1 Features

1? Efficiency up to 92%

? Simple and Easy to Design Using Off-the-Shelf

External Components

? 100-mΩ DMOS Output Switch

? 3.3-V, 5-V, and 12-V Fixed Output and Adjustable

(1.2 V to 37 V) Versions

? 50-μA Standby Current When Switched OFF

? ±2% Maximum Output Tolerance Over Full Line

and Load Conditions

? Wide Input Voltage Range: 8 V to 40 V

? External Sync Clock Capability (280 kHz to

400 kHz)

? 260-kHz Fixed Frequency Internal Oscillator

? ?40°C to 125°C Operating Junction Temperature

Range

2 Applications

? Simple to Design, High Efficiency (> 90%) Step-

Down Switching Regulators

? Efficient System Preregulator for Linear Voltage

Regulators

? Battery Chargers

? Communications and Radio Equipment Regulator

With Synchronized Clock Frequency

3 Description

The LM2677 series of regulators are monolithic

integrated circuits which provide all of the active

functions for a step-down (buck) switching regulator

capable of driving up to 5-A loads with excellent line

and load regulation characteristics. High efficiency

(>90%) is obtained through the use of a low onresistance

DMOS power switch. The series consists

of fixed output voltages of 3.3-V, 5-V, and 12-V and

an adjustable output version.

The SIMPLE SWITCHER? concept provides for a

complete design using a minimum number of external

components. The switching clock frequency can be

provided by an internal fixed frequency oscillator

(260 kHz) or from an externally provided clock in the

range of 280 kHz to 400 kHz, which allows the use of

physically smaller-sized components. A family of

standard inductors for use with the LM2677 are

available from several manufacturers to greatly

simplify the design process. The external Sync clock

provides direct and precise control of the output ripple

frequency for consistent filtering or frequency

spectrum positioning.

The LM2677 series also has built-in thermal

shutdown, current-limiting, and an ON/OFF control

input that can power down the regulator to a low

50-μA quiescent-current standby condition. The

output voltage is ensured to a ±2% tolerance.