MIC4575
Micrel
4-106
April 1998
MIC4575
200kHz Simple 1A Buck Voltage Regulator
General Description
The MIC4575 is a series of easy to use fixed and adjustable
BiCMOS step-down (buck) switch-mode voltage regulators.
The 200kHz MIC4575 duplicates the pinout and function of
the 52kHz LM2575. The higher switching frequency may
allow up to a 2:1 reduction in output filter inductor size.
The MIC4575 is available in 3.3V, and 5V fixed output
versions or a 1.23V to 20V adjustable output version. Both
versions are capable of driving a 1A 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 MIC4575 is available in TO-220 (T) and TO-263 (U)
packages for the industrial temperature range.
Typical Applications
C1
150F
35V
D1
1N5819
C2
330F
16V
L1
68H
GND
FB
SW
MIC4575-5.0BT
SHDN
8V to 24V
5.0V/1A
V
IN
3
4
2
5
1
Shutdown
Enable
Fixed Regulator
C1
22F
35V
MBRS130LT3
C2
330F
6.3V
L1
68H
GND
FB
MIC4575BU
SW
SHDN
6V to 24V
3.6V/1A
V
IN
R2
2.37k
1%
R1
1.24k
1%
4
2
3
1
5
C3
3300pF
D1
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 1A switch current
Wide 4V to 24V input voltage range
Wide 1.23V to 20V output voltage range
Requires minimum external components
< 200
A typical shutdown mode
75% efficiency (adjustable version > 75% typical)
Standard inductors and capacitors are
25% of typical LM2575 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 6V to 3.3V for Intel PentiumTM
and similar microprocessors
April 1998
4-107
MIC4575
Micrel
4
Ordering Information
Part Number
Voltage
Temperature Range
Package
MIC4575-3.3BT
3.3V
40
C to +85
C
5-lead TO-220
MIC4575-5.0BT
5.0V
40
C to +85
C
5-lead TO-220
MIC4575BT
Adjustable
40
C to +85
C
5-lead TO-220
MIC4575-3.3BU
3.3V
40
C to +85
C
5-lead TO-263
MIC4575-5.0BU
5.0V
40
C to +85
C
5-lead TO-263
MIC4575BU
Adjustable
40
C to +85
C
5-lead TO-263
Pin Description
Pin Number
Pin Name
Pin Function
1
V
IN
Supply Voltage (Input): Unregulated +4V to +40V 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.
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)
MIC4575
Micrel
4-108
April 1998
Electrical Characteristics
V
IN
= 12V; I
LOAD
= 200mA; T
J
= 25
C, bold values indicate 40
C
T
J
+85
C; unless noted.
Parameter
Condition
Min
Typ
Max
Units
MIC4575 [Adjustable]
Feedback Voltage
1.217
1.230
1.243
V
Feedback Voltage
8V
V
IN
24V, 0.2A
I
LOAD
1A
1.193
1.230
1.267
V
1.180
1.280
V
Efficiency
I
LOAD
= 1A, V
OUT
= 5V
77
%
Feedback Bias Current
50
100
nA
500
nA
MIC4575-3.3
Output Voltage
3.234
3.3
3.366
V
Output Voltage
6V
V
IN
24V, 0.2A
I
LOAD
1A
3.168
3.3
3.432
V
3.135
3.465
V
Efficiency
I
LOAD
= 1A
72
%
MIC4575-5.0
Output Voltage
4.900
5.0
5.100
V
Output Voltage
8V
V
IN
24V, 0.2A
I
LOAD
1A
4.800
5.0
5.200
V
4.750
5.250
V
Efficiency
I
LOAD
= 1A
77
%
MIC4575 / -3.3 / -5.0
Oscillator Frequency
180
200
220
kHz
Saturation Voltage
I
OUT
= 1A
1
1.3
V
1.5
V
Maximum Duty Cycle (On)
FB connected to 0V
90
95
%
Current Limit
Peak Current, t
ON
3
s
1.7
2.2
3.0
A
1.3
3.2
A
Output Leakage Current
V
IN
= 24V, FB connected to 0V
Output = 0V
0
2
mA
Output = 1V
7.5
30
mA
Quiescent Current
5
10
mA
Standby Quiescent Current
SHDN = 5V (regulator off)
50
200
A
SHDN Input Logic Level
V
OUT
= 0V (regulator off)
2.2
1.4
V
2.4
V
V
OUT
= 3.3 or 5V (regulator on)
1.2
1.0
V
0.8
V
SHDN Input Current
SHDN = 5V (regulator off)
4
30
A
SHDN = 0V (regulator on)
10
0.01
10
A
General Note: Devices are ESD protected, however, handling precautions are recommended.
Note 1:
The MIC4575 is not guaranteed to survive a short circuit to ground for input voltage above 24V.
Absolute Maximum Ratings
Supply Voltage (V
IN
) Note 1 ....................................... +40V
Shutdown Voltage (V
SHDN
) .......................... 0.3V to +36V
Output Switch (V
SW
) steady state ................................. 1V
Storage Temperature (T
S
) ......................... 65
C to 150
C
Operating Ratings
Supply Voltage (V
IN
) ................................................... +24V
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
4-109
MIC4575
Micrel
4
200kHz
Oscillator
1.23V
Bandgap
1A
Switch
Thermal
Shutdown
Current
Limit
Driver
Internal
Regulator
FB
SW
GND
V
IN
+24V max.
C
IN
C
OUT
L1
D1
Shutdown
Enable
SHDN
V
OUT
MIC4575
[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
1A
Switch
Thermal
Shutdown
Current
Limit
Driver
Internal
Regulator
FB
SW
GND
V
IN
+24V max.
C
IN
C
OUT
L1
D1
Shutdown
Enable
SHDN
V
OUT
MIC4575-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
MIC4575
Micrel
4-110
April 1998
Functional Description
The MIC4575 is a variable duty cycle switch-mode regulator
with an internal power switch. Refer to the block diagrams.
Supply Voltage
The MIC4575 operates from a +4V to +24V 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 logic-
high shuts down the internal regulator which reduces the
current to typically 50
A.
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 com-
parator output. A lower feedback voltage increases the duty
cycle.
Output Switching
When the internal switch is on, an increasing current flows
from the supply V
IN,
through external storage inductor L1, to
output capacitor C
OUT
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 C
OUT
.
Output Capacitor
External output capacitor C
OUT
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.
C1
150F
35V
D1
1N5819
C2
330F
16V
L1
68H
GND
FB
SW
MIC4575-3.3BT
SHDN
6V to 24V
3.3V/1A
V
IN
C1 Nichicon
UPL1V151MPH, ESR = 0.12
C2 Nichicon
UPL1C331MPH, ESR = 0.12
D1 Motorola
1N5819
L1
Sumida
RCH106-680K, DCR = 0.22
L1
Bi
HM77-11003, DCR = 0.233
, Note 2
3
4
2
5
1
Figure 1. 6V24V to 3.3V/1A Buck Converter
Through Hole
C1
150F
35V
D1
1N5819
C2
330F
16V
L1
68H
GND
FB
SW
MIC4575-5.0BT
SHDN
8V to 24V
5.0V/1A
V
IN
C1 Nichicon
UPL1J151MPH, ESR = 0.12
C2 Nichicon
UPL1C331MPH, ESR = 0.12
D1 Motorola
1N5819
L1
Sumida
RCH106-680K, DCR = 0.22
L2
Bi
HM77-11003, DCR = 0.233
, Note 2
3
4
2
5
1
Figure 2. 8V24V to 5V/1A Buck Converter
Through Hole
C1
68F
63V
MBR160
C2
330F
16V
L1
150H
GND
FB
SW
MIC4575BT
SHDN
16V to 24V
12V/1A
V
IN
R2
13.0k
1%
R1
1.50k
1%
C1 Nichicon
UPL1J680MPH, ESR = 0.17
C2 Nichicon
UPL1C331MPH, ESR = 0.12
D1 Motorola
MBR160
L1
Sumida
RCH110-151K, DCR = 0.23
5
1
4
2
3
Figure 3. 16V24V to 12V/1A Buck Converter, Through Hole
Note 2: Surface-
mount component.
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