Hello,
I have an isolated RS422 to UART converter. Although I placed TVS diodes for ESD protection on the RS422 lines (external side), ESD gun testing caused damage to several components within the system. The ESD gun's reference is tied to the power ground of the system, not to the isolated ground of the RS422 interface. I suspect this mismatch in reference grounds is the root cause of the issue. Is there any suggestion to improve system or test method?

 

You can place common-mode chokes on the RS422 lines before the transceiver to reduce ESD energy coupled to differential signals. Add ferrite beads or CM filters for additional high-frequency suppression.

 

You can place common-mode chokes on the RS422 lines before the transceiver to reduce ESD energy coupled to differential signals. Add ferrite beads or CM filters for additional high-frequency suppression.

There are ACM2012-201-2P-T002 common mode chokes and SM712.TCT TVS diodes on the RS422 lines. The same configuration is also used on non-isolated RS485/422 lines, and when I apply ESD using an ESD gun, there are no issues. I suspect that the problem is related to the isolation. However, I’m not sure whether this is a design-related issue that needs to be improved or if it can be resolved through the test methodology.

 

There are ACM2012-201-2P-T002 common mode chokes and SM712.TCT TVS diodes on the RS422 lines. The same configuration is also used on non-isolated RS485/422 lines, and when I apply ESD using an ESD gun, there are no issues. I suspect that the problem is related to the isolation. However, I’m not sure whether this is a design-related issue that needs to be improved or if it can be resolved through the test methodology.

Thank you for the clarification.

When testing the isolated RS422 interface, the ESD gun ground/reference should be tied to the isolated side's ground or shield, not the system ground. If your isolated RS422 interface has a shield or connector shell, connect the ESD gun ground there. If there is no shield, temporarily connect a test-only wire from the ESD gun ground to the isolated ground.

 

Thank you for the clarification.

When testing the isolated RS422 interface, the ESD gun ground/reference should be tied to the isolated side's ground or shield, not the system ground. If your isolated RS422 interface has a shield or connector shell, connect the ESD gun ground there. If there is no shield, temporarily connect a test-only wire from the ESD gun ground to the isolated ground.

Thanks, Crugrocks. Is there any documentation I can read on this topic? I have previously reviewed "How to use isolation to improve ESD, EFT and surge immunity in industrial systems", but it focuses more on how to design the system rather than how the tests are actually performed.


For example, suppose the person conducting the test makes a mistake and connects the ESD gun reference directly to the system reference. Would the diagram below help prevent the system from being damaged in such a case?

 

Thanks, Crugrocks. Is there any documentation I can read on this topic? I have previously reviewed "How to use isolation to improve ESD, EFT and surge immunity in industrial systems", but it focuses more on how to design the system rather than how the tests are actually performed.


For example, suppose the person conducting the test makes a mistake and connects the ESD gun reference directly to the system reference. Would the diagram below help prevent the system from being damaged in such a case?


View attachment 348624

You can check the following links.
https://www.analog.com/en/resources/technical-articles/esd-protection-for-io-ports.html
https://www.esdguns.com/content/10-test-setup-esd-pre-certification-compliance-testing
https://www.ti.com/lit/an/slva680a/slva680a.pdf