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LM2576-12WT

52kHz Simple 3A Buck Voltage Regulator

Micrel 

LM2576

LM2576

Micrel, Inc.

52kHz Simple 3A Buck Regulator

General Description

The LM2576 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, or 12V

fixed output. Adjustable versions have an output voltage

range from 1.23V to 37V. Both versions are capable of driving

a 3A load with excellent line and load regulation.

These regulators are simple to use because they require a

minimum number of external components and include internal

frequency compensation and a fixed-frequency oscillator.

The LM2576 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.

A standard series of inductors available from several different

manufacturers are ideal for use with the LM2576 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

output load conditions. The oscillator frequency is guaranteed

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.

Features

• 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 3A output current

• Wide input voltage range:

4V to 40V

• Wide output voltage range

1.23V to 37V

• Requires only 4 external components

• 52kHz fixed frequency internal oscillator

• Low power standby mode IQ typically < 200µA

• 80% efficiency (adjustable version typically > 80%)

• Uses readily available standard inductors

• Thermal shutdown and current limit 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)

• Isolated Flyback Converter using minimum number of

external components

• Negative Boost Converter

Typical Applications

7V–40V

Unregulated

DC Input 1

4 Feedback

+VIN LM2575-5.0 Output L1

+5V, 1A

Regulated

Output

+

CIN

100µF

3

52

Gnd On/Off

330µH

D1

1N5822

+

COUT

330µF

Note: Pin numbers are for TO-220 Package

Fixed Regulator in Typical Application

7V–40V

Unregulated

DC Input 1

+VIN

LM2575

+

CIN

100µF

3

5

Gnd On/Off

4 Feedback

Output L1

2

330µH

D1

1N5822

+

COUT

330µF

+5V, 1A

Regulated

Output

R2 3.09k

R1 1k

Note: Pin numbers are for TO-220 Package

( ) VOUT = 1.23

1

+

R2

R1

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

August 2005

1

M9999-082605-B

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