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MIC4576
Micrel, Inc.
MIC4576
200kHz Simple 3A Buck Regulator
General Description
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 2:1 reduction in output filter inductor size. The MIC4576 is available in 3.3V, and 5V fixed output versions or a 1.23V to 33V adjustable output version. Both versions are capable of driving a 3A 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 200A 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 (T) and TO-263 (U) packages for the industrial temperature range.
Features
* 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 4V to 36V input voltage range * Wide 1.23V to 33V output voltage range * Requires minimum external components * < 200A typical shutdown mode * 75% efficiency (adjustable version > 75% typical) * Standard inductors are 25% of typical LM2576 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) Battery Charger Negative boost converter Step-down to 3.3V for Intel PentiumTM and similar microprocessors
Typical Applications
Shutdown Enable
5
SHDN
SW
2
L1 33H
5V/3A
C2 1000F 16V
8V to 36V
C1 470F 63V
1
MIC4576-5.0WT VIN FB GND
3
4
D1 MBR360
Fixed Regulator
Shutdown Enable
5
SHDN
SW
2
L1 68H
R2 13.0k 1% R1 1.50k 1%
12V/3A
16V to 36V
1
C1 470F 63V
MIC4576WT FB VIN GND
3
4
MBR360
C2 1000F 16V
Adjustable 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
March 2006
1
MIC4576
MIC4576
Micrel, Inc.
Ordering Information
Standard Part Number MIC4576-3.3BT MIC4576-5.0BT MIC4576BT MIC4576-3.3BU MIC4576-5.0BU MIC4576BU RoHS Compliant Part Number* MIC4576-3.3WT MIC4576-5.0WT MIC4576WT MIC4576-3.3WU MIC4576-5.0WU MIC4576WU Voltage 3.3V 5.0V ADJ. 3.3V 5.0V ADJ. Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package TO-220-5 TO-220-5 TO-220-5 TO-263-5 TO-263-5 TO-263-5
* RoHS compliant with "high-melting solder" exemption.
Pin Configuration
5 4 3 2 1 SHDN FB GND SW VIN
TAB
5-Pin TO-220 (T)
5 4 3 2 1 SHDN FB GND SW VIN
TAB
5-Pin TO-263 (U)
Pin Description
Pin Number 1 2 3, TAB 4 Pin Name SW GND FB VIN Pin Function Supply Voltage (Input): Unregulated +4V to +36V supply voltage. Switch (Output): Emitter of NPN output switch. Connect to external storage inductor and Shottky diode. 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.
5
SHDN
MIC4576
2
March 2006
MIC4576
Micrel, Inc.
Absolute Maximum Ratings
Supply Voltage (VIN) .................................................... +40V Shutdown Voltage (VSHDN)............................-0.3V to +36V Output Switch (VSW), Steady State ............................... -1V Feedback Voltage (VFB) [Adjustable] ......................... +3.8V Storage Temperature ................................ -65C to +150C
Operating Ratings
Supply Voltage (VIN) .................................................... +36V Junction Temperature .............................................. +150C Package Thermal Resistance TO-220, TO-263 (JA) ......................................... 65C/W TO-220, TO-263 (JC) ............................................ 2C/W
Electrical Characteristics
VIN = 12V; ILOAD = 500mA; TJ = 25C, bold values indicate -40C TJ +85C; unless noted. Parameter Condition MIC4576 [Adjustable] Feedback Voltage Feedback Voltage Efficiency Maximum Duty Cycle (On) Output Leakage Current 8V VIN 36V, 0.5A ILOAD 3A ILOAD = 3A, Note 1 VIN = 36V, VFB = 1.5V output = 0V output = -1V VFB = 1.5V VFB = 1.0V 1.217 1.193 1.180 90 1.230 1.230 77 95 0 7.5 5 50 2 35 10 100 500 3.366 3.432 3.465 1.243 1.267 1.280 V V V % % mA mA mA nA nA V V V % % 2 35 10 5.100 5.200 5.250 mA mA mA V V V % % 2 35 10 mA mA mA Min Typ Max Units
Quiescent Current Feedback Bias Current MIC4576-3.3 Output Voltage Output Voltage Efficiency Maximum Duty Cycle (On) Output Leakage Current
3.234 6V VIN 36V, 0.5A ILOAD 3A ILOAD = 3A 3.168 3.135 90
3.3 3.3 72 95 0 7.5 5
VIN = 36V, VFB = 4.0V output = 0V output = -1V VFB = 4.0V 4.900 8V VIN 36V, 0.5A ILOAD 3A ILOAD = 3A 4.800 4.750 90
VFB = 2.5V
Quiescent Current MIC4576-5.0 Output Voltage Output Voltage Efficiency Maximum Duty Cycle (On) Output Leakage Current
5.0 5.0 77 95 0 7.5 5
VIN = 36V, VFB = 6.0V output = 0V output = -1V VFB = 6.0V
VFB = 4.0V
Quiescent Current
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MIC4576
MIC4576
Parameter MIC4576 / -3.3 / -5.0 Oscillator Frequency Saturation Voltage Current Limit Standby Quiescent Current SHDN Input Logic Level IOUT = 3A peak current, tON 3s; VFB = 0V VSHDN = 5V (regulator off), VFB = 0V 4.2 3.5 2.2 2.4 180 200 1.7 5.2 50 1.4 1.2 4 0.01 Condition Min Typ
Micrel, Inc.
Max 220 2.3 2.5 7.9 8.5 200 Units kHz V V A A A V V 1.0 0.8 30 10 V V A A
VOUT = 0V (regulator off)
VOUT = 3.3V or 5V (regulator on) SHDN Input Current VSHDN = 5V (regulator off) VSHDN = 0V (regulator on) -10
General Note: Devices are ESD protected, however, handling precautions are recommended. Note 1: VOUT = 5V
MIC4576
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March 2006
MIC4576
Micrel, Inc.
Block Diagrams
+36V max. VIN
Shutdown Enable
CIN
SHDN
Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit
Comparator
Driver 3A Switch 1.23V Bandgap R1 R2 GND
SW D1
L1
VOUT COUT
Error Amp. MIC4576-x.x
FB
Block Diagram with External Components Fixed Step-Down Regulator
+36V max. VIN
Shutdown Enable
CIN
SHDN
Internal Regulator 200kHz Oscillator Thermal Shutdown Current Limit
Comparator
Driver 3A Switch 1.23V Bandgap
SW D1
L1
VOUT COUT R1
Error Amp. MIC4576 [Adjustable]
FB GND
R2
Block Diagram with External Components Adjustable Step-Down Regulator
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5
MIC4576
MIC4576
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 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 50A. 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.
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. For a mathematical approach to component selection and circuit design, refer to Application Note 14.
5
SHDN
SW
2
L1 33H
3.3V/3A C2 1000F 16V 6V to 36V C1 470F 63V
5
SHDN
SW
2
L1 33H
3.3V/3A C2 1000F 16V
6V to 24V C1 470F 35V C1 C2 D1 L1 L1
1
MIC4576-3.3BT FB VIN GND
3
4
1
D1 1N5822
MIC4576-3.3BT VIN FB GND
3
4
D1 MBR360
Nichicon Nichicon Motorola Coiltronics Bi
UPL1V471MPH, ESR = 0.046 UPL1C221MPH, ESR = 0.047 1N5822 PL52C-33-1000, DCR = 0.036 HM77-30004, DCR = 0.045, Note 2
C1 C2 D1 L1 L1
Nichicon Nichicon Motorola Coiltronics Bi
UPL1J471MRH, ESR = 0.039 UPL1C102MPH, ESR = 0.047 MBR360 PL52C-33-1000 DCR = 0.036 HM77-30004, DCR = 0.045, Note 2
Figure 1. 6V-24V to 3.3V/3A Buck Converter Through Hole
Figure 2. 6V-36V to 3.3V/3A Buck Converter Through Hole
Note 2:
Surface-mount component.
MIC4576
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March 2006
MIC4576
Micrel, Inc.
5
SHDN
SW
2
L1 33H
5V/3A C2 1000F 16V
8V to 36V C1 470F 63V C1 C2 D1 L1 L1
5
SHDN
SW
2
L1 33H
5V/3A C2 1000F 16V
8V to 24V C1 470F 35V
1
MIC4576-5.0BT FB VIN GND
3
4
1
D1 1N5822
MIC4576-5.0BT VIN FB GND
3
4
D1 MBR360
C1 Nichicon C2 Nichicon D1 Motorola L1 Coiltronics L1 Bi
UPL1J471MPH, ESR = 0.046 UPL1C102MPH, ESR = 0.047 MBR5822 PL52C-33-1000, DCR = 0.036 HM77-30004, DCR = 0.045, Note 2
Nichicon Nichicon Motorola Coiltronics Bi
UPL1J471MRH, ESR = 0.039 UPL1C102MPH, ESR = 0.047 MBR360 PLS2C-33-1000, DCR = 0.036 HM77-30004, DCR = 0.045, Note 2
Figure 3. 8V-24V to 5V/3A Buck Converter Through Hole
Figure 4. 8V-36V to 5V/3A Buck Converter Through Hole
5
SHDN VIN
SW FB
2
L1 68H R2 13.0k 1% R1 1.50k 1%
12V/3A C2 1000F 16V
16V to 36V C1 470F 63V
1
MIC4576BT GND
3
4
MBR360
C1 C2 D1 L1
Nichicon Nichicon Motorola Bi
UPL1J471MPH, ESR = 0.039 UPL1C102MPH, ESR = 0.047 MBR360 HM77-29006, DCR = 0.08
Figure 5. 16V-36V to 12V/3A Buck Converter Through Hole
U1
5
VIN 8V to 36V
SHDN
SW
2
L1 33H
R1 0.1 C2 1000F 16V
VOUT 5V/4A
1
MIC4576-5.0BT FB VIN GND
3
4
D1 MBR360 C5 0.01F VIN
8 1
R3 10K
C1 470F 63V
2
3
U3 LM358
U2
5
4
SHDN
FB
4
1
C3 470F 63V C1, C3 C2, C4 D1, D2 L1, L2 R1, R2 U3
MIC4576-5.0BT SW VIN GND
3
2
L2 33H D2 MBR360
R2 0.1 C4 1000F 16V
Nichicon Nichicon Motorola Coiltronics KRL National
UPL1J471MRH, ESR = 0.039 UPL1C102MPH, ESR = 0.047 MBR360 PL52C-33-1000, DCR = 0.036 SP-1-A1-0R100J LM358
Figure 6. Parallel Switching Regulators
Note 2:
Surface-mount component.
March 2006
7
MIC4576
MIC4576
Micrel, Inc.
Package Information
0.150 D 0.005 (3.81 D 0.13) 0.400 0.015 (10.16 0.38) 0.108 0.005 (2.74 0.13) 0.177 0.008 (4.50 0.20) 0.050 0.005 (1.27 0.13)
0.241 0.017 (6.12 0.43)
0.578 0.018 (14.68 0.46)
SEATING PLANE
7 Typ. 0.550 0.010 (13.97 0.25)
0.067 0.005 (1.70 0.127)
0.268 REF (6.81 REF)
0.032 0.005 (0.81 0.13) 0.018 0.008 (0.46 0.20)
0.103 0.013 (2.620.33)
Dimensions: inch (mm)
5-Pin TO-220 (T)
0.405 0.005 0.065 0.010 202 0.050 0.005 0.176 0.005 0.060 0.005
0.360 0.005 0.600 0.025 SEATING PLANE 0.004 +0.004 -0.008
0.067 0.005 DIM. = INCH
0.032 0.003
8 MAX 0.015 0.002
0.100 0.01
5-Pin TO-263 (U)
MICREL INC.
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
2180 FORTUNE DRIVE
SAN JOSE, CA 95131
USA
This information furnished by Micrel reserves the right to change circuitry and specifications at any time without notification to the customer. Micrel Products are not 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 Pr Micrel for any damages resulting from such use or sale. (c) 2005 Micrel, Inc.
MIC4576
8
March 2006

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