The ISL9237 buck-boost operation consists of four switching FETs and an inductor, as well as a battery connecting FET (BFET). The four switching FETs are grouped into a forward-buck leg and a forward-boost leg. By operating either leg, this topology can operate in forward buck mode or forward boost mode for charging the battery. It can also operate in reverse buck mode to deliver power out of the USB port for charging an external electronic device.