Demonstration circuit 2719A is a high performance bidirectional buck-boost converter featuring the LT8708/ LT8708-1 that can operate from input voltages above, below or equal to the output voltage. The demo board input range is 10.5V to 14.5V (25VMAX). The output voltage is set at 14.5V and the output current limit at 40A. The board can operate in both forward and reverse mode.
The controller has integrated input voltage and output voltage regulators and two sets of input and output current regulators that control current flow in forward or reverse direction. Features are included that simplify bidirectional power conversion in battery/capacitor backup systems and other applications that may need regulation of VIN, VOUT, IIN and/or IOUT.
While the current mode control limits the inductor current both in normal and in reverse direction these current limits have some variation as input/output voltage changes. The forward and reverse input and output current regulators offer four accurate current limits that can be set individually.
The input voltage regulator is often used in applications with high impedance power sources and will reduce the forward current if the input voltage drops below the set point. When operating with reverse current flow, the input voltage regulator regulates the voltage at the input side.
The operating mode of the controller is determined through the MODE pin (jumper JP9 Pins 5 to 12) and can be set to discontinuous mode, hybrid discontinuous mode, forced continuous mode and Burst Mode® operation.
The LT8708 is capable of bidirectional operation when operating in the continuous conduction mode (CCM). DCM, HCM and Burst Mode operation only allow power to flow in one direction. Additional circuitry may be needed depending on the application.