LM2575
Micrel, Inc.
LM2575
52kHz Simple 1A Buck Regulator
General Description
Features
The LM2575 series of monolithic integrated circuits provide
all the active functions for a step-down (buck) switching
regulator. Fixed versions are available with a 3.3V, 5V, 12V,
fixed output. Adjustable versions have an output voltage
rangefrom1.23Vto37V. Bothversionsarecapableofdriving
a 1A load with excellent line and load regulation.
• 3.3V, 5V, 12V, 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 output current
• Wide input voltage range:
4V to 40V
These regulators are simple to use because they require a
minimumnumberofexternalcomponentsandincludeinternal
frequency compensation and a fixed-frequency oscillator.
• Wide output voltage range
1.23V to 37V
The LM2575 series offers a high efficiency replacement for
popular three-terminal adjustable linear regulators. It
substantially reduces the size of the heat sink, and in many
cases no heat sink is required.
• Requires only 4 external components
• 52kHz fixed frequency internal oscillator
• Low power standby mode I typically <200µA
Q
• 80% efficiency (adjustable version typically >80%)
• Uses readily available standard inductors
• Thermal shutdown and current limit protection
• 100% electrical thermal limit burn-in
Astandardseriesofinductorsavailablefromseveraldifferent
manufacturers are ideal for use with the LM2575 series. This
feature greatly simplifies the design of switch-mode power
supplies.
The feedback voltage is guaranteed to ±2% tolerance for
adjustable versions, and the output voltage is guaranteed to
±3% for fixed versions, within specified input voltages and
outputloadconditions.Theoscillatorfrequencyisguaranteed
to ±10%. External shutdown is included, featuring less than
200µA standby current. The output switch includes cycle-by-
cycle current limiting and thermal shutdown for full protection
under fault conditions.
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)
• Isolated Flyback Converter using minimum number of
external components
• Negative Boost Converter
Typical Applications
870 20
7V–40V
7V–40V
Unregulated
DC Input
Unregulated
+5V, 1A
+5V, 1A
4
4
Feedback
L1
330µH
Feedback
DC Input
1
Regulated
Output
1
Regulated
Output
LM2575-5.0
LM2575
5
L1
330µH
D1
Output
2
Output
2
+VIN
+VIN
+
+
+
+
R2 3.09k
R1 1k
3
5
3
C
C
IN
IN
Gnd On/Off
Gnd On/Off
D1
COUT
COUT
100µF
100µF
1N5822
1N5822
330µF
330µF
Note: Pin numbers are for TO-220 Package
Note: Pin numbers are for TO-220 Package
R2
VOUT = 1.23 1 +
( )
R1
Fixed Regulator in Typical Application
Adjustable Regulator in Fixed Output Application
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
M9999-042205
April 2005
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