AN2728 Datasheet, PDF (1/20 Pages) STMicroelectronics – ST1S12 small synchronous buck converter

AN2728
Application note
ST1S12
small synchronous buck converter
Introduction
The ST1S12 family of synchronous step-down DC-DC converters optimized for powering
low-voltage digital cores in HDD applications is generally used to replace the high-current
linear solution when the 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 (1.7 MHz) allows the use of tiny surface-mount components. A
resistor divider to set the output voltage value, an inductor, and two capacitors are required
for the adjustable version. 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 device is thermal protected and current limited to prevent damages due to accidental
short-circuit. This family of products is available in the TSOT23-5L package.
Figure 1. ST1S12 - simplified schematic
V_IN
UVLO
I_SEN
Σ
VSUM
Comp
VRST
MOSFET
CONTROL
VDRV_P _Driver
VSET
LOGIC
R_sense
OSC
VC
SW
DMD _DMD
SOFT START
SHUT DOWN
VDRV_N _Driver
REF1
FB/V_O
EN
Gnd
April 2008
Rev 1
1/20
www.st.com
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