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preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 1 general description the AP3435 is a high efficiency step-down dc-dc voltage converter. the chip operation is optimized by peak-current mode architecture with built-in synchronous power mos switchers. the oscillator and timing capacitors are all built-in providing an internal switching frequency of 1mhz that allows the use of small surface mount inductors and capacitors for portable product implementations. integrated soft start (ss), under voltage lock out (uvlo), thermal shutdown detection (tsd) and short circuit protection are designed to provide reliable product applications. the device is available in adjustable output voltage versions ranging from 0.8v to 0.9v in (2.7v v in 5.5v), and is able to deliver up to 3.5a. the AP3435 is available in psop-8 package. features ? high efficiency buck power converter ? output current: 3.5a ? low r ds(on) internal switches:100m ? (v in =5v) ? adjustable output voltage from 0.8v to 0.9v in ? wide operating voltage range: 2.7v to 5.5v ? built-in power switches for synchronous rectification with high efficiency ? feedback voltage: 800mv ? 1.0mhz constant frequency operation ? thermal shutdown protection ? low drop-out operation at 100% duty cycle ? no schottky diode required ? input over voltage protection applications ? lcd tv ? set top box ? post dc-dc voltage regulation ? pda and notebook computer figure 1. package type of AP3435 psop-8
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 2 pin configuration mp package (psop-8) 1 2 3 4 8 7 6 5 figure 2. pin configurat ion of AP3435 (top view) pin description pin number pin name function 1 vcc supply input for the analog circuit 2 nc no connection 3 gnd ground pin 4 fb feedback pin. receive the feedback voltage from a resistive divider connected across the output 5 en chip enable pin. active hi gh, internal pull-high with 200k resistor 6 pgnd power switch ground pin 7 sw switch output pin 8 vin power supply input for the mosfet switch
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 3 functional block diagram over-current comparator bias generator saw-tooth generator oscillator soft start bandgap reference current sensing control logic buffer & dead time control logic + reverse inductor current comparator over voltage comparator modulator error amplifier _ + + + + pgnd en fb sw 5 vin 8 7 6 4 vcc 1 gnd 3 _ _ _ figure 3. functional block diagram of AP3435 ordering information AP3435 - circuit type package mp: psop-8 bcd semiconductor's pb-free products, as designated wi th "g1" in the part number, are rohs compliant and green. package temperature range part number marking id packing type psop-8 -40 to 80c AP3435mptr-g1 3435mp-g1 tape & reel g1: green tr: tape & reel
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 4 absolute maximum ratings (note 1) note 1: stresses greater than those listed under ?absolute maximum ratings? may cause permanent damage to the device. these are stress ratings only, and functional op eration of the device at these or any other conditions beyond those indicated under ?recommended operating co nditions? is not implied. exposure to ?absolute maximum ratings? for extended periods may affect device reliability. recommended operating conditions parameter symbol value unit supply input for the analog circuit v cc 0 to 6.0 v power supply input for the mosfet switch v in 0 to 6.0 v sw pin switch voltage v sw -0.3 to v in +0.3 v enable input voltage v en -0.3 to v in +0.3 v sw pin switch current i sw 4.5 a power dissipation (on pcb, t a =25c) p d 2.47 w thermal resistance (junction to ambient, simulation) ja 40.43 c/w operating junction temperature t j 160 c operating temperature t op -40 to 85 c storage temperature t stg -55 to 150 c esd (human body model) v hbm 2000 v esd (machine model) v mm 200 v parameter symbol min max unit supply input voltage v in 2.7 5.5 v junction temperature range t j -40 125 c ambient temperature range t a -40 80 c
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 5 electrical characteristics v in =v cc =v en =5v, v out =1.2v, v fb =0.8v, l=2.2 h, c in =10 f, c out =22 f, t a =25c, unless otherwise specified. parameter symbol conditions min typ max unit input voltage range v in 2.7 5.5 v shutdown current i off v en =0 1 a active current i on v fb =0.95v 310 a regulated feedback voltage v fb for adjustable output voltage 0.784 0.8 0.816 v regulated output voltage accuracy v out /v out v in =2.7v to 5.5v, i out =0 to 3.5a -3 3 % peak inductor current i pk 4.5 a oscillator frequency f osc v in =2.7v to 5.5v 1.0 mhz pmosfet ron r on(p) v in =5v 100 m nmosfet ron r on(n) v in =5v 100 m en high-level input voltage v en_h 1.5 v en low-level input voltage v en_l 0.4 v en input current i en 1 a soft start time t ss 400 s maximum duty cycle d max 100 % under voltage lock out threshold v uvlo rising 2.4 v falling 2.3 hysteresis 0.1 thermal shutdown t sd hysteresis=30c 150 c input over voltage protection (iovp) v iovp rising 5.8 5.9 6.0 v hysteresis 0.3 0.4 0.5 v
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 6 typical performance characteristics figure 4. efficiency vs. output current figure 5. efficiency vs. output current figure 6. load regulation figure 7. load regulation 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 10 20 30 40 50 60 70 80 90 100 efficiency (%) output current (a) v in =5v, v out =3.3v 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 3.20 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36 3.38 3.40 output voltage (v) output current (a) v in =5v, v out =3.3v 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 10 20 30 40 50 60 70 80 90 100 efficiency (%) output current (a) v in =5v, v out =1.2v 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 output voltage (v) output current (a) v in =5v, v out =1.2v
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 7 typical performance characteristics (continued) figure 8. line regulation figure 9. line regulation figure 10. frequency vs. input voltage figure 11. frequency vs. input voltage 2.5 3.0 3.5 4.0 4.5 5.0 5.5 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 output voltage (v) input voltage (v) i out = 0 i out = 3.5a v out =1.2v 4.0 4.5 5.0 5.5 3.20 3.22 3.24 3.26 3.28 3.30 3.32 3.34 3.36 3.38 3.40 output voltage (v) input voltage (v) i out =0 i out =3.5a v out =3.3v 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 frequency (mhz) input voltage (v) v out = 1.2v 4.0 4.5 5.0 5.5 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 frequency (mhz) input voltage (v) v out = 3.3v
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 8 typical performance characteristics (continued) figure 12. enable threshold voltage vs. input voltage figure 13. current limit vs. input voltage figure 14. case temperature vs. output current figure 15. enable waveform (v in =5v, v en =0v to 5v, v out =3.3v, i out =3.5a) v en 2v/div v out 1v/div i sw 2a/div time 400 s/div 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 en threshold voltage (v) input voltage (v) h level l level 2.5 3.0 3.5 4.0 4.5 5.0 5.5 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 current limit (a) input voltage (v) 0.00.51.01.52.02.53.03.5 25 30 35 40 45 50 55 60 65 70 75 80 85 90 case temperature ( c) output current (a) v out = 1.2v
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 9 typical performance characteristics (continued) figure 16. power-on figure 17. power-off (v in =0v to 5v, v en =v in , v out =3.3v, i out =3.5a) (v in =5v to 0v, v en =v in , v out =3.3v, i out =3.5a) figure 18. short circuit protection figure 19. v out ripple (v in =5v=v en , v out =3.3v, i out =2a to short) (v in =5v=v en , v out =3.3v, i out =0a) v out 1v/div v in 2v/div i sw 2a/div time 400 s/div v out 1v/div v in 2v/div i sw 2a/div time 20ms/div time 400 s/div time 400ns/div v sw 5v/div i sw 2a/div v sw 2v/div v out 1v/div i out 2a/div v out_ac 20mv/div
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 10 typical performance characteristics (continued) figure 20. v out ripple figure 21. v out ripple (v in =5v=v en , v out =3.3v, i out =1a) ( v in =5v=v en , v out =3.3v, i out =3.5a) figure 22. load transient of 1.2v output figure 23. load transient of 3.3v output (v in =5v=v en , v out =1.2v, i out =0.5a to 2a) (v in =5v=v en , v out =3.3v, i out =0.5a to 2a) 20 m v/div v sw 5v/div time 400ns/div i sw 2a/div 20mv/div v sw 5v/div time 400ns/div i sw 2a/div time 100 s/div time 100 s/div v out_ac v out_ac v out_ac 200mv/div i out 500ma/div v out_ac 200mv/div i out 500ma/div
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 11 typical performance characteristics (continued) figure 24. ovp function (v in =5v to 6v) figure 25. leave ovp function (v in =6v to 5v) time 100 s/div v out 1v/div i out 500ma/div v in 1v/div i out 500ma/div v out 1v/div v in 1v/div time 100 s/div
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 12 fb gnd v out r1 r2 AP3435 application information the basic AP3435 application circuit is shown in figure 27, external components selection is determined by the load current and is critical wi th the selection of inductor and capacitor values. 1. inductor selection for most applications, the value of inductor is chosen based on the required ripple current with the range of 1 h to 6.8 h. the largest ripple current occurs at the highest input voltage. having a small ripple current reduces the esr loss in the output capacitor and improves the efficiency. the highest efficiency is realized at low operating frequency with small ripple current. however, larger value inductors will be required. a reasonable starting point for ripple current setting is i l =40%i max . for a maximum ripple current stays below a specified value, the inductor should be chosen according to the following equation: the dc current rating of the inductor should be at least equal to the maximum output current plus half the highest ripple current to prevent inductor core saturation. for better efficiency, a lower dc-resistance inductor should be selected. 2. capacitor selection the input capacitance, c in , is needed to filter the trapezoidal current at the source of the top mosfet. to prevent large ripple voltage, a low esr input capacitor sized for the maximum rms current must be used. the maximum rm s capacitor current is given by: it indicates a maximum value at v in =2v out , where i rms =i out /2. this simple wors e-case condition is commonly used for design because even significant deviations do not much relieve. the selection of c out is determined by the effective series resistance (esr) that is required to minimize output voltage ripple and load step transients, as well as the amount of bulk capacitor that is necessary to ensure that the control loop is stable. the output ripple, v out , is determined by: the output ripple is the highest at the maximum input voltage since i l increases with input voltage. 3. load transient a switching regulator typically takes several cycles to respond to the load curren t step. when a load step occurs, v out immediately shifts by an amount equal to i load esr, where esr is the effective series resistance of output capacitor. i load also begins to charge or discharge c out generating a feedback error signal used by the regulator to return v out to its steady-state value. during the recovery time, v out can be monitored for overshoot or ringing that would indicate a stability problem. 4. output voltage setting the output voltage of AP3435 can be adjusted by a resistive divider according to the following formula: the resistive divider senses the fraction of the output voltage as shown in figure 26. figure 26. setting the output voltage in out in out omax rms v v v v i i 2 1 )] ( [ ? = ) 1 ( 1 in out out l v v v l f i ? = ] ) ( 1 ][ ) ( [ max v v max i f v l in out l out ? = ] 8 1 [ out l out c f esr i v + ) 1 ( 8 . 0 ) 1 ( 2 1 2 1 r r v r r v v ref out + = + =
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 13 application information (continued) 5. short circuit protection when the AP3435 output node is shorted to gnd, as v fb drops under 0.4v, the chip will enter soft-start mode to protect itself, when short circuit is removed, and v fb rises over 0.4v, the AP3435 recovers back to normal operation again. if the AP3435 reaches ocp threshold while short circuit, the AP3435 will enter soft-start cycle until the current under ocp threshold. 6. efficiency considerations the efficiency of switching regulator is equal to the output power divided by the input power times 100%. it is usually useful to analyze the individual losses to determine what is limiting efficiency and which change could produce the largest improvement. efficiency can be expressed as: efficiency=100%-l1-l2-?.. where l1, l2, etc. are the individual losses as a percentage of input power. although all dissipative elements in the regulator produce losses, two major sources usually account for most of the power losses: v in quiescent current and i 2 r losses. the v in quiescent current loss dominates the efficiency loss at very light load currents and the i 2 r loss dominates the efficiency loss at medium to heavy load currents. 6.1 the v in quiescent current loss comprises two parts: the dc bias current as given in the electrical characteristics and the internal mosfet switch gate charge currents. the gate charge current results from switching the gate capacitance of the internal power mosfet switches. each cycle the gate is switched from high to low, then to high again, and the packet of charge, dq moves from v in to ground. the resulting dq/dt is the current out of v in that is typically larger than the internal dc bias current. in continuous mode, where q p and q n are the gate charge of power pmosfet and nmosfet switches. both the dc bias current and gate charge losses are proportional to the v in and this effect will be more serious at higher input voltages. 6.2 i 2 r losses are calculated from internal switch resistance, r sw and external inductor resistance r l . in continuous mode, the average output current flowing through the inductor is chopped between power pmosfet switch and nmosfet switch. then, the series resistance looking into the sw pin is a function of both pmosfet r ds(on) and nmosfet r ds(on) resistance and the duty cycle (d): therefore, to obtain the i 2 r losses, simply add r sw to r l and multiply the result by the square of the average output current. other losses including c in and c out esr dissipative losses and inductor core losses generally account for less than 2 % of total additional loss. 7. thermal characteristics in most applications, the part does not dissipate much heat due to its high efficiency. however, in some conditions when the part is operating in high ambient temperature with high r ds(on) resistance and high duty cycles, such as in ldo mode, the heat dissipated may exceed the maximum junction temperature. to avoid the part from exceeding maximum junction temperature, the user should do some thermal analysis. the maximum power dissipation depends on the layout of pcb, the thermal resistance of ic package, the rate of surrounding airflow and the temperature difference between junction and ambient. 8. input over voltage protection when input voltage of AP3435 is near 6v, the ic will enter input-over-voltage-protection. it would be shut down and there will be no output voltage in this state. as the input voltage goes down below 5.5v, it will leave input ovp and recover the output voltage. ) ( n p gate q q f i + = () () ) ( d r d r r n on ds p on ds sw ? + = 1
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 14 application information (continued) 9. pcb layout considerations when laying out the printed circuit board, the following checklist should be used to optimize the performance of AP3435. 1) the power traces, includi ng the gnd trace, the sw trace and the vin trace should be kept direct, short and wide. 2) put the input capacitor as close as possible to the vin and gnd pins. 3) the fb pin should be connected directly to the feedback resistor divider. 4) keep the switching node, sw, away from the sensitive fb pin and the node should be kept small area.
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 15 typical application AP3435 note 2: ) 1 ( 2 1 r r v v ref out + = . figure 27. typical application circuit of AP3435 v out (v) r1 (k ) r2 (k )l ( h) 3.3 31.25 10 2.2 2.5 21.5 10 2.2 1.8 12.5 10 2.2 1.2 5 10 2.2 1.0 3 10 2.2 table 1. component guide
preliminary datasheet 1.0mhz, 3.5a, synchronous step down dc-dc converter AP3435 dec. 2012 rev. 1. 0 bcd semiconductor manufacturing limited 16 mechanical dimensions psop-8 unit:mm(inch) 3.202(0.126) 3.402(0.134)
important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing co., ltd. 800 yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd., shenzhen office unit a room 1203, skyworth bldg., gaoxin ave.1.s., nanshan district, shenzhen, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corp. 30920 huntwood ave. hayward, ca 94544, usa tel : +1-510-324-2988 fax: +1-510-324-2788 - headquarters bcd semiconductor manufacturing limited no. 1600, zi xing road, shanghai zizhu sc ience-based industrial park, 200241, china tel: +86-21-24162266, fax: +86-21-24162277 bcd semiconductor manufacturing limited important notice bcd semiconductor manufacturing limited reserves the right to make changes without further not ice to any products or specifi- cations herein. bcd semiconductor manufacturing limited does not as sume any responsibility for us e of any its products for any particular purpose, nor does bcd semiconductor manufacturi ng limited assume any liability aris ing out of the application or use of any its products or circui ts. bcd semiconductor manufacturing limited does not convey any license under its patent rights or other rights nor the rights of others. - wafer fab shanghai sim-bcd semiconductor manufacturing limited 800, yi shan road, shanghai 200233, china tel: +86-21-6485 1491, fax: +86-21-5450 0008 bcd semiconductor manufacturing limited main site regional sales office shenzhen office shanghai sim-bcd semiconductor manuf acturing co., ltd. shenzhen office advanced analog circuits (shanghai) corporation shenzhen office room e, 5f, noble center, no.1006, 3rd fuzhong road, futian district, shenzhen 518026, china tel: +86-755-8826 7951 fax: +86-755-8826 7865 taiwan office bcd semiconductor (taiwan) company limited 4f, 298-1, rui guang road, nei-hu district, taipei, taiwan tel: +886-2-2656 2808 fax: +886-2-2656 2806 usa office bcd semiconductor corporation 30920 huntwood ave. hayward, ca 94544, u.s.a tel : +1-510-324-2988 fax: +1-510-324-2788 - ic design group advanced analog circuits (shanghai) corporation 8f, zone b, 900, yi shan road, shanghai 200233, china tel: +86-21-6495 9539, fax: +86-21-6485 9673 bcd semiconductor manufacturing limited http://www.bcdsemi.com bcd semiconductor manufacturing limited

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