February 2011

Doc ID 13778 Rev 3

1/23

AN2603

Application note

ST1S09 high efficiency synchronous buck converter

Introduction

The ST1S09 family of synchronous step-down DC-DC converters is optimized for powering

all low-voltage applications and, generally, to replaces high current linear solutions when

power dissipation may cause high heating of the application environment. It provides up to 2

A over an input voltage range of 2.7 V to 5.5 V.

A high 1.5 MHz switching frequency allows the use of tiny surface-mount components, and

in addition to the resistor divider to set the output voltage value, an inductor and two

capacitors are required. A low output ripple is guaranteed by the current mode PWM

topology and by the use of low ESR surface-mount ceramic capacitors.

The device is available in two versions: the ST1S09 with Power Good function and the

ST1S09I with an Inhibit function.

The device is thermally protected and current limited to prevent damage due to accidental

short circuit.

The ST1S09 family is available in the DFN6 3x3 package.

Figure 1.

Simplified schematic

Note:

1

Available only for the ST1S09I

2

Available only for the ST1S09

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