This reference design is a digitally controlled, gallium nitride (GaN) based, four-switch buck-boost DC/DC converter used for battery back-up (BBU) application. This design has a total of seven phases. Six phases are connected in parallel for battery discharging operation providing up to 8.1kW discharging power. The seventh phase is used for battery charging operation. The converter works in either buck, buck-boost, or boost mode depending on V_IN and V_OUT voltage, and transitions smoothly between each mode.