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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.

o Fixed 200kHz operation
o 3.3V, 5V, and adjustable output versions
o Voltage over specified line and load conditions:
Fixed version: ?3% max. output voltage
Adjustable version: ? 2% max. feedback voltage
o Guaranteed 3A switch current
o Wide 4V to 36V input voltage range
o Wide 1.23V to 33V output voltage range
o Requires minimum external components
o & lt; 200uA typical shutdown mode
o 75% efficiency (adjustable version & gt; 75% typical)
o Standard inductors are 25% of typical LM2576 values
o Thermal shutdown
o Overcurrent protection
o 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 200uA
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
o
o
o
o
o
o
o

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(TM)
and similar microprocessors

Typical Applications
L1
5

Shutdown
Enable

8V to 36V

1

C1
470uF
63V

SHDN

SW

MIC4576-5.0BT
FB
VIN
GND

2

5V/3A

33uH
4

D1
MBR360

3

C2
1000uF
16V

Fixed Regulator

Shutdown
Enable

16V to 36V
C1
470uF
63V

5

SHDN

SW

MIC4576BT
1

FB

VIN

2

L1
68uH

4

GND
MBR360

3

12V/3A
R2
13.0k
1%
R1
1.50k
1%

C2
1000uF
16V

Adjustable Regulator

MIC4576

4-128

April 1998o

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 1998o

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 ( & gt; 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 (?JA) ......................................... 65°C/W
TO-220, TO-263 (?JA) ........................................... 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

77
90

%

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

72
90

%

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

77
90

%

95

%

0
7.5

4-130

mA
mA

5

VFB = 6.0V

2
30
10

mA

April 1998o

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

uA

MIC4576 / -3.3 / -5.0
Oscillator Frequency
Saturation Voltage

IOUT = 3A

Current Limit

peak current, tON <= 3us; 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)

1.4

V
V

1.2

-10

1.0
0.8

V
V

4
0.01

30
10

uA
uA

General Note: Devices are ESD protected, however, handling precautions are recommended.
Note 1:

VOUT = 5V

April 1998o

4-131

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 1998o

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 50uA.
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
470uF
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

33uH
4

D1
1N5822

6V to 36V

C2
1000uF
16V

C1
470uF
63V

UPL1V471MPH, ESR = 0.046Ohm
UPL1C221MPH, ESR = 0.047Ohm
1N5822
PL52C-33-1000, DCR = 0.036Ohm
HM77-30004, DCR = 0.045Ohm, 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

33uH
4

D1
MBR360

C2
1000uF
16V

UPL1J471MRH, ESR = 0.039Ohm
UPL1C102MPH, ESR = 0.047Ohm
MBR360
PL52C-33-1000 DCR = 0.036
HM77-30004, DCR = 0.045Ohm, Note 2

Figure 2. 6V-36V to 3.3V/3A Buck Converter
Through Hole

Surface-mount component.

April 1998o

4-133

MIC4576

MIC4576

Micrel
L1
5

8V to 24V
C1
470uF
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

33uH

D1
1N5822

3

8V to 36V

C2
1000uF
16V

4

C1
470uF
63V

UPL1J471MPH, ESR = 0.046Ohm
UPL1C102MPH, ESR = 0.047Ohm
MBR5822
PL52C-33-1000, DCR = 0.036
HM77-30004, DCR = 0.045Ohm, Note 2

C1
C2
D1
L1
L1

SHDN

SW

MIC4576BT

16V to 36V

1

FB

VIN

C1
470uF
63V

Nichicon
Nichicon
Motorola
Coiltronics
Bi

2

5V/3A

33uH
4

D1
MBR360

C2
1000uF
16V

UPL1J471MRH, ESR = 0.039Ohm
UPL1C102MPH, ESR = 0.047Ohm
MBR360
PLS2C-33-1000, DCR = 0.036
HM77-30004, DCR = 0.045Ohm, Note 2

12V/3A

68uH
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
1000uF
16V

UPL1J471MPH, ESR = 0.039Ohm
UPL1C102MPH, ESR = 0.047Ohm
MBR360
HM77-29006, DCR = 0.08Ohm

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
0.1Ohm

L1
SW

2

33uH
C2
1000uF
16V

4

D1
MBR360

3

C1
470uF
63V

R3
10K

C5
0.01uF
VIN
8

2

1
3
4

U2
5

1

C3
470uF
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

33uH
D2
MBR360

R2
0.1Ohm
C4
1000uF
16V

UPL1J471MRH, ESR = 0.039Ohm
UPL1C102MPH, ESR = 0.047Ohm
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 1998o

This datasheet has been downloaded from:
www.DatasheetCatalog.com
Datasheets for electronic components.