LM2747 Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization
March 2006
LM2747
Synchronous Buck Controller with Pre-bias Startup, and
Optional Clock Synchronization
General Description
The LM2747 is a high-speed synchronous buck regulator
controller with a feedback voltage accuracy of
±
1%. It can
provide simple down conversion to output voltages as low as
0.6V. Though the control section of the IC is rated for 3 to 6V,
the driver section is designed to accept input supply rails as
high as 14V. The use of adaptive non-overlapping MOSFET
gate drivers helps avoid potential shoot-through problems
while maintaining high efficiency. The IC is designed for the
more cost-effective option of driving only N-channel MOS-
FETs in both the high-side and low-side positions. It senses
the low-side switch voltage drop for providing a simple,
adjustable current limit.
The LM2747 features a fixed-frequency voltage-mode PWM
control architecture which is adjustable from 50 kHz to 1
MHz with one external resistor. In addition, the LM2747 also
allows the switching frequency to be synchronized to an
external clock signal over the range of 250 kHz to 1 MHz.
This wide range of switching frequency gives the power
supply designer the flexibility to make better tradeoffs be-
tween component size, cost and efficiency.
Features include the ability to startup with a pre-biased load
on the output, soft-start, input undervoltage lockout (UVLO)
and Power Good (based on both undervoltage and overvolt-
age detection). In addition, the shutdown pin of the IC can be
used for providing startup delay, and the soft-start pin can be
used for implementing precise tracking, for the purpose of
sequencing with respect to an external rail.
Features
n
±
1% feedback voltage accuracy over temperature
n
Switching frequency from 50 kHz to 1 MHz
n
Switching frequency synchronize range 250 kHz to 1
MHz
n
Startup with a pre-biased output load
n
Power stage input voltage from 1V to 14V
n
Control stage input voltage from 3V to 6V
n
Output voltage adjustable down to 0.6V
n
Power Good flag and shutdown
n
Output overvoltage and undervoltage detection
n
Low-side adjustable current sensing
n
Adjustable soft-start
n
Tracking and sequencing with shutdown and soft start
pins
n
TSSOP-14 package
Applications
n
n
n
n
n
Down Conversion from 3.3V
Cable Modem, DSL and ADSL
Laser Jet and Ink Jet Printers
Low Voltage Power Modules
DSP, ASIC, Core and I/O
Typical Application
20150901
© 2006 National Semiconductor Corporation
DS201509
www.national.com
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