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TI Video Inquiry: 1.6 ESD Essentials: How to Select ESD Protection

Ray Vincent Aranzaso
Mastermind 18180 points

Hi,

In the video they used bidirectional devices even thought the inputs are 0 to +3.6V which of course would allow negative voltages to hit the USB receiver. The explanation as to why allow negative voltages wasn't an answer.

The person said in the video "In this application, both unidirectional and bidirectional diodes would be suitable, since the Vbus and D+/D- voltages will always be greater than or equal to 0 during normal operation. While unidirectional diodes would provide better negative clamping gear, single channel bidirectional ESD diodes would offer the flexibility of connecting any pin to ground and the other pin to I/O, since it is symmetrical. The same would apply to D+ and D-."

The problem is the voltage can go to a negative clamp voltage just as easy as a positive one. This would then exceed the voltage limit of the device. Unless they assume absolutely nothing gets by the TVS.


Video: training.ti.com/esd-essentials-how-select-esd-protection

1.6 ESD Essentials: How to Select ESD Protection

  • 0
    Guru 316920 points

    What gets by the TVS is likely to exceed the voltage limits of the protected device, for both unidirectional and directional TVSes. However, the remaining voltage (and current) is low enough that the built-in ESD protection can handle it.

    If you need to protect against surges that have more energy than ESD, then you should indeed avoid a bidirectional TVS.

  • 0 in reply to Clemens Ladisch
    TI__Genius 9806 points

    In addition to Clemens's valid point, its also easier to place a single channel bidirectional device on a board since the I/O and GND pins can be used interchangeably. You wouldn't have to worry about the orientation of the device. That's what the video meant by flexibility. 

    Regards,

    Matt