MIC4575
200kHz Simple 1A Buck 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 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 comp-
ensation is provided internally.
The MIC4575 is available in TO-220 (T) and TO-263 (U)
packages for the industrial temperature range.
Data sheets and support documentation can be found on
Micrel’s web site at www.micrel.com.
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
< 200µA typical shutdown mode
75% efficiency (adjustable version > 75% typical)
Standard inductors and capacitors are25% of typical
LM2575 values
•
Thermal shutdown
•
Overcurrent protection
•
100% electrical thermal limit burn-in
Applications
•
•
•
•
•
•
•
Simple high-efficiency step-down (buck) regulator
Efficient pre-regulator 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 Pentium
®
and similar
microprocessors
___________________________________________________________________________________________________________
Typical Application
Shutdown
Enable
5
SHDN
SW
2
L1
68µH
5.0V/1A
C2
330µF
16V
8V to 24V
C1
150µF
35V
1
MIC4575-5.0_T
V
IN
FB
GND
3
4
D1
1N5819
Fixed Regulator
Pentium is a registered trademark of Intel Corporation
Adjustable Regulator
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (
408
) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
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MIC4575
Ordering Information
Part Number
Standard
MIC4575-3.3BT
MIC4575-5.0BT
MIC4575BT
MIC4575-3.3BU
MIC4575-5.0BU
MIC4575BU
RoHS Compliant*
MIC4575-3.3WT
MIC4575-5.0WT
MIC4575WT
MIC4575-3.3WU
MIC4575-5.0WU
MIC4575WU
Voltage
3.3V
5.0V
Adj.
3.3V
5.0V
Adj.
Temperature Range
–40° to +85°C
–40° to +85°C
–40° to +85°C
–40° to +85°C
–40° to +85°C
–40° to +85°C
Package
5-Pin TO-220
5-Pin TO-220
5-Pin TO-220
5-Pin TO-263
5-Pin TO-263
5-Pin TO-263
* RoHS compliant with ‘high-melting solder’ exemption.
Pin Configuration
5
4
3
2
1
SHDN
FB
GND
SW
VIN
5-Pin TO-220 (T)
TAB
5-Pin TO-263 (U)
Pin Description
Pin Number
1
2
3, TAB
4
Pin Name
IN
SW
GND
FB
Pin Function
Supply Voltage (Input): Unregulated +4V to +40V 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
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MIC4575
Absolute Maximum Ratings
Supply Voltage (V
IN
)
(1)
..................................................+40V
Shutdown Voltage (V
SHDN
)............................. –0.3V to +36V
Output Switch (V
SW
) .......................................................–1V
Storage Temperature (T
s
) ........................... –65°C to 150°C
ESD
(2)
Operating Ratings
Supply Voltage (V
IN
).....................................................+24V
Junction Temperature (T
J
) ....................................... +150°C
Package Thermal Resistance
TO-220, TO-263 (θ
JA
) ........................................65°C/W
TO-220, TO-263 (θ
JC
) ..........................................2°C/W
Electrical Characteristics
(4)
V
IN
= 12V; I
LOAD
= 200mA; T
J
= 25°C,
bold
values indicate –40°C< T
J
< +85°C, unless noted.
Parameter
MIC4575 [Adjustable]
Feedback Voltage
Feedback Voltage
Efficiency
Feedback Bias Current
MIC4575-3.3
Output Voltage
Output Voltage
Efficiency
MIC4575-5.0
Output Voltage
Output Voltage
Efficiency
MIC4575 / -3.3 / -5.0
Oscillator Frequency
Saturation Voltage
Maximum Duty Cycle (On)
Current Limit
Output Leakage Current
3.234
6V
≤
V
IN
≤
24V, 0.2A
≤
I
LOAD
≤
1A
I
LOAD
= 1A
4.900
8V
≤
V
IN
≤
24V, 0.2A
≤
I
LOAD
≤
1A
I
LOAD
= 1A
180
I
OUT
= 1A
FB connected to 0V
Peak Current, t
ON
≤
3µs
V
IN
= 24V, FB connected to 0V
Output = 0V
Output = –1V
SHDN = 5V (regulator off)
V
OUT
= 0V (regulator off)
V
OUT
= 3.3 or 5V (regulator on)
SHDN = 5V (regulator off)
SHDN = 0V (regulator on)
Notes:
1. The MIC4575 is not guaranteed to survive a short circuit to ground for input voltage above 24V.
2. Devices are ESD sensitive. Handling precautions recommended.
Condition
Min
1.217
Typ
1.230
1.230
77
50
Max
1.243
1.267
1.280
100
500
3.366
3.432
3.465
Units
V
V
V
%
nA
nA
V
V
V
%
V
V
V
%
kHz
V
V
%
A
A
mA
mA
mA
µA
V
V
V
V
µA
µA
8V
≤
V
IN
≤
24V, 0.2A
≤
I
LOAD
≤
1A
I
LOAD
= 1A, V
OUT
= 5V
1.193
1.180
3.168
3.135
3.3
3.3
72
5.0
5.0
77
200
1
95
2.2
5.100
5.200
5.250
4.800
4.750
220
1.3
1.5
3.0
3.2
2
35
10
200
90
1.7
1.3
Quiescent Current
Standby Quiescent Current
SHDN Input Logic Level
SHDN Input Current
2.2
2.4
0
7.5
5
50
1.4
1.2
4
0.01
–10
1.0
0.8
30
10
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MIC4575
Functional Diagram
Block Diagram with External Components
Fixed Step-Down Regulator
Block Diagram with External Components
Adjustable Step-Down Regulator
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MIC4575
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 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.
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 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 the1.23V 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.
July 2009
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嵌入式系统
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