ESD protection of Photon (external antenna)

Hi all,

I am trying to add ESD protection in the form of TVS diode(s) to our product design. We are using an external antenna plugged in to the Photon… any suggestions of how to protect that ‘input point’ from a 16kV IEC 16000-4-2 jolt?

Thanks in advance!

You want an antenna protection TVS diode, not a logic-level TVS diode. High bandwidth and low capacitance are the keys.

http://www.st.com/en/protection-devices/rf-antenna-protection.html?querycriteria=productId=SS1815

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Cool, thanks for that. But where would I put it on our PCB? The antenna bulkhead goes through our enclosure wall (aluminum) then connects directly to the uFL connector on the Photon… Maybe between Earth GND (enclosure) and GND?

If we used a plastic enclosure, how would I add the ESD protection device?

You are trying to avoid ESD into the semiconductors, so the TVS goes from the antenna input to the antenna ground. In other words, if you have a u.FL connector or similar, it goes across it.

Returning antenna ground to USB ground or earth ground is a different question that is hard to answer since it depends your system design.

Every wire in or out of your box needs ESD protection of some kind.

A plastic enclosure does not really play a part in ESD but I would think you wanted a shielded enclosure (nickel spray on the inside) to avoid EMI. With a conductive interior plastic box, I would try to connect it (via the board standoffs) to earth ground, if possible. If that’s not available, then you can use ferrites/caps/inductors to connect it to what you have or choose to float it.

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Yes, I completely agree that the TVS across the antenna (signal-to-ground) is the correct place… my issue is that that position is not accessible on the Photon, because the u.FL is already on the Photon. So I can’t design it into my PCB. Does that make sense?

I’m trying to figure out if there is anywhere else (on my PCB) I can place a TVS to protect that u.FL connector (on Photon).

OK sorry for some reason I thought you were working on a P1.

I think you have a couple of choices:

  • Make a very small PCB with the TVS diode and two u.Fl connectors, male and female, one on each side.
  • Add the same u.Fl in/out and TVS to your existing board that the Photon plugs into and use a short u.Fl jumper cable
  • Ignore the issue and move along in life accepting the risk

I don’t think the last option is that bad–you have to figure out the economics of replacing a zapped device should it happen. If your product BOM is $1k then you should add protection but if your product BOM is $22 maybe it would be acceptable risk.

Yes, our BOM cost is low enough to take the risk (imho) but we are also trying to pass CE certification, so I think it needs to be able to pass the IEC 61000-4-2 abuse.

On another note, do you recommend we ground the chassis to our PCB or let it float?

Thanks for your thoughts :smiley:

Difficult to say–too many variable for a forum posting.

OK, thank you!