issue 3 C august 2010 www.diodes.com ? diodes incorporated, 2010 AL8805EV1 evaluation board user guide description the AL8805EV1, figure 1, is a double sided evaluati on board for the al8805 led driver with internal switch. the evaluation board is preset to drive 680 ma into a single led, or multiple leds, the maximum number of which depends on their total forw ard voltage drop. (the maximum drive current of the al8805 is 1000ma) the operating voltage is nominally 30 volts, but it can be reduced to a minimum of 6 volts. the 68uh inductor used in the circuit is based on this nomin al supply. the nominal voltage must be connected across the +vin and gnd pins. note: the evaluation board does not have reverse su pply protection. the nominal current, 680ma, is set with the 0r15 s ense resistor, r1. terminal ctrl provides a connection point for dc or pwm dimming and shutdown. warning: at 30v nominal operation with 680ma output , the led will be hot and very bright figure 1: AL8805EV1 evaluation board and connection diagram AL8805EV1 connection point definition name description vin positive supply voltage. 6 to 30v gnd supply ground (0v). ctrl internal voltage ref. pin (2.5v). this pin can be used to achieve dimming and for switching the output current off. leave floating for normal operation. led a led a connects to the external led anode led k led k connects to the external led cathode 6-30vdc 1-8 leds v
AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 2 al8805 device description the al8805 is a continuous mode inductive driver in a sot25 package, for driving one or more series-connected leds efficiently from a voltage so urce higher than the led voltage. the device includes the output switch and a current sense circ uit, which requires an external sense resistor to s et the nominal current up to 1000ma. al8805 device features drives one or more series-connected leds leds up to 1000ma. internal 30v switch. wide input voltage: 6v to 30v. inherent open circuit led protection. brightness control using dc or pwm. device applications led flashlights. high power led driving. low-voltage halogen replacement leds. automotive lighting. illuminated signs. al8805 device packages, pin and definitions sot25 pack al8805 device pin definition name pin no description sw 1 drain of ndmos switch. gnd 2 ground (0v). ctrl 3 internal voltage ref. pin (2.5v) : leave floating for normal operation. connect to gnd to turn off output current. drive with dc voltage (0.4v to 2.5v) or with pwm ( up to 5v logic level) signal to adjust output current set 4 connect a sense resistor, r1, from the set pin to vin to sense the nominal output current. nominal i out = 0.1/ r1 vin 5 input voltage: 6v to 30v. decouple to ground with a 2.2uf or higher ceramic capacitor. ordering information evalboard order number AL8805EV1 please note: evaluation boards are subject to availability and qualified sales leads. device order number al8805e5ta
AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 3 AL8805EV1 evaluation board reference design the AL8805EV1 is configured to the reference design in figure 2. the operating voltage is a nominal 30v. the nominal current is set at 680ma with a 0r15 sense resistor r1. the circuit operates in continuous mod e at approximately 188khz, with a 68uh inductor and one led. an accurate way of determining the current is to me asure the voltage on the sense resistor. a 10k resistor and a 1uf capacitor can be used to form a low pass filter; the voltage across the capacitor representing a more stable dc reading of current . 100mv represents 1 amp when using a 0r1 sense resistor. both dc and pwm dimming can be achieved by driving the ctrl pin. for dc dimming, the ctrl pin may be driven between 0.5v and 2.5v adjusting the o utput current from 25% to 100% of i led . driving the ctrl pin below 0.4v will shut down the output current. a pwm signal (low level 0.4v and high level > 2.5) allows the output curre nt to be adjusted above or below the level set by the resistor connected to se t input pin. the pwm frequency can be around 100hz to 1khz, providing a resolution of 10 bits. for low frequency pwm, c2 should be removed from th e evaluation board, to give a more accurate duty cycle . shorting r2 will connect the test pin ctrl to devic e pin ctrl, if required. for other reference designs or further applications information, please refer to the al8805 datasheet. figure 2: schematic diagram
AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 4 al8805 operation in normal operation, when voltage is applied at +vi n, the al8805 internal ndmos switch is turned on. current starts to flow through sense resistor r1, i nductor l1, and the led. the current ramps up linearly, and the ramp rate is determined by the in put voltage +vin and the inductor l1. this rising current produces a voltage ramp across r1. the inte rnal circuit of the al8805 senses the voltage across r1 and applies a proportional voltage to the input of the internal comparator. when this voltage reaches an internally set upper threshold, the ndmos switch is turned off. the inductor current continues to flow through r1, l1, the led a nd the schottky diode d1, and back to the supply rail, but it decays, with the rate of decay determi ned by the forward voltage drop of the leds and the schottky diode. this decaying current produces a fa lling voltage at r1, which is sensed by the al8805. a voltage proportional to the sense voltage across r1 is applied at the input of the internal comparator. when this voltage falls to the internal ly set lower threshold, the ndmos switch is turned on again. this switch-on-and-off cycle continues to provide the average led current set by the sense resistor r1. please refer to the datasheets for the threshold limits, al8805 internal circuits, electr ical characteristics and parameters. AL8805EV1 component list ref value package part number manufactu rer notes u1 al8805 sot25 al8805e5ta diodes zetex dc-dc converter d1 40v, 3a b240a diodes zetex schottky diode r1 0r15 0805 generic 5% r2, 1k 0805 generic 1% c1 4.7uf 50v 1210 c1210x475k5rac generic kemet x7r c2 not fitted optional soft start capacitor c3 100nf, 100v 0805 nmc0805x7r104k100 pf grm21br71h104ka01l generic nic comps murata x7r c4 100nf 100v 1206 nmc1206x7r104k100 generic nic comps x7r l1 68uh mss1038-683ml npis24h680mtrf coilcraft nic comps note: the component part numbers are correct at the time of publication. diodes inc reserves the right to substitute other parts where necessary, wi thout further notification. AL8805EV1 basic operation at full voltage 1. connect vin and gnd warning: the board does not feature reverse battery /supply protection. 2. set the psu to 30v 3. turn on the psu and the led will illuminate and the current should be approximately 680ma. warning: do not stare at the led directly.
AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 5 switching the output current off shorting the ctrl pin to gnd will cause the led cur rent to go to zero. soft start adding a c2 capacitor will create a soft-start pow er-up sequence (0.1ms/nf). this delay will reduce the pwm dimming performance. changing the led current 1. remove r1. 2. calculate and replace sense resistor, r1, the va lue of which is based on the required led current without dimming. r1 can be calculated using following equation : r1 = 0.1v/i out where i out = the led current. r1 = the sense resistor value in ohms. 0.1v is the nominal sense voltage with ctrl open circuit or set to 2.5v. the device calculator at the address below can be u sed to speed up the redesign phase: http://www.diodes.com/destools/calculators.html performance the system efficiency depends on the sense resistor , supply voltage, switching frequency and the number of leds. with a 30v supply and one led, the switching freque ncy is typically 188khz. the efficiency level is >85% . 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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AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 7 intentionally blank
AL8805EV1 issue 3 C august 2010 www.diodes.com ? diodes incorporated 2010 8 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 ? 2009, diodes incorporated www.diodes.com
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