I have used two X1 safety capacitors in series with an isolator (ISOW7842DWE). I have fault on EMC test on 64MHz. When I remove the capacitors, the EMC issue is reduced by 6dB.

I have used two safety capacitors to obtain 8kV spike protection. I do not know why there are more radiated emissions on the board when I use the safety capacitors with the isolator.

  • 2
    \$\begingroup\$ provide schematic? \$\endgroup\$ – analogsystemsrf Nov 20 '19 at 8:27
  • \$\begingroup\$ As in first comment a schematic or a more detailed description would really be needed to provide better help. When you say safety capacitors are you referring capacitors on the power pins of the isolator chip or other locations? Did you follow the specific layout guidelines in the datasheet? Do you suspect the isolator chip is the initial source of the 64MHz noise? \$\endgroup\$ – Nedd Nov 20 '19 at 10:37

With no schematic, and no board layout - it's pretty hard to know. But I would expect a typical X1 safety capacitor (which is physically quite large, and usually designed to operate around 50/60Hz) to make quite a good radiator. If you're not interested in high frequency signals, put a Class Y capacitor and a small resistor forming a low pass filter on the input.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.