QV National Semiconductor LM2596 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator General Description The LM25986 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving a 34 load with excellent line and load regulation, These devices are avail- able in fixed output voltages of 3.3V, 5V, 12V, and an adjust- able output version. Requiring a minimum number of external components, these regulators are simple to use and include internal fre- quency compensationt, 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 regu- lators, Available in a standard 5-lead TO-220 package with several different laad bend options, and a 5-lead TO-263 surface mount 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 out put voltage under specified input voltage and output load conditions, and + 15% on the oscillator frequency. External shutdown is included, featuring typically 80 wA standby cur- rent. Self protection features include a two stage frequency reducing current limit for the output switch and an over PRELIMINARY February 1996 temperature shutdown for complete protection under fault conditions, Features @ 3.3V, 5V, 12V, and adjustable output versions m 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 capability Low power standby mode, Iq typically 80 yA @ High efficiency m Uses readily available standard inductors B Thermal shutdown and current limit protection Applications m Simple high-efficiency step-down (buck) regulator m On-card switching regulators m Positive to negative converter Typical Application (Fixed cutput Voltage Versions) Teedback Vay My Unrae alates. Bt Inp.t LM2596 1 5.4 -Lead TO-220 (T) Pig 1, 3. and 5 Side _poK Ping P and 4 View 3 - ON/OFF 4 - Feed 3az< CQ 5 = Ground Top 2 - Gutput View o 1-4 y TLAH/1 2583-2 Order Number LM2596T-3,3, LM2596T-5,0, LM2596T-12 or LM2596T-ADY See NS Package Number T05D +Patant Number 6,382,918. SIMPLE SWITCHER and Switehers Made Simpie are regislered trademarks of National Semiconductor Corporation. = Cutpat ul s.o Reuulaled Gatay 2a lone tLe = ELT 220 wr tH Connection Diagrams and Ordering Information Bent and Staggered Leads, Through Hole Package TLH/12583 -1 Surface Mount Package 5-Lead TO-263 {S) df R, 5 - ON/OFF 4 Feed Back 3 = Ground 2 - Output 2 1 in Metal Tab GND TL/H/12583 -3 Order Number LM2596S-3.3, LM2596S-5.0, LM2596S-12 or LM25968-AD.) See NS Package Number TS5B 1996 National Semiconductor Corporation TL/H/12583 RRD-B30M26/Printed in U. 8. A. JoyeinBoy abeyjoA UMOG-daig VE ZH} OS} 19}4eAU0D JOaMOd eYSHOLIMS J TdWIS 96SZIN1Absolute Maximum Ratings (ote 1) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Maximum Supply Voltage 46V ON/OFF Pin Input Voltage -03 <V = +25V Feedback Pin Voltage -0.3<V<+26V Output Voltage to Ground (Steady State) -1V Power Dissipation Internally limited Storage Temperature Range 65C to + 150C ESD Susceptibility Human Body Model (Note 2) Z2kKV LM2596-3.3 Lead Temperature 5 Package Vapor Phase (60 sec.) +215C Infrared (10 sec.) + 246C T Package (Soldering, 10 sec.) + 260C Maximum Junction Temperature + 150C Operating Conditions Temperature Range Supply Voltage 40C < Ty +125C 4.5V to 40V Electrical Characteristics specifications with standard type face are for Ty = 28C, and those with boldface type apply over full Operating Temperature Range LM2596-3.3 Units a V Symbol Parameter Conditions Typ Limit (Limits) (Note 3) {Note 4) SYSTEM PARAMETERS (Note 5) Test Circuit Figure 2 Vout Output Voltage 4,75V < Vin <= 40V, 0.24 < ILoap = 34 3.3 v 3,168/3,.135 imin} 3.432/3.465 V(max) q Efficiency Vin = 12V, ILoap = 34 73 % LM2596-5.0 Electrical Characteristics specifications with standard type face are for T = 25C, and those with boldface type apply over full Operating Temperature Range LM2596-5.0 Units sue 1 Symbol Parameter Conditions Typ Limit (Limits) {Note 3) {Note 4) SYSTEM PARAMETERS (Note 5) Test Circuit Figure 2 Vout Output Voltage 7V < Vin < 40V, 0.24 <= ILoap = 34 5.0 Vv 4.800/4.750 Vimin) 5,200/5.250 Vmax) n Efficiency Vin = 12, lLoap = 3A 80 % LM2596-12 Electrical Characteristics specifications with standard type face are for T 25C, and those with boldface type apply over full Operating Temperature Range LM2596-12 Units Symbol Parameter Conditions Typ Limit (Limits) (Note 3) (Note 4) SYSTEM PARAMETERS (Note 5) Test Circuit Figure 2 Vout Output Voltage 16V < Vin <= 40V, 0.24 < ILoap = 34 12.0 Vv 11.52/11.40 Vimin) 12,.48/12.60 (max) y Efficiency Vin = 12V, ILoap = 34 90 %LM2596-ADJ Electrical Characteristics specications with standard type face are for Ty = 25C, and those with boldface type apply over full Operating Temperature Range LM2596-ADJ as Units Symbol Parameter Conditions Typ Limit (Limits) {Note 3) {Note 4) SYSTEM PARAMETERS (Note 5) Test Circuit Figure 2 Vee Feedhack Voltage 4,5V = Vin = 40V,0.24 = ILaap = 3A 1.230 v Vout programmed for 3V. Circuit of Figure 2 1.193/ 1.180 Vimin) 1.267/1.280 Vimax) n Efficiency Vin = 124, Vout = 3V, ILoap = 34 % All Output Voltage Versions Electrical Characteristics specifications with standard type face are for Ty = 25C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, Viy = 12V for the 3.3V, 5V, and Adjustable version and Vijy = 24V for the 12V version. ILgap = 500 mA LM2596-XX Units an i Symbol Parameter Conditions Typ Limit (Limits) (Note 3) {Note 4) DEVICE PARAMETERS \b Feedback Bias Current Adjustable Version Only, Veg = 1.3V 10 nA 50/100 oA (max) fo Oscillator Frequency (Note 6) 150 kHz 127/110 kHz(min) 173/173 kHz(max} VsaT Saturation Voltage lout = 3A (Notes 7 and 8) 1.16 Vv 1.4/1.6 Vi(max) pc Max Duty Cycle (ON) (Note 8) 100 % Min Duty Cycle (OFF) (Note 9) 0 lot Current Limit Peak Current (Notes 7 and 8) 45 A 3.6/3.4 A(min) 6.9/7.5 A(max) IL Output Leakage Current | (Notes 7, 9, and 10) Output = OV 50 pA(max) Output = -1V 2 mA 30 mA(Mmax) la Quiescent Current (Note 9) 5 mA 10 mA(max) Istey Standby Quiescent ON/OFF pin = 5V (OFF) (Note 10) 80 pA Current 200/260 pA(max) Ac Thermal Resistance TO-220 or TO-263 Package, Junction to Case 2 C/W aya TO-220 Package, Junction to Ambient (Note 11) 50 C/W Asa TO-263 Package, Junction to Ambient (Note 12) 50 "C/W Ba TO-263 Package, Junction to Ambient (Note 13) 30 C/W Aya TO-263 Package, Junction to Ambient (Note 14) 20 C/W ON/OFF CONTROL Test Circuit Figure 2 ON/OFF Pia Logic Input 1.3 v Vin Threshold Voltage Low (Regulator ON) 0.6 Vimax) VIL High (Regulator OFF) 2.0 Yimin) lH ON/OFF Pin Vuoaic = 2.5 (Regulator OFF) 5 pA Input Current 15 pA(Max) It Vioaic = 0.5V (Regulator ON) 0.02 BA 5 pA(max)Electrical Characteristies (continued) Note 1: Abscluta Maximum Ratings indicate limits hayend which damags te the davica may occur. Operating Ratings indicate conditions for which tha davica is intandad to be functional, but do not quarantes specific performance limits. For quarantead spacifications and tast conditions, sea the Electrical Charactaristics. Note 2: Tha human body modal is a 100 pF capacitor discharged through a 1.5k resistor into each pin. Note 3: Typical numbers ara at 25C and reprasent tha most likely norm. Note 4: All limits quaranteed at room temperature (standard type face) and at temperature extremes {bold type face). All room temperatura limits are 100% production tasted. All limits at temperature extremes are guaranteed via Correlation using standard Statistical Quality Control (SQC) mathods. All limits ara used to calculate Average Outgoing Quality Laval (AO@L). Note & External componants such as the catch dioda, inductor, input and output Capacitors, and voltage programming rasistors can atfact switching regulator systam parformance. When the LM2696 is used as shown in the Figure 2 test circuit, system parformance will ba as shown in systam parameters saction of Electrical Charactaristics. Note & The switching frequency is reduced when the sacond stage currant limit is activated. Tha amount of raduction is datermined by the saverity of currant ovarload. Note 7: No diods, inductor or capacitor connacted to output pin. Note 8: Faadback pin ramoved from output and connected to OV to force tha output transistor switch ON. Note 9: Feedback pin ramoved from output and connacted to 12V for tha 3.3V, 5V, andthe ADJ. version, and 15 for the 12V version, to force the output transistor switch OFF. Note 10: Vy = 40. Note 11: Junction to ambisnt thermal rasistanca (no axtarnal haat sink) for thea TO-220 packags mounted vertically, with tha leads soldarad to a printed circuit board with (1 oz.) copper area of approximately 1 in2. Note 12: Junction to ambient thermal resistance with the TO-263 package tab soldered to a single printed circuit board with 0.5 in? of (1 oz.) copper area. Note 13: Junction to ambient tharmal rasistance with tha TO-263 packags tab soldared toa single sided printed circuit board with 2.5 in2 of (1 oz.) copper araa. Note 14: Junction to ambiant thermal resistance with tha TO-263 package tab soldered to a double sided printed circuit board with 3 in? of (1 02.) copper araa on the LM2596S side of the board, and approximately 16 in? of copper on the other side of the p-c board. See Application Information in this dala sheet and the thermal modal in Switchers Made Simple version 4.3 sottwara. Typical Performance Characteristis (circuit of Figure 2 ) Normalized Output Voltage Line Regulation Efficiency See TT DDT _ Yin = 20v = 48 Vout = 5 BA Load 20V 15 Loan = 54 # hogy = 100 ms 90 | ta Normalized at = 2590 2 T) = 25% g cna ~ tay = 05 J 2 we 85 x x = & 3 ~ S 6 a 9g = 80 & = a a 5 3 2 ios Se -0.1 = . = 75 e E = to z -0.2 0 zs ze -03 15 1.4 65 50-25 0 425 5G 75 100 125 0 5 1 15 2 25 30 35 40 d 5 10 15 20 25 30 35 40 JUNCTION TEMPERATURE (C) INPLIT VOLTAGE (V) INPLIT VOLTAGE (Vv) TL/H/12583-4 TL/H/12583-5 TL/H/12583-6 Switch Saturation Voltage Switch Current Limit Dropout Voltage 4 5.5 Ti 1 Vin = 12 Wn = 124 = L = 33 mH = z Your = 5 Sous ing = 0.048 = 12 50 z Your = Yagg ~50m 8 5 = _ eo a = 19 3 5 ane hoao = 3A] 2 = ras = 40 oe o4s a & = L 5 og 3 a 10 a o = a - TL e 08 2 40 ? loan = 14 vi = 5 58 a oF x 0.6 5 0.8 a 1 Zz 3 4 -50 -25 0 25 50 75 100 125 50-28 0 25 50 75 100 125 SWITCH CURRENT (4) JUNCTION TEMPERATURE (C) JUNCTION TEMPERATURE (@C) TL/H/12583-7 TL/H/12583-8 TL/H/12583-9Typical Performance Characteristics (circuit of Figure 2) (Continued) Operating Quiescent Current 4.5V <4 < 40 _ swirch = 2 = = 5 Switch ON @ & 5 & Switch OFF a a 50-25 9 25 50 75 100 125 JUMCTION TEMPERATURE (C) TLAH/12583-10 ON/OFF Threshold Voltage 25 = 20 wi 3 Boe 3 a Se i 2 8 = O05 0 50-25 0 25 80 75 100 125 JUNCTION TEMPERATURE (C) TLAH/12583-13 CURRENT (pea) CURRENT (yA) FEEDBACK BIAS CURRENT (n&} Shutdown Quiescent Current uO Non orr = 5 100 T= 359 ag Ty = -409C AND 125C 60 40 za a a 1a 20 30 4 SUPPLY VOLTAGE () TL/H/12583-11 ON/OFF Pin Current (Sinking) Vin = 40 40C ST) S 125C 9 5 1 15 2025 ON/OFF PIN VOLTAGE (} TL/H/12583-14 Feedback Pin Bias Current ADJUSTABLE VERSION ONLY 25 -50 -50 -25 0 25 50 75 100 125 JUNCTION TEMPERATURE (C} TL/H/12883-16 SUPPLY VOLTAGE () FREQUECY {kHz] Minimum Operating Supply Voltage 5 Vou = 123 Loan = 12Oms a 90-25 0 25 30 75 100 125 JUNCTION TEMPERATURE (C) TL/H/12583-12 Switching Frequency 160 155 150 145 140 155 130 50-258 9 25 50 75 100 125 JUNCTION TEMPERATURE (C) TL/H/12583-15Typical Performance Characteristics (circuit of Figure 2 ) Continuous Mode Switching Waveforms Vin = 20V, Vout = 5V,ILoap = 2A L = 32 uH, Cout = 220 pF, Cour ESR = 50 mn A: Output Pin Voltage, 10V/div. 8: Inductor Currant 1A/div. : Output Ripple Voltage, 50 mV/div. Horizontal Time Base: 2 .s/div. Load Transient Response for Continuous Mode Vin = 20V, Vout = 5. ILoap = 500 mA to 2A L = 32 uw, Coyt = 220 pF, Coy7 ESR = 50 ma TL/H/1 2583-17 100 mv. A: Output Pin Voltage, 10V/div. B: Inductor Currant 0.6A/div. Discontinuous Mode Switching Waveforms Vin = 20V, Vout = 5V,ILoap = 500 mA L = 10 uH, Cout = 330 pF, Cour ESR = 45 mn TL/H/1 2583-18 C: Output Ripple Voltage, 100 mV/div. Horizontal Time Base: 2 .s/div. Load Transient Response for Discontinuous Mode Vin = 20, Vout = 5V.ILoap = 500 mA to 2A L = 10 WH, Cout = 330 pF, Coy7 ESR = 45 mn TL/H/12583-20 7 Ld tn 100 mV a A A 5 B TL/M/12563~18 A: Output Voltage, 100 mV/div. (AC) 12583=1 B: 600 mA to 2A Load Pulse A: Output Voltage, 100 mV/div. (AC) . a . a B: 500 mA to 2A Load Pulse Horizontal Time Base: 200 ps/div. Horizontal Time Base: 100 ws/div. Block Diagram Dh OFF rl 'T 220 1 200 nv TY tinee P] ovassy Eo fooasv LJ starr an EAS SEFEREKC= REGULATOR uP CCUP. + _~ 2.34 LIMIT oh Feeapack | CCMP. SWITCH + % - a1 = QreR aa ACH P| RIVER erza, | srier | S=T + 15C kHz THERWA_ 5c. LIMIT ACTIVE CAPACITOR CUPPuT FIGURE 1 TL/H/12583-21 8Test Circuit and Layout Guidelines Fixed Output Voltage Versions FEEDBACK LM2596 OUTPUT FIXED OUTPUT 1 2 UNREGULATED KEEP FEEDBACK WIRING AWAY FROM INDUCTOR FLUX REGULATED OUTPUT DC INFUT +8 Sy tT {" HEAVY LINES MUST BE KEPT SHORT AND USE GROUND PLANE CONSTRUCTION FOR BEST RESULTS Cin = 470 uF, SOV, Aluminum Electrolytic Nichicon PL Sarias Cour 220 uF, 26V Aluminum Electrolytic, Nichicen PL Sarias LOW ESR I I 1 1 I I I ! I I I I | SHORT LEADS OPTIONAL POST RIPPLE FILTER TL/H/12583-22 Adjustable Output Voltage Versions D1 6A, 40 Schotthy Restifier, 1N5826 Li 68 H, L38 Cre RI Wy4 tk 4 | FEEDBACK + WN] LM2596. J ouTPur + t P| ADJUSTABLE LOCATE THE PROGRAMMING RESISTORS NEAR THE FEEDBACK PIN USING SHORT LEADS KEEP FEEDBACK WIRING AWAY A" FROM INDUCTOR FLUX REGULATED OUTPUT 2 meen | fe, r r HEAVY LINES MUST BE KEPT SHORT AND USE GROUND PLANE CONSTRUCTION FOR BEST RESULTS RB Vout = VRer (1 + =) where Vaer = 1.23V 1 Select Ry to ba approximately 1 kf, Ro =R (you - 1] 2 1 use 41% resistor for bast stability. VRer TL/H/12583-23 Cin 470 uF, S0, Alurninum Electrolytic Nichicen PL Series Cout 220 uF, 38 Aluminum Electrolytic, Nichicen PL Series C1 5A, 40V Schottky Rectifier, 1N5825 Li 68 pH, L38 Ry 1kl,1% Cre See Application Information Saction FIGURE 2. Standard Test Circuits and Layout Guides As in any switching regulator, layout is very important. Rap- idly switching currents associated with wiring inductance can generate voltage transients which can cause problems. For minimal inductance and ground loops, the wires indicat- ed by heavy lines should be wide printed circuit traces and should be kept as short as possible, For best results, external components should he located as close to the switcher IC as possible using ground plane construction or single point grounding. lf open core inductors are used, special care must be taken as to the location and positioning of this type of induc- tor. Allowing the inductor flux to intersect sensitive feed- back, IC groundpath and Coyr 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 wiring. Physically locate both resistors near the (IC, and route the wiring away from the inductor, especially an open core type of inductor. (See application section for more information.)LM2596 Series Buck Regulator Design Procedure (Fixed Output) PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) Given: Vout = Regulated Output Voltage (3.3V, 5V or 12V) Vindmax) = Maximum DC Input Voltage ILoao(max) = Maximum Load Current 1. Inductor Selection (L1) A, Select the correct inductor value selection guide from Figures 5, 6, or 7. (Output voltages of 3.3V, 5V, or 12V respectively.) For all other voltages, see the design pro- cedure for the adjustable version, 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 induc- tor code (LXxX), , Select an appropriate inductor from the four manufac- turers part numbers listed in Figure 9. 2. Output Capacitor Selection (Coyt) A. In the majority of applications, low ESR (Equivalent Series Resistance) electrolytic capacitors between 82 pF and 820 WF and low ESR solid tantalum capaci- tors between 10 uF and 470 uF 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 uF, For additional information, see section on output ca- pacitors in application information section. B. To simplify the capacitor selection procedure, refer to the quick design component selection table shown in Figure 3. This table contains different input voltages, out- put voltages, and load currents, and lists various induc- tors and output capacitors that will provide the best de- sign solutions. . The capacitor voltage rating for electrolytic capacitors should he at least 1.5 times greater than the output volt- age, and often much higher voltage ratings are needed to satisfy the low ESR requirements for low output ripple voltage. D. For computer aided design software, see Swifchers Made Simple version 4,3 or later. 3. Catch Diode Selection (01) 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. 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 effi- ciency, and should be the first choice, aspecially in low output voltage applications. Ulira-fast recovery, or High- Procedure continued on next page. Given: Vout = 5 Vin(max) = 12V ILoap(max) = 34 1. Inductor Selection (L1) A. Use the inductor selection guide for the 5V version shown in Figure 6. B. From the inductor value selection guide shown in Fig- ure 6, the inductance region intersected by the 12V hari- zontal line and the 3A vertical line is 33 WH, and the inductor code is L40, . The inductance value required is 33 wH. From the table in Figure 9, go to the L40 line and choose an induc- tor part number from any of the four manufacturers shown. (In most instance, both through hole and surface mount inductors are available.) 2. Output Capacitor Selection (Cour) 4. See section on output capacitors in application information section. B, From the quick design component selection table shown in Figure 3, 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 volt- age needed in your application, in this example, use the 15 line. Continuing on this line are recommended in- ductors and capacitors that will provide the best overall performance. The capacitor list contains both through hole electrolytic and surface mount tantalum capacitors from four differ- ent 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 uF 35V Panasonic HFQ Series 330 uF 35V_ Nichicon PL Series . For a 5V output, a capacitor voltage rating at least 7,5 or more is needed, But even a low ESR, switching grade, 220 FF 10V aluminum electrolytic capacitor would exhibit approximately 225 mf 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 (ower ESR) should be selected. A 16V or 25V capacitor will reduce the ripple voltage by approximately half. 3. Catch Diode Selection (D1) A. Refer to the table shown in Figure 72. In this example, a 5A, 20V, 1N5823 Schottky diode will provide the best performance, and will not he overstressed even for a shorted output, Example continued on next page.LM2596 Series Buck Regulator Design Procedure (Fixed Output) (continued) PROCEDURE (Fixed Output Voltage Version) EXAMPLE (Fixed Output Voltage Version) Efficiency rectifiers also provide good results, Ultra-fast recovery diodes typically have reverse racovery times of 50 ns or less, Rectifiers such as the 1N5400 series are much too slow and should not be used. Input Capacitor (Cyy) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin to prevent large voltage 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 % 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 73 shows typical RMS current ratings for several different aluminum elec- trolytic capacitor values. For an aluminum electrolytic, the capacitor voltage rating should be approximately 1.5 times the maximum input voltage. Caution must be exercised if solid tantalum ca- pacitors are used (see Application Information on input capacitor. The tantalum capacitor voltage rating should be 2 times the maximum input voltage and it is recom- mended that they be surge current tested by the manu- facturer, Use caution when using ceramic capacitors for input by- passing, because it may cause severe ringing at the Vijy pin. For additional information, see section on input ca- pacitors in Application Information section. 4 4, Input Capacitor (Cin) 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 Vin} would be needed. The next higher capacitor voltage tating is 25V. The RMS current rating requirement for the input capaci- tor in a buck regulator is approximately 1% the DC load current. In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.54 is needed. The curves shown in Figure 7.3 can be used to select an ap- propriate input capacitor. From the curves, locate the 35 line and note which capacitor values have RMS cur- rent ratings greater than 1.54. A 680 wF/35V capacitor could be used. For a through hole design, a 680 wF/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 mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rating (see Application In- formation on input capacitors in this data sheet), The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. Conditions Inductor Output Capacitor Through Hole Electrolytic Surface Mount Tantalum Voltage | Current | Vonage. Inductance | Inductor Hraseries | PLSeries Series | 08D Series (v) (A) v) ul) (*) (FV) (uF/) (uF/V) (uE/V) 5 22 L41 470/25 560/16 330/6.3 390/6.3 3 7 22 L41 660/35 560/35 330/6,3 390/63 10 22 L41 680/35 680/35 330/6.3 390/6.3 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 2 10 33 L32 330/35 330/35 330/6.3 390/6.3 40 47 L39 330/35 270/50 220/10 330/10 8 22 L41 470/25 560/16 220/10 330/10 3 10 22 L41 60/25 560/25 220/10 330/10 15 33 L40 330/35 330/35 220/10 330/10 40 47 L39 330/35 270/85 220/10 330/10 9 22 L33 470/25 560/18 220/10 330/10 2 20 68 L3s 180/35 180/35 100/10 270/10 40 68 L3s 180/35 180/35 100/10 270/10 15 22 L41 470/25 470/25 100/16 180/16 18 33 L40 330/25 330/25 100/16 180/18 8 30 68 L44 180/25 180/25 100/16 120/20 12 40 68 L44 180/35 180/35 100/16 120/20 15 33 L32 330/25 330/25 100/16 180/16 2 20 68 L38 180/25 180/25 100/16 120/20 40 150 L42 82/25 82/25 68/20 68/25 FIGURE 3. LM2596 Fixed Voltage Quick Design Component Selection TableLM2596 Series Buck Regulator Design Procedure (Adjustable Output) PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) Given: Vout = Regulated Output Voltage Vinimax) = Maximum Input Voltage ILoao(max) = Maximum Load Current F = Switching Frequency (Fixed af a nominal 150 kHz). 1. Programming Output Voltage Gelecting R; and Re, as shown in Figure 2) Use the following formula to select the appropriate resis- tor values, R Vout = VREF (: + 7 | where VRer = 1.23V 1 Select a value for Ry between 240 and 1.5 kf. The lower resistor values minimize noise pickup in the sensi- tive feedback pin. (For the lowest temperature coeffi- cient and the best stability with time, use 1% metal film resistors.) Re = Ry (Your - 1} VREF 2. Inductor Selection (L1) A. Calculate the inductor Volt * microsecond constant E*T (V ps), from the following formula: Vout + p Vin Ysar + Yb 1000 * Teo nnz Y * HS) where Vsat = internal switch saturation voltage = 1.16V and Vp = diode forward voltage drop = 0.5V 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 &. . on the horizontal axis, select the maximum load cur- rent. 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 (LXXx)}, E. Select an appropriate inductor from the four manufac- turers part numbers listed in Figure 9. 3. Output Capacitor Selection (CoyT) A. In the majority of applications, low ESR electrolytic or solid tantalum capacitors between 82 WF and 820 pF provide the best results. This capacitor should he locat- ed close to the IC using short capacitor leads and short copper traces. Do not use capacitors larger than 820 pF. For additional information, see section on output ca- pacitors in application information section. B. To simplify the capacitor selection procedure, refer to the quick design table shown in Figure 4. This table con- tains different output voltages, and lists various output capacitors that will provide the best design solutions, . 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. EeT = (Vin Your sat}& Procedure continued on nexd page. Given: Vout = 20V Vin(max) = 28V ILoap(max) = 34 F = Switching Frequency (Fived af a nominal 150 kHz). 1. Programming Output Voltage Gelecting R; and Re, as shown in Figure 2) Select R, to be 1 kf, 1%. Solve for Ra. = R, (Vout _ ) - (= _ ) Re = Rr (jou \ 1k 1,.23V \ Re = 1k (16.26 1) = 15.26k, closest 1% value is 15.4 kf. Re = 15.4 k2, 2. Inductor Selection (L1) A. Calculate the inductor Volt * microsecond constant (E * 7), 20+05 _ 1000 EeT=(@8-20-1.18)* a es05 150 VMS ET = (6.84) 20.5 6.67 (V ws) = 34.2 (V us) 27.34 B.E*T = 34.2 (Ve us) C. ILoap(max) = 3A D. From the inductor value selection guide shown in Fig ure 8 the inductance region intersected by the 34 (V ws) horizontal line and the 3A vertical line is 47 pH, and the inductor code is L39, E. From the table in Figure 2 locate line L39, and select an inductor part number from the list of manufacturers part numbers, 3. Output Capacitor Selection (Court) A. See section on Court in Application Information sec- tion. B, From the quick design table shown in Figure 4, locate the output voltage column. From that column, locate the output voltage closest to the output voltage in your appli- cation. 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 man- ufacturers series that are listed in the table be used, In this example, through hole aluminum electrolytic ca- pacitors from several different manufacturers are avail- able. 220 wF/35V Panasonic HFQ Series 150 wF/35V Nichicon PL Series Example continued on next page. 10LM2596 Series Buck Regulator Design Procedure (Adjustable Output) PROCEDURE (Adjustable Output Voltage Version) EXAMPLE (Adjustable Output Voltage Version) . Feedforward Capacitor (Crr) (See Figure 2) For output voltages greater than approximately 10V, an additional capacitor is required. The compensation ca- pacitor is typically between 100 pF and 33 nF, and is wired in parallel with the output voltage setting resistor, Ro. It provides additional stability for high output volt- ages, low input-output voltages, and/or very low ESR output capacitors, such as solid tantalum capacitors. 1 ~ 81x 103 x Ro 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 recom- mended.) . 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, B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. . 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 effi- ciency, and should be the first choice, especially in low output voltage applications. Ultra-fast recovery, or High- Efficiency rectifiers ara also a good choice, but some types with an abrupt turn-off characteristic may cause instability or EMI problems. Ultra-fast recovery diodes typically have reverse recovery times of 50 ns or less. Rectifiers such as the 1N4001 series are much too slow and should not be used. Input Capacitor (Cyy) A low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground to prevent large voltage transients from appearing at the input In addition, the RMS current rating of the input capacitor should be selected to be at least % the DC load current. The capacitor manufacturers data sheet must be checked to assure that this current rating is not exceed- ed. The curve shown in Figure #3 shows typical RMS current ratings for several different aluminum electrolytic capacitor values. This capacitor should be located close to the IC using short leads and the voltage rating should be approxi- mately 1.5 times the maximum input voltage. lf solid tantalum input capacitors are used, it is recom- ended that they be surge current tested by the manufac- turer. Use caution when using a high dielectric constant ce- ramic capacitor for input bypassing, because it may cause severe ringing at the Viy pin. Cre For additional information, see section on input capaci- tors in application information section. . For a 204V output, a capacitor rating of at least 30V or more is needed, In this example, either a 35V or 50V capacitor would work, 4 35 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 (es- pecially 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 (Cr) The table shown in Figure 4 contains feed forward ca- pacitor values for various output voltages. In this exam- ple, a 560 pF capacitor is needed. 5, Catch Diode Selection (01) A. Reser to the table shown in Figure 72. Schottky diodes provide the best performance, and in this example a 5A, 40V, 1N5825 Schottky diode would be a good choice. The 5A diode rating is more than adequate and will not be overstressed even for a shorted output. Input Capacitor (Cjq) The important parameters for the Input capacitor are the input voltage rating and the RMS current rating. With a nominal input voltage of 28V, an aluminum electrolytic aluminum electrolytic capacitor with a voltage rating greater than 42V (1.5 x Vi) would be needed. Since the the next higher capacitor voltage rating is 50V, a 50V capacitor should be used. The capacitor voltage rating of (1.5 X Viy) is a conservative guideline, and can be modi- fied somewhat if desired, The RMS current rating requirement for the input capaci- tor of a buck regulator is approximately 1% the DC load current, In this example, with a 3A load, a capacitor with a RMS current rating of at least 1.54 is needed. The curves shown in Figure 73 can be used to select an appropriate input capacitor, From the curves, locate the 50V line and note which capacitor values have RMS cur- rent ratings greater than 1.54. Either a 470 mF or 680 uF, 50V capacitor could be used. For a through hole design, a 680 wF/S50V 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 mount designs, solid tantalum capacitors can be used, but caution must be exercised with regard to the capacitor surge current rting (see Application In- formation or input capacitors in this data sheet), The TPS series available from AVX, and the 593D series from Sprague are both surge current tested. To further simplify the buck regulator design procedure, Na- tional Semiconductor is making available computer design software fo be used with the Simple Switcher line ot swifch- ing regulators. Switchers Made Simple (version 4.3 or lat- er) is available on a 314 diskette for (8M compatible com- puters. 6.LM2596 Series Buck Regulator Design Procedure (Adjustable Output) (Continued) Through Hole Output Capacitor Surface Mount Output Capacitor Voltage Panasonic Nichicon PL Feedforward AVX q PS Sprague Feedforward ) HFQ Series Series Capacitor Series 595D Series Capacitor (HF /V) (uF /) (MF /) (uF/V) 2 820/35 820/35 33 nF 330/6,3 470/4 33 nF 4 560/35 470/35 10 0F 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 0F 100/16 180/16 1.5 0F 12 330/25 330/25 1nF 100/16 180/16 1 oF 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 16/50 220 pF FIGURE 4, Output Capacitor and Feedforward Capacitor Selection Table LM2596 Series Buck Regulator Design Procedure INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) OV ery aS 40 fy ae Lat Lao tay = IBY ey 5 = Lat fea ge Ay = 15 te 10 ia L32 Sy =o a at Sav ectiee so 133 2 > | \ = 10V 5 ! orl 5 z ay Ki] 3 u L34 5 2 ATE | = ay 3 3h L24 = oa s tt <a = Li5 M4 Los = Sv tus wv 0.6 0.8 1.0 150 2 25 3 0.6 0.8 1,0 15 2 253 MAXIMUM LOAD CURRENT {A} MAXIMUM LOAD CURRENT {A) TLAH/12583- 24 TL/H/12883-25 FIGURE 5. LM2596-3.3 FIGURE 6. LM2596-5.0 40 70 30 60 = 25Y 50 40 & 20v 30 5 1 e235 e 1av 2 - ov 2: 2 a = 15 = wvbL2t L = . 10 2 15Y L22 to g 3 ; = = L23 ; 5 14y 4 9.6 9.8 1.0 15 2 2.53 0.6 0.8 1.0 15 2 253 MAXIMUM LOAD CURRENT {A} MAXIMUM LOAD CURRENT (A) TL/H/12583- 26 TL/H/12583-27 FIGURE 7, LM2596-12 FIGURE 8. LM2596-ADY 12LM2596 Series Buck Regulator Design Procedure (continued) Inductance | Current Schott Renco Pulse Engineering Coileraft (wH) (A) Through | Surface Through Surface Through Surface Surface Hole Mount Hole Mount Hole Mount Mount Li5 22 0.99 67148350 | 67148460 | RL-1284-22-43 | RL1500-22 | PE-53815 | PE-53815-S | DO3308-223 L21 68 0.99 67144070 | 67144450 | RL-5471-5 RL1500-68 | PE-53821 | PE-53821-S | DO3316-683 L22 47 1.17 | 67144080 | 67144460 | AL-5471-6 _ PE-53822 | PE-53822-8 | DO3316-473 L23 33 1.40 67144090 | 67144470 | RL-5471-7 _ PE-53823 | PE-53823-5S | DO3316-333 L24 22 1.70 | 67148370 | 67148480 | RL-1283-22-43 PE-53824 | PE-53825-S | DO3316-223 L25 16 2.10 | 67148380 | 67148490 | AL-1283-15-43 PE-53825 | PE-53824-S | DO3316-153 L26 330 0.80 | 67144100 | 67144480 | RL-5471-1 _ PE-53826 | PE-53826-S | DO5022P-334 L27 220 1.00 67144110 | 67144490 | RL-5471-2 _ PE-53827 | PE-53827-S | DO5022P-224 L28 150 1.20 67144120 | 67144500 | RL-5471-3 _ PE-53828 | PE-53828-S | DO5022P-154 L29 100 1.47 | 67144130 | 67144510 | RL-5471-4 _ PE-53829 | PE-53829-S | DO5022P-104 L30 68 1.78 67144140 | 67144520 | RL-5471-5 _ PE-53830 | PE-53830-8 | DO5022P-683 L31 47 2.20 | 67144150 | 67144530 | AL-5471-6 PE-53831 | PE-53831-S | DO5022P-473 L32 33 2.50 | 67144160 | 67144540 | AL-5471-7 PE-53932 | PE-53932-S | DO5022P-333 L33 22 3.10 | 67148390 | 67148500 | AL-1283-22.43 _ PE-53933 | PE-53933-S | DOS5022P.223 L34 18 3.40 67148400 | 67148790 | RL-1283-15-43 _ PE-53934 | PE-53934-S | DO5022P-153 L35 220 1.70 | 67144170 - AL-5473-1 _ PE-53935 | PE-53935-S - L36 150 2.10 | 67144180 - AL-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 - AL-5472-2 PE-54038 | PE-54038-S - L39 47 3.50 | 67144210 - AL-5472-3 _ PE-54039 | PE-54039-8 - L40 33 3.50 | 67144220 | 67148290 | AL-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 - AL-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 9. Inductor Manufacturers Part NumbersLM2596 Series Buck Regulator Design Procedure (continued) Coilcraft Inc, Phone | (800) 322-2645 Nichicon Corp. Phone (708) 843-7500 FAX (708) 639-1469 FAX (708) 843-2798 Coileraft Inc., Europe Phone | +11 1236 730 595 Panasonic Phone (714) 373-7857 FAX +44 1236 730 627 FAX (714) 373-7102 Pulse Engineering Inc. | Phone | (619) 674-8100 AVX Corp. Phone (803) 448-9411 FAX (619) 674-8262 FAX (803) 448-1943 Pulse Engineering Inc., | Phone | +353 93 24 107 Sprague/ Vishay Phone (207) 324-4140 Europe FAX | +353 93 24 459 FAX (207) 324-7223 Renco Electronics ine. | Phone | (800) 645-5828 FIGURE 11. Capacitor Manufacturers Phone Numbers FAX (516) 586-5562 Schott Corp. Phone | (612) 475-1173 FAX (612) 475-1786 FIGURE 10, Inductor Manufacturers Phone Numbers 3A Diodes 44-64 Diodes VR Surface Mount Through Hole Surface Mount Through Hole Schottky Recovery Schottky Recovery Schottky Recovery Schottky Recovery 1N5820 SR502 20V | ska2 All of SA302 All of All of INSS2S All of these MBR320 these these $B520 these B0WOQ03 diodes 1N5821 diodes diodes diodes 80M | saa rated to MBR330 rated to SOWG0S rated to SR508 rated to at least 31DQ03 at least at least 1N5824 at least 50V. 1N5822 50V. 50V. SB530 50V. 40V | SK34 SR304 50WQ04 SR504 MBRS340 MBR340 1N5825 30WO04 MURS320 31DQ04 MUR320 MURS620 SB540 MUR620 50V | SK35 30WF10 SR305 50WF10 HER601 or | MBRS360 MBR350 50WOQ05 SB550 More | 30WQ05 31DQ05 50SQ080 FIGURE 12. Diode Selection Table 14Application Information PIN FUNCTIONS + VinThis 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. GroundCircuit ground, Outputinternal switch. The voltage at this pin switches between (+ Viy Vsat) and approximately 0.5V, with a duty cycle of approximately Vout/Vin. To minimize coupling to sensitive circuitry, the PC board copper area connected to this pin should be kept to a minimum. FeedbackSenses the regulated output voltage to com- plete the feedback loop. ON/OFFAllows the switching regulator circuit to be shut down using logic level signals thus dropping the total input supply current to approximately 80 wA, Pulling this pin be- low a threshold voltage of approximately 1.3V turns the reg- ulator on, and pulling this pin above 1.3V (up to a maximum of 25) 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. EXTERNAL COMPONENTS INPUT CAPACITOR CinA low ESR aluminum or tantalum bypass capacitor is needed between the input pin and ground pin. It must be located near the regulator using short leads. This capacitor prevents large voltage transients from appearing at the in- put, and provides the instantaneous current needed each time the switch turns on. The important parameters for the Input capacitor are the voltage rating and the RMS current rating. Because of the relatively high RMS currents flowing in a buck regulator's input capacitor, this capacitor should be chosen for its RMS current rating rather than its capacitance or voltage ratings, although the capacitance value and voltage rating are di- rectly related to the RMS current rating, The RMS current rating of a capacitor could be viewed as a capacitors power rating. The RMS current flowing through the capacitors internal ESR produces power which causes the internal temperature of the capacitor to rise. The RMS current rating of a capacitor is determined by the amount of current required to raise the internal temperature approxi- mately 10G above an ambient temperatura of 105C. The ability of the capacitor to dissipate this heat to the surround- ing air will determine the amount of current the capacitor can safely sustain. Capacitors that are physically large and have a large surface area will typically have higher RMS current ratings. For a given capacitor value, a higher voltage electrolytic capacitor will be physically larger than a lower voltage capacitor, and thus be able to dissipate more heat to the surrounding air, and therefore will have a higher RMS current rating. The consequences of operating an electrolytic capacitor above the RMS current rating is a shortened operating life. The higher temperature speeds up the evaporation of the capacitor s electrolyte, resulting in eventual failure. Selecting an input capacitor requires consulting the manu- facturers data sheet for maximum allowable RMS ripple cur- rent. For a maximum ambient temperature of 40C, a gener- al guideline would be to select a capacitor with a ripple cur- rent rating of approximately 50% of the DC load current, For ambient temperatures up to 70C, a current rating of 75% of the DC load current would be a good choice for a conserva- tive design, The capacitor voltage rating must be at least 1.25 times greater than the maximum input voltage, and of- ten a much higher voltage capacitor is needed to satisfy the RMS current requirements. A graph shown in Figure 73 shows the relationship between an electrolytic capacitor value, its voltage rating, and the RMS current it is rated for. These curves were obtained from the Nichicon PL series of low ESR, high reliability electrolytic capacitors designed for switching regulator ap- plications, Other capacitor manufacturers offer similar types of capacitors, but always check the capacitor data sheet. Standard electrolytic capacitors typically have much high- er ESR qumbers, lower RMS current ratings and typically have a shorter operating lifetime. Because of their small size and excellent performance, sur- face mount solid tantalum capacitors are often used for in- put bypassing, but several precautions must he observed, A small percentage of solid tantalum capacitors can short if the inrush current rating is exceeded. This can happen at turn on when the input voltage is suddenly applied, and of course, higher input voltages produce higher inrush cur- rents, Several capacitor manufacturers do a 100% surge current testing on their products to minimize this potential problem. tf high turn on currents are expected, it may be necessary to limit this current by adding either some resist- ance or inductance before the tantalum capacitor, or select a higher voltage capacitor. As with aluminum electrolytic ca- pacitors, the RMS ripple current rating must be sized to the load currant. FEEDFORWARD CAPACITOR {Adjustable Output Voltage Version) CrrA Feedforward Capacitor Cer, shown across R2 in Figure 2 is used when the ouput voltage is greater than 10V or when Court has a very low ESR, This capacitor adds lead compensation to the feedback loop and increases the phase margin for better loop stability. For Cee selection, see the design procedure section.Application Information (continues 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 Typical RMS current ratings of low ESR Electrolytic Capacitars, 190kHz, @ 108C 470 uF 330 pF 270 pF {RMS m4) 680 pF 180 uF 120 uF CAPACITOR CURRENT RATING @105 a 1 20 30 40 50 60 70 CAPACITOR VOLTAGE RATING () TL/H/12583- 28 FIGURE 13. RMS Current Ratings for Low ESR Electrolytic Capacitors (Typical) OUTPUT CAPACITOR CoutAn output capacitor is required to filter the output and provide regulator loop stability. Low impedance or low ESR Electrolytic or solid tantalum capacitors designed for switching regulator applications must be used. When select- ing an output capacitor, the important capacitor parameters are; the 100 kHz Equivalent Series Resistance (ESR), the RMS ripple current rating, voltage rating, and capacitance value. For the output capacitor, the ESR value is the most important parameter. The output capacitor requires an ESR value that has an upper and lower limit. For low output ripple voltage, a low ESR value is needed. This value is determined by the maxi- mum allowable output ripple voltage, typically 1% to 2% of the output voltage, But if the selected capacitors ESR is extremely low, there is a possibility of an unstable feedback loop, resulting in an oscillation at the output. Using the ca- pacitors listed in the tables, or similar types, will provide design solutions under all conditions. If very low output ripple voltage (less than 15 mV) is re- quired, refer to the section on Output Voltage Ripple and Transients for a post ripple filter. An aluminum electrolytic capacitors ESR value is related to the capacitance value and its voltage rating. In most cases, higher voltage electrolytic capacitors have lower ESR val- ues (see Figure 74). Often, capacitors with much higher voltage ratings may be needed to provide the low ESR val- ues required for low output ripple voltage. The output capacitor for many different switcher designs often can be satisfied with only three or four different capac- itor values and several different voltage ratings. Sea the quick design component selection tables in Figures 3 and 4 for typical capacitor values, voltage ratings, and manufac- turers capacitor types. Electrolytic capacitors are cot recommended for tempera- tures below 25C. The ESR rises dramatically at cold tem- peratures and typically rises 3X @ 25C and as much as 10 at 40C, See curve shown in Figure 75. Solid tantalum capacitors have a much better ESR spec for cold temperatures and are recommended for temperatures below 26C. 400 350 TYPICAL ESR @ 25C FOR LOW ESR SERIES ELECTROLYTIC CAPACITORS 300 250 200 150 52 uF 100 120 pF CAPACITOR ESR @ 25C {mn} 50 220 pF 0 0 19 20 30 40 50 60 70 CAPACITOR YOLTAGE RATING () TL/H/12583-29 FIGURE 14. Capacitor ESR vs Capacitor Voltage Rating {Typical Low ESR Electrolytic Capacitor) CATCH DIODE Buck regulators require a diode to provide a return path for the inductor current when the switch turns off. This must be a fast diode and must he located close to the LM2596 using short leads and short printed circuit traces. Because of their very fast switching speed and low forward voltage drop, Schottky diodes provide the best perform- ance, especially in low output voltage applications (6V and lower), Ultra-fast recovery, or High-Efficiency rectifiers are also a good choice, but some types with an abrupt turnoff characteristic may cause instability or EMI problems. 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, 500 400 300 TYPICAL 100 kHz ESR OF 220 ytF 35V LOW ESR ELECTROLYTIC CAPACITOR 200 100 80 60 30 40 30 ESR {m&) 20 -40 -20 0 20 40 60 80 100 TEMPERATURE {C} TLIH/12583-30 FIGURE 15, Capacitor ESR Change vs Temperature INDUCTOR SELECTION All switching regulators have two basic modes of operation; continuous and discontinuous, The difference between the two types relates to the inductor current, whether it is flow- ing continuously, or if it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively dif- ferent operating characteristics, which can affect the requila- tors performance and requirements, Most switcher designs will operate in the discontinuous mode when the load cur- rent is low. The LM2596 (or any of the Simple Switcher family) can be used for both continuous or discontinuous modes of opera- tion. 16Application Information (continued In many cases the preferred mode of operation is the con- tinuous mode, It offers greater output power, lower peak switch, inductor and diode currents, and can have lower out- put ripple voltage. But it does require larger inductor values to keep the inductor current flowing continuously, especially at low output load currents and/or high input voltages. To simplify the inductor selection process, an inductor se- lection guide (nomograph) was designed (see Figures 5 through &). This guide assumes that the regulator is operat- ing in the continuous mode, and selects an inductor that will allow a peak-to-peak inductor ripple current to be a certain percentage of the maximum design load current. This peak- to-peak inductor ripple current percentage is not fixed, but is allowed to change as different design load currents are se- lected. (See Figure 76.) 50 40 Alyy (% OF MAX DESIGN LOAD CURRENT) 30 Inductance Region 20 10 0.5 1.0 1.5 2.0 2.5 3.0 MAXIMUM LOAD CURRENT (A) TLAH/1 2583-31 FIGURE 16. (Aljyp) Peak-to-Peak Inductor Ripple Current {as a Percentage of the Load Current) vs Load Current By allowing the percentage of inductor ripple current to in- crease for low load currents, the inductor value and size can he kept relatively low. When operating in the continuous mode, the inductor cur- rent waveform ranges from a triangular to a sawtooth type of waveform (depending on the input voltage), with the aver- age value of this current waveform equal to the DC output load current. Inductors are available in different styles such as pot core, toroid, E-core, bobbin core, etc., as well as different core materials, such as ferrites and powdered iron. The least ex- pensive, the bobbin, rod or stick core, consists of wire woundd on a ferrite bobbin. This type of construction makes for an inexpensive inductor, but since the magnetic flux is not completely contained within the core, it generates more Electro-Magnetic Interference (EMI). This magnetic flux can induce voltages into nearby printed circuit traces, thus caus- ing problems with both the switching regulator operation and nearby sensitive circuitry, and can give incorrect scope readings because of induced voltages in the scope probe. Also see section on Open Core Inductors. When multiple switching regulators are located on the same PC board, open core magnetics can cause interference be- tween two or more of the regulator circuits, especially at high currents. A torroid or E-core inductor (closed magnetic structure) should be used in these situations, The inductors listed in the selection chart include ferrite E-core construction for Schott, ferrite bobbin core for Renco and Coilcraft, and powdered iron toroid for Pulse Engineer- ing. Exceeding an inductors maximum current rating may cause the inductor to overheat because of the copper wire losses, or the core may saturate, If the inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the winding). This can cause the switch current to rise very rapidly and force the switch into a cycle-by-cycle current limit, thus reducing the DC output load current. This can also result in overheat- ing of the inductor and/or the LM2596, Different inductor types have different saturation characteristics, and this should be kept in mind when selecting an inductor. The inductor manufacturers data sheets include current and energy limits to avoid inductor saturation. DISCONTINUOUS MODE OPERATION The selection guide chooses inductor values suitable for continuous mode operation, but for low current applications and/or high input voltages, a discontinuous mode design may be a hetter choice, It would use an inductor that would be physically smaller, and would need only one half to one third the inductance value needed for a continuous mode design. The peak switch and inductor currents will be higher in a discontinuous design, but at these low load currents (1A and below), the maximum switch current will still be less than the switch current limit, Discontinuous operation can have voltage waveforms that are considerable different than a continuous design. The output pin (switch) waveform can have some damped sinus- oidal ringing present. (See Figure 7 photo titled; Discontinu- ous Mode Switching Waveforms) This ringing is normal for discontinuous operation, and is not caused by feedback loop instabilities. In discontinuous operation, there is a peri- od of time where neither the switch or the diode are con- ducting, and the inductor current has dropped to zero, Dur- ing this time, a small amount of energy can circulate be- tween the inductor and the switch/diode parasitic capaci- tance causing this characteristic ringing. Normally this ring- ing is not a problem, unless the amplitude becomes great enough to exceed the input voltage, and even then, there is vary little energy present to cause damage, Different inductor types and/or core materials produce dit- ferent amounts of this characteristic ringing, Ferrite core in- ductors have very little core loss and therefore produce the most ringing. The higher core loss of powdered iron induc- tors produce less ringing. If desired, a series RC could be placed in parallel with the inductor to dampen the ringing. The computer aided design software Swifchers Made Sim- ple (version 4.3) will provide all component values for con- tinuous and discontinuous modes of operation. Before Ripple Filter 5 mvidiv, | Alter Fipple < : Filter TL/H/12583-32 FIGURE 17. Post Ripple Filter WaveformApplication Information (continues OUTPUT VOLTAGE RIPPLE AND TRANSIENTS The output voltage of a switching power supply operating in the continuous mode will contain a sawtooth ripple voltage at the switcher frequency, and may also contain short volt- age spikes at the peaks of the sawtooth waveform, The output ripple voltage is a function of the inductor saw- tooth ripple current and the ESR of the output capacitor, A typical output ripple voltage can range from approximately 0,5% to 3% of the output voltage, To obtain low ripple valt- age, the ESR of the output capacitor must be low, however, caution must be exercised when using extremely low ESR capacitors hecause they can affect the loop stahility, result- ing in oscillation problems, If very low output ripple voltage is needed (less than 20 mV}, a post ripple filter is recom- mended. (See Figure 2.) The inductance required is typically between 1H and 5 WH, with low DC resistance, to main- tain good load regulation, A low ESR output filter capacitor is also required to assure good dynamic load response and ripple reduction, The ESR of this capacitor may be as low as desired, because it is out of the regulator feedback loop. The photo shown in Figure 77 shows a typical output ripple voltage, with and without a post ripple filter. When observing output ripple with a scope, it is essential that a short, low inductance scope probe ground connection be used. Most scope probe manufacturers provide a special probe terminator which is soldered onto the regulator board, preferable at the output capacitor. This provides a very short scope ground thus eliminating the problems associat- ed with the 3 inch ground lead normally provided with the probe, and provides a much cleaner and more accurate pic- ture of the ripple voltage waveform. The voltage spikes are caused by the fast switching action of the output switch and the diode, and the parasitic induc- tance of the output filter capacitor, and its associated wiring. To minimize these voltage spikes, the output capacitor should be designed for switching regulator applications, and the lead lengths must be kept very short. Wiring inductance, stray capacitance, as well as the scope probe used to eval- uate these transients, all contribute to the amplitude of these spikes. When a switching regulator is operating in the continuous mode, the inductor current waveform ranges from a triangu- lar to a sawtooth type of waveform (depending on the input voltage), For a given input and output voltage, the peak-to- peak amplitude of this inductor current waveform remains constant. As the load current increases or decreases, the entire sawtooth current waveform also rises and falls. The average value (or the center) of this current waveform is equal to the DC load current, If the load current drops to a low enough level, the bottom of the sawtooth current waveform will reach zero, and the switcher will smoothly change from a continuous to a dis- continuous mode of operation. Most switcher designs (irre- gardiess how large the inductor value is) will be forced to run discontinuous if the output is lightly loaded. This is a perfectly acceptable mode of operation. Inductance Region INDUCTOR RIPPLE CURRENT (mA p-p)} 05 10 #15 20 25 3.0 TL/H/12583-33 FIGURE 18. Peak-to-Peak Inductor Ripple Current vs Load Current In a switching regulator design, knowing the value of the peak-to-peak inductor ripple current (Alig) can be useful for determining a number of other circuit parameters, Pa- rameters such as, peak inductor or peak switch current, minimum toad current before the circuit becomes discontin- uous, output ripple voltage and output capacitor ESR can all be calculated from the peak-to-peak Allo. When the induc- tor nomographs shown in Figures 5 through & are used to select an inductor value, the peak-to-peak inductor ripple current can immediately be determined. The curve shown in Figure 78 shows the range of (Alino) that can be expected for different load currents. The curve also shows how the peak-to-peak inductor ripple current (Aliyp) changes as you go from the lower border to the upper border (for a given load current) within an inductance region. The upper border represents a higher input voltage, while the lower border represents a lower input voltage (see Inductor Selection Guides). These curves are only correct for continuous mode opera- tion, and only if the inductor selection guides are used to select the inductor value Consider the following example: Vout = 5V, maximum load current of 2.54 Vin = 12V, qominal, varying between 10V and 16V, The selection guide in Figure 6 shows that the vertical line for a 2.54 load current, and the horizontal line for the 12V input voltage intersect approximately midway between the upper and lower borders of the 33 H inductance region, A 33 wH inductor will allow a peak-to-peak inductor currant (Alinp) to flow that will be a percentage of the maximum load current. Referring to Figure 7& follow the 2.5A line approximately midway into the inductance region, and read the peak-to-peak inductor ripple current (Aliyp) on the left hand axis (approximately 620 mA p-p). As the input voltage increases to 16V, it approaches the upper border of the inductance region, and the inductor rip- ple current increases. Referring to the curve in Figure 78, it can be seen that for a load current of 2.54, the peak-to- peak inductor ripple current (Aliyp) is 620 mA with 12 in, and can range from 740 mA at the upper border (16V in) to 500 mA, at the lower border (10V in). 18Application Information (continued Once the Aliyp value is known, the following formulas can be used to calculate additional information about the switch- ing regulator circuit, 1. Peak Inductor or peak switch current Al 0.62 = (L010 + tno ) = (258 + | = 281A 2. Minimum toad current before the circuit becomes discon- tinuous _ Alino _ 9,82 2 2 3. Output Ripple Voltage = (Aliyp)* (ESR of Cour) = 0.624 x 0.19 =62 mV pp _ Sutput Ripple Voltage (AVour) = 031A or 4, ESR of Cout Alinb 0.062V o62a | O OPEN CORE INDUCTORS Another possible source of increased output ripple voltage or unstable operation is from an open core inductor. Ferrite bobbin or stick inductors have magnetic lines of flux flowing through the air from one end of the bobbin to the other end. These magnetic lines of flux will induce a voltage into any wire or PC board copper trace that comes within the induc- tors magnetic field. The strangth of the magnetic field, the orientation and location of the PC copper trace to the mag- netic field, and the distance between the copper trace and the inductor, determine the amount of voltage generated in the copper trace. Another way of looking at this inductive coupling is to consider the PC board copper trace as one turn of a transformer (secondary) with the inductor winding as the primary. Many millivolts can be generated in a copper trace located near an open core inductor which can cause stability problems or high output ripple voltage problems. lf unstable operation is seen, and an open core inductor is used, its possible that the location of the inductor with re- spect to other PC traces may be the problem, To determine if this is the problem, temporarily raise the inductor away from the board by several inches and then check circuit operation. if the circuit now operates correctly, then the magnetic flux from the open core inductor is causing the problem. Substituting a closed core inductor such as a tor- roid or E-core will correct the problem, or re-arranging the PC layout may be necessary. Magnetic flux cutting the IC device ground trace, feedback trace, or the positive or neg- ative traces of the output capacitor should be minimized, Sometimes, locating a trace directly beneath a bobbin in- ductor will provide good results, provided it is exactly in the center of the inductor (because the induced voltages cancel themselves out), but if it is off center one direction or the other, then problems could arise. If flux problems are pres- ent, even the direction of the inductor winding can make a difference in some circuits. This discussion on open core inductors is not to frighten the user, but to alert the user on what kind of problems to watch out for when using them. Open core bobbin or stick induc- tors are an inexpensive, simple way of making a compact efficient inductor, and they are used by the millions in many different applications. THERMAL CONSIDERATIONS The LM2596 is available in two packages, a 5-pin TO-220 (T) and a 5-pin surface mount TO-263 (8), The TO-220 package needs a heat sink under most condi- tions, The size of the heatsink depends on the input voltage, the output voltage, the load current and the ambient tem- perature, The curves in Figure 79 show the LM2596T junc- tion temperature rises above ambient temperature for a 3A load and different input and output voltages. The data for these curves was taken with the LM2596T (TO-220 pack- age) operating as a buck switching regulator in an ambient temperature of 25C (still air). These temperature rise num- bers are all approximate and there are many factors that can affect these temperatures, Higher ambient tempera- tures require more heat sinking. The TO-263 surface mount package tab is designed to be soldered to the copper on a printed circuit board. The cop- per and the board are the heat sink for this package and the other heat producing components, such as the catch diode and inductor. The PC board copper area that the package is soldered to should be at least 0.4 in@, and ideally should have 2 or more square inches of 2 oz. (0.0028) in) copper. Additional copper area improves the thermal characteristics, but with copper areas greater than approximately 6 in, only small improvements in heat dissipation are realized. If fur- ther thermal improvements are needed, double sided, multi- layer PC board with large copper areas and/or airflow are recommended, The curves shown in Figure 20 show the LM2596S (TO-263 package) junction temperature rise above ambient tempera- ture with a 2A load for various input and output voltages. This data was taken with the circuit operating as a buck switching regulator with all components mounted on a PC board to simulate the junction temperature under actual op- erating conditions. This curve can he used for a quick check for the approximate junction temperature for various condi- tions, but be aware that there are many factors that can affect the junction temperature. When load currents higher than 2A are used, double sided or multilayer PC boards with large copper areas and/or airflow might be needed, espe- cially for high ambient temperatures and high output volt- ages. For the best thermal performance, wide copper traces and generous amounts of printed circuit board copper should be used in the board layout. (One exception to this is the output (switch) pin, which should not have large areas of copper.) Large areas of copper provide the best transfer of heat (low- er thermal resistance) to the surrounding air, and moving air lowers the thermal resistance even further, Package thermal resistance and junction temperature rise fhumbers are all approximate, and there are many factors that will affect these numbers, Some of these factors in- clude board size, shape, thickness, position, location, and even board temperature. Other factors are, trace width, total printed circuit copper area, copper thickness, single- or dou- ble-sided, muttilayer board and the amount of solder on the board, The effectiveness of the PC board to dissipate heat also depends on the size, quantity and spacing of other components on the board, as well as whether the surround- ing airis still or moving, Furthermore, some of these compo- nents such as the catch diode will add heat to the PC board and the heat can vary as the input voltage changes. For the inductor, depending on the physical size, type of core mate- rial and the DC resistance, it could either act as a heat sink taking heat away from the board, or it could add heat to the board.Application Information (continues JUNCTION TEMPERATURE RISE ABOVE AMBIENT (C) 70 0-220 Package ermalloy Heat. nk #7020 = 60 34 Load Vour = 20 = 25C, Still a 55 50 45 Your = 12 40 35 30 Your =5 25 Your 7 3 9 5 10 15 20 25 30 35 40 INPUT VOLTAGE () TL/H/12583-34 Circuit Data for Temperature Rise Curve TO-220 Package (T} Capacitors Through hole electrolytic Inductor Through hole, Renco Diode Through hole, 5A 40, Schottky PC board 3 square inches single sided 2 oz. copper (0.0028") FIGURE 19. Junction Temperature Rise, TO-220 JUNCTION TEMPERATURE RISE ABOVE AMBIENT (C) TO-268 2A 9 in? copper 0 5 10 15 20 25 30 35 49 INPUT VOLTAGE () TL/H/12683-35 Circuit Data tor Temperature Rise Curve TO-263 Package (S)} Capacitors Suriace mount tantalum, molded D" size Inductor Surface mount, Pulse Engineering, 68 H Diode Surface mount, 54 40V, Schottky PC board 9 square inches single sided 2 oz, copper (0,0028") FIGURE 20. Junction Temperature Rise, TO-263 IN| LM2596 5.0 1 D1 aF Syayyur [cen Tat , oT a1 47k gs 47k FIGURE 21. Delayed Startup a TL/H/1 2583-36 LM2596 5.0 ao) UN/UFR 3] CND TL/H/12583-37 FIGURE 22. Undervoltage Lockout for Buck Regulater DELAYED STARTUP The circuit in Figure 27 uses the the ON/OFF pin to provide a time delay between the time the input voltage is applied and the time the output voltage comes up (only the circuitry pertaining to the delayed start up is shown), As the input voltage rises, the charging of capacitor C1 pulls the ON/OFF pin high, keeping the regulator off. Once the input voltage reaches its final value and the capacitor stops charging, and resistor Re pulls the ON/OFF pin low, thus allowing the circuit to start switching. Resistor R, is included to limit the maximum voltage applied to the ON/OFF pin (maximum of 25V), reduces power supply noise sensitivity, and also limits the capacitor, C1, discharge current. When high input ripple voltage exists, avoid long delay time, be- cause this ripple can be coupled into the ON/OFF pin and cause problems. This delayed startup feature is useful in situations where the input power source is limited in the amount of current it can deliver. It allows the input voltage to rise to a higher voltage before the regulator starts operating. Buck regulators re- quire less input current at higher input voltages, UNDERVOLTAGE LOCKOUT Some applications require the regulator to remain off until the input voltage reaches a predetermined voltage. An un- dervoltage lockout feature applied to a buck regulator is shown in Figure 22, while Figures 23 and 24 applies the same feature to an inverting circuit. The circuit in Figure 23 features a constant threshold voltage for turn on and turn off (Zener voltage plus approximately one volt). If hysteresis is needed, the circuit in Figure 24 has a turn ON voltage which is different than the turn OFF voltage. The amount of hysteresis is approximately equal to the value of the output voltage. If zener voltages greater than 25V are used, an additional 47 kf resistor is needed from the ON/OFF pin to the ground pin to stay within the 25V maximum limit of the ON/OFF pin. 20Application Information (continued INVERTING REGULATOR The circuit in Figure 25 converts a positive input voltage to a negative output voltage with a common ground, The circuit operates by bootstrapping the regulators ground pin to the negative output voltage, then grounding the feedback pin, the regulator senses the inverted output voltage and regu- lates it, oi N5 S23 | ON/CFF 3 | ORD o ONSaod -3 OUTPUT TLAH/1 2583-38 This circuit has an ON/OFF thrashold of approximately 13V. FIGURE 23. Undervoliage Lockout for Inverting Regulator D1 1NS823 This example uses the LM2596-5.0 to generate a 5V out- put, but other output voltages are possible hy selecting oth- er output voltage versions, including the adjustable version. Since this regulator topology can produce an output voltage that is either greater than or less than the input voltage, the maximum output current greatly depends on both the input and output voltage. The curve shown in Figure 26 provides a guide as to the amount of output load current possible for the different input and output voltage conditions. The maximum voltage appearing across the regulator is the absolute sum of the input and output voltage, and this must he limited to a maximum of 40V. For example, when con- varting +20V to 12V, the regulator would see 32V be- tween the input pin and ground pin. The LM2596 has a max- imum input voltage spec of 40V. Additional diodes are required in this regulator configuration. Diode D1 is used to isolate input voltage ripple or noise from coupling through the Cj, capacitor to the output, under light or no load conditions. Also, this diode isolation changes the topology to closlay resemble a buck configuration thus pro- viding good closed loop stability. A Schottky diode is recom- mended for low input voltages, (because of its lower voltage drop) but for higher input voltages, a fast recovery diode could be used. Without diode D3, when the input voltage is first applied, the charging current of Cy can pull the output positive by sever- al volts for a short period of time. Adding D3 prevents the output from going positive by more than a diode voltage. yn | LM2596 Sn A] 470 pF OJ This circuit has hysteresis 5.0 5 ON/OFF 3] GND -5 Ragulater starts switching at Viy = 134 Regulater stops switching at Vy = 8V OUTPUT TL/H/12583 -3 FIGURE 24. Undervoltage Lockout with Hysteresis for Inverting Regulator DT IN5823 FEEDBACK INPUT VOLTAGE i LM2596-5.0 4 L133 uH +4.5 to +204 L i 1 POUT C1 2 0.1 S| ON/orF 3| 6ND + = tt D2 =, D3 on == Rt R2 N58 25 our 1N5400 Cin = 68 pF /25V Tant. Sprague 5950 47k 47k : -5 470 uF /50V Elec. Panasonic HFO + . OUTPUT Cout 47 wF/20 Tant. Spragua 95D 220 uF/25V Elec. Panasonic HFO TL/H/12583-40 FIGURE 25. Inverting 5V Regulator with Delayed StartupApplication Information (continues -S Gut L = 32H -20V Out MAXIMUM LOAD CURRENT (A) 0 5 10 15 20 25 INPUT VOLTAGE {) TL/H/12583-41 FIGURE 26. inverting Regulator Typical Load Current Because of differences in the operation of the inverting reg- ulator, the standard design procedure is not used to select the inductor value. In the majority of designs, a 33 wH, 3.54 inductor is the best choice. Capacitor selection can also be narrowed down to just a few values, Using the values shown in Figure 25 will provide good results in the majority of in- verting designs, This type of inverting regulator can require relatively large amounts of input current when starting up, even with light loads. Input currents as high as the LM2596 current limit (approx 4.54) are needed for at least 2 ms or more, until the output reaches its nominal output voltage. The actual time depends on the output voltage and the size of the output capacitor. Input power sources that are current limited or sources that can not deliver these currents without getting loaded down, may not work correctly. Because of the rela- tively high startup currents required by the inverting topole- gy, the delayed startup feature (C1, Ry and Rg) shown in Figure 25 is recommended. By delaying the regulator start- up, the input capacitor is allowed to charge up to a higher voltage before the switcher begins operating. A portion of the high input current needed for startup is now supplied by the input capacitor (Ci). For severe start up conditions, the input capacitor can be made much larger than normal. INVERTING REGULATOR SHUTDOWN METHODS To use the ON/OFF pin in a standard buck configuration is simple, pull it below 1.3V (@25C, referenced to ground) to turn regulator ON, pull it above 1.3V to shut the regulator OFF. With the inverting configuration, some level shifting is required, because the ground pin of the regulator is no long- er at ground, but is now setting at the negative output volt- age level. Two different shutdown methods for inverting reg- ulators are shown in Figures 27 and 28. tWenm R4 6,2k a OFF SHUTDOWN ON INPUT | y, IN LM2596 +in >} D1 1 5.0 | IN5825 my 3906 5 )ON/orF 3) GND +) Gy T7470 uF -5 - OUTPUT TL/H/12583-42 FIGURE 27. inverting Regulator Ground Referenced Shutdown Di 1IN58235 INPUT VOLTAGE . +4.5 to +254 L | tL Gn 45V --- = 470 pF | oN # 4 ON SHUTDOWN aaa OFF INPUT 47d Vin ; LM2596-5.0 R1 47k 5 | oN /orF 3] GND AA rt - I = Re = 2 47k L -5 OUTPUT OPTO-ISOLATOR TL/H/1 2583-43 FIGURE 28. Inverting Regulator Ground Referenced Shutdown using Opto Device 22Application Information (continued TYPICAL THROUGH HOLE PC BOARD LAYOUT, FIXED OUTPUT (1X SIZE), DOUBLE SIDED Copper Side Component Side REGULATED OUTPUT VOLTAGE +H + k ON/OFF GROUNE 4 - DC INPLT VOLTAGE f+ + TL/H/12583-44 Cin = 470 pF, 50V, Aluminum Electrolytic Panasonic, HFO Series Cout 330 pF, 36V, Aluminum Electrolytic Panasonic, HFS Series 01 5A, 40V Schottky Rectifier, 1N5825 L147 ,H, L389, Rance, Through Hols Tharmalloy Haat Sink #7020 TYPICAL THROUGH HOLE PC BOARD LAYOUT, ADJUSTABLE OUTPUT (1X SIZE), DOUBLE SIDED Copper Side Component Side REGULATED OLTPUT VOLTAGE \+ + a ON/OFF a CRCUND De INPUT VOLTAGE + + TL/H/12583-45 Cin 470 wF, SOV, Aluminum Electrolytic Panasonic, HFQ Series Coyt 220 nF, 36V Aluminum Elactrolytic Panasonic, HFQ Series O1 SA, 40V Schottky Rectifier, 1N5825 L1 4?7 wH, L39, Rance, Through Hole Ry 1 kf, 1% Ro Use formula in Dasign Procedure Crp See Figure 4. Thermalloy Heat Sink #7020 FIGURE 29. PC Board Layout 2324Physical Dimensions inches (millimeters) 0.1512 6.002 0.11020.016 <_ 3.844 6.05 2,79 20,25 @.035 0,005 t oases YP aga 7B O48 0.38 10.16 29-93 = } + t 0.067 40.005 TYP 1.7040.15 0.4404 0.010 .644 0.25 0.250 20.010 PIN ONE ID 6.350.25 0.134 0,015 0.015 fh p03 3.40 0,358 qWt0.28 | i. 0.3870-23 TAPERED SIDES 7 0.343 0.524 8.70 0.180 t et t 8.24 EST#0.13 0.108 2.67 t SEATING PLANE 0.059 9,002 se 0.176 40.009 1.27 20.05 - 0.704 4.47 0.23 17.88 TOSD (REV A) -Lead TO-220 (T) Order Number LM2596T-3.3, LM2596T-5.0, LM2596T-12 or LM2596T-ADJ NS Package Number T05D 25LM2596 SIMPLE SWITCHER Power Converter 150 kHz 3A Step-Down Voltage Regulator Physical Dimensions inches (mitimeters) (Continued) T| Pei go 4 99 / 19 see 0.057-0.077 [1.45-1.96] _] = =3|- t f oO) ~ F 0.028-0.088 0.425 TYP \ hs [0.71-0.97] [10.80] 0.330-0.350 PIN #1 ID "l [8.38-8.89| | o.a80 8.030 ax TYP . MAX [1.27] Ax] | | Rio.78] 0.175-0.183 | TYP if 0.260-0.280 [6.60-7.11] 0.390-0.410 [9.91- 10.41] 0.410 [19.41] | A [ (oserozel a.0g8 [0.89] calo.004[0.10] L 3 TAPERED SIDES 1 T yo-ge 1-62 1 0.000-0.006 STAN p-orr- 9-0.15] 0.490 yay o [12.45] 0,565 -_ MAX [14.35] 0.015-0.030 [4.45-4,.65] -M- i 0.048-0.052 [1.22-1.32] CONTROLLING DIMENSION: INCH 0.250 iy m [6.35] t 0.200 Win [5.93] f |< i 5-Lead TO-263 Surface Mount Package (5) Order Number LM2596S-3.3, LM25968-5.0, LM2596S-12 or LM2596S-ADJ) NS Package Number TS5B LIFE SUPPORT POLICY 0.085 ae] 14,61 | 0.085 rp + =} + 4 eae fe => 0.067 [1.70] TP 0.042 [1.07] YP LEAD POSITION OVERLAY TSSB (REY 8) NATIONALS PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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