LM2576S-3.3/TR

LM2576-XX LM2576 Series SIMPLE SWITCHER 3A Step-Down Voltage Regulator General Description Features The LM2576 series of regulators are monolithic integrated circuits that provide all the active functions for a step-down (buck) switching regulator, capable of driving 3A load with excellent line and load regulation. These devices are availableinfixedoutputvoltagesof3.3V,5V,12V,andan adjustable output version. Requiring a minimum number of external components, these regulators are simple to use and include internal frequency compensation and a fixed-frequency oscillator. The LM2576 series offers a high-efficiency replacement for popular three-terminal linear regulators. It substantially reduces the size of the heat sink, and in some cases no heat sink is required. A standard series of inductors optimized for use with the LM2576 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies. Other features include a guaranteed ± 4% tolerance on output voltage within specified input voltages and output load conditions, and ± 10% on the oscillator frequency. External shutdown is included, featuring 50 µA (typical) standby current. The output switch includes cycle-by-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. n 3.3V,5V,12V,andadjustableoutputversions n Adjustable version output voltage range, 1.23Vto37V ± 4% max over line and load conditions n Guaranteed 3A output current n Wideinputvoltagerange,40V Typical Application n n n n n n n 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 n n n n Simple high-efficiency step-down (buck) regulator Efficient pre-regulator for linear regulators On-card switching regulators Positive to negative converter (Buck-Boost) (Fixed Output Voltage Versions) FIGURE 1. http://www.hgsemi.com.cn 1 2018 AUG LM2576-XX Block Diagram 01147602 3.3V R2 = 1.7k 5V, R2 = 3.1k For ADJ. Version 12V, R2 = 8.84k R1 = Open, R2 = 0Ω 15V, R2 = 11.3k Patent Pending Absolute Maximum Ratings (Note 1) Minimum ESD Rating If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Lead Temperature (C = 100 pF, R = 1.5 kΩ) (Soldering, 10 Seconds) 2 kV 260˚C Maximum Supply Voltage LM2576 ON /OFF Pin Input Voltage Operating Ratings 45V Temperature Range −0.3V ≤ V ≤ +VIN LM2576 Output Voltage to Ground (Steady State) −1V Power Dissipation Internally Limited Storage Temperature Range −65˚C to +150˚C Maximum Junction Temperature http://www.hgsemi.com.cn −40˚C ≤ TJ ≤ +125˚C Supply Voltage LM2576 40V 150˚C 2 2018 AUG LM2576-XX LM2576-3.3 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 LM2576-3.3 Typ Limit Units (Limits) (Note 2) SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2 VOUT Output Voltage VIN = 12V, ILOAD = 0.5A 3.3 V Circuit of Figure 2 VOUT η Output Voltage 6V ≤ VIN ≤ 40V, 0.5A ≤ ILOAD ≤ 3A LM2576 Circuit of Figure 2 Efficiency 3.234 V(Min) 3.366 V(Max) 3.168/3.135 V(Min) 3.432/3.465 V(Max) 3.3 VIN = 12V, ILOAD = 3A V 75 % LM2576-5.0 Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those with Figure 2 boldface type apply over full Operating Temperature Range. Symbol Parameter Conditions LM2576-5.0 Typ Units (Limits) Limit (Note 2) SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2 VOUT Output Voltage VIN = 12V, ILOAD = 0.5A 5.0 Circuit of Figure 2 VOUT Output Voltage LM2576 http://www.hgsemi.com.cn 0.5A ≤ ILOAD ≤ 3A, V 4.900 V(Min) 5.100 V(Max) 5.0 V 8V ≤ VIN ≤ 40V 4.800/4.750 V(Min) Circuit of Figure 2 5.200/5.250 V(Max) 3 2018 AUG LM2576-XX LM2576-5.0 Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those with Figure 2 boldface type apply over full Operating Temperature Range. Symbol Parameter Conditions LM2576-5.0 Typ Units (Limits) Limit (Note 2) SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2 η Efficiency VIN = 12V, ILOAD = 3A 77 % LM2576-12 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 LM2576-12 Typ Units (Limits) Limit (Note 2) SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2 VOUT Output Voltage VIN = 25V, ILOAD = 0.5A 12 Circuit of Figure 2 VOUT η V 11.76 V(Min) 12.24 V(Max) Output Voltage 0.5A ≤ ILOAD ≤ 3A, LM2576 15V ≤ VIN ≤ 40V 11.52/11.40 V(Min) Circuit of Figure 2 12.48/12.60 V(Max) Efficiency http://www.hgsemi.com.cn VIN = 15V, ILOAD = 3A 4 12 88 V % 2018 AUG LM2576-XX Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating Temperature Range. Symbol Parameter Conditions LM2576-ADJ Typ Units (Limits) Limit (Note 2) SYSTEM PARAMETERS (Note 3) Test Circuit Figure 2 VOUT VOUT η Feedback Voltage VIN = 12V, ILOAD = 0.5A 1.230 V VOUT = 5V, 1.217 V(Min) Circuit of Figure 2 1.243 V(Max) Feedback Voltage 0.5A ≤ ILOAD ≤ 3A, LM2576 8V ≤ VIN ≤ 40V 1.193/1.180 V(Min) VOUT = 5V, Circuit of Figure 2 1.267/1.280 V(Max) Efficiency 1.230 VIN = 12V, ILOAD = 3A, VOUT = 5V V 77 % All Output Voltage Versions Electrical Characteristics Specifications with standard type face are for TJ = 25˚C, and those with boldface type apply over full Operating 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 = 500 mA. Symbol Parameter Conditions LM2576-XX Typ Units (Limits) Limit (Note 2) DEVICE PARAMETERS Ib Feedback Bias Current VOUT = 5V (Adjustable Version Only) 50 fO Oscillator Frequency (Note 11) 52 VSAT Saturation Voltage IOUT = 3A (Note 4) Max Duty Cycle (ON) (Note 5) 98 ICL Current Limit (Notes 4, 11) 5.8 Output Leakage Current (Notes 6, 7): Output = 0V Output = −1V IQ Quiescent Current (Note 6) 5 ISTBY Standby Quiescent ON /OFF Pin = 5V (OFF) 50 Current http://www.hgsemi.com.cn 5 47/42 kHz (Min) 58/63 kHz (Max) 1.8/2.0 V(Max) V % 93 %(Min) 4.2/3.5 A(Min) A 6.9/7.5 A(Max) 2 mA(Max) 30 mA(Max) 7.5 Output = −1V nA kHz 1.4 DC IL 100/500 mA mA 10 mA(Max) 200 µA(Max) µA 2018 AUG LM2576-XX 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 = 500 mA. Symbol Parameter Conditions LM2576-XX Typ Units (Limits) Limit (Note 2) DEVICE PARAMETERS θJA T Package, Junction to Ambient (Note 8) 65 θJA Thermal Resistance T Package, Junction to Ambient (Note 9) 45 θJC T Package, Junction to Case 2 θJA S Package, Junction to Ambient (Note 10) 50 ˚C/W ON /OFF CONTROL Test Circuit Figure 2 VIH ON /OFF Pin VOUT = 0V 1.4 2.2/2.4 V(Min) VIL Logic Input Level VOUT = Nominal Output Voltage 1.2 1.0/0.8 V(Max) IIH ON /OFF Pin Input ON /OFF Pin = 5V (OFF) 12 ON /OFF Pin = 0V (ON) 0 Current IIL µA 30 µA(Max) 10 µA(Max) µA 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 room temperature limits are 100% production tested. All limits at temperature extremes are guaranteed via correlation using standard Statistical Quality Control (SQC) methods. Note 3: External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the Figure 2 test circuit, system performance will be as shown in system parameters section of Electrical Characteristics. LM2576 isusedasshowninthe Note 4: Output pin sourcing current. No diode, inductor or capacitor connected to output. Note 5: Feedback pin removed from output and connected to 0V. Note 6: Feedback pin removed from output and connected to +12V for the Adjustable, 3.3V, and 5V versions, and +25V for the 12V and 15V versions, to force the output transistor OFF. Note 7: VIN = 40V (60V for high voltage version). Note 8: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with 1⁄2 inch leads in a socket, or on a PC board with minimum copper area. Note 9: Junction to ambient thermal resistance (no external heat sink) for the 5 lead TO-220 package mounted vertically, with 1⁄4 inch leads soldered to a PC board containing approximately 4 square inches of copper area surrounding the leads. Note 10: 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 11: The oscillator frequency reduces to approximately 11 kHz in the event of an output short or an overload which causes the regulated output voltage to drop approximately 40% from the nominal output voltage. This self protection feature lowers the average power dissipation of the IC by lowering the minimum duty cycle from 5% down to approximately 2%. Typical Performance Characteristics (Circuit of Figure 2) Normalized Output Voltage http://www.hgsemi.com.cn Line Regulation 6 2018 AUG LM2576-XX Typical Performance Characteristics (Circuit of Figure 2) Dropout Voltage (Continued) Current Limit 01147630 01147629 Standby Quiescent Current Quiescent Current 01147631 01147632 Switch Saturation Voltage Oscillator Frequency 01147634 01147633 http://www.hgsemi.com.cn 7 2018 AUG LM2576-XX Typical Performance Characteristics (Circuit of Figure 2) Efficiency (Continued) Minimum Operating Voltage 01147635 01147636 Quiescent Current vs Duty Cycle Feedback Voltage vs Duty Cycle 01147637 01147638 Quiescent Current vs Duty Cycle Minimum Operating Voltage 01147636 http://www.hgsemi.com.cn 01147637 8 2018 AUG LM2576-XX LM2576 Series Buck Regulator Design Procedure (Continued) INDUCTOR VALUE SELECTION GUIDES (For Continuous Mode Operation) DS011476-9 FIGURE 3. LM2576(HV)-3.3 DS011476-11 FIGURE 5. LM2576(HV)-12 DS011476-10 FIGURE 4. LM2576(HV)-5.0 FIGURE 7. LM2576(HV)-ADJ http://www.hgsemi.com.cn 9 2018 AUG LM2576-XX 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. Test Circuit and Layout Guidelines As in any switching regulator, layout is very important. Rapidly switching currents associated with wiring inductance generate voltage transients which can cause problems. For minimal inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible. Fixed Output Voltage Versions 01147607 CIN — 100 µF, 75V, Aluminum Electrolytic COUT — 1000 µF, 25V, Aluminum Electrolytic D1 — Schottky, MBR360 L1 — 100 µH, Pulse Eng. PE-92108 R1 — 2k, 0.1% R2 — 6.12k, 0.1% Adjustable Output Voltage Version 01147608 where VREF = 1.23V, R1 between 1k and 5k. FIGURE 2. http://www.hgsemi.com.cn 10 2018 AUG LM2576-XX LM2576 Series Buck Regulator Design Procedure PROCEDURE (Adjustable Output Voltage Versions) EXAMPLE (Adjustable Output Voltage Versions) 2. Inductor Selection (L1) A. Calculate E • T (V • µs) 2. Inductor Selection (L1) A. Calculate the inductor Volt • microsecond constant, E • T (V • µs), from the following formula: B. E • T = 115 V • µs C. ILOAD(Max) = 3A D. Inductance Region = H150 E. Inductor Value = 150 µH Choose from AIE part #415-0936 Pulse Engineering part #PE-531115, or Renco part #RL2445. B. Use the E • T value from the previous formula and match it with the E • T number on the vertical axis of the Inductor Value Selection Guide shown in Figure 7. 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 LM2576 switching frequency (52 kHz) and for a current rating of 1.15 x ILOAD. For additional inductor information, see the inductor section in the application hints section of this data sheet. 3. Output Capacitor Selection (COUT) 3. Output Capacitor Selection (COUT) A. The value of the output capacitor together with the inductor defines the dominate pole-pair of the switching regulator loop. For stable operation, the capacitor must satisfy the following requirement: However, for acceptable output ripple voltage select COUT ≥ 680 µF COUT = 680 µF electrolytic capacitor The above formula yields capacitor values between 10 µF and 2200 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 capacitor rate for a higher voltage than would normally be needed. 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 LM2576. 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 3.3A current rating is adequate. B. Use a 30V 31DQ03 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 http://www.hgsemi.com.cn switching regulators. Switchers Made Simple (Version 3.3) is available on a (31⁄2") diskette for IBM compatible computers from a National Semiconductor sales office in your area. 11 2018 AUG LM2576-XX Additional Applications The switch currents in this buck-boost configuration are higher than in the standard buck-mode design, thus lowering the available output current. Also, the start-up input current of the buck-boost converter is higher than the standard buck-mode regulator, and this may overload an input power source with a current limit less than 5A. Using a delayed turn-on or an undervoltage lockout circuit (described in the next section) would allow the input voltage to rise to a high enough level before the switcher would be allowed to turn on. Because of the structural differences between the buck and the buck-boost regulator topologies, the buck regulator design procedure section can not be used to to select the inductor or the output capacitor. The recommended range of inductor values for the buck-boost design is between 68 µH and 220 µH, and the output capacitor values must be larger than what is normally required for buck designs. Low input voltages or high output currents require a large value output capacitor (in the thousands of micro Farads). The peak inductor current, which is the same as the peak switch current, can be calculated from the following formula: 01147615 Typical Load Current 400 mA for VIN = −5.2V 750 mA for VIN = −7V Note: Heat sink may be required. FIGURE 11. Negative Boost Because of the boosting function of this type of regulator, the switch current is relatively high, especially at low input voltages. Output load current limitations are a result of the maximum current rating of the switch. Also, boost regulators can not provide current limiting load protection in the event of a shorted load, so some other means (such as a fuse) may be necessary. Where fosc = 52 kHz. Under normal continuous inductor current operating conditions, the minimum VIN represents the worst case. Select an inductor that is rated for the peak current anticipated. UNDERVOLTAGE LOCKOUT In some applications it is desirable to keep the regulator off until the input voltage reaches a certain threshold. An undervoltage lockout circuit which accomplishes this task is shown in Figure 12, while Figure 13 shows the same circuit applied to a buck-boost configuration. These circuits keep the regulator off until the input voltage reaches a predetermined level. VTH ≈ VZ1 + 2VBE(Q1) 01147614 FIGURE 10. Inverting Buck-Boost Develops −12V Also, the maximum voltage appearing across the regulator is the absolute sum of the input and output voltage. For a −12V output, the maximum input voltage for the LM2576 is +28V, or +48V for the LM2576HV. The Switchers Made Simple (version 3.0) design software can be used to determine the feasibility of regulator designs using different topologies, different input-output parameters, different components, etc. 01147616 Note: Complete circuit not shown. NEGATIVE BOOST REGULATOR Another variation on the buck-boost topology is the negative boost configuration. The circuit in Figure 11 accepts an input voltage ranging from −5V to −12V and provides a regulated −12V output. Input voltages greater than −12V will cause the output to rise above −12V, but will not damage the regulator. http://www.hgsemi.com.cn FIGURE 12. Undervoltage Lockout for Buck Circuit 12 2018 AUG LM2576-XX Additional Applications ing. Increasing the RC time constant can provide longer delay times. But excessively large RC time constants can cause problems with input voltages that are high in 60 Hz or 120 Hz ripple, by coupling the ripple into the ON /OFF pin. ADJUSTABLE OUTPUT, LOW-RIPPLE POWER SUPPLY A 3A power supply that features an adjustable output voltage is shown in Figure 15. An additional L-C filter that reduces the output ripple by a factor of 10 or more is included in this circuit. 01147617 Note: Complete circuit not shown (see Figure 10). FIGURE 13. Undervoltage Lockout for Buck-Boost Circuit DELAYED STARTUP The ON /OFF pin can be used to provide a delayed startup feature as shown in Figure 14. With an input voltage of 20V and for the part values shown, the circuit provides approximately 10 ms of delay time before the circuit begins switch- Note: Complete circuit not shown. FIGURE 14. Delayed Startup FIGURE15.1.2Vto37V Adjustable3APowerSupplywithLowOutputRipple Definition of Terms BUCK REGULATOR A switching regulator topology in which a higher voltage is converted to a lower voltage. Also known as a step-down switching regulator. CATCH DIODE OR CURRENT STEERING DIODE BUCK-BOOST REGULATOR A switching regulator topology in which a positive voltage is converted to a negative voltage without a transformer. The diode which provides a return path for the load current when the LM2576 switch is OFF. EFFICIENCY (η) The proportion of input power actually delivered to the load. DUTY CYCLE (D) Ratio of the output switch’s on-time to the oscillator period. http://www.hgsemi.com.cn 13 2018 AUG LM2576-XX Definition of Terms CAPACITOR EQUIVALENT SERIES RESISTANCE (ESR) The purely resistive component of a real capacitor’s impedance (see Figure 16). It causes power loss resulting in capacitor heating, which directly affects the capacitor’s operating lifetime. When used as a switching regulator output filter, higher ESR values result in higher output ripple voltages. Connection Diagrams Straight Leads 5-Lead TO-220 (T) Top View 01147621 LM2576T-XX 01147620 NS Package Number T05A FIGURE 16. Simple Model of a Real Capacitor Most standard aluminum electrolytic capacitors in the 100 µF–1000 µF range have 0.5Ω to 0.1Ω ESR. Highergrade capacitors (“low-ESR”, “high-frequency”, or “lowinductance”) in the 100 µF–1000 µF range generally have ESR of less than 0.15Ω. TO-263 (S) 5-Lead Surface-Mount Package Top View EQUIVALENT SERIES INDUCTANCE (ESL) The pure inductance component of a capacitor (see Figure 16). The amount of inductance is determined to a large extent on the capacitor’s construction. In a buck regulator, this unwanted inductance causes voltage spikes to appear on the output. OUTPUT RIPPLE VOLTAGE The AC component of the switching regulator’s output voltage. It is usually dominated by the output capacitor’s ESR multiplied by the inductor’s ripple current (∆IIND). The peakto-peak value of this sawtooth ripple current can be determined by reading the Inductor Ripple Current section of the Application hints. CAPACITOR RIPPLE CURRENT RMS value of the maximum allowable alternating current at which a capacitor can be operated continuously at a specified temperature. 01147625 LM2576S-XX NS Package Number TS5B LM2576SX-XX NS Package Number TS5B, Tape and Reel Bent, Staggered Leads 5-Lead TO-220 (T) Top View STANDBY QUIESCENT CURRENT (ISTBY) Supply current required by the LM2576 when in the standby mode (ON /OFF pin is driven to TTL-high voltage, thus turning the output switch OFF). INDUCTOR RIPPLE CURRENT (∆IIND) The peak-to-peak value of the inductor current waveform, typically a sawtooth waveform when the regulator is operating in the continuous mode (vs. discontinuous mode). OPERATING VOLT MICROSECOND CONSTANT (E • Top) The product (in VoIt • µs) of the voltage applied to the inductor and the time the voltage is applied. This E • Top 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. http://www.hgsemi.com.cn 14 01147622 LM2576T-XX Flow LB03 NS Package Number T05D 2018 AUG