LTC1773

`High Efficiency: Up to 95%
` Constant Frequency 550kHz Operation
` V<sub>IN</sub> from 2.65V to 8.5V
` VOUT from 0.8V to V_IN
` OPTI-LOOP<sup>TM</sup> Compensation Minimizes COUT
` Synchronizable up to 750kHz
` Selectable Burst Mode Operation
` Low Quiescent Current: 80A
` Low Dropout Operation: 100% Duty Cycle
` Secondary Winding Regulation
` Soft-Start
` Current Mode Operation for Excellent Line and Load Transient Response
` Low Shutdown I<sub>Q</sub> = 10A
` ±1.5% Reference Accuracy
` Precision 2.5V Undervoltage Lockout
` Available in 10-Lead MSOP

· Cellular Telephones
· RF PA Supplies
· Portable Instruments
· Wireless MODEMS
· Distributed Power Systems
· Notebook and Palm Top Computers, PDAs
· Single and Dual Cell Lithium-Ion Powered Devices

Input Supply Voltage ............................. 0.3V to 10.0V
I_TH Voltage .............................................. 0.3V to 2.5V
RUN/SS, V_FB, SENSE Voltages ................. 0.3V to V_IN
SYNC/FCB Voltage ...................................... 0.3V to V_IN
BG, TG Voltages...........................................0.3V to V_IN
SW Voltage ...................................................5V to 11V
Operating Ambient Temperature Range
(Note 2) ...............................................40°C to 85°C
Junction Temperature (Note 3) ........................... 125°C
Storage Temperature Range ..............65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................ 300°C

The LTC^®1773 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 ModeTM 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 of LTC1773 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 continuou soperation. Burst Mode operation is inhibited during synchronization or when the SYNC/FCB pin is pulled low toreduce 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.