LM2574
Micrel, Inc.
LM2574
52kHz Simple 0.5A Buck Regulator
General Description
Features
The LM2574 family is a series of easy to use fixed and ad-
justable switching voltage regulators. The LM2574 contains
all of the active circuitry necessary to construct a stepdown
(buck)switchingregulatorandrequiresaminimumofexternal
components.
• 3.3V, 5V, 12V, and adjustable output versions
• Adjustable version output 1.23V to 37V ±4% max. over
line and load conditions.
• Guaranteed 0.5A output current
• Wide input voltage, up to 40V
• Thermal shutdown and current limit protection
• Requires only 4 external components.
• Shutdown capability (standby mode)
• Low power standby mode < 200µA Typical
• High-efficiency
The LM2574 is available in 3.3V and 5V fixed output ver-
sions, or an adjustable version with an output voltage range
of 1.23V to 37V. Output voltage is guaranteed to ±4% for
specified input and load conditions.
The LM2574 can supply 0.5A while maintaining excellent
line and load regulation. The output switch includes cycle-
by-cycle current limiting, as well as thermal shutdown for full
protection under fault conditions.
• 52kHz fixed frequency internal oscillator
• Uses standard inductors
Applications
Anexternalshutdownconnectionselectsoperatingorstandby
modes. Standby current is less than 200µA.
• Simple high-efficiency step-down (buck) regulator
• Efficient pre-regulator for linear regulators
• On-card switching regulators
Heat sinks are generally unnecessary due the regulator’s
high efficiency. Adequate heat transfer is usually provided
by soldering all package pins to a printed circuit board.
• Positive to negative converter (buck-boost)
The LM2574 includes internal frequency compensation and
an internal 52kHz fixed frequency oscillator guaranteed to
±10% of the frequency.
Circuits constructed around the LM2574 use a standard
series of inductors which are available from several different
manufacturers.
All support documentation can be found on Micrel’s web site
at www.micrel.com.
Typical Application
40V MAX
UNREGULATED
DC IN
FB
VIN
REGULATED
OUTPUT
C
22µF
330µH
0.5A
IN
LM2574
OUT
PWR SIG ON/
GND GND OFF
COUT
11DQ05
220µF
Figure 1. Fixed Output Regulator Circuit
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
July 2005
1
M9999-072805