tive capacitanc e n ded pcb layo und plane on b o t his is required p aration of these i tor and its copp e d ance coupling d d its ground con n (greatest atten u n g pad. this mi january 201 ? diodes incorporat e a l8808 to be taken wit h b y controlling th e p ower dissipatio n w itching mosfe t s a resonant loo p c1 should be a s m can be used t o o n the inductanc e e of the schottk y ut o th sides. ensur e both for low e m nodes should b e e r trace such th a d ue to the adde d n ection. use 2 o u ation), place th e nimizes commo n 3 e d h e n t p s o e y e m i e a t d o r e n
AL8808 document number: ds35648 rev. 2 - 2 17 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 application information (cont.) emi and layout considerations (cont.) emc design in addition to the layout instructions above, it may be necessary to take further measures to reduce electromagnetic interferen ce (emi) and meet emc requirements. this depends on the speed of the switching tr ansitions. the fast switchi ng edges include spectral harmonics spreading into the uhf frequency range towards 500mhz. in this respect, AL8808 has been optimized to shape the switching current waveform to minimize emi while maintaining fast enough switching for high power efficiency. however, depending on the physical system design it may be necessary to add additional filtering to reduce radiated and conducted emissions. the required circui t changes depend on a number of system des ign aspects including the pcb size, the housing design and the length of external connecting wires. radiated emission typically, the filtering required to control radiated emission c onsists of one or two additional capacitors placed close to the connecting points of the wires. very often the frequency range requiring most attenuation is in the region of 100mhz to 500mhz. in order to provide be st attenuation in this frequency range, use a capacitor of 1000pf to 2200pf with cog di electric type, rated 50v or 1 00v. this capacitor provides very low esr in this frequency range. place two such capacitors, one near the v in wire connection and one near the output connection to l1. again, to ensure the best possible emi filtering (greatest a ttenuation), place the capacitor and its copper trace such that the input or output current passes directly through the capacitor mounting pad. this minimizes common im pedance coupling due to the added para sitic inductance of the copp er trace. conducted emission conducted emission limits sometimes require filtering in the lo wer frequency range, from the switching frequency itself (typica lly 200khz) up to about 30mhz. usually the requirement only applies on the input si de. the existing power supply may already include suitable m easures. if necessary add an input capacitor to reduce the ripple in this frequency range. again the capac itors and their copper traces sh ould be carefully placed to avoid inductive common impedance coup ling. sometimes an additional series f ilter inductor may be added to achieve th e desired attenuation. an additional shunt capacitor to ground is connected resulting in a pi-filter configuration.
new product AL8808 document numbe r applicati o fault conditi o the AL8808 ha s v in and the sw if the leds sho u the expected c u dramatically an d leds. the on-time of t inductor. the of f 32) causing a m high temper a the AL8808 is a temperature in temperatures a n AL8808 off. thi s the otp shutd o never switch-off j unction temper a r : ds35648 rev. 2 o n informa t o n operation s by default ope n pin will then fall u ld become sho r u rrent - so no e d the switching f t he internal pow f -time is signific a uch slower dec a a ture operati o a high efficiency excess of 100 n d hence juncti o s will allow the ju o wn j unction te m with a junction t a ture of the al8 8 - 2 t ion (cont.) n led protectio n to gnd. no exc e r ted together the e xcessive heat w requency will m o er mosfet sw i a ntly increased b a y in inductor cu r figure 45. s w o n and protec switching led d c given the c o o n temperature t nction temperat u m perature of th e t emperature bel o 8 08. w n . if the leds s h e ssive voltages w AL8808 will co n w ill be generate d o st likely decrea i tch is significan t ecause the reve r rent. w itching chara c tion river capable of o rrect thermal i m t hen the ove r -t e u re of the al880 e AL8808 is app o w +125c allo w 18 of 20 w ww.diodes.co h ould become o p w ill be seen by t h n tinue to switch a d within the al 8 se. see figure 4 t ly reduced bec a rse voltage acro s c teristics (norm a operating juncti o m pedance to fr e e mperature pro t 8 to cool down a roximately +145 w ing the designe m p en circuit the a l h e AL8808. a nd the current t 8 808. however, 4 5 for an exam p a use almost all o s s the inductor i s a l open to shor t o n temperatures e e air. if a fault t ection (otp) o f a nd potentially gi v c with a hyste r r to design the s l 8808 will stop o hrough the al8 8 the duty cycle p le of this behav o f the input volt a s now just the s c t led chain) up to +125c . t should occur t f the AL8808 wi l v ing an opportu n r esis of +10c. s ystem thermally o scillating; the s e 8 08?s internal s w at which it ope r ior at 24v input a ge is now dev e c hottky diode vo l his allows it ope t hat leads to in c l l cut in turning t n ity for the fault t o this means tha t to fully utilize t h january 201 ? diodes incorporat e a l8808 e t pin will rise t o w itch will still be a r ates will chang e voltage driving 3 e loped across th e l tage (see figur e rate with ambie n c reased ambie n t he output of th e o clear itself. t the AL8808 wi h e wide operatin g 3 e d o a t e 3 e e n t n t e ll g
AL8808 document number: ds35648 rev. 2 - 2 19 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 ordering information part number package code packaging 7? tape and reel quantity part number suffix AL8808wt-7 wt tsot25 3000/tape & reel -7 marking information tsot25 1 2 3 5 7 4 xx y w x (top view) xx : identification code w : week : a~z : 1~26 week; x : a~z : internal code y : year 0~9 a~z : 27~52 week; z represents 52 and 53 week part number package identification code AL8808wt-7 tsot25 b9 package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. a l8808 x x x x - wt : tsot25 7 : 7? tape & reel packing package tsot25 dim min max typ a ? 1.00 ? a1 0.01 0.10 ? a2 0.84 0.90 ? d ? ? 2.90 e ? ? 2.80 e1 ? ? 1.60 b 0.30 0.45 ? c 0.12 0.20 ? e ? ? 0.95 e1 ? ? 1.90 l 0.30 0.50 l2 ? ? 0.25 0 8 4 1 4 12 ? all dimensions in mm c a1 l e1 e a2 d e1 e 5x b l2 a
AL8808 document number: ds35648 rev. 2 - 2 20 of 20 www.diodes.com january 2013 ? diodes incorporated new product a l8808 suggested pad layout please see ap02001 at http://www.diodes.com/ datasheets/ap02001.pdf for latest version. important notice diodes incorporated makes no warranty of any kind, express or implied, with regards to this document, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose (and their equivalents under the laws of any jurisdiction). diodes incorporated and its subsidiaries rese rve the right to make modifications, enhanc ements, improvements, corrections or ot her changes without further notice to this document and any product descri bed herein. diodes incorporated does not assume any liability ari sing out of the application or use of this document or an y product described herein; neither does di odes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er of this document or products described herein in such applica tions 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 w hatsoever in respect of any products purchased through unauthoriz ed sales channel. should customers purchase or use diodes inco rporated products for any unintended or una uthorized application, customers shall i ndemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death a ssociated with such unintended or unauthorized application. products described herein may be covered by one or more united states, international or foreign patents pending. product 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 t his document is the final and determinative format released by diodes incorporated. life support diodes incorporated products are specifically not authorized for use as critical component s in life support devices or systems without the express written approval of the chief executive offi cer of diodes incorporated. as used herein: a. life support devices or syst ems 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 proper ly 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 devic e or system whose failure to perform can be reasonably expect ed 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 ramifi cations of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-rel ated requirements concerning the ir products and any use of diodes incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or s ystems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporate d and its representatives against any damages arisi ng out of the use of diodes incorporated pr oducts in such safety-critical, life suppor t devices or systems. copyright ? 2013, diodes incorporated www.diodes.com dimensions value (in mm) c 0.950 x 0.700 y 1.000 y1 3.199 y1 c c x (5x) y (5x)

▲Up To Search▲

Price & Availability of AL8808

	To Download AL8808 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .