LM3489

Hysteretic PFET Buck Controller with Enable Pin

General Description

The LM3489 is a high efficiency PFET switching regulator

controller that can be used to quickly and easily develop a

small, cost effective, switching buck regulator for a wide

range of applications. The hysteretic control architecture

provides for simple design without any control loop stability

concerns using a wide variety of external components. The

PFET architecture also allows for low component count as

well as ultra-low dropout, 100% duty cycle operation. An-

other benefit is high efficiency operation at light loads without

an increase in output ripple. A dedicated Enable Pin provides

a shutdown mode drawing only 7µA. Leaving the Enable Pin

unconnected defaults to on.

Current limit protection can be implemented by measuring

the voltage across the PFET’s R

need for a sense resistor. A sense resistor may be used to

improve current limit accuracy if desired. The cycle-by-cycle

current limit can be adjusted with a single resistor, ensuring

safe operation over a range of output currents.

Features

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Easy to use control methodology

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No control loop compensation required

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Wide 4.5V to 35V input range

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1.239V to V

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High efficiency 93%

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100% duty cycle operation

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Current limit protection

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Dedicated enable pin (on if unconnected)

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Shutdown mode draws only 7µA supply current

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MSOP-8

Applications

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Set-Top Box

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DSL/Cable Modem

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PC/IA

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Auto PC

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TFT Monitor

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Battery Powered Portable Applications

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Distributed Power Systems

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Always On Power

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High Power LED Driver

Typical Application Circuit

20186908

May 2006

© 2006 National Semiconductor Corporation

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