MICREL MIC4576

MIC4576
Micrel
MIC4576
200kHz Simple 3A Buck Voltage Regulator
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 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.
• 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
• < 200µA 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
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.
Applications
•
•
•
•
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The MIC4576 is available in TO-220 (T) and TO-263 (U)
packages for the industrial temperature range.
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 Pentium™
and similar microprocessors
Typical Applications
L1
5
Shutdown
Enable
8V to 36V
1
C1
470µF
63V
SHDN
SW
MIC4576-5.0BT
FB
VIN
GND
2
5V/3A
33µH
4
D1
MBR360
3
C2
1000µF
16V
Fixed Regulator
Shutdown
Enable
16V to 36V
C1
470µF
63V
5
SHDN
SW
MIC4576BT
1
FB
VIN
2
L1
68µH
4
GND
MBR360
3
12V/3A
R2
13.0k
1%
R1
1.50k
1%
C2
1000µF
16V
Adjustable Regulator
MIC4576
4-128
April 1998•
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
TAB
5
4
3
2
1
SHDN
FB
GND
SW
VIN
5-Lead TO-220 (T)
TAB
5
4
3
2
1
SHDN
FB
GND
SW
VIN
5-Lead TO-263 (U)
Pin Description
Pin Number
Pin Name
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, TAB
GND
4
FB
5
SHDN
April 1998•
Pin Function
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
Operating 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 ............................... –65°C to +150°C
Supply Voltage (VIN) ................................................... +36V
Junction Temperature ............................................. +150°C
Package Thermal Resistance
TO-220, TO-263 (θJA) ......................................... 65°C/W
TO-220, TO-263 (θJA) ........................................... 2°C/W
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]
Feedback Voltage
Feedback Voltage
8V ≤ VIN ≤ 36V, 0.5A ≤ ILOAD ≤ 3A
Efficiency
ILOAD = 3A, Note 1
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
April 1998•
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:
VOUT = 5V
April 1998•
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MIC4576
MIC4576
Micrel
Block Diagrams
+36V max.
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
+36V 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
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
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 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
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.
L1
5
6V to 24V
C1
470µF
35V
C1
C2
D1
L1
L1
1
SHDN
SW
MIC4576-3.3BT
VIN
FB
GND
3
Nichicon
Nichicon
Motorola
Coiltronics
Bi
2
For a mathematical approach to component selection and
circuit design, refer to Application Note 14.
L1
3.3V/3A
5
33µH
4
D1
1N5822
6V 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
C1
C2
D1
L1
L1
Figure 1. 6V–24V to 3.3V/3A Buck Converter
Through Hole
Note 2:
1
SHDN
SW
MIC4576-3.3BT
VIN
FB
GND
3
Nichicon
Nichicon
Motorola
Coiltronics
Bi
2
3.3V/3A
33µH
4
D1
MBR360
C2
1000µF
16V
UPL1J471MRH, ESR = 0.039Ω
UPL1C102MPH, ESR = 0.047Ω
MBR360
PL52C-33-1000 DCR = 0.036
HM77-30004, DCR = 0.045Ω, Note 2
Figure 2. 6V–36V to 3.3V/3A Buck Converter
Through Hole
Surface-mount component.
April 1998•
4-133
MIC4576
MIC4576
Micrel
L1
5
8V to 24V
C1
470µF
35V
1
SHDN
SW
MIC4576-5.0BT
VIN
FB
GND
C1 Nichicon
C2 Nichicon
D1 Motorola
L1 Coiltronics
L1 Bi
L1
5V/3A
2
5
33µH
D1
1N5822
3
8V to 36V
C2
1000µF
16V
4
C1
470µF
63V
C1
C2
D1
L1
L1
UPL1J471MPH, ESR = 0.046Ω
UPL1C102MPH, ESR = 0.047Ω
MBR5822
PL52C-33-1000, DCR = 0.036
HM77-30004, DCR = 0.045Ω, Note 2
SHDN
SW
MIC4576BT
16V to 36V
1
FB
VIN
C1
470µF
63V
Nichicon
Nichicon
Motorola
Coiltronics
Bi
2
5V/3A
33µH
4
D1
MBR360
C2
1000µF
16V
UPL1J471MRH, ESR = 0.039Ω
UPL1C102MPH, ESR = 0.047Ω
MBR360
PLS2C-33-1000, DCR = 0.036
HM77-30004, DCR = 0.045Ω, Note 2
12V/3A
68µH
4
MBR360
3
Nichicon
Nichicon
Motorola
Bi
MIC4576-5.0BT
VIN
FB
GND
3
L1
2
GND
C1
C2
D1
L1
SW
Figure 4. 8V–36V to 5V/3A Buck Converter
Through Hole
Figure 3. 8V–24V to 5V/3A Buck Converter
Through Hole
5
1
SHDN
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
Figure 5. 16V–36V to 12V/3A Buck Converter
Through Hole
U1
5
VIN
8V to 36V
1
SHDN
MIC4576-5.0BT
FB
VIN
GND
VOUT
5V/4A
R1
0.1Ω
L1
SW
2
33µH
C2
1000µF
16V
4
D1
MBR360
3
C1
470µF
63V
R3
10K
C5
0.01µF
VIN
8
2
1
3
4
U2
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 component.
MIC4576
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April 1998•