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1 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 dual high - efficiency pwm step - down dc - dc converter ? general description the AX3515 is a dual high - efficiency pulse - width - modulated (pwm) step - down dc - dc converter. it is capable of delivering 1a output current over a wide input voltage range from 2.5v to 5 .5v, the AX3515 is ideally suited for portable electronic devices that are powered from 1 - cell li - ion battery or from other power sources within the range such as cellular phones, pdas and other handheld devices. two operational modes are available: pwm/lo w - dropout auto - switch and shutdown modes. internal synchronous rectifier with low r ds(on) dramatically reduces conduction loss at pwm mode. no external schottky diode is required in practical application. the AX3515 enters low - dropout mode when normal pwm cannot provide regulated output voltage by continuously turning on the upper pmos. the AX3515 enter shutdown mode and consumes less than 0. 1 a when en pin is pulled low. the switching ripple is easily smoothed - out by small package filtering elements due to a fixed operation frequency of 1. 4 mhz. this along with small t dfn - 1 2 l ( 3x3 ) package provides small pcb area application. other features inc lude soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection. ? features - 2.5v to 5.5v input voltage range - adjustable output voltage f rom 0.6v to v in - 1a output current /per channel - high efficienc y : up to 95% - no schottky diode required - 1. 4 mhz fixed - frequency pwm operation - small 1 2 - lead t dfn package
2 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? b lock d iagram f b 1 e n 1 v i n 1 l x 1 g n d 1 o v e r - t e m p e r a t u r e a n d s h o r t - c i r c u i t p r o t e c t i o n f b s o f t - s t a r 0 . 6 v + - - + i c o m p - + i s e n s e a m p o s c s l o p e c o m p p w m l o g i c n o n - o v e r l a p c o n t r o l r e s e t s e t e n a b l e l o g i c f b 2 e n 2 v i n 2 l x 2 g n d 2 o v e r - t e m p e r a t u r e a n d s h o r t - c i r c u i t p r o t e c t i o n f b s o f t - s t a r 0 . 6 v + - - + i c o m p - + i s e n s e a m p o s c s l o p e c o m p p w m l o g i c n o n - o v e r l a p c o n t r o l r e s e t s e t e n a b l e l o g i c
3 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? pin assignment the package of AX3515 is td f n - 12 l (3 3) ; the pin assignment is given by : name description vin2 power input of channel 2. lx2 pin for switching of channel 2. gnd ground. the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. fb1 feedback of chann el 1. nc1, nc2 no connection pin. en1 chip enable of channel 1 (active high). ven1 Q vin1 power input of channel 1. lx1 pin for switching of channel 1. fb2 feedback of channel 2. en2 chip enable of channel 2 (active high). ven2 Q ? order /marking information order information top marking ? absolute maximum ratings (at t a =25 c ) characteristics symbol rating unit supply input voltage v in1 / v in2 - 0.3 to 6.5 v en1, fb1, lx1, en2, fb2 and lx2 pin voltage - 0.3 to v in + 0.3 v power dissipation, pd @ t a = 25 c pd 1. 667 w lead temperature (soldering, 10 sec.) 260 c storage temperature range t st - 65 to 150 c junction temperature t j 150 c thermal resistance from junction to case jc 8.2 c /w thermal resistance from junction to am bient ja 60 c /w note : ja is measured with the pcb copper area of approximately 1 in 2 (multi - layer). that need connect to exposed pad . 1 2 3 4 5 6 1 2 1 1 1 0 9 8 7 g n d e n 2 n c 2 f b 2 g n d 1 l x 1 v i n 1 e n 1 n c 1 f b 1 g n d 2 l x 2 v i n 2 ( t o p v i e w ) t d f n - 1 2 l ( 3 x 3 ) p a c k a g e t y p e j 1 2 : t d f n - 1 2 l ( 3 * 3 ) a x 3 5 1 5 x x x x p a c k i n g a : t a p i n g 3 p a r t n u m b e r i d c o d e : i n t e r n a l w w : 0 1 ~ 5 2 y e a r : 1 0 = 2 0 1 0 1 1 = 2 0 1 1 y y w w x 5 1 5
4 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? recommended operating conditions characteristics symbol rating unit supply input voltage v in 2.5 to 5.5 v junction temperature range t j - 40 to 125 c ambient temperature range t a - 40 to 85 c note : the device is not guaranteed to function outside its operating conditions. ? electrical characteristics (v in = 3.6v, v out = 1.2 v, l = 2.2uh, c in =4.7uf, c out = 10 uf, t a =25c, i max = 1a unless otherwise specified) characteristics symbol conditions min typ max units channel 1 and channel 2 input voltage range v in 2.5 - 5.5 v under voltage lock out threshold uvlo - 1.8 - v hystere sis - 0.1 - v quiescent current (per channel) i q i out =0ma, v fb = 1v - 250 35 0 a sd v en 1 = v en 2 =0v - 0.1 1 a fb 0.588 0.6 0.612 v output voltage accuracy out v in = 2.5v to 5.5v, 0a < i out < 1a - 3 - +3 % fb input c urrent i fb v fb = v in - 50 - 50 na rds(on) of p - mosfet r ds(on)_p v fb =0v, i out = 5 00ma - 0.3 5 - ds(on)_n i out = 5 00ma (note ) - 0.3 - lim _p 1. 2 1. 4 - a en high - level input voltage v en_h 1.5 - - v en low - l evel input voltage v en_l - - 0.4 v oscillator frequency f osc lx pin 1. 1 1. 4 1. 7 mhz maximum duty cycle v fb =0.5v 100 - - % lx leakage current i lx v in = 3.6v, v lx =0v or v lx = 3.6v - 1 - 1 a sd - 1 5 0 - c thermal shutdown hys teresis t s h - 4 0 - c note : guarantee by design .
5 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? a pplication c ircuit adjustable voltage regulator ? f unction d escriptions operation AX3515 is a dual channel, monolithic switching mode step - down dc - dc converter. it utilize s internal mosfets to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6v. it operates at a fixed switching frequency, and uses the slope compensated current mode architecture. this step - down dc - dc converter supplies 1 a output current by each channel with input voltage range from 2.5v to 5.5v. current mode pwm control slope compensated current mode pwm control provides stable switching and cycle - by - cycle current limit for excellent load and line responses and protection of the internal main switch (p - c h mosfet) and synchronous rectifier (n - ch mosfet). during normal operation, the internal p - c h mosfet is turned on for a certain time to ramp the inductor current at each rising edge of the internal 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 off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, beginning of the next clock cycle. k 330 ~ k 50 = rang : 6 r , 3 r ) 6 r 5 r + 1 ( v = v ), 3 r 2 r + 1 ( v = v 2 fb 2 out 1 fb 1 out
6 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? a pplication i nformation setting the output voltage application circuit item shows the basic application circuit with AX3515 adjustable output version. the external resistor sets t he output voltage according to the following equation: table 1 resistor select for output voltage setting v out r 3 /r 6 r 2 /r 5 1.2v 1 00 k 1 00 k 1.5v 1 00k 1 50k 1.8v 15 0k 3 00k 2.5v 15 0k 47 0k 3.3v 120k 540k inductor selection for most designs, the AX3515 operates with inductors of 2.2 h to 3.3 h. low inductance values are physically smaller but require faster switching, which results in some efficiency loss. the inductor value can be derived from the following equation: where is inductor ripple current. large value inductors lower ripple current and small value inductors result in high ripple currents. choose inductor ripple current approximately 20 % of the maximum load current 10 00ma, i l = 20 0ma. table 2 inductor select for output voltage setting ( v in =3.6v) v out 1.2v 1.5v 1.8v 2.5v inductor 2.2 uh 2.2 uh 2.2 uh 2. 2 uh part number we - tpc 7440430022 7440430022 7440430022 744043002 2 note: part type mh or m (www.we - online.com) for optimum voltage - positioning lo ad transients, choose an inductor with dc series resistance in the 50m? to 150m? range. for higher efficiency at heavy loads (above 200ma), or minimal load regulation (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 ( 10 00ma+ 100 ma). ) 6 r 5 r + 1 ( v 6 . 0 = v ), 3 r 2 r + 1 ( v 6 . 0 = v 2 out 1 out ? ? f i v v v v l osc l in out in out ? ? ? ? ? ?
7 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 input capacitor selection the input capacitor reduces the surge current drawn from the input and switc hing noise from the device. the input capacitor impedance at the switching frequency shall be less than input source impedance to prevent high 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 recommended because of their low esr and small tempe rature coefficients. a 4.7 f ceramic capacitor for most applications is sufficient. output capacitor selection the output capacitor is required to be 10 uf to keep the output voltage ripple small and to ensure regulation loop stability. the output capacitor must have low impedance at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended due to their low es r and high ripple current. compensation capacitor selection the compensation capacitors for increasing phase margin provide additi onal stability. it is required 15 pf , please r efer to demo board schematic to design. output voltage programming the resist ive divider allows the fb pin to sense a fraction of the output voltage as shown in setting the output voltage . setting the output voltage for adjustable voltage mode, the output voltage is set by an external resistive divide r according to the following equation: v out 1 = v fb 1 x (1+ r 2 /r 3 ) , v out 2 = v fb 2 x (1+ r 5 /r 6 ) where v fb is the feedback voltage (0.6v typical) a x 3 5 1 5 f b 1 g n d f b 2 r 2 r 3 r 5 r 6 v o u t 1 v o u t 2
8 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 thermal considerations the maximum power dissipation depends on the thermal resistance of ic package, pcb layo ut, the rate of surroundings airflow and temperature difference between junctions to ambient. the maximum power dissipation can be calculated by following formula : p d(max) = ( t j(max) - t a ) / ja where t j(max) is the maximum junction temperature, t a is the ambient temperature and the ja is the junction to ambient thermal resistance. for recommended operating conditions specification of AX3515 dc/dc converter, where t j(max) is the maximum junc tion temperature of the die and t a is the ambient temperature. the junction to ambient thermal resistance ja is layout dependent. for t dfn - 1 2 l ( 3x3 ) packages, the thermal resistance ja is 60 c/w on the 1 in 2 multi - layer pcb copper area (the ic exposed pa d must be connect ed to the pcb copper area) two - layers thermal test board. the maximum power dissipation at t a = 25 c can be calculated by following formula: p d(max) = (125 c - 25 c ) / ( 60 c/w) = 1.667 w for t dfn - 1 2 l ( 3x3 ) package the maximum power dissip ation depends on operating ambient temperature for fixed t j(max) and thermal resistance ja . layout guide 1. input capacitors (c5, c1) are necessarily closed to ic. 2. feedback low - side resistor s (r3, r6) ground trace close to input capacitor s ground trace. 3. a ll power trace is wide and short. 4. feedback trace must keep in d u ctors trace away e n 1 f b 2 1 1 0 2 3 4 7 8 9 f b 1 v i n 2 g n d 2 v i n 1 g n d 1 l x 1 e x p o s e d p a d 5 6 e n 2 l x 2 1 2 1 1 n c 1 n c 2 v i a t o v i n 2 v i a t o v i n 1 r 2 r 3 r 6 r 5 c 5 c 4 c 6 c 1 c 8 c 2 l 1 l 2
9 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? t ypical characteristics
10 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? t ypical characteristics (c ountinous )
11 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? t ypical characteristics (c ountinous ) v in = 5v, v out = 1.2v, r load = no load v in = 5v, v out = 1.2v, r load = 1? v in = 5v, v out = 1.2v, r load = no load v in = 5v, v out = 1.2v v in = 5v, v out = 1.2v, i out = 0 a ? 1a v in = 3.3 v, v out = 1.2 v, i out = 0 a ? 1a
12 / 12 a xelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 oct . 18 , 20 1 1 AX3515 ? p ackage o utlines symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a 0.70 0.75 0.80 0.028 0.030 0.031 a1 0.00 0.02 0.05 0.000 0.001 0.002 a3 0.20 ref 0.008 ref b 0.18 0.25 0.28 0.008 0.010 0.011 d 3.00 b sc 0.118 bsc d2 2.40 2.50 2.55 0.094 0.098 0.100 e 3.00 bsc 0.118 bsc e2 1.50 1.60 1.65 0.059 0.063 0.065 e 0.45 bsc 0.018 bsc l 0.30 0.40 0.50 0.012 0.016 0.002 k 0.20 - - 0.008 - -

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