1/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 1mhz, 2.5a synchronous step-down converter ? general description the AX3517 is a 1mhz constant frequency cu rrent mode pwm step- down converter. it is ideal for portable equipment requiring very high current up to 2.5a from single-cell lithium-ion batteries while still achieving ov er 90% efficiency during peak load conditions. the AX3517 also can run at 100% duty cycle for low dropout operation, extending battery life in portable systems while light load operation provides very low output ripple for noise sensitive applications. the AX3517 can supply up to 2.5a output load curr ent from a 2.8v to 5.5v input voltage and the output voltage can be regulated as low as 0.8v. the high switching frequency minimizes the size of ex ternal components while keeping switching losses low. the internal slope compensation setting allows the device to operate with smaller inductor values to optimize size and provide efficient oper ation. the AX3517 is available in adjustable (0.8v to vin) output voltage. the device is available in sop-8l pb-free package. ? features - 2.8v to 5.5v input voltage range - output voltages from 0.8v to vin - high efficiency: up to 94 % - 1mhz constant frequency operation - with power saving mode - up to 2.5a output current - no schottky diode required - current mode operation for excell ent line and load transient response - current limit and therma l shutdown protection - short circuit protect (scp) - build-in soft start function - sop-8l pb-free package
2/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? block diagram ? pin assignment the package of AX3517 is sop-8l; t he pin assignment is given by: name description svin signal supply input pin ref reference output pin sgnd signal ground pin fb output feedback pin en enable pin, inte rnal pull-high function. h normal operation l shutdown pgnd power ground pin sw switch output pin. connect external inductor here. minimize trace area at this pin to reduce emi. pvin power supply input pin ? order/marking information order information top marking package type s: sop-8l AX3517 packing a : taping x x logo ax 3 part number id code:internal ww:01~52 year: 10=2010 11=2011 5 1 7 yy wwx
3/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? absolute maximum ratings (at t a =25c) characteristics symbol rating unit pvin, svin, ref pin voltage v ss - 0.3 to v ss + 6.5 v feedback pin voltage v fb v ss - 0.3 to v in + 0.3 v en pin voltage v run v ss - 0.3 to v in + 0.3 v switch pin voltage v sw v ss - 0.3 to v in + 0.3 v power dissipation pd ( t j -t a ) / ja mw storage temperature range t st -40 to +150 c operating temperature range t op -40 to +85 c junction temperature t j +125 c thermal resistance from junction to case jc 40 c/w thermal resistance from junction to ambient ja 120 c/w note: ja is measured with the pcb copper area of approximately 1 in 2 (multi-layer). ? electrical characteristics (v in =v en =3.3v, t a =25c, unless otherwise specified) characteristics symbol conditions min typ max units supply voltage range v in 2.8 - 5.5 v feedback voltage v fb 0.784 0.800 0.816 v feedback bias current i fb v fb = 0.85v - - 30 na ref voltage v ref i ref =0, v in =2.8v to 5.5v - 0.8 - v quiescent current i ccq v fb = 1v - 250 400 ua shutdown supply current i sd v en =0v - 4 10 ua switching current limit i limit 3 3.5 - a line regulation v out /v out v in = 3v~5.5v - 0.04 0.4 %/v load regulation v out /v out i out = 0.01 to 2.5a - 0.5 1 % oscillation frequency f osc sw pin 0.8 1 1.2 mhz r ds(on) of p-ch mosfet r dson v fb =0v, i out =1a - 120 - m ? r ds(on) of n-ch mosfet r dson (note1) - 100 - m ? en pin lo g ic input threshold v enl - - 0.4 v
4/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 voltage v enh 1.5 - - en pin input current i enh v en =v in - 0.1 1 ua i enl v en =0v - 4 8 ua efficiency effi v in =5v, v out =3.3v,i out =2a - 92 - % thermal shutdown t sd - 150 - c thermal shutdown h y steresis t sh - 40 - c note1: guaranteed by design. ? application circuit v out = 0.8 * (1+r2/r3) r3 600k c1 22uf c2 22uf vout=1.2v vin=2.8 to 5.5v r2 = 300k~820k l1 2.2uh r2 300k AX3517 pvin en sgnd sw fb c5 15pf svin pgnd r1 10r c3 100nf c4 100nf ref ? function descriptions operation AX3517 is a monolithic switching mode step-do wn dc-dc converter. it utilizes internal mosfets to achieve high efficiency and can generate very low output voltage by using internal reference at 0.8v. it operates at a fixed switching frequency, and uses the slope compensated current mode architecture. this step-down dc-dc converter supplies 2500ma output current at input vo ltage range from 2.8v to 5.5v.
5/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 current mode pwm control slope compensated current mode pwm c ontrol provides stable switching and cycle-by-cycle current limit for excellent load and line responses and protection of the internal main switch (p-ch mosfet) and syn chronous rectifier (n-ch mosfet). during normal operation, the internal p-ch mosfet is turned on for a certain time to ramp the inductor current at each rising edge of the inte rnal oscillator, and switched off when the peak inductor current is above the error voltage. the current comparator, i comp , limits the peak inductor current. when the main switch is o ff, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, i zero , or the beginning of the next clock cycle. ? application information setting the output voltage application circuit item shows the basic application circuit with AX3517 adjustable output version. the external resistor sets the output voltage according to the following equation: v out = 0.8v (1+ 3 r 2 r ) table 1 resistor select for output voltage setting v out r3 r2 1.2v 600k 300k 1.5v 380k 330k 1.8v 310k 390k 2.5v 220k 470k 3.3v 150k 470k inductor selection for most designs, the AX3517 operates with inductors of 2.2 h to 3.3h. low inductance values are physically smaller but require faster swit ching, which results in some efficiency loss. where is inductor ripple cu rrent. large value inductors lo wer ripple current and small value inductors result in high ripple currents. choose inductor ripple current approximately 15% of the maximum load current 2500ma, i l = 375ma.
6/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 for output voltages above 3.0v, when li ght-load efficiency is important, the recommended inductor is 2.2h. for optimum vo ltage-positioning l oad transients, choose an inductor with dc series resistance in the 30m ? to 100m ? range. for higher efficiency at heavy loads (above 300ma), or minimal load regulat ion (but some transient overshoot), the resistance should be kept below 100m ? . 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 (2500ma + 190ma). input capacitor selection the input capacitor reduces the surge cu rrent drawn from the input and switching noise from the device. the input capacitor impedance at the switching frequency shall be less than input source impedance to prevent hi gh frequency switching current passing to the input. a low esr input capacitor sized for maximum rms current must be used. ceramic capacitors with x5r or x7r dielectrics are highly recomm ended because of their low esr and small temperature coefficients. a 22f ce ramic capacitor for most applications is sufficient. output capacitor selection the output capacitor is required to keep the output voltage rippl e small and to ensure regulation loop stability. the output capacito r must have low impedance at the switching frequency. ceramic capacitors with x5r or x7 r dielectrics are re commended due to their low esr and high ripple current. a 22f ceramic capac itor for most applications is sufficient. compensation capacitor selection the compensation capacitor (c5) for incr easing phase margin provides additional stability. refer to demo board schematic, the c5 optimum value is 15pf for all conditions. layout guide pvin fb sgnd lx ref svin pgnd AX3517 8 1 2 3 4 5 6 7 en c1 c3 vin r1 l1 vout c2 r2 r3 c3 and c4 must be placed between pin and sgnd as closer as possible sw should be connected to inductor by wide and short trace, keep sensitive components away from this trace c1 must be placed between pvin and pgnd as closer as possible, vin trace should be wide and short. vin c5 gnd c4
7/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? typical characteristics 0 100 200 300 400 500 2.5 3 3.5 4 4.5 5 5.5 v in (v) i ccq (ua) v in v.s. i ccq 0.80 0.85 0.90 0.95 1.00 1.05 1.10 1.15 1.20 2.5 3 3.5 4 4.5 5 5.5 v in (v) frequency (mhz) v in v.s. frequency 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 2.5 3 3.5 4 4.5 5 5.5 v in (v) en threshold voltage (v) v in v.s. en threshold voltage enh enl 1.180 1.185 1.190 1.195 1.200 1.205 1.210 1.215 1.220 2.5 3 3.5 4 4.5 5 5.5 v in (v) v out (v) line regulation i out =300ma 1.180 1.185 1.190 1.195 1.200 1.205 1.210 1.215 1.220 0 0.5 1 1.5 2 2.5 i out (a) v out (v) load regulation v in =5v 0 40 80 120 160 200 2.5 3 3.5 4 4.5 5 5.5 v in (v) r ds(on) (m ? ) v in v.s. r ds(on) p-mos n-mos i out =1a
8/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? typical characteristics (continues) 0.60 0.70 0.80 0.90 1.00 1.10 1.20 1.30 1.40 1.50 -40 -25 0 25 50 75 100 125 temperature frequency (mhz) temperature v.s. frequency 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 -40 -25 0 25 50 75 100 125 temperature v out (v) temperature v.s. vout v in =5v i out =300ma 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 00.511.522.5 i out (a) efficiency efficiency (v in =3.3v) v out =1.2v v out =1.8v v out =2.5v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0 0.5 1 1.5 2 2.5 i out (a) efficiency efficiency (v in =5v) v out =1.2v v out =1.8v v out =2.5v v out =3.3v power on v in =5v, v out =1.2v, i out =1.8a (c ref =100nf) enable on v in =5v, v out =1.2v, i out =1.8a(c ref =100nf)
9/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? typical characteristics (continues) power on v in =5v, v out =1.2v, i out =1.8a (c ref =10nf) enable on v in =5v, v out =1.2v, i out =1.8a(c ref =10nf) power on v in =5v, v out =3.3v, i out =2.0a(c ref =10nf) enable on v in =5v, v out =3.3v, i out =2.0a(c ref =10nf) load transient response v in =5v, v out =1.2v, i out = 0.3a~2.3a load transient response v in =5v, v out =3.3v, i out = 0.3a~2.3 a
10/10 axelite confidential materials, do not copy or distribute without written consent . rev.1.2 oct.06, 2010 AX3517 ? package outlines detail a l h e a a2 a1 e d 7 (4x) b y c detail a symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.75 - - 0.069 a1 0.1 - 0.25 0.04 - 0.1 a2 1.25 - - 0.049 - - c 0.1 0.2 0.25 0.0075 0.008 0.01 d 4.7 4.9 5.1 0.185 0.193 0.2 e 3.7 3.9 4.1 0.146 0.154 0.161 h 5.8 6 6.2 0.228 0.236 0.244 l 0.4 - 1.27 0.015 - 0.05 b 0.31 0.41 0.51 0.012 0.016 0.02 e 1.27 bsc 0.050 bsc y - - 0.1 - - 0.004 0 o - 8 o 0 o - 8 o mold flash shall not exceed 0.25mm per side jedec outline: ms-012 aa
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