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AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 1 of 12 www.diodes.com january 2011 ? diodes incorporated new product description the AP8800A is a step-down dc/dc converter designed to drive leds with a constant cu rrent. the device can drive up to 7 leds, depending on the forw ard voltage of the leds, in series from a voltage source of 8v to 28v. series connection of the leds provides identical led currents resulting in uniform brightness and eliminating the need for ballast resistors. the AP8800A switc hes at frequency up to 600khz. this allows the use of small size external components, hence minimizing the pcb area needed. maximum output current of AP8800A 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 switches off the output mosfet simplifying pwm dimming. pin assignments 4 set 5v in sw 1 ctrl 3 gnd 2 (top view) tsot23-5 features ? led driving current up to 370ma ? better than 5% accuracy ? high efficiency up to 95% ? operating input voltage from 8v to 28v ? simple, versatile solution requiring only 4 components ? pwm/dc input for dimming control ? built-in output open-circuit protection ? tsot23-5: available in ?green? molding compound (no br, sb) with lead free finish / rohs compliant (note 1) applications ? mr16 lamps ? general illumination lamps notes: 1. eu directive 2002/95/ec (rohs). all applicab le rohs exemptions applied. please visit our website at http://www.diodes.com /products/lead_free.html . typical application circuit sw gnd set vin ctrl
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 2 of 12 www.diodes.com january 2011 ? diodes incorporated new product pin descriptions pin name pin number descriptions sw 1 switch pin. connect inductor/freewheeling diode here, minimizing track length at this pin to reduce emi. gnd 2 gnd pin ctrl 3 dimming and on/off control input. ? input voltage of 0.2v or lower forces t he device into low current standby mode and shuts off the output. an open-drain/collector pwm signal allows the output current to be adjusted below the level set by the resist or connected to set input pin. ? the input impedance is about 50k ? , and if the pin is left open v ctrl = v ref . ? drive with dc voltage (0.3v < v ctrl < 2.5v) to adjust output current from 24% to 200% of i outnom set 4 set nominal output current pin. configures the output cu rrent of the device. v in 5 input supply pin. must be locally decoupled to gnd with > 2.2f x7r ceramic capacitor ? see applications section for more information. absolute maximum ratings symbol parameter ratings unit v in continuous v in pin voltage relative to gnd -0.3~30 v v set set voltage relative to v in v in -5 ~ v in +0.3 v v sw sw voltage relative to gnd -0.3~30 v v ctrl ctrl pin input voltage -0.3 ~ 5 v i sw switch current 0.45 a t j junction temperature 105 c t lead lead temperature soldering 300 c t st storage temperature range -55 to +150 c caution: the absolute maximum ratings ar e rated values exceeding which the product could suffer physical damage. these values must therefore not be exceeded under any condition. semiconductor devices are esd sensitive and may be damaged by ex posure to esd events. suitable esd precautions should be take n when handling and transporting these devices. recommended operating conditions symbol parameter min max unit v in operating input voltage relative to gnd 8.0 28 v v ctrldc voltage range for 24% to 200% dc dimming relative to gnd 0.3 2.5 v v ctrll voltage low for pwm dimming relative to gnd 0.2 v i sw continuous average switch current (note 2) 370 ma d pwm duty cycle range applied to ctrl (f < 500hz) 0.01 1 f sw switching frequency 600 khz t a ambient temperature range -40 105 c notes: 2. refer to figure 4 for the device derating curve.
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 3 of 12 www.diodes.com january 2011 ? diodes incorporated new product electrical characteristics v in =12v, t a =25 o c, unless otherwise specified. symbol parameter conditions min typ. max unit i q quiescent current v ctrl = 1.25v, f sw = 250khz 300 650 a i sd shutdown current v ctrl = 0v 20 30 a v thd internal threshold voltage 95 100 105 mv v ref internal reference voltage 1.25 v i set set pin input current v set =v in -0.1 1.3 a r ds(on) on resistance of mosfet 1.5 2.2 ? i sw-lkg switch leakage current 5 a f sw switching frequency with l = 100h adj pin floating l = 100h i out = 350ma @ 1 led (v led = 3.4v) 250 khz t ss soft start time time taken for output current to reach 90% of final value after v ctrl = 0.3v 500 s t pd internal comparator propagation delay 55 ns ja thermal resistance junction-to- ambient tsot23-5 (note 3) 200 c/w notes: 3. test condition for tsot23-5: device mounted on fr-4 pcb (25mm x 25mm 1oz 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.
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 4 of 12 www.diodes.com january 2011 ? diodes incorporated new product typical characteristics 0 100 200 300 400 50 0 04 8 12 16 20 24 28 input voltage (v) quiescent c urrent (switching) vs. input voltage t= 25c a quiescent current (a) 0 5 10 15 20 2 5 04 81216 20 24 28 input voltage (v) shutdow n current (non-sw itching) vs. input voltage shutdown current (a) t = 25c a 1.2415 1.242 1.242 5 48 12 16 20 24 28 input voltage (v) r eference voltage vs. input voltage t = 25c a reference voltage (v) 1.235 1.24 1.245 1.25 1.25 5 -40 -15 10 35 60 85 11 0 ambient temperature ( c) reference voltage vs. ambient temperature v = 12v in v (v) ref 0 0.2 0.4 0.6 0.8 1 1.2 1.4 01234 5678910 input voltage (v) reference voltage vs. input voltage (low voltage) t = 25c a reference voltage (v) 1.2 1.4 1.6 1.8 2.2 2.4 -40 -15 10 35 60 85 11 0 ambient temperature (c) power switch on-resistance vs. ambient temperature v = 12v in 2 1 power switch on-resistance ( )
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 5 of 12 www.diodes.com january 2011 ? diodes incorporated new product typical characteristics (continued) -2 -1 0 1 2 -40 -15 10 35 60 85 110 ambient temperature (c) c hange in led current vs. ambient temperature v = 12v l = 100h r = 0.33 in s deviation from nominal set current(%) 50 100 150 200 300 350 00.51 1.5 2 2.5 3 v (v) output current vs. v ctrl ct rl r = 0.3 s 250 0 i mean (ma) out r = 0.56 s r = 1 s
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 6 of 12 www.diodes.com january 2011 ? diodes incorporated new product applications information (t a = 25c unless otherwise stated) led current control r set c2 l1 c1 u1 sw gnd set vin ctrl vsupply AP8800A d1 d2 d3 d4 d5 c3 figure 1. mr16 typical configuration the led current is controlled by the resistor r set in figure 1. with the ctrl pin left floating and the external current sense resistor, r set (greater than 0.3 ? ) is connected between v in and set, the nominal average output current in the leds is: set r thd v led i = where v thd is nominally 1.25v if the ctrl pin is driven by an external voltage (lower than 2.5v), the average led current in this case is: set r thd v ref v ctrl v led i = the graph in figure 2 gives values of nominal average output current for several values of current setting resistor (r set ) in the typical application circuit shown on figure 1, fo r different voltages applied on the ctrl pin. led current versus rset and vctrl 0.3 0.33 0.39 0.47 0.56 3 0.56 0.68 0.75 0.82 1 1.2 3 0.3 0.39 0.47 0.56 0.68 0.82 1 1.2 1.5 2 3 1.2 1 0.82 0.68 1.5 2 1.5 2 0 50 100 150 200 250 300 350 400 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 2. led current setting vs r set and v ctrl
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 7 of 12 www.diodes.com january 2011 ? diodes incorporated new product applications information (continued) (t a = 25c unless otherwise stated) inductor selection a 68 h inductor or higher, is recommended for most ap 8800a applications with input voltage at 12v. figure 3 displays the resulting switching frequency with various main circuit parameters: supply voltage, inductor value and number of leds to be driven. switching frequency 47 68 100 470 100 150 470 150 220 220 0 100 200 300 400 500 600 700 0 50 100 150 200 250 300 350 400 450 500 inductor value [uh] frequency [khz] 12v - 1led 24v - 3 leds 28v - 4leds figure 3. switching frequency vs supply voltage, inductor, and number of leds capacitor selection a low esr capacitor should be used for input decoupling, as t he esr of this capacitor appears in series with the supply source impedance and lowers overall efficiency. this capacitor has to supply the relatively high peak current to the coil and smooth the current ripple on the in put supply. a minimum value of 1 f is acceptable if the dc input source is close to the device, but higher values will improve pe rformance at lower input voltages, especia lly when the source impedance is high. the input capacitor should be placed as close as possible to the ic. for ac input sources a bigger capacitor ( 300uf in the case of 12c ac) to guarantee the accuracy of the led current. for maximum stability over temperature an d voltage, capacitors with x7r, x5r, or better dielectric are recommended. capacitors with y5v dielectric are not suitable for decoupling in this application and should not be used. diode selection for maximum efficiency and performance, the rectifier (d1) s hould be a fast low capacitance sbr diode with low reverse leakage at the maximum operating voltage and temperature. the recommended diode for use with this part is the sbr1a40, with a current rating above the peak coil current and a conti nuous current rating higher than the maximum output load current. it is very important to consider the reverse leakage of the diode when operating above 85c. excess leakage will increase the power dissipation in the device.
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 8 of 12 www.diodes.com january 2011 ? diodes incorporated new product applications information (continued) (t a = 25c unless otherwise stated) led current dimming the led current can be dimmed in two ways; either by applying a dc signal to the ctrl pin or by applying a pulse width modulated (pwm) signal to the ctrl pin. a dc signal from 0.3v to 2.5v applied to the ctrl pin will vary the led current from 24% to 200% of nominal led current. this gives an approximate 8:1 dimming range; care, however, should be exercised when overdriving the ctrl pin to 200% led current not to exceed the power dissipation of the package. a pwm signal with a max resolution of 8bit can be applied to ctrl regulate the output current to a value below the nominal average value set by resistor r set . pwm dimming gives a wider average led current variation and is more accurate at lower average led currents than by applying dc voltage to the ctrl pin to achieve average led current dimming. the recommended method of driving the ct rl pin and controlling the amplitude of the pwm waveform is to use a small npn switching transistor as shown below: this scheme uses the 50k resistor between t he adj pin and the internal voltage reference as a pull-up resistor for the external transistor eg mmbt3904.
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 9 of 12 www.diodes.com january 2011 ? diodes incorporated new product applications information (continued) (t a = 25c unless otherwise stated) thermal considerations the graph below in figure 4, gives details for the power derat ing of the AP8800Awt. this assumes the device to be mounted on a 25x25mm pcb with 1oz copper standing in still air. 0 50 100 150 200 250 300 350 400 450 -40 -25 -10 5 20 35 50 65 80 95 110 ambient temperature (c) power dissipation (mw) figure 4. derating curve soft-start an external capacitor from the ctrl pin to ground will provi de 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 contro l voltage at t he input of the comparator. the soft-start time is 0.5ms/nf.
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 10 of 12 www.diodes.com january 2011 ? diodes incorporated new product applications information (continued) application example the typical application for the AP8800A is the mr16 appl ication driving 1w rated leds from a 12v ac supply. sw gnd set vin ctrl AP8800A component list quantity pcb ident value description suggested source 1 u1 AP8800A led driver ic diodes inc. 1 d1, d2, d3, d4, d5 sbr1a40 input bridge & freewheeling diode diodes inc. 1 r1 0r15 resistor, 0805, +/-1% <+/-300ppm koa sr732attdr150f kemet 1 c1 330uf 20v electrolytic capacitor kemet 1 c2 1uf >=25v x7r 1206 generic kemet c1206105k5rac7800 (50v) nic nmc1206x7r105k50f (50v) kemet nic components 1 c3 100nf >=25v x7r 0805 generic kemet c0805c104k5rac (50v) nic nmc0805x7r104k50trpf (50v) kemet nic components 1 l1 100uh lps6235 - series coilcraft
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 11 of 12 www.diodes.com january 2011 ? diodes incorporated new product ordering information (continued) AP8800A wt -7 package packing 7 : tape & reel wt : tsot23-5 AP8800A wt -7 package packing 7 : tape & reel wt : tsot23-5 device package code packaging (note 4) 7? tape and reel quantity part number suffix AP8800Awt-7 wt tsot23-5 3000/tape & reel -7 notes: 4. pad layout as shown on di odes inc. suggested pad layout document ap 02001, which can be found on our website at ht tp://www.diodes.com/d atasheets/ap02001.pdf. marking information (1) tsot23-5 1 2 3 5 7 4 xx y w x (top view) xx : identification code w : week : a~z : 1~26 week; x : a~z : internal code y : year 0~9 a~z : 27~52 week; z represents 52 and 53 week part number package identification code AP8800Awt-7 tsot23-5 az package outline dimensions (all dimensions in mm) (1) package type: tsot23-5
AP8800A cost effective 28v buck 1-w led driver AP8800A document number: ds35100 rev. 2 - 2 12 of 12 www.diodes.com january 2011 ? diodes incorporated new product 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 reserve the right to make modifications, enhancements, improvements, corrections or ot her changes without further notice to this document and any product described herein. diodes incorporated does not assume any liabi lity arising out of the application or use of this document or any product described herein; 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 desc ribed herein in such applications 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 incorporated products for any unintended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fee s arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized a pplication. 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 components in life support 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 perform when properly 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 device or system whose failure to perform can be reasonably expected 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 ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of diodes incorporated products in such safety-critical, 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 representatives against any damages arising out of the use of diodes incorporated products in such safety-critical, life support devices or systems. copyright ? 2011, diodes incorporated www.diodes.com

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