January 2005
LM2657
Dual Synchronous Buck Regulator Controller
General Description
Features
n Input voltage range from 4.5V to 28V
The LM2657 is an adjustable 200kHz-500kHz dual channel
voltage-mode controlled high-speed synchronous buck
regulator controller ideally suited for high current applica-
tions. The LM2657 requires only N-channel FETs for both
the upper and lower positions of each 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 resistors 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 two
independently programmable outputs switch 180˚ out of
phase (interleaved switching) reducing the input capacitor
and filter requirements. The input voltage range is 4.5V to
28V while the output voltages are adjustable down to 0.6V.
n Synchronous dual-channel interleaved switching
n Forced-PWM or Pulse-skip modes
n Lossless bottom-side FET current sensing
n Adaptive duty cycle clamp
n High current N-channel FET drivers
n Low shutdown supply current
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
n Switching frequency adjustable 200kHz-500kHz
n TSSOP-28 package
Standard supervisory and control features include Soft-start,
Power Good, output Under-voltage and Over-voltage protec-
tion, Under-voltage Lockout, and chip Enable.
Applications
n Low Output Voltage High-Efficiency Buck Regulators
Typical Application (Channel 2 in parenthesis)
20134704
© 2005 National Semiconductor Corporation
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