LM3686

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SNVS520E – AUGUST 2008 – REVISED MAY 2013

LM3686 Step-Down DC-DC Converter with Integrated Post Linear Regulators System and

Low-Noise Linear Regulator

Check for Samples: LM3686

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FEATURES

APPLICATIONS

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DC-DC REGULATOR

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Moblie TV

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Hand-Held Radios

Factory Programmed)

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Personal Digital Assistants

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600 mA Maximum Load Capability (LILO =

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Palm-top PCs

OFF)

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Portable Instruments

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3 MHz PWM Fixed Switching Frequency (Typ.)

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Battery-Powered Devices

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Automatic PFM/PWM Mode Switching

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Portable Personal Clients

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Internal Synchronous Rectification for High

Efficiency

DESCRIPTION

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Internal Soft Start

The LM3686 is a step-down DC-DC converter with

one integrated very low dropout linear regulator and a

DUAL RAIL LINEAR REGULATOR: LILO

low noise linear regulator optimized for powering

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Load Transients < 50 mV Peak Typ.

ultra-low voltage circuits from a single Li-Ion cell or 3

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Line Transients < 1 mV Peak Typ.

cell NiMH/NiCd batteries. It provides three outputs

with combined load current up to 900 mA over an

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input voltage range from 2.7V to 5.5V.

Factory Programmed)

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The device offers superior features and performance

for many applications. Automatic intelligent switching

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350 mA Maximum Load Capability (Large FET)

between PWM low-noise and PFM low-current mode

LINEAR REGULATOR: LDO

offers improved system control. During full-power

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Load Transients < 80 mV Peak Typ.

operation, a fixed-frequency 3 MHz (typ.), PWM

mode drives loads from ~70 mA to 600 mA max.

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Line Transients < 1 mV Peak Typ.

Hysteretic PFM mode extends the battery life through

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reduction of the quiescent current to 28

μA (typ.) at

Factory Programmed)

light load and system standby. Internal synchronous

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rectification provides high efficiency.

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300 mA Maximum Load Capability

Three enable pins allow the separate operation of

COMBINED GLOBAL FEATURES

either the DC-DC, post-regulation linear regulator or

the linear regulator alone. If the DC-DC is not

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enabled during startup of the post-regulation linear

Higher

regulator, a parallel small pass transistor supplies the

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900 mA Maximum Combined Load Capability

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Operates From a Single Li-Ion Cell or 3 Cell

the combined operation where both enables are

raised

together,

the

small

pass

transistor

is

NiMH/NiCd Batteries

deactivated and the big pass transistor provides 350

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Only Six Tiny Surface-mount External

mA output current. In shutdown mode (Enable pins

Components Required (One Inductor, Five

pulled low), the device turns off and reduces battery

Ceramic Capacitors)

consumption to 2.5

μA (typ.).

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12–bump DSBGA

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2

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PRODUCTION DATA information is current as of publication date.

Copyright © 2008–2013, Texas Instruments Incorporated

Products conform to specifications per the terms of the Texas

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