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TPD4E1U06: Chassis ground or digital ground connection

Peter Borenstein
Mastermind 8695 points
Part Number: TPD4E1U06

Should the ground pin of protection diodes be connected to the chassis ground or the digital ground? Would you answer this question differently for Ethernet or USB?

I am using the TPD4E1U06 to protect my Ethernet and USB data lines.

My "chassis grounds" are the metal jacket surrounding an ethernet RJ45 jack and USB jack. The reference design for TI's DK-TM4C129X dev kit separates the metal jacket of an Ethernet plug to digital ground through a 1MOhm and high voltage cap (page 30): http://www.ti.com/lit/ug/spmu360a/spmu360a.pdf

The diodes (D14) used for Ethernet are only differential; I'm not following the example directly. I have the same question for the USB connection on the same page. The example shows the ESD diodes D5, D6, and D7 going strait to digital ground. Wouldn't you be more protected if those diodes went through R36? Why treat zaps on the connector shield different from zaps on the data bus?

  • 0
    Mastermind 8695 points

    Maybe the Ethernet TPD4E1U06 protection diode ground shouldn't be connected to anything?

  • 0 in reply to Peter Borenstein
    TI__Expert 3500 points

    Peter-

    The best way to protect the device would be to connect the ground pin to the chassis ground so as to shunt as much current away from fragile electronics. This answer will be the same for any interface protocol, as fundamentally ESD protection is the same regardless of device.

    Does that answer your question? Let me know if you need any more help!

    Thanks

    Alec

  • 0 in reply to Alec Forbes
    Mastermind 8695 points
    Hi Alec,

    Your answer may be the best decision, but I was hoping for a little more incite than just picking one of the options I proposed.

    Why do TI Launchpads chose to use a digital ground reference for USB protection diodes instead of the chassis as you proposed?

    Ethernet doesn't share a common ground. Wouldn't referencing the the protection diodes to my local chassis ground cause the diodes to clamp down if the switch is a few volts higher than my device?