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Power USB VBUS in Autos with the LT8697

Trevor Crane - Design Engineer Jul 15th 2013

USB sockets appear in an increasing number of car models as portable devices become more ubiquitous. The USB interface delivers power to portable devices via the 5V VBUS and ground lines. Depending on the USB version and the portable device, the VBUS sources up to 2.1A. 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 5V VBUS supply drops out at high USB device current. The LT®8697 fixes this problem. It is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator designed to power 5V USB applications. A precise <1% initial tolerance output voltage and programmable cable drop compensation maintain accurate 5V regulation at the USB socket at the end of a long cable. Accurate and programmable output current limit, a power good indicator pin and an output current monitor pin improve system reliability and safety and eliminate the need for a USB switch IC. These features allow the user to implement latch-off or auto-retry functionality. Dual input feedback limits the output voltage to 5.85V despite cable drop compensation, protecting USB devices and allowing 5V regulation on the output of a USB switch.

Power USB VBUS in Autos with the LT8697 - Video Poster Image