LM27241
Synchronous Buck Regulator Controller for Mobile
Systems
General Description
Features
The LM27241 is an adjustable 200kHz-500kHz single channel 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 highefficiency 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 reduce 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 protection, under-voltage lockout, soft-shutdown and enable.
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Input voltage range from 5.5V to 28V
Forced-PWM or Pulse-skip modes
Lossless bottom-side FET current sensing
Adaptive duty cycle clamping
High current N-channel FET drivers
Low shutdown supply currents
Reference voltage accurate to within ± 1.5%
Output voltage adjustable down to 0.6V
Power Good flag and Chip Enable
Under-voltage lockout
Over-voltage/Under-voltage protection
Soft-start and Soft-shutdown
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
20120104
© 2005 National Semiconductor Corporation
DS201201
www.national.com
LM27241 Synchronous Buck Regulator Controller for Mobile Systems
May 2005
