1. ABSTRACT

The ST1S03 is a step down DC-DC converter optimized for powering the low-voltage digital core in HDD

applications and, generally, replacing the high current linear solution when the power dissipation may

cause excessive heating of the application environment. It provides up to 1.5A over an input voltage range

of 3V to 16V. A high switching frequency (1.5MHz) allows the use of tiny surface-mount components, as

well as the use of a resistor divider to set the output voltage value. Only an inductor, a Schottky diode and

two capacitors are required. Besides, a low output ripple is guaranteed by the current mode PWM

topology and by the use of low E.S.R. SMD ceramic capacitors. The device is thermal protected and

current limited to prevent damages due to accidental short circuit. The ST1S03 is available in DFN6 (3x3)

package.

Figure 1: Assembled Board

2. INTRODUCTION

Purpose of this application note is to provide a brief summary of the specifications and the functionality of

the application board.

The ST1S03 is an adjustable current mode PWM step-down DC/DC converter with internal 1.5A power

switch.

It is a complete 1.5A switching regulator with an internal compensation that eliminates additional

components.

The constant frequency, current mode, PWM architecture and stable operation with ceramic capacitors

results in a low, predictable output ripple. In order to maintain the regulation with light load, the device

starts to work in pulse skipping. In a typical application where the input voltage is 5V and Vout is 1.2V, the

device goes in pulse skipping for Iout lower than 15mA.

December 2004

1/6

AN2093

APPLICATION NOTE

ST1S03

BUCK CONVERTERS FOR HDD POWER SUPPLIES

Rev. 2