AN2093 Datasheet, PDF (1/6 Pages) STMicroelectronics – BUCK CONVERTERS FOR HDD POWER SUPPLIES

AN2093
APPLICATION NOTE
ST1S03
BUCK CONVERTERS FOR HDD POWER SUPPLIES
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
Rev. 2
1/6