1 Features

• 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 on-resistance 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.

1. For all available packages, see the orderable addendum at the end of the data sheet.

Typical Application