LM2675

SIMPLE SWITCHER® Power Converter High Efficiency 1A Step-Down Voltage Regulator

General Description

The LM2675 series of regulators are monolithic integrated circuits built with a LMDMOS process. These regulators provide all the active functions for a step-down (buck) switching regulator, capable of driving a 1A load current with excellent line and load regulation. These devices are available in fixed output voltages of 3.3V, 5.0V, 12V, and an adjustable output version.

Requiring a minimum number of external components, these regulators are simple to use and include patented internal frequency compensation (Patent Nos. 5,382,918 and 5,514,947) and a fixed frequency oscillator.

The LM2675 series operates at a switching frequency of 260 kHz, thus allowing smaller sized filter components than what would be needed with lower frequency switching regulators. Because of its very high efficiency (>90%), the copper traces on the printed circuit board are the only heat sinking needed.

A family of standard inductors for use with the LM2675 are available from several different manufacturers. This feature greatly simplifies the design of switch-mode power supplies using these advanced ICs. Also included in the datasheet are selector guides for diodes and capacitors designed to work in switch-mode power supplies.

Other features include a guaranteed ±1.5% tolerance on output voltage within specified input voltages and output load conditions, and ±10% on the oscillator frequency. External shutdown is included, featuring typically 50 µA stand-by current. The output switch includes current limiting, as well as thermal shutdown for full protection under fault conditions.

To simplify the LM2675 buck regulator design procedure, there exists computer design software, LM267X Made Simple version 6.0.

Features

• Efficiency up to 96%
• Available in SO-8, 8-pin DIP and LLP packages
• Computer Design Software LM267X Made Simple (version 6.0)
• Simple and easy to design with
• Requires only 5 external components
• Uses readily available standard inductors
• 3.3V, 5.0V, 12V, and adjustable output versions
• Adjustable version output voltage range: 1.21V to 37V
• ±1.5% max output voltage tolerance over line and load conditions
• Guaranteed 1A output load current
• 0.25Ω DMOS Output Switch
• Wide input voltage range: 8V to 40V
• 260 kHz fixed frequency internal oscillator
• TTL shutdown capability, low power standby mode
• Thermal shutdown and current limit protection

Typical Applications

• Simple High Efficiency (>90%) Step-Down (Buck) Regulator
• Efficient Pre-Regulator for Linear Regulators
• Positive-to-Negative Converter

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Supply Voltage 45V

ON/OFF Pin Voltage −0.1V ≤ V_SH ≤ 6V

Switch Voltage to Ground −1V

Boost Pin Voltage V_SW + 8V

Feedback Pin Voltage −0.3V ≤ V_FB ≤ 14V

ESD Susceptibility

Human Body Model (Note 2) 2 kV

Power Dissipation Internally Limited

Storage Temperature Range −65˚C to +150˚C

Lead Temperature

M Package

Vapor Phase (60s) +215˚C

Infrared (15s) +220˚C

N Package (Soldering, 10s) +260˚C

LLP Package (See AN-1187)

Maximum Junction Temperature +150˚C

Operating Ratings

Supply Voltage 6.5V to 40V

Junction Temperature Range −40˚C ≤ T_J ≤ +125˚C

Typical Application

Connection Diagrams

16-Lead LLP Surface Mount Package Top View 8-Lead Package Top View

Block Diagram