Unlike other converters, this IC can select and take power from the appropriate power source. If the ac adapter is present, the chip derives power from the adapter. Otherwise, it takes power from the USB port. And if neither source is connected, the IC will grab power from the battery.
The chip is not merely selecting the AC or USB power source when either is available, though. It's actually using that source to directly power the device in which it is used. The selected input source is routed to the output, where it provides one supply voltage, and to the chips' two dc-dc converters and hot-swap controller, which generate three other supplies (Figure 1).