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AL8807A document number: ds35990 rev. 1 - 2 1 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a high efficiency low emi wide analog dimming range 36v 1a/1.3a buck led driver description the AL8807A is a step-down dc/dc converter designed to drive leds with a constant current. the device can drive up to 9 white high brightness leds in series from a voltage source of 6v to 36v. the AL8807A has an extended ctrl pin voltage range; increasing its analog dimming range to greater than 10:1. the improved analog dimming range makes it suitable for a variety of lighting applications requiring wide analog dimming ranges. the AL8807A 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 AL8807A is set via an external resistor connected between the v in and set input pins. over temperature protection is in corporated so that should a fault occur the device will automatically shut-down and only restart when its junction temperature has cooled down, features ? led driving current up to 1a/1.3a ? better than 5% accuracy ? high efficiency up to 96% ? optimally controlled switching speeds ? operating input voltage from 6v to 36v ? wide analog input range for dimming control (>10:1) ? built-in protection features: ? open-circuit led protection ? led chain short circuited ? over-temperature protection ? msop-8ep and sot25: available in ?green? molding compound (no br, sb) with lead free finish/ rohs compliant ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) pin assignments (top view) sw ctrl v in set 1 gnd 2 3 5 4 sot25 (top view) set gnd gnd ctrl v in n/c sw sw 1 2 3 4 8 7 6 5 msop-8ep applications ? general illumination lamps ? 12v powered led lamps ? wide analog dimming range led lamps 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 AL8807A v in set sw ctrl gnd c2 r1 c1 d1 l1 analog dimming input: v in : 6 ~ 36v www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 2 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a pin descriptions pin name pin number function 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 led current analog dimming control input. ? no pwm dimming function. connected to internal 2.5v v ref via 50k ? resistor. so if left open circuit v ctrl = v ref = 2.5v and 100% led current is achieved - giving nominal average output current i outnom = 0.1/r s for analog dimming drive with analog voltage < 2.5v (0.25v < v ctrl < 2.5v adjusts output current from 10% to 100% of i outnom . device will dim the led current lower than this level but at reduced accuracy. some devices will not totally turn off the led current. soft-start can be implemented by c onnecting a capacitor to ctrl pin. the amount of soft-start is dependent on ramp-up of input supply voltage and capacitor on ctrl pin. see apps section. set 4 1 set nominal output current pin. configure 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. it should be connected to gnd and thermal mass for enhanced thermal impedance. it should not be used as electr ical ground conduction path. n/c ? 7 no connection ? may be connected to gnd. functional block diagram 5v voltage regulator AL8807A sw set v in ctrl gnd uvlo analog dimming control v ref 2.5v v ctrlh 2.55v 50k ? + ? + otp www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 3 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a absolute maximum ratings (@t a = +25c, unless otherwise specified.) 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 to +40 v v sw sw voltage relative to gnd -0.3 to +40 v v ctrl ctrl pin input voltage -0.3 to +6 v i sw-rms dc or rms switch current sot25 1.25 a msop-8ep 1.5 i sw-pk peak switch current (< 10% duty cycle) 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' sp ecified above, may cause permanent damage to the device. these are stress ratings only; functional operation of the device at these 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 expos ure to esd events. suitable esd precautions should be taken when handling and transporting these devices. recommended operating conditions (@t a = +25c, unless otherwise specified.) symbol parameter min max unit v in operating input voltage 6.0 36 v v ctrl ctrl pin input voltage range for 10% to 100% analog dimming (note 4) 0.25 2.50 v f sw maximum switching frequency at 100% dimming 0.7 mhz i sw continuous switch current (note 5) sot25 1 a msop-8ep 1.3 t j junction temperature range -40 +125 c notes: 4. AL8807A analog dimming range extends below 10% but at redu ced led current accuracies and may not turn completely off. switching frequencies will also be increased. 5. maximum switch current is dependent on power dissipation and junction temperature. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 4 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a electrical characteristics (@t a = +25c, 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 ctrl pin floating output not switching (note 6) 350 a i s input supply current f = 250khz 1.8 5 ma v th set current threshold voltage ctrl pin floating 95 100 105 mv v th-h set threshold hysteresis 20 % v th-10% 10% set current threshold voltage v ctrl = 0.25v 4 10 15 mv i set set pin input current v set = v in -0.1 16 22 a r ctrl ctrl pin input resistance referred to internal reference 50 k ? v ref internal reference voltage 2.5 v r ds(on) on resistance of sw mosfet i sw = 0.3a sot25 0.25 0.40 ? msop-8ep 0.18 0.35 t r sw rise time v sense = 100 20mv, 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 = 36v 0.5 a t otp over-temperature shutdown 150 c t otp-hyst over-temperature hysteresis 25 c ja thermal resistance junction-to-ambient (note 7) sot25 (note 8) 250 c/w msop-8ep (note 9) 69 jl thermal resistance junction-to-lead (note 10) sot25 (note 8) 50 jc thermal resistance junction-to-case (note 11) msop-8ep (note 9) 4.3 notes: 6. AL8807A does not have a low power standby mode but curre nt consumption is reduced when output is not being switched . 7. refer to figure 40 for the device derating curve. 8. test condition for sot25: device mounted on fr-4 pc b (25mm x 25mm 1oz copper, minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. for better t hermal performance, larger copper pad for heat-sink is needed. 9. test condition for msop-8ep: device mounted on fr-4 pcb (51mm x 51mm 2oz copper, minimum recommended pad layout on top la yer and thermal vias to bottom layer with maximum area ground plane. for better thermal performance, larger copper pad for heat -sink is needed. 10. dominant conduction path via gnd pin (pin 2). 11. dominant conduction path via exposed pad. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 5 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a typical performance characteristics (@t a = +25c, unless otherwise specified.) 0 6 12 18 24 30 v (v) figure 1 supply current (not switching) vs. input voltage in v = 0v v t = +25c ctrl a set in = v 36 3 9 15 21 27 33 400 0 50 100 250 300 350 i(a) in 150 200 -60 -40 -20 0 20 40 60 80 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 v (v) ctrl ctrl figure 2 i vs. v ctrl i ctrl (a) v = v= 12v set in t = +25c a v = open v = vin t = +25c ctrl set a 0 3 12 21 33 36 v (v) figure 3 vs. input voltage (ctrl pin open circuit) in v ctrl 6 9 15 18 24 27 30 3.0 0.0 0.5 1.0 1.5 2.0 2.5 v (v) ctrl -40 -15 10 35 60 85 110 ambient temperature (c) figure 4 v vs. temperature ctrl 2.48 2.49 2.50 2.51 2.52 v(v) ctrl v = open v = v = 12v ctrl set in 300 6 1218243036 input voltage figure 5 sw r vs. input voltage ds(on) 240 180 120 60 0 r (m ) ds(on) 100 150 200 250 300 350 400 -40 10 35 60 85 110 -15 ambient temperature (c) figure 6 sw r vs. temperature ds(on) r (m ) ds(on) www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 6 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a typical performance characteristics (cont.) (@t a = +25c, unless otherwise specified.) 10ns/div 2v/div t a =25oc figure 7 sw output rise time 10ns/div 2v/div t a =25oc figure 8 sw output fall time -0.10 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 -2% 0% 2% 4% 6% 8% 10% 12% 14% 16% 18% 20% 22% 012345 ctrl voltage (v) figure 9 led current (different sense resistor) vs. v ctrl led c u r r e n t e r r o r (%) led current (a) v = 12v 2 leds l = 68h t = 25c in a r = 100m s r = 150m s led current r = 150m s r = 100m s led current error 0.0 0.2 0.4 0.6 0.8 1.0 1.2 012345 ctrl voltage (v) figure 10 led current (different inductor) vs. v ctrl led c u r r en t (a) l = 33h l = 68 ~ 220h v = 12v 2 leds r = 100m t = 25c in s a 0.00 0 0.1 0.2 0.3 0.4 0.5 ctrl pin voltage (v) figure 11 led current (zoomed in) vs. v ctrl v = 12v 2 leds r = 100m t = 25c in s a l = 33h l = 68 ~ 220h led c u r r e n t (a) 0.05 0.10 0.15 0.20 0.2 5 1200 0 200 400 600 800 1000 swi t c h i n g f r e q u e n c y (k h z) 0123 45 ctrl voltage (v) figure 12 switching frequency vs. v ctrl v = 12v in 2 leds r = 100m t = +25c s a l = 33h l = 220h l = 100h l = 68h www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 7 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a typical performance characteristics (cont.) (@t a = +25c, unless otherwise specified.) 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 13 duty cycle vs. input voltage r = 150m l = 33h t = 25c 2 leds ctrl open s a d u t y c y c le (%) 6 9 12 15 18 21 24 27 30 30 36 input voltage (v) figure 14 efficiency vs. input voltage 100 70 75 80 85 90 95 e f f i c ie n c y (%) l= 68h r = 300m ctrl floating t = +25c s a 1led 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds 0 100 200 300 400 500 600 700 800 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 15 switching frequency vs. input voltage 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds r = 300m l = 68h t = 25c ctrl open s a 1 led swi t c h in g f r e q u en c y ( k h z) 0.3 0.31 0.32 0.33 0.34 0.35 0.36 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 16 330ma led current vs. input voltage led current (a) 0.60 0.62 0.64 0.66 0.68 0.70 0.72 0.74 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 17 670ma led current vs. input voltage 1 led 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds r = 150m l = 68h t = 25c ctrl open s a led c u r r e n t (a) 0.90 0.95 1.00 1.05 1.10 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 18 1a led current vs. input voltage 1 led 2 leds 3 leds 4 leds 5 leds 6 leds 7 leds 8 leds r = 100m l = 68h t = 25c v = open s a ctrl led c u r r e n t (a) www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 8 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a typical performance characteristics (670ma led current) (@t a = +25c, unless otherwise specified.) 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 e n t e r r o r (%) 4 -4 -6 -2 6 5 leds 6 leds 7 leds 8 leds l = 100h r = 150m 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 50 0 swi t c h in g f r e q u en c y (k h z) 250 100 150 1 led 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 5 leds 6 leds 7 leds 8 leds l = 68h r = 150m 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 22 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 1 led 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 23 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 (%) 6 -2 -6 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 24 switching frequency vs. input voltage 800 700 500 400 100 0 swi t c h i n g f r e q u e n 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 www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 9 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a typical performance characteristics (1a led current) (@t a = +25c, unless otherwise specified.) 5 leds 6 leds 7 leds 8 leds l = 100h r = 100m t = 25c v = open s a ctrl 1 led 2 leds 3 leds 4 leds 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 e n 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 26 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 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 = 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 28 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 1 led 100 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 e n 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 30. 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 www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 10 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information AL8807A operation the AL8807A is a hysteretic led current switching regulator so metimes known as an equal ripple switching regulator. in normal o peration, when voltage is applied at +v in (see figure 31), the AL8807A internal switch is turned on. current starts to flow through sense resistor r 1 , inductor l1, and the leds. the current ramps up linearly, and the ramp rate is determined by the input voltage +v in , and the inductor l1 (see figure 32). this rising current produces a voltage ramp across r 1 . the internal circuit of the a l8807a senses the voltage across r 1 and applies a proportional voltage to the input of the internal comparator. when this voltage reaches an internally se t upper threshold, the internal switch is turned off. the inductor current continues to flow through r 1 , l1, the leds and the schottky diode d1, and back to the supply rail, but it decays, with the rate of decay determined by the fo rward voltage drop of the leds and the schottky diode. this decaying current produces a falling voltage at r 1 , which is sensed by the AL8807A. a voltage proportional to the sense voltage across r 1 is applied at the input of the internal comparator. when this voltage falls to the internally set lower threshold, the internal sw itch is turned on again. this switch-on-and-off cycle continues to provide the average led current set by the sense resistor r 1, with a switching current determined by the input voltage and led chain voltage. in normal operation the off time is relatively constant (determi ned mainly by the led chain voltage) with only the on-time vary ing as the input voltage changes. at duty cycles up to around 80% the ramp of the le d/switch current is very linear; however, as the duty cycle approaches 95% the led current ramp starts to become more exponential. this has two effects: 1. the overall on time starts to increase lowering the overall switching frequency. 2. the average led current starts to increase ? which may impact accuracy. AL8807A v in set sw ctrl gnd c2 r1 c1 d1 l1 analog dimming input: v in : 6 ~ 36v figure 31 typical application circuit v in = 12v t a = 25c 2 leds 20ns/div no c2 ch2: 2v/div ch4: 100ma/div ch4: led current ch2: sw pin figure 32 typical operating waveform (c2 not fitted) led current control with the ctrl pin open circuit, the led current is determi ned by the resistor, r1, (see figure 31), connected between v in and set. the nominal average output current in the led(s) is defined as: 1r v i th led = where v th is nominally 100mv for example for a desired led current of 660ma the resulting resistor is: ?== m150 66.0 1.0 i v 1r led th www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 11 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) analog dimming further control of the led current can be achieved by driving the ctrl pin with an external voltage lower than 2.5v; the averag e led current becomes: set th ref ctrl led r v v v i = where v ref is nominally 2.5v the led current decreases linearly with the ctrl voltage when v ctrl 2.5v, as in figure 9 for 2 different current levels. note that 100% brightness setting corresponds to v ctrl = v ref , nominally 2.5v. if a voltage greater than 2.6v is applied to the ctrl pin an internal clamp is activated which results in the internal reference voltage being applied to the hysteresis control circuitry. this prevents the led current from being overdriven and will still set the led current to approximately. set th led r v i = 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 012345 ctrl voltage (v) figure 33 led current vs. ctrl pin voltage r = 100m s r = 150m s v = 12v 2 leds l in = 68h t = 25c a led current (a) as the ctrl pin is reduced below 2.5v the sense voltage will proportionally decrease. th is means that the time taken for the le d/switch current to ramp up to the upper threshold will decr ease. the AL8807A, being a hysteretic conver ter, automatically compensates for the r eduction in led current by reducing its lower threshold voltage and therefore it s off-time. it therefore remains in continuous conduction mode maintaining a better dimming accuracy than other peak-s witch current control topologies. a result of the reduced on- and off-times results in an increase of the switching frequency. this phenomenon can be seen in fi gure 34. 1200 0 200 400 600 800 1000 s wi t c hing f r e q u e n c y (khz) 0123 45 ctrl voltage (v) figure 34 switching frequency vs. v ctrl v = 12v in 2 leds r = 100m t = +25c s a l = 33h l = 220h l = 100h l = 68h ultimately at very small ctrl pin voltages the AL8807A will switch much faster than its nominal switching frequency which due t o propagation delays leads to a non-linear degrading of accuracy. the degradation in linear dimming accuracy at small ctrl pin voltages can be improved by using larger value inductors which cause the AL8807A to oscillate at lower frequencies. a further cause of loss of linearity as small ctrl pin voltages is the internal offsets of the control loop; at a ctrl pin volt age of 0.25v the nominal led current sense voltage has been reduced to 10mv. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 12 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) soft start the AL8807A does not have in-built soft-star t action; this can be seen in figure 35. led current 200ma/div v in 2v/div v ctrl 2v/div 2ms/div figure 35 start up without any capacitor on ctrl pin (v in = 12v, i led = 667ma, 2 leds) at power?up v in rises exponentially, due to the bulk capacitor, the internal reference will reach 2.5v before v in reaches the under-voltage lock- out turn-on threshold at around 5.6v. this causes the ctrl pin voltage to rise and reaches 2.5v ? 100% led current - before th e AL8807A fully turns on. when the AL8807A turns on, its output switch turn s causing the inductor current to increase until it reaches th e upper threshold of the sense current level and the switching process begins. adding an external capacitor from the ctrl pin to ground will provide a soft-start delay (see figures 36 and 37). AL8807A ctrl gnd hysteresis control analog dimming v ref 2.5v v ctrlh 2.55v 50k c dim figure 36 soft start led current 200ma/div v in 2v/div v ctrl 2v/div 2ms/div figure 37 soft start with 100nf capacitor on ctrl pin adding a capacitor to the ctrl pin provides a soft-start by incr easing the time taken for the ctrl voltage to rise to 2.5v and by slowing down the rate of rise of the control voltage at the input of the co mparator in the hysteresis control block (refer to figure 36). th is capacitor has 2 effects: 1. it reduces the minimum start-up current. the bigger the capac itor the lower the ctrl pin voltage will be when uvlo level is exceeded and the output switch turns on.. 2. the rate at which the inductor/led current is ramped up is dependent on the size of the capacitor. as can been seen in figure 37 adding a capacitor increases the time taken for the out put to reach 90% of its final value. there are many factors which set the initial current and ramp ra te. some practical examples are shown below with conditions vin 12v l=68uh 2 leds at 667ma, c dim initial current 90% rise time 0nf 80ma 0.45ms 10nf 80ma 0.55ms 22nf 80ma 0.8ms 47nf 80ma 1.8ms 100nf 80ma 4.2ms 470nf 40ma 42ms www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 13 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) input bulk cap acitor selection the small size of ceramic capacitors makes them ideal for AL8807A applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperat ure ranges than other types such as z5u. a 2.2 f input capacitor is sufficient for most in tended applications of AL8807A; however a 4.7 f input capacitor is suggested for input voltages approaching 36v. diode selection for maximum efficiency and performance, the rectifier (d1) shoul d be a fast low capacitance schottky diode with low reverse lea kage at the maximum operating voltage and temperature. the schottky diode also provides better efficiency than silicon pn diodes, due to a combination of lower forward voltage and reduced recovery time. it is important to select parts with a peak current rating abov e the peak coil current and a continuous current rating higher t han the maximum output load current. in particular, it is recommended to have a diode voltage rating at least 15% higher than the operating vo ltage to ensure safe operation during the switching and a current rating at least 10% higher than the average diode current. the power rating is ve rified by calculating the power loss through the diode. schottky diodes, e.g. b240 or b140, with their low forward volt age drop and fast reverse recovery, are the ideal choice for al8 807a applications. inductor selection recommended inductor values for the AL8807A are in the range 33 h to 100 h. higher values of inductance are recommended at higher supply voltages as they result in lower switching frequencies which in tu rn reduce the errors due to switching delays. higher val ues of inductance also result in a smalle r change in output current over the supply v oltage range. (see graphs). figure 38 inductor value with input voltage and number of leds the inductor should be mounted as close to the device as possible with low resistance/ stray inductance connections to the sw pi n. the chosen coil should have a saturation cu rrent higher than the peak output current and a continuous current rating above the required mean output current. suitable coils for use with the AL8807A are listed in the table below: part no. l (h) dcr (v) i sat (a) manufacturer mss1038-333 33 0.093 2.3 coilcraft www.coilcraft.com mss1038-683 68 0.213 1.5 npis64d330mtrf 33 0.124 1.1 nic www.niccomp.com www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 14 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) the inductor value should be chosen to main tain operating duty cycle and switch 'on'/'off' times over the supply voltage and lo ad current range. the following equations can be used as a guide, with re ference to figure 39 ? typical switching waveform. switch ?on? time () rrr x ivv il t swlsavg led in on ++ ?? = switch ?off? time () 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 in = 12v t a = 25c 2 leds 20ns/div sw pin: 2v/div on off figure 39 typical switching waveform v led is the total led forward voltage (v) r sw is the switch resistance ( ? ) {= 0.25 ? nominal (sot25)} v d is the diode forward voltage at the required load current (v) thermal considerations for continuous conduction mode of operation, the absolute maximum junction temperature must not be exceeded. the maximum power dissipation depends on several factors: 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, 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 AL8807A?s junction to ambient thermal resistance, ja and device power dissipation. ja , is layout dependent and package dependent; the AL8807Aw5?s ja on a 25 x 25mm single layer pcb with 1oz copper standing in still air is approximately +250c/w and around 130c/w on a 51mm x 51mm dual layer board with maximum coverage top and bottom and 3 vias. the maximum power dissipation at t a = +25c can be calculated by the following formulas: 0 0.2 0.4 0.6 0.8 1.2 1.4 1.6 -40 -25 -10 5 20 35 50 65 80 95 110 125 1.0 msop-8ep 51mm x 51mm sot25 51mm x 51mm sot25 25mm x 25mm p o we r dissi p a t i o n (w) ambient temperature (c) figure 40 derating curve for different pcb p d(max) = (+125c ? +25c) / (250c/w) = 0.4w for single-layer 25mm x25mm pcb p d(max) = (+125c ? +25c) / (130c/w) =0.77w for dual layer 51mm x 51mm pcb figure 40, shows the power derating of the AL8807Aw5 on two different pcbs and the AL8807Amp on one pcb. sot25 ? 25mm x 25mm: AL8807Aw5?s ja on a 25 x 25mm single layer pcb with 1oz copper sot25 ? 25mm x 25mm: AL8807Aw5?s ja on a 51mm x 51mm dual layer board with maximum coverage top and bottom and 3 vias msop-8ep - 51mm x 51mm: AL8807Amp?s ja on a 51mm x 51mm dual layer board with maximum coverage top and bottom and 4 vias figure 40 shows that the msop-8ep version of the AL8807A can handle more power than its sot25 version. so the AL8807Amp is the preferred variant when operating at larger supply voltage rails (> 24v) and/or driving larger led currents. this is especially t rue in high power density/space constraint applications such as high power 24vac mr16 applications. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 15 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) emi and layout considerations the AL8807A is a switching regulator with fast edges and measures small differential voltages; as a result of this care has to be taken with decoupling and layout of the pcb.to help with these effects t he AL8807A has been developed to minimi se radiated emissions by co ntrolling the switching speeds of the internal power mosfet. the rise and fall times are controlled to get the right compro mise between power dissipation due to switching losses and radiat ed emi. the turn- on edge (falling edge) dominates the radiated emi which is due to an interaction between the schottky diode (d1), switching mos fet and pcb tracks. after the schottky diode reverse recovery time of aro und 5ns has occurred; the falling edge of the sw pin sees a reson ant loop between the schottky diode capacitance and the track inductance, l track , see figure 41. the tracks from the sw pin to the anode of the schottky diode, d1, and then from d1?s cathode to the decoupling capacitors c1 should be as short as possible. there is an inductance internally in the AL8807A this can be assumed to be around 1nh. for pcb tracks a figure of 0.5nh per mm can be used to estimate the primary resonant frequency. if the track is capable of handling 1a increasing the thickness will have a minor effect on the inductance and length will dominate the size of the inductance. the resonant frequency of any oscillation is determined by the combined inductance in the track and the effective capacitance of the schottky diode. l tr ac k ~5nh c 1 100nf d1 AL8807A sw gnd c d1 figure 41 pcb loop resonance an example of good layout is shown in figure 42 - the stray track inductance should be less than 5nh. figure 42 recommended pcb layout recommendations for minimising radiated emi and other transients and thermal 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 avo id ringing. 3. the ground return path from c1 must be a low impedance 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 AL8807A 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 th e point the wires are joined to the pcb. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 16 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a application information (cont.) fault condition operation open circuit leds the AL8807A has by default open led protection. if the leds shou ld become open circuit the AL8807A will stop oscillating; the s et pin will rise to v in and the sw pin will then fall to gnd. no excessive voltages will be seen by the AL8807A. led chain shorted together if the led chain should become shorted together (the anode of the t op led becomes shorted to the cathode of the bottom led) the AL8807A will continue to switch and the current through the AL8807A?s internal switch will still be at the expected current - so no excessiv e heat will be generated within the AL8807A. however, the duty cycle at which it operates will change dramatically and the switching frequency will most likely decrease. see figure 43 for an example of this behavior at 24v input voltage driving 3 leds. the on-time of the internal power mosfet switch is signific antly reduced because almost all of the input voltage is now develop ed across the inductor. the off-time is significantly increased because the reverse voltage across t he inductor is now just the schottky diod e voltage (see figure 43) causing a much slower decay in inductor current. v in =24v, t a 25c l = 68h 3leds 10s/div 5v/div + 11v offset 200ma/div ? 10v/div v sw i led normal operation leds shorted together figure 43 switching characteristics (nor mal operation to led chain shorted out) high temperature operation and protection the AL8807A is a high efficiency switching led driver capable of operating junction temperatures up to +125c . this allows it operate with ambient temperature in excess of 100c given the correct thermal impedance to free air. if a fault should occur that leads to i ncreased ambient temperatures and hence junction temperature then the over-temperat ure protection (otp) of the AL8807A will cut in turning the o utput of the AL8807A off. this will allow the junction temperature of the al8 807a to cool down and potentially giving an opportunity for the fault to clear itself. the otp shutdown junction temperature of the AL8807A is approximately +150c with a hysteresis of +25c. this means that the al 8807a will never switch-off with a junction temperature below +125c allowing the designer to design the system thermally to fully utilize the wide operating junction temperature of the AL8807A. www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 17 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a ordering information AL8807A xx - xx package w5 : sot25 mp : msop-8ep packing 7 : 7? tape & reel 13 : 13? tape & reel part number status package code packaging 7? tape and reel quantity part number suffix AL8807Aw5-7 preview (note 11) w5 sot25 3000/tape & reel -7 AL8807Amp-13 new product mp msop-8ep 2500/tape & reel -13 note: 11. expected release in 4q 2012. 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 AL8807Aw5-7 sot25 c6 (2) msop-8ep (top view) 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 logo part number 8 7 6 5 y w x e AL8807A 1 2 3 4 part number package AL8807Amp-13 msop-8ep www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 18 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. (1) 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 www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 19 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a suggested pad layout please see ap02001 at http://www.diodes.com /datasheets/ap02001.pdf for latest version. (1) 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 g x c y y2 y1 x1 x z y c1 c2 c2 g www.datasheet.net/ datasheet pdf - http://www..co.kr/
AL8807A document number: ds35990 rev. 1 - 2 20 of 20 www.diodes.com september 2012 ? diodes incorporated new product a l8807a 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, enhancements, 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 arising 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 user 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 a nd 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 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 associ ated 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. 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 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 ramifica tions of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all l egal, regulatory and safety-related 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 ? 2012, diodes incorporated www.diodes.com www.datasheet.net/ datasheet pdf - http://www..co.kr/

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