LM2576 3.0 A, 15 V, Step−Down Switching Regulator The LM2576 series of regulators are monolithic integrated circuits ideally suited for easy and convenient design of a step−down switching regulator (buck converter). All circuits of this series are capable of driving a 3.0 A load with excellent line and load regulation. http://onsemi.com These devices are available in fixed output voltages of 3.3 V, 5.0 V, 12 V, 15 V, and an adjustable output version. These regulators were designed to minimize the number of external components to simplify the power supply design. Standard series of TO−220 1 TV SUFFIX inductors optimized for use with the LM2576 are offered by several CASE 314B different inductor manufacturers. 5 Since the LM2576 converter is a switch−mode power supply, its Heatsink surface connected to Pin 3 efficiency is significantly higher in comparison with popular three−terminal linear regulators, especially with higher input voltages. In many cases, the power dissipated is so low that no heatsink is required or its size could be reduced dramatically. A standard series of inductors optimized for use with the LM2576 are available from several different manufacturers. This feature TO−220 greatly simplifies the design of switch−mode power supplies. T SUFFIX The LM2576 features include a guaranteed ±4% tolerance on output CASE 314D 1 voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency (±2% over 0°C to 125°C). External shutdown is included, featuring 80 (cid:2)A (typical) standby current. The 5 Pin 1. Vin output switch includes cycle−by−cycle current limiting, as well as 2. Output thermal shutdown for full protection under fault conditions. 3. Ground 4. Feedback Features 5. ON/OFF • 3.3 V, 5.0 V, 12 V, 15 V, and Adjustable Output Versions • Adjustable Version Output Voltage Range, 1.23 to 37 V ±4% Maximum Over Line and Load Conditions • Guaranteed 3.0 A Output Current D2PAK • D2T SUFFIX Wide Input Voltage Range 1 CASE 936A • Requires Only 4 External Components 5 • 52 kHz Fixed Frequency Internal Oscillator Heatsink surface (shown as terminal 6 in • TTL Shutdown Capability, Low Power Standby Mode case outline drawing) is connected to Pin 3 • High Efficiency • Uses Readily Available Standard Inductors ORDERING INFORMATION • Thermal Shutdown and Current Limit Protection See detailed ordering and shipping information in the package • dimensions section on page 24 of this data sheet. Moisture Sensitivity Level (MSL) Equals 1 • Pb−Free Packages are Available DEVICE MARKING INFORMATION See general marking information in the device marking Applications section on page 25 of this data sheet. • Simple High−Efficiency Step−Down (Buck) Regulator • Efficient Pre−Regulator for Linear Regulators • On−Card Switching Regulators • Positive to Negative Converter (Buck−Boost) • Negative Step−Up Converters • Power Supply for Battery Chargers © Semiconductor Components Industries, LLC, 2006 1 Publication Order Number: January, 2006 − Rev. 8 LM2576/D

LM2576 Typical Application (Fixed Output Voltage Versions) Feedback U7.n0r eVg u−l a4t0e dV +Vin LM2576 4 100L 1(cid:2)H DC Input 1 Output 5.0 V Regulated 100 C(cid:2)iFn 3 GN 5 ON/OF2F D1N15822 Cout Output 3.0 A Load D 1000 (cid:2)F Representative Block Diagram and Typical Application Unregulated +Vin 3.1 V Internal ON/OFF ON/OFF Output R2 DC Input 1 Regulator 5 Voltage Versions ((cid:3)) Cin 3.3 V 1.7 k 5.0 V 3.1 k 4 12 V 8.84 k Feedback 15 V 11.3 k Current R2 Fixed Gain Limit For adjustable version Error Amplifier Comparator R1 = open, R2 = 0 (cid:3) Driver Regulated R1 1.0 k Freq Latch L1 Output Shift Output Vout 18 kHz 1.0 Amp 2 1.235 V Switch GND D1 Cout Band−Gap 52 kHz Thermal Reference Oscillator Reset Shutdown 3 Load This device contains 162 active transistors. Figure 1. Block Diagram and Typical Application MAXIMUM RATINGS Rating Symbol Value Unit Maximum Supply Voltage Vin 45 V ON/OFF Pin Input Voltage − −0.3 V ≤ V ≤ +Vin V Output Voltage to Ground (Steady−State) − −1.0 V Power Dissipation Case 314B and 314D (TO−220, 5−Lead) PD Internally Limited W Thermal Resistance, Junction−to−Ambient R(cid:4)JA 65 °C/W Thermal Resistance, Junction−to−Case R(cid:4)JC 5.0 °C/W Case 936A (D2PAK) PD Internally Limited W Thermal Resistance, Junction−to−Ambient R(cid:4)JA 70 °C/W Thermal Resistance, Junction−to−Case R(cid:4)JC 5.0 °C/W Storage Temperature Range Tstg −65 to +150 °C Minimum ESD Rating (Human Body Model: C = 100 pF, R = 1.5 k(cid:3)) − 2.0 kV Lead Temperature (Soldering, 10 seconds) − 260 °C Maximum Junction Temperature TJ 150 °C Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage may occur and reliability may be affected. http://onsemi.com 2

LM2576 OPERATING RATINGS (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.) Rating Symbol Value Unit Operating Junction Temperature Range TJ −40 to +125 °C Supply Voltage Vin 40 V SYSTEM PARAMETERS (Note 1 Test Circuit Figure 15) ELECTRICAL CHARACTERISTICS (Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for the 12 V version, and Vin = 30 V for the 15 V version. ILoad = 500 mA. For typical values TJ = 25°C, for min/max values TJ is the operating junction temperature range that applies Note 2, unless otherwise noted.) Characteristics Symbol Min Typ Max Unit LM2576−3.3 (Note 1 Test Circuit Figure 15) Output Voltage (Vin = 12 V, ILoad = 0.5 A, TJ = 25°C) Vout 3.234 3.3 3.366 V Output Voltage (6.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A) Vout V TJ = 25°C 3.168 3.3 3.432 TJ = −40 to +125°C 3.135 − 3.465 Efficiency (Vin = 12 V, ILoad = 3.0 A) η − 75 − % LM2576−5 (Note 1 Test Circuit Figure 15) Output Voltage (Vin = 12 V, ILoad = 0.5 A, TJ = 25°C) Vout 4.9 5.0 5.1 V Output Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A) Vout V TJ = 25°C 4.8 5.0 5.2 TJ = −40 to +125°C 4.75 − 5.25 Efficiency (Vin = 12 V, ILoad = 3.0 A) η − 77 − % LM2576−12 (Note 1 Test Circuit Figure 15) Output Voltage (Vin = 25 V, ILoad = 0.5 A, TJ = 25°C) Vout 11.76 12 12.24 V Output Voltage (15 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A) Vout V TJ = 25°C 11.52 12 12.48 TJ = −40 to +125°C 11.4 − 12.6 Efficiency (Vin = 15 V, ILoad = 3.0 A) η − 88 − % LM2576−15 (Note 1 Test Circuit Figure 15) Output Voltage (Vin = 30 V, ILoad = 0.5 A, TJ = 25°C) Vout 14.7 15 15.3 V Output Voltage (18 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A) Vout V TJ = 25°C 14.4 15 15.6 TJ = −40 to +125°C 14.25 − 15.75 Efficiency (Vin = 18 V, ILoad = 3.0 A) η − 88 − % LM2576 ADJUSTABLE VERSION (Note 1 Test Circuit Figure 15) Feedback Voltage (Vin = 12 V, ILoad = 0.5 A, Vout = 5.0 V, TJ = 25°C) Vout 1.217 1.23 1.243 V Feedback Voltage (8.0 V ≤ Vin ≤ 40 V, 0.5 A ≤ ILoad ≤ 3.0 A, Vout = 5.0 V) Vout V TJ = 25°C 1.193 1.23 1.267 TJ = −40 to +125°C 1.18 − 1.28 Efficiency (Vin = 12 V, ILoad = 3.0 A, Vout = 5.0 V) η − 77 − % 1. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2576 is used as shown in the Figure 15 test circuit, system performance will be as shown in system parameters section. 2. Tested junction temperature range for the LM2576: Tlow = −40°C Thigh = +125°C http://onsemi.com 3

LM2576 DEVICE PARAMETERS ELECTRICAL CHARACTERISTICS (Unless otherwise specified, Vin = 12 V for the 3.3 V, 5.0 V, and Adjustable version, Vin = 25 V for the 12 V version, and Vin = 30 V for the 15 V version. ILoad = 500 mA. For typical values TJ = 25°C, for min/max values TJ is the operating junction temperature range that applies [Note 2], unless otherwise noted.) Characteristics Symbol Min Typ Max Unit ALL OUTPUT VOLTAGE VERSIONS Feedback Bias Current (Vout = 5.0 V Adjustable Version Only) Ib nA TJ = 25°C − 25 100 TJ = −40 to +125°C − − 200 Oscillator Frequency Note 3 fosc kHz TJ = 25°C − 52 − TJ = 0 to +125°C 47 − 58 TJ = −40 to +125°C 42 − 63 Saturation Voltage (Iout = 3.0 A Note 4) Vsat V TJ = 25°C − 1.5 1.8 TJ = −40 to +125°C − − 2.0 Max Duty Cycle (“on”) Note 5 DC 94 98 − % Current Limit (Peak Current Notes 3 and 4) ICL A TJ = 25°C 4.2 5.8 6.9 TJ = −40 to +125°C 3.5 − 7.5 Output Leakage Current Notes 6 and 7, TJ = 25°C IL mA Output = 0 V − 0.8 2.0 Output = −1.0 V − 6.0 20 Quiescent Current Note 6 IQ mA TJ = 25°C − 5.0 9.0 TJ = −40 to +125°C − − 11 Standby Quiescent Current (ON/OFF Pin = 5.0 V (“off”)) Istby (cid:2)A TJ = 25°C − 80 200 TJ = −40 to +125°C − − 400 ON/OFF Pin Logic Input Level (Test Circuit Figure 15) V Vout = 0 V VIH TJ = 25°C 2.2 1.4 − TJ = −40 to +125°C 2.4 − − Vout = Nominal Output Voltage VIL TJ = 25°C − 1.2 1.0 TJ = −40 to +125°C − − 0.8 ON/OFF Pin Input Current (Test Circuit Figure 15) (cid:2)A ON/OFF Pin = 5.0 V (“off”), TJ = 25°C IIH − 15 30 ON/OFF Pin = 0 V (“on”), TJ = 25°C IIL − 0 5.0 3. 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 dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%. 4. Output (Pin 2) sourcing current. No diode, inductor or capacitor connected to output pin. 5. Feedback (Pin 4) removed from output and connected to 0 V. 6. Feedback (Pin 4) removed from output and connected to +12 V for the Adjustable, 3.3 V, and 5.0 V versions, and +25 V for the 12 V and 15 V versions, to force the output transistor “off”. 7. Vin = 40 V. http://onsemi.com 4

LM2576 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) 1.0 1.4 ANGE (%) 00..68 VINLioonar =md =a2 l0i5z 0Ve0d matA TJ = 25°C ANGE (%) 11..20 ITLJo a=d 2=5 5°C00 mA H 0.4 H 0.8 C C GE 0.2 GE 0.6 3.3 V, 5.0 V and ADJ A A OLT 0 OLT 0.4 T V −0.2 T V 0.2 PU −0.4 PU 0 12 V and 15 V T T U U O −0.6 O −0.2 V, out −0.8 V, out−0.4 −1.0 −0.6 −50 −25 0 25 50 75 100 125 0 5.0 10 15 20 25 30 35 40 TJ, JUNCTION TEMPERATURE (°C) Vin, INPUT VOLTAGE (V) Figure 2. Normalized Output Voltage Figure 3. Line Regulation 2.0 6.5 V) L ( ILoad = 3.0 A Vin = 25 V NTIA 1.5 T (A) 6.0 E N R E E R DIFF 1.0 CUR 5.5 T T U U TP ILoad = 500 mA TP 5.0 U U O O PUT − 0.5 L1 = 150 (cid:2)H I, O 4.5 IN Rind = 0.1 (cid:3) 0 4.0 −50 −25 0 25 50 75 100 125 −50 −25 0 25 50 75 100 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 4. Dropout Voltage Figure 5. Current Limit 20 A) 200 μ mA) 18 VMoeuat s=u 5re.0d Vat ENT ( 180 VON/OFF = 5.0 V T ( 16 Ground Pin RR 160 EN TJ = 25°C CU 140 URR 14 ENT 120 Vin = 40 V T C 12 ILoad = 3.0 A SC 100 N E QUIESCE 81.00 ILoad = 200 mA NDBY QUI 8600 Vin = 12 V , Q TA 40 I 6.0 S , y 20 b 4.0 st 0 0 5.0 10 15 20 25 30 35 40 I −50 −25 0 25 50 75 100 125 Vin, INPUT VOLTAGE (V) TJ, JUNCTION TEMPERATURE (°C) Figure 6. Quiescent Current Figure 7. Standby Quiescent Current http://onsemi.com 5

LM2576 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) A) 200 1.6 μ NT ( 180 V) 1.4 RE 160 E ( R G 1.2 CU 140 TJ = 25°C TA −40°C NT 120 VOL 1.0 CE N ES 100 TIO 0.8 25°C UI A BY Q 8600 ATUR 0.6 125°C STAND 40 V, Ssat 00..42 , y 20 b st 0 0 I 0 5 10 15 20 25 30 35 40 0 0.5 1.0 1.5 2.0 2.5 3.0 Vin, INPUT VOLTAGE (V) SWITCH CURRENT (A) Figure 8. Standby Quiescent Current Figure 9. Switch Saturation Voltage 8.0 5.0 6.0 4.5 Adjustable Version Only %) UENCY ( 42.0.0 VN25ion°r =mC a1l2iz Ved at GE (V) 43..05 REQ 0 OLTA 3.0 F V 2.5 D −2.0 T E U 2.0 Z P ORMALI −−46..00 , INVin 11..50 VILoouatd (cid:2) = 510.203 m VA N −8.0 0.5 −10 0 −50 −25 0 25 50 75 100 125 −50 −25 0 25 50 75 100 125 TJ, JUNCTION TEMPERATURE (°C) TJ, JUNCTION TEMPERATURE (°C) Figure 10. Oscillator Frequency Figure 11. Minimum Operating Voltage 100 A) 80 Adjustable Version Only n T ( 60 N RE 40 R U C 20 N PI 0 K C −20 A B D −40 E E F −60 , b I −80 −100 −50 −25 0 25 50 75 100 125 TJ, JUNCTION TEMPERATURE (°C) Figure 12. Feedback Pin Current http://onsemi.com 6

LM2576 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) 50 V A 0 100 mV Output 4.0 A Voltage 0 Change B 2.0 A − 100 mV 0 4.0 A 3.0 A C 2.0 A Load 2.0 A Current 0 1.0 A D 0 5 (cid:2)s/DIV 100 (cid:2)s/DIV Figure 13. Switching Waveforms Figure 14. Load Transient Response Vout = 15 V A: Output Pin Voltage, 10 V/DIV B: Inductor Current, 2.0 A/DIV C: Inductor Current, 2.0 A/DIV, AC−Coupled D: Output Ripple Voltage, 50 mV/dDIV, AC−Coupled Horizontal Time Base: 5.0 (cid:2)s/DIV http://onsemi.com 7

LM2576 Fixed Output Voltage Versions Feedback 4 Vin LM2576 L1 1 Fixed Output 100 (cid:2)H Output Vout 2 3 GN 5 ON/OFF 7U.nD0r CeVg I−un lp4au0tet Vd C10in0 (cid:2)F D D1 C10o0ut0 (cid:2)F Load MBR360 Cin − 100 (cid:2)F, 75 V, Aluminium Electrolytic Cout − 1000 (cid:2)F, 25 V, Aluminium Electrolytic D1 − Schottky, MBR360 L1 − 100 (cid:2)H, Pulse Eng. PE−92108 R1 − 2.0 k, 0.1% R2 − 6.12 k, 0.1% Adjustable Output Voltage Versions Feedback 4 Vin LM2576 L1 1 Adjustable 100 (cid:2)H Vout Output 5,000 V 2 3 GN 5 ON/OFF 7U.nD0r CeVg I−un lp4au0tet Vd C10in0 (cid:2)F D D1 C10o0ut0 (cid:2)F R2 Load MBR360 R1 (cid:3) (cid:5) V (cid:2)V 1.0(cid:4)(cid:2)R2 out ref(cid:2) R1 (cid:3) (cid:5) V R2(cid:2)R1 out(cid:2)–(cid:2)1.0 V ref Where Vref = 1.23 V, R1 between 1.0 k and 5.0 k Figure 15. Typical Test Circuit PCB LAYOUT GUIDELINES As in any switching regulator, the layout of the printed On the other hand, the PCB area connected to the Pin 2 circuit board is very important. Rapidly switching currents (emitter of the internal switch) of the LM2576 should be associated with wiring inductance, stray capacitance and kept to a minimum in order to minimize coupling to sensitive parasitic inductance of the printed circuit board traces can circuitry. generate voltage transients which can generate Another sensitive part of the circuit is the feedback. It is electromagnetic interferences (EMI) and affect the desired important to keep the sensitive feedback wiring short. To operation. As indicated in the Figure 15, to minimize assure this, physically locate the programming resistors near inductance and ground loops, the length of the leads to the regulator, when using the adjustable version of the indicated by heavy lines should be kept as short as possible. LM2576 regulator. For best results, single−point grounding (as indicated) or ground plane construction should be used. http://onsemi.com 8

LM2576 PIN FUNCTION DESCRIPTION Pin Symbol Description (Refer to Figure 1) 1 Vin This pin is the positive input supply for the LM2576 step−down switching regulator. In order to minimize voltage transients and to supply the switching currents needed by the regulator, a suitable input bypass capacitor must be present (Cin in Figure 1). 2 Output This is the emitter of the internal switch. The saturation voltage Vsat of this output switch is typically 1.5 V. It should be kept in mind that the PCB area connected to this pin should be kept to a minimum in order to minimize coupling to sensitive circuitry. 3 GND Circuit ground pin. See the information about the printed circuit board layout. 4 Feedback This pin senses regulated output voltage to complete the feedback loop. The signal is divided by the internal resistor divider network R2, R1 and applied to the non−inverting input of the internal error amplifier. In the Adjustable version of the LM2576 switching regulator this pin is the direct input of the error amplifier and the resistor network R2, R1 is connected externally to allow programming of the output voltage. 5 ON/OFF It allows the switching regulator circuit to be shut down using logic level signals, thus dropping the total input supply current to approximately 80 (cid:2)A. The threshold voltage is typically 1.4 V. Applying a voltage above this value (up to +Vin) shuts the regulator off. If the voltage applied to this pin is lower than 1.4 V or if this pin is left open, the regulator will be in the “on” condition. DESIGN PROCEDURE Buck Converter Basics This period ends when the power switch is once again The LM2576 is a “Buck” or Step−Down Converter which turned on. Regulation of the converter is accomplished by is the most elementary forward−mode converter. Its basic varying the duty cycle of the power switch. It is possible to schematic can be seen in Figure 16. describe the duty cycle as follows: The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is d(cid:2)ton, where T is the period of switching. T on, the input voltage is connected to the input of the inductor. For the buck converter with ideal components, the duty The output of the inductor is the output voltage, and the cycle can also be described as: rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected d(cid:2)Vout across the inductor, the inductor current begins to linearly V in ramp upwards, as described by the following equation: Figure 17 shows the buck converter, idealized waveforms (cid:3) (cid:5) I (cid:2) Vin–Vout ton of the catch diode voltage and the inductor current. L(on) L Von(SW) During this “on” period, energy is stored within the core material in the form of magnetic flux. If the inductor is properly designed, there is sufficient energy stored to carry the requirements of the load during the “off” period. e g SPwowitcehr L Volta SPwowitcehr SPwowitcehr SPwowitcehr SPwowitcehr de Off On Off On o Di VD(FWD) Vin D Cout RLoad Time Figure 16. Basic Buck Converter Ipk The next period is the “off” period of the power switch. nt When the power switch turns off, the voltage across the urre ILoad(AV) C inductor reverses its polarity and is clamped at one diode or Imin voltage drop below ground by the catch diode. The current uct Power Power nd Diode Switch Diode Switch now flows through the catch diode thus maintaining the load I current loop. This removes the stored energy from the Time inductor. The inductor current during this time is: Figure 17. Buck Converter Idealized Waveforms (cid:3) (cid:5) V –V t I (cid:2) out D off L(off) L http://onsemi.com 9

LM2576 Procedure (Fixed Output Voltage Version) In order to simplify the switching regulator design, a step−by−step design procedure and some examples are provided. Procedure Example Given Parameters: Given Parameters: Vout = Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V) Vout = 5.0 V Vin(max) = Maximum Input Voltage Vin(max) = 15 V ILoad(max) = Maximum Load Current ILoad(max) = 3.0 A 1. Controller IC Selection 1. Controller IC Selection According to the required input voltage, output voltage and According to the required input voltage, output voltage, current, select the appropriate type of the controller IC output current polarity and current value, use the LM2576−5 voltage version. controller IC 2. Input Capacitor Selection (Cin) 2. Input Capacitor Selection (Cin) To prevent large voltage transients from appearing at the input A 100 (cid:2)F, 25 V aluminium electrolytic capacitor located near and for stable operation of the converter, an aluminium or to the input and ground pins provides sufficient bypassing. tantalum electrolytic bypass capacitor is needed between the input pin +Vin and ground pin GND. This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value. 3. Catch Diode Selection (D1) 3. Catch Diode Selection (D1) A.Since the diode maximum peak current exceeds the A.For this example the current rating of the diode is 3.0 A. regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design the diode should have a current rating equal to the maximum current limit of the LM2576 to be able to withstand a continuous output short B.The reverse voltage rating of the diode should be at least B.Use a 20 V 1N5820 Schottky diode, or any of the 1.25 times the maximum input voltage. suggested fast recovery diodes shown in Table 1. 4. Inductor Selection (L1) 4. Inductor Selection (L1) A.According to the required working conditions, select the A.Use the inductor selection guide shown in Figures 19. correct inductor value using the selection guide from Figures 18 to 22. B.From the appropriate inductor selection guide, identify the B.From the selection guide, the inductance area intersected inductance region intersected by the Maximum Input by the 15 V line and 3.0 A line is L100. Voltage line and the Maximum Load Current line. Each region is identified by an inductance value and an inductor code. C.Select an appropriate inductor from the several different C.Inductor value required is 100 (cid:2)H. From Table 2, choose manufacturers part numbers listed in Table 2. an inductor from any of the listed manufacturers. The designer must realize that the inductor current rating must be higher than the maximum peak current flowing through the inductor. This maximum peak current can be calculated as follows: (cid:3) (cid:5) I (cid:2)I (cid:4) Vin–Vout ton p(max) Load(max) 2L where ton is the “on” time of the power switch and V out 1.0 ton (cid:2) Vin x fosc For additional information about the inductor, see the inductor section in the “Application Hints” section of this data sheet. http://onsemi.com 10

LM2576 Procedure (Fixed Output Voltage Version) (continued)In order to simplify the switching regulator design, a step−by−step design procedure and some examples are provided. Procedure Example 5. Output Capacitor Selection (Cout) 5. Output Capacitor Selection (Cout) A.Since the LM2576 is a forward−mode switching regulator A.Cout = 680 (cid:2)F to 2000 (cid:2)F standard aluminium electrolytic. with voltage mode control, its open loop 2−pole−1−zero frequency characteristic has the dominant pole−pair determined by the output capacitor and inductor values. For stable operation and an acceptable ripple voltage, (approximately 1% of the output voltage) a value between 680 (cid:2)F and 2000 (cid:2)F is recommended. B.Due to the fact that the higher voltage electrolytic capacitors B.Capacitor voltage rating = 20 V. generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor’s voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0 V regulator, a rating at least 8.0 V is appropriate, and a 10 V or 16 V rating is recommended. Procedure (Adjustable Output Version: LM2576−ADJ) Procedure Example Given Parameters: Given Parameters: Vout = Regulated Output Voltage Vout = 8.0 V Vin(max) = Maximum DC Input Voltage Vin(max) = 25 V ILoad(max) = Maximum Load Current ILoad(max) = 2.5 A 1. Programming Output Voltage 1. Programming Output Voltage (selecting R1 and R2) To select the right programming resistor R1 and R2 value (see Select R1 and R2: Figure 2) use the following formula: (cid:3) (cid:5) (cid:3) (cid:5) Vout(cid:2)1.23 1.0(cid:4) RR21 Select R1 = 1.8 k(cid:3) Vout(cid:2)Vref 1.0(cid:4) RR21 where Vref = 1.23 V (cid:3)V (cid:5) (cid:3) (cid:5) out 8.0V Resistor R1 can be between 1.0 k and 5.0 k(cid:3). (For best R2(cid:2)R1 V (cid:6)1.0 (cid:2)1.8k 1.23V(cid:6)1.0 ref temperature coefficient and stability with time, use 1% metal film resistors). (cid:3) (cid:5) R2 = 9.91 k(cid:3), choose a 9.88 k metal film resistor. V out R2(cid:2)R1 –1.0 V ref 2. Input Capacitor Selection (Cin) 2. Input Capacitor Selection (Cin) To prevent large voltage transients from appearing at the input A 100 (cid:2)F, 150 V aluminium electrolytic capacitor located near and for stable operation of the converter, an aluminium or the input and ground pin provides sufficient bypassing. tantalum electrolytic bypass capacitor is needed between the input pin +Vin and ground pin GND This capacitor should be located close to the IC using short leads. This capacitor should have a low ESR (Equivalent Series Resistance) value. For additional information see input capacitor section in the “Application Hints” section of this data sheet. 3. Catch Diode Selection (D1) 3. Catch Diode Selection (D1) A.Since the diode maximum peak current exceeds the A.For this example, a 3.0 A current rating is adequate. regulator maximum load current the catch diode current rating must be at least 1.2 times greater than the maximum load current. For a robust design, the diode should have a current rating equal to the maximum current limit of the LM2576 to be able to withstand a continuous output short. B.The reverse voltage rating of the diode should be at least B.Use a 30 V 1N5821 Schottky diode or any suggested fast 1.25 times the maximum input voltage. recovery diode in the Table 1. http://onsemi.com 11

LM2576 Procedure (Adjustable Output Version: LM2576−ADJ) (continued) Procedure Example 4. Inductor Selection (L1) 4. Inductor Selection (L1) A.Use the following formula to calculate the inductor Volt x A.Calculate E x T [V x (cid:2)s] constant: microsecond [V x (cid:2)s] constant: ExT(cid:2)(cid:3)V –V (cid:5) Vout x 106 [Vx(cid:2)s] ExT(cid:2)(25–8.0)x 8.0 x 1000(cid:2)80[Vx(cid:2)s] in out V F[Hz] 25 52 in B.Match the calculated E x T value with the corresponding B.E x T = 80 [V x (cid:2)s] number on the vertical axis of the Inductor Value Selection Guide shown in Figure 22. This E x T constant is a measure of the energy handling capability of an inductor and is dependent upon the type of core, the core area, the number of turns, and the duty cycle. C.Next step is to identify the inductance region intersected by C.ILoad(max) = 2.5 A the E x T value and the maximum load current value on the Inductance Region = H150 horizontal axis shown in Figure 25. D.From the inductor code, identify the inductor value. Then D.Proper inductor value = 150 (cid:2)H select an appropriate inductor from Table 2. Choose the inductor from Table 2. The inductor chosen must be rated for a switching frequency of 52 kHz and for a current rating of 1.15 x ILoad. The inductor current rating can also be determined by calculating the inductor peak current: (cid:3) (cid:5) I (cid:2)I (cid:4) Vin–Vout ton p(max) Load(max) 2L where ton is the “on” time of the power switch and V ton (cid:2) Voinut x f1o.s0c For additional information about the inductor, see the inductor section in the “External Components” section of this data sheet. 5. Output Capacitor Selection (Cout) 5. Output Capacitor Selection (Cout) A.Since the LM2576 is a forward−mode switching regulator A. with voltage mode control, its open loop 2−pole−1−zero Cout (cid:7)13,300x 8x21550 (cid:2) 332.5μF frequency characteristic has the dominant pole−pair determined by the output capacitor and inductor values. To achieve an acceptable ripple voltage, select Cout = 680 (cid:2)F electrolytic capacitor. For stable operation, the capacitor must satisfy the following requirement: V in(max) C (cid:7)13,300 [μF] out V xL[μH] out B.Capacitor values between 10 (cid:2)F and 2000 (cid:2)F will satisfy the loop requirements for stable operation. To achieve an acceptable output ripple voltage and transient response, the output capacitor may need to be several times larger than the above formula yields. C.Due to the fact that the higher voltage electrolytic capacitors generally have lower ESR (Equivalent Series Resistance) numbers, the output capacitor’s voltage rating should be at least 1.5 times greater than the output voltage. For a 5.0 V regulator, a rating of at least 8.0 V is appropriate, and a 10 V or 16 V rating is recommended. http://onsemi.com 12

LM2576 LM2576 Series Buck Regulator Design Procedures (continued) Indicator Value Selection Guide (For Continuous Mode Operation) 60 60 40 L680 H1000 H680 H470 H330 H220 H150 20 L470 40 V) 15 V) E ( L330 E ( 20 L680 G G TA 10 L220 TA 15 L470 L L VO 8.0 L150 VO 12 L330 T T PU 7.0 L100 PU 10 L220 N N M I L68 M I 9.0 L150 U 6.0 U M M L100 MAXI L47 MAXI 8.0 L68 L47 5.0 7.0 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0 2.5 3.0 0.3 0.4 0.5 0.6 0.8 1.0 1.2 1.5 2.0 2.5 3.0 IL, MAXIMUM LOAD CURRENT (A) IL, MAXIMUM LOAD CURRENT (A) Figure 18. LM2576−3.3 Figure 19. LM2576−5 60 60 GE (V) 433050 H1500 GE (V) 433005 H1500 A 25 H1000 A UT VOLT 20 H680 H470 H330 H220 H150 UT VOLT 2252 H1000 H680 H470 H330 H220 H150 P 18 P N N XIMUM I 16 L680 L470 L330 L220 XIMUM I 2109 L680 L470 L330 L220 A L150 A L150 M 15 L100 M 18 L100 L68 L68 14 17 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0 2.5 3.0 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0 2.5 3.0 IL, MAXIMUM LOAD CURRENT (A) IL, MAXIMUM LOAD CURRENT (A) Figure 20. LM2576−12 Figure 21. LM2576−15 300 250 H2000 200 s) H1500 H1000 μV 150 H680 H470 E ( H330 M 100 H220 TI 90 H150 E 80 LTAG 7600 L680 L470 O 50 L330 V 45 L220 T, 40 L150 E 35 L100 L68 30 L47 25 20 0.3 0.4 0.5 0.6 0.8 1.0 1.5 2.0 2.5 3.0 IL, MAXIMUM LOAD CURRENT (A) Figure 22. LM2576−ADJ http://onsemi.com 13

LM2576 Table 1. Diode Selection Guide Schottky Fast Recovery 3.0 A 4.0 − 6.0 A 3.0 A 4.0 − 6.0 A Through Surface Through Surface Through Surface Through Surface VR Hole Mount Hole Mount Hole Mount Hole Mount 20 V 1N5820 SK32 1N5823 MBR320P SR502 SR302 SB520 30 V 1N5821 SK33 1N5824 50WQ03 MBR330 30WQ03 SR503 SR303 SB530 MUR320 MURS320T3 MUR420 MURD620CT 31DQ03 31DF1 MURD320 HER602 50WF10 HER302 30WF10 40 V 1N5822 SK34 1N5825 MBRD640CT MBR340 30WQ04 SR504 50WQ04 (all diodes (all diodes (all diodes (all diodes SR304 MBRS340T3 SB540 rated rated rated rated 31DQ04 MBRD340 to at least to at least to at least to at least 100 V) 100 V) 100 V) 100 V) 50 V MBR350 SK35 SB550 50WQ05 31DQ05 30WQ05 SR305 60 V MBR360 MBRS360T3 50SQ080 MBRD660CT DQ06 MBRD360 SR306 NOTE: Diodes listed in bold are available from ON Semiconductor. Table 2. Inductor Selection by Manufacturer’s Part Number Inductor Inductor Code Value Tech 39 Schott Corp. Pulse Eng. Renco L47 47 (cid:2)H 77 212 671 26980 PE−53112 RL2442 L68 68 (cid:2)H 77 262 671 26990 PE−92114 RL2443 L100 100 (cid:2)H 77 312 671 27000 PE−92108 RL2444 L150 150 (cid:2)H 77 360 671 27010 PE−53113 RL1954 L220 220 (cid:2)H 77 408 671 27020 PE−52626 RL1953 L330 330 (cid:2)H 77 456 671 27030 PE−52627 RL1952 L470 470 (cid:2)H * 671 27040 PE−53114 RL1951 L680 680 (cid:2)H 77 506 671 27050 PE−52629 RL1950 H150 150 (cid:2)H 77 362 671 27060 PE−53115 RL2445 H220 220 (cid:2)H 77 412 671 27070 PE−53116 RL2446 H330 330 (cid:2)H 77 462 671 27080 PE−53117 RL2447 H470 470 (cid:2)H * 671 27090 PE−53118 RL1961 H680 680 (cid:2)H 77 508 671 27100 PE−53119 RL1960 H1000 1000 (cid:2)H 77 556 671 27110 PE−53120 RL1959 H1500 1500 (cid:2)H * 671 27120 PE−53121 RL1958 H2200 2200 (cid:2)H * 671 27130 PE−53122 RL2448 NOTE: *Contact Manufacturer http://onsemi.com 14

LM2576 Table 3. Example of Several Inductor Manufacturers Phone/Fax Numbers Phone + 1−619−674−8100 Pulse Engineering, Inc. Fax + 1−619−674−8262 Phone + 353−9324−107 Pulse Engineering, Inc. Europe Fax + 353−9324−459 Phone + 1−516−645−5828 Renco Electronics, Inc. Fax + 1−516−586−5562 Phone + 33−1−4115−1681 Tech 39 Fax + 33−1−4709−5051 Phone + 1−612−475−1173 Schott Corporation Fax + 1−612−475−1786 EXTERNAL COMPONENTS Input Capacitor (C ) Output Capacitor (C ) in out The Input Capacitor Should Have a Low ESR For low output ripple voltage and good stability, low ESR For stable operation of the switch mode converter a low output capacitors are recommended. An output capacitor ESR (Equivalent Series Resistance) aluminium or solid has two main functions: it filters the output and provides tantalum bypass capacitor is needed between the input pin regulator loop stability. The ESR of the output capacitor and and the ground pin, to prevent large voltage transients from the peak−to−peak value of the inductor ripple current are the appearing at the input. It must be located near the regulator main factors contributing to the output ripple voltage value. and use short leads. With most electrolytic capacitors, the Standard aluminium electrolytics could be adequate for capacitance value decreases and the ESR increases with some applications but for quality design, low ESR types are lower temperatures. For reliable operation in temperatures recommended. below −25°C larger values of the input capacitor may be An aluminium electrolytic capacitor’s ESR value is needed. Also paralleling a ceramic or solid tantalum related to many factors such as the capacitance value, the capacitor will increase the regulator stability at cold voltage rating, the physical size and the type of construction. temperatures. In most cases, the higher voltage electrolytic capacitors have lower ESR value. Often capacitors with much higher RMS Current Rating of C in voltage ratings may be needed to provide low ESR values The important parameter of the input capacitor is the RMS that, are required for low output ripple voltage. current rating. Capacitors that are physically large and have large surface area will typically have higher RMS current The Output Capacitor Requires an ESR Value ratings. For a given capacitor value, a higher voltage That Has an Upper and Lower Limit electrolytic capacitor will be physically larger than a lower As mentioned above, a low ESR value is needed for low voltage capacitor, and thus be able to dissipate more heat to output ripple voltage, typically 1% to 2% of the output the surrounding air, and therefore will have a higher RMS voltage. But if the selected capacitor’s ESR is extremely low current rating. The consequence of operating an electrolytic (below 0.05 (cid:3)), there is a possibility of an unstable feedback capacitor beyond the RMS current rating is a shortened loop, resulting in oscillation at the output. This situation can operating life. In order to assure maximum capacitor occur when a tantalum capacitor, that can have a very low operating lifetime, the capacitor’s RMS ripple current rating ESR, is used as the only output capacitor. should be: At Low Temperatures, Put in Parallel Aluminium Irms > 1.2 x d x ILoad Electrolytic Capacitors with Tantalum Capacitors Electrolytic capacitors are not recommended for where d is the duty cycle, for a buck regulator temperatures below −25°C. The ESR rises dramatically at d(cid:2)ton(cid:2)Vout cold temperatures and typically rises 3 times at −25°C and T V as much as 10 times at −40°C. Solid tantalum capacitors in and d(cid:2)ton(cid:2) |Vout| for abuck(cid:6)boost regulator. have much better ESR spec at cold temperatures and are T |Vout| (cid:4) Vin recommended for temperatures below −25°C. They can be also used in parallel with aluminium electrolytics. The value of the tantalum capacitor should be about 10% or 20% of the total capacitance. The output capacitor should have at least 50% higher RMS ripple current rating at 52 kHz than the peak−to−peak inductor ripple current. http://onsemi.com 15

LM2576 Catch Diode ripple voltage. On the other hand it does require larger Locate the Catch Diode Close to the LM2576 inductor values to keep the inductor current flowing The LM2576 is a step−down buck converter; it requires a continuously, especially at low output load currents and/or fast diode to provide a return path for the inductor current high input voltages. when the switch turns off. This diode must be located close To simplify the inductor selection process, an inductor to the LM2576 using short leads and short printed circuit selection guide for the LM2576 regulator was added to this traces to avoid EMI problems. data sheet (Figures 18 through 22). This guide assumes that the regulator is operating in the continuous mode, and Use a Schottky or a Soft Switching selects an inductor that will allow a peak−to−peak inductor Ultra−Fast Recovery Diode Since the rectifier diodes are very significant sources of ripple current to be a certain percentage of the maximum losses within switching power supplies, choosing the design load current. This percentage is allowed to change as rectifier that best fits into the converter design is an different design load currents are selected. For light loads important process. Schottky diodes provide the best (less than approximately 300 mA) it may be desirable to performance because of their fast switching speed and low operate the regulator in the discontinuous mode, because the forward voltage drop. inductor value and size can be kept relatively low. They provide the best efficiency especially in low output Consequently, the percentage of inductor peak−to−peak voltage applications (5.0 V and lower). Another choice current increases. This discontinuous mode of operation is could be Fast−Recovery, or Ultra−Fast Recovery diodes. It perfectly acceptable for this type of switching converter. has to be noted, that some types of these diodes with an Any buck regulator will be forced to enter discontinuous abrupt turnoff characteristic may cause instability or mode if the load current is light enough. EMI troubles. A fast−recovery diode with soft recovery characteristics can better fulfill some quality, low noise design requirements. V DI Table 1 provides a list of suitable diodes for the LM2576 A/ 2.0 A 0 regulator. Standard 50/60 Hz rectifier diodes, such as the Inductor 1. 1N4001 series or 1N5400 series are NOT suitable. Current ON Waveform TI U 0 A L Inductor O S The magnetic components are the cornerstone of all 2.0 A RE Power L switching power supply designs. The style of the core and A Switch C the winding technique used in the magnetic component’s Current TRI R design has a great influence on the reliability of the overall Waveform E V 0 A power supply. Using an improper or poorly designed inductor can cause HORIZONTAL TIME BASE: 5.0 (cid:2)s/DIV high voltage spikes generated by the rate of transitions in Figure 23. Continuous Mode Switching Current current within the switching power supply, and the Waveforms possibility of core saturation can arise during an abnormal operational mode. Voltage spikes can cause the Selecting the Right Inductor Style semiconductors to enter avalanche breakdown and the part Some important considerations when selecting a core type can instantly fail if enough energy is applied. It can also are core material, cost, the output power of the power supply, cause significant RFI (Radio Frequency Interference) and the physical volume the inductor must fit within, and the EMI (Electro−Magnetic Interference) problems. amount of EMI (Electro−Magnetic Interference) shielding Continuous and Discontinuous Mode of Operation that the core must provide. The inductor selection guide The LM2576 step−down converter can operate in both the covers different styles of inductors, such as pot core, E−core, continuous and the discontinuous modes of operation. The toroid and bobbin core, as well as different core materials regulator works in the continuous mode when loads are such as ferrites and powdered iron from different relatively heavy, the current flows through the inductor manufacturers. continuously and never falls to zero. Under light load For high quality design regulators the toroid core seems to conditions, the circuit will be forced to the discontinuous be the best choice. Since the magnetic flux is contained mode when inductor current falls to zero for certain period within the core, it generates less EMI, reducing noise of time (see Figure 23 and Figure 24). Each mode has problems in sensitive circuits. The least expensive is the distinctively different operating characteristics, which can bobbin core type, which consists of wire wound on a ferrite affect the regulator performance and requirements. In many rod core. This type of inductor generates more EMI due to cases the preferred mode of operation is the continuous the fact that its core is open, and the magnetic flux is not mode. It offers greater output power, lower peak currents in contained within the core. the switch, inductor and diode, and can have a lower output http://onsemi.com 16

LM2576 When multiple switching regulators are located on the inductor and/or the LM2576. Different inductor types have same printed circuit board, open core magnetics can cause different saturation characteristics, and this should be kept interference between two or more of the regulator circuits, in mind when selecting an inductor. especially at high currents due to mutual coupling. A toroid, pot core or E−core (closed magnetic structure) should be used in such applications. V DI Do Not Operate an Inductor Beyond its 0.4 A mA/ Maximum Rated Current Inductor 00 Exceeding an inductor’s maximum current rating may Current N 2 Waveform O cause the inductor to overheat because of the copper wire 0 A UTI losses, or the core may saturate. Core saturation occurs when OL the flux density is too high and consequently the cross 0.4 A ES Power R sectional area of the core can no longer support additional L Switch A C lines of magnetic flux. Current TI This causes the permeability of the core to drop, the Waveform ER 0 A V inductance value decreases rapidly and the inductor begins to look mainly resistive. It has only the DC resistance of the HORIZONTAL TIME BASE: 5.0 (cid:2)s/DIV winding. This can cause the switch current to rise very rapidly and force the LM2576 internal switch into Figure 24. Discontinuous Mode Switching Current cycle−by−cycle current limit, thus reducing the DC output Waveforms load current. This can also result in overheating of the GENERAL RECOMMENDATIONS Output Voltage Ripple and Transients Minimizing the Output Ripple Source of the Output Ripple In order to minimize the output ripple voltage it is possible Since the LM2576 is a switch mode power supply to enlarge the inductance value of the inductor L1 and/or to regulator, its output voltage, if left unfiltered, will contain a use a larger value output capacitor. There is also another way sawtooth ripple voltage at the switching frequency. The to smooth the output by means of an additional LC filter (20 output ripple voltage value ranges from 0.5% to 3% of the (cid:2)H, 100 (cid:2)F), that can be added to the output (see Figure 34) output voltage. It is caused mainly by the inductor sawtooth to further reduce the amount of output ripple and transients. ripple current multiplied by the ESR of the output capacitor. With such a filter it is possible to reduce the output ripple voltage transients 10 times or more. Figure 25 shows the Short Voltage Spikes and How to Reduce Them difference between filtered and unfiltered output waveforms The regulator output voltage may also contain short of the regulator shown in Figure 34. voltage spikes at the peaks of the sawtooth waveform (see The lower waveform is from the normal unfiltered output Figure 25). These voltage spikes are present because of the of the converter, while the upper waveform shows the output fast switching action of the output switch, and the parasitic ripple voltage filtered by an additional LC filter. inductance of the output filter capacitor. There are some other important factors such as wiring inductance, stray Heatsinking and Thermal Considerations capacitance, as well as the scope probe used to evaluate these The Through−Hole Package TO−220 transients, all these contribute to the amplitude of these The LM2576 is available in two packages, a 5−pin spikes. To minimize these voltage spikes, low inductance TO−220(T, TV) and a 5−pin surface mount D2PAK(D2T). capacitors should be used, and their lead lengths must be Although the TO−220(T) package needs a heatsink under kept short. The importance of quality printed circuit board most conditions, there are some applications that require no layout design should also be highlighted. heatsink to keep the LM2576 junction temperature within the allowed operating range. Higher ambient temperatures Voltage spikes caused by require some heat sinking, either to the printed circuit (PC) switching action Filtered of the output board or an external heatsink. Output switch and the Voltage parasitic The Surface Mount Package D2PAK and its inductance of the output capacitor Heatsinking ALONV The other type of package, the surface mount D2PAK, is CTIDI designed to be soldered to the copper on the PC board. The UnOfiltuetrpeudt VERTRIRESOLU20 mV/ cthoep poetrh earn dh ethaet pbrooadrdu cairneg t hceo mhepaotsniennkt sf,o rs uthchis apsa ctkhaeg ec aatnchd Voltage diode and inductor. The PC board copper area that the package is soldered to should be at least 0.4 in2 (or 260 mm2) HORIZONTAL TIME BASE: 5.0 (cid:2)s/DIV and ideally should have 2 or more square inches (1300 mm2) Figure 25. Output Ripple Voltage Waveforms of 0.0028 inch copper. Additional increases of copper area http://onsemi.com 17

LM2576 beyond approximately 6.0 in2 (4000 mm2) will not improve Packages on a Heatsink heat dissipation significantly. If further thermal If the actual operating junction temperature is greater than improvements are needed, double sided or multilayer PC the selected safe operating junction temperature determined boards with large copper areas should be considered. In in step 3, than a heatsink is required. The junction order to achieve the best thermal performance, it is highly temperature will be calculated as follows: recommended to use wide copper traces as well as large TJ = PD (R(cid:4)JA + R(cid:4)CS + R(cid:4)SA) + TA areas of copper in the printed circuit board layout. The only exception to this is the OUTPUT (switch) pin, which should where R(cid:4)JC is the thermal resistance junction−case, not have large areas of copper (see page 8 ‘PCB Layout R(cid:4)CS is the thermal resistance case−heatsink, Guideline’). R(cid:4)SA is the thermal resistance heatsink−ambient. If the actual operating temperature is greater than the Thermal Analysis and Design selected safe operating junction temperature, then a larger The following procedure must be performed to determine heatsink is required. whether or not a heatsink will be required. First determine: 1. P maximum regulator power dissipation in the Some Aspects That can Influence Thermal Design D(max) application. It should be noted that the package thermal resistance and 2. T ) maximum ambient temperature in the the junction temperature rise numbers are all approximate, A(max application. and there are many factors that will affect these numbers, 3. T maximum allowed junction temperature such as PC board size, shape, thickness, physical position, J(max) (125°C for the LM2576). For a conservative location, board temperature, as well as whether the design, the maximum junction temperature surrounding air is moving or still. should not exceed 110°C to assure safe Other factors are trace width, total printed circuit copper operation. For every additional +10°C area, copper thickness, single− or double−sided, multilayer temperature rise that the junction must board, the amount of solder on the board or even color of the withstand, the estimated operating lifetime traces. of the component is halved. The size, quantity and spacing of other components on the 4. R(cid:4)JC package thermal resistance junction−case. board can also influence its effectiveness to dissipate the heat. 5. R(cid:4)JA package thermal resistance junction−ambient. 12 to 40 V Feedback (Refer to Maximum Ratings on page 2 of this data sheet or Unregulated R(cid:4)JC and R(cid:4)JA values). DC Input +Vin LM2576−12 4 68L 1(cid:2)H The following formula is to calculate the approximate 1 Output total power dissipated by the LM2576: 100 C(cid:2)iFn 2 3 GN 5 ON/OFF D1 Cout PD = (Vin x IQ) + d x ILoad x Vsat D 1N5822 2200 (cid:2)F where d is the duty cycle and for buck converter −12 V @ 0.7 A d(cid:2)ton(cid:2)VO, ReOguutlpautetd T V in Figure 26. Inverting Buck−Boost Develops −12 V I (quiescent current) and V can be found in the Q sat LM2576 data sheet, ADDITIONAL APPLICATIONS V is minimum input voltage applied, in Inverting Regulator V is the regulator output voltage, O An inverting buck−boost regulator using the LM2576−12 I is the load current. Load is shown in Figure 26. This circuit converts a positive input The dynamic switching losses during turn−on and voltage to a negative output voltage with a common ground turn−off can be neglected if proper type catch diode is used. by bootstrapping the regulators ground to the negative Packages Not on a Heatsink (Free−Standing) output voltage. By grounding the feedback pin, the regulator For a free−standing application when no heatsink is used, senses the inverted output voltage and regulates it. the junction temperature can be determined by the following In this example the LM2576−12 is used to generate a expression: −12 V output. The maximum input voltage in this case TJ = (R(cid:4)JA) (PD) + TA cannot exceed +28 V because the maximum voltage appearing across the regulator is the absolute sum of the where (R(cid:4)JA)(PD) represents the junction temperature rise input and output voltages and this must be limited to a caused by the dissipated power and T is the maximum A maximum of 40 V. ambient temperature. http://onsemi.com 18

LM2576 0.7T Ahi st oc itrhceu oitu ctopnuft iwguhreanti othne iisn apbulte v tool tdaegleiv iesr 1 a2p pVr ooxri hmigatheelry. Ipeak (cid:8) ILoad(VVin (cid:4) |VO|) (cid:4) Vin2Lxton in 1 At lighter loads the minimum input voltage required drops |V | ttoop aoplporgoyx cimana tperloyd 4u.c7e Van, boeuctapuust ev othltea gbeu cthka−tb, oino sitts r aebgsuolalutoter whereton (cid:2) Vin (cid:4)O|VO| x f1o.s0c, and fosc (cid:2) 52kHz. value, is either greater or less than the input voltage. Under normal continuous inductor current operating Since the switch currents in this buck−boost configuration conditions, the worst case occurs when V is minimal. in are higher than in the standard buck converter topology, the available output current is lower. 12 V to 25 V This type of buck−boost inverting regulator can also Unregulated Feedback require a larger amount of startup input current, even for DC Input +Vin 4 L1 LM2576−12 68 (cid:2)H light loads. This may overload an input power source with Cin 1 Output a current limit less than 5.0 A. 100 (cid:2)F C1 2 /50 V 0.1 (cid:2)F 5 ON/OFF3 GN Such an amount of input startup current is needed for at D D1 Cout least 2.0 ms or more. The actual time depends on the output R1 1N5822 2200 (cid:2)F voltage and size of the output capacitor. 47 k R2 /16 V Because of the relatively high startup currents required by 47 k this inverting regulator topology, the use of a delayed startup −12 V @ 700 m A or an undervoltage lockout circuit is recommended. Regulated Using a delayed startup arrangement, the input capacitor Output can charge up to a higher voltage before the switch−mode Figure 27. Inverting Buck−Boost Regulator regulator begins to operate. with Delayed startup The high input current needed for startup is now partially supplied by the input capacitor C . in It has been already mentioned above, that in some +Vin +Vin situations, the delayed startup or the undervoltage lockout LM2576−XX 1 features could be very useful. A delayed startup circuit applied to a buck−boost converter is shown in Figure 27, Cin R1 100 (cid:2)F 47 k Figure 33 in the “Undervoltage Lockout” section describes Shutdown 5 ON/OFF 3 GN an undervoltage lockout feature for the same converter Input D 5.0 V topology. Off 0 R3 Design Recommendations: On 470 R2 The inverting regulator operates in a different manner 47 k than the buck converter and so a different design procedure −Vout has to be used to select the inductor L1 or the output MOC8101 capacitor C . out The output capacitor values must be larger than what is NOTE: This picture does not show the complete circuit. normally required for buck converter designs. Low input voltages or high output currents require a large value output Figure 28. Inverting Buck−Boost Regulator Shutdown capacitor (in the range of thousands of (cid:2)F). Circuit Using an Optocoupler The recommended range of inductor values for the inverting converter design is between 68 (cid:2)H and 220 (cid:2)H. To With the inverting configuration, the use of the ON/OFF select an inductor with an appropriate current rating, the pin requires some level shifting techniques. This is caused inductor peak current has to be calculated. by the fact, that the ground pin of the converter IC is no The following formula is used to obtain the peak inductor longer at ground. Now, the ON/OFF pin threshold voltage current: (1.3 V approximately) has to be related to the negative output voltage level. There are many different possible shut down methods, two of them are shown in Figures 28 and 29. http://onsemi.com 19

LM2576 +V Shutdown Another important point is that these negative boost Off Input converters cannot provide current limiting load protection in 0 On the event of a short in the output so some other means, such R2 as a fuse, may be necessary to provide the load protection. 5.6 k +Vin +Vin Delayed Startup 1 There are some applications, like the inverting regulator LM2576−XX Cin already mentioned above, which require a higher amount of 100 (cid:2)F startup current. In such cases, if the input power source is Q1 limited, this delayed startup feature becomes very useful. 2N3906 5 ON/OFF 3 GN D To provide a time delay between the time when the input voltage is applied and the time when the output voltage R1 12 k −Vout comes up, the circuit in Figure 31 can be used. As the input voltage is applied, the capacitor C1 charges up, and the voltage across the resistor R2 falls down. When the voltage NOTE: This picture does not show the complete circuit. on the ON/OFF pin falls below the threshold value 1.3 V, the Figure 29. Inverting Buck−Boost Regulator Shutdown regulator starts up. Resistor R1 is included to limit the Circuit Using a PNP Transistor maximum voltage applied to the ON/OFF pin. It reduces the power supply noise sensitivity, and also limits the capacitor Negative Boost Regulator C1 discharge current, but its use is not mandatory. This example is a variation of the buck−boost topology When a high 50 Hz or 60 Hz (100 Hz or 120 Hz and it is called negative boost regulator. This regulator respectively) ripple voltage exists, a long delay time can experiences relatively high switch current, especially at low cause some problems by coupling the ripple into the input voltages. The internal switch current limiting results in ON/OFF pin, the regulator could be switched periodically lower output load current capability. on and off with the line (or double) frequency. The circuit in Figure 30 shows the negative boost configuration. The input voltage in this application ranges from −5.0 V to −12 V and provides a regulated −12 V output. If the input voltage is greater than −12 V, the output will rise +Vin +Vin LM2576−XX above −12 V accordingly, but will not damage the regulator. 1 C1 0.1 (cid:2)F 5 ON/OFF 3 GN D Cin Cout 100 (cid:2)F 4 2200 (cid:2)F R1 Vin LM2576−12 Feedback Low Esr 47 k R472 k 1 Output 100 C(cid:2)iFn 3 GND 5 ON/O2FF 1N5820 NOTE: This picture does not show the complete circuit. Vout = −12 V Figure 31. Delayed Startup Circuitry Typical Load Current Vin 100 (cid:2)H 400 mA for Vin = −5.2 V Undervoltage Lockout 750 mA for Vin = −7.0 V Some applications require the regulator to remain off until −5.0 V to −12 V the input voltage reaches a certain threshold level. Figure 32 Figure 30. Negative Boost Regulator shows an undervoltage lockout circuit applied to a buck regulator. A version of this circuit for buck−boost converter Design Recommendations: is shown in Figure 33. Resistor R3 pulls the ON/OFF pin The same design rules as for the previous inverting high and keeps the regulator off until the input voltage buck−boost converter can be applied. The output capacitor reaches a predetermined threshold level with respect to the Cout must be chosen larger than would be required for a what ground Pin 3, which is determined by the following standard buck converter. Low input voltages or high output expression: currents require a large value output capacitor (in the range (cid:3) (cid:5) of thousands of (cid:2)F). The recommended range of inductor Vth(cid:8)VZ1(cid:4) 1.0(cid:4)RR21 VBE(Q1) values for the negative boost regulator is the same as for inverting converter design. http://onsemi.com 20

LM2576 Under normal continuous inductor current operating conditions, the worst case occurs when V is minimal. +Vin +Vin in LM2576−XX 1 10R 2k 47R 3k C10in0 (cid:2)F 5 ON/OFF 3 GN +Vin +Vin LM2576−XX D 1 Z1 R2 R3 Cin 1N5242B 15 k 47 k 100 (cid:2)F 5 ON/OFF 3 GN D Q1 2N3904 Z1 10R 1k Vth ≈ 13 V 1N5242B Vth ≈ 13 V Q1 2N3904 R1 NOTE: This picture does not show the complete circuit. 15 k Vout Figure 32. Undervoltage Lockout Circuit for Buck Converter NOTE: This picture does not show the complete circuit. The following formula is used to obtain the peak inductor Figure 33. Undervoltage Lockout Circuit for current: Buck−Boost Converter I (cid:8) ILoad(Vin (cid:4) |VO|) (cid:4) Vinxton Adjustable Output, Low−Ripple Power Supply peak V 2L in 1 A 3.0 A output current capability power supply that |V | whereton (cid:2) Vin (cid:4)O|VO| x f1o.s0c, and fosc (cid:2) 52kHz. feaTtuhrise sr eagnu aldatjours tdaeblliev oerust p3u.0t vAo ltiangtoe 1is. 2s hVow ton 3in5 FVig ouuretp 3u4t.. The input voltage ranges from roughly 3.0 V to 40 V. In order to achieve a 10 or more times reduction of output ripple, an additional L−C filter is included in this circuit. 40 V Max Feedback Unregulated 4 DC Input +Vi1n LM2574−Adj Output 150L1 (cid:2)H 20L 2(cid:2)H VOoulttapguet 2 1.2 to 35 V @ 3.0 A Cin 3 GN 5 ON/OFF R2 100 (cid:2)F D 50 k D1 Cout C1 1N5822 2200 (cid:2)F 100 (cid:2)F R1 1.21 k Optional Output Ripple Filter Figure 34. 1.2 to 35 V Adjustable 3.0 A Power Supply with Low Output Ripple http://onsemi.com 21

LM2576 THE LM2576−5 STEP−DOWN VOLTAGE REGULATOR WITH 5.0 V @ 3.0 A OUTPUT POWER CAPABILITY. TYPICAL APPLICATION WITH THROUGH−HOLE PC BOARD LAYOUT Feedback 4 Unregulated +Vin L1 LM2576−5 +Vin = 7.0D Cto I4n0p uVt 1 Output 150 (cid:2)H Regulated Output 2 Vout1 = 5.0 V @ 3.0 A 3 GN 5 ON/OFF D C1 100 (cid:2)F ON/OFF D1 Cout /50 V 1N5822 1000 (cid:2)F /16 V GNDin GNDout C1 − 100 (cid:2)F, 50 V, Aluminium Electrolytic C2 − 1000 (cid:2)F, 16 V, Aluminium Electrolytic D1 − 3.0 A, 40 V, Schottky Rectifier, 1N5822 L1 − 150 (cid:2)H, RL2444, Renco Electronics Figure 35. Schematic Diagram of the LM2576−5 Step−Down Converter LM2576 0 0 _ 0 6 0 0 0 U1 D1 + C2 C1 Vou + t ON/OFF +Vin L1 GND- GNDout in NOTE: Not to scale. NOTE: Not to scale. Figure 36. Printed Circuit Board Layout Figure 37. Printed Circuit Board Layout Component Side Copper Side http://onsemi.com 22

LM2576 THE LM2576−ADJ STEP−DOWN VOLTAGE REGULATOR WITH 8.0 V @ 1.0 A OUTPUT POWER CAPABILITY. TYPICAL APPLICATION WITH THROUGH−HOLE PC BOARD LAYOUT 4 Feedback Unregulated DC Input +Vin L1 +Vin = 10 V to 40 V 1 LM2576−ADJ Output 150 (cid:2)H ROeugtpuulat t eFdiltered 2 R2 Vout2 = 8.0 V @ 3.0 A 3 GN 5 ON/OFF 10 k D C1 100 (cid:2)F D1 C2 /50 V 1N5822 1000 (cid:2)F R1 ON/OFF /16 V 1.8 k (cid:3) (cid:5) V (cid:2)V (cid:4) 1.0(cid:4)R2 out ref R1 C1 − 100 (cid:2)F, 50 V, Aluminium Electrolytic Vref = 1.23 V C2 − 1000 (cid:2)F, 16 V, Aluminium Electrolytic R1 is between 1.0 k and 5.0 k D1 − 3.0 A, 40 V, Schottky Rectifier, 1N5822 L1 − 150 (cid:2)H, RL2444, Renco Electronics R1 − 1.8 k(cid:3), 0.25 W R2 − 10 k(cid:3), 0.25 W Figure 38. Schematic Diagram of the 8.0 V @ 3.0 A Step−Down Converter Using the LM2576−ADJ 0 LM2576 0 _ 9 5 0 0 0 U1 D1 R1 R2 ON/OFF C1 + + C2 Vout +Vin L1 GNDin GNDout NOTE: Not to scale. NOTE: Not to scale. Figure 39. Printed Circuit Board Layout Figure 40. Printed Circuit Board Layout Component Side Copper Side References • National Semiconductor LM2576 Data Sheet and Application Note • National Semiconductor LM2595 Data Sheet and Application Note • Marty Brown “Practical Switching Power Supply Design”, Academic Press, Inc., San Diego 1990 • Ray Ridley “High Frequency Magnetics Design”, Ridley Engineering, Inc. 1995 http://onsemi.com 23

LM2576 ORDERING INFORMATION Nominal Operating Device Output Voltage Temperature Range Package Shipping† LM2576TV−ADJ TO−220 (Vertical Mount) LM2576TV−ADJG TO−220 (Vertical Mount) (Pb−Free) LM2576T−ADJ TO−220 (Straight Lead) LM2576T−ADJG TO−220 (Straight Lead) 50 Units/Rail (Pb−Free) LM2576D2T−ADJ 1.23 V to 37 V TJ = −40° to +125°C D2PAK (Surface Mount) LM2576D2T−ADJG D2PAK (Surface Mount) (Pb−Free) LM2576D2T−ADJR4 D2PAK (Surface Mount) LM2576D2T−ADJR4G D2PAK (Surface Mount) 2500 Tape & Reel (Pb−Free) LM2576TV−3.3 TO−220 (Vertical Mount) LM2576TV−3.3G TO−220 (Vertical Mount) (Pb−Free) LM2576T−3.3 TO−220 (Straight Lead) LM2576T−3.3G TO−220 (Straight Lead) 50 Units/Rail (Pb−Free) LM2576D2T−3.3 3.3 V TJ = −40° to +125°C D2PAK (Surface Mount) LM2576D2T−3.3G D2PAK (Surface Mount) (Pb−Free) LM2576D2TR4−3.3 D2PAK (Surface Mount) LM2576D2TR4−3.3G D2PAK (Surface Mount) 2500 Tape & Reel (Pb−Free) LM2576TV−005 TO−220 (Vertical Mount) LM2576TV−5G TO−220 (Vertical Mount) (Pb−Free) LM2576T−005 TO−220 (Straight Lead) LM2576T−005G TO−220 (Straight Lead) 50 Units/Rail (Pb−Free) LM2576D2T−005 5.0 V TJ = −40° to +125°C D2PAK (Surface Mount) LM2576D2T−005G D2PAK (Surface Mount) (Pb−Free) LM2576D2TR4−005 D2PAK (Surface Mount) LM2576D2TR4−5G D2PAK (Surface Mount) 2500 Tape & Reel (Pb−Free) LM2576TV−012 TO−220 (Vertical Mount) LM2576TV−012G TO−220 (Vertical Mount) (Pb−Free) LM2576T−012 TO−220 (Straight Lead) LM2576T−012G TO−220 (Straight Lead) 50 Units/Rail (Pb−Free) LM2576D2T−012 12 V TJ = −40° to +125°C D2PAK (Surface Mount) LM2576D2T−012G D2PAK (Surface Mount) (Pb−Free) LM2576D2TR4−012 D2PAK (Surface Mount) LM2576D2TR4−012G D2PAK (Surface Mount) 2500 Tape & Reel (Pb−Free) †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. http://onsemi.com 24

LM2576 ORDERING INFORMATION Nominal Operating Device Output Voltage Temperature Range Package Shipping† LM2576TV−015 TO−220 (Vertical Mount) LM2576TV−015G TO−220 (Vertical Mount) (Pb−Free) LM2576T−015 TO−220 (Straight Lead) LM2576T−15G 15 V TJ = −40° to +125°C TO−220 (Straight Lead) 50 Units/Rail (Pb−Free) LM2576D2T−015 D2PAK (Surface Mount) LM2576D2T−15G D2PAK (Surface Mount) (Pb−Free) †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. MARKING DIAGRAMS TO−220 TO−220 D2PAK TV SUFFIX T SUFFIX D2T SUFFIX CASE 314B CASE 314D CASE 936A LM LM LM LM 2576−xxx 2576D2T−xxx 2576T−xxx 2576T−xxx AWLYWWG AWLYWWG AWLYWWG AWLYWWG 1 5 1 5 1 5 1 5 xxx = 3.3, 5.0, 12, 15, or ADJ A = Assembly Location WL = Wafer Lot Y = Year WW= Work Week G = Pb−Free Package http://onsemi.com 25

LM2576 PACKAGE DIMENSIONS TO−220 TV SUFFIX CASE 314B−05 ISSUE L B C NOTES: 1. DIMENSIONING AND TOLERANCING PER ANSI Q −P− OCHPATIMOFNEARL E 2. YC1O4N.5TMR,O 1L9L8I2N.G DIMENSION: INCH. 3. DIMENSION D DOES NOT INCLUDE INTERCONNECT BAR (DAMBAR) PROTRUSION. DIMENSION D INCLUDING PROTRUSION SHALL NOT EXCEED 0.043 (1.092) MAXIMUM. A U INCHES MILLIMETERS S L W V DIM MIN MAX MIN MAX A 0.572 0.613 14.529 15.570 K F B 0.390 0.415 9.906 10.541 C 0.170 0.180 4.318 4.572 D 0.025 0.038 0.635 0.965 E 0.048 0.055 1.219 1.397 F 0.850 0.935 21.590 23.749 G 0.067 BSC 1.702 BSC H 0.166 BSC 4.216 BSC 5X J KJ 00..091050 01..012050 202..388610 207..693450 G 0.24 (0.610)M T H L 0.320 0.365 8.128 9.271 5X D QN 0.104.3020 B0S.C153 3.585.1628 B3S.C886 0.10 (0.254)M T P M N S −−− 0.620 −−− 15.748 U 0.468 0.505 11.888 12.827 −T− SPELAATNIENG WV 0.0−9−−0 00..711305 2.2−8−−6 128..769649 TO−220 T SUFFIX CASE 314D−04 ISSUE F −T− SEATING NOTES: PLANE 1.DIMENSIONING AND TOLERANCING PER ANSI B Y14.5M, 1982. −Q− DETAIL A−A C 2.CONTROLLING DIMENSION: INCH. B1 E 3.DIMENSION D DOES NOT INCLUDE INTERCONNECT BAR (DAMBAR) PROTRUSION. DIMENSION D INCLUDING PROTRUSION SHALL NOT EXCEED 10.92 (0.043) MAXIMUM. U A INCHES MILLIMETERS L DIM MIN MAX MIN MAX 12345 A 0.572 0.613 14.529 15.570 K B 0.390 0.415 9.906 10.541 B1 0.375 0.415 9.525 10.541 C 0.170 0.180 4.318 4.572 D 0.025 0.038 0.635 0.965 E 0.048 0.055 1.219 1.397 G 0.067 BSC 1.702 BSC J H 0.087 0.112 2.210 2.845 G H J 0.015 0.025 0.381 0.635 D 5 PL KL 00..937270 10..034655 284..182180 296..257413 0.356 (0.014)M T Q M Q 0.140 0.153 3.556 3.886 U 0.105 0.117 2.667 2.972 B B1 DETAIL A−A http://onsemi.com 26

LM2576 PACKAGE DIMENSIONS D2PAK D2T SUFFIX CASE 936A−02 ISSUE C −T− TERMINAL 6 N1O.TDEISM:ENSIONING AND TOLERANCING PER ANSI A OCHPATIMOFNEARL E U 2. YC1O4N.5TMR,O 1L9L8I2N.G DIMENSION: INCH. 3. TAB CONTOUR OPTIONAL WITHIN DIMENSIONS A AND K. K S 4. DIMENSIONS U AND V ESTABLISH A MINIMUM V MOUNTING SURFACE FOR TERMINAL 6. B 5. DIMENSIONS A AND B DO NOT INCLUDE MOLD H FLASH OR GATE PROTRUSIONS. MOLD FLASH 1 2 3 4 5 AND GATE PROTRUSIONS NOT TO EXCEED 0.025 M L (0.635) MAXIMUM. INCHES MILLIMETERS D DIM MIN MAX MIN MAX N P A 0.386 0.403 9.804 10.236 0.010 (0.254) M T G R B 0.356 0.368 9.042 9.347 C 0.170 0.180 4.318 4.572 D 0.026 0.036 0.660 0.914 E 0.045 0.055 1.143 1.397 G 0.067 BSC 1.702 BSC H 0.539 0.579 13.691 14.707 K 0.050 REF 1.270 REF C L 0.000 0.010 0.000 0.254 M 0.088 0.102 2.235 2.591 N 0.018 0.026 0.457 0.660 P 0.058 0.078 1.473 1.981 R 5 (cid:2) REF 5 (cid:2) REF S 0.116 REF 2.946 REF U 0.200 MIN 5.080 MIN V 0.250 MIN 6.350 MIN SOLDERING FOOTPRINT* 8.38 0.33 1.702 0.067 10.66 0.42 1.016 3.05 0.04 0.12 16.02 0.63 (cid:3) (cid:5) mm SCALE 3:1 inches *For additional information on our Pb−Free strategy and soldering details, please download the ON Semiconductor Soldering and Mounting Techniques Reference Manual, SOLDERRM/D. http://onsemi.com 27

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