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I'm wondering why I don't see ESD protection for ground (can you even protect ground from ESD?) - If there is a large electrostatic discharge straight onto the ground plane wouldn't that voltage spike of the ground level damage all the electronics using that ground ? Wouldn't it be the same as zapping any other pin of the IC with a huge voltage spike ?

Thanks in advance!

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  • \$\begingroup\$ Ground usually isn't connected to any gate of a MOS transistor. The gates are the ones which need protection. Drain and source are low-ohmic so they don't. \$\endgroup\$ – Janka Oct 5 '17 at 23:21
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It could, if the current was extremely high or the layout was bad.

I saw a device (a data drive plugged into a computer) some years ago, and it was being used on a circuit connected to the mains- risky at the best of times but it was nominally okay. Due to sloppiness and rushing, the ground lead wire on the drive (a braided wire with a ring terminal, flapping around) accidentally touched the "hot" which vaporized the trace to wall plug ground but there was still a capacitor from the now 120VAC node to +5V, which blew out every single chip in the drive and the computer. It also caused a potentially dangerous voltage to appear where it shouldn't. Ideally that would have just blown a circuit breaker or tripped a GFCI.

Less catastrophically if there is a path to ground from an external terminal that is not direct, but passes through other circuitry, glitches or even damage are possible from ESD.

Beware of current paths that may exist through your design where current is not limited in some way.

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In electronics Ground by definition means a 0V reference but often ill defined.

In power industry in means bonded to earth ground according to local standards.

But it has an undefined impedance to Earth ground but is usually a) inductive, B) floating or c) solid ground with copper ground plane. or some other variant. The charge voltage to a "unknown" can easily inject a ground shift with respect the human ground that generated the ESD.

You don't protect ground , rather protect the equipment poorly connected to earth ground or keep it floating only for safety reasons and protect the signals from egress or ingress to local ground using high inductance well-balanced RF CM transformer (ethernet) or high current CM choke on AC with Y cap filters or lossy Ferrite CM chokes. (DC and external mic)

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  • \$\begingroup\$ "Ground by definition means a 0V reference", but if there is a positive discharge onto the floating ground, wouldn't the relative voltage between ground and Vcc drop to 0 before the protection diode starts conducting? And during this time, would't an MCU in this circuit see a brown/blackout? How do people typically protect against this failure mode? \$\endgroup\$ – bigjosh Feb 4 '19 at 5:07
  • \$\begingroup\$ Ground shift induced Discharge can cause failures with inductive grounds. Ground is Common mode which is why distributed supply caps, micro visa , shielding and twisted pair are important to keep this common-mode interference from becoming a local differential signal. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Feb 4 '19 at 9:55

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