90735_LM2576

© Semiconductor Components Industries, LLC, 2006 January, 2006 − Rev. 8 1 Publication Order Number: LM2576/D 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. 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 inductors optimized for use with the LM2576 are offered by several different inductor manufacturers. Since the LM2576 converter is a switch−mode power supply, its 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 greatly simplifies the design of switch−mode power supplies. The LM2576 features include a guaranteed ±4% tolerance on output 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 �A (typical) standby current. The output switch includes cycle−by−cycle current limiting, as well as thermal shutdown for full protection under fault conditions. Features • 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 • Wide Input Voltage Range • 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 • Moisture Sensitivity Level (MSL) Equals 1 • Pb−Free Packages are Available Applications • 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 See detailed ordering and shipping information in the package dimensions section on page 24 of this data sheet. ORDERING INFORMATION 1 5 TO−220 TV SUFFIX CASE 314B 1 5 Heatsink surface connected to Pin 3 TO−220 T SUFFIX CASE 314D Pin 1. Vin 2. Output 3. Ground 4. Feedback 5. ON/OFF D2PAK D2T SUFFIX CASE 936A Heatsink surface (shown as terminal 6 in case outline drawing) is connected to Pin 3 1 5 http://onsemi.com See general marking information in the device marking section on page 25 of this data sheet. DEVICE MARKING INFORMATION LM2576 http://onsemi.com 2 Figure 1. Block Diagram and Typical Application 7.0 V − 40 V Unregulated DC Input L1 100 �H GN D +Vin 1 Cin 100 �F 3 ON/OFF5 Output 2 Feedback 4 D1 1N5822 Cout 1000 �F Typical Application (Fixed Output Voltage Versions) Representative Block Diagram and Typical Application Unregulated DC Input +Vin 1 Cout Feedback 4 Cin L1 D1 R2 R1 1.0 k Output 2 GND 3 ON/OFF 5 Reset Latch Thermal Shutdown 52 kHz Oscillator 1.235 V Band−Gap Reference Freq Shift 18 kHz Comparator Fixed Gain Error Amplifier Current Limit Driver 1.0 Amp Switch ON/OFF 3.1 V Internal Regulator Regulated Output Vout Load Output Voltage Versions 3.3 V 5.0 V 12 V 15 V R2 (�) 1.7 k 3.1 k 8.84 k 11.3 k For adjustable version R1 = open, R2 = 0 � LM2576 5.0 V Regulated Output 3.0 A Load This device contains 162 active transistors. 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�JA 65 °C/W Thermal Resistance, Junction−to−Case R�JC 5.0 °C/W Case 936A (D2PAK) PD Internally Limited W Thermal Resistance, Junction−to−Ambient R�JA 70 °C/W Thermal Resistance, Junction−to−Case R�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�) − 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. LM2576 http://onsemi.com 3 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 LM2576 http://onsemi.com 4 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 �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) �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. LM2576 http://onsemi.com 5 I Q , Q U IE S C E N T C U R R E N T (m A ) 40 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) V o ut , O U T P U T V O LT A G E C H A N G E ( % ) V o ut , O U T P U T V O LT A G E C H A N G E ( % ) , S TA N D B Y Q U IE S C E N T C U R R E N T ( TJ, JUNCTION TEMPERATURE (°C) I O , O U T P U T C U R R E N T (A ) TJ, JUNCTION TEMPERATURE (°C) Vin, INPUT VOLTAGE (V) Vin, INPUT VOLTAGE (V) IN P U T − O U T P U T D IF F E R E N T IA L (V ) TJ, JUNCTION TEMPERATURE (°C) Figure 2. Normalized Output Voltage TJ, JUNCTION TEMPERATURE (°C) Figure 3. Line Regulation Figure 4. Dropout Voltage Figure 5. Current Limit Figure 6. Quiescent Current Figure 7. Standby Quiescent Current ILoad = 200 mA ILoad = 3.0 A Vin = 12 V Vin = 40 V L1 = 150 �H Rind = 0.1 � ILoad = 500 mA ILoad = 3.0 A Vout = 5.0 V Measured at Ground Pin TJ = 25°C VON/OFF = 5.0 V μA ) 1.0 0.6 0.2 0 −0.2 −0.4 −1.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 −0.2 −0.4 −0.6 2.0 1.5 1.0 0.5 0 6.5 6.0 5.5 5.0 4.5 4.0 20 18 16 14 12 10 8.0 6.0 4.0 200 180 160 140 120 100 80 60 20 0 1251007550250−25−50 403530252015105.00 1251007550250−25−50 1251007550250−25−50 403530252015105.00 1251007550250−25−50 −0.8 −0.6 0.4 0.8 Vin = 20 V ILoad = 500 mA Normalized at TJ = 25°C ILoad = 500 mA TJ = 25°C 3.3 V, 5.0 V and ADJ 12 V and 15 V Vin = 25 V I s tb y LM2576 http://onsemi.com 6 V sa t, S AT U R A T IO N V O LT A G E ( V ) 2.0 2.5 3.0 4.0 I b , F E E D B A C K P IN C U R R E N T (n A ) , S TA N D B Y Q U IE S C E N T C U R R E N T (μA ) I s tb y , I N P U T V O LT A G E ( V ) TJ, JUNCTION TEMPERATURE (°C) SWITCH CURRENT (A) N O R M A LI Z E D F R E Q U E N C Y ( % ) TJ, JUNCTION TEMPERATURE (°C) Figure 8. Standby Quiescent Current Vin, INPUT VOLTAGE (V) Figure 9. Switch Saturation Voltage Figure 10. Oscillator Frequency Figure 11. Minimum Operating Voltage Figure 12. Feedback Pin Current Vin = 12 V Normalized at 25°C TJ = 25°C Adjustable Version Only 200 180 140 120 100 80 60 40 20 0 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 8.0 6.0 4.0 2.0 0 −2.0 −4.0 −6.0 −8.0 −10 5.0 4.5 3.5 1.5 1.0 0.5 0 40302520151050 0 0.5 1.0 1.5 2.0 3.0 1251007550250−25−50 1251007550250−25−50 TJ, JUNCTION TEMPERATURE (°C) Adjustable Version Only 100 80 60 40 20 0 −20 −40 −60 −80 −100 1251007550250−25−50 160 35 2.5 −40°C 25°C 125°C Vout � 1.23 V ILoad = 500 mA TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) V in LM2576 http://onsemi.com 7 2.0 A 0 0 A B C 100 �s/DIV5 �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 �s/DIV 50 V 0 4.0 A 2.0 A 100 mV Output Voltage Change 0 3.0 A 2.0 A 1.0 A 0 4.0 A − 100 mV Load Current TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 15) D LM2576 http://onsemi.com 8 Figure 15. Typical Test Circuit D1 MBR360 L1 100 �H Output 2 4 Feedback Cout 1000 �F Cin 100 �F LM2576 Fixed Output1 53 ON/OFFGN D Vin Load Vout D1 MBR360 L1 100 �H Output 2 4 Feedback Cout 1000 �F Cin 100 �F LM2576 Adjustable1 53 ON/OFFGN D Vin Load Vout 5,000 V Fixed Output Voltage Versions Adjustable Output Voltage Versions Vout � Vref� �1.0�� R2 R1 � R2 � R1�Vout V ref �–�1.0� Where Vref = 1.23 V, R1 between 1.0 k and 5.0 k R2 R1 Cin − 100 �F, 75 V, Aluminium Electrolytic Cout − 1000 �F, 25 V, Aluminium Electrolytic D1 − Schottky, MBR360 L1 − 100 �H, Pulse Eng. PE−92108 R1 − 2.0 k, 0.1% R2 − 6.12 k, 0.1% 7.0 V − 40 V Unregulated DC Input 7.0 V − 40 V Unregulated DC Input PCB LAYOUT GUIDELINES As in any switching regulator, the layout of the printed circuit board is very important. Rapidly switching currents associated with wiring inductance, stray capacitance and parasitic inductance of the printed circuit board traces can generate voltage transients which can generate electromagnetic interferences (EMI) and affect the desired operation. As indicated in the Figure 15, to minimize inductance and ground loops, the length of the leads indicated by heavy lines should be kept as short as possible. For best results, single−point grounding (as indicated) or ground plane construction should be used. On the other hand, the PCB area connected to the Pin 2 (emitter of the internal switch) of the LM2576 should be kept to a minimum in order to minimize coupling to sensitive circuitry. Another sensitive part of the circuit is the feedback. It is important to keep the sensitive feedback wiring short. To assure this, physically locate the programming resistors near to the regulator, when using the adjustable version of the LM2576 regulator. LM2576 http://onsemi.com 9 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 �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 The LM2576 is a “Buck” or Step−Down Converter which is the most elementary forward−mode converter. Its basic schematic can be seen in Figure 16. The operation of this regulator topology has two distinct time periods. The first one occurs when the series switch is on, the input voltage is connected to the input of the inductor. The output of the inductor is the output voltage, and the rectifier (or catch diode) is reverse biased. During this period, since there is a constant voltage source connected across the inductor, the inductor current begins to linearly ramp upwards, as described by the following equation: IL(on) � �Vin – Vout� ton L 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. Figure 16. Basic Buck Converter DVin RLoad L Cout Power Switch The next period is the “off” period of the power switch. When the power switch turns off, the voltage across the inductor reverses its polarity and is clamped at one diode voltage drop below ground by the catch diode. The current now flows through the catch diode thus maintaining the load current loop. This removes the stored energy from the inductor. The inductor current during this time is: IL(off) � �Vout – VD� toff L This period ends when the power switch is once again turned on. Regulation of the converter is accomplished by varying the duty cycle of the power switch. It is possible to describe the duty cycle as follows: d � ton T , where T is the period of switching. For the buck converter with ideal components, the duty cycle can also be described as: d � Vout Vin Figure 17 shows the buck converter, idealized waveforms of the catch diode voltage and the inductor current. Power Switch Figure 17. Buck Converter Idealized Waveforms Power Switch Off Power Switch Off Power Switch On Power Switch On Von(SW) VD(FWD) Time Time ILoad(AV) Imin Ipk Diode Diode Power Switch D io de V ol ta ge In du ct or C ur re nt LM2576 http://onsemi.com 10 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: Vout = Regulated Output Voltage (3.3 V, 5.0 V, 12 V or 15 V) Vin(max) = Maximum Input Voltage ILoad(max) = Maximum Load Current Given Parameters: Vout = 5.0 V Vin(max) = 15 V ILoad(max) = 3.0 A 1. Controller IC Selection According to the required input voltage, output voltage and current, select the appropriate type of the controller IC output voltage version. 1. Controller IC Selection According to the required input voltage, output voltage, current polarity and current value, use the LM2576−5 controller IC 2. Input Capacitor Selection (Cin) To prevent large voltage transients from appearing at the input and for stable operation of the converter, an aluminium or 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. 2. Input Capacitor Selection (Cin) A 100 �F, 25 V aluminium electrolytic capacitor located ne