OSCILLATOR

RAMP

GENERATOR

OUTPUT

SHORT

PROTECTION

THERMAL

SHUTDOWN

DRIVER

CONTROL LOGIC

PWM

COMP.

Ref3

Ref2

NCP

OVERVOLTAGE

DETECTOR

ERROR

AMP

OLP

Ref4

LIGHT-LOAD

CHECK COMP

ECO COMP

FB

GND

SW

VIN

EN

BYPASS

CONTROL

FB

Ref1

MODE

SOFT

START

LM3281

SNVSA38 – NOVEMBER 2014

www.ti.com

7 Detailed Description

7.1 Overview

The LM3281 is a size- and performance-optimized step-down DC-DC converter for powering power amplifiers,

front-end modules, wireless connectivity solutions, and a wide variety of other applications. The device

complements the portfolio of SuPA (Supply for PA) products by combining small solution size, low dropout

analog bypass with smooth mode transitions, very low standby current for always-on applications, very low ripple

with “forced PWM” mode operation, high maximum output current, ability to drive large load capacitance while

retaining transient performance, and soft start to limit start-up current.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Small Solution Size

Solution size less than 7.5 mm2 is possible using the LM3281 in combination with only three small passive

components.

7.3.2 Automatic Analog Bypass with Low Dropout

An internal bypass transistor under analog control automatically engages as VIN falls below the VOUT target.

Output stays regulated in analog bypass mode until full dropout. The parallel impedance of this additional bypass

transistor with normal DC-DC output path reduces VOUT voltage drop-out, maximizing VOUT supply voltage to the

load at low VIN conditions. The analog implementation provides a smooth transition among regulation and bypass

modes, avoiding VOUT distortion.

10

Submit Documentation Feedback

Copyright © 2014, Texas Instruments Incorporated

Product Folder Links: LM3281