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ame 1 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter the AME5285 is a synchronous rectified step-down converter with internal power mosfets. it achieves 5a continous 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. this device is available in sop-8/pp package with ex- posed pad for low thermal resistance. n general description n features n applications n typical application l 5a output current l 55m w /45m w internal power mosfet switch l stable with low esr output ceramic capacit -ors l up to 95% efficiency l less than 10 m a shutdown current l wide switching frequency range from 300khz~1.4mhz l thermal shutdown l cycle by cycle over current protection and hiccup l output adjustable from 0.8v to v in l short circuit frequency protection l green products meet rohs standards l tv l distributed power systems l pre-regulator for linear regulators ame 5285 sw r freq 30 k on off vin 5 v c in 10 m f c 2 optional c 1 680 pf r 3 5 . 1 k in en comp gnd freq r 1 6 k r 2 24 k c out 22 m f fb vout 1 v 5 a l 1 1 . 5 m h
ame 2 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n functional block diagram otp soft start + + - 0 . 9 v 0 . 8 v vref slope osc enable uvlo pwm in sw sw pgnd en freq comp gnd fb - + ea current sense ircmp - + logic driver - + ovp current limit
ame 3 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n pin configuration sop-8/pp top view AME5285-azaxxx 1. comp 2. gnd 3. en 4. in 5. sw 6. sw 7. freq 8. fb note: connect exposed pad (heat sink on the back) to gnd. 1 3 2 4 ame 5285 5 6 7 8 n pin description * die attach: conductive epoxy pin number 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. internal pull high with a resistor. pull en below 0.6v 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. note that a capacitor is required from sw to bs to power the high-side switch. 7 f req 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.
ame 4 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n ordering information number of pins package type pin configuration AME5285 - x x x xxx output voltage a 1. comp z: sop/pp a: 8 adj: adjustable (sop-8/pp) 2. gnd 3. en 4. in 5. sw 6. sw 7. freq 8. fb pin configuration package type number of pins output voltage
ame 5 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n recommended operating conditions n thermal information * measure q jc on backside center of exposed pad. ** mil-std-202g 210f n absolute maximum ratings maximum unit -0.3v to +6v v -0.7v to v in +0.7v v -0.3v to v in +0.3v v hbm 2 kv m m 200 v parameter esd classification supply voltage s witch voltage en, fb, comp, freq to gnd 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 parameter package die attach symbol maximum unit thermal resistance* (junction to case) q j c 15 thermal resistance (junction to ambient) q ja 75 internal power dissipation p d 1.333 mw maximum junction temperature 150 o c 260 o c lead temperature (soldering 10sec)** conductive epoxy o c / w sop-8/pp
ame 6 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n electrical specifications v in =5v, t a =25 o c, unless otherwise noted. parameter symbol test condition min typ max units input voltage range 3 5.5 v input uvlo 2 2.3 2.6 v v en =5v (no switching) shutdown current i shdn v en =0v 10 m a feedback voltage v fb 0.784 0.8 0.816 v feedback current i fb -50 50 na load regulation 0a ame 7 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n detailed description normal operation the AME5285 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 low- side current limit reached 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 AME5285 employs internal soft-start circuitry to reduce supply inrush current during startup conditions. over temperature protection the in most applications the AME5285 does not dissi- pate much heat due to high efficiency. but, in applica- tions where the AME5285 is running at high ambient tem- perature with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maximum junction temperature of the part. if the junc- tion temperature reaches approximately 170 o c, the inter- nal high-side power switch will be turned off and the sw switch will become high impedance. short circuit protection when the output is shorted to ground, the frequency of the oscillator is reduced to about 1/4 of the normal fre- quency to ensure that the inductor current has more time to decay, thereby preventing runaway. meanwhile, AME5285 enters hiccup mode, the average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator.
ame 8 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n application information for a fixed output voltage, the output ripple is highest at maximum input voltage since d i l increases with input voltage. 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 AME5285 is set by a resistive divider according to the following formula: some standard value of r1, r2 for most commonly used output voltage values are listed in table 1. v out (v) r1(k w ) r2(k w ) 1.1 7 .5 2 0 1.2 1 0 2 0 1.5 17 .4 20 1.8 3 0 2 4 2.5 5 1 2 4 3.3 7 5 2 4 . 2 1 1 8 . 0 volt r r v out ? ? + = 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 : 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 , where i rms =i out /2. for simplification, use an input capacitor 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 re- quirement for c out has been met, the rms current rating generally far exceeds the i ripple(p-p) requirement. the output ripple d v out is determined by: ? ? ? ? ? - = d in out out l v v v l f i 1 1 ? ? ? ? ? + d @ d out l out fc esr i v 8 1 ( ) in out in out omax v v v v i - @
ame 9 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter loop compensation the AME5285 employs peak current mode control for easy use and fast transient response. peak current mode control eliminates the double pole effect of the output l- c filter. it greatly simplifies the compensation loop de- sign. with peak current mode control, the buck power stage can be simplified to be a one-pole and one-zero system 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: 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 AME5285, fb pin and comp pin are the inverting input and the output of internal transconductance error amplifier (ea). a series rc and cc compensation net- work connected to comp pin provides one pole and one zero: for r c < ame 10 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter efficiency considerations although all dissipative elements in the circuit produce losses, one major source usually account for most of the losses in AME5285 circuits: i 2 r losses. the i 2 r loss dominates the efficiency loss at medium to high load currents. 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 bottom mosfet r ds(on) and the duty cycle (d) as fol- lows: 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 multi- ply the result by the square of the average output cur- rent. 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 AME5285 does not dissipate much heat due to its high efficiency. but, in applications where the AME5285 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 170 o c, both power switches will be turned off and the sw switch will be- come high impedance.
ame 11 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n typical operating circuit table 1. recommended components selectin for fsw = 1.4mhz figure 3. AME5285 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 1.1 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 v in 3 v to 5 v ame 5285 sw r freq chip enable 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 1 3 4 2 5 , 6 8 7 gnd 9 ( exposed pad )
ame 12 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n characterization curve efficiency vs. output current efficiency vs. output current efficiency vs. output current efficiency vs. output current e f f i c i e n c y ( % ) 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 v out = 1 v output current ( a ) 0 10 20 30 40 50 60 70 80 90 100 v in = 5 v r freq = 30 k 0 10 20 30 40 50 60 70 80 90 100 output current ( a ) e f f i c i e n c y ( % ) 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 v out = 1 v v in = 5 v r freq = nc 100 0 10 20 30 40 50 60 70 80 90 output current ( a ) e f f i c i e n c y ( % ) 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 v out = 3 . 3 v v in = 5 v r freq = 30 k 0 10 20 30 40 50 60 70 80 90 100 0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 output current ( a ) e f f i c i e n c y ( % ) v out = 3 . 3 v v in = 5 v r freq = nc
ame 13 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n characterization curve (contd.) load step load step v in = 5v v out = 3.3v i out = 1ma to 5a r freq =30k 1) v out = 100mv/div 2) i l = 2a/div v in = 5v v out = 1v i out = 1ma to 5a r freq =30k 1) v out = 50mv/div 2) i l = 2a/div power on from en power on form vin v in = 5v v out = 3.3v r freq =nc 1) v en = 2v/div 2) v out = 2v/div 3) i l = 5a/div v in = 5v v out = 3.3v r freq =nc 1) v in = 2v/div 2) v out = 2v/div 3) i l = 5a/div time ( 100 m sec / div ) 1 2 time ( 100 m sec / div ) 1 2 time ( 5 . 0 ms / div ) 1 3 2 1 3 2 time ( 2 . 0 ms / div )
ame 14 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n characterization curve (contd.) power off from en v in = 5v v out = 3.3v r freq =nc 1) v en = 2v/div 2) v out = 2v/div 3) i l = 5a/div power off from vin v in = 5v v out = 3.3v r freq =nc 1) v in = 2v/div 2) v out = 2v/div 3) i l = 5a/div short circuit test v in = 5v v out = 3.3v r freq =nc 1) v in = 5v/div 2) v out = 2v/div 3) i l = 5a/div quiescent current vs. input voltage 1 2 time ( 100 ms / div ) v in = 5 v v out = 3 . 3 v 3 1 3 2 time ( 5 . 0 ms / div ) time ( 5 . 0 ms / div ) 1 3 2 380 390 400 410 420 430 440 450 460 470 480 490 3 . 5 4 . 0 4 . 5 5 . 0 input voltage ( v ) q u i e s c e n t c u r r e n t ( m a ) v out = 3 . 3 v r freq = nc
ame 15 AME5285 rev. b.01 5a, 300khz ~ 1.4mhz synchronous rectified step-down converter n tape and reel dimension carrier tape, number of components per reel and reel size sop-8pp pin 1 w p a m e a m e 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 n package dimension sop-8pp 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 b e e e 2 c front view side view top view d 1 e 1 l 1 d a 1 a a 2 q pin 1
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. , november 2012 document: a005-ds5285-b.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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