Power Dissipation Analysis & Circuit Design for Sync Switching Battery Charger

The bqSWITCHER(TM) (bq24100/03/05/08/13/15) is a highly integrated, switch-mode, Li-ion and Li-polymer battery charger IC. With two power MOSFETs, the gate drivers, and the controller fully integrated in the chip, the circuit design as well as the PCB layout has been appreciably simplified. However, it is still important to have a good understanding of the charger circuit design, layout principles, and issues and to have the capability to calculate the circuit parameters and power losses for better thermal design. This application report presents the fundamentals of synchronous switching, buck-based battery charger circuit, the loss calculation, and the PCB layout design guideline. A design example is given to demonstrate the entire process of a charger design based on the bqSWITCHER.