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LM2574 LM2574HV SIMPLE SWITCHER 0 5A Step Down Voltage Regulator General Description The LM2574 series of regulators are monolithic integrated circuits that provide all the active functions for a step down buck switching regulator capable of driving a 0 5A load with excellent line and load regulation These devices are available in fixed output voltages of 3 3V 5V 12V 15V 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 LM2574 series offers a high efficiency replacement for popular three terminal linear regulators Because of its high efficiency the copper traces on the printed circuit board are normally the only heat sinking needed A standard series of inductors optimized for use with the LM2574 are available from several different manufacturers This feature greatly simplifies the design of switch mode power supplies Other features include a guaranteed 4 tolerance on out put voltage within specified input voltages and output load conditions and 10 on the oscillator frequency External shutdown is included featuring 50 A typical standby cur rent The output switch includes cycle by cycle current limit ing as well as thermal shutdown for full protection under fault conditions Features n 3 3V 5V 12V 15V and adjustable output versions n Adjustable version output voltage range 1 23V to 37V 57V for HV version 4 max over line and load conditions n Guaranteed 0 5A output current n Wide input voltage range 40V up to 60V for HV version n Requires only 4 external components n 52 kHz fixed frequency internal oscillator n TTL shutdown capability low power standby mode n High efficiency n Uses readily available standard inductors n Thermal shutdown and current limit protection Applications n Simple high efficiency step down buck regulator n Efficient pre regulator for linear regulators n On card switching regulators n Positive to negative converter Buck Boost Typical Application Fixed Output Voltage Versions Patent Pending SIMPLE SWITCHER is a trademark of National Semiconductor Corporation DS011394 1 Note Pin numbers are for 8 pin DIP package June 1999 LM2574 LM2574HV SIMPLE SWITCHER 0 5A Step Down Voltage Regulator 1999 National Semiconductor CorporationDS Connection Diagrams 8 Lead DIP DS011394 2 No internal connection but should be soldered to PC board for best heat transfer Top View Order Number LM2574 3 3HVN LM2574HVN 5 0 LM2574HVN 12 LM2574HVN 15 LM2574HVN ADJ LM2574N 3 3 LM2574N 5 0 LM2574N 12 LM2574N 15 or LM2574N ADJ See NS Package Number N08A 14 Lead Wide Surface Mount WM DS011394 3 Top View Order Number LM2574HVM 3 3 LM2574HVM 5 0 LM2574HVM 12 LM2574HVM 15 LM2574HVM ADJ LM2574M 3 3 LM2574M 5 0 LM2574M 12 LM2574M 15 or LM2574M ADJ See NS Package Number M14B 2 Absolute Maximum Ratings Note 1 If Military Aerospace specified devices are required please contact the National Semiconductor Sales Office Distributors for availability and specifications Maximum Supply Voltage LM257445V LM2574HV63V ON OFF Pin Input Voltage 0 3V V VIN Output Voltage to Ground Steady State 1V Minimum ESD Rating C 100 pF R 1 5 k 2 kV Storage Temperature Range 65 C to 150 C Lead Temperature Soldering 10 seconds 260 C Maximum Junction Temperature150 C Power DissipationInternally Limited Operating Ratings Temperature Range LM2574 LM2574HV 40 C TJ 125 C Supply Voltage LM257440V LM2574HV60V LM2574 3 3 LM2574HV 3 3 Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range SymbolParameterConditionsLM2574 3 3Units Limits LM2574HV 3 3 TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VOUTOutput VoltageVIN 12V ILOAD 100 mA3 3V 3 234V Min 3 366V Max VOUTOutput Voltage4 75V VIN 40V 0 1A ILOAD 0 5A3 3V LM25743 168 3 135V Min 3 432 3 465V Max VOUTOutput Voltage4 75V VIN 60V 0 1A ILOAD 0 5A3 3 LM2574HV3 168 3 135V Min 3 450 3 482V Max EfficiencyVIN 12V ILOAD 0 5A 72 LM2574 5 0 LM2574HV 5 0 Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range SymbolParameterConditionsLM2574 5 0Units Limits LM2574HV 5 0 TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VOUTOutput VoltageVIN 12V ILOAD 100 mA5V 4 900V Min 5 100V Max VOUTOutput Voltage7V VIN 40V 0 1A ILOAD 0 5A5V LM25744 800 4 750V Min 5 200 5 250V Max VOUTOutput Voltage7V VIN 60V 0 1A ILOAD 0 5A5 LM2574HV4 800 4 750V Min 5 225 5 275V Max EfficiencyVIN 12V ILOAD 0 5A 77 3 LM2574 12 LM2574HV 12 Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range SymbolParameterConditionsLM2574 12Units Limits LM2574HV 12 TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VOUTOutput VoltageVIN 25V ILOAD 100 mA12V 11 76V Min 12 24V Max VOUTOutput Voltage15V VIN 40V 0 1A ILOAD 0 5A12V LM257411 52 11 40V Min 12 48 12 60V Max VOUTOutput Voltage15V VIN 60V 0 1A ILOAD 0 5A12 LM2574HV11 52 11 40V Min 12 54 12 66V Max EfficiencyVIN 15V ILOAD 0 5A 88 LM2574 15 LM2574HV 15 Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range SymbolParameterConditionsLM2574 15Units Limits LM2574HV 15 TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VOUTOutput VoltageVIN 30V ILOAD 100 mA15V 14 70V Min 15 30V Max VOUTOutput Voltage18V VIN 40V 0 1A ILOAD 0 5A15V LM257414 40 14 25V Min 15 60 15 75V Max VOUTOutput Voltage18V VIN 60V 0 1A ILOAD 0 5A15 LM2574HV14 40 14 25V Min 15 68 15 83V Max EfficiencyVIN 18V ILOAD 0 5A 88 LM2574 ADJ LM2574HV ADJ Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range Unless otherwise specified VIN 12V ILOAD 100 mA SymbolParameterConditionsLM2574 ADJUnits Limits LM2574HV ADJ TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VFBFeedback VoltageVIN 12V ILOAD 100 mA1 230V 1 217V Min 1 243V Max 4 LM2574 ADJ LM2574HV ADJ Electrical Characteristics Continued Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range Unless otherwise specified VIN 12V ILOAD 100 mA SymbolParameterConditionsLM2574 ADJUnits Limits LM2574HV ADJ TypLimit Note 2 SYSTEM PARAMETERS Note 3 Test CircuitFigure 2 VFBFeedback Voltage7V VIN 40V 0 1A ILOAD 0 5A1 230V LM2574VOUTProgrammed for 5V Circuit ofFigure 21 193 1 180V Min 1 267 1 280V Max VFBFeedback Voltage7V VIN 60V 0 1A ILOAD 0 5A1 230 LM2574HVVOUTProgrammed for 5V Circuit ofFigure 21 193 1 180V Min 1 273 1 286V Max EfficiencyVIN 12V VOUT 5V I LOAD 0 5A 77 All Output Voltage Versions Electrical Characteristics Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range Unless otherwise specified VIN 12V for the 3 3V 5V and Adjustable version VIN 25V for the 12V version and VIN 30V for the 15V version ILOAD 100 mA SymbolParameterConditionsLM2574 XXUnits Limits LM2574HV XX TypLimit Note 2 DEVICE PARAMETERS IbFeedback Bias Current Adjustable Version Only VOUT 5V 50100 500nA fOOscillator Frequency see Note 10 52kHz 47 42kHz Min 58 63kHz Max VSATSaturation VoltageIOUT 0 5A Note 4 0 9V 1 2 1 4V max DCMax Duty Cycle ON Note 5 98 93 Min ICLCurrent LimitPeak Current Notes 4 10 1 0A 0 7 0 65A Min 1 6 1 8A Max ILOutput Leakage Notes 6 7 Output 0V2mA Max CurrentOutput 1V7 5mA Output 1V30mA Max IQQuiescent Current Note 6 5mA 10mA Max ISTBYStandby QuiescentON OFF Pin 5V OFF 50 A Current200 A Max JAThermal ResistanceN Package Junction to Ambient Note 8 92 JAN Package Junction to Ambient Note 9 72 C W JAM Package Junction to Ambient Note 8 102 JAM Package Junction to Ambient Note 9 78 5 All Output Voltage Versions Electrical Characteristics Continued Specifications with standard type face are for TJ 25 C and those with boldface type apply over full Operating Tempera ture Range Unless otherwise specified VIN 12V for the 3 3V 5V and Adjustable version VIN 25V for the 12V version and VIN 30V for the 15V version ILOAD 100 mA SymbolParameterConditionsLM2574 XXUnits Limits LM2574HV XX TypLimit Note 2 ON OFF CONTROL Test CircuitFigure 2 VIHON OFF Pin LogicVOUT 0V 1 42 2 2 4V Min VILInput LevelVOUT Nominal Output Voltage1 21 0 0 8V Max IHON OFF Pin InputON OFF Pin 5V OFF 12 A Current30 A Max IILON OFF Pin 0V ON 0 A 10 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 in tended to be functional but do not guarantee specific performance limits For guaranteed specifications and test conditions see the Electrical Characteristics Note 2 All limits guaranteed at room temperature Standard type face and at temperature extremes bold type face All room temperature limits are 100 produc tion 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 Note 3 External components such as the catch diode inductor input and output capacitors can affect switching regulator system performance When the LM2574 is used as shown in theFigure 2test circuit system performance will be as shown in system parameters section of Electrical Characteristics Note 4 Output pin sourcing current No diode inductor or capacitor connected to output pin Note 5 Feedback pin removed from output and connected to 0V Note 6 Feedback pin removed from output and connected to 12V for the Adjustable 3 3V and 5V versions and 25V for the 12V and 15V versions to force the output transistor OFF Note 7 VIN 40V 60V for high voltage version Note 8 Junction to ambient thermal resistance with approximately 1 square inch of printed circuit board copper surrounding the leads Additional copper area will lower thermal resistance further See application hints in this data sheet and the thermal model in Switchers Made Simple software Note 9 Junction to ambient thermal resistance with approximately 4 square inches of 1 oz 0 0014 in thick printed circuit board copper surrounding the leads Ad ditional copper area will lower thermal resistance further See Note 8 Note 10 The oscillator frequency reduces to approximately 18 kHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40 from the nominal output voltage This self protection feature lowers the average power dissipation of the IC by lowering the minimum duty cycle from 5 down to approximately 2 Typical Performance Characteristics Circuit ofFigure 2 Normalized Output Voltage DS011394 27 Line Regulation DS011394 28 Dropout Voltage DS011394 29 6 Typical Performance Characteristics Circuit ofFigure 2 Continued Current Limit DS011394 30 Supply Current DS011394 31 Standby Quiescent Current DS011394 32 Oscillator Frequency DS011394 33 Switch Saturation Voltage DS011394 34 Efficiency DS011394 35 Minimum Operating Voltage DS011394 36 Supply Current vs Duty Cycle DS011394 37 Feedback Voltage vs Duty Cycle DS011394 38 7 Typical Performance Characteristics Circuit ofFigure 2 Continued Feedback Pin Current DS011394 39 Junction to Ambient Thermal Resistance DS011394 40 Continuous Mode Switching Waveforms VOUT 5V 500 mA Load Current L 330 H DS011394 6 Notes A Output Pin Voltage 10V div B Inductor Current 0 2 A div C Output Ripple Voltage 20 mV div AC Coupled Horizontal Time Base 5 s div Discontinuous Mode Switching Waveforms VOUT 5V 100 mA Load Current L 100 H DS011394 7 Notes A Output Pin Voltage 10V div B Inductor Current 0 2 A div C Output Ripple Voltage 20 mV div AC Coupled Horizontal Time Base 5 s div 500 mA Load Transient Response for Continuous Mode Operation L 330 H COUT 300 F DS011394 8 Notes A Output Voltage 50 mV div AC Coupled B 100 mA to 500 mA Load Pulse Horizontal Time Base 200 s div 250 mA Load Transient Response for Discontinuous Mode Operation L 68 H COUT 470 F DS011394 9 Notes A Output Voltage 50 mV div AC Coupled B 50 mA to 250 mA Load Pulse Horizontal Time Base 200 s div 8 Block Diagram DS011394 10 R1 1k 3 3V R2 1 7k 5V R2 3 1k 12V R2 8 84k 15V R2 11 3k For Adj Version R1 Open R2 0 Note Pin numbers are for the 8 pin DIP package FIGURE 1 9 Test Circuit and Layout Guidelines As in any switching regulator layout is very important Rap idly switching currents associated with wiring inductance generate voltage transients which can cause problems For minimal inductance and ground loops the length of the leads indicated by heavy lines should be kept as short as pos sible Single point grounding as indicated or ground plane construction should be used for best results When using the Adjustable version physically locate the programming resis tors near the regulator to keep the sensitive feedback wiring short Fixed Output Voltage Versions DS011394 11 CIN 22 F 75V Aluminum Electrolytic COUT 220 F 25V Aluminum Electrolytic D1 Schottky 11DQ06 L1 330 H 52627 for 5V in 3 3V out use 100 H RL 1284 100 R1 2k 0 1 R2 6 12k 0 1 Adjustable Output Voltage Version DS011394 12 FIGURE 2 10 Test Circuit and Layout Guidelines Continued U S Source Note 1 Pulse Engineering 619 674 8100 P O Box 12236 San Diego CA 92112 Note 2 Renco Electronics Inc 516 586 5566 60 Jeffryn Blvd East Deer Park NY 11729 Contact Manufacturer European Source Note 3 NPI APC 44 0 634 290588 47 Riverside Medway City Estate Strood Rochester KentME2 4DP UK Contact Manufacturer InductorPulse Eng RencoNPI Value Note 1 Note 2 Note 3 68 H RL 1284 68 43NP5915 100 H RL 1284 100 43NP5916 150 H52625RL 1284 150 43NP5917 220 H52626RL 1284 220 43NP5918 5919 330 H52627RL 1284 330 43NP5920 5921 470 H52628RL 1284 470 43NP5922 680 H52629RL 1283 680 43NP5923 1000 H52631RL 1283 1000 43 1500 H RL 1283 1500 43 2200 H RL 1283 2200 43 FIGURE 3 Inductor Selection by Manufacturer s Part Number 11 LM2574 Series Buck Regulator Design Procedure PROCEDURE Fixed Output Voltage Versions EXAMPLE Fixed Output Voltage Versions Given VOUT Regulated Output Voltage 3 3V 5V 12V or 15V VIN Max Maximum Input Voltage ILOAD Max Maximum Load Current Given VOUT 5V VIN Max 15V ILOAD Max 0 4A 1 Inductor Selection L1 A Select the correct Inductor value selection guide fromFig ures 4 5 6 orFigure 7 Output voltages of 3 3V 5V 12V or 15V respectively For other output voltages see the design procedure for the adjustable version B From the inductor value selection guide identify the induc tance region intersected by VIN Max and ILOAD Max C Select an appropriate inductor from the table shown inFig ure 3 Part numbers are listed for three inductor manufactur ers The inductor chosen must be rated for operation at the LM2574 switching frequency 52 kHz and for a current rating of 1 5 x ILOAD For additional inductor information see the in ductor section in the Application Hints section of this data sheet 1 Inductor Selection L1 A Use the selection guide shown inFigure 5 B From the selection guide the inductance area intersected by the 15V line and 0 4A line is 330 C Inductor value required is 330 H From the table inFigure 3 choose Pulse Engineering PE 52627 Renco RL 1284 330 or NPI NP5920 5921 2 Output Capacitor Selection COUT A The value of the output capacitor together with the inductor defines the dominate pole pair of the switching regulator loop For stable operation and an acceptable output ripple voltage approximately 1 of the output voltage a value between 100 F and 470 F is recommended B The capacitor s voltage rating should be at least 1 5 times greater than the output voltage For a 5V regulator a rating of at least 8V is appropriate and a 10V or 15V rating is recom mended Higher voltage electrolytic capacitors generally have lower ESR numbers and for this reason it may be necessary to se lect a capacitor rated for a higher voltage than would normally be needed 2 Output Capacitor Selection COUT A COUT 100 F to 470 F standard aluminum electrolytic B Capacitor voltage rating 20V 3 Catch Diode Selection D1 A The catch diode current rating must be at least 1 5 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 cur rent limit of the LM2574 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 3 Catch Diode Selection D1 A For this example a 1A current rating is adequate B Use a 20V 1N5817 or SR102 Schottky diode or any of the suggested fast recovery diodes shown inFigure 9 4 Input Capacitor CIN An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable operation 4 Input Capacitor CIN A 22 F aluminum electrolytic capacitor located near the input and ground pins provides sufficient bypassing 12 LM2574 Series Buck Regulator Design Procedure Continued INDUCTOR VALUE SELECTION GUIDES For Continuous Mode Operation DS011394 26 FIGURE 4 LM2574HV 3 3 Inductor Selection Guide DS011394 13 FIGURE 5 LM2574HV 5 0 Inductor Selection Guide DS011394 14 FIGURE 6 LM2574HV 12 Inductor Selection Guide DS011394 15 FIGURE 7 LM2574HV 15 Inductor Selection Guide 13 LM2574 Series Buck Regulator Design Procedure Continued PROCEDURE Adjustable Output Voltage Versions EXAMPLE Adjustable Output Voltage Versions Given VOUT Regulated Output Voltage VIN Max Maximum Input Voltage ILOAD Max Maximum Load Current F Switching Frequency Fixed at 52 kHz Given VOUT 24V VIN Max 40V ILOAD Max 0 4A F 52 kHz 1 Programming Output Voltage Selecting R1 and R2 as shown in Figure 2 Use the following formula to select the appropriate resistor values R1can be between 1k and 5k For best temperature coeffi cient a