AP8803 document number: ds31970 rev. 5 - 2 1 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 30v 1a buck led driver 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 provides identical led currents resulting in uniform brightness 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 shuts 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 ? tsot25: available in ?green? molding compound (no br, sb) with lead free finish/ rohs compliant ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) pin assignments 1 2 3 4 5 set v in ctrl gnd sw top view notes: 1. no purposely added lead. fully eu directiv e 2002/95/ec (rohs) & 2011/6 5/eu (rohs 2) compliant. 2. see http://www.diodes.com for more in formation about diodes incorpor ated?s definitions of halogen and antimony free, "green " and lead-free. 3. halogen and antimony free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm t otal br + cl) and <1000ppm antimony compounds. typical applications circuit l1 r set c1 AP8803 ctrl v in set sw gnd 12v_dc
AP8803 document number: ds31970 rev. 5 - 2 2 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 pin descriptions pin name function 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. configure 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 device 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. functional block diagram absolute maximum ratings (@t a = +25c, unless otherwise specified.) symbol parameter rating unit v in continuous v in pin voltage -0.3 to +30 v transient (t < 0.5s) 40 v sw sw voltage -0.3 to +30 v transient (t < 0.5s) 40 v ctrl ctrl pin input voltage -0.3 to +6 v i sw switch current 1.25 a esd hbm human body model esd 500 v esd mm machine model esd <100 v t j junction temperature 150 c t lead lead temperature soldering 300 c t st storage temperature range -65 to +150 c caution: stresses greater than the 'absolute maximum ratings' sp ecified above, may cause permanent damage to the device. these are stress ratings only; functional operation of the device at these or any other conditions exceeding those i ndicated in this specification is not impl ied. device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. 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
AP8803 document number: ds31970 rev. 5 - 2 3 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 recommended operating conditions (@t a = +25c, unless otherwise specified.) 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 5) 1 a t a ambient temperature range -40 +125 c duty cycle using inductor 100h (note 4) 0.1 0.95 notes: 4. 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. 5. refer to figure 8 for the device derating curve. electrical characteristics (@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 5) 1 a i sw_leakage switch leakage current 8 a f osc switching frequency 0.7 mhz ja thermal resistance junction-to- ambient tsot25 (note 6) 125 c/w notes: 5. refer to figure 8 for the device derating curve. 6. test condition for tsot25: device mounted on fr-4 pcb, 25mm x 25mm, 2oz copper , minimum recommended pad layout on top layer and thermal vias to bottom layer ground plane. for better thermal performance, larger copper pad for heat-sink is needed.
AP8803 document number: ds31970 rev. 5 - 2 4 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 application information AP8803 operation the AP8803 is a hysteretic led current switching regulator some times known as an equal ripple switching regulator. in normal op eration, when voltage is applied at +v in (see figure 1), the AP8803 internal switch is turned on. cu rrent starts to flow through sense resistor r 1 , inductor l1, and the leds. the current ramps up linearly, and the ramp rate is determined by the input voltage +v in , and the inductor l1 (see figure 2). l1 r set c1 AP8803 ctrl v in set sw gnd 12v_dc figure 1 typical configuration figure 2 typical switching waveform this rising current produces a voltage ramp across r set . the internal circuit of the AP8803 senses the voltage across r set and applies a proportional voltage to the input of the internal comparator. when this voltage reaches an internally se t upper threshold, the internal switch is turned off. the inductor current continues to flow through r set , l1, the leds and the schottky diode d1, and back to the supply ra il, but it decays, with the rate of decay determined by the forward voltage drop of the leds and the schottky diode. this decaying current produces a falling voltage at r set , which is sensed by the AP8803. a voltage proportional to the sense voltage across r set is applied at the input of the internal comparator. when this voltage falls to the internally set lower threshold, the interna l switch is turned on again. this switch-on-and-off cycle continues to provi de the average led current set by the sense resistor r set, with a switching current determined by the input voltage and led chain voltage. in normal operation the off time is relatively constant (determi ned mainly by the led chain voltage) with only the on-time vary ing as the input voltage changes. at duty cycles up to around 80% the ramp of the led/switch current is very linear; however, as the duty cycle approaches 95% the led current ramp starts to become more exponential. this has two effects: 1. the overall on time starts to increase lowering the overall switching frequency. 2. the average led current starts to increase ? which may impact accuracy. 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 current in the led(s) is defined as: set th led r v i = where v th is nominally 100mv
AP8803 document number: ds31970 rev. 5 - 2 5 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 application information (cont.) 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 num ber 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 ty pical 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. 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 powerd i123 package, with their low forward voltage drop and fast reve rse 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.
AP8803 document number: ds31970 rev. 5 - 2 6 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 application information (cont.) led current dimming the led current can be dimmed in two ways; 1. analog dimming : where a dc voltage is applied to the ctrl pin. or 2. pwm dimming : where a pulse width modulated (pwm) signal is applied to the ctrl pin. analog dimming 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 = a dc signal from 0.3v to 2.5v applied to the ctrl pin will vary t he led current from 24% to 200% of nominal led current. this g ives an approximate 8:1 dimming range; care, should be ex ercised when overdriving the ctrl pin to 200% of nominal led current not to ex ceed the power dissipation of the package. the graph in figure 4 shows values of nominal average output current for 3 values of current setting resistor (r set ) in the typical application circuit shown on figure 1, for differ ent voltages applied on the ctrl pin. it can be used to determine the r set value based on the desired led current and the condit ion 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 value [ohms] led current [ma] led current @ vctrl = 1.25v led current @ vctrl = 2.5v led current @ vctrl = 0.625v figure 4 led current setting vs. r set and v ctrl
AP8803 document number: ds31970 rev. 5 - 2 7 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 application information (cont.) 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 curren t to a value above or below the nominal average value set by resistor r set . to achieve this resolution the pwm frequency has to be lower than 500hz. figure 5 shows the typical pwm response of the ap8800a. an internal filter produces a rump figure 5 typical pwm dimming waveform the recommended method of driving the ctrl pin and controlling the am plitude of the pwm waveform is to use a small npn switchin g transistor as shown below: figure 6 open collector pwm dimming circuit this scheme uses the internal 200k resistor between the ctrl pin and the internal volt age reference as a pull-up resistor for the external transistor eg mmbt3904. soft-start an external capacitor from the ctrl pin to ground will provide soft-start delay , by increasing the time taken for the voltage o n this pin to rise to the turn-on threshold and by slowing down the rate of rise of the control voltage at the input of the comparator. the soft-start time is 0.5ms/nf.
AP8803 document number: ds31970 rev. 5 - 2 8 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 application information (cont.) fault condition operation the AP8803 has by default open led protection. if the leds s hould become open circuit the AP8803 will stop oscillating; the set pin will rise to v in and the sw pin will then fall to gnd. no excessive voltages will be seen by the AP8803. if the leds should become shorted together the AP8803 will continue to switch however the duty cycle at which it will operate w ill change dramatically and the switching frequency will most likely decrease. the on-time of the internal power mosfet switch will be sig nificantly reduced because almost all of the input vo ltage is now developed across the inductor. the off-time will be significantly increa sed because the reverse voltage across the inductor is now just the schottky diode voltage (see figure 7) causing a much slower decay in induct or current. during this condition the inductor current will remain within its controlled levels and so no excessive heat will be generated within the AP8803. figure 7 switching characteristics (normal open to short led chain) thermal considerations the graph below in figure 8, gives details for power dissipation derating. this a ssumes the device to be mounted on a 25 x 25mm 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 8 power dissipation derating curve the maximum power dissipation is affected by pcb area and the area of copper associated with the lx pin as well as other compon ents on the pcb generating heat ? such as the i nductor, capacitor or rectifiers.
AP8803 document number: ds31970 rev. 5 - 2 9 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 ordering information part number package code packaging 7? tape and reel quantity part number suffix AP8803wtg-7 wt tsot25 3000/tape & reel -7 marking information part number package identification code al8803wt-7 tsot25 ay package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. tsot25 dim min max typ a ? 1.00 ? a1 0.01 0.10 ? a2 0.84 0.90 ? d ? ? 2.90 e ? ? 2.80 e1 ? ? 1.60 b 0.30 0.45 ? c 0.12 0.20 ? e ? ? 0.95 e1 ? ? 1.90 l 0.30 0.50 l2 ? ? 0.25 0 8 4 1 4 12 ? all dimensions in mm c a1 l e1 e a2 d e1 e 5x b 4x 1 l2 a xx : identification code y : year 0~9 w : week: a~z: 1~26 week a~z: 27~52 week; z represents 52 and 53 week
AP8803 document number: ds31970 rev. 5 - 2 10 of 10 www.diodes.com august 2012 ? diodes incorporated a p8803 suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the latest version. 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, enhanc ements, 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 an y product described herein; neither does di odes incorporated convey any license under its patent or trademark rights, nor the rights of others. any customer or us er 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 and 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 component s 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 ? 2012, diodes incorporated www.diodes.com dimensions value (in mm) c 0.950 x 0.700 y 1.000 y1 3.199 y1 c c x (5x) y (5x)
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