This KBA provides a brief summary about and highlights the possible need for board-level ESD protection for RF devices.
Radio chips are designed for and tested against different chip-level ESD standards, such as Human Body Model (HBM), Machine Model (MM) and Charged Device Model (CDM). These chip-level test results are summarized in the RF IC’s Qualification Reports.
However, in a real-world application a final module/board has to resist and stand against an ESD shock. For this purpose, the final electronic product has to be tested against a different, more stringent standard that simulates and replicates the real world ESD stress conditions. This system-level ESD standard is the IEC 61000-4-2, for instance. System/module designers should take care to comply with the IEC 61000-4-2 system-level ESD standard. This KBA provides some board-level insights about how to make an RF design more immune against ESD.
For more technical details, please refer to Silicon Labs' application note AN895. This application note provides recommendations on ESD protection circuits and shows test results measured with the Si4x6x chip family, however the suggested protection circuits can also be utilized with any other RF chip families.
For an RF design the most ESD-sensitive part is the RF path, including the antenna, matching network and RF ports. Secondly, the supply and GND paths are also sensitive, and lastly any GPIO or other paths connected to the RF chip directly.
So, the antenna definitely needs special care during design and assembly into the end product. ESD protection can be enhanced by:
- antenna placement: end-user shouldn't be able to touch it in any case.
- design an antenna with direct GND connection, e.g. inverted-F antenna.
- protection circuit elements in the RF path: parallel inductors, capacitors, TVS diodes.
Many circuit designs have the supply trace connected to the PA externally, for which cases the supply trace may also need care and ESD protection.
Lastly, any push-button or interface, that can be touched by the user of the end-product during normal usage, may also need to be ESD-protected. These are, typically, GPIO ports of RF devices.
Please see AN895 application note for recommended ESD protection circuits and for more technical details.