I am looking at a 3-pad SMD EMI filter chip (see photo) which is marked on the top with "222J". I am familiar with reading the markings on top of resistors and capacitors, but am not sure how to interpret the markings on a EMI/RFI filter.

enter image description here

  • \$\begingroup\$ These values are not standardized and are most likely only meaningful in the context of a manufacturer, you'll need to find the manufacturer: electronics.stackexchange.com/questions/334128/… \$\endgroup\$
    – Voltage Spike
    May 1, 2019 at 16:42
  • \$\begingroup\$ no datasheet??? \$\endgroup\$ May 1, 2019 at 16:47
  • \$\begingroup\$ I ran a reverse image search and I found out the product number. The datasheet can be found here. \$\endgroup\$
    – user103380
    May 1, 2019 at 16:52
  • \$\begingroup\$ @KingDuken I updated the question with a photo of the actual part \$\endgroup\$ May 1, 2019 at 16:55

1 Answer 1


This is an LC feedthru filter which means it is bidirectional.

The 222J refers to 2200 pF shunt cap. enter image description here


simulate this circuit – Schematic created using CircuitLab

They cannot control the ferrite inductance L and loss values with J accuracy but they can control the buried cap value.

So one vendor may have a slightly different Series Resonant Frequency than another.

But this TDK part guarantees at least 25 dB attenuation into 50 Ohms from 45 to 105 MHz. Actual could be as much as 30 MHz to 300 MHz for the TDK part.

  • \$\begingroup\$ How did you determine this was a TDK part? \$\endgroup\$ May 1, 2019 at 18:28
  • 1
    \$\begingroup\$ I used a TDK datasheet which looked like your original photo, not the actual part. Thanks to @KingDuken 's search. \$\endgroup\$ May 1, 2019 at 18:43
  • \$\begingroup\$ I still am not clear on the meaning of the "J" \$\endgroup\$ May 2, 2019 at 15:44
  • \$\begingroup\$ Normally a J suffix after value means 5% ( F ± 1% G ± 2% J ± 5% K ± 10% M ± 20% ) but it's relation to tolerance of centre notch MHz is unknown to me ( since that depends on LC product), the letter is OEM specific as many do not use this suffix. But if you find one, then you probably found the OEM. \$\endgroup\$ May 2, 2019 at 15:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

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