The power FET provides an essential safety function in a battery management system (BMS), isolating the battery pack from either a load or a charger in errant conditions. Proper functionality of the power FETs requires the designer to understand the load conditions, the battery pack limitations and to have an understanding of the functional block circuitry. This white paper discusses the detection blocks and how they apply to the state of the power FETs to ensure safe operation of Li-ion battery packs. We’ll also explain the inner functionally of each sub block and design considerations for different applications.