December 2003

1

M9999-122303

LM2574

Micrel

LM2574

52kHz Simple 0.5A Buck Regulator

General Description

The LM2574 family is a series of easy to use fixed and

adjustable switching voltage regulators. The LM2574 con-

tains 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 versions,

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.

An external shutdown connection selects operating or standby

modes. Standby current is less than 200

µA.

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 < 200

µA 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)

Ordering Information

Part Number

Junction Temp. Range

Package

LM2574BN

–40

°C to +85°C

8-pin Plastic DIP

LM2574-3.3BN

–40

°C to +85°C

8-pin Plastic DIP

LM2574-5.0BN

–40

°C to +85°C

8-pin Plastic DIP

Micrel, Inc. • 1849 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 944-0970 • http://www.micrel.com