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issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 1 of 12 AL8806EV4 user guide performance 9v to 30v dc input (with 2 leds) 1.5a led current drives 1 led or several leds in series brightness control using dc or pwm inherent open circuit led protection ambient temperature range -40c to +105c ordering information order number AL8806EV4 please note: evaluation boards are subject to availability and qualified sales leads. introduction this evaluation circuit demonstrates the al8806 high efficiency 30v 1.5a buck led driver. for detailed information on the al8806, please see the datasheet at: http://www.diodes.com/datasheets/al8806.pdf the evaluation board is preset to drive its maximum current of 1.5a into a single led or multiple leds, the maximum number of which depends on their total forward voltage drop. emc filtering is included to meet international standards including the radiated emission requirements of en55015 and en55022 class b. the circuit operates in continuous switching mode at a frequency of approximately 170khz when driving 2 leds each having a forward voltage drop of approximately 3.4v at 1.5a. the construction uses a double-sided fr4 printed circuit board, 63 x 40 x 1.7 mm with 2oz/sq ft copper (70m). components are mounted on one side only. note: the evaluation board does not have reverse supply protection.
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 2 of 12 quick start guide suitable test equipment count description manufacturer part number 1 adjustable power supply, up to 30v 2a thurlby thandar cpx400a 2 digital multimeter fluke 179 1 digital storage oscilloscope tektronix tds2024b 2 led, high brightness, 2a, connected on suitable heat conducting pcb lamp operation 1. set the power supply to 12.0v but do not switch on. set the current limit to 2.0a. 2. connect up the AL8806EV4 board to the equipment as in figure 1 below. set dmm1 and dmm2 to measure current up to 2a. figure 1: test schematic 3. cover the leds to avoid dazzling. 4. switch on the power supply. this should illumin ate the leds. note that the input current (dmm1) depends on the led volt drop. the input cur rent is approximately 900ma if the total led volt drop is about 6.9v. the output current (d mm2) is approximately 1.47a. the input voltage can be varied from approximately 8.5vdc to 30vdc and the current regulation observed is typically within 2%. caution: the leds are very bright. ensure they ar e hidden from direct view, or covered with a dispersi ng filter. the lid from an aerosol can is convenient for this. also the leds are very hot. do not touch!!
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 3 of 12 observe switching waveform 5. the switching waveform can be observed on an osc illoscope. 6. set the oscilloscope as follows: channel 1 sensitivity: 2v/div (at probe tip) time base: 2s/div trigger source: ch1 trigger mode: auto 7. connect the ground lead of a 10x probe to one of the plated fixing holes of the AL8806EV4, and touch the probe tip onto the anode of d1 as in figure 2 below. on the oscilloscope, press run/stop to capture the waveform. the cursor readout indicates a switching frequency of 170khz approximately Csee figure 3 . (this frequency is dependent on the led volt drop.) figure 2: waveform capture dimming both dc and pwm dimming can be achieved by driving the ctrl input pin. for dc dimming, the ctrl pin may be driven between 0.5v and 2.5v adjust ing the output current from 25% to 100% of the maximum value of 1.5a nominal. driving the ctrl pi n below 0.4v will shut down the output current. a pwm signal (low level 0.4v and high level > 2.5v) allows the output curr ent to be adjusted up to 1.5a. the pwm frequency can be around 100hz to 1kh z, providing a resolution of 10 bits. in this case, c3 should be removed or reduced from the eval uation board (see AL8806EV4 schematic below) to give a more accurate control.
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 4 of 12 figure 3: oscilloscope waveform radiated emi performance, en55022: results of AL8806EV4 test at an independent emc test facility. input: 12vdc load: 2 leds, 1.5a (by courtesy of cass industries, limited)
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 5 of 12 0r1 r1 33uh l1 1uf 25v x7r c4 vin gnd gnd ctrl 1k r3 4.7uf 50v x7r c1 100nf 100v x7r c3 cathode anode ctrl ctrl pin anode sw cathode dfls230lh d1 100nf 100v x7r c2 1.5nf 100v c0g c11 4.7uf 50v x7r c5 vin 8 set 1 sw 5 ctrl 4 gnd 2 gnd 3 sw 6 nc 7 tab 9 al8806 u1 0r2 r2 not fitted c12 1.5nf 100v c0g c10 not fitted c9 not fitted c8 not fitted c6 not fitted c7 gnd gnd gnd gnd gnd gnd gnd vin gnd AL8806EV4 schematic
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 6 of 12 pcb copper layout & silk screen C top pcb copper layout & silk screen Cbottom
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 7 of 12 parts list count designator description package manufacturer part number 2 c1 c5 capacitor, 4.7f 10% 50v x7r 1210 kemet c1210x475k5rac 2 c2 c3 capacitor, 100nf 10% 100v x7r 0805 nic murata nmc0805x7r104k100pf grm21br71h104ka01l 1 c4 capacitor, 1uf 10% 100v x7r 1206 generic nic nmc1206x7r104k100 0 c6 C c9, c12 not fitted 2 c10 c11 capacitor, 1.5nf 100v cog 0805 generic 1 l1 inductor, shielded, 33h 20% coilcraft nic wrth mss1038-333ml npis104f330mtrf 744-066-330 1 r1 resistor, 0.1ohms 1% 1206 generic 1 r2 resistor, 0.2ohms 1% 1206 generic 1 r3 resistor, 1k 1% 0805 generic 1 d1 diode, schottky, 30v 2a dfls230lh powerdi123 diodes inc dfls230lh-7 1 u1 ic, led driver, al8806 msop-8ep diodes inc al8806mp8 -13 i/o count designator description function manufacturer part number 1 vin loop terminal dc supply + input hughes 100-108 1 gnd loop terminal dc supply C input hughes 100-108 1 ctrl loop terminal dimming control input hughes 100-108 1 led a loop terminal led anode load hughes 100-108 1 led k loop terminal led cathode load hughes 100-108 recommended operating conditions symbol parameter min max units vdc input supply voltage, vdc 8 30 v vout load voltage 0 vdc-1.5 v t a operating ambient temperature -40 +105 c
AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 8 of 12 current setting the led current is set by the sense resistor value, r sense . on this pcb, there are two resistors in parallel. r sense = r 1 * r 2 / (r 1 + r 2 ) for the schematic values this gives a resistance of 0.1 * 0.2 (0.1 + 0.2) = 0.0667 ohms. the led current flows through r sense . the sense voltage is 100mv, so the led current i s simply i led = 0.1/ r sense for the schematic values this gives an led current of 0.1/0.0667 = 1.500 a nominally. in practice there is a slight reduction in current partly due t o the resistance of the pcb copper, depending on th e pcb layout. at 1.5a this reduction is typically 1 to 2% using AL8806EV4. the following table gives commercially available re sistor values for typical current requirements, allowing a current error of 3% maximum not includin g the effect of pcb copper. a power limit of 250mw is assumed for the 0805 size resistors with 5 0% de-rating. led current r1, ohms r2, ohms 150ma 0.68 do not fit 300ma 0.33 do not fit 380ma 0.51 do not fit 500ma 0.2 do not fit 660ma 0.15 do not fit 1a 0.1 do not fit 1.1a 0.15 0.22 1.5a 0.1 0.2 performance the performance of the AL8806EV4 demonstrated shows the capability to regulate led current. the led current of 1.5a is approximately 2% lower than the calculated value. this is partly due to copper resistance. with a load of 2 leds, the current cha nges by less than 2% over the input voltage range from 9vdc to 30vdc. with 2 leds and a supply of 12 vdc, the circuit operates in continuous mode with a switching frequency of approximately 170khz. power efficiency is approximately 95%. the radiated emission of AL8806EV4 is approximately 18db below the limits of en55015 and is also well within the limit of en55022 class b. (in the application of al8806, the radiation depends very much upon pcb layout and filtering.) for further advice, please contact your local diode s field applications engineer, or one of our sales offices listed on the back page of this docum ent.
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AL8806EV4 issue 2 C july 2011 ? diodes incorporated 2011 www.diodes.com 12 of 12 sales offices the americas 3050 e. hillcrest drive westlake village, ca 91362-3154 tel: (+1) 805 446 4800 fax: (+1) 805 446 4850 europe kustermannpark balanstra?e 59, d-81541 mnchen germany tel: (+49) 894 549 490 fax: (+49) 894 549 4949 taiwan 7f, no. 50, min chuan road hsin-tien taipei, taiwan tel: (+886) 289 146 000 fax: (+886) 289 146 639 shanghai rm. 606, no.1158 changning road shanghai, china tel: (+86) 215 241 4882 fax (+86) 215 241 4891 shenzhen room a1103-04, anlian plaza, #4018 jintian road futian cbd, shenzhen, china tel: (+86) 755 882 849 88 fax: (+86) 755 882 849 99 korea 6 floor, changhwa b/d, 1005-5 yeongtong-dong, yeongtong-gu, suwon-si, gyeonggi-do, korea 443-813 tel: (+82) 312 731 884 fax: (+82) 312 731 885 important notice diodes incorporated makes no warranty of any kind, express or implied, with regard to this document, including, but not limited to, the implie d warranties of merchantability and fitness for a particular purpose (and their equival ents under the laws of any jurisdiction). diodes incorporated and its subsidiaries reserve th e right to make modifications, enhancements, improv ements, corrections or other changes without further notice to this document and any product described herein. diodes incorporated does not assume any liability arising out of the ap plication or use of this document or any product de scribed herein; neither does diodes incorporated convey any license under i ts patent or trademark rights, nor the rights of ot hers. any customer or user of this document or products described here in in such applications shall assume all risks of s uch use and will agree to hold diodes incorporated and all the companies w hose products are represented on diodes incorporate d website, harmless against all damages. diodes incorporated does not warrant or accept any liability whatsoever in respect of any products pur chased through unauthorized sales channels. should customers purch ase or use diodes incorporated products for any uni ntended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representativ es harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any c laim of personal injury or death associated with such unintended or unauthoriz ed application. products described herein may be covered by one or more united states, international or foreign patent s pending. product names and markings noted herein may also be covered by one or more united states, international or for eign trademarks. life support diodes incorporated products are specifically not a uthorized for use as critical components in life su pport devices or systems without the express written approval of the chief executive officer of diodes incorporated. as used herein: a. life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to per form when properly used in accordance with instruct ions for use provided in the labeling can be reasonably expecte d to result in significant injury to the user. b. a critical component is any component in a lif e support device or system whose failure to perform can be reasonably be expected to cause the failure of the life suppor t device or to affect its safety or effectiveness. customers represent that they have all necessary ex pertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulato ry and safety-related requirements concerning their products and any use of diodes incorporated products in such safety-crit ical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by diodes incorporated. further, customers must fully indemnify diodes incorporated and its representati ves against any damages arising out of the use of diodes incorporat ed products in such safety-critical, life support d evices or systems. copyright ? 2011, diodes incorporated www.diodes.com

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