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Dealing with USB current overshoot during insertion

Posted: 19 Aug 2009     Print Version  Bookmark and Share

Keywords:USB current  current overshoot  insertion USB 

You can inadvertently trigger an unwanted system reset by inserting a simple pen drive or other peripheral into a USB port. One should, therefore, provide a current limiter in front of the port, for protection against shorts and overloads that may be connected to the port itself.

One characteristic of this interface is the possibility of supplying power to the various peripherals you might connect, such as a pen drive, small hard disk, modem, MP3 reader or memory card. A server board fed by a 12V main power rail, for example, includes a buck converter that steps the rail down to 3.3V for powering digital logic. It also includes a step-up circuit that boosts the 3.3V rail to the standard voltage for a USB port (5V, with 500mA current capability).

A problem can occur when you insert peripherals: the sudden load on the port's 5V pin usually is not purely resistive, but has a capacitive component that can cause a rapid and high-amplitude rise in current, to levels well above the 500mA limit for a USB port.

View the PDF document for more information.

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