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Low Dropout 550kHz DC/DC Controller Operates from Inputs as Low as 2V

Design note for the LTC1622 step-down controller featuring a 2.5V/4A buck converter and a 3.3V/1A Zeta converter for handheld applications using 2V to 8.5V inputs.

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Overview

This design document details the LTC1622 high-efficiency step-down DC/DC controller, focusing on its application in handheld portable devices. The controller operates at a fixed 550kHz frequency, synchronizable up to 750kHz, and supports input voltages from 2V to 8.5V. The document provides schematics and performance data for two configurations: a 2.5V/4A buck converter and a 3.3V/1A Zeta converter (step-up/step-down). Key features discussed include OPTI-LOOP compensation for transient response optimization, Burst Mode operation for low-load efficiency, and 100% duty cycle for low dropout operation. Technical specifications cover short-circuit protection via current foldback and thermal considerations for the external P-channel MOSFET.

Use Cases

  • Handheld computers
  • Single or dual Lithium-Ion battery-powered devices
  • 2- to 6-cell NiCd/NiMH battery packs
  • Portable electronics requiring 2.5V or 3.3V regulation
  • High-efficiency point-of-load power conversion

Topics

LTC1622
DC/DC controller
step-down converter
Zeta converter
buck converter
Si4463DY
low dropout
Burst Mode
OPTI-LOOP
550kHz
handheld electronics
battery power

Referenced Parts

LTC1622

Linear Technology

The LTC1622 is a versatile high efficiency step-down controller

BH510-1013

BH Electronics

BH ELECTRONICS BH510-1013

1N4148

Generic

low cost diode, D2... 1N4148

IR20BQ015

International Rectifier

D1 IR20BQ015

CEP123-2R0

Sumida

SUMIDA CEP123-2R0

Si4463DY

Vishay Siliconix

Si4463DY