Comments on How to protect RF switches from ESD?
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How to protect RF switches from ESD?
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:
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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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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