ST ISA055V1 User Manual

0.7 A / 1.2 V synchronous buck converter

with enable function based on the ST1S12XX

Features

■ Step-down current mode PWM (1.7 MHz) DC-

DC converter

■ Fixed output voltage of 1.2 V

■ 0.7 A output current capability

■ 3% DC output voltage tolerance

■ Synchronous rectification

■ Enable function

■ Internal soft-start

■ Typical efficiency: > 90%

■ Not switching quiescent current: max 600 µA

over temperature range

■ R

■ Uses tiny capacitors and inductors

typ. 250 mΩ and 400 mΩ

DS(on)

STEVAL-ISA055V1

Data Brief

STEVAL-ISA055V1

Description

This demonstration board is based on the
ST1S12 family of synchronous step-down DC-DC
converters optimized for powering low-voltage
digital cores in HDD (hard disk drive) applications
and is generally used to replace high-current
linear solutions when power dissipation may
cause high heating of the application
environment.

It provides up to 0.7 A over an input voltage range
of 2.5 V to 5.5 V. A high switching frequency of 1.7
MHz allows the use of tiny surface-mount
components. For the adjustable version, a resistor
divider to set the output voltage value, an
inductor, and two capacitors are required. Only an
inductor and 2 capacitors are needed for the 1.2 V
and 1.8 V fixed version. A low output ripple is
guaranteed by the current mode PWM topology
and by the use of low ESR surface-mount ceramic
capacitors.

The ST1S12 device is thermal protected and
current limited to prevent damage due to

accidental short-circuit. This family of products is
available in the TSOT23-5L package.

September 2008 Rev 1 1/4

For further information contact your local STMicroelectronics sales office.

www.st.com

4

Schematic diagram STEVAL-ISA055V1

1 Schematic diagram

Figure 1. ST1S12 circuit schematic diagram

V

IN

V

4

IN

R

EN

1

EN

GND

C

IN

2

ST1S12

R2

L

3

SW

V

OUT

V

FB

5

GND

R1

C

OUT

AM00303

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