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ame 1 AME5269 rev . b.01 c 2a, 28v , 340khz synchronous re ctif ied ste p-down converter ie l 2a output current l w ide 4.75v to 28v operating in put ra nge l integrated power mosfet switches l output adjusta ble from 0.925v to 25v l up to 95% efficiency l progra mma ble soft start l sta ble with low esr cera mic output ca pa citors l cycle-by cycle over current protection l fixed 340khz frequency l in put u nder v oltage lockout l system protected by over-current limiting, over-voltage prote ction a nd thermal shut -down l green products meet rohs sta ndards the AME5269 is a f ixed frequency monolithic synchro- nous buck regulator that a cce pts in put voltage from 4.75v to 28v . t wo nmos switche s with low on-re sista nce are integrated on the die. current mode topology is used forfa st tra n sient re spon se a nd good loop sta bility . shutdown mode reduces the input supply current to less tha n 1 m a. an a djusta ble soft-start prevents inrush current at turn-on. this device is availa ble in sop-8 pa ck age. n general de scri ption n fe ature s n application s s l distributed power syste m l networking syste m l fpga, dsp , asic power supplie s l notebook computers n t ypical application i n e n g n d s w c o m p f b v i n 1 2 v l 1 1 5 m h b s s s c 1 1 0 m f / 3 5 v x 2 r 4 1 0 0 k w c 5 1 0 n f r 1 4 4 . 2 k w r 2 1 0 k w c 2 2 2 m f / 1 0 v x 2 c 4 0 . 1 m f c 3 / 3 . 3 n f r 3 / 6 . 9 8 k w v o u t 5 v 2 a a m e 5 2 6 9 c 6 ( o p t i o n a l )
ame 2 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n functional block diagram otp ovp uvlo bs vin sw gnd fb comp ss en 1 . 1 v 0 . 3 v 0 . 925 v 2 . 5 v 1 . 5 v ovdet osc slope ea 6 ua clamp current sense amp lockout cmp shutdown cmp otdet uvlo ircmp logic pwm s r q internal regulators 5 v mh ml ovp clk in
ame 3 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n pin configuration sop-8 top view AME5269-ahaxxx 1. bs 2. in 3. sw 4. gnd 5. fb 6. comp 7. en die attach: 8. ss conductive epoxy 1 3 2 4 5 6 7 8 ame 5269
ame 4 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n pin description sop-8 pin number pin name pin description 1 bs high-side gate drive boost input. bs supplies the drive for the high-side n- channel mosfet switch. connect a 0.01 m f or greater capacitor from sw to bs to power the high side switch. 2 in power input. in supplies the power to the ic, as well as the step-down converter switches. drive in with a 4.75v to 28v power source. bypass in to gnd with a suitable large capacitor to eliminate noise on the input to the ic. 3 sw power switching output. sw is the switching node that supplies power to the output. connect the output lc filter from sw to the output load. note that a capacitor is required from sw to bs to power the high-side switch. 4 gnd ground. connect the exposed pad to pin 4. 5 fb feedback input. fb senses the output voltage to regulate that voltage. drive fb with a resistive voltage divider from the output voltage. the feedback reference voltage is 0.925v. 6 comp compensation node. comp is used to compensate the regulation control loop. connect a series rc network from comp to gnd to compensate the regulation control loop. in some cases, an additional capacitor from comp to gnd is required. 7 en enable input. en is a digital input that turns the regulator on or off. drive en higher than 2.7v to turn on the regulator, drive it lower than 1.1v to turn it off. pull up to the in pin with 100k w resister for automatic start up. 8 ss soft-start control input. ss controls the soft-start period. connect a capacitor from ss to gnd to set the soft-start period. add a 0.1uf capacitor set the soft-start period to 15ms. to disable the soft start feature, leave the ss unconnected.
ame 5 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n ordering information AME5269 - x x x xxx pin configuration package type number of pins output voltage a 1. bs h: sop a: 8 adj: adjustable (sop-8) 2. in 3. sw 4. gnd 5. fb 6. comp 7. en 8. ss pin configuration package type number of pins output voltage
ame 6 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n available options note: 1. the first 2 places represent product code. it is assigned by ame such as bm. 2. y is year code and is the last number of a year. such as the year code of 2008 is 8. 3. a bar on top of first letter represents green part such as a5269. 4. the last 3 places mxx represent marking code. it contains m as date code in "month", xx as ln code and that is for ame internal use only. please refer to date code rule section for detail information. 5. please consult ame sales office or authorized rep./distributor for the availability of output voltage and package type. part number marking output voltage package operating ambient temperature range AME5269-ahaadj a5269 bmymxx adj sop-8 -40 o c to +85 o c n absolute maximum ratings parameter maximum unit supply voltage -0.3v to +30v v switch voltage -1v to v in +0.3 v boost switch voltage -0.3v to v sw + 6 v all other pins -0.3v to +6 v en voltage -0.3v to v in v esd classification (hbm) 2 kv esd classification (mm) 200 v
ame 7 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n recommended operating conditions n thermal information * measure q jc on center of molding compound if ic has no tab. ** mil-std-202g 210f parameter rating unit ambient temperature range -40 to +85 o c junction temperature range -40 to +125 o c storage temperature range -65 to +150 o c parameter package die attach symbol maximum unit thermal resistance* (junction to case) q jc 31 thermal resistance (junction to ambient) q ja 90 internal power dissipation p d 1.111 w 150 260 o c lead temperature (soldering 10 sec)** sop-8 conductive epoxy o c / w maximum junction temperature
ame 8 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n electrical specifications v in = 12v, t a = 25 o c, unless otherwise noted. parameter symbol min typ max units shutdown current i shdn 1 3.0 a supply current 1.3 1.5 ma feedback voltage v fb 0.9 0.925 0.95 v ovp threshold voltage 1.10 v error amplifier voltage gain a ea 400 v/v error amplifier transconductance g ea 800 a/v high-side switch on resistance r ds,on,hi 135 m w low-side switch on resistance r ds,on,lo 105 m w switch leakage current i sw,lk 10 a high-side switch current limit 2.4 a low-side switch current limit 1.1 a comp to current sense transconductance g cs 5.2 a/v 300 340 380 khz 270 400 khz short circuit oscillation frequency f osc,scr 116 khz maximum duty cycle d max 90 % minimum on time t on,min 220 ns 3.8 4.05 4.3 v 3.5 4.7 v input undervoltage lockout hysteresis v uvlo,hyst 210 mv soft-start current source i ss 6 a soft-start period t ss 15 ms 2.2 2.5 2.7 v 2.2 2.7 v en shutdown threshold voltage 1.1 1.56 2 v en shutdown threshold voltage hysteresis 210 mv en lockout hysteresis 210 mv thermal shutdown temperature otp 160 o c thermal shutdown hysteresis oth 20 o c restore, temperature decreasing v ss = 0v c ss = 0.1f -40 o c ?? t a ?? +85 o c shutdown, temperature increasing v en rising en lockout threshold voltage v en t a = 25 o c v fb = 0v input undervoltage lockout v uvlo v in rising, t a = 25 o c -40 o c ?? t a ?? +85 o c v fb = 0.8v from drain to source current limit oscillation frequency f osc,cl t a = 25 o c -40 o c ?? t a ?? +85 o c v en = 0v, v sw = 0v minimum duty cycle d ic = 10a test condition v en = 0v v en = 2.0v, v fb = 1.0v 4.75v ?? v in ?? 28v
ame 9 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n detailed description oscillator frequency the internal free running oscillator sets the pwm fre- quency at 340khz. enable and soft start the en pin provides electrical on/off control of the regu- lator. once the en pin voltage exceeds the lockout thresh- old voltage, the regulator starts operation and the soft start begins to ramp. if the en pin voltage is pulled below the lockout threshold voltage, the regulator stops switching and the soft start resets. connecting the pin to ground or to any voltage less than 1.1v will disable the regulator and activate the shutdown mode. to limit the start-up inrush current, a soft-start circuit is used to ramp up the refer- ence voltage from 0v to its final value, linearly. the soft- start time is 15 ms typically. under voltage lockout (uvlo) the AME5269 incorporates an under voltage lockout cir- cuit to keep the device disabled when v in (the input volt- age) is below the uvlo start threshold voltage. during power up, internal circuits are held inactive and the soft start is grounded until v in exceeds the uvlo start thresh- old voltage. once the uvlo start threshold voltage is reached, the soft start is released and device start-up be- gins. the device operates until v in falls below the uvlo stop threshold voltage. the typical hysteresis in the uvlo comparator is 210mv. over current protection overcurrent limiting is implemented by monitoring the current through the high side mosfet. if this current ex- ceeds the over-current threshold limit, the overcurrent in- dicator is set true. the system will ignore the over-current indicator for the leading edge blanking time at the begin- ning of each cycle to avoid any turn-on noise glitches. once overcurrent indicator is set true. the high-side mosfet is turned off for the rest of the cycle after a propa- gation delay. this over-current limiting mode is called cycle-by-cycle current limiting. over-voltage protection the AME5269 has an over-voltage protection (ovp) cir- cuit to minimize voltage overshoot when recovering from output fault conditions. the ovp circuit include an over- voltage comparator to compare the fb pin voltage and a threshold of 120% x v fb . once the fb pin voltage is higher than the threshold, the comp pin and the ss pin are dis- charged to gnd, forcing the high-side mosfet off. when the fb pin voltage drops lower than the threshold, the high- side mosfet will be enabled again. thermal shutdown the AME5269 protects itself from overheating with an internal thermal shutdown circuit. if the junction tempera- ture exceeds the thermal shutdown trip point, the voltage reference is grounded and the high-side mosfet is turned off. the part is restarted under control of the soft start circuit automatically when the junction temperature drops 30 o c below the thermal shutdown trip point. component selection setting the output voltage the output voltage is using a resistive voltage divider con- nected from the output voltage to fb. it divides the output voltage down to the feedback voltage by the ratio: the output voltage is: 2 1 2 r r r v v out fb + = 2 2 1 925 . 0 r r r v out + =
ame 10 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n detailed description (contd.) inductor the inductor is required to supply constant current to the load while being driven by the switched input voltage. a larger value inductor will have a larger physical size, higher series resistance, and lower saturation current. it will result in less ripple current that will in turn result in lower output ripple voltage. make sure that the peak induc- tor current is below the maximum switch current limit. determine inductance is to allow the peak-to peak ripple current to be approximately 30% of the maximum switch current limit. the inductance value can be calculated by: where fs is the switching frequency, v in is the input voltage, v out is the output voltage, and d i l is the peak-to- peak inductor ripple current. choose an inductor that will not saturate under the maximum inductor peak current, calculated by: where i load is the load current. the choice of which style inductor to use mainly depends on the price vs. size re- quirements and any emi constraints. input capacitor the input current to the step-down converter is discon- tinuous, therefore a capacitor is required to supply the ac current while maintaining the dc input voltage. use low esr capacitors for the best performance. ceramic capaci- tors are preferred, but tantalum or low-esr electrolytic capacitors will also be suggested. choose x5r or x7r dielectrics when using ceramic capacitors. since the input capacitor (c1) absorbs the input switching current, it requires an adequate ripple current rating. the rms current in the input capacitor can be estimated by: at v in = 2v out , where ic1 = i load /2 is the worst-case condition occurs. for simplification, use an input capaci- tor with a rms current rating greater than half of the maxi- mum load current. when using ceramic capacitors, make sure that they have enough capacitance to provide suffi- cient charge to prevent excessive voltage ripple at input. when using electrolytic or tantalum capacitors, a high quality, small ceramic capacitor, i.e. 0.1 m f, should be placed as close to the ic as possible. the input voltage ripple for low esr capacitors can be estimated by: where c1 is the input capacitance value. output capacitor the output capacitor (c2) is required to maintain the dc output voltage. ceramic, tantalum, or low esr electrolytic capacitors are recommended. low esr capacitors are preferred to keep the output voltage ripple low. the output voltage ripple can be estimated by: where r esr is the equivalent series resistance (esr) value of the output capacitor and c2 is the output capaci- tance value. when using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. for simpli- fication, the output voltage ripple can be estimated by: when using tantalum or electrolytic capacitors, the esr dominates the impedance at the switching frequency. for simplification, the output ripple can be approximated to: the characteristics of the output capacitor also affect the stability of the regulation system. the AME5269 can be optimized for a wide range of capacitance and esr values. ? ? ? ? - = in out in out load c v v v v i i 1 1 ? ? ? ? - d = in out l s out v v i f v l 1 ? ? ? ? - + = in out s out load lp v v l f v i i 1 2 ? ? ? ? - = d in out in out s load in v v v v f c i v 1 1 ? ? ? ? ? + ? ? ? ? - = d 2 8 1 1 c f r v v l f v v s esr in out s out out ? ? ? ? - = d in out s out out v v c l f v v 1 2 8 2 esr in out s out out r v v l f v v ? ? ? ? - = d 1
ame 11 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n detailed description (contd.) compensation components AME5269 has current mode control for easy compensa- tion and fast transient response. the system stability and transient response are controlled through the c omp pin. c omp is the output of the internal transconductance error amplifier. a series capacitor-resistor combination sets a pole-zero combination to govern the characteristics of the control system. the dc gain of the voltage feedback loop is given by: where v fb is the feedback voltage (0.925v), a vea is the error amplifier voltage gain, g cs is the current sense transconductance and r load is the load resistor value. the system has two poles of importance. one is due to the output capacitor and the load resistor, and the other is due to the compensation capacitor (c3) and the output resistor of the error amplifier. these poles are located at: where g ea is the error amplifier transconductance. the system has one zero of importance, due to the com- pensation capacitor (c3) and the compensation resistor (r3). this zero is located at: the system may have another zero of importance, if the output capacitor has a large capacitance and/or a high esr value. the zero, due to the esr and capacitance of the output capacitor, is located at: in this case, a third pole set by the compensation ca- pacitor (c6) and the compensation resistor (r3) is used to compensate the effect of the esr zero on the loop gain. this pole is located at: the goal of compensation design is to shape the con- verter transfer function to get a desired loop gain. the system crossover frequency where the feedback loop has the unity gain is important. lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system insta- bility. a good standard is to set the crossover frequency below one-tenth of the switching frequency. to optimize the compensation components, the following procedure can be used . 1. choose the compensation resistor (r3) to set the desired crossover frequency. determine r3 by the following equation: where f c is the desired crossover frequency which is typically below one tenth of the switching frequency. 2. choose the compensation capacitor (c3) to achieve the desired phase margin. for applications with typical inductor values, setting the compensation zero (fz1) be- low one-forth of the crossover frequency provides suffi- cient phase margin. determine c3 by the following equation: where r3 is the compensation resistor. out fb ea cs load vdc v v a g r a = vea ea p a c g f = 3 2 1 p load p r c f = 2 2 1 2 p 3 3 2 1 1 r c f z = p esr esr r c f = 2 2 1 p 3 6 2 1 3 r c f p = p fb out cs ea fb out cs ea c v v g g fs c v v g g f c r < = 1 . 0 2 2 2 2 3 p p c f r c > 3 2 4 3 p
ame 12 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter 3. determine if the second compensation capacitor (c6) is required. it is required if the esr zero of the output capaci- tor is located at less than half of the switching frequency, or the following relationship is valid: if this is the case, then add the second compensation ca- pacitor (c6) to set the pole fp3 at the location of the esr zero. determine c6 by the equation: 2 2 2 1 s esr f r c < p n detailed description (contd.) 3 2 6 r r c c esr =
ame 13 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n characterization curve efficiency vs. output current efficiency vs. output current frequency vs. temperature v in = 12v v out = 5v i out = 2000ma c ss = 0.1 m f 1) en = 5v/div 2) v out = 2v/div 3) i l = 2a/div 4) i out = 2a/div start-up form en 0 10 20 30 40 50 60 70 80 90 100 100 1000 10000 output current ( ma ) e f f i c i e n c y ( % ) v out = 3 . 3 v v in = 12 v c in = 20 m f c out = 44 m f l = 10 m h 0 10 20 30 40 50 60 70 80 90 100 100 1000 10000 output current ( ma ) e f f i c i e n c y ( % ) v out = 5 v v in = 12 v c in = 20 m f c out = 44 m f l = 15 m h 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 - 50 - 25 0 + 25 + 50 + 75 + 100 + 125 f r e q u e n c y ( k h z ) temperature ( o c ) v in = 12 v 1 3 2 4 4 ms / div
ame 14 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter power off from en n characterization curve v in = 12v v out = 5v i out = 2000ma c ss = 0.1 m f 1) en = 5v/div 2) v out = 5v/div 3) i l = 2a/div 4) i out = 2a/div load step load step load step v in = 12v v out = 3.3v i out = 0ma to 2000ma c ss = 470pf, t a =25 o c 1) v comp = 1v/div 2) v out = 500mv/div 3) i l = 2a/div 4) i out = 2a/div v in = 12v v out = 5v i out = 0ma to 2000ma c ss = 470pf, t a =25 o c 1) v comp = 1v/div 2) v out = 500mv/div 3) i l = 2a/div 4) i out = 2a/div v in = 12v v out = 3.3v i out = 500ma to 2000ma c ss = 470pf, t a =25 o c 1) v comp = 1v/div 2) v out = 500mv/div 3) i l = 2a/div 4) i out = 2a/div 1 3 2 4 400 m s / div 1 3 2 4 200 m s / div 1 3 2 4 200 m s / div 1 3 2 4 200 m s / div
ame 15 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie load step v in = 12v v out = 5v i out = 500ma to 2000ma c ss = 470pf, t a =25 o c 1) v comp = 1v/div 2) v out = 500mv/div 3) i l = 2a/div 4) i out = 2a/div stead state test 1 3 2 4 2 m s / div v in = 12v v out = 5v i out = 0ma c ss = 470pf 1) v in = 50v/div 2) v comp = 20mv/div 3) i l = 500ma/div 4) i out = 500ma/div n characterization curve 1 3 2 4 200 m s / div
ame 16 AME5269 rev. b.01 2a, 28v, 340khz synchronous rectified step-down converter n date code rule 1: january 7: july 2: february 8: august 3: march 9: september 4: april a: october 5: may b: november 6: june c: december month code n tape and reel dimension carrier tape, number of components per reel and reel size sop-8 pin 1 w p a m e a m e package carrier width (w) pitch (p) part per full reel reel size sop-8 12.00.1 mm 4.00.1 mm 2500pcs 3301 mm
ame 17 AME5269 rev. b.01 c 2a, 28v, 340khz synchronous rectified step-down converter ie n package dimension sop-8 7 o ( 4 x ) c top view side view front view d e l a a 2 a 1 e b c h pin 1 min max min max a 1.35 1.75 0.0531 0.0689 a 1 0.10 0.30 0.0039 0.0118 a2 b 0.33 0.51 0.0130 0.0201 c 0.17 0.25 0.0067 0.0098 d 4.70 5.33 0.1850 0.2098 e 3.80 4.00 0.1496 0.1575 e l 0.40 1.27 0.0157 0.0500 h 5.80 6.30 0.2283 0.2480 y - 0.10 - 0.0039 q 0 o 8 o 0 o 8 o 1.473 ref 0.0580ref 1.27 bsc 0.0500 bsc symbols millimeters inches
life support policy: these products of ame, inc. are not authorized for use as critical components in life-support devices or systems, without the express written approval of the president of ame, inc. ame, inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information. ? ame, inc. , october 2012 document: 3003-ds5269-b.01 corporate headquarter ame, inc. 8f, 12, wenhu st., nei hu taipei, taiwan. 114 tel: 886 2 2627-8687 fax: 886 2 2659-2989 www.ame.com.tw e-mail: sales@ame.com.tw

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