LM1575J-5.0-QML

LM1575_07 NSC | Alldatasheet

Document overview

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Technical content

Features

■ 3.3V, 5V, 12V, 15V, and adjustable output versions ■ Adjustable version output voltage range, 1.23V to 37V (57V for HV version) ±4% max over line and load conditions ■ Guaranteed 1A output current ■ Wide input voltage range, 40V up to 60V for HV version ■ Requires only 4 external components ■ 52 kHz fixed frequency internal oscillator ■ TTL shutdown capability, low power standby mode ■ High efficiency ■ Uses readily available standard inductors ■ Thermal shutdown and current limit protection ■ P+ Product Enhancement tested

Applications

■ Simple high-efficiency step-down (buck) regulator ■ Efficient pre-regulator for linear regulators ■ On-card switching regulators ■ Positive to negative converter (Buck-Boost) Typical Application (Fixed Output Voltage Versions) 1147501 Note: Pin numbers are for the TO-220 package. SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation © 2007 National Semiconductor Corporation 11475 www.national.com LM1575/LM2575/LM2575HV Series SIMPLE SWITCHER 1A Step-Down Voltage Regulator

Block Diagram and Typical Application 1147502 3.3V, R2 = 1.7k 5V, R2 = 3.1k 12V, R2 = 8.84k 15V, R2 = 11.3k For ADJ. Version R1 = Open, R2 = 0Ω Note: Pin numbers are for the TO-220 package. FIGURE 1. www.national.com 2 LM1575/LM2575/LM2575HV

(XX indicates output voltage option. See Ordering Information table for complete part number.) Straight Leads 5–Lead TO-220 (T) 1147522 Top View LM2575T-XX or LM2575HVT-XX See NS Package Number T05A Bent, Staggered Leads 5-Lead TO-220 (T) 1147523 Top View 1147524 Side View LM2575T-XX Flow LB03 or LM2575HVT-XX Flow LB03 See NS Package Number T05D 16–Lead DIP (N or J) 1147525 *No Internal Connection Top View LM2575N-XX or LM2575HVN-XX See NS Package Number N16A LM1575J-XX-QML See NS Package Number J16A 24-Lead Surface Mount (M) 1147526 *No Internal Connection Top View LM2575M-XX or LM2575HVM-XX See NS Package Number M24B TO-263(S) 5-Lead Surface-Mount Package 1147529 Top View 1147530 Side View LM2575S-XX or LM2575HVS-XX See NS Package Number TS5B 3 www.national.com LM1575/LM2575/LM2575HV

Ordering Information

Package NSC Standard High Temperature Type Package Voltage Rating Voltage Rating Range Number (40V) (60V) 5-Lead TO-220 T05A LM2575T-3.3 LM2575HVT-3.3 Straight Leads LM2575T-5.0 LM2575HVT-5.0 LM2575T-12 LM2575HVT-12 LM2575T-15 LM2575HVT-15 LM2575T-ADJ LM2575HVT-ADJ 5-Lead TO-220 T05D LM2575T-3.3 Flow LB03 LM2575HVT-3.3 Flow LB03 Bent and LM2575T-5.0 Flow LB03 LM2575HVT-5.0 Flow LB03 Staggered Leads LM2575T-12 Flow LB03 LM2575HVT-12 Flow LB03 LM2575T-15 Flow LB03 LM2575HVT-15 Flow LB03 LM2575T-ADJ Flow LB03 LM2575HVT-ADJ Flow LB03 16-Pin Molded N16A LM2575N-5.0 LM2575HVN-5.0 −40°C ≤ TJ ≤ +125°C DIP LM2575N-12 LM2575HVN-12 LM2575N-15 LM2575HVN-15 LM2575N-ADJ LM2575HVN-ADJ 24-Pin M24B LM2575M-5.0 LM2575HVM-5.0 Surface Mount LM2575M-12 LM2575HVM-12 LM2575M-15 LM2575HVM-15 LM2575M-ADJ LM2575HVM-ADJ 5-Lead TO-263 TS5B LM2575S-3.3 LM2575HVS-3.3 Surface Mount LM2575S-5.0 LM2575HVS-5.0 LM2575S-12 LM2575HVS-12 LM2575S-15 LM2575HVS-15 LM2575S-ADJ LM2575HVS-ADJ 16-Pin Ceramic J16A LM1575J-3.3-QML DIP LM1575J-5.0-QML LM1575J-12-QML −55°C ≤ TJ ≤ +150°C LM1575J-15-QML LM1575J-ADJ-QML www.national.com 4 LM1575/LM2575/LM2575HV

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 LM1575/LM2575 45V LM2575HV 63V ON /OFF Pin Input Voltage −0.3V ≤ V ≤ +VIN Output Voltage to Ground (Steady State) −1V Power Dissipation Internally Limited Storage Temperature Range −65°C to +150°C Maximum Junction Temperature 150°C Minimum ESD Rating (C = 100 pF, R = 1.5 k Ω) 2 kV Lead Temperature (Soldering, 10 sec.) 260°C Operating Ratings Temperature Range LM1575 −55°C ≤ TJ ≤ +150°C LM2575/LM2575HV −40°C ≤ TJ ≤ +125°C Supply Voltage LM1575/LM2575 40V LM2575HV 60V LM1575-3.3, LM2575-3.3, LM2575HV-3.3

Electrical Characteristics

Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range . Symbol Parameter Conditions Typ LM1575-3.3 LM2575-3.3 Units (Limits) LM2575HV-3.3 Limit Limit (Note 2) (Note 3) SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2 VOUT Output Voltage VIN = 12V, ILOAD = 0.2A 3.3 V Circuit of Figure 2 3.267 3.234 V(Min) 3.333 3.366 V(Max) VOUT Output Voltage 4.75V ≤ VIN ≤ 40V, 0.2A ≤ ILOAD ≤ 1A 3.3 V LM1575/LM2575 Circuit of Figure 2 3.200/3.168 3.168/3.135 V(Min) VOUT Output Voltage 4.75V ≤ VIN ≤ 60V, 0.2A ≤ ILOAD ≤ 1A 3.3 V LM2575HV Circuit of Figure 2 3.200/3.168 3.168/3.135 V(Min) η Efficiency VIN = 12V, ILOAD = 1A 75 % LM1575-5.0, LM2575-5.0, LM2575HV-5.0 Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range. Symbol Parameter Conditions Typ LM1575-5.0 LM2575-5.0 Units (Limits) LM2575HV-5.0 Limit Limit (Note 2) (Note 3) SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2 VOUT Output Voltage VIN = 12V, ILOAD = 0.2A 5.0 V Circuit of Figure 2 4.950 4.900 V(Min) 5.050 5.100 V(Max) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 5.0 V LM1575/LM2575 8V ≤ VIN ≤ 40V 4.850/4.800 4.800/4.750 V(Min) Circuit of Figure 2 5.150/5.200 5.200/5.250 V(Max) 5 www.national.com LM1575/LM2575/LM2575HV

Symbol Parameter Conditions Typ LM1575-5.0 LM2575-5.0 Units (Limits) LM2575HV-5.0 Limit Limit (Note 2) (Note 3) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 5.0 V LM2575HV 8V ≤ VIN ≤ 60V 4.850/4.800 4.800/4.750 V(Min) Circuit of Figure 2 5.175/5.225 5.225/5.275 V(Max) η Efficiency VIN = 12V, ILOAD = 1A 77 % LM1575-12, LM2575-12, LM2575HV-12 Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range . Symbol Parameter Conditions Typ LM1575-12 LM2575-12 Units (Limits) LM2575HV-12 Limit Limit (Note 2) (Note 3) SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2 VOUT Output Voltage VIN = 25V, ILOAD = 0.2A 12 V Circuit of Figure 2 11.88 11.76 V(Min) 12.12 12.24 V(Max) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 12 V LM1575/LM2575 15V ≤ VIN ≤ 40V 11.64/11.52 11.52/11.40 V(Min) Circuit of Figure 2 12.36/12.48 12.48/12.60 V(Max) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 12 V LM2575HV 15V ≤ VIN ≤ 60V 11.64/11.52 11.52/11.40 V(Min) Circuit of Figure 2 12.42/12.54 12.54/12.66 V(Max) η Efficiency VIN = 15V, ILOAD = 1A 88 % LM1575-15, LM2575-15, LM2575HV-15 Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range . Symbol Parameter Conditions Typ LM1575-15 LM2575-15 Units (Limits) LM2575HV-15 Limit Limit (Note 2) (Note 3) SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2 VOUT Output Voltage VIN = 30V, ILOAD = 0.2A 15 V Circuit of Figure 2 14.85 14.70 V(Min) 15.15 15.30 V(Max) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 15 V LM1575/LM2575 18V ≤ VIN ≤ 40V 14.55/14.40 14.40/14.25 V(Min) Circuit of Figure 2 15.45/15.60 15.60/15.75 V(Max) VOUT Output Voltage 0.2A ≤ ILOAD ≤ 1A, 15 V LM2575HV 18V ≤ VIN ≤ 60V 14.55/14.40 14.40/14.25 V(Min) Circuit of Figure 2 15.525/15.675 15.68/15.83 V(Max) η Efficiency VIN = 18V, ILOAD = 1A 88 % www.national.com 6 LM1575/LM2575/LM2575HV

LM1575-ADJ, LM2575-ADJ, LM2575HV-ADJ Specifications with standard type face are for TJ= 25°C, and those with boldface type apply over full Operating Temperature Range. Symbol Parameter Conditions Typ LM1575-ADJ LM2575-ADJ Units (Limits) LM2575HV-ADJ Limit Limit (Note 2) (Note 3) SYSTEM PARAMETERS (Note 4) Test Circuit Figure 2 VOUT Feedback Voltage VIN = 12V, ILOAD = 0.2A 1.230 V VOUT = 5V 1.217 1.217 V(Min) Circuit of Figure 2 1.243 1.243 V(Max) VOUT Feedback Voltage 0.2A ≤ ILOAD ≤ 1A, 1.230 V LM1575/LM2575 8V ≤ VIN ≤ 40V 1.205/1.193 1.193/1.180 V(Min) VOUT = 5V, Circuit of Figure 2 1.255/1.267 1.267/1.280 V(Max) VOUT Feedback Voltage 0.2A ≤ ILOAD ≤ 1A, 1.230 V LM2575HV 8V ≤ VIN ≤ 60V 1.205/1.193 1.193/1.180 V(Min) VOUT = 5V, Circuit of Figure 2 1.261/1.273 1.273/1.286 V(Max) η Efficiency VIN = 12V, ILOAD = 1A, VOUT = 5V 77 % All Output Voltage Versions Specifications with standard type face are for TJ = 25°C, and those with boldface type apply over full Operating Temperature 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 = 200 mA. Symbol Parameter Conditions Typ LM1575-XX LM2575-XX Units (Limits) LM2575HV-XX Limit Limit (Note 2) (Note 3) DEVICE PARAMETERS Ib Feedback Bias Current VOUT = 5V (Adjustable Version Only) 50 100/500 100/500 nA fO Oscillator Frequency (Note 13) 52 kHz 47/43 47/42 kHz(Min) 58/62 58/63 kHz(Max) VSAT Saturation Voltage IOUT = 1A (Note 5) 0.9 V DC Max Duty Cycle (ON) (Note 6) 98 % 93 93 %(Min) ICL Current Limit Peak Current (Notes 5, 13) 2.2 A IL Output Leakage (Notes 7, 8) Output = 0V 2 2 mA(Max) Current Output = −1V 7.5 mA Output = −1V 30 30 mA(Max) IQ Quiescent Current (Note 7) 5 mA 10/12 10 mA(Max) ISTBY Standby Quiescent ON /OFF Pin = 5V (OFF) 50 μA Current 200/500 200 μA(Max) 7 www.national.com LM1575/LM2575/LM2575HV

Symbol Parameter Conditions Typ LM1575-XX LM2575-XX Units (Limits) LM2575HV-XX Limit Limit (Note 2) (Note 3) θJA Thermal Resistance T Package, Junction to Ambient (Note 9) 65 θJA T Package, Junction to Ambient (Note 10) 45 °C/W θJC T Package, Junction to Case 2 θJA N Package, Junction to Ambient (Note 11) 85 θJA M Package, Junction to Ambient (Note 11) 100 θJA S Package, Junction to Ambient (Note 12) 37 ON /OFF CONTROL Test Circuit Figure 2 IIH ON /OFF Pin Input ON /OFF Pin = 5V (OFF) 12 μA Current 30 30 μA(Max) IIL ON /OFF Pin = 0V (ON) 0 μA 10 10 μA(Max) Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All limits are used to calculate Average Outgoing Quality Level, and all are 100% production tested. Note 3: All limits guaranteed at room temperature (standard type face) and at temperature extremes (bold type face). All room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. Note 4: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM1575/ LM2575 is used as shown in the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics. Note 5: Output (pin 2) sourcing current. No diode, inductor or capacitor connected to output pin. Note 6: Feedback (pin 4) removed from output and connected to 0V. Note 7: Feedback (pin 4) 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 8: VIN = 40V (60V for the high voltage version). Note 9: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ½ inch leads in a socket, or on a PC board with minimum copper area. Note 10: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with ½ inch leads soldered to a PC board containing approximately 4 square inches of copper area surrounding the leads. Note 11: Junction to ambient thermal resistance with approximately 1 square inch of pc board copper surrounding the leads. Additional copper area will lower thermal resistance further. See thermal model in Switchers made Simple software. Note 12: If the TO-263 package is used, the thermal resistance can be reduced by increasing the PC board copper area thermally connected to the package: Using 0.5 square inches of copper area, θJA is 50°C/W; with 1 square inch of copper area, θJA is 37°C/W; and with 1.6 or more square inches of copper area, θJA is 32°C/W. Note 13: 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%. Note 14: Refer to RETS LM1575J for current revision of military RETS/SMD. www.national.com 8 LM1575/LM2575/LM2575HV

Typical Performance Characteristics (Circuit of Figure 2) Normalized Output Voltage 1147532 Line Regulation 1147533 Dropout Voltage 1147534 Current Limit 1147535 Quiescent Current 1147536 Standby Quiescent Current 1147537 9 www.national.com LM1575/LM2575/LM2575HV

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(TO-263) (See (Note 12)) 1147528 Switching Waveforms 1147506 VOUT = 5V A: Output Pin Voltage, 10V/div B: Output Pin Current, 1A/div C: Inductor Current, 0.5A/div D: Output Ripple Voltage, 20 mV/div, AC-Coupled Horizontal Time Base: 5 μs/div Load Transient Response 1147507 11 www.national.com LM1575/LM2575/LM2575HV

Test Circuit and Layout Guidelines As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance gener- ate 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 possible. Single- point grounding (as indicated) or ground plane construction should be used for best results. When using the Adjustable version, physically locate the programming resistors near the regulator, to keep the sensitive feedback wiring short. Fixed Output Voltage Versions 1147508 CIN — 100 μF, 75V, Aluminum Electrolytic COUT — 330 μF, 25V, Aluminum Electrolytic D1 — Schottky, 11DQ06 L1 — 330 μH, PE-52627 (for 5V in, 3.3V out, use 100 μH, PE-92108) Adjustable Output Voltage Version 1147509 where VREF = 1.23V, R1 between 1k and 5k. R1 — 2k, 0.1% R2 — 6.12k, 0.1% Note: Pin numbers are for the TO-220 package. FIGURE 2. www.national.com 12 LM1575/LM2575/LM2575HV

LM2575 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) = 20V ILOAD(Max) = 0.8A 1. Inductor Selection (L1) A. Select the correct Inductor value selection guide from Figures 3, 4, 5, 6 (Output voltages of 3.3V, 5V, 12V or 15V respectively). For other output voltages, see the design procedure for the ad- justable version. B. From the inductor value selection guide, identify the inductance region intersected by V IN(Max) and I LOAD(Max), and note the in- ductor code for that region. C. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown in Figure 9. Part numbers are listed for three inductor manufacturers. The inductor chosen must be rated for operation at the LM2575 switching frequency (52 kHz) and for a current rating of 1.15 × ILOAD. For additional inductor information, see the inductor section in the Application Hints section of this data sheet. 1. Inductor Selection (L1) A. Use the selection guide shown in Figure 4. B. From the selection guide, the inductance area intersected by the 20V line and 0.8A line is L330. C. Inductor value required is 330 μH. From the table in Figure 9, choose AIE 415-0926, Pulse Engineering PE-52627, or RL1952. 2. Output Capacitor Selection (COUT) A. The value of the output capacitor together with the inductor de- fines the dominate pole-pair of the switching regulator loop. For stable operation and an acceptable output ripple voltage, (approx- imately 1% of the output voltage) a value between 100 μF and 470 μF 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 recommended. Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason it may be necessary to select a ca- pacitor rated for a higher voltage than would normally be needed. 2. Output Capacitor Selection (COUT) A. COUT = 100 μF to 470 μF standard aluminum electrolytic. B. Capacitor voltage rating = 20V. 3. Catch Diode Selection (D1) A. The catch-diode current rating must be at least 1.2 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 LM2575. 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 30V 1N5818 or SR103 Schottky diode, or any of the suggested fast-recovery diodes shown in Figure 8. 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 47 μF, 25V aluminum electrolytic capacitor located near the input and ground pins provides sufficient bypassing. 13 www.national.com LM1575/LM2575/LM2575HV

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 = 10V VIN(Max) = 25V ILOAD(Max) = 1A 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. R1 can be between 1k and 5k. (For best temperature coefficient and stability with time, use 1% metal film resistors) 1.Programming Output Voltage (Selecting R1 and R2) R2 = 1k (8.13 − 1) = 7.13k, closest 1% value is 7.15k 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant, E • T (V • μs), from the following formula: 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 Selec- tion Guide shown in Figure 7. C. On the horizontal axis, select the maximum load current. D. Identify the inductance region intersected by the E • T value and the maximum load current value, and note the inductor code for that region. E. Identify the inductor value from the inductor code, and select an appropriate inductor from the table shown in Figure 9. Part numbers are listed for three inductor manufacturers. The inductor chosen must be rated for operation at the LM2575 switching frequency (52 kHz) and for a current rating of 1.15 × ILOAD. For additional inductor information, see the inductor section in the application hints section of this data sheet. 2. Inductor Selection (L1) A. Calculate E • T (V • μs) B. E • T = 115 V • μs C. ILOAD(Max) = 1A D. Inductance Region = H470 E. Inductor Value = 470 μH Choose from AIE part #430-0634, Pulse Engineering part #PE-53118, or Renco part #RL-1961. 3. Output Capacitor Selection (COUT) A. The value of the output capacitor together with the inductor de- fines the dominate pole-pair of the switching regulator loop. For stable operation, the capacitor must satisfy the following require- ment: The above formula yields capacitor values between 10 μF and 2000 μF that will satisfy the loop requirements for stable operation. But to achieve an acceptable output ripple voltage, (approximately 1% of the output voltage) and transient response, the output capacitor may need to be several times larger than the above formula yields. B. The capacitor's voltage rating should be at last 1.5 times greater than the output voltage. For a 10V regulator, a rating of at least 15V or more is recommended. Higher voltage electrolytic capacitors generally have lower ESR numbers, and for this reason it may be necessary to select a ca- pacitor rate for a higher voltage than would normally be needed. 3. Output Capacitor Selection (COUT) However, for acceptable output ripple voltage select COUT ≥ 220 μF COUT = 220 μF electrolytic capacitor (Continued) (Continued) 15 www.national.com LM1575/LM2575/LM2575HV

PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions) 4. Catch Diode Selection (D1) A. The catch-diode current rating must be at least 1.2 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 LM2575. The most stressful condition for this diode is an overload or shorted output. See diode selection guide in Figure 8. B. The reverse voltage rating of the diode should be at least 1.25 times the maximum input voltage. 4. Catch Diode Selection (D1) A. For this example, a 3A current rating is adequate. B. Use a 40V MBR340 or 31DQ04 Schottky diode, or any of the suggested fast-recovery diodes in Figure 8. 5. Input Capacitor (CIN) An aluminum or tantalum electrolytic bypass capacitor located close to the regulator is needed for stable operation. 5. Input Capacitor (CIN) A 100 μF aluminum electrolytic capacitor located near the input and ground pins provides sufficient bypassing. To further simplify the buck regulator design procedure, National Semiconductor is making available computer design software to be used with the Simple Switcher line of switching regulators. Switchers Made Simple (version 3.3) is available on a (3½″) diskette for IBM compatible computers from a National Semiconductor sales office in your area. www.national.com 16 LM1575/LM2575/LM2575HV

INPUT CAPACITOR (CIN) To maintain stability, the regulator input pin must be bypassed with at least a 47 μF electrolytic capacitor. The capacitor's leads must be kept short, and located near the regulator. If the operating temperature range includes temperatures be- low −25°C, the input capacitor value may need to be larger. With most electrolytic capacitors, the capacitance value de- creases and the ESR increases with lower temperatures and age. Paralleling a ceramic or solid tantalum capacitor will in- crease the regulator stability at cold temperatures. For maxi- mum capacitor operating lifetime, the capacitor's RMS ripple current rating should be greater than 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 flowing continuously, or if it drops to zero for a period of time in the normal switching cycle. Each mode has distinctively different operating characteristics, which can affect the regulator per- formance and requirements. The LM2575 (or any of the Simple Switcher family) can be used for both continuous and discontinuous modes of oper- ation. The inductor value selection guides in Figure 3 through Figure 7 were designed for buck regulator designs of the continuous inductor current type. When using inductor values shown in the inductor selection guide, the peak-to-peak inductor ripple current will be approximately 20% to 30% of the maximum DC current. With relatively heavy load currents, the circuit oper- ates in the continuous mode (inductor current always flowing), but under light load conditions, the circuit will be forced to the discontinuous mode (inductor current falls to zero for a period of time). This discontinuous mode of operation is perfectly acceptable. For light loads (less than approximately 200 mA) it may be desirable to operate the regulator in the discontin- uous mode, primarily because of the lower inductor values required for the discontinuous mode. The selection guide chooses inductor values suitable for con- tinuous mode operation, but if the inductor value chosen is prohibitively high, the designer should investigate the possi- bility of discontinuous operation. The computer design soft- ware Switchers Made Simple will provide all component values for discontinuous (as well as continuous) mode of op- eration. Inductors are available in different styles such as pot core, toriod, E-frame, bobbin core, etc., as well as different core materials, such as ferrites and powdered iron. The least ex- pensive, the bobbin core type, consists of wire wrapped on a ferrite rod core. This type of construction makes for an inex- pensive inductor, but since the magnetic flux is not completely contained within the core, it generates more electromagnetic interference (EMI). This EMI can cause problems in sensitive circuits, or can give incorrect scope readings because of in- duced voltages in the scope probe. The inductors listed in the selection chart include ferrite pot core construction for AIE, powdered iron toroid for Pulse En- gineering, and ferrite bobbin core for Renco. An inductor should not be operated beyond its maximum rat- ed current because it may saturate. When an inductor begins to saturate, the inductance decreases rapidly and the inductor begins to look mainly resistive (the DC resistance of the wind- ing). This will cause the switch current to rise very rapidly. Different inductor types have different saturation characteris- tics, and this should be kept in mind when selecting an in- ductor. The inductor manufacturer's data sheets include current and energy limits to avoid inductor saturation. INDUCTOR RIPPLE CURRENT When the switcher is operating in the continuous mode, the inductor current waveform ranges from a triangular to a saw- tooth type of waveform (depending on the input voltage). For a given input voltage and output voltage, the peak-to-peak amplitude of this inductor current waveform remains constant. As the load current rises or falls, the entire sawtooth current waveform also rises or falls. The average DC value of this waveform is equal to the DC load current (in the buck regu- lator configuration). If the load current drops to a low enough level, the bottom of the sawtooth current waveform will reach zero, and the switcher will change to a discontinuous mode of operation. This is a perfectly acceptable mode of operation. Any buck switching regulator (no matter how large the inductor value is) will be forced to run discontinuous if the load current is light enough. OUTPUT CAPACITOR An output capacitor is required to filter the output voltage and is needed for loop stability. The capacitor should be located near the LM2575 using short pc board traces. Standard alu- minum electrolytics are usually adequate, but low ESR types are recommended for low output ripple voltage and good sta- bility. The ESR of a capacitor depends on many factors, some which are: the value, the voltage rating, physical size and the type of construction. In general, low value or low voltage (less than 12V) electrolytic capacitors usually have higher ESR numbers. The amount of output ripple voltage is primarily a function of the ESR (Equivalent Series Resistance) of the output capac- itor and the amplitude of the inductor ripple current ( ΔIIND). See the section on inductor ripple current in Application Hints. The lower capacitor values (220 μF–680 μF) will allow typi- cally 50 mV to 150 mV of output ripple voltage, while larger- value capacitors will reduce the ripple to approximately 20 mV to 50 mV. Output Ripple Voltage = (ΔIIND) (ESR of COUT) To further reduce the output ripple voltage, several standard electrolytic capacitors may be paralleled, or a higher-grade capacitor may be used. Such capacitors are often called “high-frequency,” “low-inductance,” or “low-ESR.” These will reduce the output ripple to 10 mV or 20 mV. However, when operating in the continuous mode, reducing the ESR below 0.05Ω can cause instability in the regulator. Tantalum capacitors can have a very low ESR, and should be carefully evaluated if it is the only output capacitor. Because of their good low temperature characteristics, a tantalum can www.national.com 18 LM1575/LM2575/LM2575HV

be used in parallel with aluminum electrolytics, with the tan- talum making up 10% or 20% of the total capacitance. The capacitor's ripple current rating at 52 kHz should be at least 50% higher than the peak-to-peak inductor ripple cur- rent. CATCH DIODE Buck regulators require a diode to provide a return path for the inductor current when the switch is off. This diode should be located close to the LM2575 using short leads and short printed circuit traces. Because of their fast switching speed and low forward voltage drop, Schottky diodes provide the best efficiency, especially in low output voltage switching regulators (less than 5V). Fast- Recovery, High-Efficiency, or Ultra-Fast Recovery diodes are also suitable, but some types with an abrupt turn-off charac- teristic may cause instability and EMI problems. A fast-recov- ery diode with soft recovery characteristics is a better choice. Standard 60 Hz diodes (e.g., 1N4001 or 1N5400, etc.) are also not suitable. See Figure 8 for Schottky and “soft” fast- recovery diode selection guide. OUTPUT VOLTAGE RIPPLE AND TRANSIENTS The output voltage of a switching power supply will contain a sawtooth ripple voltage at the switcher frequency, typically about 1% of the output voltage, and may also contain short voltage spikes at the peaks of the sawtooth waveform. The output ripple voltage is due mainly to the inductor saw- tooth ripple current multiplied by the ESR of the output ca- pacitor. (See the inductor selection in the application hints.) The voltage spikes are present because of the fast switching action of the output switch, and the parasitic inductance of the output filter capacitor. To minimize these voltage spikes, spe- cial low inductance capacitors can be used, and their lead lengths must be kept short. Wiring inductance, stray capaci- tance, as well as the scope probe used to evaluate these transients, all contribute to the amplitude of these spikes. An additional small LC filter (20 μH & 100 μF) can be added to the output (as shown in Figure 15) to further reduce the amount of output ripple and transients. A 10 × reduction in output ripple voltage and transients is possible with this filter. FEEDBACK CONNECTION The LM2575 (fixed voltage versions) feedback pin must be wired to the output voltage point of the switching power sup- ply. When using the adjustable version, physically locate both output voltage programming resistors near the LM2575 to avoid picking up unwanted noise. Avoid using resistors greater than 100 kΩ because of the increased chance of noise pickup. ON /OFF INPUT For normal operation, the ON /OFF pin should be grounded or driven with a low-level TTL voltage (typically below 1.6V). To put the regulator into standby mode, drive this pin with a high-level TTL or CMOS signal. The ON /OFF pin can be safely pulled up to +VIN without a resistor in series with it. The ON /OFF pin should not be left open. GROUNDING To maintain output voltage stability, the power ground con- nections must be low-impedance (see Figure 2). For the TO-3 style package, the case is ground. For the 5-lead TO-220 style package, both the tab and pin 3 are ground and either con- nection may be used, as they are both part of the same copper lead frame. With the N or M packages, all the pins labeled ground, power ground, or signal ground should be soldered directly to wide printed circuit board copper traces. This assures both low in- ductance connections and good thermal properties. HEAT SINK/THERMAL CONSIDERATIONS In many cases, no heat sink is required to keep the LM2575 junction temperature within the allowed operating range. For each application, to determine whether or not a heat sink will be required, the following must be identified: 1. Maximum ambient temperature (in the application). 2. Maximum regulator power dissipation (in application). 3. Maximum allowed junction temperature (150°C for the LM1575 or 125°C for the LM2575). For a safe, conservative design, a temperature approximately 15°C cooler than the maximum temperature should be selected. 4. LM2575 package thermal resistances θJA and θJC. Total power dissipated by the LM2575 can be estimated as follows: PD = (VIN) (IQ) + (VO/VIN) (ILOAD) (VSAT) where IQ (quiescent current) and V SAT can be found in the Characteristic Curves shown previously, V IN is the applied minimum input voltage, V O is the regulated output voltage, and ILOAD is the load current. The dynamic losses during turn- on and turn-off are negligible if a Schottky type catch diode is used. When no heat sink is used, the junction temperature rise can be determined by the following: ΔTJ = (PD) (θJA) To arrive at the actual operating junction temperature, add the junction temperature rise to the maximum ambient tempera- ture. TJ = ΔTJ + TA If the actual operating junction temperature is greater than the selected safe operating junction temperature determined in step 3, then a heat sink is required. When using a heat sink, the junction temperature rise can be determined by the following: ΔTJ = (PD) (θJC + θinterface + θHeat sink) The operating junction temperature will be: TJ = TA + ΔTJ As above, if the actual operating junction temperature is greater than the selected safe operating junction tempera- ture, then a larger heat sink is required (one that has a lower thermal resistance). When using the LM2575 in the plastic DIP (N) or surface mount (M) packages, several items about the thermal prop- erties of the packages should be understood. The majority of the heat is conducted out of the package through the leads, with a minor portion through the plastic parts of the package. Since the lead frame is solid copper, heat from the die is readily conducted through the leads to the printed circuit board copper, which is acting as a heat sink. For best thermal performance, the ground pins and all the unconnected pins should be soldered to generous amounts of printed circuit board copper, such as a ground plane. Large areas of copper provide the best transfer of heat to the sur- rounding air. Copper on both sides of the board is also helpful in getting the heat away from the package, even if there is no direct copper contact between the two sides. Thermal resis- 19 www.national.com LM1575/LM2575/LM2575HV

Note: Pin numbers are for the TO-220 package. FIGURE 15. 1.2V to 55V Adjustable 1A Power Supply with Low Output Ripple

converted to a negative voltage without a transformer. Ratio of the output switch's on-time to the oscillator period. when the LM2575 switch is OFF. The proportion of input power actually delivered to the load. higher ESR values result in higher output ripple voltages. FIGURE 16. Simple Model of a Real Capacitor in the continuous mode (vs. discontinuous mode). inductor current is always flowing and never drops to zero, vs. zero for a period of time in the normal switching cycle. tance of the wire and the available source current. of turns, and the duty cycle.

Physical Dimensions inches (millimeters) unless otherwise noted 16-Lead Ceramic Dual-in-Line (J) Order Number LM1575J-3.3/883, LM1575J-5.0/883, LM1575J-12/883, LM1575J-15/883, or LM1575J-ADJ/883 24-Lead Wide Surface Mount (WM) Order Number LM2575M-5.0, LM2575HVM-5.0, LM2575M-12, LM2575HVM-12, LM2575M-15, LM2575HVM-15, LM2575M-ADJ or LM2575HVM-ADJ www.national.com 24 LM1575/LM2575/LM2575HV

16-Lead Molded DIP (N) Order Number LM2575N-5.0, LM2575HVN-5.0, LM2575N-12, LM2575HVN-12, LM2575N-15, LM2575HVN-15, LM2575N-ADJ or LM2575HVN-ADJ 5-Lead TO-220 (T) Order Number LM2575T-3.3, LM2575HVT-3.3, LM2575T-5.0, LM2575HVT-5.0, LM2575T-12, LM2575HVT-12, LM2575T-15, LM2575HVT-15, LM2575T-ADJ or LM2575HVT-ADJ 25 www.national.com LM1575/LM2575/LM2575HV

TO-263, Molded, 5-Lead Surface Mount Order Number LM2575S-3.3, LM2575HVS-3.3, LM2575S-5.0, LM2575HVS-5.0, LM2575S-12, LM2575HVS-12, LM2575S-15, LM2575HVS-15, LM2575S-ADJ or LM2575HVS-ADJ www.national.com 26 LM1575/LM2575/LM2575HV

Bent, Staggered 5-Lead TO-220 (T) Order Number LM2575T-3.3 Flow LB03, LM2575HVT-3.3 Flow LB03, LM2575T-5.0 Flow LB03, LM2575HVT-5.0 Flow LB03, LM2575T-12 Flow LB03, LM2575HVT-12 Flow LB03, LM2575T-15 Flow LB03, LM2575HVT-15 Flow LB03, LM2575T-ADJ Flow LB03 or LM2575HVT-ADJ Flow LB03 27 www.national.com LM1575/LM2575/LM2575HV

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