Features

• Operates with Input as Low as 4V
• Output Range Down to 1.21V
• Constant 500kHz Switching Frequency
• Uses All Surface Mount Components
• Inductor Size Reduced to 1.8µH
• Saturating Switch Design: 0.07 Ohms
• Shutdown Current: 20µA
• Easily Synchronizable
• Cycle-by-Cycle Current Limiting
• 4.5A Switch
• Current Mode Control

Typical Application

Description

The LT1959 is a 500kHz monolithic buck mode switching regulator functionally identical to the LT1506 but optimized for lower output voltage applications. It will operate down to 1.21V output compared to 2.42V for the LT1506. A 4.5A switch is included on the die along with all the necessary oscillator, control and logic circuitry. High switching frequency allows a considerable reduction in the size of external components. The topology is current mode for fast transient response and good loop stability.

A special high speed bipolar process and new design techniques achieve high efficiency at high switching frequency. Efficiency is maintained over a wide output current range by keeping quiescent supply current to 4mA and by utilizing a supply boost capacitor to saturate the power switch.

The LT1959 fits into standard 7-pin DD and fused lead SO-8 packages. Full cycle-by-cycle short-circuit protection and thermal shutdown are provided. Standard surface mount external parts are used, including the inductor and capacitors. There is the optional function of shutdown or synchronization. A shutdown signal reduces supply current to 20µA. Synchronization allows an external logic level signal to increase the internal oscillator from 580kHz to 1MHz.