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ap1538 18v 3a 300khz buck converter ap1538 rev. 5 1 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated ? input voltage : 3.6v to 18v ? output voltage : 0.8v to v cc ? output current : up to 3a ? duty ratio: 0% to 99% pwm control ? oscillation frequency: 300khz typical ? soft-start like, current limit and enable function ? thermal shutdown function ? built-in internal sw p-channel mos ? sop-8l and sop-8l-dep: available in ?green? molding compound (no br, sb) ? lead free finish / rohs compliant (note 1) ap1538 consists of step-down switching regulator with pwm control. these devices include a reference voltage source, oscillation circuit, error amplifier, internal pmos. ap1538 provides low-ripple power, high efficiency, and excellent transient characteristics. the pwm control circuit is able to vary the duty ratio linearly from 0 up to 99%. this converter also contains an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. an enable function, an over current protect function and a short circuit protect function are built inside, and when ocp or scp happens, the operation frequency will be reduced from 300khz to 50khz. also, an internal compensation block is built in to minimum external component count. with the addition of an internal p-channel power mos, a coil, capacitors, and a diode connected externally, these ics can function as step-down switching regulators. they serve as ideal power supply units for portable devices when coupled with the sop-8l and sop-8l-dep mini-packages, providing such outstanding features as low current consumption. since this converter can accommodate an input voltage up to 18v, it is also suitable for the operation via an ac adapter. ? pc motherboard ? lcd monitor ? graphic card ? dvd-video player ? telecom equipment ? adsl modem ? printer and other peripheral equipment ? microprocessor core supply typical application circuit ap 1538 + - v ss en cc r a r b d1 ** fb vcc output cvcc v out = 5v/3a v in r ocset ocset c out c in option * c ocset c en r en option 100k l1 22uh 6.8k 1.3k 3k 0.1uf + - c 0.1uf 470uf *** 470uf 0.1uf notes: * typical feedback compensation (cc): 5600pf. ** suggested diodes power schottky p/n: b540 series or pds540. *** suggested c out for v out < 1v; 680uf. v out = v fb x ( 1+ r a /r b ) r b = 0.7k~5k ohm features general description applications
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 2 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated ordering information ap 1538 xxx g - 13 package packing s : sop-8l green 13 : tape & reel g : green sdp : sop-8l-dep device package code packaging (note 2) 13? tape and reel quantity part number suffix ap1538sg-13 s sop-8l 2500/tape & reel -13 AP1538SDPG-13 sdp sop-8l-dep 2500/tape & reel -13 notes: 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 2. pad layout as shown on diodes inc. suggested pad layout document ap02001, which can be found on our website at http://www.diodes.com/datasheets/ap02001.pdf. pin assignments (1) sop-8l (2) sop-8l-dep (dual exposed pads) 1 2 3 4 8 7 6 5 fb output ocset output en vss vss v cc ( top view ) 1 2 3 4 8 7 6 5 fb output ocset output en vss vss v cc 1 2 ( top view ) (note 3) notes: 3. exposed pad 1 is connected to vss and exposed pad 2 is connected to output. the board layout for exposed pads needs to be considered to avoid short circuit.
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 3 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated pin descriptions pin name pin no. description fb 1 feedback pin en 2 power-off pin h: normal operation (step-down operation) l: step-down operation stopped (all circuits deactivated) ocset 3 add an external resist or to set max output current v cc 4 ic power supply pin output 5, 6 switch pin. connect external inductor/diode here. minimize trace area at this pin to reduce emi v ss 7, 8 gnd pin block diagram oscillation circuit reference voltage source with soft start pwm-switched control circuit + - vss v en en 90ua ocset fb vcc thermal shutdown output
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 4 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated absolute maxi mum ratings symbol parameter rating unit esd hbm human body model esd protection 5.5 kv esd mm machine model esd protection 200 v v cc v cc pin voltage v ss - 0.3 to v ss + 20 v v fb feedback pin voltage v ss - 0.3 to v cc v v en en pin voltage v ss - 0.3 to v cc v v out switch pin voltage v ss - 0.3 to v cc v p d power dissipation internally limited mw t j operating junction temperature range -40 to +125 o c t st storage temperature range -65 to +150 o c caution: the absolute maximum ratings are rated values exceeding which the product could suffer physical damage. these values must therefore not be exceeded under any conditions. recommended oper ating conditions symbol parameter min max unit v in input voltage (note 4) 3.6 18 v i out output current 0 3 a t a operating ambient temperature -20 +85 o c notes: 4. for the operations in low input voltage, ap1538 can tolerate down to 3.6v but max output current loading will be le ss than 3a. for nominal applications in such low input voltage range, especially lower than 4v, a higher rocset with larger heat sink is recommended.
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 5 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated electrical characteristics (v in = 12v, t a = 25c, unless otherwise specified) symbol parameter conditions min typ. max unit v fb feedback voltage i out = 0.1a 0.784 0.8 0.816 v i fb feedback bias current i out = 0.1a - 0.1 0.5 a i shdn current consumption during power off v en = 0v - 10 - a ? v out / v in line regulation v in = 5v~18v - 1 2 % ? v out / v out load regulation i out = 0.1 to 3a - 0.2 0.5 % f osc oscillation frequency measure waveform at sw pin 240 300 400 khz f osc1 frequency of current limit or short circuit protection measure waveform at sw pin - 50 - khz v ih en pin input voltage evaluate oscillation at sw pin 2.0 - - v v il evaluate oscillation stop at sw pin - - 0.8 i sh en pin input leakage current en pin high - 20 - a i sl en pin low - -10 - a i ocset ocset pin bias current -- 75 90 105 a r ds(on) internal mosfet r ds(on) v in =5v, v fb =0v - 110 - m ? v in =12v, v fb =0v - 70 - effi efficiency v in =12v, v out = 5v i out =3 a - 92 - % t shdn thermal shutdown threshold - 150 - c t hys thermal shutdown hysteresis - 55 - c jc thermal resistance junction-to-case sop-8l (note 5) - 24 - o c/w sop-8l-dep (note 5) - 26 - notes: 5. test condition for sop-8l and sop-8l-dep: devices mounted on 2oz copper, minimum recommended pad layout on top & bo ttom layer with thermal vias, double sided fr-4 pcb.
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 6 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated typical perform ance characteristics v in vs. frequency (v out = 3.3v, i out = 0.2a) 306 308 310 312 314 316 318 320 322 324 326 0 2 4 6 8 10 12 14 16 18 v in (v) f os c (khz) v in vs . v fb (v out = 3.3v, i out = 0.2a) 0.780 0.785 0.790 0.795 0.800 0.805 0.810 0.815 0.820 024681012141618 v in (v) v fb (v) line regulation (v out = 3.3v, i out = 0.2a) 3.00 3.05 3.10 3.15 3.20 3.25 3.30 3.35 3.40 024681012141618 v in (v) v out (v) load regulation (v in = 12v ) 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 3.33 3.34 3.35 0.0 0.5 1.0 1.5 2.0 2.5 3.0 i out (a) v out (v) efficiency (v in = 12v ) 0 10 20 30 40 50 60 70 80 90 100 0.0 1.0 2.0 3.0 i out (a) efficiency (%) vout=3.3v vout=5v switch current limit (t a = 25c) 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 0 2 4 6 8 10 12 14 16 18 v in (v) current limit (a) rocset=6.8k rocset=3.9k
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 7 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated typical performance characteristics (continued) current limit vs. temperature (v in =12v, r ocset =6.8k) 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 -25 0 25 50 75 100 ambient temperature (c) current limit (a) v out ripple (v in = 12v, v out = 3.3v, i out = 0.1a) v out ripple (v in = 12v, v out = 3.3v, i out = 3.0a) load transient response (v in = 12v, v out = 3.3v, i out = 0.1~3a)
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 8 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated test circuit a fb v cc v ss en open open fb en + - oscillation output output a fb en + - + - v output ocset ocset ocset enable function test feedback function test operation function test v cc v cc v ss v ss
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 9 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated functional description pwm control the ap1538 is a dc/dc converter that employs pulse width modulation (pwm) scheme. its pulse width varies in the range of 0% to 99%, based on the output current loading. the output ripple voltage caused by the pwm high frequency switching can easily be reduced through an output filter. therefore, this converter provides a low ripple output supply over a broad range of input voltage & output current loading under voltage lockout the under voltage lockout circuit of the ap1538 assures that the high-side mosfet driver remains in the off state whenever the supply voltage drops below 3.3v. normal operation resumes once v cc rises above 3.5v. current limit protection the current limit threshold is set by external resistor r ocset connected from v cc supply to ocset pin. the internal sink current i ocset (90ua typical) across this resistor sets the voltage at ocset pin. when the pwm voltage is less than the voltage at ocset, an over-current condition is triggered. the current limit threshold is given by the following equation: riri ocset ocset ds(on) peak = 2 )i( + > ii out(max) peak where, in out out in v v lfs vv i ? = i peak is the output peak current; r ds (on) is the mosfet on resistance; f s is the pwm frequency (300khz typical). also, the inductor value will affect the ripple current ? i. the above equation is recommended for input voltage range of 5v to 18v. for input voltage lower than 5v or ambient temperature over 100c, higher r ocset is recommended. the recommended minimum r ocset value is summarized below: v out (v) v in (v) 5v 12v 18v 0.8 4.7k 3.0k 3.3k 1.0 5.6k 3.0k 3.9k 1.2 5.6k 3.0k 3.9k 1.8 5.6k 3.0k 3.9k 2.5 5.6k 3.0k 3.9k 3.3 5.6k 3.0k 3.9k 5.0 n/a 3.0k 4.7k inductor selection for most designs, the operates with inductors of 22h to 33h. the inductor value can be derived from the following equation: in out out in v v fs vv l ? ? = i where i l is inductor ripple current. large value inductors lower ripple current and small value inductors result in high ripple current. choose inductor ripple current approximately 15% of the maximum load current 3a, i l =0.45a. the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (3a+0.225a). input capacitor selection this capacitor should be located close to the ic using short leads and the voltage rating should be approximately 1.5 times the maximum input voltage. the rms current rating requirement for the input capacitor of a buck regulator is approximately 1 2 the dc load current. a low esr input capacitor sized for maximum rms current must be used. a 470f low esr capacitor for most applications is sufficient. output capacitor selection the output capacitor is required to filter the output voltage and provides regulator loop stability. the important capacitor parameters are the 100khz equivalent series resistance (esr), the rms ripples current rating, voltage rating and capacitance value. for the output capacitor, the esr value is the most important parameter. the output ripple can be calculated from the following formula. esr i v l ripple = the bulk capacitor?s esr will determine the output ripple voltage and the initial voltage drop after a high slew-rate transient. an aluminum electrolytic capacitor's esr value is related to the capacitance and its voltage rating. in most case, higher voltage electrolytic capacitors have lower esr values. most of the time, capacitors with much higher voltage ratings may be needed to provide the low esr values required for low output ripple voltage. pcb layout guide if you need low t c & t j or large pd (power dissipation), the dual sw pins(5& 6) and vss pins(7& 8)on the sop-8l package are internally connected to die pad, the evaluation board should be allowed for maximum copper area at output (sw) pins. 1. connect fb circuits (r 1 , r 2 , c 1 ) as closely as possible and keep away from inductor flux for pure v fb . 2. connect c3 to vcc and vss pin as closely as possible to get good power filter effect. 3. connect r4 to vcc and ocset pin as closely as possible. 4. connect ground side of the c2 & d1 & c4 as closely as possible and use ground plane for best performance.
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 10 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated top side layout guide bottom side layout guide functional description (continued) use vias to conduct the heat into the backside of pcb layer. the heat sink at output (sw) pins should be allowed for maximum solder-painted area. keep the gap of exposed pads from short circuit. recommended exposed-pads gap: 30~40mil (0.75~1mm) brown: ic exposed pads. red: recommended layout. reference pads layout dimension: output: 90 x 50 mil v ss: 90 x 60 mil
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 11 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated ap1538 + - v ss en c1 r1 r2 fb vcc output c3 v out v in r4 ocset c4 c2 option c7 c6 r5 option l1 + - c8 d1 figure: layout numbering comparison. marking information (1) sop-8l ( top view ) ap1538 yy ww x x logo part number 5 8 4 1 ww : week : 01~52; 52 yy : year : 08, 09,10~ g : green x : internal code represents 52 and 53 week (2) sop-8l-dep ( top view ) ap1538 yy ww x x logo part no. 5 8 4 1 e ww : week : 01~52; 52 yy : year : 08, 09,10~ g : green x : internal code represents 52 and 53 week sop-8l-dep functional description (continued)
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 12 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated package information ( all dimensions in mm ) (1) package type: sop-8l 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 (2) package type: sop-8l-dep 1 9 ( a l l s i d e ) 0.35typ. 4 5 4 5 8 r 0 . 1 0.3/0.5 1.27typ. 4.85/4.95 seating plane gauge plane 5.90/6.10 0.62/0.82 0.254 0/0.13 view"a" view"a" 1.4/1.5 1.63max. 3.85/3.95 land pattem recommendation (unit: mm) exposed pad bottom view exposed pad 1 4 5 8 1.15typ. 2.05typ. 2.15typ. 0.685 0.713 0.20 0.9 c l 1.7 1.7 c l 1 4 5 8 8x-0.60 5.4 2.35 6x-1.27 1.8 1.8 1.0 c l 0.95 1.65 c l top view 0.15/0.25 8x-1.55 0 / 8
ap1538 18v 3a 300khz buck converter ap1538 rev. 5 13 of 13 october 2009 ds31451 www.diodes.com ? diodes incorporated 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 liability arising out of the application or use of this document or any product described herein; neither does diodes incorpora ted convey any license under its patent or trademark rights, nor the rights of others. any customer or user of this document or pr oducts 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 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 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 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 ? 2009, diodes incorporated www.diodes.com

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