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x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r september 2009 rev. 1.0.0 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 XRP7657 is a non synchronous voltage mode pwm step down (buck) regulator capable of a constant output current up to 2amps. a wide 4.75v to 25v input voltage range allows for single supply operations from industry standard 5v, 12v and 24v power rails. with a 420khz constant operating frequency and integrated high side switch, the XRP7657 reduces the overall component count and solution footprint. in addition to a 2% output setpoint accuracy, this device provides high efficiency, low ripple and excellent line and load regulation. an enable function and soft start feature allow for controlled power up sequencing implementation. built-in over current, output short-circuit and over temperature protection insure safe operations under abnormal operating conditions. the XRP7657 is offered in a rohs compliant, ?green?/halogen free 8-pin soic package. applications ? distributed power architectures ? point of load converters ? audio-video equipments ? medical & industrial equipments features ? 2a constant output current ? 4.75v to 25v wide input voltage ? pwm voltage mode control ? 420khz constant operations ? up to 94% efficiency ? adjustable output voltage ? 0.8v to 21v range ? 2% accuracy ? soft-start and enable function ? built-in thermal, over current and output short circuit protection ? rohs compliant, ?green?/halogen free 8-pin soic package typical application diagram fig. 1: XRP7657 application diagram
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 2/11 rev. 1.0.0 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 ............................................................ -0.3v to 30v comp, fb pin voltage .................................... -0.3v to 6v sw, en pin voltag e ...................................... -0.3v to v in storage temperatur e .............................. - 65c to 150c power dissipat ion ................................ internal ly limited junction temperature t j ....................................... 150c lead temperature (sol dering, 10 se c) ................... 260c esd rating (hbm - huma n body mode l) .................... 2kv operating ratings input voltage range v in .............................. 4.75v to 25v output voltage range v out ............................ 0.8v to 21v junction temperature t j range ................. -40c to 125c thermal resistance ja (junction to ambient, no he at sink, free air) ........ 100c/w electrical specifications specifications with standard type are for an ambient temperature of t a = 25c only; limits applying over the full operating junction temperature range are denoted by a ???. minimum and maximum limits are guarant eed through test, design, or statistical correlation. typical values repres ent the most likely parametric norm at t a = 25c, and are provided for reference purposes only. unless otherwise indicated, v in = 12v, v out = 5v, t a = 25c. parameter min. typ. max. units conditions input voltage v in 4.75 25 shutdown quiescent current i shdn 44 60 a v en =0.4v quiescent current i q 1.3 2 ma v en =2.0v, v fb =1.3v feedback voltage v fb 0.784 0.800 0.816 v v in =5v to 25v feedback bias current i fb -0.1 -0.5 a v fb =1.3v switch current limit i lim 2.5 3.4 a oscillator frequency f osc 336 420 504 khz oscillator frequency f osc1 40 khz v fb =0.52v, current limit activated or short circuit protection mode error amplifier voltage gain g v 1000 v/v error amplifier transconductance g s 700 a/v en pin threshold high v h 1.5 v en pin threshold low v l 0.7 v en pin input leakage current i en -5 -10 a v en =2.5v internal pmos on resistance r ds(on) 130 150 m ? v in = v en =12v, v fb =0.65v, i out =12a maximum duty cycle d max 100 % v fb =0.65v, i sw =0.1a thermal shutdown t otsd 155 c thermal shutdown hysteresis t hys 20 c
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 3/11 rev. 1.0.0 block diagram fig. 2: XRP7657 block diagram pin assignment fig. 3: XRP7657 pin assignment
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 4/11 rev. 1.0.0 pin description name pin number description nc 1 no connect vin 2 supply voltage input pin. bypass vin to gnd with a suitable large capacitor to eliminate noise on the input sw 3 power switch output pin. sw is the switch node that supplies power to the output gnd 4 ground signal pin fb 5 feedback pin. through an external resistor divider network, fb senses the output voltage and regulates it. to prevent current limit run away in a short circuit fault condition, the frequency feedback comparator lowers the oscillator frequency to 40khz when the fb voltage is below 0.52v. the feedback threshold voltage is 0.8v comp 6 compensation pin. this pin is the output of the error amplifier. frequency compensation is done at this pin by connecting a series rc to gr ound (parallel a c if necessary) en 7 enable pin. drive en pin high to turn on the device, drive it low to turn off.defaul t of this pin is high level. nc 8 no connect ordering information part number junction temperature range marking package packing quantity note 1 note 2 XRP7657edtr-f -40c t a +125c XRP7657e yyww x soic8 2.5k/tape & reel rohs compliant halogen free XRP7657evb XRP7657 evaluation board ?yy? = year ? ?ww? = work week ? ?x? = lot number
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 5/11 rev. 1.0.0 typical performance characteristics all data taken at v in =12v, v out =5v, t a =25c, unless otherwise specified - schematic and bom from application information section of this datasheet. fig. 4: efficiency vs. output current fig. 5: operation frequency vs. temperature fig. 6: supply quiescent current vs. input voltage fig. 7: efficiency vs. input voltage fig. 8:shutdown quiescent current vs. input voltage fig. 9: ocp current limit vs. temperature
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 6/11 rev. 1.0.0 fig. 10: feedback voltage vs. temperature fig. 11: ocp current limit vs. input voltage fig. 12: ocp frequency vs. temperature fig. 13: output voltage vs. output current fig. 14: output current vs. input voltage (t a =25c) fig. 15: output current vs. input voltage (t a =85c)
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 7/11 rev. 1.0.0 application information theory of operation XRP7657 is a non-synchronous voltage mode pwm buck regulator featuring an integrated p-channel switching fet. using a pfet enables the regulator to operate at 100% duty cycle. additional features include preset switching frequency of 420khz and preset soft-start. safety features include under-voltage lock-out (uvlo), over-current protection (ocp), over- temperature protection (ovp) and short-circuit protection. t ypical a pplication s chematics s etting the output voltage output voltage v out is set by placing a resistor divider between output of the regulator and feedback pin. resistors r 1 and r 2 are calculated from the following equation: 1 where v ref is the reference voltage set internally at 0.8v nominal. e nable signal the enable pin can be used to turn the regulator on and off. pulling the enable below 0.7v puts the regulator in shutdown mode with a corresponding quiescent current of less than 60a. if enable is not going to be used it should be tied to v in . selecting diode d1 d1 must be a schottky diode and selected for voltage rating v r , current rating i f and power rating p. the voltage rating should be greater than v in in order to block the input voltage when the internal pfet is on. as a rule of thumb d1 voltage rating should be 50% larger than v in . a simplified rule for current rating is to select a diode capable of conducting the converter?s output current. s electing inductor l1 l1 should have saturation current rating i sat greater than the converter output current. as a rule of thumb i sat should be twice the output current. the inductance value can be calculate from the following equation: 1 1 ? where: v in is converter input voltage v out is converter output voltage f is the nominal switching frequency, 420khz il is the peak to peak inductor current ripple usually set to 30% of i out o utput capacitor selection either ceramic or alel capacitors can be used. select the output capacitor for voltage rating, capacitance and equivalent series resistance (esr). nominally the voltage rating is selected to be twice as large as the ou tput voltage. select the capacitance to satisfy the specification for output voltage overshoot/undershoot caused by current step load. a steady-state output current i out corresponds to inductor stored energy of ? x l x i out 2 . a sudden decrease in i out forces the energy surplus in l to be absorbed by c out . this causes an overshoot in output voltage that is co rrected by power switch reduced duty cycle. use the following equation to calculate c out :
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 8/11 rev. 1.0.0 where: i 2 is the load step high current i 1 is the load step low current v outs is output voltage including overshoot v out is steady-state output voltage i nput capacitor selection ceramic capacitors are recommended since they have low esr and low esl. therefore they are more effect ive in providing the pulsating input current required by the buck converter. voltage rating of the capacitor should be at least 50% higher than the converter input voltage. see following design examples for required value of c in . c ompensation a type-iii compensation is used to stabilize the loop. a detailed explanation of calculating component values for type-iii compensations is given in exar?s application note anp-16. compensation was calculated based on a cross-over frequency (f c ) of 40khz and ramp voltage of 0.5v. component cp, which is mentioned in anp-16, has not been used here. typical applications 24v to 5v ? 2a p oint of l oad c onverter ref. qty manufacturer part number size description u1 1 exar XRP7657 soic-8 2a 25v non-synchronous buck regulator d1 1 central semicon. cmsh3-40ma sma schotkky, 40v, 3a l1 1 cooper bussmann dr74-220 7.6x7.6mm 22uh coil 2.4a 48.9mohm c in 1 murata corp. grm32er61e106k 1210 ceramic cap 10f, 25v,x5r,1210 c out 1 murata corp. grm31cr61c226m 1206 ceramic cap 22f, 16v,x5r, 1206 cz3 1 murata corp. grm188r71h471k 0603 ceramic cap 470pf, 50v,x7r, 0603 cz2 1 murata corp. grm188r71h562k 0603 ceramic cap 5600pf, 50v,x7r,0603 r1 1 panasonic erj-3ekf6812v 0603 res 68.1k ohm, 1%, 0603, smd r2 1 panasonic erj-3ekf1302v 0603 res 13k ohm, 1%, 0603 smd rz3 1 panasonic erj-3ekf0801v 0603 res 0.8k ohm, 1%, 0603 smd rz2 1 panasonic erj-3ekf5621v 0603 res 5.62k ohm, 1%, 0603 smd
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 9/11 rev. 1.0.0 12v to 3.3v ? 2a p oint of l oad c onverter ref. qty manufacturer part number size description u1 1 exar XRP7657 soic-8 2a 25v non-synchronous buck regulator d1 1 central semicon. cmsh3-40ma sma schotkky, 40v, 3a l1 1 cooper bussmann dr74-100 7.6x7.6mm 10uh coil 2.4a 48.9mohm c in 1 murata corp. grm32er61e226k 1210 ceramic cap 22f, 25v,x5r,1210 c out 1 murata corp. grm31cr61c226m 1206 ceramic cap 22f, 16v,x5r, 1206 cz3 1 murata corp. grm188r71h331k 0603 ceramic cap 330pf, 50v,x7r, 0603 cz2 1 murata corp. grm188r71h272k 0603 ceramic cap 2700pf, 50v,x7r,0603 r1 1 panasonic erj-3ekf6812v 0603 res 68.1k ohm, 1%, 0603, smd r2 1 panasonic erj-3ekf2152v 0603 res 21.5k ohm, 1%, 0603 smd rz3 1 panasonic erj-3ekf1151v 0603 res 1.15k ohm, 1%, 0603 smd rz2 1 panasonic erj-3ekf8061v 0603 res 8.06k ohm, 1%, 0603 smd
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 10/11 rev. 1.0.0 package specification soic-8
x x r r p p 7 7 6 6 5 5 7 7 2 2 a a , , 2 2 5 5 v v 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 w w m m s s t t e e p p d d o o w w n n r r e e g g u u l l a a t t o o r r ? 2009 exar corporation 11/11 rev. 1.0.0 revision history revision date description 1.0 09/25/09 initial release of datasheet 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 publication in order to improve design, performance or reliability. 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 contained here in are only for illustr ation 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 us e of any of its products in life support applications 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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