MIC4576
Micrel
MIC4576
4-128
April 1998
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 200
A
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 compensa-
tion is provided internally.
The MIC4576 is available in TO-220 (T) and TO-263 (U)
packages for the industrial temperature range.
Typical Applications
C1
470F
63V
D1
MBR360
C2
1000F
16V
L1
33H
GND
FB
SW
MIC4576-5.0BT
SHDN
8V to 36V
5V/3A
V
IN
3
4
2
5
1
Shutdown
Enable
Fixed Regulator
C1
470F
63V
MBR360
C2
1000F
16V
L1
68H
GND
FB
SW
MIC4576BT
SHDN
16V to 36V
12V/3A
V
IN
R2
13.0k
1%
R1
1.50k
1%
5
1
4
2
3
Shutdown
Enable
Adjustable Regulator
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
< 200
A 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
April 1998
4-129
MIC4576
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
MIC4576BT
Adjustable
40
C to +85
C
5-lead TO-220
MIC4576-3.3BU
3.3V
40
C to +85
C
5-lead TO-263
MIC4576-5.0BU
5.0V
40
C to +85
C
5-lead TO-263
MIC4576BU
Adjustable
40
C to +85
C
5-lead TO-263
Pin Configuration
TAB
5
SHDN
4
FB
3
GND
2
SW
1
V
IN
5-Lead TO-220 (T)
TAB
5
SHDN
4
FB
3
GND
2
SW
1
V
IN
5-Lead TO-263 (U)
Pin Description
Pin Number
Pin Name
Pin Function
1
V
IN
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
Ground
4
FB
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.
5
SHDN
Shutdown (Input): Logic low enables regulator. Logic high (> 2.4V) shuts
down regulator.
MIC4576
Micrel
MIC4576
4-130
April 1998
Electrical Characteristics
V
IN
= 12V; I
LOAD
= 500mA; T
J
= 25
C, bold values indicate 40
C
T
J
+85
C; unless noted.
Parameter
Condition
Min
Typ
Max
Units
MIC4576 [Adjustable]
Feedback Voltage
1.217
1.230
1.243
V
Feedback Voltage
8V
V
IN
36V, 0.5A
I
LOAD
3A
1.193
1.230
1.267
V
1.180
1.280
V
Efficiency
I
LOAD
= 3A, Note 1
77
%
Maximum Duty Cycle (On)
V
FB
= 1.0V
90
95
%
Output Leakage Current
V
IN
= 36V, V
FB
= 1.5V
output = 0V
0
2
mA
output = 1V
7.5
30
mA
Quiescent Current
V
FB
= 1.5V
5
10
mA
Feedback Bias Current
50
100
nA
500
nA
MIC4576-3.3
Output Voltage
3.234
3.3
3.366
V
Output Voltage
6V
V
IN
36V, 0.5A
I
LOAD
3A
3.168
3.3
3.432
V
3.135
3.465
V
Efficiency
I
LOAD
= 3A
72
%
Maximum Duty Cycle (On)
V
FB
= 2.5V
90
95
%
Output Leakage Current
V
IN
= 36V, V
FB
= 4.0V
output = 0V
0
2
mA
output = 1V
7.5
30
mA
Quiescent Current
V
FB
= 4.0V
5
10
mA
MIC4576-5.0
Output Voltage
4.900
5.0
5.100
V
Output Voltage
8V
V
IN
36V, 0.5A
I
LOAD
3A
4.800
5.0
5.200
V
4.750
5.250
V
Efficiency
I
LOAD
= 3A
77
%
Maximum Duty Cycle (On)
V
FB
= 4.0V
90
95
%
Output Leakage Current
V
IN
= 36V, V
FB
= 6.0V
output = 0V
0
2
mA
output = 1V
7.5
30
mA
Quiescent Current
V
FB
= 6.0V
5
10
mA
Absolute Maximum Ratings
Supply Voltage (V
IN
) ................................................... +40V
Shutdown Voltage (V
SHDN
) .......................... 0.3V to +36V
Output Switch (V
SW
), Steady State ............................... 1V
Feedback Voltage (V
FB
) [Adjustable] ......................... +3.8V
Storage Temperature ............................... 65
C to +150
C
Operating Ratings
Supply Voltage (V
IN
) ................................................... +36V
Junction Temperature ............................................. +150
C
Package Thermal Resistance
TO-220, TO-263 (
JA
) ......................................... 65
C/W
TO-220, TO-263 (
JA
) ........................................... 2
C/W
April 1998
4-131
MIC4576
MIC4576
Micrel
Parameter
Condition
Min
Typ
Max
Units
MIC4576 / -3.3 / -5.0
Oscillator Frequency
180
200
220
kHz
Saturation Voltage
I
OUT
= 3A
1.7
2.3
V
2.5
V
Current Limit
peak current, t
ON
3
s; V
FB
= 0V
4.2
5.2
6.9
A
3.5
7.5
A
Standby Quiescent Current
V
SHDN
= 5V (regulator off), V
FB
= 0V
50
200
A
SHDN Input Logic Level
V
OUT
= 0V (regulator off)
2.2
1.4
V
2.4
V
V
OUT
= 3.3V or 5V (regulator on)
1.2
1.0
V
0.8
V
SHDN Input Current
V
SHDN
= 5V (regulator off)
4
30
A
V
SHDN
= 0V (regulator on)
10
0.01
10
A
General Note: Devices are ESD protected, however, handling precautions are recommended.
Note 1:
V
OUT
= 5V
MIC4576
Micrel
MIC4576
4-132
April 1998
200kHz
Oscillator
1.23V
Bandgap
3A
Switch
Thermal
Shutdown
Current
Limit
Driver
Internal
Regulator
FB
SW
GND
V
IN
+36V max.
C
IN
C
OUT
L1
D1
Shutdown
Enable
SHDN
V
OUT
MIC4576
[Adjustable]
R1
R2
Com-
parator
Error
Amp.
V
OUT
V
REF
R1
R2
+ 1
R1
R2
V
OUT
V
REF
1
200kHz
Oscillator
1.23V
Bandgap
3A
Switch
Thermal
Shutdown
Current
Limit
Driver
Internal
Regulator
FB
SW
GND
V
IN
+36V max.
C
IN
C
OUT
L1
D1
Shutdown
Enable
SHDN
V
OUT
MIC4576-x.x
R1
R2
Com-
parator
Error
Amp.
Block Diagram with External Components
Adjustable Step-Down Regulator
Block Diagram with External Components
Fixed Step-Down Regulator
Block Diagrams
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