1/9 ax elite confidential materials, do not copy or distribute without written consent . rev.1.2 aug.19, 2010 AX3122 5a synchronous buck converter ? general description AX3122 consists of step-down switching regulator with synchronous pwm converter . these devise include a reference voltage source, os cillation circuit, error amplifier, internal pmos and external nmos etc. AX3122 provides 5a high current, low-ri pple power, high efficiency, and excellent transient characteristics. the pwm control circui t is able to the duty ratio linearly form 0 up to 100%. an over current protec t function and short circuit prot ect function are built inside, and when ocp or scp happens, the operation fr equency will be reduced. also, an external compensation is easily to system stable. with the addition of internal pmos, external nmos, a coil and capacitors externally, these ics can function as step-down switching regulators. the device serve 5a high power supply system, the external nmos can r educe ic temperature and promote system efficiency for heavy load. since this conv erter can accommodate an input voltage up to 23v. ? fea tures - input voltage 4.5v to 23v - output voltage v fb to v cc - duty ratio 0% to 100% p wm control - oscillation frequency 250khz typ. - current limit (cl). - thermal shutdown function. - short circuit protect (scp). - built-in internal p-channel mos and drive external n-channel mos. - sop-8l with exposed pad 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.1.2 aug.19, 2010 AX3122 ? block diagram pvcc oscillation circuit + - gaten comp fb sw thermal shutdown - pwm switched control circuit pmos clm gnd vcc dead time sense zero crossing reference voltage vfb=0.62v pre-driver ? pin assignment the package of AX3122 is sop-8l-ep; the pin assignment is given by: name description comp compensation pin gnd ground pin vcc ic power supply pin pvcc driver power supply pin sw switch pin. connect external inductor here. gaten nmos control pin sense zero-crossing sense input pin fb feedback pin ? order/marking information order information top marking package type es: sop-8l-ep AX3122 xx x packing blank : tube a : taping logo y ax 3 part number id code:internal ww: 01~52 year: 10=2010 11=2011 1 22 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.1.2 aug.19, 2010 AX3122 ? absolute maximum ratings (at t a =25c) characteristics symbol rating unit vcc,pvcc pin volta g e v cc v ss - 0.3 to v ss + 24 v feedback pin volta g e v fb v ss - 0.3 to v cc v gaten pin volta g e v gaten v ss - 0.3 to v cc v sense pin volta g e v sense v ss - 0.3 to v cc v comp pin volta g e v comp v ss - 0.3 to 5 v switch pin volta g e v sw v ss - 0.8 to v cc + 0.3 v power dissipation pd internall y limited mw stora g e temperature ran g e t st -40 to +165 c junction temperature ran g e t j -40 to +150 c operatin g suppl y volta g e v op 4.5 to 23 v thermal resistance from junction to case jc 15 c/w thermal resistance from junction to ambient ja 40 c/w note: ja is measured with the pcb copper area(need connect to exposed pad) of approximately 1 in 2 (multi-layer). ? electrical characteristics (v in = 12v, v out =3.3v, t a =25c, unless otherwise specified) characteristics symbol conditions min typ max units feedback voltage v fb i out =0.1a 0.605 0.620 0.635 v feedback bias current i fb i out =0.1a - 0.1 0.5 ua quiescent current i ccq v fb =1.2v force driver off - 6 8 ma switch current limit i sw-lim 5.5 - - a line regulation v out /v out v in = 4.5v~23v, i out =0.2a - 0.1 0.5 % load regulation v out /v out i out = 0.1a to 5a - 0.1 0.5 % oscillation frequency f osc sw pin 200 250 300 khz short oscillation frequency f osc1 v fb <0.4v - 60 - khz dead time t dr rising - 50 - ns t df falling - 50 - internal pmos r dson r ds(on)-p v in =5v, v fb =0v - 90 150 m ? v in =12v, v fb =0v - 50 120 gaten driving time t drive rising, c gate =1000pf - 80 - ns falling, c gate =1000pf - 60 - ns thermal shutdown t sd - 150 - c thermal shutdown h y steresis t sh - 30 - c 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.1.2 aug.19, 2010 AX3122 ? application circuit c1 470uf c5 470uf 1 2 l1 r2 13k r4 3k v in =4.5~20v vout = 3.3v/5a r3 c6 0.1uf fb 2 3 comp 1 pvcc 4 vcc 8 sw 6 snese 7 gnd 5 AX3122 r2 r4 vfb = 0.62v ; r4 suggest 3k ~ 6.8k vout = vfb x (1 + ) c2 0.1uf c3 1nf c8 c9 r5 q1 ap4800 gaten c4 470uf r7 4.7k shutdown enable vin<15v , r5=4r7 ; vin>=15v , r5=3r3 4r7 cout esr range v in v out r3( ? ) c8 c9 30m~80m ? 4.5v~20v 1.2v~5v 1.2k 10n 2.2n 80m~300m ? 4.5v~20v 1.2v~5v 820 10n 560p ? function descriptions pwm control the AX3122 consists of dc/dc converte rs that employ a synchronous pulse-width modulation (pwm) system. the synchronous conv erter is built inside pmos and outside control nmos in order to reduce ic temper ature for heavy load. in converters of the AX3122, the pulse width varies in a range from 0 to 100%, according to the load current. the ripple voltage produced by the switchi ng can easily be removed through a filter because the switching frequency re mains constant. therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current. setting the output voltage application circuit item shows the bas ic application circuit with adjustable output version. the external resistor sets the output voltage according to the following equation: ? ? ? ? ? ? ??? 4 2 1620 r r v v out . 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.1.2 aug.19, 2010 AX3122 table 1 resistor select for output voltage setting v out r4 r2 5.0v 4.7k 33k 3.3v 3k 13k 2.5v 3.3k 10k 1.8v 6.8k 13k 1.5v 3.3k 4.7k 1.184v 3.3k 3.0k 1.0v 3.3k 2.0k comp compensation pin. the comp pin connec ts r3 and c8 to gnd for all condition. in low esr output capacitor, r3=1.2k ? and c8=10nf. when esr>80m ? , r3 can be changed to 820 ? . please refer the application circuit table. inductor selection for most designs, the inductor is sugges ted 22h to 33h. please refer the below table to design. l1 recommend value (v in =12v ,i out =5a) v out 1.2v 1.8v 2.5v 3.3v 5v l1 value 22uh 22h 22uh 33uh 33uh 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 5a, i l =0.75a. 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 (5a+0.375a). input capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. the input capacito r impedance at the switch ing frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. a low esr input capacitor size d for maximum rms current must be used. the capacitor voltage rating should be at least 1.5 times greater than the input voltage, and often much higher voltage ratings are needed to satisfy. 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.1.2 aug.19, 2010 AX3122 output capacitor selection the output capacitor is required to k eep the output voltage rippl e small and to ensure regulation loop stability. the output capacito r must have low impedance at the switching frequency. a low esr capacitor sized for ma ximum rms current must be used. the low esr requirements needed for low output ripple voltage. in heavy load, the two parallel 470uf of output capacitor is must be used that can be system more stability. the capacitor voltage rating should be at least 1.5 times greater than the input voltage, and often much higher voltage ratings are needed to satisfy. layout guidance (please refer layout picture) when laying out the pc board, the following suggestions should be taken to ensure proper operation of the AX3122. these items are also illustrated graphically in below. 1. the power traces, including the source tr ace, the output trace and the inductor trace should be kept short, direct and wi de to allow large current flow. 2. the power ground is keep input capacitor ?s (c1) ground closed and far away signal ground. 3. the c3 bypass capacitor must be closed to v cc and gnd pin. 4. the exposed pad is connecting to sw trace closely and widely. (reduce ic temperature) 5. do not trace signal line under inductor. (AX3122 pcb layout -top view) 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.1.2 aug.19, 2010 AX3122 ? typical characteristics 0.600 0.605 0.610 0.615 0.620 0.625 0.630 0.635 0.640 4.5 7.5 10.5 13.5 16.5 19.5 22.5 vin vs feedback voltage vin (v) feedback voltage (v) 0.600 0.605 0.610 0.615 0.620 0.625 0.630 0.635 0.640 012345 load vs feedback voltage load (a) feedback voltage (v) 0.580 0.590 0.600 0.610 0.620 0.630 0.640 0.650 0.660 -40 -20 0 25 50 85 105 125 temperaure vs feedback voltage temperature () feedback voltage (v) 150 170 190 210 230 250 270 290 310 330 350 -40 -20 0 25 50 85 105 125 temperaure vs frequency temperature () frequency (khz) 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 efficienc y test ( vi n = 5 v ) load (a) efficiency (%) vout=1.2v vout=1.8v vout=2.5v vout=3.3v 0 10 20 30 40 50 60 70 80 90 100 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 effi c i e n cy t est (v i n =12 v) load (a) efficiency (%) vout=1.2v vout=1.8v vout=2.5v vout=3.3v vout=5.0v 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.1.2 aug.19, 2010 AX3122 ? typical characteristics (continues) power-on wave (vin=12v, vout=2.5v, load=5a) power-on wave (vin=5v, vout=1.2v, load=5a) load transient (vin=12v, vout=2.5v, load=0.5~4.5a) load transient (vin=5v, vout=1.2v, load=0.5~4.5a) 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.1.2 aug.19, 2010 AX3122 ? package outlines detail a l h e a a2 a1 e d 7 (4x) b y c detail a y x expose pad symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.75 - - 0.069 a 1 0 - 0.15 0 - 0.06 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 x - 2.34 - - 0.092 - y - 2.34 - - 0.092 - 0 o - 8 o 0 o - 8 o mold flash shall not exceed 0.25mm per side jedec outline: ms-012 ba v?mw`r?y?b? w w w . g o f o t e c h . c o m
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