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x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r january 2011 rev. 1.1.0 exar corporation www.exar.com 48720 kato road, fremont ca 94538, usa tel. +1 510 668-7000 ? fax. +1 510 668-7001 general description the xrp6124 is a non synchronous step down (buck) controller for up to 5amps point of loads. a wide 3v to 30v input voltage range allows for single supply operations from industry standard 3.3v, 5v, 12v and 24v power rails. with a proprietary constant on-time (cot) control scheme, the xrp6124 provides extremely fast line and lo ad transient response while the operating frequency remains nearly constant. it requires no loop compensation hence simplifying circuit implementation and reducing overall component count. the xrp76124 also implements an emulated esr circuitry allowing usag e of ceramic output capacitors and insuring stable operations without the use of extr a external components. built-in soft start preven ts high inrush currents while under voltage lock-out and output short protections insure safe operations under abnormal operating conditions. the xrp6124 is available in a rohs compliant, green/halogen free spac e-saving 5-pin sot23 package. applications ? point of load conversions ? audio-video equipments ? industrial and medical equipments ? distributed power architecture features ? 5a point-of-load capable ? down to 1.2v output voltage conversion ? wide input voltage range ? 3v to 18v: xrp6124 ? 4.5v to 30v: xrp6124hv ? constant on-time operations ? constant frequency operations ? no external compensation ? supports ceramic output capacitors ? built-in 2ms soft start ? short circuit protection ? <1a shutdown current ? rohs compliant, green/halogen free 5-pin sot23 package typical application diagram figure 1: xrp6124 application diagram
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 2/12 rev. 1.1.0 absolute maximum ratings these are stress ratings only and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. exposure to absolute maximum rating conditions for extended periods of time may affect reliability. v in (xrp6124) ............................................ -0.3v to 20v v in (xrp6124hv) ........................................ -0.3v to 32v gate ...................................................... vi n-gate<8v fb, en ..................................................... -0.3v to 5.5v storage temperatur e .............................. -65c to 150c power dissipat ion ................................ internally limited lead temperature (sol dering, 10 se c) ................... 300c esd rating (hbm - huma n body mode l) .................... 2kv operating ratings input voltage range v in (xrp6124) ................ 3.0v to 18v input voltage range v in (xrp6124hv) ............ 4.5v to 30v junction temperature range .................... -40c to 125c thermal resistance ja .....................................191c/w electrical specifications specifications are for an operat ing junction temperature of t j = 25c only; limits applying over the full operating junction temperature range are denoted by a ???. minimum and maximum limits are guaranteed through test, design, or statistical correlation. typical values represent th e most likely parametric norm at t j = 25c, and are provided for reference purposes only. unless otherwise indicated, v in = 3.0v to 18v, t j = ?40c to 125c. parameter min. typ. max. units conditions uvlo turn-on threshold 2.5 2.8 3.0 v ? xrp6124 uvlo turn-on threshold 3.8 4.2 4.5 v ? xrp6124hv uvlo hysteresis 0.1 v operating input voltage range 3.0 18 v ? xrp6124 4.5 30 v ? xrp6124hv shutdown vin current 1.5 3 a en=0v, v in =12v operating vin current 0.5 1 ma vfb=1.2v and after fault reference voltage 0.792 0.8 0.808 v 0.784 0.8 0.816 v ? vsc_th, feedback pin short circuit latch threshold 0.50 0.55 0.65 v ? t on , switch on-time 0.4 0.5 0.6 s ? v in =12v, xrp6124 t on , switch on-time 0.4 0.5 0.6 s ? v in =24v, xrp6124hv t off_min , minimum off-time 250 350 ns ? v in =12v soft start time 2 ms en turn-on threshold 2 v en turn-off threshold 1 v en bias current 0.01 0.1 a gate driver pull-down resistance 6 9 ? gate driver pull-up resistance 5 8 ? tr, gate rise time 45 ns c gate =1nf tf, gate fall time 35 ns c gate =1nf vin - gate voltage difference 5.5 6.4 8 v ? vin=12v vin - gate voltage difference 2.6 v ? vin=3.0v
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 3/12 rev. 1.1.0 block diagram figure 2: xrp6124 block diagram pin assignment 1 2 3 5 4 xrp61 24 en gnd fb vi n gate figure 3: xrp6124 pin assignment pin description name pin number description en 1 enable pin. actively pull high to enable the part. gnd 2 ground fb 3 feedback pin gate 4 gate pin. connect to gate of pfet. this pin pulls the gate of the pfet approximately 6v below vin in order to turn on the fet. for 6v>vin>3v the gate pulls to within 0.4v of ground. therefore a pfet with a gate rating of 2.6v or lower should be used. vin 5 input voltage ordering information part number temperature range marking package packing quantity note 1 note 2 xrp6124es0.5-f -40c t j 125c 5-pin sot23 bulk halogen free 0.5s/18v max xrp6124estr0.5-f -40c t j 125c 5-pin sot23 2.5k/tape & reel halogen free 0.5s/18v max xrp6124hves0.5-f -40c t j 125c 5-pin sot23 bulk halogen free 0.5s/30v max xrp6124hvestr0.5-f -40c t j 125c 5-pin sot23 2.5k/tape & reel halogen free 0.5s/30v max xrp6124evb xrp6124 evaluation board ?yy? = year ? ?ww? = work week ? ?x? = lot number
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 4/12 rev. 1.1.0 typical performance characteristics all data taken at t j = t a = 25c, unless otherwise specified ? curves are based on schematic and bom from application information section of this datasheet. refer to figure 20 for xrp6124 and to figure 21 for xrp6124hv. fig. 4: efficiency versus i out , v in =12v fig. 5: efficiency versus i out , v in =24v fig. 6: t on versus v in fig. 7: t on versus v in fig. 8: load regulation fig. 9: load regulation
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 5/12 rev. 1.1.0 fig. 10: line regulation fig. 11: line regulation fig. 12: steady state, v in =12v, v out =3.3v, i out =3a fig. 13: steady state, v in =24v, v out =5.0v, i out =3a fig. 14: load step transient response, 1.4a-3a-1.4a fig. 15: load step transient response, 1.4a-3a-1.4a xrp6124hves0.5-f xrp6124es0.5-f v out ac coupled 10mv / div lx 10v/div i l 2a/div lx 20v/div v out ac coupled 20mv / div i l 2a/div xrp6124es0.5-f 1s/div 2s/div xrp6124es0.5-f xrp6124hves0.5-f v out ac coupled 100mv / div v out ac coupled 200mv / div i out 1a/div i out 1a/div 10s/div 20s/div 90mv 180mv
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 6/12 rev. 1.1.0 fig. 16: load step transient response corresponding to a ccm-dcm transition, 0.05a-1.6a-0.05a fig. 17: load step transient response corresponding to a ccm-dcm transition, 0.05a-1.6a-0.05a fig. 18: shutdown current versus v in , v en =0v fig. 19: shutdown current versus v in , v en =0v xrp6124es0.5-f xrp6124hves0.5-f v out ac coupled 100mv / div v out ac coupled 200mv / div i out 1a/div i out 1a/div 50s/div 50s/div 90mv 180mv
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 7/12 rev. 1.1.0 theory of operation theory of operation the xrp6124 utilizes a proprietary constant on-time (cot) control with emulated esr. the on-time is internally set and automatically adjusts during operatio n, inversely with the voltage v in , in order to maintain a constant frequency. therefore th e switching frequency is independent of the inductor and capacitor size, unlike hysteretic controllers. the emulated esr ramp allows the use of ceramic capacitors for output filtering. at the beginning of each cycle, the xrp6124 turns on the p-channel fet for a fixed duration. the on-time is internally set and adjusted by v in . at the end of the on-time the fet is turned off, for a predetermined minimum off time t off-min (nominally 250ns). after the t off-min has expired the voltage at feedback pin fb is compared to a voltage ramp at the feedback comparators positive input. once v fb drops below the ramp voltage, the fet is turned on and a new cycle starts. this voltage ramp constitutes an emulated esr and makes possible the use of ceramic capacitors, in addition to other capacitors, as output filter for th e buck converter. v oltage o ptions the xrp6124 is available in two voltage options as shown in ta ble 1. the low-voltage and high-voltage options have t on of 0.5s at 12v in and 24v in respectively. note that t on is inversely proportional to v in . the constant of proportionality k, for ea ch voltage option is shown in table 1. variation of t on versus v in is shown graphically in figures 6 and 7. voltage rating (v) part number t on (s) k=t on xv in ( s.v) 3-18 xrp6124es0.5-f 0.5 @ 12v in 6 4.5-30 xrp6124hves0.5-f 0.5 @ 24v in 12 table 1 : xrp6124 voltage options for a buck converter the switching frequency fs can be expressed in terms of v in , v out and t on as follows: on in out t v v fs = since for each voltage option, the product of v in and t on is the constant k shown in table 1, then switching frequency is determined by v out as shown in table 2. v out switching frequency fs(khz) xrp6124es0.5-f xrp6124hves0.5-f 1.2 200 100 1.5 250 125 1.8 300 150 2.5 417 208 3.3 550 275 5.0 833 417 12 --- 1000 table 2: switching frequency fs for the xrp6124 voltage options where it is advantageous, the high-voltage option may be used for low-voltage applications. for example a 12v in to 5v out conversion using a low-voltage option will result in switching fr equency of 833khz as shown in table 2. if it is desired to increase the converter efficiency , then switching losses can be reduced in half by using a high-voltage option operating at a switching frequency of 417khz. v out maximum output current i out (a) xrp6124es0.5-f xrp6124hves0.5-f 3.3v in 5.0v in 12v in 18v in 24v in 1.2 5 5 4 --- --- 1.5 5 5 4 4 --- 1.8 5 5 4 4 4 2.5 4 4 4 4 4 3.3 --- 4 3 4 4 5.0 --- --- 3 3 3 12 --- --- --- 2 2 table 3: maximum recommended i out short - circuit protection the purpose of this feat ure is to prevent an accidental short-circui t at the output from damaging the converter. the xrp6124 has a short-circuit comparator that constantly monitors the feedback node, after soft-start is
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 8/12 rev. 1.1.0 finished. if the feedback voltage drops below 0.55v, equivalent to output voltage dropping below 69% of nominal, the comparator will trip causing the ic to latch off. in order to restart the xrp6124, the input voltage has to be reduced below uvlo threshold and then increased to its normal operating point. soft - start to limit in-rush current the xrp6124 has an internal soft-start. the nominal soft-start time is 2ms and commences when v in exceeds the uvlo threshold. as explained above, the short-circuit comparator is enabled as soon as soft-start is complete. therefore if the input voltage has a very slow rising edge such that at the end of soft-start the output voltage has not reached 69% of its final value then the xrp6124 will latch-off. enable by applying a logic-level signal to the enable pin en the xrp6124 can be turned on and off. pulling the enable below 1v shuts down the controller and reduces the v in leakage current to 1.5a nominal as seen in figure 18. enable signal should always be applied after the input voltage or concurrent with it. otherwise xrp6124 will latch up. in applications where an independent enable si gnal is not available, a zener diode can be used to derive v en from v in . discontinuous conduction mode , dcm because xrp6124 is a non-synchronous controller, when load current i out is reduced to less than half of peak-to-peak inductor current ripple il, the converter enters dcm mode of operation. the switching frequency fs is now i out dependent and no longer governed by the relationship shown in table 2. as i out is decreased so does fs until a minimum switching frequency, typically in the range of few hundred hertz, is reached at no load. this contributes to good co nverter efficiency at light load as seen in figures 4 and 5. the reduced fs corresponding to light load, however, increases the output voltage ripple and causes a slight increase in output voltage as seen in figures 8 and 9. another effect of reduced fs at light load is slow down of transient response when a load step transitions from a high load to a light load. this is shown in figures 16 and 17. application information setting the output voltage use an external resistor divider to set the output voltage. progra m the output voltage from: ? ? ? ? ? ? ? = 1 8 . 0 2 1 out v r r where: r1 is the resistor between v out and fb r2 is the resistor between fb and gnd (nominally 2k ? ) 0.8v is the nominal feedback voltage. feed - forward capacitor cff cff, which is placed in parallel with r1, provides a low-impeda nce/high-frequency path for the output voltage ripple to be transmitted to fb. it also helps get an optimum transient response. an initial value for cff can be calculated from: 1 1 . 0 2 1 r fs cff = where: fs is the switching frequency from table 2 this value can be adjusted as necessary to provide an optimum lo ad step transient response.
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 9/12 rev. 1.1.0 output inductor select the output inductor l1 for inductance l, dc current rating i dc and saturation current rating i sat . i dc should be larger than regulator output current. i sat , as a rule of thumb, should be 50% higher than the regulator output current. calculate the inductance from: () ? ? ? ? ? ? ? ? ? = in l out out in v fs i v v v l where: i l is peak-to-peak inductor current ripple nominally set to 30% of i out f s is nominal switching frequency from table 2 output capacitor c out select the output capacitor for voltage rating, capacitance c out and equivalent series resistance esr. the volt age rating, as a rule of thumb, should be twice the output voltage. when calculating the re quired capacitance, usually the overriding requirement is current load-step transient. if the unloading transient requirement (i.e., when i out transitions from a high to a low current) is met, then usually the loading transient requirement (when i out transitions from a low to a high current) is met as well. therefore calculate the c out capacitance based on th e unloading transient requirement from: () ? ? ? ? ? ? ? ? ? + ? = 2 2 2 2 out transient out low high out v v v i i l c where: l is the inductance calc ulated in the preceding step i high is the value of i out prior to unloading. this is nominally set equal to regulator current rating. i low is the value of i out after unloading. this is nominally set equal to 50% of regulator current rating. v transient is the maximum permissible voltage transient corresponding to the load step mentioned above. v transient is typically specified from 3% to 5% of v out . esr of the capacitor has to be selected such that the output voltage ripple requirement v out(ripple) , nominally 1% of v out , is met. voltage ripple v out(ripple) is composed mainly of two components: the resistive ripple due to esr and capacitive ripple due to c out charge transfer. for applications requiring low voltage ripple, ceramic capacitors are recommended because of their low esr which is typically in the range of 5m ? . therefore v out(ripple) is mainly capacitive. fo r ceramic capacitors calculate the v out(ripple) from: fs c i out l = 8 v ) out(ripple where: c out is the value calculated above if tantalum or electrolytic capacitors are used then v out(ripple) is essentially a function of esr: esr i l = v ) out(ripple input capacitor c in select the input capacitor for voltage rating, rms current rating and capacitance. the voltage rating, as a rule of thumb, should be 50% higher than the regulator?s maximum input voltage. calculate the capacitor?s current rating from: () d d i out ? = 1 i rms cin, where: i out is regulator?s maximum current d is duty cycle (d=v out /v in ) calculate the c in capacitance from: () in in out in out out v v fs v v v i ? = 2 in c where: v in is the permissible in put voltage ripple, nominally set to 1% of v in .
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 10/12 rev. 1.1.0 typical applications 12v to 3.3v / 3a c onversion xrp6124es vin gnd gate fb en d1 mbra340 l1, 4.7uh dr74-4r7-r m1 irf9335 r1, 1% 6.34k r2, 1% 2k cff 1nf 1 2 34 5 c out , x5r 2x22uf, 10v c in , x5r 22uf, 25v v in 6v to 18v v out 3.3v/3a fig. 20: 12v to 3.3v/3a regulator 24v to 5v / 3a c onversion xrp6124hves vin gnd gate fb en d1 mbra340 l1, 8.2uh hcm0730 m1 dmp4050sss r1, 1% 10.5k r2, 1% 2k cff 0.47nf 1 2 34 5 c out , x5r 2x22uf, 16v c in , x5r 10uf, 50v v in 8v to 30v v out 5.0v/3a fig. 21: 24v to 5v/3a regulator
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 11/12 rev. 1.1.0 package specification 5- pin sot23
x x r r p p 6 6 1 1 2 2 4 4 n n o o n n - - s s y y n n c c h h r r o o n n o o u u s s p p f f e e t t s s t t e e p p - - d d o o w w n n c c o o n n t t r r o o l l l l e e r r ? 2011 exar corporation 12/12 rev. 1.1.0 revision history revision date description 1.0.0 01/26/2011 initial release of datasheet 1.1.0 01/31/2011 corrected typo (changed v to i) on formula under input capacitor c in paragraph for further assistance email: customersupport@exar.com exar technical documentation: http://www.exar.com/techdoc/default.aspx? e xar c orporation h eadquarters and s ales o ffices 48720 kato road fremont, ca 94538 ? usa tel.: +1 (510) 668-7000 fax: +1 (510) 668-7030 www.exar.com notice exar corporation reserves the right to make changes to the products contained in this pu blication in order to improve design, performance or reliabilit y. exar corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and make s no representation that the circuits are free of patent infringement. charts and schedules contai ned here in are only for illustration purposes and may vary depending upon a user?s specific application. while the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. exar corporation does not recommend the use of any of its products in life support applic ations where the failure or malfunction of the product can reasonably be expected to cause fa ilure of the life support system or to significantly affect it s safety or effectiveness. products are not authorized for use in such applications unless exar corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of exar corporation is adequately protected under the circumstances. reproduction, in part or whole, without the prior written consent of exar corporation is prohibited.

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