ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 1 of 8 www.diodes.com march 2011 ? diodes incorporated description the ap8803 is a step-down dc/dc converter designed to drive leds with a constant current. the device can drive up to 7 leds, depending on the forward voltage of the leds, in series from a voltage source of 8v to 30v. series connection of the leds prov ides identical led currents resulting in uniform bright ness and eliminating the need for ballast resistors. the ap8803 switches at frequency up to 700khz. this allows the use of small size external components, hence minimizing the pcb area needed. maximum output current of ap8803 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 0.2v or lower at ctrl shut s down the output at sw and puts the device into a low-current standby state. features ? led driving current up to 1a ? high efficiency up to 92% ? operating input voltage up to 30v ? high switching frequency up to 700khz ? pwm/dc input for dimming control ? built-in output open-circuit protection ? tsot23-5 is available in ?green? mold compound ? (no br, sb) and lead free finish/rohs compliant (note 1) pin assignments tsot23-5 1 2 3 4 5 set v in ctrl gnd sw top view notes: 1. eu directive 2002/95/ec (roh s). all applicable rohs exemptions applied. please visit our website at http://www.diodes.com/products/lead_free.html. typical application circuit l1 r set c1 ap8803 ctrl v in set sw gnd 12v_dc figure 1. typical application circuit
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 2 of 8 www.diodes.com march 2011 ? diodes incorporated pin descriptions pin name description sw switch pin. connect inductor/freewheeling diode here , minimizing track length at this pin to reduce emi. gnd gnd pin set set nominal output current pin. conf igure the output current of the device. ctrl dimming and on/off control input. ? leave floating for normal operation. (v ctrl = v ref = 1.25v giving nominal average output current i outnom = 0.1/r s ) ? drive to voltage below 0.2v to turn off output current ? drive with dc voltage (0.3v < v ctrl < 1.25v) to adjust output current from 25% to 100% of i outnom ? input voltage of 0.2v or lower forces the devic e into low current standby mode and shuts off the output. a pwm signal allows the output current to be adjusted above or below the level set by the resistor connected to set input pin. v in input supply pin. must be locally decoupled to gnd with > 2.2f x7r ceramic capacitor. absolute maximum ratings symbol parameter rating unit v in continuous v in pin voltage -0.3~30 v transient (t < 0.5s) 40 v sw sw voltage -0.3~30 v transient (t < 0.5s) 40 v ctrl ctrl pin input voltage -0.3 ~ 6 v i sw switch current 1.25 a t j junction temperature 150 c t lead lead temperature soldering 300 c t st storage temperature range -65 to +150 c caution: the absolute maximum ratings are rated values exceedi ng which the product could suffer physical damage. these values m ust therefore not be exceeded under any condition. semiconductor devices are esd sensitive and may be damaged by expos ure to esd events. suitable esd precautions should be taken when handling and transporting these devices recommended operating conditions symbol parameter min max unit v in operating input voltage 8.0 30 v v ctrlh voltage high 0.3 2.5 v v ctrll voltage low 0.25 v i sw continuous switch current (note 3) 1 a t a ambient temperature range -40 125 c duty cycle using inductor 100h (note 2) 0.1 0.95 notes: 2. for most applications the led current will be within 8% over the duty cycle range specifi ed. duty cycle accuracy is a lso dependent on propagation delay. smaller size inducto rs can be used but led current accuracy may be greater than 8% at extremes of duty cycle. this is most noticeable at low duty cycles (less than 0.1) or when the input voltage is high and only one led is being driven. 3. refer to figure 4 for the device derating curve.
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 3 of 8 www.diodes.com march 2011 ? diodes incorporated electrical characteristics (v in = 12v, t a = 25c, unless otherwise specified.) symbol parameter conditions min typ. max unit v insu internal regulator start up threshold v in rising 5.65 v v insd internal regulator shutdown threshold v in falling 5.55 v i q quiescent current ctrl pin floating f = 250khz 1.8 5 ma v thd internal threshold voltage 92 100 108 mv i set set pin input current v set = v in -0.1 1.25 10 a v ref internal reference voltage 1.25 v r ds ( on ) on resistance of mosfet i sw = 1a 0.5 1 ? i sw continuous switch current (note 3) 1 a i sw _ leaka g e switch leakage current 8 a f osc switching frequency 0.7 mhz ja thermal resistance junction-to- ambient tsot23-5 (note 4) 125 c/w notes: 3. refer to figure 4 for the device derating curve. 4. test condition for tsot23-5: device m ounted on fr-4 pcb, 25mm x 25mm, 2oz copper, minimum recommended pad layout on top lay er and thermal vias to bottom layer ground plane. for better thermal performance, larger copper pad for heat-sink is needed.
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 4 of 8 www.diodes.com march 2011 ? diodes incorporated applications information led current control the led current is controlled by the resistor r set in figure 1. connected between v in and set the nominal average output curr ent in the led(s) is defined as: set thd led r v i = if the ctrl pin is driven by an external voltage (lower than 2.5v), the average led current is: set thd ref ctrl led r v v v i = the graph in figure 2 gives values of nominal average output cu rrent for several values of current setting resistor (rset) in the typical application circuit shown on figure 1, for diffe rent voltages applied on the ctrl pin. it can be used to determine the rset value based on the desir ed led current and the condition of the ctrl pin (floating or driven with an external dc voltage lower than 2.5v and higher than 0.2v). led current versus rset and vctrl 0.2 0.3 0.39 0.47 3 0.82 1 1.5 2 3 0.82 0.75 2 1.5 1 0.75 0.47 0.3 0.1 0.15 0 200 400 600 800 1000 1200 0 0.15 0.3 0.45 0.6 0.75 0.9 1.05 1.2 1.35 1.5 1.65 1.8 1.95 2.1 2.25 2.4 2.55 2.7 2.85 3 rset val ue [ohms] led current [ma] led current @ vctrl = 1.25v led current @ vctrl = 2.5v led current @ vctrl = 0.625v figure 2. led current setting vs rset and vctrl inductor selection a 33 h inductor (or higher) is recommended for most ap8803 applications with input voltage at 24v. figure 3 displays the resulting switching frequency varying the main circuit parameters: supply voltage, inductor value and number of leds to be driven. in particular, the graph in figure 3 gives values of nominal sw itching frequency for several values of inductors (l1) in the typical application circuit shown on figure 1, for different input voltages and load condition. it can be used to determine the inductor value based on the desired switching frequency and the input and load conditions.
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 5 of 8 www.diodes.com march 2011 ? diodes incorporated applications information (continued) switching frequency @ i led =1a 33 47 68 220 470 100 150 68 33 47 220 100 150 0 100 200 300 400 500 600 0 50 100 150 200 250 300 350 400 450 500 inductor value [uh] frequency [khz] 12v - 1 led 24v - 3 leds 30v - 5 leds figure 3. switching frequency vs. supply voltage, inductor, and number of leds capacitor selection the small size of ceramic capacitors makes them ideal for ap8803 applications. x5r and x7r types are recommended because they retain their capacitance over wider voltage and temperature ranges than other types such as z5u. a 2.2 f input capacitor is sufficient for most intended applications of ap8803. diode selection schottky diodes, e.g. b240 or dfls240l in the proprietary powerdi?123 package, with their low forward voltage drop and fast reverse recovery, are the ideal choice for ap8803 applications. in addition, super barrier rectifier devices (as sbr2a40p 1) can be used for their enhanced thermal performances. pwm dimming a pulse width modulated (pwm) signal with a max resolution of 8-bit, can be applied to the ctrl pin to change the output current to a value above or below th e nominal average value set by resistor r set . to achieve this resolution the pwm frequency has to be lower than 500hz. the recommended method of driving the ctrl pin and controlling the amplitude of the pwm waveform is to use a small npn switching transistor as shown below: this scheme uses the internal 200k resistor between the ctrl pin and the in ternal voltage reference as a pull-up resistor for the external transistor eg mmbt3904.
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 6 of 8 www.diodes.com march 2011 ? diodes incorporated applications information (continued) thermal considerations the graph below in figure 4, gives details for power dissipat ion derating. this assumes the device to be mounted on a 25x25mm pcb with 1oz copper standing in still air. 0 0.2 0.4 0.6 0.8 1 1.2 -50 -25 0 25 50 75 100 125 150 ambient temperature (c) power dissipation (w) figure 4. power dissipation derating curve
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 7 of 8 www.diodes.com march 2011 ? diodes incorporated ordering information package wt : tsot23-5 packing 7 : 7? tape & reel a p8803 x - 7 device package code packaging (note 2) 7? tape and reel quantity part number suffix ap8803wtg-7 wt tsot23-5 3000/tape & reel -7 marking information package outline dimensions tsot23-5 ay : identification code y : year 0~9 w : week: a~z: 1~26 week a~z: 27~52 week; z represents 52 and 53 week 1 2 3 5 7 4 ay y w
ap8803 30v 3w buck led driver ap8803 document number: ds31970 rev. 4 - 2 8 of 8 www.diodes.com march 2011 ? diodes incorporated 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, enhancements, 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 any product described he rein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or user 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 a nd 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. life support diodes incorporated products are specifically not authorized for use as critical com ponents 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 ? 2011, diodes incorporated www.diodes.com
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