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Comments on How to protect RF switches from ESD?

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How to protect RF switches from ESD?

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Assume that I have some generic antenna connector, followed by a pi-filter/50ohm impedance matching components, then a DC blocking cap (as per the RF switch recommendations) and then a RF switch for split tx/rx semiduplex transceiver, as in this schematic:

antenna schematic

How do I best protect this RF switch from ESD coming in from human fingers touching the antenna connector? I need the highest ESD class (4) of the IEC61000−4−2, meaning 8kV contact discharge, 15kV air discharge.

I'm considering a specialized "ultra-low capacitance" TVS diode such as ESD8472 (rated up to 20kV), which is bidirectional.

Questions:

  • Is this TVS diode the way to go?
  • If so, where do I place it in this schematic? Directly on the antenna or somewhere else?
  • How to determine the suitable breakdown voltage? I'm assuming it should be based on the RF switch supply which is 3.3V.
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2 comment threads

Hello Lundin. I think it would help if you can specify what is the general configuration of your syst... (2 comments)
Are you going for the formal IEC 61000−4−2 certification test? Sometimes passing a test it a harder ... (2 comments)
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In this case the antenna connector is the standard horrible little U.FL, which is connected with coaxial to a bigger one grounded to chassis. The main ESD risk is when someone is connecting or removing the coax. It's quite easy to touch the center pin with ones fingers on a U.FL. [from this comment by the O.P.]

Your vulnerable U.FL connector is inside the chassis. I'm assuming that only trained personnel will be working inside of your chassis (no user-serviceable parts, etc).

Put a note in the service manual that the person who unplugs the U.FL plug should wear ESD protection. Put ESD warning stickers inside the chassis too, for a good measure. I've seen this approach in medical devices.

[Edit. Just piling up reference material.]
SiLabs application note AN895. Fig. 19 shows an example for ESD protection circuit for a radio antenna port.

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2 comment threads

App note (1 comment)
That won't work for this application (3 comments)
App note
Lundin‭ wrote about 1 year ago

I think I've seen this app note before, I use the very Silabs parts that they use as example. But most of it is generic ESD and the figure 19 didn't really bring anything new other than "take care about the parasitics of the selected TVS diode", which was already mentioned in the question here. Figure 20 is curious though, it's a new idea to me to use the capacitance of the TVS to form the pi filter. Is that common? I've never seen it before.