LM27241 Datasheet, PDF (1/27 Pages) National Semiconductor (TI) – Synchronous Buck Regulator Controller for Mobile Systems

May 2005
LM27241
Synchronous Buck Regulator Controller for Mobile
Systems
General Description
The LM27241 is an adjustable 200kHz-500kHz single chan-
nel voltage-mode controlled high-speed synchronous buck
regulator controller. It is ideally suited for battery powered
applications such as laptop and notebook computers. The
LM27241 requires only N-channel FETs for both the upper
and lower positions of the synchronous stage. It features line
feedforward to improve the response to input transients. At
very light loads, the user can choose between the high-
efficiency Pulse-skip mode or the constant frequency
Forced-PWM mode. Lossless current limiting without the use
of external sense resistor is made possible by sensing the
voltage drop across the bottom FET. A unique adaptive duty
cycle clamping technique is incorporated to significantly re-
duce peak currents under abnormal load conditions. The
input voltage range is 5.5V to 28V while the output voltage is
adjustable down to 0.6V.
Standard supervisory and control features include soft-start,
power good, output under-voltage and over-voltage protec-
tion, under-voltage lockout, soft-shutdown and enable.
Features
n Input voltage range from 5.5V to 28V
n Forced-PWM or Pulse-skip modes
n Lossless bottom-side FET current sensing
n Adaptive duty cycle clamping
n High current N-channel FET drivers
n Low shutdown supply currents
n Reference voltage accurate to within ±1.5%
n Output voltage adjustable down to 0.6V
n Power Good flag and Chip Enable
n Under-voltage lockout
n Over-voltage/Under-voltage protection
n Soft-start and Soft-shutdown
n Switching frequency adjustable 200kHz-500kHz
Applications
n Notebook Chipset Power Supplies
n Low Output Voltage High Efficiency Buck Regulators
Typical Application
See Figure 17 for Expanded View
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