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ap65450 document number: ds37135 rev. 2 - 2 1 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 4a, 18v, 650khz adaptive cot step - down converter description the ap65450 is an adaptive constant on - time mode synchronous buck converter providing high efficiency, excellent transient response and high dc output accuracy for low - voltage regulation in digital tv and monitor. the constant - on - time control scheme handles wide input/output voltage ratios and provides low external component count. the internal proprietary circuit enables the device t o adopt both low equivalent series resistance (esr) output capacitors, such as sp - cap or poscap and ultra - low esr ceramic capacitors. the adaptive on - time control supports seamless transition between continuous conduction mode (ccm) at higher load condit ions and discontinuous conduction mode (dcm) at lighter load conditions. dcm allows ap65450 to maintain high efficiency at light load conditions. the ap65450 also features programmable soft - start, uvlo, otp and ocp to protect the circuit. this ic is avail able in so - 8 ep package. features ? fixed frequency emulated constant on - time control ? good stability independent of the output capacitor esr ? fast load transient response ? synchronous rectification: 65m internal high - side switch and 36m internal low - side switch ? wide input voltage range: 4.5v to 1 8 v ? output voltage range: 0.76v to 6v ? 4a continuous output current ? 650khz switching frequency ? built - in over current limit ? built - in thermal shutdown protection ? programmable soft - start ? pre - biased start - up ? totally lead - free & fully rohs compliant (n otes 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 note s: 1 . no purposely added lead. fully eu directive 2002/95/ec (rohs) & 2011/65/eu (rohs 2) compliant. 2. see http://www.diodes.com/quality/lead_free.html for more information about diodes incorporateds definitions of hal ogen - and antimony - free, "green" and lead - f ree . 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 a p 6 5 4 5 0 l 1 1 . 5 h r 1 8 . 2 5 k r 2 2 2 . 1 k c 5 0 . 1 f c 2 4 4 f c 1 2 0 f c 4 8 . 2 n f o n o f f 8 i n 4 s s 1 e n 3 v r e g 5 6 s w 7 b s t 2 f b c 3 1 f 5 g n d i n p u t o u t p u t v o u t 1 . 0 5 v v i n 1 2 v s w v r e g 5 s s e n b s g n d v i n ( t o p v i e w ) 1 2 3 4 8 7 6 5 f b s o - 8 e p
ap65450 document number: ds37135 rev. 2 - 2 2 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 pin description s pin name pin number function so - 8 ep en 1 enable input. en is a digital input that turns the regulator on or off. drive en high to turn on the regulator, drive it low to turn off. pull up with 100k resistor for automatic startup. 1f (typical) capacito side nmos switch. a 0.1f (typical) capacitor is functional block diagram figure 2 functional block diagram
ap65450 document number: ds37135 rev. 2 - 2 3 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 absolute maximum ratings ( note 4) ( @ t a = +25c, unless otherwise specified.) symbol parameter rating unit vin supply voltage - 0.3 to 20 v vreg5 vreg5 pin voltage - 0.3v to +6.0 v vsw switch node voltage - 1.0 to vin +0.3 v vbs bootstrap voltage - 0.3 to v sw +6 .0 v vfb feedback voltage - 0.3v to +6 .0 v ven enable/uvlo voltage - 0.3v to +6 .0 v vss soft - start pin - 0.3v to +6 .0 v vgnd gnd pin voltage - 0.3 to 0.3 v tst storage temperature - 65 to +150 c tj junction temperature +160 c tl lead temperature +260 c esd susceptibility (note 5 ) hbm human body model 2 kv mm machine model 200 v notes: 4 . stresses greater than the 'absolute maximum ratings' specified above may cause permanent damage to the device. these are stress ratings o nly; functional operation of the device at these or any other conditions exceeding those indicated in this specification is not im plied. device reliability may be a ffected 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 take n when handling and transporting these dev ices. thermal resistance (note 6 ) symbol parameter rating unit ja junction to ambient so - 8ep 70 c/w jc junction to case so - 8ep 30 c/w note: 6 . test condition: so - 8: device mounted on 1"x1" fr - 4 substrate pcb, 2oz copper, with minimum recommended pad layout. recommended operating conditions ( note 7) ( @ t a = +25c, unless otherwise specified.) symbol parameter min max unit v in supply voltage 4. 5 1 8 .0 v t j operating junction temperature range - 40 + 12 5 c t a operating ambient temperature range - 40 +85 c note: 7 . the device function is not guaranteed outside of the recommended operating conditions.
ap65450 document number: ds37135 rev. 2 - 2 4 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 electrical characteristics (@ t a = +25c, v in = 12v, unless otherwise specified.) parameter symbol conditions min typ max unit supply voltage (vin pin) input voltage v in 4.5 1 8 v quiescent current i q v fb =0.85v 0. 9 ma shutdown supply current i shdn v en =0v 3.6 10 a under voltage lockout uvlo threshold v uvlo v in rising test vreg5 voltage 3.45 3.75 4.05 v uvlo hysteresis v hys v in falling test vreg5 voltage 0.19 0.32 0.45 v enable (en pin) en high - level input voltage v enh 1.9 v en low - level input voltage v enl 0.6 v voltage reference (fb pin) feedback voltage v fb v out =1.05v 0.753 0.765 0.777 v feedback bias current i fb v fb =0.8v - 0.1 0 0.1 a vreg5 output vreg5 output voltage v vreg5 6.0v ap65450 document number: ds37135 rev. 2 - 2 5 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 typical performance characteristics (@ t a = +25c, v in = 12v, v out = 3.3v, unless otherwise specified.) 85?c - 40?c 25?c 85?c 25?c - 40?c v in =18v i o = 1 a i o = 10m a v in =12v v in =4.5v
ap65450 document number: ds37135 rev. 2 - 2 6 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 typical performance characteristics ( cont.) ( @ t a = +25c, v in = 12v, v out = 1 . 05 v, unless otherwise specified.) v o =3.3v v o = 5v v o = 3.3v v o = 2.5v v o = 1.05v v o = 1.2v v o = 1.5v v o = 1.8v v o =2.5v v o =1.8v v o =1.5v v o =5v v o = 5v v o = 3.3v v o = 2.5v v o = 1.8v v o = 1.5v v o = 1.05v v o = 1.2v v o =1.05v v o =1.2v v o = 3.3v v o = 1.8v v o = 1.05v
ap65450 document number: ds37135 rev. 2 - 2 7 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 typical performance characteristics ( cont.) ( @ t a = +25c, v in = 12v, v out = 1.05v, l = 1.5h, c1 = 20f, c2 = 44 f, unless otherwise specified.) steady state test 4a time - 1s/div startup through vin no load time - 500s/div startup through vin 4a load time - 500s/div startup with vreg5 no load time - 1ms/div shutdown through vin no load time - 50ms/div shutdown through vin 4a load time - 200s/div startup through ven no load time - 2ms/div startup through ven 4a load time - 2ms/div short circuit test time - 100s/div shutdown through ven no load time - 20ms/div shutdown through ven 4a load time - 20ms/div short circuit recovery time - 1ms/div dcm voltage ripple (io=30ma) time - 1s/div voltage ripple at output (io=4a) time - 400ns/div voltage ripple at input (io=4a) time - 400ns/div vin (12v/div ) v out (1v/div ) iout (1 a /div ) sw (1 0v /div ) vin (12v/div ) v out (1v/div ) iout ( 4a /div ) sw (1 0v /div ) vin (12v/div ) v out (1v/div ) iout ( 4a /div ) sw (1 0v /div ) vin (12v/div ) v out (1v/div ) iout ( 1a /div ) sw (1 0v /div ) v e n (3 v/div ) v out (1v/div ) iout ( 1a /div ) sw (1 0v /div ) v e n (3 v/div ) v out (1v/div ) iout ( 4a /div ) sw (1 0v /div ) v e n (3 v/div ) v out (1v/div ) iout ( 4a /div ) sw (1 0v /div ) v e n (3 v/div ) v out (1v/div ) iout ( 1a /div ) sw (1 0v /div ) v out ( 500m v/div ) iout ( 2a /div ) v out ( 500m v/div ) iout ( 2a /div ) vin _ac (500m v/div ) v out_ac (50m v/div ) iout ( 4a /div ) sw ( 5v /div ) v out_ac (50m v/di v) sw ( 5v /div ) vout_ac ( 20m v/div ) sw ( 5v /div ) v in_ac ( 100m v/div ) sw ( 5v /div ) e n ( 3 v/div ) v reg5 ( 5 v/div ) vout ( 500mv /div )
ap65450 document number: ds37135 rev. 2 - 2 8 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 application information figure 3 typical application of ap 65450
ap65450 document number: ds37135 rev. 2 - 2 9 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 application information (cont.) power save mode the ap65450 is designed with power save mode (psm) at light load conditions for high efficiency. the ap65450 automatically re duces the switching frequency and change the ton time to tmin - on time during a light load condition to get high efficiency and low output ripple . as the output current decreases form heavy load condition, the inductor current decreases as well, eventually comes close to zero cu rrent, which is the boundary between ccm and dcm. the low side mosfet is turned off when the inductor current reaches zero level. the load is provided only by output capacitor, when fb voltage is lower than 0.76v, the next cycle on cycle is beginning. the on - time is the minimum on time that benefit for decreasing v out ripple at light load condition. when the output current in creases from light to heavy load, the switching frequency increases to keep output voltage. the transition point to light load operation can be calculated using the following equation: t on is on - time enable above the en high - level input voltage, the internal regulator is turned on and the quiescent current can be measured above this threshold. the enable (en) input allows the user to control turning on or off the regulator. to enable the ap65450, en must be pulled above the en high - level input voltage and to disable the ap65450, en must be pulled below en low - level input voltage. in figure 3, en has a positive voltage through a 100k? pull - up to vin. no supply input is required for en. soft - start the soft - start time of the ap65450 is programmable by selecting different c ss value. when the en pin becomes high, the c ss is charged by a 6a current source, generating a ramp signal fed into non - inverting input of the error comparator. reference voltage v ref or the internal soft - start voltage ss whichever is smaller dominates the behavior of the non - inverting inputs of the error amplifier. accordingly, the output voltage will follow the ss signal and ramp up smoothly to its target level. the capacitor value required for a g iven soft - start ramp time can be expressed as: where c ss is the required capacitor between ss pin and gnd, t ss is the desired soft - start time and v fb is the feedback voltage. over current protection (ocp) figure 4 shows the over current protection (ocp) scheme of ap65450. in each switching cycle, the inductor current is sensed by monitoring the low - side mosfet in the off period. when the voltage between gnd pin and sw pin is smaller than the over current trip level, the ocp will be trig gered and the controller keeps the off state. a new switching cycle will begging when the measured voltage is larger than limit voltage. the internal counter is incremented when ocp is triggered. after 16 sequential cycles, the internal ocl (over curren t logic) threshold is set to a lower level, reducing the available output current. when a switching cycle occurs where the switch current is below the lower ocl threshold, the counter is reset and ocl limit is returned to higher value. because the r ds(on ) of mosfet increases with temperature, v limit has xppm/ c temperature coefficient to compensate this temperature dependency of r ds(on) . figure 4 over current protection scheme under voltage lockout the ap65450 provides an under voltage lockout circuit to prevent it from undefined status when startup. the uvlo circuit shuts down the device when v in drops below 3.45v. the uvlo circuit has 320mv hysteresis, which means the device starts up again when v reg rise to 3.75v (non - latch) . thermal shutdown if the junction temperature of the device reaches the thermal shutdown limit of 160 c, the ap65450 shuts itself off, and both hmos and lmos will be turned off. the output is discharge with the internal transistor. when the junction cools to the required level (130c nominal), the devi ce initiates soft - start as during a normal power - up cycle. on t v ? ? ? 2l out in v load i ss fb ss c ss t i v ? ? o c c o m p a r a t o r - 2 6 6 m v q 1 q 2 s q r
ap65450 document number: ds37135 rev. 2 - 2 10 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 application information (cont.) setting the output voltage the output voltage can be adjusted from 1.000 to 5v 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 tradeoff between efficiency and output voltage accuracy. for high values of r1 there is less current consumption in the feedback network. however the trade - off is output voltage accuracy due to the bias current in the error amplifier. r1 can be determined by the following equation: inductor calculating the inductor value is a critical factor in designing a buck converter. for most designs, the following equation can be used to calculate the inductor value; where is the inductor ripple current , and is the buck converter switching frequency. choose the inductor ripple current to be 30% of the maximum load current. the maximum inductor peak current is calculated from: peak current determines the required saturation current rating, which influences the size of the inductor. saturating the inductor decreases the converter efficiency while increasing the temperatures of the inductor and the internal mosfets. hence choosing an inductor w ith appropriate saturation current rating is important. a 1h to 3.3h inductor with a dc cu rrent rating of at least 25% percent higher than the maximum load current is recommended for most applications. for highest efficiency, the inductors dc resistance should be less than 100m. use a larger inductance for im proved efficiency under light loa d conditions. the phase boost can be achieved by adding an additional feed forward capacitor (c7) in parallel with r1. output voltage (v) c7(pf) l1(h) c8+c9(f) 1 ? ? ? ? table 2 recommended component selection figure 5 . feedback divider network output voltage (v) r1 (k) r2 (k) 1 6.81 22.1 1.05 8.25 22.1 1.2 12.7 22.1 1.5 21.5 22.1 1.8 30.1 22.1 2.5 49.9 22.1 3.3 73.2 22.1 5 124 22.1 table 1 resistor selection for common output ? ? ? ? ? ? ? ? ? 1 0.765 v r r out 2 1 l i 2 i i i l load l(max) ? ? sw f sw l in out in out f i v ) v (v v l ? ? ? ? ?
ap65450 document number: ds37135 rev. 2 - 2 11 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 application information (cont.) input capacitor the input capacitor reduces the surge current drawn from the input supply and the switching noise from the device. the input capacitor has to sustain the ripple current produced during the on time on the upper mosfet. it must have a low esr to minimize the losses. the rms current rating of the input capacitor is a critical parameter that must be higher than the rms input curren t. as a rule of thumb, select an input capacitor which has an 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, greater than 10f 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 output voltage. the output capacitor is a basic component for the fast response of the power supply. in fact, during load transient, for the firs t few microseconds it supplies the current to the load. the converter recognizes t he load transient and sets the duty cycle to maximum, but the current slope is limited by the inductor value. maximum capacitance required can be calculated from the following equation: esr of the output capacitor dominates the output voltage ripple. the amount of ripple can be calculated from the equation below: an output capacitor with ample capacitance and low esr is the best option. for most applications, a 22 f to 68 f ceramic capacitor will be sufficient . where is the maximum output voltage overshoot. bootstrap capacitor to ensure the proper operation, a ceramic capacitor must be connected between the vbst and sw pin. a 0.1f ceramic capacitor is sufficient. vreg5 capacitor to ensure the proper operation, a ceramic capacitor must be connected between the vreg5 and gnd pin. a 1f ceramic capacitor is sufficient. . pc board layout 1. the ap65450 works at 4a load current, heat dissipation is a major concern in layout the pcb. a 2oz copper in both top and bot tom layer is recommended. 2. provide sufficient vias in the thermal exposed pad for heat dissipate to the bottom layer. 3. provide sufficient vias in the output capacitor gnd side to dissipate heat to the bottom layer. 4. make the bottom layer under the device as gnd layer for heat dissipation. the gnd layer should be as large as possible to provide better thermal effect. 5. make the vin capacitors as close to the device as possible. 6. make the vreg5 capacitor as close to the device as possible. 7. the thermal pad of the device should b e soldered directly to the pcb exposed copper plane to work as a heatsink. the thermal vias in the exposed copper plane increase the heat transfer to the bottom layer. 2 out 2 out 2 inductor out o v ) v v ( ) 2 i l(i c ? ? ? ? v esr * i vout inductor capacitor ?
ap65450 document number: ds37135 rev. 2 - 2 12 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 figure 6 pc board layout ordering information part number package code part marking tape and reel quantity part number suffix ap 65450 sp - 13 sp so - 8ep 2500 - 13 marking information (1) so - 8 ep package outline dimensions (all d imensions in mm . ) please see ap02002 at http://www.diodes.com/datasheets/ap02002.pdf for the latest version. (1) so - 8 ep 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 a p 6 5 4 5 0 x x - 1 3 p a c k i n g p a c k a g e s p : s o - 8 e p 1 3 : t a p e & r e e l ( t o p v i e w ) a p 6 5 4 5 0 y y w w x l o g o p a r t n o 5 8 4 1 e w w : w e e k : 0 1 ~ 5 2 ; 5 2 y y : y e a r : 0 8 , 0 9 , 1 0 ~ g : g r e e n r e p r e s e n t s 5 2 a n d 5 3 w e e k e : s o - 8 e p b l a n k s o - 8 x x : i n t e r n a l c o d e 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 1 4 8 5
ap65450 document number: ds37135 rev. 2 - 2 13 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 suggested pad layout please see ap02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. (1) so - 8 ep 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 c y1 x1 x y y2 x2
ap65450 document number: ds37135 rev. 2 - 2 14 of 14 www.diodes.com november 2014 ? diodes incorporated ap65450 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 other c hanges without further notice to this document and any product described herein. diodes incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does diodes incorporated convey any license unde r its patent or trademark rights, nor the rights of others. any customer or user of this document or products described 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 diod es incorporated website, harmless against all damages. diodes incorporated do es not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel. should customers purchase or use diodes incorporated products for any unintended or unauthorized application, customers shall indemni fy and hold diodes incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising ou t of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized applicat ion. products described herein may be covered by one or more united states, international or foreign patents pending. product nam es and markings noted herein may also be covered by one or more united states, international or foreign trademarks. this doc ument is written in english but may be translated into multiple languages for reference. only the english version of this do cument is the final and determinative format released by diodes incorporated. life support diodes incorporated products are speci fically 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 system s 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 i n 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 expe cted to cause the failure of the life support device or to affect its safety or effectiveness. custom ers represent that they have all necessary expertise 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, regulatory and safety - related requirements c oncerning 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, cus tomers 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 ? 2014, diodes incorporated www.diodes.com

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