LINEAR LT3971 User Guide and Manual

LINEAR TECHNOLOGY DECEMBER 2009 VOLUME XIX NUMBER 4

1.2A Buck Converters

IN THIS ISSUE… COVER ARTICLE Draw Only 2.8µA When 1.2A Buck Converters Draw Only 2.8µA When Regulating Zero Load, Accept 38VIN or 55VIN .....................................1 Regulating Zero Load, John Gardner Linear in the News ..............................2 Accept 38VIN or 55VIN DESIGN FEATURES by John Gardner 775 Nanovolt Noise Measurement

Introduction

for a Low Noise Voltage Reference ...........................................................6 In modern battery-powered systems, Jim Williams

extending battery life and intelligently

One way to demonstrate the

managing power is paramount. To

Monolithic Synchronous Step-Down low current performance Regulator Sources 3A or Sinks 1.5A conserve power, these systems actively

in TSSOP or 3mm × 4mm QFN ...........10 of the LT3971 is to drive

switch between idle and active states.

Genesia Bertelle

it from a charged bulk

The voltage regulators in these sys-

Designing a Solar Cell tems should be able to do the same. input capacitor. A 1000µF

Battery Charger ................................12

A regulator must also maintain a well- capacitor, charged to 16V,

Jim Drew

regulated output voltage during low

is enough for the LT3971 to

High Current/High Speed LED Driver current idle states so it can quickly

regulate a 3.3V output with

Revolutionizes PWM Dimming ............16

and automatically adjust to changing

Josh Caldwell no load for over an hour.

load conditions and provide voltage for Produce High DC/DC Step-Down Ratios keep-alive functions.

in Tight Spaces with 30ns Minimum For example, remote monitoring 1.2A and include many features of a On-Time Controller in 3mm × 3mm QFN

systems spend most of their time in a high performance 1.2A buck regula-

.........................................................20 Theo Phillips low power idle state, but require bursts tor, including programmable fixed

of high power for transmitting data. frequency operation, the ability to be

New Generation of 14-Bit 150Msps

Microcontrollers and memory require a synchronized to an external clock,

ADCs Dissipates a Third the Power of the Previous Generation without regulated voltage, even when idling, to soft-start, and a shutdown/enable Sacrificing AC Performance ..............23

hold state. These types of applications pin. The wide input voltage ranges of

Clarence Mayott

require minimal current consumption these parts—4.3V–38V for the LT3971 Robust, Quiet, Stable Power Supply for in the idle state to maximize battery and 4.3V–55V for the LT3991—satisfy

Active Antenna Systems with Built-In

life, and a seamless transition to active the requirements of automotive, indus-

Protection and Diagnostic Capabilities

.........................................................26 mode when called on to supply several trial, and distributed supplies.

Sam Rankin and Steve Knoth watts of power.

The LT®3971 and LT3991 are ul- Ultralow 1.7µA Quiescent

DESIGN IDEAS tralow quiescent current monolithic, Current in Light Load ....................................................29–37

step-down regulators that maintain When the output load is low, the

(complete list on page 29)

high performance at both heavy and LT3971 and LT3991 decrease the light loads. They draw only 1.7µA of switching frequency to deliver power

New Device Cameos ...........................38

quiescent current when in light load to the output only when needed.

Design Tools ......................................39

situations, but can also source up to continued on page

Sales Offices .....................................40

L, Linear Express, Linear Technology, LT, LTC, LTM, Bode CAD, Burst Mode, Filter CAD, LTspice, OPTI-LOOP, Over-The- Top, Poly Phase, Switcher CAD, µModule and the Linear logo are registered trademarks of Linear Technology Corporation. Adaptive Power, Bat-Track, C-Load, Direct Sense, Easy Drive, Filter View, Hot Swap, Linear View, LTBi CMOS, LTCMOS, LTpower CAD, LTpower Play, Micropower Switcher CAD, Multimode Dimming, No Latency ∆Σ, No Latency Delta-Sigma, No RSENSE, Operational Filter, Panel Protect, Power Path, Power SOT, Safe Slot, Smart Start, SNEAK-A-BIT, Soft Span, Stage Shedding, Super Burst, Thin SOT, Timer Blox, Triple Mode, True Color PWM, Ultra Fast and VLDO are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.