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ame 1 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n typical application the AME5287 is a synchronous rectified step-down converter with internal power mosfets. it achieves 3a continuous output current over a wide switching frequency range with excellent load and line regulation. current mode operation provides fast transient response and eases of loop stabilization. internal soft-start mini- mizes the inrush supply current at startup. the circuit protection includes cycle-by-cycle current limiting, out- put short circuit frequency protection and thermal shut- down. in shutdown mode, the regulator reduces the cur- rent less than 1 m a of supply current. this device is available in sop-8/pp ,dfn-8 package with exposed pad for low thermal resistance. n general description n applications figure 1. 3.3v at 3a step-down regulators. figure 2. 1v at 3a step-down regulators. l tv l distributed power systems l pre-regulator for linear regulators l digital cameras n features l 3a output current l stable with low esr output ceramic capacitors l pre-regulator for linear regulators l up to 95% efficiency l less than 1 m a shutdown current l wide switching frequency range from 300khz~2mhz l thermal protection l cycle-by-cycle over current protection l output adjustable from 0.8v to v in l short circuit protection l green products meet rohs standards ame 5287 sw r freq 18 k w on off v in 5 v c in 10 m f c 2 optional c 1 680 pf r 3 25 k w in en comp gnd freq r 1 75 k w r 2 24 k w c out 22 m f fb v out 3 . 3 v l 2 . 2 m h ame 5287 sw r freq 18 k w on off v in 3 v ~ 5 v c in 10 m f c 2 optional c 1 680 pf r 3 8 . 2 k w in en comp gnd freq r 1 6 k w r 2 24 k w c out 22 m f fb v out 1 v l 1 . 5 m h
ame 2 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n functional block diagram sop-8/pp top view AME5287-azaadj 1. comp 2. gnd 3. en 4. in 5. sw 6. sw 7. freq 8. fb 9. gnd (exposed pad) * die attach: conductive epoxy note. connect exposed pad (heat sink on the back) to gnd. dfn-8c (3mmx3mmx0.75mm) top view AME5287-avaadj 1. comp 2. gnd 3. en 4. in 5. sw 6. sw 7. freq 8. fb 9. gnd (exposed pad) * die attach: conductive epoxy n pin configuration otp soft start + + - 0 . 8 v vref slope osc enable uvlo pwm in sw sw pgnd en freq comp gnd fb - + ea current sense ircmp - + logic driver current limit short circuit 1 3 2 4 ame 5287 5 6 7 8 9 8 7 6 1 2 3 4 ame 5287 5 9
ame 3 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n pin description pin no. pin name pin description 1 c omp 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. 2 g nd ground. connect the exposed pad to gnd. 3 e n enable. pull en below 0.4v to shut down the regulator. 4 i n power input. in supplies the power to the ic, as well as the step-down converter switches. bypass in to gnd with a suitable large capacitor to eliminate noise on the input to the ic. 5, 6 s w 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. 7 freq frequency adjust pin. add a resistor from this pin to ground determines the switching frequency. 8 f b 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 0.8v. 9 g nd ground. connect the exposed pad to gnd.
ame 4 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n ordering information AME5287 - x x x xxx pin configuration package type number of pins output voltage a 1. comp z: sop/pp a: 8 adj: adjustable (sop-8/pp) 2. gnd v: dfn (dfn-8c) 3. en 4. in 5. sw 6. sw 7. freq 8. fb 9. gnd pin configuration package type number of pins output voltage
ame 5 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n absolute maximum ratings n recommended operating conditions parameter symbol rating unit ambient temperature range t a -40 to +85 junction temperature range t j -40 to +125 storage temperature range t stg -65 to +150 o c n thermal information * measure q jc on backside center of exposed pad. ** mil-std-202g 210f parameter package die attach symbol maximum unit sop - 8 / pp 15 dfn-8c 8.2 sop - 8 / pp 75 dfn-8c 70 sop - 8 / pp 1.333 dfn-8c 1.429 maximum junction temperature 150 o c 260 o c o c / w w lead temperature (soldering 10 sec)** p d q ja q j c conductive epoxy thermal resistance (junction to ambient) thermal resistance* (junction to case) internal power dissipation parameter symbol maximum unit supply voltage v in 6 v s witch voltage v sw -1.5v to v in +0.7v v en, fb, comp, freq to gnd -0.3v to v in +0.3v v hbm 2 kv m m 200 v esd classification
ame 6 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n electrical specifications v in =5v, t a =25 o c, unless otherwise noted. parameter symbol test condition min typ max units input voltage v in 3 5.5 v input uvlo v uvlo 2.3 v quiescent current i q v en = 5 v , v fb =0.7v (no switching) 600 m a shutdown current i shdn v en =0v 1 m a feedback voltage v fb 0.784 0.8 0.816 v feedback current i fb -50 50 n a load regulation reg load 0a ame 7 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter normal operation the AME5287 uses a user adjustable frequency, cur- rent mode step-down architecture with internal mosfet switch. during normal operation, the internal high-side (pmos) switch is turned on each cycle when the oscilla- tor sets the sr latch, and turned off when the compara- tor resets the sr latch. the peak inductor current at which comparator resets the sr latch is controlled by the output of error amplifier ea. while the high-side switch is off, the low-side switch turns on until either the induc- tor current starts to reverse or the beginning of the next switching cycle. dropout operation the output voltage is dropped from the input supply for the voltage which across the high-side switch. as the input supply voltage decreases to a value approaching the output voltage, the duty cycle increases toward the maximum on-time. further reduction of the supply volt- age forces the high-side switch to remain on for more than one cycle until it reaches 100% duty cycle. soft-start the AME5287 has a built-in digital soft-start to control the output voltage rise and limit the current surge at the start-up. when the internal soft-start begins, and count 896 switching cycles, soft start is complete, the converter enters steady state operation. hiccup mode during hiccup mode, the AME5287 disables the high- side mosfet and begins a cool down period of 8320 switching cycles. at the conclusion of this cool down period, the regulator performs an internal 896 cycle soft start identical to the soft start at turn-on. n detailed description under voltage protection under voltage protection will activate once the feed- back voltage falls below 0.4v, the operating frequency is switched to 1/10 of normal switching frequency and after four-times hiccup mode counted, the internal high-side power switch will be turned off,and latched. unless re- start the power supply. over temperature protection in most applications the AME5287 does not dissipate much heat due to high efficiency. but, in applications where the AME5287 is running at high ambient tempera- ture with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maxi- mum junction temperature of the part. if the junction temperature reaches approximately 160 o c, the internal high-side power switch will be turned off and the sw switch will become high impedance. inductor selection for most applications, the value of the inductor will fall in the range of 2.2 m h to 4.7 m h. its value is chosen based on the desired ripple current. large value inductors lower ripple current and small value inductors result in higher ripple currents. higher v in or v out also increase the ripple current d i l : ? ? ? ? ? - = d in out t ou l v v v l f i 1 1
ame 8 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 a reasonable inductor current ripple is usually set as 1/ 3 to 1/5 of maximum out current. 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. for better efficiency, choose a low dcr in- ductor. capacitor selection in continuous mode, the source current of the top mosfet is a square wave of duty cycle v out /v in . to prevent large voltage transients, a low esr input capaci- tor sized for maximum rms current must be used. the maximum rms capacitor current is given by: c in requires i rms this formula has a maximum at v in =2v out , wherei rms =i out /2. for simplification, use an input capaci- tor with a rms current rating greater than half of the maximum load current. the selection of c out is driven by the required effective series resistance (esr). typically, once the esr require- ment for c out has been met, the rms current rating gen- erally far exceeds the i ripple(p-p) requirement. the output ripple d v out is determined by: d v out for a fixed output voltage, the output ripple is highestat maximum input voltage since d i l increases with input volt- age. when choosing the input and output ceramic capaci- tors, choose the x5r or x7r dielectric formulations. these dielectrics have the best temperature and voltage char- acteristics of all the ceramics for given value and size. output voltage programming the output voltage of the AME5287 is set by a resistive divider according to the following formula: loop compensation the AME5287 employs peak current mode control for easy use and fast transient response. peak current mode control eliminates the double pole effect of the output lc filter. it greatly simplifies the compensation loop design. with peak current mode control, the buck power stagecan be simplified to be a one-pole and one-zero sys- tem in frequency domain. the pole can be calculated by: the zero is a esr zero due to output capacitor and its esr. it can be calculated by: . 2 1 1 8 . 0 volt r r v out ? ? + = l out p r c f = p 2 1 1 cout out z esr c f = p 2 1 1 ? ? ? ? ? + d @ out l fc esr i 8 1 ( ) in out in out omax v v v v i - @
ame 9 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter where c out is the output capacitor, r l is load resis- tance; esr cout is the equivalent series resistance of output capacitor. the compensation design is to shape the converter close loop transfer function to get desired gain and phase. for most cases, a series capacitor and resistor network con- nected to the comp pin sets the pole-zero and is ad- equate for a stable high-bandwidth control loop. in the AME5287, fb pin and comp pin are the invert- ing input and the output of internal transconductance er- ror amplifier (ea). a series r 3 and c 1 compensation net- work connected to comp pin provides one pole and one zero: for r 3 <AME5287 circuits: i 2 r losses. the i 2 r loss dominates the efficiency loss at medium to high load cur- rents. the i 2 r losses are calculated from the resistances of the internal switches, r sw , and external inductor r l . in continuous mode, the average output current flowing through inductor l is "chopped" between the main switch and the synchronous switch. thus the series resistance looking into the sw pin is a function of both top and bot- tom mosfet r ds(on) and the duty cycle (d) as follows: r sw = (r ds(on)top )(d) + (r ds(on)bottom )(1-d) the r ds(on) for both the top and bottom mosfets can be obtained from electrical characteristics table. thus, to obtained i 2 r losses, simply add r sw to r l and multiply the result by the square of the average output current. ea ea ea ea p a c g g a r c f ? ? ? ? ? ? + = 1 3 1 2 2 2 1 p p 3 1 2 2 1 r c f z = p cs ea out fb out c g g c v v f r = p 2 3 3 1 r r c c l out =
ame 10 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 other losses including c in and c out esr dissipative losses and inductor core losses generally account for less than 2% total additional loss. thermal considerations in most application the AME5287 does not dissipate much heat due to its high efficiency. but, in applications where the AME5287 is running at high ambient tempera- ture with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maxi- mum junction temperature of the part. if the junction temperature reaches approximately 160 o c, both power switches will be turned off and the sw switch will be- come high impedance.
ame 11 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n typical operating circuit table 1. recommended components selectin for fsw = 2mhz figure 3. AME5287 regulators layout diagram v out (v) c in ( m f) r1(k w ) r2(k w ) r3(k w ) c1 ( pf ) l( m h) c out ( m f ) 3.3 10 75 24 25 680 2.2 22 2.5 10 51 24 20 680 2.2 22 1.8 10 30 24 15 680 1.5 22 1.5 10 21 24 13 680 1.5 22 1.2 10 12 24 11 680 1.5 22 1 10 6 24 8.2 680 1.5 22 v in comp fb freq sw v out gnd r 3 c 1 c in r 2 r 1 r freq l 1 c out c in must be placed between v in and gnd as close as possible sw pad should be connected together to inductor by wide and short trace , keep sensitive components away from this trace . gnd 1 2 3 4 5 6 7 8 v in gnd sw sw v out connect the fb pin directly to feedback resistors . the ground area must provide adequate heat dissipating area to the thermal pad and using multiple vias to help thermal dissipation . place the input and output capacitors as close to the ic as possible en ame 5287 sw r freq chip enable v in 2 . 5 v to 5 v c in 10 m f c 2 optional c 1 r 3 in en comp gnd freq r 1 r 2 c out fb v out l gnd ( exposed pad ) 4 3 1 2 5 , 6 8 7 9
ame 12 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n characterization curve efficiency vs. output current efficiency vs. output current efficiency vs. output current efficiency vs. output current 0 10 20 30 40 50 60 70 80 90 100 0 500 1000 1500 2000 2500 3000 output current ( ma ) e f f i c i e n c y ( % ) v in = 5 v r freq = 18 k v out = 1 . 2 v v out = 3 . 3 v v out = 2 . 5 v v out = 1 . 0 v v out = 1 . 8 v 0 10 20 30 40 50 60 70 80 90 100 0 500 1000 1500 2000 2500 3000 output current ( ma ) e f f i c i e n c y ( % ) v in = 5 v r freq = 30 k v out = 3 . 3 v v out = 2 . 5 v v out = 1 . 8 v v out = 1 . 2 v v out = 1 . 0 v 0 10 20 30 40 50 60 70 80 90 100 0 500 1000 1500 2000 2500 3000 output current ( ma ) e f f i c i e n c y ( % ) v in = 5 v r freq = 47 k v out = 1 . 0 v v out = 1 . 2 v v out = 1 . 8 v v out = 2 . 5 v v out = 3 . 3 v 0 10 20 30 40 50 60 70 80 90 100 0 500 1000 1500 2000 2500 3000 output current ( ma ) e f f i c i e n c y ( % ) v in = 5 v r freq = nc v out = 1 . 0 v v out = 1 . 2 v v out = 1 . 8 v v out = 2 . 5 v v out = 3 . 3 v
ame 13 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n characterization curve (contd.) load step load step load step load step 1) v out = 200mv/div 2) i l = 2a/div 1) v out = 200mv/div 2) i l = 2a/div 1) v out = 200mv/div 2) i l = 2a/div 1) v out = 200mv/div 2) i l = 2a/div time ( 200 m sec / div ) 2 1 v in = 3 . 3 v v out = 1 . 0 v i out = 1 a to 3 a time ( 200 m sec / div ) 2 1 v in = 3 . 3 v v out = 1 . 8 v i out = 1 a to 3 a time ( 200 m sec / div ) 2 1 v in = 5 . 0 v v out = 1 . 0 v i out = 1 a to 3 a time ( 200 m sec / div ) 2 1 v in = 5 . 0 v v out = 3 . 3 v i out = 1 a to 3 a
ame 14 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n characterization curve (contd.) power on from v in power off from v in 1) v in = 5v/div 2) vsw = 5v/div 3) v out = 1v/div 4) i l = 2a/div 1) v in = 5v/div 2) vsw = 5v/div 3) v out = 1v/div 4) i l = 5a/div start-up from en power off from en 1) en = 5v/div 2) v sw = 5v/div 3) v out = 1v/div 4) i l = 2a/div 1) en= 5v/div 2) v sw = 5v/div 3) v out = 1v/div 4) i l = 5a/div 2 1 3 4 2 . 0 ms / div 2 . 0 ms / div 2 1 3 4 2 . 0 ms / div 2 1 3 4 1 . 0 ms / div 1 2 3 4
ame 15 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n characterization curve (contd.) v fb vs. temperature frequency vs. temperature 150 200 250 300 350 400 450 - 40 - 25 - 10 + 5 + 20 + 35 + 50 + 65 + 80 + 95 + 110 + 125 temperature ( c ) f r e q u e n c y ( k h z ) v in = 5 v steady state test steady state test 1) v out = 10mv/div 2) v sw = 2v/div 1) v out = 10mv/div 2) v sw = 2v/div 2 1 400 ns / div v in = 5 v v out = 1 . 1 v i out = 3 a 400 ns / div 2 1 v in = 5 v v out = 3 . 3 v i out = 3 a 0 . 77 0 . 78 0 . 79 0 . 80 0 . 81 0 . 82 - 40 - 25 - 10 + 5 + 20 + 35 + 50 + 65 + 80 + 95 + 110 + 125 temperature ( c ) v f b ( v ) v in = 5 v
ame 16 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 ? characterization curve (contd.) frequency vs. supply voltage short circuit test short circuit test 150 200 250 300 350 400 450 3.5 4 4.5 5 5.5 input voltage (v) frequency (khz) v out = 3.3v frequency vs. output current 200 210 220 230 240 250 260 270 280 290 300 200 400 600 800 1000 1200 1400 1600 1800 2000 iout (ma) frequency (khz) v in =5.0v v out = 3.3v 1) v out = 1v/div 2) i out = 2a/div 1) v out = 2v/div 2) i out = 2a/div time (100ms/div) 2 1 v in =5v v out =1v time (100ms/div) 2 1 v in =5v v out =3.3v
ame 17 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n tape and reel dimension dfn-8c (3mmx3mmx0.75mm) w p pin 1 a m e a m e carrier tape, number of components per reel and reel size sop-8/pp carrier tape, number of components per reel and reel size pin 1 w p a m e a m e package carrier width (w) pitch (p) part per full reel reel size dfn-8c (3x3x0.75mm) 12.00.1 mm 4.00.1 mm 3000pcs 3301 mm package carrier width (w) pitch (p) part per full reel reel size sop-8/pp 12.00.1 mm 4.00.1 mm 2500pcs 3301 mm
ame 18 3a, 300khz ~ 2mhz synchronous rectified step-down converter AME5287 rev. a.01 n package dimension sop-8/pp b e e e 2 c front view side view top view d 1 e 1 l 1 d a 1 a a 2 ? pin 1 min max min max a 1.350 1.750 0.053 0.069 a1 0.000 0.150 0.000 0.006 a2 1.350 1.600 0.053 0.063 c 0.100 0.250 0.004 0.010 e 3.750 4.150 0.148 0.163 e1 5.700 6.300 0.224 0.248 l1 0.300 1.270 0.012 0.050 b 0.310 0.510 0.012 0.020 d 4.720 5.120 0.186 0.202 e q 0 o 8 o 0 o 8 o e2 2.150 2.513 0.085 0.099 d1 2.150 3.402 0.085 0.134 1.270 bsc 0.050 bsc symbols millimeters inches
ame 19 AME5287 rev. a.01 3a, 300khz ~ 2mhz synchronous rectified step-down converter n package dimension (contd.) dfn-8c (3mmx3mmx0.75mm) min max min max a 0.700 0.800 0.028 0.031 d 2.900 3.100 0.114 0.122 e 2.900 3.100 0.114 0.122 e 0.600 0.700 0.024 0.028 d1 2.200 2.400 0.087 0.094 e1 1.400 1.600 0.055 0.063 b 0.180 0.320 0.007 0.013 l 0.375 0.575 0.015 0.023 g 0.153 0.253 0.006 0.010 g1 0.000 0.050 0.000 0.002 symbols millimeters inches top view bottom view rear view e d e a g g 1 b l e 1 d 1 pin 1 identification
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: tu003-ds5287-a.01 corporate headquarter ame, inc. 8f, 12, wenhu st., nei-hu taipei 114, taiwan . tel: 886 2 2627-8687 fax: 886 2 2659-2989 www.ame.com.tw e-mail: sales@ame.com.tw

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