The LM5117 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 LM5117 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 LM5117’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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