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.