This document describes the design of the LTC3805-5 negative buck converter, which can output –3.3V at 3A from a –10V to –14V input voltage.
The document presents a circuit design for a negative buck converter that steps down a negative voltage, specifically generating -3.3V at 3A from a -12V rail. The design utilizes the LTC3805-5 controller IC, which provides essential functions such as short-circuit protection with adjustable current levels, converter enable/disable control, and a programmable switching frequency.
The circuit description details the power train components including an inductor (L1), diode (Di), and MOSFET (Q1). Key design considerations discussed include sensing the output voltage referenced to system ground while the controller is referenced to the negative voltage. The note also covers performance characteristics, noting approximately 90% efficiency and overcurrent protection behavior where input current limits to 20mA at short-circuit conditions.
The design generates -3.3V at 3A from a negative input rail.
The converter enters this state when the output current reaches 5.0A.
The circuit operates with an input ranging from -12V to -14V.