Multi-topology controller in a small MSOP-EP
The LTC3805IMSE-5#PBF is a current-mode switching regulator controller that handles boost, flyback, and SEPIC topologies from a single part number — one BOM line covers several isolated and non-isolated designs. It comes in a 10-MSOP-EP package (3.00 mm width, exposed pad) shipped in a tube, not tape-and-reel, so the pick-and-place feeder setup and shelf storage differ from the reeled variant. The supply range is 3.95 V to 9.5 V on Vcc — tight enough that the input rail needs regulation; a raw battery drooping below 3.95 V drops the controller out.
Switching frequency and clock sync
Switching frequency is programmable from 70 kHz to 700 kHz, and the part accepts an external clock sync — useful for placing the switching harmonics away from a sensitive IF band or ADC sampling rate. Maximum duty cycle is 80%, which caps the step-up ratio in boost mode; for a higher ratio the design moves to a flyback or SEPIC with a transformer turns ratio.
Temperature grade and board integration
Control features include an enable pin and soft-start — the soft-start ramps the duty cycle on power-up, limiting inrush current into the output capacitor and transformer core.