LT1959 4.5A, 500kHz Step-Down Switching Regulator UFEATURESDESCRIPTIO ■ Operates with Input as Low as 4V The LT®1959 is a 500kHz monolithic buck mode switching ■ Output Range Down to 1.21V regulator functionally identical to the LT1506 but optimized ■ Constant 500kHz Switching Frequency for lower output voltage applications. It will operate down ■ Uses All Surface Mount Components to 1.21V output compared to 2.42V for the LT1506. A 4.5A ■ Inductor Size Reduced to 1.8 µ H switch is included on the die along with all the necessary ■ Saturating Switch Design: 0.07Ω oscillator, control and logic circuitry. High switching fre- ■ Shutdown Current: 15µA quency allows a considerable reduction in the size of ex- ■ Easily Synchronizable ternal components. The topology is current mode for fast ■ Cycle-by-Cycle Current Limiting transient response and good loop stability. ■ 4.5A Switch A special high speed bipolar process and new design tech- ■ Current Mode Control niques achieve high efficiency at high switching frequency. U Efficiency is maintained over a wide output current range APPLICATIO S by keeping quiescent supply current to 3.8mA and by uti- lizing a supply boost capacitor to saturate the power switch. ■ Portable Computers ■ Battery-Powered Systems The LT1959 fits into standard 7-pin DD and fused lead ■ Battery Chargers SO-8 packages. Full cycle-by-cycle short-circuit protection ■ Distributed Power and thermal shutdown are provided. Standard surface ■ 5V to 3.3V Conversion mount external parts are used, including the inductor and ■ 5V to 2.5V Conversion capacitors. There is the optional function of shutdown or ■ 5V to 1.8V Conversion synchronization. A shutdown signal reduces supply current to 15µA. Synchronization allows an external logic level sig- nal to increase the internal oscillator from 580kHz to 1MHz. , LTC and LT are registered trademarks of Linear Technology Corporation. UTYPICAL APPLICATIONEfficiency vs Load Current5V to 1.8V Down Converter 90 VOUT = 3.3V D2 VIN = 5V 1N914 L = 10µH 85 C2 0.68µF L1 BOOST 5µH OUTPUT INPUT 80 VIN V 1.8V 5V SW C3 R1 4A OPEN + LT1959 10µF TO EFFICIENCY (%) OR 1.21k 50µF SHDN FB HIGH 75 CERAMIC C1 = ON GND VC + R2 100µF, 10V CC D1 2.49k SOLID 1.5nF MBRS330T3 TANTALUM 70 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 1959 TA01 LOAD CURRENT (A) 1959 TA02 1
