LM3670

Miniature Step-Down DC-DC Converter for Ultra Low

Voltage Circuits

General Description

The LM3670 step-down DC-DC converter is optimized for

powering ultra-low voltage circuits from a single Li-Ion cell or

3 cell NiMH/NiCd batteries. It provides up to 350 mA load

current, over an input voltage range from 2.5V to 5.5V. There

are several different fixed voltage output options available as

well as an adjustable output voltage version.

The device offers superior features and performance for

mobile phones and similar portable applications with com-

plex power management systems. Automatic intelligent

switching between PWM low-noise and PFM low-current

mode offers improved system control. During full-power op-

eration, a fixed-frequency 1 MHz (typ). PWM mode drives

loads from

∼70 mA to 350 mA max, with up to 95% efficiency.

Hysteretic PFM mode extends the battery life through reduc-

tion of the quiescent current to 15 µA (typ) during light

current loads and system standby. Internal synchronous rec-

tification provides high efficiency (90 to 95% typ. at loads

between 1 mA and 100 mA). In shutdown mode (Enable pin

pulled low) the device turns off and reduces battery con-

sumption to 0.1 µA (typ.).

The LM3670 is available in a SOT23-5 package. A high

switching frequency - 1 MHz (typ) - allows use of tiny

surface-mount components. Only three external surface-

mount components, an inductor and two ceramic capacitors,

are required.

Features

n

V

n

2.5V

≤ V

IN

≤ 5.5V

n

15 µA typical quiescent current

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350 mA maximum load capability

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1 MHz PWM fixed switching frequency (typ.)

n

Automatic PFM/PWM mode switching

n

Available in fixed output voltages as well as an

adjustable version

n

SOT23-5 package

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Low drop out operation - 100% duty cycle mode

n

Internal synchronous rectification for high efficiency

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Internal soft start

n

0.1 µA typical shutdown current

n

Operates from a single Li-Ion cell or 3 cell NiMH/NiCd

batteries

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Only three tiny surface-mount external components

required (one inductor, two ceramic capacitors)

n

Current overload protection

Applications

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Mobile phones

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Hand-Held Radios

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Personal Digital Assistants

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Palm-top PCs

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Portable Instruments

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Battery Powered Devices

Typical Application

20075801

FIGURE 1. 1.8V - Fixed Output Voltage - Typical Application Circuit

December 2004

© 2004 National Semiconductor Corporation

DS200758

www.national.com