What this controller does on your LED string
The LT3761IMSE-1#PBF is a DC DC controller designed to drive a single LED string with constant current regulation, using an external switch — the internal MOSFET is not included, so the power stage is sized by your choice of FET and inductor. Dimming is dual-mode: analog current adjust and PWM duty-cycle control, both present on the same pin — you can blend them or switch between them without changing the board layout.
Switching frequency and inductor sizing
The oscillator runs from 100 kHz to 1 MHz, set by a single resistor to ground. A 200 kHz design uses a larger inductor but lower switching losses; 1 MHz shrinks the magnetics but demands a faster gate driver and careful PCB layout to keep the switch-node ringing under control. Because the controller lacks an internal switch, the switching frequency choice directly sets the FET gate charge losses — a 1 MHz design with a 10 nC gate FET dissipates 10 mW just in gate drive, which is fine in the 16-MSOP-EP package's thermal pad but worth budgeting.