July 2005

1

M9999-072805

LM2574

Micrel, Inc.

LM2574

52kHz Simple 0.5A Buck Regulator

General Description

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) switching regulator and requires a minimum of external

components.

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.

Anexternalshutdownconnectionselectsoperatingorstandby

modes. Standby current is less than 200µA.

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.

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

PWR

GND

SIG

GND

ON/

OFF

OUT

FB

LM2574

22µF

40V MAX

UNREGULATED

DC IN

REGULATED

OUTPUT

0.5A

11DQ05

220µF

330µH

Figure 1. Fixed Output Regulator Circuit

Features

• 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

• 52kHz fixed frequency internal oscillator

• Uses standard inductors

Applications

• Simple high-efficiency step-down (buck) regulator

• Efficient pre-regulator for linear regulators

• On-card switching regulators

• Positive to negative converter (buck-boost)

Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com