Data Brief
For further information contact your local STMicroelectronics sales office.
September 2008 Rev 1 1/4
4
STEVAL-ISA055V1
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
■RDS(on) typ. 250 mΩ and 400 mΩ
■Uses tiny capacitors and inductors
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.
STEVAL-ISA055V1
www.st.com
Schematic diagram STEVAL-ISA055V1
2/4
1 Schematic diagram
Figure 1. ST1S12 circuit schematic diagram
VFB
SW
GND
VIN
VOUT
2
3
EN
1
5
4
L
R1
COUT
R2
GND
VIN
CIN
REN
ST1S12
AM00303
STEVAL-ISA055V1 Revision history
3/4
2 Revision history
Table 1. Document revision history
Date Revision Changes
18-Sep-2008 1 Initial release.
STEVAL-ISA055V1
4/4
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