LTC1773 - Synchronous Step-Down DC/DC Controller

The LTC1773 is a current mode synchronous buck regulator controller that drives external complementary power MOSFETs using a fixed frequency architecture. The operating supply range is from 2.65V to 8.5V, making it suitable for 1- or 2-cell lithium-ion battery powered applications. Burst Mode operation provides high efficiency at low load currents. 100% duty cycle provides low dropout operation which extends operating time in battery-operated systems.

The operating frequency is internally set at 550kHz, allowing the use of small surface mount inductors. For switching-noise sensitive applications, it can be synchronized up to 750kHz. Peak current limit is user programmable with an external high side sense resistor. A SYNC/FCB control pin guarantees regulation of secondary windings regardless of load on the main output by forcing continuous operation. Burst Mode operation is inhibited during synchronization or when the SYNC/FCB pin is pulled low to reduce noise and RF interference. Soft-start is provided by an external capacitor.

Synchronous rectification increases efficiency and eliminates the need for a Schottky diode, saving components and board space. The LTC1773 comes in a 10-lead MSOP package.

Features
  • High Efficiency: Up to 95%
  • Constant Frequency 550kHz Operation
  • VIN from 2.65V to 8.5V
  • VOUT from 0.8V to VIN
  • OPTI-LOOP™ Compensation Minimizes COUT
  • Synchronizable up to 750kHz
  • Selectable Burst Mode Operation
  • Low Quiescent Current: 80µA
  • Low Dropout Operation: 100% Duty Cycle
  • Secondary Winding Regulation
  • Soft-Start
  • Current Mode Operation for Excellent Line and Load Transient Response
  • Low Quiescent Current: 80µA
  • Low Shutdown IQ = 10µA
  • ±1.5% Reference Accuracy
  • Precision 2.5V Undervoltage Lockout
  • Available in 10-Lead MSOP
Typical Application

Applications
  • Cellular Telephones
  • RF PA Supply
  • Portable Instruments
  • Wireless MODEMS
  • Distributed Power Systems
  • Notebook and Palm Top Computers, PDAs
  • Single and Dual Cell Lithium-Ion Powered Devices
Packaging
Order Information
Part NumberPackageTempPrice(1-99)Price (1k)*
LTC1773EMS#PBFMS-10E$2.90$2.50
LTC1773EMS#TRPBFMS-10E$2.56
Demo Boards
Part NumberDescriptionPrice
DC309ALTC1773EMS | 3A Synchronous Buck Regulator, 2.8V to 8.5V Input, 1.5V/1.8V/2.5V/3.3V @ 2.5A avg / 3A peak$100.00
DC431ALT1725CGN LTC1773EMS | Telecom Input, Isolated 3 Output DC/DC Converter, +36V to +72V Input, Vout = 5V/1A, 3.3V/5A, 2.5V/4AContact Factory
Datasheet
Design Note
Reliability Data
LT Journal
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R384 Reliability Data
Feb 2001 Synchronous Buck Controller Extends Battery Life and Fits in a Small Footprint
LTC1773 Footprints and Symbols