App note: Improving USB system reliability with transient suppressors

Adding transient suppressors to USB devices [PDF!] can help prevent damage from static discharge. This is important because USB devices are handled without protection, carried in pockets, tossed in bags, etc.

Because frequent human interaction with the USB system occurs as a result of its attractive hot-plugging ability, there is the possibility for large ESD strikes and damage to crucial system elements. The ESD protection included on the existing hardware is typically in the 2-kV to 4-kV range for the human body model (HBD) and 200-V to 300-V for the machine model (MM). The ESD voltage levels found in a normal USB operating environment can exceed these levels.

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  1. Yes transient suppressor is a good idea, and not only for USB… All externally reachable connectors should also be protected this way!

    I used the cheaper PRTR5V0U2X on my USBug LPC1343 Development Board.

    For an even more compact design, you can also use the EClamp2522P, with integrated 22 ohm series resistors and 1k5 pull-up.

    Noise suppression/protection for EMC is also a mandatory step for professional products!

  2. it’s probably worth-whlle mentioning that this app note (appears) to be aimed at USB 1.1. Depending on the capacitance of the TVS you put on the lines, they can slow things down enough to cause issues with higher speed USB standards.

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