MIC4574 Micrel, Inc. MIC4574 200kHz Simple 0.5A Buck Regulator General Description Features The MIC4574 is a series of easy to use fixed and adjustable BiCMOS step-down (buck) switch-mode voltage regulators. The 200kHz MIC4574 duplicates the pinout and function of the 52kHz LM2574. The higher switching frequency may allow up to a 2:1 reduction in output filter inductor size. The MIC4574 is available in 3.3V, and 5V fixed output versions or a 1.23V to 20V adjustable output version. Both versions are capable of driving a 0.5A load with excellent line and load regulation. The feedback voltage is guaranteed to ±2% tolerance for adjustable versions, and the output voltage is guaranteed to ±3% for fixed versions, within specified voltages and load conditions. The oscillator frequency is guaranteed to ±10%. In shutdown mode, the regulator draws less than 200µA standby current. The regulator performs cycle-by-cycle current limiting and thermal shutdown for protection under fault conditions. This series of simple switch-mode regulators requires a minimum number of external components and can operate using a standard series of inductors. Frequency compensation is provided internally. • Fixed 200kHz operation • 3.3V, 5V, and adjustable output versions • Voltage over specified line and load conditions: Fixed version: ±3% max. output voltage Adjustable version: ±2% max. feedback voltage • Guaranteed 0.5A switch current • Wide 4V to 24V input voltage range • Wide 1.23V to 20V output voltage range • Requires minimum external components • < 200µA typical shutdown mode • 75% efficiency (adjustable version > 75% typ.) • Standard inductors and capacitors are 25% of typical LM2574 values • Thermal shutdown • Overcurrent protection • 100% electrical thermal limit burn-in Applications • • • • • Simple high-efficiency step-down (buck) regulator Efficient preregulator for linear regulators On-card switching regulators Positive-to-negative converter (inverting buck-boost) Isolated flyback converter using minimum external components • Negative boost converter The MIC4574 is available in the DIP (N) package and is rated over the industrial temperature range. Data sheets and support documentation can be found on Micrel’s web site at www.micrel.com. Typical Application Shutdown Enable 8V to 24V C1 47µF 35V 3 5 SHDN SW MIC4574-5.0BN FB VIN SGND PGND 2 7 L1 5.0V/0.5A 100µH 1 4 D1 1N5819 C2 220µF 16V Fixed Regulator Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com June 2005 1 M9999-062105 MIC4574 Micrel, Inc. Ordering Information Standard Part Number Pb-Free MIC4574-3.3BN MIC4574-3.3YN MIC4574-5.0BN MIC4574-5.0YN MIC4574BN MIC4574YN Voltage Temperature Range Package 3.3V –40°C to +85°C 8-pin DIP 5.0V –40°C to +85°C 8-pin DIP Adjustable –40°C to +85°C 8-pin DIP Pin Configuration FB 1 8 NC SGND 2 7 SW SHDN 3 6 NC PGND 4 5 VIN 8-Pin DIP (N) Pin Description Pin Number Pin Name 1 FB 2 SGND Signal Ground. 3 SHDN Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts down regulator. 4 PGND Power Ground. 5 VIN Supply Voltage (Input): Unregulated +4V to +24V supply voltage. 7 SW Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. 6, 8 NC Not internally connected. Solder to printed circuit for maximum heat transfer. M9999-062105 Pin Function Feedback (Input): Output voltage feedback to regulator. Connect to output of supply for fixed versions. Connect to 1.23V tap of resistive divider for adjustable versions. 2 June 2005 MIC4574 Micrel, Inc. Absolute Maximum Ratings (Note 1) Operating Ratings (Note 2) Supply Voltage (VIN), Note 5 ...................................... +40V Shutdown (VSHDN) ....................................... –0.3V to +36V Output Switch (VSW) steady state ................................. –1V Junction Temperature (TJ) ...................................... +150°C Storage Temperature ............................... –65°C to +150°C ESD Rating, Note 3 Supply Voltage (VIN) ................................................... +24V Package Thermal Resistance θJA Plastic DIP .................................................. 130°C/W Electrical Characteristics (Note 4) VIN =12V; ILOAD = 100mA; TA = 25°C, bold values indicate –40°C ≤ TA ≤ +85°C; unless noted Parameter Condition Min Typ Max Units 1.217 1.230 1.243 V 1.193 1.180 1.230 1.267 1.280 V V MIC4574 [Adjustable] Feedback Voltage Feedback Voltage 8V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A Efficiency ILOAD = 0.5A, VOUT = 5V 77 Feedback Bias Current % 50 100 500 nA nA 3.234 3.3 3.366 V 3.168 3.135 3.3 3.432 3.465 V V MIC4574-3.3 Output Voltage Output Voltage 6V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A Efficiency 72 % MIC4574-5.0 Output Voltage Output Voltage 8V ≤ VIN ≤ 24V, 0.1A ≤ ILOAD ≤ 0.5A 4.900 5.0 5.100 V 4.800 4.750 5.0 5.200 5.250 V V Efficiency 77 % MIC4574 / -3.3 / -5.0 Oscillator Frequency 180 Saturation Voltage IOUT = 0.5A Maximum Duty Cycle (On) FB connected to 0V Current Limit Peak Current, tON ≤ 3µs Output Leakage Current VIN = 24V, FB connected to 6V Output = 0V Output = –1V SHDN = 5V (regulator off) SHDN Input Logic Level VOUT = 0V (regulator off) Note 1. Note 2. Note 3. Note 4. Note 5. 1 1.3 1.5 V V 0.7 0.65 1.0 1.6 1.8 A A 0 7.5 2 35 mA mA 5 10 mA 50 200 µA 2.2 2.4 SHDN = 5V (regulator off) SHDN = 0V (regulator on) kHz 95 VOUT = 3.3V or 5V (regulator on) SHDN Input Current 220 90 Quiescent Current Standby Quiescent Current 200 –10 % 1.4 V V 1.2 1.0 0.8 V V 4 0.01 30 10 µA µA Exceeding the absolute maximum rating may damage the device. The device is not guaranteed to function outside its operating rating. Devices are ESD sensitive. Handling precautions recommended. Specification for packaged product only. The MIC4574 is not guaranteed to survive a short circuit to ground for input voltage above 24V. June 2005 3 M9999-062105 MIC4574 Micrel, Inc. Block Diagrams +24V max. VIN Shutdown Enable SHDN CIN Internal Regulator Thermal Shutdown 200kHz Oscillator Current Limit Driver Comparator L1 SW VOUT 0.5A Switch D1 COUT 1.23V Bandgap Error Amp. R1 FB R2 MIC4574-x.x GND Block Diagram with External Components Fixed Step-Down Regulator +24V max. VIN Shutdown Enable SHDN CIN Internal Regulator Thermal Shutdown 200kHz Oscillator VOUT Current Limit R1 Comparator Driver V REF R2 R1 + 1 R2 VOUT VREF 1 L1 SW VOUT 0.5A Switch D1 COUT Error Amp. 1.23V Bandgap R1 FB MIC4574 [Adjustable] R2 GND Block Diagram with External Components Adjustable Step-Down Regulator M9999-062105 4 June 2005 MIC4574 Micrel, Inc. A higher feedback voltage increases the error amplifier output voltage. A higher error amplifier voltage (comparator inverting input) causes the comparator to detect only the peaks of the sawtooth, reducing the duty cycle of the comparator output. A lower feedback voltage increases the duty cycle. Output Switching When the internal switch is on, an increasing current flows from the supply VIN, through external storage inductor L1, to output capacitor COUT and the load. Energy is stored in the inductor as the current increases with time. When the internal switch is turned off, the collapse of the magnetic field in L1 forces current to flow through fast recovery diode D1, charging COUT. Output Capacitor External output capacitor COUT provides stabilization and reduces ripple. Return Paths During the on portion of the cycle, the output capacitor and load currents return to the supply ground. During the off portion of the cycle, current is being supplied to the output capacitor and load by storage inductor L1, which means that D1 is part of the high-current return path. Functional Description The MIC4574 is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply Voltage The MIC4574 operates from a +4V to +24V unregulated input. Highest efficiency operation is from a supply voltage below +15V. Enable/Shutdown The shutdown (SHDN) input is TTL compatible. Ground the input if unused. A logic-low enables the regulator. A logic-high shuts down the internal regulator which reduces the current to typically 50µA. Feedback Fixed versions of the regulator have an internal resistive divider from the feedback (FB) pin. Connect FB directly to the output line. Adjustable versions require an external resistive voltage divider from the output voltage to ground, connected from the 1.23V tap to FB. Duty Cycle Control A fixed-gain error amplifier compares the feedback signal with a 1.23V bandgap voltage reference. The resulting error amplifier output voltage is compared to a 200kHz sawtooth waveform to produce a voltage controlled variable duty cycle output. June 2005 5 M9999-062105 MIC4574 Micrel, Inc. Applications Information The applications circuits that follow have been constructed and tested. Refer to “Application Note 15” for additional information, including efficiency graphs and manufacturer’s addresses and telephone numbers for most circuits. L1 3 6V to 24V 5 C1 47µF 35V SHDN MIC4574-3.3BN VIN FB SGND PGND 2 C1 C2 D1 L1 SW Nichicon Nichicon Motorola Sumida 4 For a mathematical approach to component selection and circuit design, refer to “Application Note 14.” 3.3V/0.5A 7 3 100µH 8V to 24V C2 220µF 16V 1 D1 1N5819 C1 47µF 35V 16V to 24V C1 33µF 63V 5 C1 C2 D1 L1 7 SW Nichicon Nichicon Motorola Sumida L1 220µH MIC4574BN FB VIN SGND PGND 2 Nichicon Nichicon Motorola Sumida 4 7 L1 5.0V/0.5A 100µH 1 D1 1N5819 C2 220µF 16V UPL1J470MEH, ESR = 0.34Ω UPL1C221MPH, ESR = 0.16Ω 1N5819 RCH875-101K, DCR = 0.28Ω Figure 2. 8V–24V to 5V/0.5A Buck Converter Through Hole Figure 1. 6V–24V to 3.3V/0.5A Buck Converter Through Hole SHDN SW MIC4574-5.0BN FB VIN SGND PGND 2 C1 C2 D1 L1 UPL1V470MEH, ESR = 0.34Ω UPL1C221MPH, ESR = 0.16Ω 1N5819 RCH875-101K, DCR = 0.28Ω 3 5 SHDN 1 MBR160 4 12V/0.5A R2 13.0k 1% R1 1.50k 1% C2 220µF 16V UPL1J330MEH, ESR = 0.35Ω UPL1C221MPH, ESR = 0.16Ω MBR160 RCH106-221K, DCR = 0.78Ω Figure 3. 16V–24V to 12V/0.5A Buck Converter Through Hole M9999-062105 6 June 2005 MIC4574 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) 0.380 (9.65) 0.320 (8.13) 0.0375 (0.952) 8-Pin DIP (N) MICREL INC. TEL 2180 FORTUNE DRIVE + 1 (408) 944-0800 FAX SAN JOSE, CA 95131 USA + 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, Incorporated. June 2005 7 M9999-062105