I'm currently trying to ESD protect a design I'm working on by using TVS diodes. I'm placing these diodes on user interface components (pushbuttons, switches, exposed pins, etc.).

In the process of doing this, I had placed a TVS diode parallel to an IC's power pin, where I had also previously placed a decoupling capacitor. Because the voltage across a capactior can't change instantaneously, I'm curious if any ESD would just be filtered by the cap.

Question: Do decoupling capacitors offer ESD protection?

  • Some kind of...but it is better to install the TVS where the electronics is exposed to external signal that might carries the ESD. – Marko Buršič Nov 8 '16 at 17:19
  • TVS diodes are low Z in conduction. Caps are low Z to high dV/dt transients and C ratio divider rules apply when considering 300pF HBM source to 300nF shunt is 1000:1 reduction. and more with 0.1uF but higher then ESR of cap raises voltage drop with current. – Tony EE rocketscientist Nov 8 '16 at 17:29
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    Capacitors definitely help for exactly the reason you say. It is very wise to keep the TVS diodes in the design through the layout stage. When you actually build the boards, you can consider building and testing withou the TVS not installed. If you pass ESD, great. If not, you have an easy solution (still have to test it). – mkeith Nov 8 '16 at 17:45
  • Installing TVS in parallel to power bypass capacitor on a steady power rail was a wasteful idea. If you are working to protect a device that fails industrial ESD testing, you need to better grasp the concept of ESD, learn a concept of shielding, grounding, determine likely ESD discharge path, instead of placing TVS randomly whenever you see a spot. – Ale..chenski Nov 8 '16 at 18:05
  • @AliChen I stated in my question that I was placing TVS diodes on likely spots a user may touch. What makes you say "instead of placing TVS randomly whenever you see a spot"? – Izzo Nov 8 '16 at 19:11

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