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AL8807 document number: ds35281 rev. 5 - 2 1 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 high efficiency low 36v 1a buck led driver description the AL8807 is a step-down dc/dc converter designed to drive leds with a constant current. 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, msop-8ep: 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) pin assignments sot25 (top view) sw gnd ctrl set v in (top view) msop-8ep set gnd gnd ctrl v in n/c sw sw applications ? mr16 lamps ? general illumination lamps ? 12v powered led lamps ? 24v powered 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/quality/lead_free.html for more in formation about diodes incorporated?s definitions of halogen- a nd antimony-free, "green" and lead-free. 3. halogen- and antimony-free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds. typical applications circuit ? 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 document number: ds35281 rev. 5 - 2 2 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 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 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. 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 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 (@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 1.6 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 'absol ute maximum ratings' specified above, may cause permanent damage to the device. these are stress ratings only; functional operation of the device at thes e or any other conditions exceeding those indi cated in this specification is not imp lied. 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 ex posure 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 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 document number: ds35281 rev. 5 - 2 3 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 electrical characteristics (@v in = 12, 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 output not switching (note 4) 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 internal 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 to 12v to 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 5) sot25 (note 6) 250 ? c/w msop-8ep (note 7) 69 ? jl thermal resistance junction-to-lead (note 8) sot25 (note 6) 50 ? jc thermal resistance junction-to-case (note 9) msop-8ep (note 7) 4.3 notes: 4. 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 5. refer to figure 35 for the device derating curve. 6. test condition for sot25: device mounted on fr-4 pcb (25 mm 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. 7. 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 8. dominant conduction path via gnd pin (pin 2). 9. dominant conduction path via exposed pad.
AL8807 document number: ds35281 rev. 5 - 2 4 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 typical performance characteristics 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 number: ds35281 rev. 5 - 2 5 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 typical performance characteristics (cont.) led current led current error l = 68h, r = 150m t = 25c, v = 12v ctrl = pwm, f = 500hz 1 led s ain pwm 020406080100 pwm duty cycle figure 7. i vs. pwm duty cycle led 9 8 7 6 4 3 2 0 led current error (%) 5 1 0.8 led current (a) 0.7 0.6 0.5 0 0.4 0.3 0.2 0.1 6 9 12 18 21 24 27 30 36 v (v) figure 8. sw r vs. input voltage in ds(on) 15 33 300 270 210 150 30 0 r (m ) ds(on) ? 90 240 180 120 60 v = open v = v ctrl set in t = 25c a -40 -15 35 60 110 10 85 ambient temperature ( c) figure 9. sw r vs. temperature ? ds(on) v = open v = v= 12v ctrl set in 400 250 150 100 r (m ) ds(on) ? 350 300 200 6 9 12 15 18 21 24 27 30 33 36 input voltage (v) figure 10. duty cycle vs. input voltage 100 90 80 70 60 40 30 20 10 0 50 d u t y c y c le (%) 2 leds 3 leds l = 68h r = 100m t = 25c v = open s a ctrl ? figure. 11 sw output rise time figure. 12 sw output fall time
AL8807 document number: ds35281 rev. 5 - 2 6 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 typical performance characteristics (cont.) (670led current) 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 en 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 document number: ds35281 rev. 5 - 2 7 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 typical performance characteristics (cont.) (1a led current msop-8ep) 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 i n g f r e q u e n c y (k h z) 400 100 200
AL8807 document number: ds35281 rev. 5 - 2 8 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 typical performance characteristics (cont.) (1.3a led current msop-8ep) 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 number: ds35281 rev. 5 - 2 9 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information the AL8807 is a hysteretic (also known as equal ripple) led driv er with integrated power switch. it is available in two package s that provide a pcb area-power dissipation capability compromise. it is recommended that at higher led currents/smaller pcbs that the msop-8ep vers ion is used to maximize the allowable led current over a wider ambient temperature range. AL8807 operation in normal operation, when voltage is applied at +v in , the AL8807 internal switch is turned on. curr ent 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 +vin and the ind uctor l1. this rising current produces a voltage ramp across r 1 . the internal circuit of the AL8807 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 forwar d voltage drop of the leds and the schottky diode. this decaying current produces a falling voltage at r 1 , which is sensed by the AL8807. 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 . led current control the led current is controlled by the resistor r1 in figure 30. figure 30 typical application circuit connected between v in and set the nominal average output current in the led(s) is defined as: 1r v i thd led ? for example for a desired led current of 660ma and a default voltage v ctrl =2.5v the resulting resistor is: ???? m150 66.0 1.0 i v 1r led thd dc dimming further control of the led current can be ac hieved by driving the ctrl pin with an ex ternal voltage (between 0.4v and 2.5v); th e average led current becomes: set thd ref ctrl led r v v v i ? with 0.5v v ctrl 2.5v the led current varies linearly with v ctrl , as in figure 2. if the ctrl pin is brought higher than 2.5v, the led current will be clamped to approximately 100% and follows set thd led r v i ? . when the ctrl voltage falls below the threshold, 0.4v, t he output switch is turned off which allows pwm dimming.
AL8807 document number: ds35281 rev. 5 - 2 10 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) pwm dimming led current can be adjusted digitally, by applying a low frequency pulse width modulated (pwm) logi c 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 p wm 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 ex pense 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%. 0 100 200 300 400 500 600 700 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% pwm dimming [%] led current [ma ] figure 31 pwm dimming at 500hz zooming in at duty cycles below 10% shows: figure 32 low duty cycle pwm dimming at 300hz the accuracy of the low duty cycle dimming is affected by both 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 leve ls directly from a logic output with either an open drain o utput or push pull output stage.
AL8807 document number: ds35281 rev. 5 - 2 11 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) soft start the AL8807 does not have in-built soft-start action ? this provides very fast turn off of the output the stage improving pwm di mming 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. adding a capacitor increases the time taken for the output to reach 90% of its final value, this delay is 0.1ms/nf, but will im pact on the pwm dimming accuracy depending on the delay introduced. figure 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 r equired, by shunting a capacitor c2 across the led(s) as shown al ready in the circuit schematic. a value of 1 f will reduce the supply ripple current by a factor three (approx.). proportionally lo wer ripple can be achieved with higher ca pacitor values. note that the capacitor will not affect operating fr equency or efficiency, but it will increase start-up delay, by redu cing 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 v ersion without altering the mean current value. capacitor selection the small size of ceramic capacitors makes them ideal for al8 807 applications. x5r and x7r types are recommended because they r etain their capacitance over wider voltage and temperatur e ranges than other types such as z5u. a 2.2 f input capacitor is sufficient for most intended applications of AL8807; however a 4.7 f input capacitor is suggested for input voltages approaching 36v.
AL8807 document number: ds35281 rev. 5 - 2 12 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) diode selection for maximum efficiency and performance, the rectifier (d1) should be a fast low capac itance schottky diode with low reverse lea kage at the maximum operating voltage and temperature. the schottky diode al so 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 above 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 voltage t o ensure safe operation during the switching and a current rating at least 10% higher t han the average diode current. the power rating is verified 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 807 applications. inductor selection recommended inductor values for the AL8807 are in the range 33 h to 100 h. higher values of inductance are recommended at higher supply voltages in order to minimi ze errors due to switching delays, whic h result in increased ripple and lower efficiency. higher va lues of inductance also result in a smaller change in output current over the s upply voltage range. (see graphs). figure 34 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 current higher than t he peak output current and a continuous current rating above the required mean output current. suitable coils for use with the AL8807 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 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.
AL8807 document number: ds35281 rev. 5 - 2 13 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) the following equations can be used as a guide, with 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 operation, t he absolute maximum junction temperature mu st 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 ca lculated 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 250c/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 cop per standing in still air and the AL8807mp on an fr4 51x51mm pcb with 2oz copper standing in still air. figure 35 derating curve for different pcb
AL8807 document number: ds35281 rev. 5 - 2 14 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) emi and layout considerations the AL8807 is a switching regulator with fast edges and measures sm all differential voltages; as a result of this care has to b e taken with decoupling and layout of the pcb.to help with these effects the AL8807 has been developed to minimise radiated emissions by con trolling the switching speeds of the internal power mosfet. the rise and fa ll times are controlled to get the right compromise between power dissipation due to switching losses and radiated emi. the turn-on edge (falling edge) dominates the radiated emi which is due to an interactio n between the schottky diode (d1), switching mosfet and pcb tracks. after the schottky diode reverse recovery time of around 5ns has occurre d; the falling edge of the sw pin sees a resonant loop between the sc hottky diode capacitance and the track inductance, l track , see figure 36. figure 36 pcb loop resonance 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 s hould be as short as possible. there is an inductance internally in the AL8807 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 capac itance of the schottky diode. an example of good layout is shown in figure 37 - the stray track inductance should be less than 5nh. figure 37 recommended pcb layout
AL8807 document number: ds35281 rev. 5 - 2 15 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) recommendations for minimising radiated emi and ot her 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 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 th e point the wires are joined to the pcb a typical application for the AL8807 is an led mr16 lamp (schematic shown in figure 38). figure 38 mr16 circuit schematic an evaluation board for the AL8807 (named the AL8807ev2) for mr16 is available on request from your local diodes? sales represe ntative. this board follows diodes? recommendations for low emi. images of the top layer and bottom layers are shown in figure 39. figure 39 recommended mr16 pcb layout
AL8807 document number: ds35281 rev. 5 - 2 16 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 application information (cont.) the associated emi measurements for this board using the AL8807 is shown in figure 40. figure 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 including lighting. the bottom magenta line is the noise floor of the test chamber. the mid dle purple line is the emi emitted radiation of the AL8807 over 30mhz to 1000mhz. this shows that the AL8807 passes the standard with at least 16db ma rgin. mr16 lamps typically operate from 12v dc or 12v ac , using conventional electr omagnetic 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 same conditions as the emi tests at an free air temperature of 25 c. it is anticipated that the internal junction temperature is approximately 6c hotter than the surface temperature. figure 41 thermal picture of AL8807ev2 at 12v dc 2 white leds at 660ma the thermal image shows that components increasing the board te mperature are the inductor, schottky diodes and the AL8807. an inductor choice of 33h with saturation current higher than 1.1a, will limit the frequency variation between 180khz and 400k hz 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 regulation is better than 0.1ma/v in for a dc input voltage in the rang e from 8v to 18v.
AL8807 document number: ds35281 rev. 5 - 2 17 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 ordering information package packing w5 : sot25 mp : msop-8ep 7 : 7? tape & reel 13 : 13? tape & reel a l8807 xx - xx part number status package code packaging 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 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
AL8807 document number: ds35281 rev. 5 - 2 18 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 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
AL8807 document number: ds35281 rev. 5 - 2 19 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the 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 x z y c1 c2 c2 g g x c y y2 y1 x1
AL8807 document number: ds35281 rev. 5 - 2 20 of 20 www.diodes.com march 2013 ? diodes incorporated a l8807 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 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 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 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 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

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