LM2745 Datasheet, PDF (1/23 Pages) National Semiconductor (TI) – Synchronous Buck Controller with Pre-bias Startup, and Optional Clock Synchronization

May 2005
LM2745/8
Synchronous Buck Controller with Pre-bias Startup, and
Optional Clock Synchronization
General Description
The LM2745/8 are high-speed synchronous buck regulator
controllers with an accurate feedback voltage accuracy of
±1.5%. It can provide simple down conversion to output
voltages as low as 0.6V. Though the control sections of the
IC are rated for 3 to 6V, the driver sections are 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 MOSFETs 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 LM2745/8 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 LM2745
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 Switching frequency from 50 kHz to 1 MHz
n Switching frequency synchronize range 250 kHz to 1
MHz (LM2745 Only)
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 ±1.5% feedback voltage accuracy over temperature
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 Down Conversion from 3.3V
n Cable Modem, DSL and ADSL
n Laser Jet and Ink Jet Printers
n Low Voltage Power Modules
n DSP, ASIC, Core and I/O
Typical Application
© 2005 National Semiconductor Corporation DS201374
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