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ESD protection guides

Roman Lutig , 04-08-2021, 04:50 AM
Right now I am working on PCB, where I have a lot of the connectors and my client wants that this PCB should be extremely protected as strong as it can be.
My concern right now is the ESD protection of the circuit. I read a lot of the design guides, but still have questions regarding this field. I will share them with you, maybe you may create one additional video about it or even do a simulation if this is possible.

1. Which lines for sure I need to protect?
- For sure all dana lines of the connector which go outside the enclosure, button, touch screens, and all points where user have access.
What about other connectors which are inside the enclosure and connect 2 PCBs together, or sensors that are connected by wires?
Do I need to protect the battery connector - for the rechargeable li-ion battery and for the standard alkaline battery 1.2V?

2. Do I need to protect the power line(from a connector, for example, USB Vbus) if it is not a wire trace but a solid plane?

3. How far from the connector pin I may put the ESD protection?

I understand that closer it is better but in the real life it not always possible to put ESP very close.
If belief to this application note https://toshiba.semicon-storage.com/....jsp?did=68869 on page 22, picture 5.1, we can't protect the chip if will put ESD protection close to it because of increased impedance for the return current.

But based on this it tells that we may move ESD from connector till our impedance from connector to ESD Z1 is lower than impedance from connector to chip Z2. Attached picture for reference.
robertferanec , 04-09-2021, 04:16 AM
I am not expert for ESD, but this is what I normally do:

1) That is what I normally do, everything what goes out of enclosure and people can touch it. I do not use ESD on signals inside enclosure/system (most chips already have basic ESD protection).
2) I do not normally use ESD protection on power lines.
3) I place ESD protection as close as possible with direct connection to the pin (e.g. no VIAs) and I do not route anything unprotected close to it, so I am sure it will discharge in the protection device instead of jumping to the other traces in my PCB. According to the picture 5.1, I believe, if you place protection device close the the connector, impedance will be lower in most cases - so in most cases it will work.
qdrives , 04-14-2021, 09:25 AM
0. "... as strong as it can be", normally you would simply say up to 15kV air discharge (https://en.wikipedia.org/wiki/IEC_61000-4-2)
1a. Anything the user can touch.
1b. For cables the questions is also: are they shielded. ESD for cable/wire is also the ends: connectors and sensors themselves.
2. Power lines generally have enough capacitance and other filtering that it is no problem. For ESD that is, when you are talking about surge, it is a different story.
3. A trace is an impedance. So putting a TVS diode close to the connector will make it take all the energy. The impedance is then lowering the effect for the IC. For simple digital inputs a simple RC filter (with 10..100nF) is enough.

ESD is like a small capacitor charged with a high voltage. Put a large capacitor next to the connection, and the voltage would only change a small bit. Impedance of the circuit is important though.
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