The USB interface delivers power to portable devices via the 5 V VBUS and ground lines. Depending on the USB version and the portable device, the VBUS sources up to 2.1 A. In a car, this high VBUS current presents a challenge.
Often, car electronics including the VBUS regulator reside in a box in the dash while some of the USB sockets may be placed in the back seat. The cabling between the VBUS regulator and the socket can be several meters in length and twice that counting the return trip. Long cables mean high resistance, so the 5 V VBUS supply drops out at high USB device current. The LT®8697 fixes this problem. See the video.