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.

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

* 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