issue 1 C december 2011 www.diodes.com ? diodes incorporated, 2011 al8807ev3 evaluation board user guide description the al8807ev3, figure 1, is a double sided evaluation board for the al8807 step-down, or buck, led driver with internal switch. the evaluation board is preset to drive 1a into a single led, or multiple leds, the maximum number of which depends on their total forward voltage drop and the supply voltage. the operating voltage is nominally 36 volts, but it ca n be reduced to a minimum of 6 volts. the 68uh inductor used in the circuit is based on this nominal su pply. the evaluation board should be connected as in figure 1 below. note: the evaluation board does not have reverse su pply protection. the nominal current, 1a, is set with the 0r1 sense re sistor, r1. terminal ctrl provides a connection point for dc or p wm dimming and shutdown. warning: at 36v nominal operation with 1a output, t he led will be hot and very bright figure 1: al8807ev3 evaluation board and connection di agram 1-8 leds 6-36vdc v +
al8807ev3 issue 1 C december 2011 www.diodes.com ? diodes incorporated 2011 2 al 8807 ev3 connection po int definition name description vin positive supply voltage. 6 to 36v 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 al 8807 device description the al8807 is a continuous mode inductive driver in a so t25 package, for driving one or more series-connected leds efficiently from a voltage source h igher than the led voltage. the device includes the output switch and a current sense circuit, which requires an external sense resistor to set the nominal current up to 1a. al 8807 device features drives one or more series-connected leds leds up to 1a. internal 40v switch. wide input voltage: 6v to 36v. 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. al 8807 device packages, pin and definitions 1 2 3 4 5 6 7 8 gnd ctrl gnd n.c. set v in sw sw top view sot25 package msop8ep package al 8807 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 36v. decouple to ground wi th a 2.2uf or higher ceramic capacitor.
al8807ev3 issue 1 C december 2011 www.diodes.com ? diodes incorporated 2011 3 ordering information evalboard order number al8807ev3 please note: evaluation boards are subject to availability and qualified sales leads. device order number al8807mp-13 al8807ev3 evaluation board reference design the al8807ev3 is configured to the reference design i n figure 2. the operating voltage is up to 36v. the nominal curre nt is set at 1a with a 0r1 sense resistor r1. the circuit operates in continuous mode between appro ximately 40khz and 130khz, depending on the input voltage, and with a 68uh inductor and one l ed. 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 out put current from 25% to 100% of i led . driving the ctrl pin below 0.4v will shut down the o utput current. a pwm signal (low level 0.4v and high level > 2.5) allows the output current to be adjusted above or below the level set by the resistor connected to set in put 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 the evaluation board, to give a more accurate duty cycle . shorting r2 will connect the test pin ctrl to device p in ctrl, if required. for other reference designs or further applications information, please refer to the al8807 datasheet. figure 2: schematic diagram
al8807ev3 issue 1 C december 2011 www.diodes.com ? diodes incorporated 2011 4 al8807 operation in normal operation, when a voltage is applied at +v in, the al8807 internal ndmos switch is turned on. current starts to flow through sense resistor r1, inductor l1, and the led. the current ramps up linearly, the ramp rate being determined by the inp ut voltage +vin and the inductor l1. this rising current produces a voltage ramp across r1. the internal circuit of the al8807 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 an d the schottky diode d1, and back to the supply rail, but it decays, with the rate of decay determin ed by the forward voltage drop of the leds and the schottky diode. this decaying current produces a falling voltage at r1, which is sensed by the al8807. a voltage proportional to the sense voltage acr oss r1 is applied at the input of the internal comparator. when this voltage falls to the internally 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 thr eshold limits, al8807 internal circuits, electrical characteristics and parameters. al8807ev3 component list ref value package part number manufactu rer notes u1 al8807 msop al8807mp-13 diodes zetex dc-dc converter d1 60v, 2a dfls260 diodes zetex schottky diode r1 0r1 1206 GENERIC 1% 250mw r2 not fitted r3 1k0 0805 GENERIC GENERIC 1% 125mw c1, c5 4.7uf 50v 1210 c1210x475k5rac GENERIC kemet x7r c2, c3 100nf, 100v 0805 nmc0805x7r104k100 pf grm21br71h104ka01l GENERIC nic comps murata x7r c4 1uf 100v 1206 nmc1206x7r104k100 GENERIC nic comps x7r c6, c7, c8, c9 c12 0805 not fitted GENERIC fit to improve emc performance if required c10, c11 1n5, 100v 0805 GENERIC l1 68uh mss1038-683ml npis24h680mtrf npis104f680mtrf coilcraft nic comps note: the component part numbers are correct at the t ime of publication. diodes inc reserves the right to substitute other parts where necessary, wit hout further notification.
al8807ev3 issue 1 C december 2011 www.diodes.com ? diodes incorporated 2011 5 al8807ev3 basic operation at full voltage 1. connect vin and gnd warning: the board does not feature reverse battery/s upply protection. 2. set the psu to 36v 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. switching the output current off shorting the ctrl pin to gnd will cause the led curr ent to go to zero. soft start adding a c2 capacitor will create a soft-start power -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 value of which is based on the required led current without dimming. r1 can be calculated using f ollowing 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 ci rcuit or set to 2.5v. the device calculator at the address below can be used to speed up the redesign phase: http://www.diodes.com/destools/calculators.html performance the system efficiency depends on the sense resistor, su pply voltage, switching frequency and the number of leds. with a 12v supply and two leds, the switching frequenc y is typically 102khz, and the efficiency level is 88% . 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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al8807ev3 issue 1 C december 2011 www.diodes.com ? diodes incorporated 2011 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 implied w arranties of merchantability and fitness for a particular purpose (and their equivalents 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 m ore 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 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 life support device or system whose failure to perform c an 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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