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a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 1 - de s cri p t i o n f eat u r es the A7111 is a constant frequency, 1.5mhz, slope compensated current mode pwm stepdown converter working under an input voltage range of 2.5v to 5.5v. this feature makes the A7111 suitable for single cell liion battery - powered applic ations. the internal synchronous rectifier is desired to increase efficiency without an external schottky diode. 100% duty cycle capability extends battery life in portable devices, while the quiescent current is 200 a at no load, and drops to < 1a in shutdown. pulse skipping mode operation increases efficiency at light loads, further extending battery life. the A7111 is offered in a low profile (1mm) 5 - pin, thin sot - 23 package, and is available in an adjustable version and fixed output versions of 1.0v, 1.2v, 1.5v , 1.8v, 2.5v and 3.3v. the A7111 is available in sot -25 and dfn6(2x2) package. o rde r i nf o rm a t i o n p ac k ag e t y pe p ar t n um ber sot - 25 e5 A7111 e5r - xx A7111 e5vr - xx dfn6 (2x2) j6 A7111j6r - xx A7111j6vr - xx note xx: output voltage 33=3.3v,adj=adjustable r: tape & reel v: halogen free package ait provides all rohs products suffix v means halogen free package ? high efficiency: up to 96% ? 1.5mhz constant switching frequency ? current mode operation for excellent line and load transient response ? no schottky diode required ? 2.5v to 5.5v input voltage range ? 1.0v,1.2v,1.5v,1.8v,2.5v and 3.3v fixed/adjustable output voltage ? 100% duty cycle in dropout mode ? low quiescent current: 200a ? over temperature protecti on ? short circuit protection ? shutdown quiescent current < 1a ? available in sot - 25 and dfn6(2x2) package appl i c at i o n ? cellular and smart phones ? wireless handsets and dsl modems ? microprocessors and dsp core supplies ? pdas ? digital still and video cameras ? mp3 /mp4/mp5 players ? portable instruments ? gps receivers t ypi c al a p p l ic a t i on ci r cui t figure 1. A7111 - adj typical application circuit
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 2 - p i n de s cri p t i o n top view top view p i n # sy m b o l f u nc t i on so t - 23 df n 6 1 2 en regulator enable control input. drive en above 1.5v to turn on the part. drive en below 0.3v to turn it off. in shutdown, all functions are disabled drawing <1ka supply current. do not leave en floating. 2 1 , 5 gnd ground 3 4 sw powe r switch output. it is the switch note connection to external ind uctor. this pin connects to the drains of the internal p - ch and n - ch mosfet switches. 4 3 v in supply input pin. must be closely decoupled to gnd, pin 2, with a 2.2f or greater ceramic cap acitor . 5 6 v fb /v out v fb (adj) : feedback input pin. connect fb to the center point of the external resistor divider. the feedback threshold voltage is 0.6v. v out (fixed): out put voltage pin. an internal resistive divider divides the output voltage down f or comparison to the internal reference voltage.
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 3 - abso l u t e m ax i m u m r at i n g s input supply voltage - 0.3v to +6v en , v fb voltages - 0.3v to +v in sw voltages - 0.3v to (v in +0.3v) p- channel switch source current (dc) 1.1 a n- channel switch sink current (dc) 1.1a peak sw sink and source current 1.5a operating temperature range - 40c to +85c junction temperature note +125c storage temperature range - 65c to +150c lead temperature (soldering, 10s) +300c stresses above may cause permanent damage to the device. t hese are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the electrical characteristics i s not implied. exposure to absolute m aximum rating conditions for extended periods may affect device reliability. note : t j is calculated from the ambient temperature ta and power dissipation pd according to the fo llowing formula: t j = t a + (p d ) x (220c/w) t h er m al r esi st an c e p ac k ag e ja jc sot -25 2 50 c/w 1 30 c/w dfn6 165 c/w 20c/w note : thermal resistance is specified with approximately 1 square of 1 oz copper
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 4 - e l e ct ri ca l cha ra ct e ri s t i cs v in = v en = 3.6v, t a = 25c, unless otherwise specified . p ar a met er c ond i t i ons m in t yp m ax un it input voltage range 2.5 - 5.5 v input dc supply current active mode shutdown mode v fb = 0.5v or v out = 90% v fb = 0v, v in = 4.2v - - 200 0.1 300 1.0 a a regulated feedback voltage t a = +25c 0.5880 0.6000 0.6120 v t a = 0c t a 85c 0.5865 0.6000 0.6135 v t a = - 40c t a 85c 0.5850 0.6000 0.6150 v v fb input bias current v fb = 0.65v - - 30 na reference voltage line regulation v in = 2.5v to 5.5v - 0.04 0.4 %/v regulated output voltage 12v - 40c t a 85c 1.164 1.200 1.236 v 18v - 40c t a 85c 1.746 1.800 1.854 v output overvoltage lockout v ovl =v ovl -v fb , adjustable version 20 50 80 mv v ovl = v ovl C v out , fixed version 2.5 7.8 13 % output voltage line regulation v in = 2.5v to 5.5v - 0.04 0.40 % output voltage load regulation - 0.5 - % peak inductor current v in =3v, v fb =0.5v or v out =90% duty cycle <35% - 1.3 - a oscillator frequency v fb =0.6v or v out =100% 1.2 1.5 1.8 mhz r ds(on) of p - ch mosfet i sw = 300ma - 0.40 0.50 ? r ds(on) of n - ch mosfet i sw = - 300ma - 0.35 0.45 ? sw leakage v en = 0v, v sw = 0v or 5v, v in = 5v - 0.01 1 a en threshold - 40c t a 85c 0.3 1.1 1.30 v en leakage current - 0.01 1 a
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 5 - t y p i ca l p e rf o rm a n ce cha ra ct e ri s t i cs 1. output voltage vs load current 2. efficiency vs output c urrent 3. reference voltage vs temperature 4. output voltage vs input voltage 5. supply current vs supply voltage 6. start_up from shutdown
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 6 - 7. load step 8. load step 9. load step 10. load step 11. pulse skipping mode 12. output short
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 7 - b l o c k d i a g r a m
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 8 - d e t a il e d in f or m a t ion o p er at i on the a 7111 uses a constant frequency, current mode step - down architecture. both the main switch (p - channel mosfet) and the synchronous rectifier (n - channel mosfet) are integrated internally. this step - down dc - dc converter can supply 600ma output current over a wide input voltage range from 2.5v to 5.5v. the over voltage comparator ovdet guards against transient overshoots >7.8% by turning the main switch off and keeping it off until the fault is removed. c ur r ent mo de p w m c ont r ol slope compensated current mode pwm control provides stable switching and cycle by - cycle current limit for excellent load and line responses. during normal operation, the internal main switch i s turned on for a certain time to ramp the inductor current at each rising edge of the internal oscill ator, and turned off when the peak inductor current reaches the controlled value. 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, as indicated by t h e current reversal comparator, i rcmp , or the beginning of the next clock cycle. p u l s e s k i p pi n g mod e o p er a t i on at very light loads, the A7111 will automatically enter pulse skipping mode to increase efficiency, further extending battery life. in this mode, the control loop skips pwm pulses while maintaining output in regulation, and the switching frequency depends on the load condition. this is a kind of pfm mode operation. d r o po ut o p er at i on when the input voltage decreases toward the value of the output voltage, the A7111 will keep the main switch on for more than one switching cycle and increases the duty cycle note5 until it reaches 100%. the output voltage then is the input voltage minus the voltage drop across the main switch and the inductor. a t low i nput supply voltage, the r ds(on) of the p - channel mosfet increases, and the efficiency of the converter decreases. caution must be exercised to ensure the heat dissipated not to exceed the maximum junction temperature of the ic. note 5: the duty cycle d of a step - down converter is defined as: where t on is the main switch on time, and f osc is the oscillator frequency (1.5mhz).
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 9 - s hor t c i r c u i t p r ot ec t i o n the A7111 has short circuit protection. when output is shorted to ground, the oscillator frequency is red uced to prevent the inductor current from increasing beyond the pfet current limit. the pfet curr ent limit is also reduced to lower the short circuit current. the frequency and current limit will return to the norm al values once the short circuit condition is removed and the feedback voltage reaches 0.6v. m ax i mum lo ad c ur r en t the A7111 will operate with input supply voltage as low as 2.5v, however the maximum load current decreases at lower input voltage due to large ir drop on the main switch and synchronous rectifier. a pp l i c at i on i nf or mat i o n figure 2 below shows the basic application circuit with A7111 fixed output versions. figure 2. basic application circuit with fixed output versions s et t i n g t he o u t pu t v ol t ag e figure 1 of page #1 shows the basic a pplication circuit with A7111 adjustable output version. the external resistor sets the output voltage according to the following equation: table 1 - resistor selection vs output voltage setting v out r1 r2 1.0v 180 120 1.2v 180 180 1.5v 180 270 1.8v 1 80 360 2.5v 158 499 3.3v 180 810
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 10 - i nduc t or s el ec t i o n the output inductor is selected to limit the ripple current to some predetermined value, typically 20%~40% of the full load current at the maximum input voltage. in continuous mode, the ripple current is determined by: a reasonable starting point for setting ripple current is i l = 240ma (40% of 600ma). for output voltages above 2.0v, when efficiency at light load condition is important, the minimum recommended inductor is 2.2 h. for optimum voltag e- positioning load transients, choose an inductor with dc series resistance below 150m . for higher efficiency at heavy loads (above 200ma), or minimal load regulatio n (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. thus, a 720ma rated inductor should be enough for most applications (600ma+120ma). i npu t c a pac i t or s e l ec t i on the input capacitor reduces the surge current drawn from the input and switching noise from the device. the input capacitor impedance at the switching frequency shall be less than input sour ce impedance to prevent high frequency switching current passing to the input. in continuous mode, the s ource current of the main switch is a square wave of duty cycle v out /v in . to prevent large voltage transients, a low esr input capacitor sized for the maximum rms current must be used. the maximum rms capacitor current is given by: this formula has a maximum at v in = 2v out , where i rms = i out /2. this simple worst - case condition is commonly used for design because even significant deviations do not offer much r elief. ceramic capacitors with x5r or x7r dielectrics are recommended due to their low esr and high ripple current. o ut put c a pac i t or s el ec t i on the output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. the output capacitor must have low impedance at the switching frequency. cerami c capacitors with x5r or x7r dielectrics are recommended due to their low esr and high ripple curr ent. the output ripple v out is determined by:
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 11 - e f f i c i e nc y c ons i der a t i ons l ay out c o ns i d er at i ons when laying out the printed circuit board, the following checklist should be used to ensure proper operation of the A7111 . these items are also illustrated graphically in figures 5 and 6. check the following in your layout : 1. the power traces, consisting of the gnd trace, the sw trace and the v in trace should be kept short, direct and wide. 2. does the v fb pin connect directly to the feedback resistors? the resistive divider r1/r2 must b e connected between the (+) plate of c out and ground. 3. does the (+) plate of c in connect to v in as closely as possible? this capacitor provides the ac current to the internal power mosfets. 4. keep the switching node, sw, away from the sensitive v fb node. 5. k eep the ( - ) plates of c in and c out as close as possible. figure 3. A7111 - adj layout circuit figure 4. A7111 - 1.8 layout circuit
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 12 - figure 5. A7111 - adj suggested layout figure 6. A7111 - xx (fixed) suggested layout
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 13 - p a c k a g e i n f o r m a t i o n dimension i n sot - 25 (unit: mm) s y mb ol m in m ax a 1.050 1.250 a1 0.000 0.100 a2 1.050 1.150 b 0.300 0.500 c 0.100 0.200 d 2.820 3.020 e 1.500 1.700 e1 2.650 2.950 e 0.950(bsc) e1 1.800 2.000 l 0.300 0.600 0 8
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 14 - dimension in dfn6(2x2) package (unit: mm) s y mb ol m in m ax a 0.700 0.800 a1 0.000 0.050 a3 0.175 0.250 b 0.200 0.350 d 1.9 50 2.05 0 d2 1.000 1.450 e 1.950 2.050 e2 0.500 0.850 e 0.650typ. l 0.300 0.400
a i t s em i c ond u ctor i n c . www.ait - ic.com a 71 11 1.5 mhz, 1a synchronous psm/pwm buck (step - down) dc - dc converter rev1. 1 - may 2011 released , feb 201 3 revised - - 15 - i m p o rt a nt no t i ce ait semiconductor inc. (ait) reserves the right to make changes to any its product, specifications, to discontinue any integrated circuit product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. ait semiconductor inc.'s integrated circuit products are not designed, i ntended, authorized, or warranted to be suitable for use in life support applications, devices or systems or other critical applications. use of ait products in such applications is understood to be fully at the risk of the customer. as us ed herein may involve potential risks of death, personal injury, or servere property, or environmental da mage. in order to minimize risks associated with the customer's applications, the customer should provide adequate design and operating safeguards. ait semiconductor inc. assumes to no liability to customer product design or applica tion support. ait warrants the performance of its products of the specifications applicable at the time of sa le.

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