1/9 ax elite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 pwm control 2a step-down converter ? general description AX3101 cons ists of step-down switching regulator with pw m control. these devise include a reference voltage source, oscillation circuit, error amplifier, internal pmos and etc. AX3101 provides low-ripple power, hi gh efficiency, and excellent transient characteristics. the pwm control circuit is able to every the duty ratio linearly form 0 up to 100%. this converter also contains an error amp lifier circuit as well as a soft-start circuit that prevents overshoot at startup. an enable function, an over current protect function and short circuit protect function are built inside, and when ocp or scp happens, the operation frequency will be reduced. also, an internal co mpensation 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 port able devices when coupled with the sop-8l package, providing such outstanding features as low current consumption. since this converter can accommodate an input voltage up to 20v, it is also suitable for the operation via an ac adapter. ? fea tures - input voltage 3.6v to 20v - output voltage 0.8v to v cc - duty ratio 0% to 100% p wm control - oscillation frequency 330khz typ. - soft-start (ss), current li mit (cl), enable function. - thermal shutdown function. - short circuit protect (scp). - built-in internal sw p-channel mos. - sop-8l pb-free package. v?mw`r?y?b? w w w . g o f o t e c h . c o m
2/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? block diagram vcc oscillation circuit reference voltage source with soft start + - vss v en en ocset fb sw thermal shutdown 110ua - pwm switched control circuit ? pin assignment the package of AX3101 is sop-8l; t he pin assignment is given by: name description fb feedback pin en power-off pin h normal operation(step-down) l step-down operation stopped (all circuits deactivated) ocse t add an external resistor to set max switch output current. v cc ic power supply pin v ss gnd pin sw switch pin. connect external inductor and diode here. ? order/marking information order information top marking package type s: sop-8l AX3101 x x x packing blank : tube a : taping frequency blank : 330khz logo y ax 3 part number id code:internal ww: 01~52 year: 10=2010 11=2011 1 01 ywwx v?mw`r?y?b? w w w . g o f o t e c h . c o m
3/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? absolute maximum ratings (at t a =25c) characteristics symbol rating unit vcc pin voltage v cc v ss - 0.3 to v ss + 22 v feedback pin voltage v fb v ss - 0.3 to v cc v on/off pin voltage v en v ss - 0.3 to v cc + 0.3 v switch pin voltage v sw v ss - 0.3 to v cc + 0.3 v power dissipation pd internally limited mw storage temperature range t st -40 to +150 c operating junction temperature range t j -20 to +125 c operating supply voltage v op +3.6 to +20 v output current i out 0 to 2 a thermal resistance from junction to case jc 25 c/w thermal resistance from junction to ambient ja 70 c/w note: ja is measured with the pcb copper area(need connect to sw pins) of approximately 1 in 2 (multi-layer). ? electrical characteristics (v in = 12v, v out =3.3v t a =25c, unless otherwise specified) characteristics s y mbol conditions min t y p max units feedback volta g e v fb i out =0.1a 0.784 0.800 0.816 v quiescent current i ccq v fb =1.2v force driver of f - 3 5 ma feedback bias current i fb i out =0.1a - 0.1 0.5 ua shutdown suppl y current i sd v en =0v - 2 10 ua ocset pin bias current i ocset 110 130 150 ua switch current i sw 3.0 - - a line regulation t v out /v out v cc =8v~20v, i out =0.2a - 1 2 % load re g ulation t v out / v out i out = 0.1 to 2 a - 0.2 0.5 % oscillation frequenc y f osc sw pin 260 330 400 khz en pin logic input threshold voltage v sh hi g h ( re g ulator on ) 2.0 - - v v sl low ( re g ulator off ) - - 0.8 en pin input current i sh v en =2.5v ( on ) - 20 - ua i sl v en =0.3v ( off ) - -10 - ua soft-start time t ss 0.3 4 8 ms internal mosfet r dson r dson v cc =5v, v fb =0v - 100 140 m ? v cc =12v, v fb =0v - 70 100 efficiency i out = 1a effi v cc = 12v, v out = 5v - 92 - % i out = 2a - 92 - v?mw`r?y?b? w w w . g o f o t e c h . c o m
4/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? application circuit c2 470uf c4 470uf 1 2 l1 33uh r1 6.8k r2 1.3k vin+12v on/off c1 1nf vout = 5v/2a r3 1.3k r4 100k d1 b340 c8 0.1uf fb 1 en 2 ocset 3 vcc 4 sw 5 sw 6 vss 7 vss 8 AX3101 r1 r2 vfb = 0.8v ; r2 suggest 0.8k ~ 6k vout = vfb x (1 + ) c3 0.1uf option l1 recommend value (v in =12v ,i out =2a,) v out 1.8 v 2.5v 3.3v 5v l1 value 18uh 22uh 27uh 33uh ? function descriptions wm control the AX3101 consists of dc/dc converte rs that employ a pulse-width modulation (pwm) system. in converters of the AX3101, the pulse width va ries in a range from 0 to 100%, according to the load current. the ri pple voltage produced by the switching can easily be removed through a filter because the switching frequency remains constant. therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current. rds (on) current limiting the current limit threshold is setting by t he external resistor (r3) connecting from v cc supply to ocset pin. the internal 130ua sink cu rrent crossing the resist or sets the voltage at pin of ocset. when the pwm voltage is less than the voltage at ocset, an over-current condition is triggered. please refer to the formula for setting the minimum current limit value: r i i ds(on) ocset .r3 sw(min) 080 ?? ? (normally, the i sw(min) setting more than i out 1.0a ). example: i sw = (0.13ma x 1.3k + 0.08)/ 0.070 ? = 3.56a - (v in =12v) i sw = (0.13ma x 2.5k + 0.08)/ 0.10 ? = 4.05a - (v in =5v) v?mw`r?y?b? w w w . g o f o t e c h . c o m
5/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 setting the output voltage application circuit item shows the basic application circuit with adjustable output version. the external resistor sets the output voltage according to the following equation: ? ? ? ? ? ? ??? 2 1 18.0 r r v v out table 1 resistor select for output voltage setting v out r2 r1 5v 1.3k 6.8k 5.6k 30k 3.3v 1.5k 4.7k 5.6k 18k 2.5v 2.2k 4.7k 1.8v 2k 2.5k 1.5v 2.2k 2.0k 1.2v 3k 1.5k 1.0v 3k 0.75k the r2 setting 5.6k that no load current can be reduce to under 4ma for el cap. inductor selection for most designs, the operates with inductors of 15h to 33h. the inductor value can be derived from the following equation: ? ? f i v vvv l osc l in out in out ?? ?? ? ? where is inductor ripple current. large va lue inductors lower ripple current and small value inductors result in high rippl e currents. choose inductor ripple current approximately 15% of the maximum load current 2a, i l =0.3a. 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 (2a+0.15a). 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 c apacitor sized for maximum rms current must be used. a 220f low esr capacitor for most applications is sufficient. v?mw`r?y?b? w w w . g o f o t e c h . c o m
6/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 output capacitor selection the output capacitor is required to filter t he output and provide r egulator loop stability. the important capacitor parameters are; the 100khz equivalent series resistance (esr), the rms ripples current rating, voltage ra ting, and capacitance value. for the output capacitor, the esr value is the most import ant parameter. the esr can be calculated from the following formula. esr i v l ripple ??? = 0.33a x 130m ? = 43mv an aluminum electrolytic capacitor's esr value is related to the capacitance and its voltage rating. in most case, higher voltage el ectrolytic 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. it is recommended to replace this low esr capacitor by us ing a 330f low esr values < 130m . pcb layout guide if you need low tc and tj or large pd(power dissipation), the dual sw pins(5 and 6) and v ss pins(7 and 8)on the sop-8l package are internally connected to die pad, the pcb layout should allow for maximum po ssible copper area at the sw pins. 1. connect c3 to v cc and v ss pin as closely as possible to get good power filter effect. 2. connect r3 to v cc and ocset pin as closely as possible. 3. connect ground side of the c2 and d1 as closely as possible. the heat sink copper of pcb area should be solder-painted without masked. use through hole to conduct the heat into the backside of pcb bypass c3 need closely from ic?s v cc to v ss pins. v?mw`r?y?b? w w w . g o f o t e c h . c o m
7/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? typical characteristics vfb vs vin iccq vs vin vfb vs vin 0.780 0.785 0.790 0.795 0.800 0.805 0.810 0.815 0.820 3579111315171921 vin(v) vfb(v) iccq v s v in 0.0 1.0 2.0 3.0 4.0 5.0 6.0 3 5 7 9 11 13 15 17 19 21 vin(v) iccq(ma ) fosc vs vin fosc vs temperature fosc vs vin 280.0 290.0 300.0 310.0 320.0 330.0 340.0 350.0 360.0 3579111315171921 vin(v) fosc(khz) fos c v s temperature 280.0 290.0 300.0 310.0 320.0 330.0 340.0 350.0 360.0 -20 0 20 40 60 80 100 120 temp ( ) fosc(khz) vfb vs temperature iccq vs temperature vfb vs temperature 0.780 0.785 0.790 0.795 0.800 0.805 0.810 0.815 0.820 -20 0 20 40 60 80 100 120 temp ( ) vfb(v) iccq vs temperature 0.0 1.0 2.0 3.0 4.0 5.0 6.0 -20 0 20 40 60 80 100 120 temp ( ) iccq(ma ) v?mw`r?y?b? w w w . g o f o t e c h . c o m
8/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? typical characteristics (continuous) output ripple (v in =12v, v out =5v, i out =2a) power on test wave (v in =12v, v out =5v, i out =2a ) load transient response (v in =12v, v out =5v, i out =0.1~2a) en pin on test wave (v in =12v, v out =5v, i out =2a ) efficiency (v in =12v, v out =5v/3.3v) efficiency (v in =5v, v out =3.3v/2.5v) vin=12v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.5 1.0 1.5 2.0 iout(a) efficiency(%) vout=5v vout=3.3v vin=5v 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.5 1.0 1.5 2.0 iout (a) efficiency(%) vout=2.5v vin=3.3v v?mw`r?y?b? w w w . g o f o t e c h . c o m
9/9 axelite confidential materials, do not copy or distribute without written consent . rev.1.9 aug.05, 2010 AX3101 ? 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 a 1 0.1 - 0.25 0.04 - 0.1 a 2 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 v?mw`r?y?b? w w w . g o f o t e c h . c o m
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