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MIC4576
Micrel
MIC4576
200kHz Simple 3A Buck Voltage 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
L1
Shutdown Enable 5
SHDN
SW
2
5V/3A
33H
4
8V to 36V C1 470F 63V
1
MIC4576-5.0BT FB VIN GND
3
D1 MBR360
C2 1000F 16V
Fixed Regulator
L1 68H
4
Shutdown Enable
5
SHDN MIC4576BT VIN GND
3
SW FB
2
12V/3A R2 13.0k 1% R1 1.50k 1%
16V to 36V C1 470F 63V
1
MBR360
C2 1000F 16V
Adjustable Regulator
MIC4576
4-128
April 1998*
MIC4576
Micrel
Ordering Information
Part Number MIC4576-3.3BT MIC4576-5.0BT MIC4576BT MIC4576-3.3BU MIC4576-5.0BU MIC4576BU Voltage 3.3V 5.0V Adjustable 3.3V 5.0V Adjustable Temperature Range -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C Package 5-lead TO-220 5-lead TO-220 5-lead TO-220 5-lead TO-263 5-lead TO-263 5-lead TO-263
Pin Configuration
5 4 3 2 1 SHDN FB GND SW VIN
TAB
5-Lead TO-220 (T)
5 4 3 2 1
SHDN FB GND SW VIN
TAB
5-Lead TO-263 (U)
Pin Description
Pin Number 1 2 3, TAB 4 Pin Name VIN SW GND FB 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
April 1998*
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MIC4576
MIC4576
Micrel
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 (JA) ........................................... 2C/W
Electrical Characteristics
VIN = 12V; ILOAD = 500mA; TJ = 25C, bold values indicate -40C TJ +85C; unless noted. Parameter 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 VFB = 1.0V VIN = 36V, VFB = 1.5V output = 0V output = -1V VFB = 1.5V 90 1.217 1.193 1.180 1.230 1.230 77 95 0 7.5 5 50 2 30 10 100 500 1.243 1.267 1.280 V V V % % mA mA mA nA nA Condition 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 VFB = 2.5V VIN = 36V, VFB = 4.0V output = 0V output = -1V VFB = 4.0V 4.900 8V VIN 36V, 0.5A ILOAD 3A ILOAD = 3A VFB = 4.0V VIN = 36V, VFB = 6.0V output = 0V output = -1V VFB = 6.0V 90 4.800 4.750 90 3.168 3.135
3.3 3.3 72 95 0 7.5 5
3.366 3.432 3.465
V V V % %
2 30 10
mA mA mA
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
5.100 5.200 5.250
V V V % %
2 30 10
mA mA mA
Quiescent Current
MIC4576
4-130
April 1998*
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 VOUT = 0V (regulator off) VOUT = 3.3V or 5V (regulator on) SHDN Input Current VSHDN = 5V (regulator off) VSHDN = 0V (regulator on) 2.2 2.4 4.2 3.5 180 200 1.7 5.2 50 1.4 1.2 4 0.01 1.0 0.8 30 10 220 2.3 2.5 6.9 7.5 200 Condition Min Typ Max
Micrel
Units
kHz V V A A A V V V V A A
-10
General Note: Devices are ESD protected, however, handling precautions are recommended. Note 1: VOUT = 5V
April 1998*
4-131
MIC4576
MIC4576
Micrel
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 VOUT V REF
R1 +1 R2 1
R1 Comparator Driver 3A Switch 1.23V Bandgap
R2
VOUT VREF
SW D1
L1 VOUT COUT
Error Amp. MIC4576 [Adjustable]
R1 FB GND R2
Block Diagram with External Components Adjustable Step-Down Regulator
MIC4576
4-132
April 1998*
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 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. 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.
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.
L1
5
SHDN
SW
2
3.3V/3A 6V to 36V C1 470F 63V
L1
5
33H
4
SHDN
SW
2
3.3V/3A
33H
4
6V to 24V C1 470F 35V
1
MIC4576-3.3BT VIN FB GND
3
D1 1N5822
C2 1000F 16V
1
MIC4576-3.3BT VIN FB GND
3
D1 MBR360
C2 1000F 16V
C1 C2 D1 L1 L1
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.
April 1998*
4-133
MIC4576
MIC4576
L1
5
Micrel
L1
5
SHDN
SW
2
5V/3A 8V to 36V C1 470F 63V
33H
4
SHDN
SW
2
5V/3A
33H
4
8V to 24V C1 470F 35V
1
MIC4576-5.0BT VIN FB GND
3
D1 1N5822
C2 1000F 16V
1
MIC4576-5.0BT VIN FB GND
3
D1 MBR360
C2 1000F 16V
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
C1 C2 D1 L1 L1
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 GND
3
SW FB
2
L1 68H R2 13.0k 1% R1 1.50k 1%
12V/3A
16V to 36V C1 470F 63V
MIC4576BT
1
4
MBR360
C2 1000F 16V
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
L1 SW
2
R1 0.1
VOUT 5V/4A
VIN 8V to 36V
SHDN
33H
4
1
MIC4576-5.0BT FB VIN GND
3
D1 MBR360 C5 0.01F VIN
8 1
R3 10K
C2 1000F 16V
C1 470F 63V
2
3
U3 LM358
U2
5
4 4
SHDN
FB
1
C3 470F 63V
MIC4576-5.0BT SW VIN GND
3
L2
2
R2 0.1 C4 1000F 16V
33H D2 MBR360
C1, C3 C2, C4 D1, D2 L1, L2 R1, R2 U3
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.
MIC4576
4-134
April 1998*

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