LM3485

Hysteretic PFET Buck Controller

General Description

The LM3485 is a high efficiency PFET switching regulator

controller that a system designer can use to quickly and

easily develop a small, low cost, switching buck regulator for

a wide range of applications. The use of a hysteretic control

scheme provides for simple design without any control loop

stability concerns using a wide variety of external compo-

nents. The PFET architecture also allows for low component

count as well as ultra-low dropout operation. Another benefit

is high efficiency operation at light loads without an increase

in output ripple. Current limit protection circuit is provided by

measuring the voltage across the PFET’s R

nating a costly sense resistor. The current limit can be ad-

justed allowing for designs at various output currents and

costs.

Features

n

Easy to use control methodology

n

No control loop compensation required

n

4.5V to 35V wide input range

n

1.242V to V

n

High Efficiency 93%

n

100% duty cycle

n

n

Current limit protection

n

MSOP-8

Applications

n

Set-Top Box

n

DSL/Cable Modem

n

PC/IA

n

Auto PC

n

TFT Monitor

n

Battery Powered Portable Applications

n

Distributed Power Systems

n

Always On Power

Typical Application Circuit

20034608

May 2002

© 2002 National Semiconductor Corporation

DS200346

www.national.com