The LM25117 is a synchronous buck controller intended for step-down regulator
applications from a high voltage or widely varying input supply. The control method is based upon
current mode control utilizing an emulated current ramp. Current mode control provides inherent
line feed-forward, cycle-by-cycle current limiting and ease of loop compensation. The use of an
emulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowing
reliable control of very small duty cycles necessary in high input voltage applications.
The operating frequency is programmable from 50 kHz to 750 kHz. The LM25117 drives
external high-side and low-side NMOS power switches with adaptive dead-time control. A
user-selectable diode emulation mode enables discontinuous mode operation for improved efficiency
at light load conditions. A high voltage bias regulator that allows external bias supply further
improves efficiency. The LM25117’s unique analog telemetry feature provides average output current
information. Additional features include thermal shutdown, frequency synchronization, hiccup mode
current limit and adjustable line undervoltage lockout.
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