issue 3 C august 2009 www.diodes.com ? diodes incorporated, 2009 ap8800ev1 user guide description the ap8800ev1, figure 1, is a pcb constructed using an fr4 base for evaluating the ap8800 led driver with internal switch in sop-8l package. the evaluation board can be used to drive an external choice of leds; the total forward voltage across th e leds depending on the number and type connected. [1] the suggested operating voltage for the evaluation board ranges from 8v to 28v maximum. higher voltage means lower supply current. the nominal current for the evaluation board is set at 300ma with a 0r33 sense resistor, r1. test point ctrl provides a connection point for dc or pwm dimming and shutdown. note: the evaluation board does not have reverse polarit y protection warning: with 300ma output, the connected led will be hot and very bright figure 1: ap8800ev1 evaluation board ap8800 device description the ap8800 is a step-down dc/dc converter designed to drive leds with a constant current. the device can drive up to thirteen leds, depending lar gely on the forward voltage of the leds, in series from a voltage source of 8v to 28v. series connecti on of the leds provides identical led currents resulting in uniform brightness and eliminates the need for ballast resistors. the ap8800 switches at frequencies up to 500khz. this allows the use of s mall size external components, hence minimizing the pcb area needed. maximum output current of ap8800 is set via an exte rnal 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 0.2v or lower at ctrl shu ts down the output at sw and puts the device into a low-current standby state. the device includes the output switch and a current sense circuit, which requires an external sense resistor to set the nominal current up to 300ma.
ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 2 ap8800 device features led driving current up to 350ma input voltage from 8v to 28v high efficiency up to 92% high switching frequency up to 500khz minimum pwm/dc input for dimming control built-in soft-start function built-in output open-circuit protection sop-8l, msop-8l and dfn3030-10 are available in green molding compound (no br, sb) lead free finish/rohs compliant device applications commercial & industrial lighting small lcd panel backlighting appliance interior lighting architecture detail lighting ap8800 device packages, pin and definitions (1) sop-8l (2) msop-8l sop-8l 1 23 4 5 6 7 8 ( top view ) rsvd gnd ap8800 sw nc ctrl set nc v in msop-8l 1 23 4 5 6 7 8 ( top view ) rsvd gnd ap8800 sw nc ctrl set nc v in (3) dfn3030-10 ( top view ) 1 2 5 3 4 6 8 7 10 9 dfn3030-10 gnd rsvd nc ctrl sw nc v in nc set nc ap8800 pin description name description sw switch pin. connect inductor/freewheeling diode her e. minimize trace area at this pin to reduce emi. gnd gnd pin set set nominal output current pin. configure the o utput current of the device. ctrl dimming and on/off control input. input voltage of 0.2v or lower forces the device into low current standby mode and shut off the output. a pw m signal allows the output current to be adjusted above or below the level set by the resist or connected to set input pin. the input impedance is about 200k, and if the pin i s left open v ctrl = v ref v in input supply pin. must be locally bypassed with a capacitor. nc no connection ordering information evalboard order number ap8800ev1 please note: evaluation boards are subject to availability and qualified leads. device order number device package tape & reel s (sop8l) -13 m8 (msop-8l) -13 ap8800 fn(dfn3030-10) -7
ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 3 ap8800ev1 evaluation board reference design the ap8800ev1 is an evaluation board configured to be used with the ap8800 in sop-8l package. the target application is a driver for one or more series-connected leds for luminaires in both commercial and automotive applications. the maximum operating voltage for the evaluation bo ard is 28v , and a 0r33 sense resistor r1 sets the nominal current at 300ma. an accurate way of determining the current, avoidin g the need to insert an ammeter in the current path, is to measure the voltage on the sense resist or. a 10k resistor and a 1uf capacitor can be used to form a low pass filter and the voltage across th e capacitor represents a more stable dc reading of current. using this method, 100mv represents 0.3 am p when using a 0r33 sense resistor. the ctrl pin connects to a low pass filter within t he ap8800 chip to provide some decoupling, but the external capacitor c2 (100nf) can be used to p rovide additional decoupling to reduce any high frequency noise as well as providing soft start fun ction. both dc and pwm dimming can be achieved by driving the ctrl pin. for dc dimming, the ctrl pin may be driven between 0.3v and 1.25v. driving the c trl pin below 0.2v will shut down the output current. for pwm dimming, an external open-collecto r npn transistor or open-drain n-channel mosfet can be used to drive the ctrl pin. the pwm f requency can be around 100hz to 1 khz. for better resolution, pwm capacitor c2 should be r emoved on the evaluation board, to give a more accurate duty cycle . shorting r2 will connect the test pin ctrl to devic e pin ctrl if needed. the external capacitor c2 on the ctrl pin sets the soft start time. the amoun t of soft start time achievable is approximately 0.5ms/nf. for other reference designs or further applications information, please refer to the ap8800 datasheet.
ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 4 ap8800 operation in normal operation, when voltage is applied at v in , the ap8800s internal ndmos switch is turned on. current starts to flow through sense resistor r 1, inductor l1, and the led(s). the current ramps up linearly. the ramp rate is determined by the inp ut voltage v in and inductor l1. this rising current produces a voltage ramp across r1. the internal cir cuit of the ap8800 senses this voltage 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, led(s), schottky diode d1, and back to the supply rail. the current decays, with the rate of decay determined by the forward voltage dro p of the leds and the schottky diode. this decaying current produces a falling voltage at r1 w hich is sensed by the ap8800. a voltage proportional to the sense voltage across r1 is appl ied at the input of the internal comparator. when this voltage falls to the internally set lower thre shold, the ndmos switch is turned on again. this switch-on-and-off cycle continues to provide an ave rage current (set by the sense resistor r1) to the leds. please refer to the datasheet for the thresho ld limits, ap8800 internal circuits, electrical characteristics and parameters. ap8800ev1 evaluation board - bom ref value package part number manufacturer notes u1 ap8800 sop-8l AP8800SG diodes inc dc-dc converter d1 40v, 1a sma b140 diodes inc schottky diode r1 0r33 0805 ncst10fr330ftrf generic nic 1% r2 0r0 0805 generic - - c1,c4 1uf 50v 1206 nmc1206x7r105k50f nic 10% c2 - - not fitted - - c3 100nf, 100v 0805 c0805c104k1rac nmc0805x7r104k100 kemet nic 10% l1 100uh - mss6132 100uh npis53d101mtrf coilcraft nic 100uh the fr4 pcb design, with adequate copper top and bo ttom and plated through vias for thermal coupling, guarantees a good thermal dissipation for the ap8800 device. other sources of heat are the schottky diode, the inductor and the sense resistor , therefore care must be taken in their placement. warning: at 28v operation with 300ma output, the bo ard temperature rises by around 50c from ambient after 30 minutes of operation.
ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 5 figure 3: component layout and circuit board view ap8800ev1 connection point definition name description vin positive supply voltage. gnd supply ground (0v). ctrl internal voltage ref. pin (1.25v). this pin ca n be used to achieve dimming and soft-start, and for switching the output current of f. leave floating for normal operation. see 'circuit features' section to achieve dimming, soft-start and for switching the output current off. led a led a connects to the external led anode led k led k connects to the external led cathode ap8800ev1 basic operation at full voltage 1. connect external leds across test pins led a ( anode) and led k (cathode). the number of external leds that can be connected depends on t heir operating power and forward voltage drop, but typically 7 x 3.2v leds can be co nnected using a 28v rail. for an external load other than leds, the positive terminal of the load should be connected to the anode and the negative to the cathode. 2. connect vin and gnd. warning: the board does not have reverse battery/su pply protection. 3. set the psu to the desired input voltage (usuall y between 8v and 28v) 4. turn on the psu. the external leds will illumina te and the current should be approximately 300ma 5. the switching waveforms on the sw pin can be acq uired using the test point j1 warning: do not stare at the leds directly.
ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 6 circuit features n.b. remove power whilst changing components! soft-start 1. the ap8800 has a in-built soft start function. a ca pacitor, c2 may be fitted to the evaluation board to increase the soft start time by slowing th e rise time of the adjust pin at start-up at the rate of 0.5ms/nf. the board is supplied with a zero -ohm resistor in position r2. please see the data sheet for further details. pwm 1. remove the soft start capacitor c2 2. refer to the datasheet for instructions on how t o perform pwm switching off the output current 3. shorting the ctrl pin to gnd will cause the led current to go to zero. releasing this pin will switch on the system (creating a soft-start power u p sequence if the c2 capacitor is used). changing the led current 1. remove r1 2. calculate and fit a new sense resistor, r1, the value of which is based on the required led current without dimming. r1 can be calculated using following equation : r1= 0.1v / i led where i led = the led current. r1 = the sense resistors value in ohms. 0.1v is the nominal sense voltage with ctrl open ci rcuit or set to 1.25v. performance the system efficiency depends on the sense resistor , supply voltage, switching inductor, and the number of leds. with a 28v supply and 7 leds, the switching frequen cy is typically 320 khz and efficiency levels >90% are achievable. visit our website www.diodes.com to find useful tools for circuit design and simula tion. reference [1] ap8800 datasheet C www.diodes.com
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ap8800ev1 issue 3 C august 2009 www.diodes.com ? diodes incorporated 2009 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 purchase or use diodes incorporate d products for any unintended or unauthorized appli cation, customers shall indemnify and hold diodes incorpora ted and its representatives harmless against all cl aims, damages, expenses, and attorney fees arising out of, directl y or indirectly, any claim of personal injury or de ath associated with such unintended or unauthorized 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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