MIC4576 Micrel MIC4576 200kHz Simple 3A Buck Voltage Regulator Preliminary Information General Description Features The MIC4576 is a series of easy to use fixed and adjustable BiCMOS step-down (buck) switch-mode voltage regulators. The 200kHz MIC4576 duplicates the pinout and function of the 52kHz LM2576. The higher switching frequency may allow up to a 4:1 reduction in output filter inductor values. The MIC4576 is available in 3.3V, and 5V fixed output versions or a 1.23V to 30V adjustable output version. Both versions are capable of driving a 3A load with excellent line and load regulation. • 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 3A switch current • Wide input voltage range: 4V to 36V • Wide output voltage range: 1.23V to 30V • Requires minimum external components • Shutdown mode < 200µA typ. • 75% efficiency (adjustable version > 75% typ.) • Standard inductors are 25% of typical LM2576 values • Thermal shutdown • Overcurrent protection • 100% electrical thermal limit burn-in 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. The MIC4576 is available in TO-220 (BT) and TO-263 (BU) packages for the industrial temperature range. Applications • • • • • • • Simple high-efficiency step-down (buck) regulator Efficient pre-regulator for linear regulators On-card switching regulators Positive to negative converter (inverting buck-boost) Battery Charger Negative boost converter Step-down to 3.3V for Intel Pentium™ and similar microprocessors Typical Applications Shutdown Enable +8V to +36V 33µH SHDN MIC4576-5.0 MBR360 COUT 1000µF FB VIN CIN 470µF +5V, 3A SW GND Fixed Regulator Shutdown Enable 33µH SHDN MIC4576 +6V to +36V MBR360 2.18k 1% FB VIN CIN 470µF +3.39V, 3A SW 1.24k 1% GND COUT 1000µF Adjustable Regulator MIC4576 4-128 1997 MIC4576 Micrel Ordering Information Part Number Voltage Temperature Range Package MIC4576-3.3BT 3.3V –40°C to +85°C 5-lead TO-220 MIC4576-5.0BT 5.0V –40°C to +85°C 5-lead TO-220 Adjustable –40°C to +85°C 5-lead TO-220 3.3V –40°C to +85°C 5-lead TO-263 5.0V –40°C to +85°C 5-lead TO-263 Adjustable –40°C to +85°C 5-lead TO-263 MIC4576BT MIC4576-3.3BU MIC4576-5.0BU MIC4576BU Pin Configuration 5 4 3 2 1 5 4 3 2 1 SHDN FB GND SW VIN Tab GND SHDN FB GND SW VIN Tab GND 5-Lead TO-220 (T) 5-Lead TO-263 (U) Pin Description 1997 Pin Number Pin Name Pin Function 1 VIN Supply Voltage (Input): Unregulated +4V to +36V supply voltage. 2 SW Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. 3 GND 4 FB 5 SHDN Ground 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. Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts down regulator. 4-129 MIC4576 MIC4576 Micrel Absolute Maximum Ratings Supply Voltage (VIN) ..................................................... 40V Shutdown (VSHDN) ....................................... –0.3V to +36V Output Switch (VSW), Steady State ............................... –1V Feedback Voltage (VFB) [Adjustable] ......................... +3.8V Operating Junction Temperature .............................. 160°C Package Thermal Resistance θJA TO-220, TO-263 ............................................ 65°C/W θJC TO-220, TO-263 ............................................. 2°C/W Storage Temperature ................................. –65°C to 150°C Electrical Characteristics VIN = 12V; ILOAD = 500mA; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ +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 MIC4576 [Adjustable] (Note 1) Feedback Voltage Feedback Voltage 8V ≤ VIN ≤ 36V, 0.5A ≤ ILOAD ≤ 3A Efficiency ILOAD = 3A Maximum Duty Cycle (On) VFB = 1.0V Output Leakage Current VIN = 36V, VFB = 1.5V output = 0V output = –1V Quiescent Current 90 77 % 95 % 0 7.5 2 30 mA mA 5 10 mA 50 100 500 nA nA 3.234 3.3 3.366 V 3.168 3.135 3.3 3.432 3.465 V V VFB = 1.5V Feedback Bias Current MIC4576-3.3 Output Voltage Output Voltage 6V ≤ VIN ≤ 36V, 0.5A ≤ ILOAD ≤ 3A Efficiency ILOAD = 3A Maximum Duty Cycle (On) VFB = 2.5V Output Leakage Current VIN = 36V, VFB = 4.0V output = 0V output = –1V Quiescent Current 90 72 % 95 % 0 7.5 2 30 mA mA 5 10 mA 4.900 5.0 5.100 V 4.800 4.750 5.0 5.200 5.250 V V VFB = 4.0V MIC4576-5.0 Output Voltage Output Voltage 8V ≤ VIN ≤ 36V, 0.5A ≤ ILOAD ≤ 3A Efficiency ILOAD = 3A Maximum Duty Cycle (On) VFB = 4.0V Output Leakage Current VIN = 36V, VFB = 6.0V output = 0V output = –1V Quiescent Current MIC4576 90 VFB = 6.0V 4-130 77 % 95 % 0 7.5 2 30 mA mA 5 10 mA 1997 MIC4576 Parameter Micrel Condition Min Typ Max Units 180 200 220 kHz 1.7 2.3 2.5 V V 5.2 6.9 7.5 A A 50 200 µA MIC4576 / -3.3 / -5.0 Oscillator Frequency Saturation Voltage IOUT = 3A Current Limit peak current, tON ≤ 3µs; VFB = 0V Standby Quiescent Current VSHDN = 5V (regulator off), VFB = 0V SHDN Input Logic Level VOUT = 0V (regulator off) 4.2 3.5 2.2 2.4 VOUT = 3.3V or 5V (regulator on) SHDN Input Current VSHDN = 5V (regulator off) VSHDN = 0V (regulator on) –10 1.4 V V 1.2 1.0 0.8 V V 4 0.01 30 10 µA µA General Note: Devices are ESD protected, however, handling precautions are recommended. Note 1: 1997 VOUT = 5V 4-131 MIC4576 MIC4576 Micrel Block Diagrams +7V to +36V VIN Shutdown Enable SHDN CIN Internal Regulator Thermal Shutdown 200kHz Oscillator Current Limit Driver Comparator L1 SW VOUT 3A Switch D1 COUT 1.23V Bandgap Error Amp. R1 FB R2 MIC4576-x.x GND Block Diagram with External Components Fixed Step-Down Regulator +7V to +36V 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 3A Switch D1 COUT Error Amp. 1.23V Bandgap R1 FB MIC4576 [Adjustable] R2 GND Block Diagram with External Components Adjustable Step-Down Regulator MIC4576 4-132 1997 MIC4576 Micrel Functional Description The MIC4576 is a variable duty cycle switch-mode regulator with an internal power switch. Refer to the block diagrams. Supply Voltage The MIC4576 operates from a +4V to +36V unregulated input. Highest efficiency operation is from a supply voltage around +15V. Enable/Shutdown The shutdown (SHDN) input is TTL compatible. Ground the input if unused. A logic-low enables the regulator. A logichigh 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. A higher feedback voltage increases the error amplifier output voltage. A higher error amplifier voltage (comparator “–” 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. 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. 1997 For a mathematical approach to component selection and circuit design, refer to Application Note 14. 4-133 MIC4576 MIC4576 Micrel L1 5 6V to 24V 1 C1 470µF 35V C1 C2 D1 L1 L1 SHDN SW MIC4576-3.3BT FB VIN GND 2 5 33µH 4 D1 1N5822 3 Nichicon Nichicon Motorola Coiltronics Bi L1 3.3V/3A 8V to 36V C2 1000µF 16V C1 470µF 63V UPL1V471MPH, ESR = 0.046Ω UPL1C221MPH, ESR = 0.047Ω 1N5822 PL52C-33-1000, DCR = 0.036Ω HM77-30004, DCR = 0.045Ω, Note 2 L1 6V to 36V 1 C1 470µF 63V C1 C2 D1 L1 L1 SHDN SW MIC4576-3.3BT FB VIN GND 2 D1 MBR360 3 Nichicon Nichicon Motorola Coiltronics Bi MIC4576-5.0BT FB VIN GND Nichicon Nichicon Motorola Coiltronics Bi 3.3V/3A 5 1 C1 470µF 63V SHDN SW FB VIN 8V to 24V C1 470µF 35V 1 SHDN SW MIC4576-5.0BT FB VIN GND C1 Nichicon C2 Nichicon D1 Motorola L1 Coiltronics L1 Bi 3 33µH 4 D1 1N5822 L1 2 12V/3A 68µH 4 MBR360 3 Nichicon Nichicon Motorola Bi R2 13.0k 1% R1 1.50k 1% C2 1000µF 16V UPL1J471MPH, ESR = 0.039Ω UPL1C102MPH, ESR = 0.047Ω MBR360 HM77-29006, DCR = 0.08Ω U1 5V/3A D1 MBR360 Figure 5. 16V–36V to 12V/3A Buck Converter Through Hole 5 L1 C2 1000µF 16V 4 GND C1 C2 D1 L1 UPL1J471MRH, ESR = 0.039Ω UPL1C102MPH, ESR = 0.047Ω MBR360 PL52C-33-1000 DCR = 0.036 HM77-30004, DCR = 0.045Ω, Note 2 2 33µH UPL1J471MRH, ESR = 0.039Ω UPL1C102MPH, ESR = 0.047Ω MBR360 PLS2C-33-1000, DCR = 0.036 HM77-30004, DCR = 0.045Ω, Note 2 MIC4576BT 16V to 36V C2 1000µF 16V Figure 2. 6V–36V to 3.3V/3A Buck Converter Through Hole 5 5V/3A 2 Figure 4. 8V–36V to 5V/3A Buck Converter Through Hole 33µH 4 SW 3 C1 C2 D1 L1 L1 Figure 1. 6V–24V to 3.3V/3A Buck Converter Through Hole 5 1 SHDN VIN 8V to 36V 1 C2 1000µF 16V SHDN R1 0.1Ω L1 SW MIC4576-5.0BT FB VIN GND 2 VOUT 5V/4A 33µH C2 1000µF 16V 4 D1 MBR360 3 C1 470µF 63V R3 10K C5 0.01µF VIN UPL1J471MPH, ESR = 0.046Ω UPL1C102MPH, ESR = 0.047Ω MBR5822 PL52C-33-1000, DCR = 0.036 HM77-30004, DCR = 0.045Ω, Note 2 8 2 1 3 4 U2 Figure 3. 8V–24V to 5V/3A Buck Converter Through Hole 5 1 C3 470µF 63V SHDN FB MIC4576-5.0BT SW VIN GND 3 C1, C3 C2, C4 D1, D2 L1, L2 R1, R2 U3 U3 LM358 Nichicon Nichicon Motorola Coiltronics KRL National 4 L2 2 33µH D2 MBR360 R2 0.1Ω C4 1000µF 16V UPL1J471MRH, ESR = 0.039Ω UPL1C102MPH, ESR = 0.047Ω MBR360 PL52C-33-1000, DCR = 0.036 SP-1-A1-0R100J LM358 Figure 6. Parallel Switching Regulators Note 2 Surface Mount. MIC4576 4-134 1997