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AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 1 of 15 www.diodes.com july 2010 ? diodes incorporated new product description the AP5101 is a current mode step-down converter with a built-in power mosfet to enable smallest solution size power conversion. with the low series resistance power switch it enables a constant output current of up to 1.5a over a wide input supply range. the load and line regulation has excellent response time over the operating input vo ltage and temperature range. the AP5101 is self protected, through a cycle-by-cycle current limiting algorithm and an on chip thermal protection. the AP5101 will provide the voltage conversion with a low count of widely available st andard external components. the AP5101 is available in so-8 package. pin assignments so-8 ( top view ) 1 2 3 4 8 7 6 5 gnd bst fb comp sw gnd en in features ? v in 4.75 to 22v ? 1.5a peak output current ? stable with low esr ceramic output capacitors ? external compensation ? up to 92% efficiency ? 0.1a shutdown mode ? fixed 1.4mhz frequency ? thermal shutdown ? cycle-by-cycle over current protection ? output adjustable from 0.81v to 15v ? so-8: available in ?green? molding compound (no br, sb) ? lead free finish/ rohs compliant (note 1) applications ? distributed power systems ? battery charger ? pre-regulator for linear regulators ? wled driver note: 1. eu directive 2002/95/ec (rohs). all applicable rohs exemptions applied. please visit our website at http://www.diodes.com/products/lead_free.html . typical application circuit 1 7 2 6 4,8 5 3 in en gnd comp fb sw bst AP5101 output 3.3v 1.5a c2 c3 r3 r2 c4 l1 input 4.75v to 22v r1 c1 on off d1 figure 1 typical application circuit
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 2 of 15 www.diodes.com july 2010 ? diodes incorporated new product typical application circuit (continiued) 6 in en gnd comp fb sw bst AP5101 output 3.3v 1.5a c2 22f/6.3v ceramic x2 c3 3nf r3 5.6k r2 16.2k 1% c4 10nf l1 4.7uh input 4.75v to 22v r4 100k r1 49.9k 1% c1 10uf/25v ceramic 4,8 3 2 5 1 7 d1 b340a figure 2. 1.4mhz, 3.3v output at 1.5a step-down converter
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 3 of 15 www.diodes.com july 2010 ? diodes incorporated new product pin descriptions so-8 ( top view ) 1 2 3 4 8 7 6 5 gnd bst fb comp sw gnd en in pin name pin number descriptions sw 1 switch output. this is the reference for the floating top gate driver. in 2 supply voltage. the AP5101 operates from a +4.75v to +22v unregulated input. a decoupling capacitor c1 is required to prevent large voltage spikes from appearing at the input. place this capacitor near the ic. en 3 on/off control input. do not leave this pi n floating. to turn the device on, pull en above 1.2v and to turn it off pull below 0.4v. if enable/disable is not used, connect a 100k ? resistor between en to v in . gnd 4 ground. this pin is the voltage refere nce for the regulated output voltage. for this reason care must be taken in its layout. this node should be placed outside of the d1 to c1 ground path to prevent switching current spikes from inducing voltage noise into the part. fb 5 feedback. to set the output voltage, con nect this pin to the output resistor divider or directly to v out . to prevent current limit run away during a current limit condition, the frequency foldback comparator lowers the oscillator frequency when the fb voltage is below 400mv. comp 6 compensation. comp is used to compensate the regulation control loop. connect a series rc network from comp to gnd. bst 7 bootstrap. to form a boost circuit, a capacitor is connected between sw and bst pins to form a floating supply ac ross the power switch driver. this capacitor is needed to drive the power switch?s gate above the supply voltage. typical values for c bst range from 0.1uf to 1uf. gnd 8 ground. this pin is the voltage refere nce for the regulated output voltage. all control circuits are referenced to this pin. for this reason care must be taken in its layout.
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 4 of 15 www.diodes.com july 2010 ? diodes incorporated new product absolute maximum ratings (note 2) symbol parameter rating unit v in supply voltage 26 v v sw switch voltage ?0.3 to v in + 0.3 v v bs boost voltage v sw + 6 v all other pins ?0.3 to +6 v t st storage temperature -65 to +150 c t j junction temperature +150 c t l lead temperature +260 c esd susceptibility hbm human body model 2 kv mm machine model 200 v note: 2. exceeding these ratings may damage the device. thermal resistance (note 3) symbol parameter rating unit ja junction to ambient 120 c/w jc junction to case 15 c/w note: 3. test condition for so-8: measur ed on approximately 1? square of 1 oz copper. recommended operating conditions (note 4) symbol parameter min max unit v in supply voltage 4.75 22 v t a operating ambient temperature range -40 +85 c v out output voltage 0.81 15 v note: 4. the device function is not guaran teed outside of the recommended operating conditions.
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 5 of 15 www.diodes.com july 2010 ? diodes incorporated new product electrical characteristics (v in = 12v, t a = +25c, unless otherwise noted) note: 5. guaranteed by design symbol parameter test conditions min typ. max unit v fb feedback voltage 4.75v v in 22v 0.790 0.810 0.830 v i fb feedback current v fb = 0.8v 0.1 a r ds(on) switch-on resistance (note 5) 0.35 ? switch leakage v en = 0v, v sw = 0v 10 a current limit (note 5) 2.5 a g cs current sense transconductance output current to comp pin voltage 1.3 a/v a vea error amplifier voltage gain (note 5) 400 v/v g ea error amplifier transconductance ic = 10a 850 ua/v f sw oscillator frequency v fb = 0.6v 1.1 1.4 1.7 mhz fold-back frequency v fb = 0v 500 khz maximum duty cycle v fb = 0.6v 65 % t on minimum on-time (note 5) 100 ns under voltage lockout threshold rising 3.8 4.0 4.2 v under voltage lockout threshold hysteresis 100 mv en input low voltage 0.4 v en input high voltage 1.2 v en input current v en = 2v 2.1 a v en = 0v 0.1 a i s supply current (shutdown) v en = 0v 0.1 1.0 a i q supply current (quiescent) v en = 2v, v fb = 1v 0.5 0.7 ma thermal shutdown (note 5) 150 c
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 6 of 15 www.diodes.com july 2010 ? diodes incorporated new product typical performance characteristics v in =12v, v out =3.3v, l =4.7uh, c1=10uf, c2=22uf, ta=+25 ? c, unless otherwise noted. steady state test i out =0.5a time- 1us/div load transient test i out =0.2a to 0.8a. step at 0.8a/us time- 100us/div start-up through enable (no load) time- 50us/div start-up through enable (i out =1a, resistive load) time- 50us/div shutdown through enable (no load) time- 50us/div shutdown through enable (i out =1a, resistive) time- 50us/div
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 7 of 15 www.diodes.com july 2010 ? diodes incorporated new product typical performance characteristics (continued) v in =12v, v out =3.3v, l =4.7uh, c1=10uf, c2=22uf, ta=+25 ? c, unless otherwise noted. short circuit entry time- 50us/div short circuit recovery time- 100us/div current sense transconductance (gcs) gcs= 1.5a/(comp2-comp1)=1.5a/(1.8-0.65) =1.3a/v time- 2us/div
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 8 of 15 www.diodes.com july 2010 ? diodes incorporated new product applications information operation the AP5101 is a current mode control, asyn chronous buck regulator. current mode control assures excellent line and load regulation and a wide loop bandwidth for fast response to load transients. figure. 3 depicts the functional block diagram of AP5101. the operation of one switchin g can be explained as follows. at the beginning of each cycle, hs (high-side) mosfet is off. the ea output voltage is higher than the current sense amplifier output, and the current co mparator?s output is low. the rising edg e of the 1.4mhz oscillator clock signal sets t he rs flip-flop. its output turns on hs mosfet. when the hs mosfet is on, inductor curr ent starts to increase. the current se nse amplifier senses and amplifies the inductor current. since the current mode control is subject to sub-harmonic oscillations that peak at half the switching frequency, ramp slope compensation is utilized. this will help to stabilize the power supply. this ramp compensation is summed to the current sense amplifier output and compared to t he error amplifier output by the pwm comparator. when the sum of the current sense amplifier out put and the slope compensation signal exce eds the ea output volt age, the rs flip- flop is reset and hs mosfet is turned off. the external schottky rectifier diode (d1) co nducts the inductor current. for one whole switching cycle, if the sum of the current sens e amplifier 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 vo ltage of 0.81v. this also in creases the inductor current as it is proportional to the ea voltage. regulator reference ramp generator oscillator 1.4mhz/500khz rsen 25mo + - current sense amplifier r s q r driver regulator 7 1 5 4 3 2 in en fb gnd + - ea error amplifier + - + - bst sw pwm comparator current limit comparator 6 comp 8 gnd figure 3. functional block diagram
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 9 of 15 www.diodes.com july 2010 ? diodes incorporated new product applications information (continued) component selection the output voltage can be adjusted from 0.81v to 15v using an external resistor divider. table 1 shows a list of resistor selection for common output voltages. resistor r1 is se lected 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 cu rrent in the error amplifier. r2 can be determined by the following equation: ? ? ? ? ? ? ? ? ? = 1 0.81 out v 2 r 1 r v out (v) r 1 (k ? ) r 2 (k ? ) 1.8 80.6 (1%) 64.9 (1%) 2.5 49.9 (1%) 23.7 (1%) 3.3 49.9 (1%) 16.2 (1%) 5.0 49.9 (1%) 9.53 (1%) table 1. resistor selection for common output voltage compensation components the AP5101 has an external comp pin through which system stability and transient response can be controlled. comp pin is the output of the internal tr ans-conductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to control the characteristi cs of the control system. the dc gain of the voltage feedback loop is given by: out v fb v vea a cs g load r vdc a = where v fb is the feedback voltage (0.810v), r load is the load resistor value, g cs is the current sens e trans-conductance and a vea is the error amplifier voltage gain. the control loop transfer function incorporates two poles. o ne 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 a3c2 ea g p1 f = load r2c2 1 p2 f = where g ea is the error amplifier trans-conductance. one zero is present due to the compensation capacitor (c3) and the compensation resistor (r3). this zero is located at: 3r3c2 1 z1 f =
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 10 of 15 www.diodes.com july 2010 ? diodes incorporated new product applications information (continued) the goal of compensation design is to shape the converter transfer function to get a desired loop gain. the system crossover frequency 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 switch ing frequency. use the following procedure to optimize the compensat ion components: 1. choose the compensation resistor (r3) to set the desired crossover frequency. determine the r3 value by the following equation: fb v out v cs g ea g fs1.02c2 fb v out v cs g ea g fc2c2 3r < = where f c is the crossover frequency, which is typicall y less than one-tenth of the switching frequency. 2. choose the compensation capacitor (c3) to achiev e the desired phase margin. set the compensation zero, f z1 , to below one-fourth of the crossover frequency to provide sufficient ph ase margin. determine the c3 value by the following equation: fc3r 2 3c > where r3 is the compensa tion resistor value. 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 f l i in v ) out v in (v out v l ? = where l i is the inductor ripple current. and f sw 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: 2 l i load i l(max) i += peak current determines the required saturation current rating, which influences the size of the inductor. saturating the inductor decreases the converter efficiency while increasing t he temperatures of the inducto r, the mosfet and the diode. hence choosing an inductor with 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 200m ? . use a larger inductance for improved efficiency under light load conditions.
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 11 of 15 www.diodes.com july 2010 ? diodes incorporated new product applications information (continued) input capacitor the input capacitor reduces the surge current drawn from the i nput supply and the switching noise from the device. the input capacitor has to sustain the ripple curre nt produced during the on time on the upper mosfet. it must hence have a low esr to minimize the losses. due to large di/dt through the input capacitors, electrolytic or ceramics should be used. if a tant alum must be used, it must b e surge protected. otherwise, capacitor failure could occur. for most applications, a 4.7f ceramic capacitor is sufficient. output capacitor the output capacitor keeps the output voltage ripple small, ensur es feedback loop stability and reduces the overshoot of the output voltage. the output capacitor is a basic component for t he fast response of the power supply. in fact, during load transient, for the first few microseconds it supplies the current to the load. the converter recognizes the load transient and sets the duty cycl e to maximum, but the current slope is limited by the inducto r value. maximum capacitance required can be calc ulated from the following equation: 2 out v 2 ) out v v( 2 ) 2 inductor i out l(i o c ?+ + = where v is the maximum output voltage overshoot. esr of the output capacit or dominates the output voltage ripple. the amount of ripple can be calculated from the equation below: esr inductor i capacitor vout = an output capacitor with ample capacitance and low esr is the best option. for most applications, a 22f ceramic capacitor will be sufficient. external diode the external diode?s forward current must not exceed the maximu m output current. since power dissipation is a critical factor when choosing a diode, it can be calculated from the equation below: 0.3v out i) in v out v (1 diode p ?= note: 0.3v is the voltage drop across the schottky diode. a di ode that can withstand this power dissipation must be chosen. pc board layout this is a high switching frequency converte r. hence attention must be paid to the sw itching currents interference in the layout . switching current from one power device to another can generate voltage transients ac ross the impedances of the interconnecting bond wires and circuit traces. these interconnecting impedances should be minimized by using wide, short printed circuit traces. the input capacitor needs to be as clos e as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin.
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 12 of 15 www.diodes.com july 2010 ? diodes incorporated new product applications information (continued) external bootstrap diode it is recommended that an external bootstrap diode be added when t he input voltage is no greater than 5v or the 5v rail is available in the system. this helps improve the efficiency of t he regulator. the bootstrap diode can be a low cost one such as in4148 or bat54. AP5101 bst sw 10nf boost diode 5v 7 1 figure 4. external bootstrap diode manufacturer part number inductance(h) max dcr (? ) current rating (a) dimensions l x w x h (mm 3 ) toko a921cy-4r7m 4.7 0. 027 1.66 6.0 x 6.3 x 3.0 sumida cdrh4d28c/ld 4.7 0. 036 1.50 5.1 x 5.1 x 3.0 wurth electronics 7440530047 4.7 0.038 2.00 5. 8 x 5.8 x 2.8 table 2. suggested surface mount inductors
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 13 of 15 www.diodes.com july 2010 ? diodes incorporated new product ordering information AP5101 s g - 13 package packing green g : green s : so-8 13 : tape & reel device package code packaging (note 6) 13? tape and reel quantity part number suffix AP5101sg-13 s so-8 2500/tape & reel -13 note: 6. pad layout as shown on diodes inc. suggest ed pad layout document ap02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. marking information ( top view ) AP5101 yy ww x x logo part no 5 8 4 1 ww : week : 01~52; yy : year : 10, 11, 12~ g : green x : internal code 52 represents 52 and 53 week
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 14 of 15 www.diodes.com july 2010 ? diodes incorporated new product package outline dimensions (all dimensions in mm) 1.27typ 0.3/0.5 7~9 4.85/4.95 3.85/3.95 5.90/6.10 0.15/0.25 7~9 0.62/0.82 0.10/0.20 gauge plane 0.254 seating plane 0.35max. 45 detail "a" detail "a" 1.30/1.50 1.75max. land pattern recommendation (unit: mm) 6x-1.27 8x-1.55 8x-0.60 5.4 0/8
AP5101 1.5a step-down converter with 1.4mhz switching frequency AP5101 document number: ds32258 rev. 1 - 2 15 of 15 www.diodes.com july 2010 ? 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 rese rve the right to make modifications, enhanc ements, 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 an y product described herein; neither does diodes incorporated convey any license under its patent or trademark rights, nor the rights of othe rs. 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 incorp orated website, harmless against all damages. diodes incorporated does not warrant or accept any liability what soever in respect of any prod ucts purchased through unauthoriz ed sales channel. should customers purchase or use diodes in corporated products for any unintended or unauthorized application, customers shall indemnify and hold diodes incorporated and its representatives har mless against all claims, damages, expenses, and attorney fee s arising out of, directly or indirectly, any claim of personal injury or death a ssociated 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 specifica lly not authorized for use as critical co mponents 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 pr operly used in accordance with instructions for use provided in the labeling can be reasonably expected to re sult 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 t he safety and regulatory ramifications of their life support dev ices or systems, and acknowledge and agree that they are solely responsi ble for all legal, regulatory and safety-related requirements concerning their products and any use of diode s incorporated products in such safety-cri tical, 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 repr esentatives against any damages ar ising out of the use of diodes incorporated products in such safety-c ritical, life support devices or systems. copyright ? 2010, diodes incorporated www.diodes.com

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