The LM25117 is a synchronous buck controller intended for step-down regulatorapplications from a high voltage or widely varying input supply. The control method is based uponcurrent mode control utilizing an emulated current ramp. Current mode control provides inherentline feed-forward, cycle-by-cycle current limiting and ease of loop compensation. The use of anemulated control ramp reduces noise sensitivity of the pulse-width modulation circuit, allowingreliable 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 drivesexternal high-side and low-side NMOS power switches with adaptive dead-time control. Auser-selectable diode emulation mode enables discontinuous mode operation for improved efficiencyat light load conditions. A high voltage bias regulator that allows external bias supply furtherimproves efficiency. The LM25117’s unique analog telemetry feature provides average output currentinformation. Additional features include thermal shutdown, frequency synchronization, hiccup modecurrent limit and adjustable line undervoltage lockout.