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AP65503 document number: ds37127 rev. 1 - 2 1 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 light load improved 5a, 750khz synch dc/dc buck converter description the AP65503 is a 750khz switching frequency external compensated synchronous dc/dc buck converter. it has integrated low r dson high and low side mosfets. the AP65503 enables continues load current of up to 5a with efficiency as high as 96%. the AP65503 implements an automatic custom light load efficiency improvement algorithm. the AP65503 features current mode control operation, which enables fast transient response times and easy loop stabilization. the AP65503 simplifies board layout and reduces space requirements with its high level of integration and minimal need for external components, making it ideal for distributed power architectures. the AP65503 is available in a standard green so-8ep package and is rohs compliant. features ? v in 4.75v to 17v ? 5a continuous output current, 7a peak ? efficiency up to 96% ? automated light load improvement ? v out adjustable to 2.5 to 12v ? 750khz switching frequency ? external programmable soft-start ? enable pin ? ocp with hiccup and thermal protection ? totally lead-free & fully rohs compliant (notes 1 & 2) ? halogen and antimony free. ?green? device (note 3) pin assignments applications ? gaming consoles ? flat screen tv sets and monitors ? set top boxes ? distributed power systems ? home audio ? consumer electronics ? network systems ? fpga, dsp and asic supplies ? green electronics 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/quality/lead_free.html for more in formation about diodes incorporated?s definitions of halogen- a nd antimony-free, "green" and lead-free. 3. halogen- and antimony-free "green? products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total br + cl) and <1000ppm antimony compounds. typical applications circuit figure 1 typical application circuit
AP65503 document number: ds37127 rev. 1 - 2 2 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 pin descriptions pin name pin number function bs 1 high-side gate drive boost input. bs supplies the drive for the high-side n-channel mosfet a 0.01f or greater capacitor from sw to bs to power the high side switch. in 2 power input. in supplies the power to the ic, as well as the step-down converter switches. drive in with a 4.75v to 17v power source. bypass in to gnd with a suitably large capacitor to eliminate noise on the input to the ic. see input capacitor. sw 3 power switching output. sw is the switching node that supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switch. gnd 4 ground fb 5 feedback input. fb senses the output voltage and r egulates it. drive fb with a resistive voltage divider connected to it from the output voltage. the feedback threshold is 0.800v. see setting the output voltage. comp 6 compensation node. comp is used to compensate t he regulation control loop. connect a series rc network from comp to gnd. in some cases, an addi tional capacitor from comp to gnd is required. see compensation components. en 7 enable input. en is a digital input that turns the regulator on or off. drive en high to turn on the regulator; low to turn it off. attach to in with a 100k ? pull up resistor for automatic startup. ss 8 soft-start control input. ss controls the soft-start pe riod. connect a capacitor from ss to gnd to set the soft-start period. a 0.1f capacitor sets the so ft-start period to 13ms. to disable the soft-start feature, leave ss floating. ep ep exposed pad is connected to ground functional block diagram figure 2 functional block diagram
AP65503 document number: ds37127 rev. 1 - 2 3 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 absolute maximum ratings (note 4) (@t a = +25c, unless otherwise specified.) symbol parameter rating unit v in supply voltage -0.3 to 20 v v sw switch node voltage -1.0 to v in +0.3 v v bs bootstrap voltage v sw -0.3 to v sw +6.0 v v fb feedback voltage -0.3v to +6.0 v v en enable/uvlo voltage -0.3v to +6.0 v v comp comp voltage -0.3v to +6.0 v t st storage temperature -65 to +150 c t j junction temperature +160 c t l lead temperature +260 c esd susceptibility (note 5) hbm human body model 1.5 kv mm machine model 150 v notes: 4. stresses greater than the 'absolute maximum ratings' specified 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 indicated in this specification is not implied. device reliability may be affected by exposure to absolute maximum rating conditions for extended periods of time. 5. semiconductor devices are esd sensitive and may be damaged by exposure to esd events. suitable esd precautions should be ta ken when handling and transporting these devices. thermal resistance symbol parameter rating unit ja junction to ambient so-8ep (note 6) 43 c/w jc junction to case so-8ep (note 6) 6.3 c/w note: 6. test condition: so-8ep: device mounted on fr-4 subs trate (2s2p) 2"x2" pcb, with 2oz copper trace thickness and min imum recommended pad on top layer and thermal vias to bottom layer ground plane. recommended operating conditions (note 7) (@t a = +25c, unless otherwise specified.) symbol parameter min max unit v in supply voltage 4.75 17.0 v t a operating ambient temperature range -40 +85 c note: 7. the device function is not guaranteed outside of the recommended operating conditions.
AP65503 document number: ds37127 rev. 1 - 2 4 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 electrical characteristics (@t a = +25c, v in = 12v, unless otherwise specified.) symbol parameter test conditions min typ max unit i shdn shutdown supply current v en = 0v ? 0.3 3.0 a i q supply current (quiescent) v en = 2.0v, v fb = 1.0v ? 0.3 1.5 ma r ds(on)1 high-side switch on-resistance (note 8) ? ? 80 ? m ? r ds(on)2 low-side switch on-resistance (note 8) ? ? 32 ? m ? i limit hs current limit minimum duty cycle ? 7 ? a i limit ls current limit from drain to source ? 0.9 ? a high-side switch leakage current v en = 0v, v sw = 0v, v sw =12v ? 0 10 a avea error amplifier voltage gain (note 8) ? ? 800 ? v/v gea error amplifier transconductance ? i c = 10a ? 1000 ? a/v gcs comp to current sense transconductance ? ? 2.8 ? a/v f sw oscillator frequency v fb = 0.75v 660 750 840 khz f fb fold-back frequency v fb = 0v ? 0.30 ? f sw d max maximum duty cycle v fb = 800mv ? 90 ? % t on minimum on time ? ? 160 ? ns v fb feedback voltage t a = -40c to +85c ? 800 ? mv feedback overvoltage threshold ? ? 1.0 ? v v en_rising en rising threshold ? 0.7 0.8 1.2 v en lockout threshold voltage ? 2.2 2.5 2.7 v en lockout hysteresis ? ? 220 ? mv inuv vth v in under voltage threshold rising ? 3.80 4.05 4.40 v inuv hys v in under voltage threshold hysteresis ? ? 250 ? mv soft-start current v ss = 0v ? 6 ? a soft-start period c ss = 0.1f ? 13 ? ms t sd thermal shutdown (note 8) ? ? 160 ? c note: 8. guaranteed by design
AP65503 document number: ds37127 rev. 1 - 2 5 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 typical performance characteristics (@t a = +25c, v in = 12v, v out = 3.3v, unless otherwise specified.)
AP65503 document number: ds37127 rev. 1 - 2 6 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 typical performance characteristics (cont.) (@t a = +25c, v in = 12v, v out = 3.3v, unless otherwise specified.)
AP65503 document number: ds37127 rev. 1 - 2 7 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 typical performance characteristics (cont.) (@t a = +25c, v in = 12v, v out = 3.3v, l = 4.7h, c1 = 44f, c2 = 72f, unless otherwise specified.) steady state test 5a time-2s/div startup through vin no load time-5ms/div startup through vin 5a load time-5ms/div load transient test 2.5 to 5a time-2ms/div shutdown through vin no load time-200ms/div shutdown through vin 5a load time-100ms/div short circuit test time-50s/div short circuit recovery time-2ms/div load transient test 2.5 to 5a time-50s/div load transient test 5a to 2.5a time-50s/div
AP65503 document number: ds37127 rev. 1 - 2 8 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 application information theory of operation the AP65503 is a 5a current mode control, synchronous buck regulator with built in power mosfets. current mode control assures excellent line and load regulation and a wide loop bandwidth for fast respons e to load transients. the figure 1 depicts the functional bl ock diagram of AP65503. the operation of one switching cycle can be explained as follows. at the beginning of each cycle, hs (high-side) mosfet is off. the error amplifier (ea) output voltage is higher than the current sense am plifier output, and the current comparator?s output is low. th e rising edge of the 750khz oscillator clock signal sets the rs flip-flop. its output turns on hs mosfet. the current sense amplifier is reset for e very switching cycle. when the hs mosfet is on, inductor current starts to increase. the current sense am plifier senses and amplifies the inductor cu rrent. since the current mode control is subject to s ub-harmonic oscillations that peak at half t he switching frequency, ramp slope compensa tion is utilized. this will help to stabilize the power supply. this ramp compens ation is summed to the current sense amplifier output and compar ed to the error amplifier output by the pwm comparator. when the sum of the cu rrent sense amplifier output and the slope compensation signal ex ceeds the ea output voltage, the rs flip-flop is reset and hs mosfet is turned off. for one whole cycle, if the sum of the current sense amplif ier output and the slope compensation signal does not exceed the ea output, then the falling edge of the oscillator clock resets the flip-flop. the output of the error amplifier increases when feedback voltage (v fb) is lower than the reference voltage of 0.8v. this also increases the induc tor current as it is proportional to the comp voltage. if in one cycle the current in the power mosfet does not reach th e comp set current value, the power mosfet will be forced to t urn off. when the hs mosfet turns off, the synchronous ls mosfet turns on unt il the next clock cycle begins. there is a ?dead time? between the hs turn off and ls turn on that prevents the switches from ?shooting through? from the input supply to ground. the voltage loop is compensated through an internal transconduct ance amplifier and can be adjusted through the external compens ation components. enable above the ?en rising threshold?, the inter nal regulator is turned on and the quiescent current can be measured above this thres hold. the enable (en) input allows the user to control turning on or off the regulator. to enable the AP65503, en must be pulled above the ?en l ockout threshold voltage? and to disable the AP65503, en must be pulled below ?en lockout threshold voltage - en lockout hysteresis? (2.2v-0.22v =1.98v). automated no-load and light-load operation the AP65503 operates in light load high effi ciency mode during light load operation. t he advantage of this light load high effi ciency mode is low power loss at no-load and light-load conditi ons. the AP65503 automatically detects the output current and enters the light load high efficiency mode. the output current reaches a critical level at which the transitions between the light-load and heavy current mode occurs . once the output current exceeds the critical level, the AP65503 transitions fr om light load high efficiency m ode to continuous pwm mode. external soft start soft start is traditionally implemented to prevent the excess inru sh current. this in turn prevents the converter output volta ge from overshooting when it reaches regulation. the AP65503 has an internal current s ource with a soft start capacitor to ramp the reference voltag e from 0v to 0.800v. the soft start current is 6a. the soft start sequence is reset when there is a thermal shutdown, under voltage lockout (uvlo) or when the part is disabled using the en pin. external soft start can be calculated from the formula below: dt dv * c ss i = where; i ss = soft start current c = external capacitor dv=change in feedback voltage from 0v to maximum voltage dt = soft start time
AP65503 document number: ds37127 rev. 1 - 2 9 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 application information (cont.) current limit protection in order to reduce the total power dissipation and to protect the application, AP65503 has cycle-by-cycle current limiting impl ementation. the voltage drop across the internal high-side mosf et is sensed and compared with the internally set current limit threshold. this voltage drop is sensed at about 30ns after the hs turns on. when the peak inductor current exceeds the set current limit threshold, current lim it protection is activated. during this time the feedback voltage (vfb) drops down . when the voltage at the fb pin reaches 0.3v, the internal o scillator shifts the frequency from the normal operating frequency of 750khz to a fold-back frequency of 102khz. the current limit is reduced to 70% of nominal current limit when the part is operating at 102khz. this low fold-back frequency prevents runaway current. under voltage lockout (uvlo) under voltage lockout is implemented to prevent the ic from in sufficient input voltages. the AP65503 has a uvlo comparator tha t monitors the input voltage and the internal bandgap reference. if the input voltage falls below 4.0v, the AP65503 will latch an under vo ltage fault. in this event the output will be pulled low and power has to be re-cycled to reset the uvlo fault. over voltage protection when the AP65503 fb pin exceeds 20% of the nominal regulation voltage of 0.800v, the over voltage comparator is tripped and the comp pin and the ss pin are discharged to gnd, forcing the high-side switch off. thermal shutdown the AP65503 has on-chip thermal protection that prevents damage to the ic when the die temperature exceeds safe margins. it imp lements a thermal sensing to monitor the operating j unction temperature of the ic. once the die temperature rises to approximately +160c , the thermal protection feature gets activated. the inter nal thermal sense circuitry turns the ic of f thus preventing the power switch from damage. a hysteresis in the thermal sense circui t allows the device to cool down to approx imately +120c before the ic is enabled again through soft start. this thermal hysteresis feature prevents undesir able oscillations of the t hermal protection circuit. setting the output voltage the output voltage can be adjusted from 0.800v to 16v using an external resistor divider. table 1 shows a list of resistor selection for common output voltages. resistor r1 is selected based on a design tr adeoff between efficiency and output voltage accuracy. for high va lues of r1 there is less current consumption in the feedback network. however the tr ade off is output voltage accuracy due to the bias current i n the error amplifier. r1 can be determined by the following equation: ? ? ? ? ? ? ? ? ? ? = 1 0.8 out v 2 r 1 r figure 3 feedback divider network table 1 resistor selection for common output voltages v out (v) r1 (k ? ) r2 (k ? ) 2.5 21.5 10 3.3 31.6 10 5 52.3 10 12 140 10
AP65503 document number: ds37127 rev. 1 - 2 10 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 application information (cont.) compensation components the AP65503 has an external comp pin through which system stabilit y and transient response can be c ontrolled. comp pin is the o utput of the internal trans-conductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to control the characteristics of the control system. the dc gain of the voltage feedback loop is given by: out fb vea cs load vdc v v a g r a = where v fb is the feedback voltage (0.800v), r load is the load resistor value, g cs is the current sense trans-conductance and a vea is the error amplifier voltage gain. the control loop transfer function incorpor ates two poles one is due to the compensation capacitor (c3) and the output resistor of error amplifier, and the other is due to the output capacitor and the load resistor . these poles are located at: vea ea p1 a 3 c 2 g f = load p2 r 2 c 2 1 f = where g ea is the error amplifier trans-conductance. one zero is present due to the compensation capacitor (c3) an d the compensation resistor (r3). this zero is located at: 3 r 3 c 2 1 f z1 = the goal of compensation design is to shape the converter transfer function to get a desired loop gain. the system crossover fr equency where the feedback loop has the unity gain is crucial. a rule of thumb is to set the crossover frequency to below one-tenth of the switching frequency. use the following procedure to optimize the compensation components: 1. choose the compensation resistor (r3) to set the desired cr ossover frequency. determine the r3 value by the following equati on: fb out cs g ea fb out cs ea v v g fs 1 . 0 2 c 2 v v g g fc 2 c 2 3 r < = where f c is the crossover frequency, which is typically less than one tenth of the switching frequency. 2. choose the compensation capacitor (c3) to achieve the desired phase margin set the compensation zero, f z1 , to below one fourth of the crossover frequency to provide sufficient phase margin. determine the c3 value by the following equation: fc 3 r 2 3 c > where r3 is the compensation resistor value. vout (v) c in /c1 (f) c out /c2 (f) rc/r3 (k ? ) cc/c3 (nf) l1 (h) 2.5 44 72 10.5 6.8 4.7 3.3 44 72 10.5 6.8 4.7 5 44 72 10.5 6.8 4.7 12 44 72 10.5 6.8 6.5 - 10 table 2 recommended component selection inductor calculating the inductor value is a critic al factor in designing a buck converter. for most designs, the following equation can be used to calculate the inductor value; sw l in out in out f ? i v ) v (v v l ? ? ? ? = where l ? i is the inductor ripple current. and sw f is the buck converter switching frequency.
AP65503 document number: ds37127 rev. 1 - 2 11 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 application information (cont.) inductor (cont.) choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current is calculated from: 2 ? i i i l load l(max) + = peak current determines the required saturation current rating, which influences the size of the inductor. saturating the induc tor decreases the converter efficiency while increasing the te mperatures of the inductor and the internal mosfets. hence choosing an inductor wit h appropriate saturation current rating is important. a 1h to 10h inductor with a dc current rating of at least 25 % percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductor ?s dc resistance should be less than 100m ? . use a larger inductance for im proved efficiency under light load conditions. input capacitor the input capacitor reduces the surge current drawn from the i nput supply and the switching noise from the device. the input ca pacitor has to sustain the ripple current produced during the on time on the upp er mosfet. it must hence have a low esr to minimize the losses . the rms current rating of the input capacitor is a critical paramet er that must be higher than the rms input current. as a rule of thumb, select an input capacitor which has rms rating that is greater than half of the maximum load current. due to large di/dt through the input capacitors, electrolytic or ceramics should be used. if a tantalum must be used, it must b e surge protected. otherwise, capacitor failure could occur. for most applications, a 44f ceramic capacitor is sufficient. output capacitor the output capacitor keeps the output voltage ripple small, ensures feedback loop stability and reduces the overshoot of the ou tput voltage. the output capacitor is a basic component for the fast response of t he power supply. in fact, during load transient, for the first few microseconds it supplies the current to the load. the converter recognizes the l oad transient and sets the duty cycle to maximum, but the curre nt slope is limited by the inductor value. maximum capacitance required can be calc ulated from the following equation: esr of the output capacitor dominates the output voltage ripple. the amount of ripple can be ca lculated from the equation below : esr * ? i vout inductor capacitor = an output capacitor with ample capacitance and low esr is the bes t option. for most applications , a 72f ceramic capacitor will be sufficient. 2 out 2 out 2 inductor out o v ) v v ( ? ) 2 ? i l(i c ? + + = where ? v is the maximum output voltage overshoot.
AP65503 document number: ds37127 rev. 1 - 2 12 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 application information (cont.) pc board layout this is a high switching frequency converter. hence attention must be paid to the switching currents interference in the layout . switching current from one power device to another can generate voltage transient s across the impedances of the interconnecting bond wires and ci rcuit traces. these interconnecting impedances shoul d be minimized by using wide, short printed circ uit traces. note that the in to gnd deco upling capacitors need to be immediately adjacent to the in and gnd pins of the device (u1), and 12 thermal vias from the back side th ermal pad to the gnd plane are essential to achieve t he best operation at full load current. figure 4 pc board layout external bootstrap diode it is recommended that an external bootstrap diode be added when the input voltage is no greater than 5v or the 5v rail is avai lable in the system. this helps to improve the efficiency of the regulator. this solution is also applicable for d > 65%. the bootstrap diod e can be a low cost one such as bat54 or a schottky that has a low v f . figure 5 external bootstrap compensation components recommended diodes: part number voltage/current rating vendor b130 30v, 1a diodes inc sk13 30v, 1a diodes inc
AP65503 document number: ds37127 rev. 1 - 2 13 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 ordering information part number package code part marking identification code tape and reel quantity part number suffix AP65503sp-13 sp so-8ep na 2500 -13 note: 9. for packaging details, go to our website at http://www.diodes.com/p roducts/packages.html marking information so-8ep
AP65503 document number: ds37127 rev. 1 - 2 14 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 package outline dimensions (all dimensions in mm.) please see ap02002 at http://www.diodes.com /datasheets/ap02002.pdf for latest version. so-8ep suggested pad layout please see ap02001 at http://www.diodes.com/dat asheets/ap02001.pdf for the latest version. so-8ep so-8ep (sop-8l-ep) dim min max typ a 1.40 1.50 1.45 a1 0.00 0.13 - b 0.30 0.50 0.40 c 0.15 0.25 0.20 d 4.85 4.95 4.90 e 3.80 3.90 3.85 e0 3.85 3.95 3.90 e1 5.90 6.10 6.00 e - - 1.27 f 2.75 3.35 3.05 h 2.11 2.71 2.41 l 0.62 0.82 0.72 n - - 0.35 q 0.60 0.70 0.65 all dimensions in mm dimensions value(in mm) c 1.270 x 0.802 x1 3.502 x2 4.612 y 1.505 y1 2.613 y2 6.500 gauge plane seating plane e1 e n e b a 45 e0 h f exposed pad bottom view l q c 7 4 3 9 (all sides) a1 d 14 85 c y1 x1 x y y2 x2
AP65503 document number: ds37127 rev. 1 - 2 15 of 15 www.diodes.com april 2014 ? diodes incorporated a p65503 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 ari sing 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 w hatsoever 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. this document is written in english but may be translated into multiple languages for reference. only the english version of t his document is the final and determinative format released by diodes incorporated. 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 ? 2014, diodes incorporated www.diodes.com

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