USB chargers/dischargers are complex electronic devices that must to fulfill performance requirements and safety rules. A controller’s design methodology helps ensure that requirements are satisfied consistently and efficiently. This work proposes a co-design systematic method to calculate the parameters of both the controller and the bidirectional buck converter, where the control system is formed by a sliding mode controller in cascade with a PI controller. The performance criteria of the USB standard restrict the value of the capacitor/inductor of the power converter and the PI voltage controller constants, which is supported with mathematical analyses. Finally, the validation is performed in the PSIM simulator considering commercial elements.