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al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 1 of 21 www.diodes.com june 2012 ? diodes incorporated description the al8807 is a step-down dc/dc converter designed to drive leds with a constant cu rrent. the device can drive up to 9 leds, depending on the forward voltage of the leds, in series from a voltage source of 6v to 36v. series connection of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors. the al8807 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 al8807 is set via an external resistor connected between the v in and set input pins. dimming is achieved by applying either a 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. features ? led driving current up to 1.3a (msop-8ep) ? better than 5% accuracy ? high efficiency up to 96% ? optimally controlled switching speeds ? operating input voltage from 6v to 36v ? pwm/dc input for dimming control ? built-in output open-circuit protection ? sot25: available in ?green? molding compound (no br, sb) with lead free finish/ rohs compliant (note 1) ? msop-8ep available in ?green? molding compound (no br, sb) with lead free finish / rohs compliant (note 1) pin assignments applications ? mr16 lamps ? general illumination lamps ? 12v powered led lamps ? 24v powered led lamps notes: 1. eu directive 2002/95/ec (rohs) & 2011/65/eu (rohs 2). all applicable rohs exemptions applied.please visit our webs ite at http://www.diodes.com /products/lead_free.html . typical application circuit sot25 (top view) sw gnd ctrl set v in (top view) msop-8e p set gnd gnd ctrl v in n/c sw sw ? 100 nf c1 1f c4 d1 dfls 2100 d2 dfls 2100 d3 dfls 2100 d5 dfls 2100 d4 dfls 2100 gnd sw gnd ctrl set v in u1 al8807 0r15 r1 l1 33h 100nf c5 150f c2 150f c3 p1 p2 a node cathode
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 2 of 21 www.diodes.com june 2012 ? diodes incorporated pin descriptions pin name pin numbe r descriptions sot25 msop-8ep sw 1 5, 6 switch pin. connect inductor/freewheeling diode here, minimizing track length at this pin to reduce emi. gnd 2 2, 3 gnd pin ctrl 3 4 dimming and on/off control input. ? leave floating for normal operation. (v ctrl = v ref = 2.5v giving nominal average output current i outnom = 0.1/r s ) ? drive to voltage below 0.4v to turn off output current ? drive with dc voltage (0.5v < v ctrl < 2.5v) to adjust output current from 20% to 100% of i outnom ? a pwm signal (low level 0.4v and high level > 2.6; transition times less than 1us) allows the output current to be adjusted below the level set by the resistor connected to set input pin. set 4 1 set nominal output current pin. c onfigure the output current of the device. v in 5 8 input supply pin. must be locally decoupled to gnd with > 2.2f x7r ceramic capacitor ? see applications section for more information. ep - ep exposed pad/tab connect to gnd and thermal mass for enhanced thermal impedance. should not be used as electrical ground conduction path. n/c - 7 no connection absolute maximum ratings symbol parameter ratings unit esd hbm human body model esd protection 2.5 kv esd mm machine model esd protection 200 v v in continuous v in pin voltage relative to gnd -0.3~40 v v sw sw voltage relative to gnd -0.3~40 v v ctrl ctrl pin input voltage -0.3 ~ 6 v i sw-rms dc or rms switch current sot25 1.25 a msop-8ep 1.6 i sw-pk peak switch current (<10%) 2.5 a t j junction temperature 150 c t lead lead temperature soldering 300 c t st storage temperature range -65 to +150 c caution: stresses greater than the 'absolute maximum ratings' specified above, may cause perm anent damage to the device. these are stress ratings only; functional operation of the device at thes e or any other conditions exceeding those i ndicated in this specification is not impl ied. device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. semiconductor devices are esd sensitive and may be damaged by exposu re to esd events. suitable esd precautions should be taken when handling and transporting these devices. recommended operating conditions symbol parameter min max unit v in operating input voltage relative to gnd 6.0 36 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 f sw maximum switching frequency 1 mhz i sw continuous switch current sot25 1 a msop-8ep 1.3 t j junction temperature range -40 125 c
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 3 of 21 www.diodes.com june 2012 ? diodes incorporated electrical characteristics v in =12v, t a =25 o c, unless otherwise specified. symbol parameter conditions min typ max unit v insu internal regulator start up threshold v in rising 5.9 v v insh internal regulator hysteresis threshold v in falling 100 300 mv i q quiescent current output not switching (note 2) 350 a i s input supply current ctrl pin floating f = 250khz 1.8 5 ma 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 22 a r ctrl ctrl pin input resistance referred to inte rnal reference 50 k? v ref internal reference voltage 2.5 v r ds(on) on resistance of sw mosfet i sw = 1a 0.25 0.4 ? t r sw rise time v sense = 10020mv f sw = 250khz v sw = 0.1v~12v~0.1v c l = 15pf 12 ns t f sw fall time 20 ns i sw_leakage switch leakage current v in =30v 0.5 a ja thermal resistance junction-to- ambient (note 3) sot25 (note 4) 250 c/w msop-8ep (note 5) 69 jl thermal resistance junction-to- lead (note 6) sot25 (note 4) 50 jc thermal resistance junction-to- case (note 7) msop-8ep (note 5) 4.3 notes: 2. al8807 does not have a low power standby mode but current consumption is reduced when outp ut switch is inhibited: v sense = 0v. parameter is tested with v ctrl 2.5v 3. refer to figure 35 for the device derating curve. 4. test condition for sot25: device mounted on fr-4 pcb (25m m x 25mm 1oz copper, minimum recommended pad layout on top layer a nd thermal vias to bottom layer ground plane. for better thermal performance, larger copper pad for heat-sink is needed. 5. test condition for msop-8ep: device mounted on fr-4 pcb (51mm x 51mm 2oz copper, minimum recommended pad layout on top laye r and thermal vias to bottom layer with maximum area ground plane. for better thermal performance, larger copper pad for heat-s ink is needed 6. dominant conduction path via gnd pin (pin 2). 7. dominant conduction path via exposed pad.
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 4 of 21 www.diodes.com june 2012 ? diodes incorporated typical performance characteristics (t a = 25c unless otherwise stated) 400 350 100 0 i (a) in 300 50 v = 0v v = v t = 25c ctrl set in a 250 150 200 0 3 6 9 15 18 21 24 27 30 33 v (v) figure 1. supply current (not switching) vs. input voltage in 12 36 900 800 200 0 f r e q u e n c y (k h z) 700 100 600 300 400 01234 v figure 2. switching frequency vs. v ctrl ctrl 5 500 v = 12v 1 led r = 150m t = 25c in set a l = 33h l = 68h l = 100h 100 90 70 60 40 30 20 0 led c u r r e n t (a) 0.0 0.5 1.0 1.5 2.0 3.0 3.5 4.0 4.5 5.0 5.5 ctrl pin voltage (v) figure 3. led current vs. v ctrl 2.5 0.0 0.5 1.0 1.5 2.5 3.0 3.5 4.0 4.5 5.0 v (v) figure 4. i vs. v ctrl ctrl ctrl 2.0 5.0 80 60 -40 -60 i (a) ctrl 40 -20 0 20 v = v = 12v t = 25c set in a 3 2.5 2 1.5 0.5 0 v (v) ctrl 1 v = open v = v ctrl set in t = 25c a 0 3 6 9 12 18 21 24 27 30 36 v (v) figure 5. v vs. input voltage (ctrl pin open circuit) in ctrl 15 33 -40 -15 10 35 60 85 110 ambient temperature (c) figure 6. v vs. temperature ctrl 2.52 2.51 2.50 2.49 2.48 v (v) ctrl v = open v = v= 12v ctrl set in
al8807 document numbe r typical p e l e er r l t c 1 0 9 8 7 6 4 3 2 0 led current error (%) 5 1 - 40 0 25 0 15 0 10 0 r (m ) ds(on) 35 0 30 0 20 0 r : ds35281 rev. 4 e rformanc e figure. 11 s w e d current r or l = 68h, r = 150m t = 25c, v = 12v c trl = pwm, f = 1 led s ai n pwm 20 40 pwm d figure 7. i led - 40 -15 1 amb figure 9. s 0 0 0 0 0 0 0 - 2 e charact e w output ris e led cur r = 500hz 60 8 d uty cycle vs. pwm duty c 35 6 0 1 0 ient temperatur e s w r vs. te ds(on) v v high e w w e ristics (co n e time r ent 8 0100 c ycle 0.8 l e d c u r r e n t ( a ) 0.7 0.6 0.5 0 0.4 0.3 0.2 0.1 0 11 0 85 e (c) te mperature v = open v = v = 12v ctrl set in fficienc y 5 of 21 w w.diodes.com n t.) (t a = 25 l e d c u r r e n t ( a ) r ( ) 0 y low e m c unless ot h figure 69 fig u 300 270 210 150 30 0 r ( m ) ds(on) 90 240 180 120 60 69 1 figu r 100 90 80 70 60 40 30 20 10 0 50 d u t y c y c le (%) 2 leds m i 36v 1a b h erwise stat e . 12 sw outp u 12 18 21 v ( u re 8. sw r in ds(o n 15 1 2151821 input vol t r e 10. duty cycl e 3 leds a l b uck led ? diode s e d) u t fall time 24 27 30 ( v) vs. input volta g n ) 3 v = v = v ctrl set t = 25 c a 24 27 30 3 t age (v) e vs. input volta g l = 68h r = 100 m t = 25 c v = o s a ctrl l 8807 driver june 2012 s incorporated 36 g e 3 3 open v in c 3 336 g e m c o pen
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 6 of 21 www.diodes.com june 2012 ? diodes incorporated typical performance characteristics (670ma led current) (t a = 25c) 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 13. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 14. switching frequency vs. input voltage 350 300 200 50 0 swi t c h in g f r e q u en c y (k h z) 250 100 150 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 15. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 16. switching frequency vs. input voltage 500 450 300 250 50 0 swi t c h in g f r e q u en c y (k h z) 350 150 100 200 400 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 17. led current deviation vs. input voltage 10 8 4 2 0 -4 -8 -10 led c u r r e n t e r r o r (%) 1 led 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds l = 33h r = 150m t = 25c v = open s a ctrl 6 -2 -6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 18. switching frequency vs. input voltage 800 700 500 400 100 0 swi t c h in g f r e q u en c y (k h z) 1 led 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds l = 33h r = 150m t = 25c v = open s a ctrl 600 300 200
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 7 of 21 www.diodes.com june 2012 ? diodes incorporated typical performance characteristics (1a led current msop-8ep) (t a = 25c) 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 19. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 5 leds 6 leds 7 leds 8 leds l = 100h r = 100m t = 25c v = open s a ctrl 2 leds 3 leds 4 leds 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 20. switching frequency vs. input voltage 350 300 200 0 swi t c h in g f r e q u en c y (k h z) 250 50 150 1 led 100 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 21. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 22. switching frequency vs. input voltage 350 300 200 0 swi t c h i n g f r e q u e n c y (k h z) 250 50 150 100 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 23. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 24. switching frequency vs. input voltage 600 500 300 0 swi t c h in g f r e q u en c y (k h z) 400 100 200
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 8 of 21 www.diodes.com june 2012 ? diodes incorporated typical performance characteristics (1.3a led current msop-8ep) (t a = 25c) 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 25. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 5 leds 6 leds 7 leds 8 leds l = 100h r = 77m t = 25c v = open s a ctrl 2 leds 3 leds 4 leds 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 26. switching frequency vs. input voltage 250 200 100 0 swi t c h in g f r e q u en c y (k h z) 150 1 led 50 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 27. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 5 leds 6 leds 7 leds 8 leds l = 68h r = 77m t = 25c v = open s a ctrl 2 leds 3 leds 4 leds 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 28. switching frequency vs. input voltage 300 250 150 0 swi t c h in g f r e q u en c y (k h z) 200 100 1 led 50 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 29. led current deviation vs. input voltage 10 8 2 0 -8 -10 led c u r r en t e r r o r (%) 4 -4 -6 -2 6 5 leds 6 leds 7 leds 8 leds l = 33h r = 77m t = 25c v = open s a ctrl 2 leds 3 leds 4 leds 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 30. switching frequency vs. input voltage 600 500 300 0 swi t c h i n g f r e q u e n c y (k h z) 400 200 1 led 100
al8807 document numbe r applicati o the al8807 i packages tha currents/small e temperature r a al8807 op e in normal ope sense resisto r voltage +vin a this rising cu r applies a prop when this vol t flow through r determined b y this decaying voltage acros s the internal s w sense resistor led curren t the led curr e connected be t i led for example f o = v 1r dc dimmin g further contro the average l e led i = with 0.5v v c 2.5v, the led when the ct r r : ds35281 rev. 4 o n informa t i s a hystereti c t provide a p e r pcbs that a nge. e ration ration, when v r r 1 , inductor l a nd the inducto r rent produces ortional voltag e t age reaches a r 1 , l1, the le d y the forward v o current produ s r 1 is applied w itch is turned r 1 . t control e nt is controlle d t ween v in and 1r v thd = o r a desired l e = 66 .0 1.0 i v led thd g l of the led c u e d current be c set thd ref ctrl r v v v = c trl 2.5v th e current will be r l voltage fall s - 2 t ion c (also known p cb area-po w the msop-8 e v oltage is appli l 1, and the l e r l1. a voltage ra m e to the input o a n internally se t d s and the sc o ltage drop of t ces a falling v at the input of on again. thi s d by the resist o set the nomi n e d current of 6 6 m 150 u rrent can be a c omes: e led current clamped to a p s below the thr e high e w w as equal rip p w er dissipatio n e p version is u ed at +v in , th e e ds. the curr e m p across r 1 . t o f the internal c t upper thresh o hottky diode d t he leds and t v oltage at r 1 , w the internal co s switch-on-an o r r1 in figure fig. 30 typi c n al average o u 6 0ma and a d e chieved by dri v varies linearl y p proximately 1 0 e shold, 0.4v, t h fficienc y 9 of 21 w w.diodes.com p le) led drive n capability c o u sed to maxi m e al8807 inte r e nt ramps up l t he internal ci c omparator. o ld, the intern a d 1, and back t o t he schottky di o w hich is sens e mparator. wh e d-off cycle co n 30. c al applicati u tput current in e fault voltage v v ing the ctrl y with v ctrl , a 0 0% and follo w h e output swit c y low e m r with integra t o mpromise. it m ize the allow a r nal switch is t l inearly, and t h rcuit of the a l a l switch is tur n o the supply r a o de. e d by the al8 8 e n this voltage n tinues to pro v on circuit the led(s) is d v ctrl =2.5v th e pin with an ex t a s in figure 2. w s set thd led r v i = c h is turned off m i 36v 1a b t ed power swi t is recomme n a ble led curr e t urned on. cu r h e ramp rate i s l 8807 senses t n ed off. the in d a il, but it dec a 8 07. a voltage falls to the int e v ide the avera g d efined as: e resulting resi s t ernal voltage ( if the ctrl p . which allows p a l b uck led ? diode s t ch. it is avai l n ded that at h e nt over a wi d r rent starts to f s determined b t he voltage ac r d uctor current c a ys, with the r a proportional t o e rnally set low e g e led curre n s tor is: ( between 0.4v in is brought h p wm dimming. l 8807 driver june 2012 s incorporated l able in two h igher led d er ambient f low through b y the input r oss r 1 and c ontinues to a te of decay o the sense e r threshold, n t set by the and 2.5v); h igher than
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 10 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) 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 pr oduce an average output curren t proportional to the duty cycle of the control signa l. in particular, a pwm signal with a max resolution of 10bit can be applied to the ctrl pin to change the output current to a value below the nominal 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 1% for pwm ranging from 1% to 100%. zooming in at duty cycles below 10% shows: the accuracy of the low duty cycle dimming is affected by bo th the pwm frequency and also the switching frequency of the al8807. for best accuracy/resolution the switching frequency should be increased while the pwm frequency should be reduced. the ctrl pin is designed to be driven by both 3.3v and 5v logic levels directly from a logic output with either an open drain output or push pull output stage. 0 102030405060708090100 pwm dimming (%) fig. 31 pwm dimming @ 500hz l e d c u r r e n t (m a ) 700 600 500 400 300 200 100 0 01 03 05 07 09 01 0 0 300hz pwm duty cycle (%) fig. 32 low duty cycle pwm dimming @ 300hz d e vi a ti o n f r o m i d e a l l o a d c u r r e n t ( % ) 4.5 4.0 3.0 2.5 2.0 1.0 0.5 0 3.5 1.5 v = 12v l = 68h r = 0.15 t = 25c 2 leds in dc s a
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 11 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) soft start the al8807 does not have in-built soft-start action ? this prov ides very fast turn off of the output the stage improving pwm dimming accuracy; nonetheless, adding an external capacitor from the ctrl pin to ground will provide a soft-start delay. this is achieved by increasing the time taken for the ctrl voltage to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. addi ng a capacitor increases the time taken for the output to reach 90% of its final value, this delay is 0.1ms/nf, but will impact on the pwm dimming accuracy depending on the delay introduced. fig. 33 soft start with 22nf capacitor on ctrl pin (v in = 30v, i led = 667ma, 1 led) reducing output ripple peak to peak ripple current in the led(s) can be reduced, if required, by shunting a capacitor c2 across the led(s) as shown already in the circuit schematic. a value of 1 f will reduce the supply ripple current by a factor thr ee (approx.). proportionally lower ripple can be achieved with higher capacitor values. note that the capacitor will not affe ct operating frequency or efficienc y, but it will increase start- up delay, by reducing the rate of rise of led voltage. by adding this capacitor the current waveform through the led(s) changes from a triangular ramp to a more sinusoidal ve rsion without altering the mean current value. capacitor selection the small size of ceramic capacitors makes them ideal for al8807 applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as z5u. a 2.2 f input capacitor is sufficient for most inte nded applications of al8807; however a 4.7 f input capacitor is suggested for input voltages approaching 36v.
al8807 document numbe r applicati o diode selec for maximum leakage at th e pn diodes, du it is important the maximum operating volt a diode current. schottky diod e al8807 appli c inductor se l recommende d higher values which result i n current over t h the inductor s pin. the chosen c o the required m suitable coils f the inductor v load current r a r : ds35281 rev. 4 o ns inform a tion efficiency and e maximum op e e to a combin a to select parts output load cu a ge to ensure the power ra t e s, e.g. b240 c ations. l ection d inductor valu of inductance n increased ri p h e supply volta g hould be mou n o il should have m ean output cu r f or use with th e pa r mss103 8 mss103 8 npis64 d v alue should b e a nge. - 2 a tion (cont. performance, e rating voltag e a tion of lower f o with a peak c u rrent. in parti c safe operatio n t ing is verified b or b140, with es for the al8 8 are recomme n p ple and lowe r g e range. (se e fig. 34 indu n ted as close t o a saturation c u r rent. e al8807 are l i r t no. 8 -333 8 -683 d 330mtrf e chosen to m a high e w w ) the rectifier ( d e and tempera t o rward voltage u rrent rating a b c ular, it is reco m n during the s w b y calculating t their low forw a 8 07 are in the n ded at higher r efficiency. hi g e graphs). ctor value wi t o the device a s u rrent higher t h i sted in the tab l (h) d ( 33 0. 68 0. 33 0. a intain operatin fficienc y 12 of 21 w w.diodes.com d 1) should be a t ure. the sc h and reduced r b ove the peak c m mended to h a w itching and a t he power loss a rd voltage dr o range 33 h to supply voltag e g her values o f t h input v olta g s possible with h an the peak o le below: d cr ( v) i s a (a ) 093 2. 3 213 1. 5 124 1. 1 g duty cycle a n y low e m a fast low cap a h ottky diode al s r ecovery time. c oil current an d a ve a diode v o a current ratin g through the di o p and fast re v 100 h. e s in order to m f inductance a l g e and numb e low resistanc e o utput current a a t ) m 3 coilcra f 5 1 nic w w n d switch 'on'/' o m i 36v 1a b a citance schot t s o provides b e d a continuou s o ltage rating at g at least 10 % ode. v erse recover y m inimize error s l so result in a e r of leds e / stray inducta n a nd a continuo u m anufacture r f t www.coilcra f w w.niccomp.co m o ff' times over t a l b uck led ? diode s t ky diode with e tter efficiency s current rating least 15% hig h % higher than t y , are the ide a s due to switc h smaller chan g n ce connection u s current rati n f t.com m t he supply volt l 8807 driver june 2012 s incorporated low reverse than silicon higher than h er than the t he average a l choice for h ing delays, g e in output s to the sw n g above age and
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 13 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) the following equations can be used as a guide, wi th reference to figure 1 - operating waveforms. switch ?on? time switch ?off? time () rrr x ivv il t swlsavg led in on ++ ?? = () rr x ivv il t lsavgdled off + ++ = where: l is the coil inductance (h) r l is the coil resistance ( ? )r s is the current sense resistance ( ? ) i avg is the required led current (a) i is the coil peak-peak ripple current (a) {internally set to 0.3 x iavg} v in is the supply voltage (v) v led is the total led forward voltage (v) r sw is the switch resistance ( ? ) {=0.5 ? nominal} v d is the diode forward voltage at the required load current (v) thermal considerations for continuous conduction mode of operati on, the absolute maximum junction temperature must not be exceeded. the maximum power dissipation depends on several fact ors: the thermal resistance of the ic package ja , pcb layout, airflow surrounding the ic, and difference between junction and ambient temperature. the maximum power dissipation can be calculated using the following formula: p d(max) = (t j(max) ? t a ) / ja where t j(max) is the maximum operating junction temperature, t a is the ambient temperature, and ja is the junction to ambient thermal resistance. the recommended maximum operating junction temperature, t j , is 125c and so maximum ambient temperature is determined by the al8807?s junction to ambient thermal resistance, ja and device power dissipation. ja , is layout dependent and package dependent; the al8807w5?s ja on a 25x25mm single layer pcb with 1oz copper standing in still air is approximately 25 0c/w (160c/w on a four-layer pcb). the maximum power dissipation at t a = 25c can be calculated by the following formulas: p d(max) = (125c ? 25c) / (250c/w) = 0.4w for single-layer pcb p d(max) = (125c ? 25c) / (160c/w) = 0.625w for standard four-layer pcb figure 35, shows the power derating of the al8807w5 on two ( one single-layer and four-layer) different 25x25mm pcb with 1oz copper standing in still air and the al8807mp on an fr4 51x51mm pcb with 2oz copper standing in still air. -40 -25 -10 5 20 35 50 65 80 90 110 125 ambient temperature (c) fig. 35 derating curve for different pcb 1600 p o we r d issi p a t i o n (mw) 1400 1200 1000 800 600 400 200 0 sot25_1 layer msop-8ep sot25_4 layer
al8807 document numbe r applicati o emi and la y the al8807 i s taken with de c emissions by c right compro m dominates th e tracks. after t resonant loop the tracks fro m c1 should be for pcb trac k handling 1a i n inductance. t capacitance o f than 5nh. r : ds35281 rev. 4 o ns inform a y out consid e s a switching r e c oupling and l a c ontrolling the m ise between p e radiated emi t he schottky d between the s m the sw pin t as short as p o k s a figure of 0 n creasing the he resonant fr e f the schottky d - 2 a tion (cont. e rations e gulator with f a a yout of the p c switching spe e p ower dissipa t which is due d iode reverse r s chottky diode c t o the anode o o ssible. there 0 .5nh per mm thickness will e quency of an y d iode. an exa m place d1 a inductor a s minimize r f high e w w ) a st edges and m c b.to help wit h e ds of the inte r t ion due to s w to an interacti r ecovery time c apacitance a n fig. 36 p c o f the schottk y is an inducta n can be used t o have a mino r y oscillation is d m ple of good l a a node , sw pin and s close as possible t r inging f ig. 37 reco fficienc y 14 of 21 w w.diodes.com m easures sm a h these effects r nal power mo w itching losse s on between t h of around 5ns n d the track in d c b loop re s y diode, d1, an n ce internally i n o estimate the r effect on the d etermined by a yout is show n vin sw g n t o mmended p y low e m a ll differential v o the al8807 h sfet. the ri s s and radiated h e schottky di o has occurred d uctance, l tra s onance d then from d 1 n the al8807 primary reso n inductance a the combined n in figure 37 - t set ctrl n d cb layout m i 36v 1a b o ltages; as a r e as been devel s e and fall tim e emi. the t u o de (d1), swi t ; the falling e d ck , see figure 1 ?s cathode to this can be as n ant frequency nd length will inductance in t he stray track a l b uck led ? diode s e sult of this ca r oped to minim e s are controll e u rn-on edge (f a t ching mosf e d ge of the s w 36. the decouplin g sumed to be a . if the track i s dominate the the track and t inductance sh o l 8807 driver june 2012 s incorporated r e has to be ise radiated e d to get the a lling edge) e t and pcb w pin sees a g capacitors a round 1nh. s capable of size of the t he effective o uld be less
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 15 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) recommendations for minimising radiated emi and ot her transients and therma l considerations are: 1. the decoupling capacitor (c1) has to be placed as close as possible to the v in pin and d1 cathode 2. the freewheeling diode?s (d1) anode, the sw pin and the inductor have to be placed as close as possible to each other to avoid ringing. 3. the ground return path from c1 must be a low impeda nce path with the ground plane as large as possible 4. the led current sense resistor (r1) has to be placed as close as possible to the v in and set pins. 5. the majority of the conducted heat from the al8807 is through the gnd pin 2. a maximum earth plane with thermal vias into a second earth plane will minimise self-heating 6. to reduce emissions via long leads on the supply input and leds low rf impedance capacitors (c2 and c5) should be used at the point the wires are joined to the pcb a typical application for the al8807 is an led mr16 lamp (schematic shown in figure 38). fig. 38 mr16 circuit schematic an evaluation board for the al8807 (named the al8807ev2) for mr16 is available on request from your local diodes? sales representative. this board follows diodes ? recommendations for low emi. images of the top layer and bottom layers are shown in figure 39. fig. 39 recommended mr16 pcb layout
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 16 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) the associated emi measurements for this board using the al8807 is shown in figure 40. fig 40. al8807ev2 radiated emi performance the emi performance was measured at 12v dc driving two white leds (v f = 3.1v at 660ma) on the al8807ev2. the red bold line is for en55022 class b used for domestic equipment includin g lighting. the bottom magenta li ne is the noise floor of the test chamber. the middle purple line is the emi emitted radiation of t he al8807 over 30mhz to 1000mhz. this shows that the al8807 passes the standard with at least 16db margin. mr16 lamps typically operate from 12v dc or 12v ac , using conventional electromagnetic transformers or electronic transformers. in enclosed lamps such mr16 the ability for the device to operate at high ambient temperatures is critical and figure 41 shows the surface temperature of the al8807 on al8807ev2 in operation under the sa me conditions as the emi tests at an free air temperature of 25oc. it is antic ipated that the internal junc tion temperature is approximatel y 6 oc hotter than the surface temperature. fig 41. thermal picture of al8807ev2 at 12v dc 2 white leds at 660ma the thermal image shows that components increasing the boar d temperature are the inductor, schottky diodes and the al8807.
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 17 of 21 www.diodes.com june 2012 ? diodes incorporated applications information (cont.) an inductor choice of 33h with saturation current higher than 1.1a, will limit the frequenc y variation between 180khz and 400khz over the whole input voltage variation (8v to 18v), and therefore represent the best choice for an mr16 solution also taking into account the size constraint of the lamp. the al8807 guarantees high performance levels with both 12v ac and 12v dc power supplies. the efficiency is generally higher than 81% and current regulat ion is better than 0.1ma/v in for a dc input voltage in the rang e from 8v to 18v.
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 18 of 21 www.diodes.com june 2012 ? diodes incorporated ordering information device status package code packaging (note 8) 7? tape and reel quantity part number suffix AL8807W5-7 new product w5 sot25 3000/tape & reel -7 al8807mp-13 new product mp msop-8ep 2500/tape & reel -13 notes: 8. pad layout as shown on diodes inc. suggested pad layout document ap02001, which can be found on our website at: http://www.diodes.com/datasheets/ap02001.pdf . marking information (1) sot25 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 AL8807W5-7 sot25 b6 (2) msop-8ep part number package al8807mp-13 msop-8ep package packing w5 : sot25 mp : msop-8ep 7 : 7? tape & reel 13 : 13? tape & reel al8807 xx - xx al8807 y w x e 1234 8765 logo part number a~z : lead free a~z: green msop-8ep y : year : 0 - 9 w : week : a~z : 1 ~ 26 week; a~z : 27~52 week z represents 52 and 53 week
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 19 of 21 www.diodes.com june 2012 ? diodes incorporated package outline dimensions (all dimensions in mm) (1) package type: sot25 (2) msop-8ep sot25 dim min max typ a 0.35 0.50 0.38 b 1.50 1.70 1.60 c 2.70 3.00 2.80 d ? ? 0.95 h 2.90 3.10 3.00 j 0.013 0.10 0.05 k 1.00 1.30 1.10 l 0.35 0.55 0.40 m 0.10 0.20 0.15 n 0.70 0.80 0.75 0 8 ? all dimensions in mm msop-8ep dim min max typ a - 1.10 - a1 0.05 0.15 0.10 a2 0.75 0.95 0.86 a3 0.29 0.49 0.39 b 0.22 0.38 0.30 c 0.08 0.23 0.15 d 2.90 3.10 3.00 d1 1.60 2.00 1.80 e 4.70 5.10 4.90 e1 2.90 3.10 3.00 e2 1.30 1.70 1.50 e3 2.85 3.05 2.95 e - - 0.65 l 0.40 0.80 0.60 a 0 8 4 x - - 0.750 y - - 0.750 all dimensions in mm a m j l d b c h k n 1 d a a1 a2 e e y x seating plane gauge plane l d 8xb see detail c detail c c a e1 e3 a3 e2 4 x 1 0 4 x 1 0 0.25 d1
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 20 of 21 www.diodes.com june 2012 ? diodes incorporated suggested pad layout 1) package type: sot25 2) msop-8ep dimensions value (in mm) z 3.20 g 1.60 x 0.55 y 0.80 c1 2.40 c2 0.95 dimensions value (in mm) c 0.650 g 0.450 x 0.450 x1 2.000 y 1.350 y1 1.700 y2 5.300 x z y c1 c2 c2 g g x c y y2 y1 x1
al8807 high efficiency low emi 36v 1a buck led driver al8807 document number: ds35281 rev. 4 - 2 21 of 21 www.diodes.com june 2012 ? diodes incorporated 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 described herein. diodes incorporated does not assume any liability ari sing out of the application or use of this document or any product described herein; neither does diodes 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 in corporated and all the companies w hose products are represented on diodes incorporated website, harmless against all damages. diodes incorporated does not warrant or accept any liability what soever in respect of any pr oducts purchased through unauthoriz ed sales channel. should customers purchase or use diodes in corporated products for any unintended or unauthorized application, customers shall i ndemnify and hold diodes incorporated and its representatives harmless agai nst all claims, damages, expenses, and attorney fees arising 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. product names and markings noted herein may also be covered by one or mo re united states, international or foreign trademarks. life support diodes incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the chief executive officer 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 prop erly 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 ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsible fo r all legal, regulatory and safety -related requirements concerning their products and any use of diodes incorporated products in such safety-cri tical, life support devices or systems, notwithstanding any devic es- or systems- related information or support that may be provided by diodes inco rporated. further, customers must fully indemnify diodes inc orporated and its representatives against any damages aris ing out of the use of diodes incorporated products in such safety-critical, life su pport devices or systems. copyright ? 2012, diodes incorporated www.diodes.com

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