LM2574 Micrel, Inc. LM2574 52kHz Simple 0.5A Buck Regulator General Description Features The LM2574 family is a series of easy to use fixed and adjustable switching voltage regulators. The LM2574 contains all of the active circuitry necessary to construct a stepdown (buck) switching regulator and requires a minimum of external components. The LM2574 is available in 3.3V and 5V fixed output versions, or an adjustable version with an output voltage range of 1.23V to 37V. Output voltage is guaranteed to ±4% for specified input and load conditions. The LM2574 can supply 0.5A while maintaining excellent line and load regulation. The output switch includes cycleby-cycle current limiting, as well as thermal shutdown for full protection under fault conditions. An external shutdown connection selects operating or standby modes. Standby current is less than 200µA. Heat sinks are generally unnecessary due the regulator’s high efficiency. Adequate heat transfer is usually provided by soldering all package pins to a printed circuit board. The LM2574 includes internal frequency compensation and an internal 52kHz fixed frequency oscillator guaranteed to ±10% of the frequency. Circuits constructed around the LM2574 use a standard series of inductors which are available from several different manufacturers. All support documentation can be found on Micrel’s web site at www.micrel.com. • 3.3V, 5V, 12V, and adjustable output versions • Adjustable version output 1.23V to 37V ±4% max. over line and load conditions. • Guaranteed 0.5A output current • Wide input voltage, up to 40V • Thermal shutdown and current limit protection • Requires only 4 external components. • Shutdown capability (standby mode) • Low power standby mode < 200µA Typical • High-efficiency • 52kHz fixed frequency internal oscillator • Uses standard inductors Typical Application 40V MAX UNREGULATED DC IN • • • • 330µH LM2574 PWR GND Simple high-efficiency step-down (buck) regulator Efficient pre-regulator for linear regulators On-card switching regulators Positive to negative converter (buck-boost) FB VIN CIN 22µF Applications OUT SIG ON/ GND OFF 11DQ05 REGULATED OUTPUT 0.5A COU T 220µF Figure 1. Fixed Output Regulator Circuit Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com July 2005 1 M9999-072805 LM2574 Micrel, Inc. Ordering Information Part Number Junction Temp. Range Package LM2574YN –40ºC to +85ºC 8-pin Plastic DIP LM2574-3.3YN –40ºC to +85ºC 8-pin Plastic DIP LM2574-5.0YN –40ºC to +85ºC 8-pin Plastic DIP Standard Pb-Free LM2574BN LM2574-3.3BN LM2574-5.0BN Pin Configuration 8 NC FB 1 7 OUTPUT SIG GND 2 ON/OFF 3 6 NC PWR GND 4 5 VIN 8-Pin DIP (N) M9999-072805 2 July 2005 LM2574 Micrel, Inc. Absolute Maximum Ratings(1) Operating Ratings(1) Maximum Supply Voltage LM2574...................................................................... 45V OFF Pin Input Voltage ................................ –0.3V ≤ V ≤ VIN Output Voltage to Ground (Steady State) ...................... –1V Power Dissipation ..................................... Internally Limited Storage Temperature Range (TS) ............. –65°C to +150°C Minimum ESD Rating C = 100pF, R = 1.5kΩ ................................................ 2kV FB Pin ........................................................................ 1kV Lead Temperature (soldering, 10 sec.) ...................... 260°C Supply Voltage LM2574...................................................................... 40V Temperature Range LM2574...........................................–40°C ≤ TJ ≤ +125°C Maximum Junction Temperature (TJ.......................... 150°C Electrical Characteristics(2) Specifications with standard typeface are for TJ = 25°C, and those with boldface type apply over full Operating Temperature Range. Unless otherwise specified, VIN = 12V, and ILOAD = 100mA. Symbol Parameter Condition System Parameters, Adjustable VOUT Feedback Voltage VOUT Feedback Voltage (LM2574) η Efficiency System Parameters, 3.3V VOUT Regulators(3), Regulators(3), Output Voltage VOUT Output Voltage (LM2574-3.3) η Efficiency Min Typ Max Units 1.217 1.230 1.243 V 1.193 1.180 1.230 1.267 1.280 V V Test Circuit Figure 2 VIN = 12V, ILOAD = 0.1A, VOUT = 5V 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V 78 % Test Circuit Figure 3 VIN = 12V, ILOAD = 0.1A, VOUT = 3.3V 0.1A ≤ ILOAD ≤ 0.5A, 4.75V ≤ VIN ≤ 40V, VOUT = 3.3V 3.234 3.3 3.366 V 3.168 3.135 3.3 3.432 3.465 V V VIN = 12V, ILOAD = 0.1A 73 % System Parameters, 5V Regulators(3), Test Circuit Figure 3 VOUT Output Voltage VOUT Output Voltage (LM2574-5.0) η Efficiency VIN = 12V, ILOAD = 0.1A, VOUT = 5V 0.1A ≤ ILOAD ≤ 0.5A, 7V≤ VIN ≤ 40V, VOUT = 5V VIN = 12V, ILOAD = 0.1A, VOUT = 5V 4.900 5.0 5.100 V 4.800 4.750 5.0 5.200 5.250 V V 78 % Notes: 1. “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur. “Operating Ratings” indicate for which the device is intended to be functional, but do not guarantee specific performance limits. For guaranteed specifications and test conditions, see “Electrical Characteristics.” 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 testing. 3. External components such as the catch diode, inductor, input and output capacitors can affect switching regulator system performance. When the LM2574 is used as shown in Figure 1 test circuit, system performance will be shown in system parameters section of “Electrical Characteristics.” July 2005 3 M9999-072805 LM2574 Micrel, Inc. Electrical Characteristics Symbol Parameter Condition Min Typ Max Units 50 100 500 nA nA 52 58 63 kHz kHz 0.8 1.2 1.4 V V Device Parameters, Adjustable Regulator IB Feedback Bias Current VOUT = 5V Device Parameters, Fixed and Adjustable Regulators fo Oscillator Frequency Note 8 VSAT Saturation Voltage IOUT = 0.5A(4) 47 42 DC Max Duty Cycle (ON) Note 5 ICL Current Limit Peak Current, tON ≤ 3µs(4) IL Output Leakage Current VIN, Note 6, Output = 0V Note 6, Output = –1V IQ ISTBY 93 98 0.7 0.65 1.0 7.5 % 1.6 1.8 A 2 30 mA Quiescent Current Note 6 5 10 mA Standby Quiescent Current ON/OFF Pin = 5V (OFF) 50 200 µA θJA Thermal Resistance N Package, Junction VIH ON/OFF Input Level VOUT = 0V VIL ON/OFF Input Level VOUT = 5V IIH ON/OFF Logic Current ON/OFF Logic Current to Ambient(7) 85 °C/W 1.4 V V On/Off Control, Fixed and Adjustable Regulators Test Circuit Figures 2, 3 IIL 2.2 2.4 1.2 1.0 0.8 V V ON/OFF = 5V (OFF) 4 30 µA ON/OFF = 0V (ON) 0.01 10 µA Notes: 4. Output (pin 2) sourcing current. No diode, inductor, or capacitor connected to input. 5. Feedback (pin 4) removed from output and connected to 0V. 6. Feedback (pin 4) removed from output and connected to 12V to force the output transistor OFF. 7. Junction-to-ambient thermal resistance with approximately 1 square inches of PC board copper surrounding the leads. Test Circuit FB VIN CIN 22µF LM2574 (adjustable) OUT PWR SIG ON/ GND GND OFF 330µH 11DQ06 COU T 220µF 3.09k 1k Figure 2. Adjustable Regulator Test Circuit VIN CIN 22µF FB LM2574– 3.3, 5, 12 OUT P W R S I G ON/ GND GND O F F 330µH 11DQ06 COU T 220µF Figure 3. Fixed Regulator Test Circuit M9999-072805 4 July 2005 LM2574 Micrel, Inc. Typical Characteristics (Circuit of Figure 1) Supply Current vs. Duty Cycle Supply Current 20 20.0 Measured at Ground Pin TJ = 25˚C VOUT = 5V 18 16 12 10.0 10 I LO AD = 100 mA VIN from 7V to 40V 2.5 10 20 30 40 50 60 0 0 20 INPUT VOLTAGE ( V) V IN = 25V 40 60 80 100 D U TY C YC LE ( % ) JU N C TI O N TEM PER ATU R E ( ˚ C ) Efficiency 100 1.1 -55˚C -40˚C 0.7 0 0.1 0.2 0.3 0.4 0.5 60 Line Regulation 3.5 8 3.0 6 2.5 4 0 2.0 2 -25 100 75 50 25 Normalized Output Voltage VIN = 12V I LO AD = 100mA Normalized toTJ = 25˚C VOUT = 5V 25 -75 5 10 15 20 25 INPUT VOLTAGE ( V) 30 -100 -75 -50 -25 0 25 50 75 100 125150 JU N C TI O N TEM PER ATU R E ( ˚ C ) Oscillator Frequency Normalized at 25˚ C +4 2.0 1.5 Dropout Voltage I LO AD = 0.5A ∆VOUT = 5% R IND = 0.2Ω +2 0 -2 -50 -4 -75 --6 JU N C TI O N TEM PER ATU R E ( ˚ C ) 50 -50 0 0 25 50 75 100125150 35 40 75 -6 -25 -100 -75 -50 -25 0 Normalized toVIN = 10V VOUT = 5V ILO AD = 100mA TJ = 25 0 +6 10 15 20 25 30 100 -2 -4 +8 5 Feedback Pin Current 10 0.5 0 -75 -50 -25 0 25 50 75 100125150 J U N C TI O N TEM PER ATU R E ( ˚ C ) 0 INPUT VOLTAGE ( V) 4.0 VOUT = 1.23V I LO AD = 100 mA VOUT = 3V 65 14 12 1.0 0.5A 70 5.0 4.5 1.5 100 mA 75 SW I TC H C U R R EN T ( A) Minimum Operating Voltage 100 mA 80 25˚C JU N C TI O N TEM PER ATU R E ( ˚ C ) July 2005 85 0.5 125˚C 150˚C 0.3 0.5A 90 1 0 -75 -50 -25 0 25 50 75 100125 150 VOUT = 12V 95 0.9 0.5 0 -75 -50 -25 0 25 50 75 100 125150 Switch Saturation Voltage Current Limit 1.5 VIN = 12V 50 5.0 6 VON/OFF = 5V 100 7.5 I LO AD to 0.5A 0 VIN = 40V 150 15.0 12.5 4 200 17.5 14 8 Standby Quiescent Current 1.0 VIN = 40V 0.5 I LO AD = 100 mA VIN = 12V -8 -75 -50 -25 0 25 50 75 100125150 0 -75 -50 -25 0 25 50 75 100125150 J U N C TI O N TEM PER ATU R E ( ˚ C ) JU N C TI O N TEM PER ATU R E ( ˚ C ) 5 M9999-072805 LM2574 Micrel, Inc. Typical Performance Characteristics (continued) 25 20 15 10 5 Normalized Feedback Voltage* Feedback Voltage vs Duty Cycle* 20 VIN = 12V I LO AD = 100mA Normalized toTJ = 25˚ C I LO AD = 100 mA 15 10 5 0 VIN = 40V 0 -5 -10 -5 VIN = 7V -10 -15 -20 -25 -75 -50 -25 0 -15 -20 25 50 75 100125150 JU N C TI O N TEM PER ATU R E ( ˚ C ) 0 20 40 60 80 100 D U TY C YC LE ( % ) * Adjustable version only M9999-072805 6 July 2005 LM2574 Micrel, Inc. Block Diagrams V IN 1 F EED BACK 4 INTERNAL REGULATOR 1.23V BAND-GAP REFERENCE ON/OFF V IN INTERNAL REGULATOR 1 + - F EED BACK 1/2 AMP SW ITCH COM PARAT OR + - 52 kHz OSCILLATOR ON/OFF 5 ON/OFF 2 OUTPUT 3 GND FIXED GAIN E R R OR A M P FIXED GAIN E R R OR A M P 3.1k 1.0k 5 ON/OFF 4 + - DRIVER 2 RESET THERMAL SHUTDOWN CURRENT LIMIT 3 1/2 AMP SW ITCH COM PARAT OR + - DRIVER OUTPUT 1.23V BAND-GAP REFERENCE GND 52 kHz OSCILLATOR RESET THERMAL SHUTDOWN CURRENT LIMIT Note: Pin numbers are for the TO-220 package Fixed Regulator July 2005 Adjustable Regulator 7 M9999-072805 LM2574 Micrel, Inc. Package Information PIN 1 DIMENSIONS: INCH (MM) 0.380 (9.65) 0.370 (9.40) 0.255 (6.48) 0.245 (6.22) 0.135 (3.43) 0.125 (3.18) 0.300 (7.62) 0.013 (0.330) 0.010 (0.254) 0.018 (0.57) 0.130 (3.30) 0.100 (2.54) 0.0375 (0.952) 0.380 (9.65) 0.320 (8.13) 8-Pin DIP (N) MICREL INC. TEL 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com This information furnished by Micrel in this data sheet is believed to be accurate and reliable. However no responsibility is assumed by Micrel for its use. Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser's use or sale of Micrel Products for use in life support appliances, devices or systems is a Purchaser's own risk and Purchaser agrees to fully indemnify Micrel for any damages resulting from such use or sale. © 2003 Micrel, Inc. M9999-072805 8 July 2005