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LM2596 3astep-down voltageregulator general description the LM2596 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 3a load with excellent line and load regulation. these devices are available in fixed output voltages of 3.3v, 5v, 12v, and an adjustable output version. requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation, and a fixed-frequency oscillator. the LM2596 series operates at a switching frequency of 150 khz thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. available in a standard 5-lead to-220 package with several different lead bend options, and a 5-lead to-263 surf ace m ount package. a standard series of inductors are available from several different manufacturers optimized for use with the LM2596 series. this feature greatly simplifies the design of switch-mode power supplies. other features include a guaranteed 4% tolerance on output voltage under specified input voltage and output load conditions, and 15% on the oscillator frequency. external shutdown is included, featuring typically 80 a standby current. self protection features include a two stage frequency reducing current limit for the output switch and an over temperature shutdown for complete protection under fault conditions. features ? 3.3v, 5v, 12v, and adjustable output versions ? adjustable version output voltage range, 1.2v to 37v ? 4% max over line and load conditions ? available in to-220 and to-263 packages ? guaranteed 3a output load current ? input voltage range up to 40v ? requires only 4 external components ? excellent line and load regulation specifications ? 150 khz fixed frequency internal oscillator ? ttl shutdown capab ility ? low power standby mode, i q typically 80 a ? high efficiency ? uses readily available standard inductors ? thermal shutdown and current limit protection applications ? simple high-efficiency step-down (buck) regulator ? on-card switching regulators ? positive to negative converter typical application (fixed output voltage versions) block diagram +v in LM2596 5.0 + c in 680 f l1 220 f c out + 12v 1 2 3 4 5 5.0v + - + - 150khz osc act ive capacitor amp + - latch driver com com - + - + start up + + gm r2 2.5v feedback on/ off v in output gnd 1 beijing estek electronics co.,ltd
pin functions +v in - this is the positive input supply for the ic switching regulator. a suitable input bypass capacitor must be present at this pin to minimize voltage transients and to supply the switching currents needed by the regulator. ground - circuit ground. output - internal switch. the voltage at this pin switches between (+v in - v sat ) and approximately -0.5v, with a duty cycle of approximately v out /v in . to minimize coupling to sensitive circuitry, the pc board copper area connected to this pin should be kept to a minimum. feedback ?senses the regulated output voltage to complete the feedback loop. on/off - allows the switching regulator circuit to be shut down using logic level signals thus dropping the total input supply current to approximately 80 a. pulling this pin below a threshold voltage of approximately 1.3v turns the regulator on, and pulling this pin above 1.3v (up to a maximum of 25v) shuts the regulator down. if this shutdown feature is not needed, the on /off pin can be wired to the ground pin or it can be left open, in either case the regulator will be in the on condition. absolute maximum ratings (note 1) maximum supply voltage 45v on /off pin input voltage -0.3 v +25v feedback pin voltage -0.3 v +25v output voltage to ground (steady state) -1v power dissipation internally limited storage temperature range -65 0 c to +150 0 c esd susceptibility human body model (note 2) 2 kv lead temperature s package vapor phase (60 sec.) +215 0 c infrared (10 sec.) +245 0 c t package (soldering, 10 sec.) +260 0 c maximum junction temperature +150 0 c operating conditions temperature range -40 0 c t j +125 0 c supply voltage 4.5v to 40v LM2596-3.3 electrical characteristics specifications with standard type face are for t j = 25 0 c, and those with boldface type apply over full operating temperature range LM2596-3.3 symbol parameter conditions typ (note 3) limit (note 4) units (limits) system parameters (note 5)test circuit figure 1 v out output voltage 4.7v5 v in 40v, 0.2a i load 3a 3.3 3.168/ 3.135 3.432/ 3.465 v v(min) v(max) efficiency v in =12v, i load =3a 73 % LM2596-5.0 electrical characteristics specifications with standard type face are for t j = 25 0 c, and those with boldface type apply over full operating temperature range LM2596-5.0 symbol parameter conditions typ (note 3) limit (note 4) units (limits) system parameters (note 5)test circuit figure 1 v out output voltage 7v v in 40v, 0.2a i load 3a 5.0 4.800/ 4.750 5.200/ 5.250 v v(min) v(max) efficiency v in =12v, i load =3a 80 % LM2596-12 electrical characteristics specifications with standard type face are for t j = 25 0 c, and those with boldface type apply over full operating temperature range LM2596-12 symbol parameter conditions typ (note 3) limit (note 4) units (limits) system parameters (note 5)test circuit figure 1 v out output voltage 15v v in 40v, 0.2a i load 3a 12.0 11.52/ 11.40 12.48/ 12.60 v v(min) v(max) efficiency v in =12v, i load =3a 90 % LM2596-adj electrical characteristics 2 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
3 specifications with standard type face are for t j = 25 0 c, and those with boldface type apply over full operating temperature range LM2596-adj symbol parameter conditions typ (note 3) limit (note 4) units (limits) system parameters (note 5)test circuit figure 1 v out output voltage 4.5v v in 40v, 0.2a i load 3a v out programmed for 3v. circuit of figure 1. 1.230 1.193/ 1.180 1.267/ 1.280 v v(min) v(max) efficiency v in =12v, v out =3v, i load =3a 73 % all output voltage versions electrical characteristics specifications with standard type face are for t j = 25 0 c, and those with boldface type apply over full operating temperature rang e. unless otherwise specified, v in = 12v for the 3.3v, 5v, and adjustable version and v in = 24v for the 12v version. i load = 500 ma LM2596-xx symbol parameter conditions typ (note 3) limit (note 4) units (limits) device parameters i b feedback bias current adjustable version only, v fb =1.3v 10 50/ 100 na na (max) f o oscillator frequency (note 6) 150 127/ 110 173/ 173 khz khz (min) khz (max) v sat saturation voltage i out =3a (notes 7, 8) 1.16 1.4/ 1.5 v v (max) dc max duty cycle (on) min duty cycle (off) (note 8) (note 9) 100 0 % i cl current limit peak current (notes 7, 8) 4.5 3.6/ 3.4 6.9/ 7.5 a a (min) a (max) output=0v (notes 7, 9) 50 a (max) i l output leakage current output=-0.9v (note 10) 10 30 ma ma (max) i q quiescent current (note 9) 5 10 ma ma (max) i stby standby quiescent current on/off pin=5v (off) (note 10) 80 200/ 250 a a (max) jc thermal resistance to-220 or to-263 package, junction to case 2 0 c/w ja to-220 package, junction to ambient (note 11) 50 0 c/w ja to-263 package, junction to ambient (note 12) 50 0 c/w ja to-263 package, junction to ambient (note 13) 30 0 c/w ja to-263 package, junction to ambient (note 14) 20 0 c/w on/off control test circuit figure 1 v ih v il on/off pin logic input threshold voltage low (regulator on) high (regulator off) 1.3 0.6 2.0 v v (max) v (min) i h v logic =2.5v (regulator off) 5 15 a a (max) i l on/off pin input current v logic =0.5v (regulator on) 0.02 5 a a (max) note 1: absolute maximum ratings indicate limits beyond which damage to the device may occur. operating ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. for guaranteed specifications and test conditions, see the electrical characteristics. note 2: the human body model is a 100 pf capacitor discharged through a 1.5k resistor into each pin. note 3: typical numbers are at 25 0 c and represent the most likely norm. note 4: all limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). all room temperature limits are 100% production tested. all limits at temperature extremes are guaranteed via correlation using standard statistical quality control (sqc) methods. all limits are used to calculate average outgoing quality level (aoql). note 5: external components such as the catch diode, inductor, input and output capacitors, and voltage programming resistors can affect switching regulator system performance. when the LM2596 is used as shown in the figure 1 test circuit, system performanc e will be as shown in system parameters section of electrical characteristics. beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
note 6: the switching frequency is reduced when the second stage current limit is activated. the amount of reduction is determined by the severity of current over-load. note 7: no diode, inductor or capacitor connected to output pin. note 8: feedback pin removed from output and connected to 0v to force the output transistor switch on. note 9: feedback pin removed from output and connected to 12v for the 3.3v, 5v, and the adj. version, and 15v for the 12v version, to force the output transistor switch off. note 10: v in = 40v. note 11: junction to ambient thermal resistance (no external heat sink) for the to-220 package mounted vertically, with the leads soldered to a printed circuit board with (1 oz.) copper area of approximately 1 in 2 note 12: junction to ambient thermal resistance with the to-263 package tab soldered to a single printed circuit board with 0.5 in 2 of (1 oz.) copper area. note 13: junction to ambient thermal resistance with the to-263 package tab soldered to a single sided printed circuit board with 2.5 in 2 of (1 oz.) copper area. note 14: junction to ambient thermal resistance with the to-263 package tab soldered to a double sided printed circuit board with 3 in 2 of (1 oz.) copper area on the LM2596s side of the board, and approximately 16 in 2 of copper on the other side of the p-c board. typical performance characteristics (circuit of figure 1) normalized output voltage line regulation efficiency switch saturation voltage switch current limit dropout voltage 1.5 1.0 0.5 0 -0.5 -1.0 -50 -25 0 25 50 75 0 5 10 15 20 25 30 35 40 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 input voltage (v) 0 5 10 15 20 25 30 35 40 65 70 75 80 85 90 95 input voltage (v) e f f i c i e n c y ( % ) 3.3v 5v 12v 20v 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 0 12 3 4 switch current (a) s a t u r a t i o n v o l t a g e ( v ) v =12v in t=-40c j 0 25 c 0 125 c 0 -50 -25 0 25 50 75 5.5 5.0 4.5 4.0 3.5 s w i t c h c u r r e n t l i m i t ( a ) v=12v v=5v in out -50 -25 0 25 50 75 1.6 1.4 1.2 1.0 0.8 0.6 i=3a load i=1a load 4 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
typical performance characteristics (circuit of figure 1) (continued) operating quiescent current shutdown quiescent current minimum operating supply voltage on/off threshold voltage on/off pin current (sinking) switching frequency feedback pin bias current -50 -25 0 25 50 75 s u p p l y c u r r e n t ( m a ) 0 4 8 12 16 20 24 i=0 switch c u r r e n t ( a ) 0 10 20 30 40 120 100 80 60 40 20 0 supply voltage ( v) t=25c j 0 v=5v on/ off _ -50 -25 0 25 50 75 0 1 2 3 4 5 s u p p l y v o l t a g e ( v ) -50 -25 0 25 50 75 2.5 2.0 1.5 1.0 0.5 t h r e s h o l d v o l t a g e ( v ) off on 8 7 6 5 4 3 2 1 0 0 5 10 15 20 25 on/ of pin voltage (v) c u r r e n t ( a ) __ -50 -25 0 25 50 75 160 155 150 145 140 135 130 f r e q u e n c y ( k h z ) -50 -25 0 25 50 75 -5.0 -2.5 0 2.5 5.0 7.5 10 f e e d b a c k b i a s c u r r e n t ( n a ) a djustable version only 5 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
typical performance characteristics continuous mode switching waveforms v in =20v, v out =5v, i load =2a l=32 h, c out =220 f, c out esr=50m ? ? ? ? discontinuous mode switching waveforms v in =20v, v out =5v, i load =500ma l=10 h, c out =330 f, c out esr=45m ? ? ? ? 20v 10v 0v 2a 1a 0a ac/ div a b c a: output pin voltage, 10v/ div b: inductor current 1a/ div c: output ri pple voltage, 50mv/ div horizontal time base: 2 s/ div load transient response for continuous mode v in =20v, v out =5v, i load =500ma to 2a l=32 h, c out =220 f, c out esr=50m ? ? ? ? load transient response for discontinuous mode v in =20v, v out =5v, i load =500ma to 2a l=10 h, c out =330 f, c out esr=45m ? ? ? ? 20v 10v 0v 1a 0a ac/ div a b c a : output pin voltage, 10v/ div b: inductor current 1a/ div c: output ri pple voltage, 100mv/ div horizontal time base: 2 s/ div 1a 0a ac div a b a: output voltage, 100mv/ div.(ac) b: 500ma to 2a load pulse horizontal time base: 100 s/ div a: output voltage, 100mv/ div. (ac) b: 500ma to 2a load pulse horizontal time base: 200 s/ div 1a 0a ac div a b 6 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
test circuit and layout guidelines figure 1. standard test circuits and layout guides as in any switching regulator, layout is very important. rapidly switching currents associated with wiring inductance can gener ate voltage transients which can cause problems. for minimal inductance and ground loops, the wires indicated by heavy lines should be wide printed circuit traces and should be kept as short as possible. for best results, external components should be located as close to the switcher lc as possible using ground plane construction or single point grounding. if open core inductors are used, special care must be taken as to the location and positioning of this type of inductor. allowing the inductor flux to intersect sensitive feedback, lc groundpath and c out wiring can cause problems. when using the adjustable version, special care must be taken as to the location of the feedback resistors and the associated w iring. physically locate both resistors near the ic, and route the wiring away from the inductor, especially an open core type of indu ctor. + l1 c out + c in 2 3 4 5 +v in + l1 + fixed output voltage versions c - 470f, 50v, aluminum electrolytic nichicon ?pl series? in c - 220 f, 25v, aluminum electrolytic nichicon ?pl series? d1 - 5a, 40v schottky rectifer, 1n5825 l1 - 68 h, l38 out + l1 c out + c in 2 3 4 5 +v in + r1 r2 c ff adjustable output voltage versions select r1 to be approximately 1 c - 470f, 50v, aluminum electrolytic nichicon ?pl series? in k, use a 1% resistor for best stability. c - 220 f, 35v, aluminum electrolytic nichicon ?pl series? d1 - 5a, 40v schottky rectifer, 1n5825 l1 - 68 h, l38 r1 - 1k , 1% c - see application information section ? ? out ff v=v(1+ ) out ref r = r ( -1) 21 where v = 1.23v ref v v out ref r r 2 1 7 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
LM2596 series buck regulator design procedure (fixed output) procedure (fixed output voltage version) example (fixed output voltage version) given: given: v out = regulated output voltage (3.3v, 5v or 12v) v out =5v v in (max) = maximum dc input voltage v in (max) = 12v i load (max) = maximum load current i load (max) = 3a 1. inductor selection (l1) 1. inductor selection (l1) a. select the correct inductor value selection guide from figures figure 4, figure 5,or figure 6. (output voltages of 3.3v, 5v, or 12v respectively.) for all other voltages, see the design procedure for the adjustable version. a. use the inductor selection guide for the 5v version shown in figure 5. b. from the inductor value selection guide, identify the inductance region intersected by the maximum input voltage line and the maximum load current line. each region is identified by an inductance value and an inductor code (lxx). b. from the inductor value selection guide shown in figure 5, the inductance region intersected by the 12v horizontal line and the 3a vertical line is 33 h, and the inductor code is l40. c. select an appropriate inductor from the four manufacturer?s part numbers listed in figure 8. c. the inductance value required is 33 h. from the table in figure 8, go to the l40 line and choose an inductor part number from any of the four manufacturers shown. (in most in-stance, both through hole and surface m ount inductors are available.) 2. output capacitor selection (c out ) 2. output capacitor selection (c out ) a. in the majority of applications, low esr (equivalent series resistance) electrolytic capacitors between 82 f and 820 f and low esr solid tantalum capacitors between 10 f and 470 f provide the best results. this capacitor should be located close to the ic using short capacitor leads and short copper tr aces. do not use capacitors larger than 820 f. a. see section on output capacitors in application information section. b. to simplify the capacitor selection procedure, refer to the quick design component selection table shown in figure 2. this table contains different input voltages, output voltages, and load currents, and lists various inductors and output capacitors that will provide the best design solutions. b. from the quick design component selection table shown in figure 2, locate the 5v output voltage section. in the load current column, choose the load current line that is closest to the current needed in your application, for this example, use the 3a line. in the maximum input voltage column, select the line that covers the input voltage needed in your application, in this example, use the 15v line. continuing on this line are recommended inductors and capacitors that will provide the best overall performance. the capacitor list contains both through hole electrolytic and surface m ount tantalum capacitors from four different capacitor manufacturers. it is recommended that both the manufacturers and the manufacturer?s series that are listed in the table be used. in this example aluminum electrolytic capacitors from several different manufacturers are available with the range of esr numbers needed. 330 f 35v panasonic hfq series 330 f 35v nichicon pl series c. the capacitor voltage rating for electrolytic capacitors should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low esr requirements for low output ripple voltage. c. for a 5v output, a capacitor voltage rating at least 7.5v or more is needed. but even a low esr, switching grade, 220f 10v aluminum electrolytic capacitor would exhibit approximately 225 mw of esr (see the curve in figure 14 for the esr vs voltage rating). this amount of esr would result in relatively high output ripple voltage. to reduce the ripple to 1% of the output voltage, or less, a capacitor with a higher value or with a higher voltage rating (lower esr) should be selected. a 16v or 25v capacitor will reduce the ripple volt-age by approximately half. 3. catch diode selection (d1) 3. catch diode selection (d1) a. the catch diode current rating must be at least 1.3 times greater than the maximum load current. also, if the power supply design must withstand a continuous output short, the diode should have a current rating equal to the maximum current limit of the LM2596. the most stressful condition for this diode is an overload or shorted output condition. a. refer to the table shown in figure 11. in this example, a 5a, 20v, 1n5823 schottky diode will provide the best performance, and will not be overstressed even for a shorted output. b. the reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. c. this diode must be fast (short reverse recovery time) and must be located close to the LM2596 using short leads and short printed circuit traces. because of their fast switching speed and low forward voltage drop, schottky diodes provide the best performance and efficiency, and should be the first choice, especially in low output voltage applications. ultra-fast recovery, or high-efficiency rectifiers also provide good results. ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. rectifiers such as the 1n5400 series are much too slow and should not be used. 8 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
procedure (fixed output voltage version) example (fixed output voltage version) 4. input capacitor (c in ) 4. input capacitor (c in ) a low esr aluminum or tantalum bypass capacitor is needed between the input pin and ground pin to prevent large volt-age transients from appearing at the input. this capacitor should be located close to the ic using short leads. in addition, the rms current rating of the input capacitor should be selected to be at least 1/2 the dc load current. the capacitor manufacturers data sheet must be checked to assure that this current rating is not exceeded. the curve shown in figure 9 shows typical rms current ratings for several different aluminum electrolytic capacitor values. for an aluminum electrolytic, the capacitor voltage rating should be approximately 1.5 times the maximum input voltage. the tantalum capacitor voltage rating should be 2 times the maximum input voltage and it is recommended that they be surge current tested by the manufacturer. use caution when using ceramic capacitors for input bypassing, b ecause it may cause severe ringing at the v in pin. the important parameters for the input capacitor are the input voltage rating and the rms current rating. with a nominal input voltage of 12v, an aluminum electrolytic capacitor with a voltage rating greater than 18v (1.5 x v in ) would be needed. the next higher capacitor voltage rating is 25v. the rms current rating requirement for the input capacitor in a buck regulator is approximately 1 /2 the dc load current. in this example, with a 3a load, a capacitor with a rms current rating of at least 1.5a is needed. the curves shown in figure 9 can be used to select an appropriate input capacitor. from the curves, locate the 35v line and note which capacitor values have rms current ratings greater than 1.5a. a 680f/35v capacitor could be used. for a through hole design, a 680f/35v electrolytic capacitor (panasonic hfq series or nichicon pl series or equivalent) would be adequate. other types or other manufacturers capacitors can be used provided the rms ripple current ratings are adequate. for surface m ount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating. the tps series available from avx, and the 593d series from sprague are both surge current tested. LM2596 series buck regulator design procedure (fixed output) (continued) output capacitor conditions inductor through hole electrolytic surface mount tantalum output voltage (v) load current (a) max input voltage (v) inductance ( h) inductor (#) panasonic hfq series ( f/v) nichicon pl series ( f/v) avx tps series ( f/v) sprague 595d series ( f/v) 5 22 l41 470/25 560/16 330/6.3 390/6.3 7 22 l41 560/35 560/35 330/6.3 390/6.3 10 22 l41 680/35 680/35 330/6.3 390/6.3 3 40 33 l40 560/35 470/35 330/6.3 390/6.3 6 22 l33 470/25 470/35 330/6.3 390/6.3 10 33 l32 330/35 330/35 330/6.3 390/6.3 3.3 2 40 47 l39 330/35 270/50 220/10 330/10 8 22 l41 470/25 560/16 220/10 330/10 10 22 l41 560/25 560/25 220/10 330/10 15 33 l40 330/35 330/35 220/10 330/10 3 40 47 l39 330/35 270/35 220/10 330/10 9 22 l33 470/25 560/16 220/10 330/10 20 68 l38 180/35 180/35 100/10 270/10 5 2 40 68 l38 180/35 180/35 100/10 270/10 15 22 l41 470/25 470/25 100/16 180/16 18 33 l40 330/25 330/25 100/16 180/16 30 68 l44 180/25 180/25 100/16 120/20 3 40 68 l44 180/35 180/35 100/16 120/20 15 33 l32 330/25 330/25 100/16 180/16 20 68 l38 180/25 180/25 100/16 120/20 12 2 40 150 l42 82/25 82/25 68/20 68/25 figure 2. LM2596 fixed voltage quick design component selection table LM2596 series buck regulator design procedure (adjustable output) procedure (adjustable output voltage version) example (adjustable output voltage version) given: given: v out = regulated output voltage v out = 20v v in (max) = maximum input voltage v in (max) = 28v i load (max) = maximum load current i load (max) = 3a f=switching frequency (fixed at a nominal 150 khz). f=switching frequency (fixed at a nominal 150 khz). 1. programming output voltage (selecting r 1 and r 2 , as shown in figure 1) use the following formula to select the appropriate resistor values. ) r r (1 v v 1 2 ref out + = where v 1.23 v ref = select a value for r 1 between 240 ? and 1.5k ? . the lower resistor values minimize noise pickup in the sensitive feedback pin. (for the lowest temperature coefficient and the best stability with time, use 1% metal film resistors.) 1. programming output voltage (selecting r 1 and r 2 , as shown in figure 1) select r 1 to be 1 k ? , 1%. solve for r 2 . 1) v 1.23 v 20 k( 1 1) v v ( r r ref out 1 2 ? = ? = r 2 =1k (16.26-1)=15.26k, closest 1% value is 15.4k ? r 2 = 15.4 k ? . 9 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
procedure (adjustable output voltage version) example (adjustable output voltage version) 1) v v ( r r ref out 1 2 ? = 2. inductor selection (l1) 2. inductor selection (l1) a. calculate the inductor volt microsecond constant e ? t (v ? s), from the following formula: s) (v khz 150 1000 v v v v v ) v v (v t e d sat in d out sat out in ? ? + ? + ? ? ? = ? where v sat = internal switch saturation voltage = 1.16v and v d = diode forward voltage drop = 0.5v a. calculate the inductor volt ? microsecond constant (e ? t), s) (v 150 1000 5 . 0 16 . 1 28 5 . 0 20 ) 16 . 1 20 28 ( t e ? ? + ? + ? ? ? = ? s) (v . s) (v . . . ) . ( t e ? = ? ? ? = ? 2 34 67 6 34 27 5 20 84 6 b. use the e ? t value from the previous formula and match it with the e ? t number on the vertical axis of the inductor value selection guide shown in figure 7. b. e ? t=34.2 (v ? s) c. on the horizontal axis, select the maximum load current. c. i load (max) = 3a d. identify the inductance region intersected by the e ? t value and the maximum load current value. each region is identified by an inductance value and an inductor code (lxx). d. from the inductor value selection guide shown in figure 7, the inductance region intersected by the 34 (v ? s) horizontal line and the 3a vertical line is 47 h, and the inductor code is l39. e. select an appropriate inductor from the four manufacturer?s part numbers listed in figure 8. e. from the table in figure 8, locate line l39, and select an inductor part number from the list of manufacturers part numbers. 3. output capacitor selection (c out ) 3. output capacitor seiection (c out ) a. in the majority of applications, low esr electrolytic or solid tantalum capacitors between 82 f and 820 f provide the best results. this capacitor should be located close to the ic using short capacitor leads and short copper traces. do not use capacitors larger than 820 f. b. to simplify the capacitor selection procedure, refer to the quick design table shown in figure 3. this table contains different output voltages, and lists various output capacitors that will provide the best design solutions. b. from the quick design table shown in figure 3, locate the output voltage column. from that column, locate the output voltage closest to the output voltage in your application. in this example, select the 24v line. under the output capacitor section, select a capacitor from the list of through hole electrolytic or surface mount tantalum types from four different capacitor manufacturers. it is recommended that both the manufacturers and the manufacturers series that are listed in the table be used. in this example, through hole aluminum electrolytic capacitors from several different manufacturers are available. 220 f/35v panasonic hfq series 150 f/35v nichicon pl series c. the capacitor voltage rating should be at least 1.5 times greater than the output voltage, and often much higher voltage ratings are needed to satisfy the low esr requirements needed for low output ripple voltage. c. for a 20v output, a capacitor rating of at least 30v or more is needed. in this example, either a 35v or 50v capacitor would work. a 35v rating was chosen, although a 50v rating could also be used if a lower output ripple voltage is needed. other manufacturers or other types of capacitors may also be used, provided the capacitor specifications (especially the 100 khz esr) closely match the types listed in the table. refer to the capacitor manufacturers data sheet for this information. 4. feedforward capacitor (c ff ) (see figure 1) 4. feedforward capacitor (c ff ) for output voltages greater than approximately 10v, an additional capacitor is required. the compensation capacitor is typically between 100 pf and 33 nf, and is wired in parallel with the output voltage setting resistor, r2. it provides additional stability for high output voltages, low input-output voltages, and/or very low esr output capacitors, such as solid tantalum capacitors. 2 ff r 10 31 1 c = this capacitor type can be ceramic, plastic, silver mica, etc. (because of the unstable characteristics of ceramic capacitors made with z5u material, they are not recommended.) the table shown in figure 3 contains feed forward capacitor values for various output voltages. in this example, a 560 pf capacitor is needed. 3 10 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
LM2596 series buck regulator desing procedure (adjustable output) through hole output capacitor surface mount output capacitor output voltage (v) panasonic hfq series ( f/v) nichicon pl series ( f/v) feedforward capacitor avx tps series ( f/v) sprague 595d series ( f/v) feedforward capacitor 2 820/35 820/35 33 nf 330/6.3 470/4 33 nf 4 560/35 470/35 10 nf 330/6.3 390/6.3 10 nf 6 470/25 470/25 3.3 nf 220/10 330/10 3.3 nf 9 330/25 330/25 1.5 nf 100/16 180/16 1.5 nf 12 330/25 330/25 1 nf 100/16 180/16 1 nf 15 220/35 220/35 680 pf 68/20 120/20 680 pf 24 220/35 150/35 560 pf 33/25 33/25 220 pf 28 100/50 100/50 390 pf 10/35 15/50 220 pf figure 3. output capacitor and feedforward capacitor selection table LM2596 series buck regulator design procedure inductor value selection guides (for continuous mode operation) figure 4. LM2596-3.3 figure 6. LM2596-12 l29 l21 l30 l31 l40 l22 l23 l32 l33 l34 l16 l15 l24 l25 6 8 h 4 7 h 3 3 h 2 2 h 1 5 h 0.6 0.8 1.0 1.5 2.0 2.5 3.0 maximum load current (a) 5v 6v 7v 8v 10v 15v 20v 40v m a x i m u m i n p u t v o l t a g e ( v ) 0.6 0.8 1.0 1.5 2.0 2.5 3.0 maximum load current (a) 14v 16v 18v 19v 17v 25v 30v 40v m a x i m u m i n p u t v o l t a g e ( v ) 20v 15v l27 l28 l36 l43 l37 l38 l30 l39 l40 l31 l32 l33 l34 l24 l23 l22 l21 l29 1 0 0 h 1 5 0 h 6 8 h 4 7 h 3 3 h 2 2 h 1 5 h 11 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator
figure 5. LM2596-5.0 figure 7. LM2596-adj LM2596 series buck regulator design procedure (continued) schott renco pulse engineering coilcraft inductance ( h) cur- rent (a) through hole surface mount through hole surface mount through hole surface mount surface mount l15 22 0.99 67148350 67148460 rl- 1284-22-43 rl 1500-22 pe- 53815 pe- 53815-s do 3308-223 l21 68 0.99 67144070 67144450 rl-5471-5 rl 1500-68 pe- 53821 pe- 53821-s do 3316-683 l22 47 1.17 67144080 67144460 rl-5471-6 - pe-53822 pe- 53822-s do 3316-473 l23 33 1.40 67144090 67144470 rl-5471-7 - pe-53823 pe- 53823-s do 3316-333 l24 22 1.70 67148370 67148480 rl- 1283-22-43 - pe- 53824 pe- 53825-s do 3316-223 l25 15 2.10 67148380 67148490 rl- 1283-15-43 - pe- 53825 pe- 53824-s do 3316-153 l26 330 0.80 67144100 67144480 rl-5471-1 - pe-53826 pe- 53826-s do 5022p-334 l27 220 1.00 67144110 67144490 rl-5471-2 - pe-53827 pe- 53827-s do 5022p-224 l28 150 1.20 67144120 67144500 rl-5471-3 - pe-53828 pe- 53828-s do 5022p-154 l29 100 1.47 67144130 67144510 rl-5471-4 - pe-53829 pe- 53829-s do 5022p-104 l30 68 1.78 67144140 67144520 rl-5471-5 - pe-53830 pe- 53830-s do 5022p-683 l31 47 2.20 67144150 67144530 rl-5471-6 - pe-53831 pe- 53831-s do 5022p-473 l32 33 2.50 67144160 67144540 rl-5471-7 - pe-53932 pe- 53932-s do 5022p-333 l33 22 3.10 67148390 67148500 rl- 1283-22-43 - pe- 53933 pe- 53933-s do 5022p-223 l34 15 3.40 67148400 67148790 rl- 1283-15-43 - pe- 53934 pe- 53934-s do 5022p-153 l35 220 1.70 67144170 - rl-5473-1 - pe-53935 pe- 53935-s - l36 150 2.10 67144180 - rl-5473-4 - pe-54036 pe- 54036-s - l37 100 2.50 67144190 - rl-5472-1 - pe-54037 pe- 54037-s - l38 68 3.10 67144200 - rl-5472-2 - pe-54038 pe- 54038-s - l39 47 3.50 67144210 - rl-5472-3 - pe-54039 pe- 54039-s - l40 33 3.50 67144220 67148290 rl-5472-4 - pe-54040 pe- 54040-s - l41 22 3.50 67144230 67148300 rl-5472-5 - pe-54041 pe- 54041-s - l42 150 2.70 67148410 - rl-5473-4 - pe-54042 pe- 54042-s - l43 100 3.40 67144240 - rl-5473-2 - pe-54043 - l44 68 3.40 67144250 - rl-5473-3 - pe-54044 - figure 8. inductor manufacturers part numbers 7v 8v 9v 10v 12v 15v 20v 40v 0.6 0.8 1.0 1.5 2.0 2.5 3.0 maximum load current (a) m a x i m u m i n p u t v o l t a g e ( v ) l29 l38 l39 l30 l21 l31 l40 l32 l33 l34 l25 l23 l22 l24 1 0 0 h 6 8 h 4 7 h 3 3 h 2 2 h 1 5 h 0.6 0.8 1.0 1.5 2.0 2.5 3.0 maximum load current (a) 4 5 6 7 8 9 10 15 20 25 30 40 50 60 70 e t ( v s ) ? ? l27 l35 l28 l36 l29 l21 l30 l38 l43 l44 l37 l22 l31 l39 l23 l15 l24 l40 l32 l33 l34 l25 3 3 h 2 2 h 1 5 h 4 7 h 6 8 h 1 0 0 h 1 5 0 h 2 2 0 h 0 10 20 30 40 50 60 70 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 capacitor voltage rating (v) figure 9. rms current ratings for low esr electrolytic capacitors (typical) 12 beijing estek electronics co.,ltd LM2596 3astep-down voltageregulator

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