I am wondering about situation, where there is an ESD to specific part of circuit, conatining IC. As I know TVS diode has defined delay time - it will not protect immadiately. My question is - what is happening while this delay time? Is this high spike of voltage passed to IC? How is this possible, that IC survives it?
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1\$\begingroup\$ Keep in mind that an ESD event, or at least an accepted model for a ESD event like that for the human body (the Human Body Model, or HBM) has a finite rise time, on the order of a couple of ns. It is not instantaneous. \$\endgroup\$– SteveShCommented Feb 13, 2021 at 1:43
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2 Answers
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Every protection component has a reaction time, MOVs are slower and TVS faster, for example. As Barry said you often have picoseconds of protection time.
In reality the pass-thru residue is further attenuated by trace capacitance and there are usually protection diodes inside the chip. ESD damage in this case occurs when the protection diodes burn out, actually a thermal effect; if the surge is short and delayed by the trace capacitance it is simply dissipated.
By the way, ferrite beads (usually for HF noise) also helps because an ESD surge is actually an UHF (or higher) pulse and ferrites are resistive in that range.
There are components that are horribly sensible to ESD (like RF GaAs FETs) and these need even more complex protection. Datasheets detail the requirement.
answered Feb 13, 2021 at 7:56
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TVS diodes can respond to transients within several picoseconds. In fact, their response time is limited by wiring inductance. As such, they can protect almost all common electronic components from ESD events.
