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SN6501: EMI Suppression capacitor for SN6501

Part Number: SN6501

Hello,

We are using SN6501 with 750313769 transformer for generating an isolated power from 3.3V to 5V.

Input: 3.3V with its return connected Earth/Chassis

Output: 5V with its return floating (one of the 3-Ph voltages. 400Vrms with respect to Earth potential)

For meeting EMI/EMC requirements, do we need to add a HV capacitor across the isolation transformer for common mode noise? We found these capacitor requirements in typical flyback circuits. 

In datasheet/EVM guides we have not found any EMI test results or recommendations.

We need to comply with following.

EN55011 Conducted Emission Class B.
EN55011 Radiated Emission Class B.

Please let us know if any application notes/recommendations/test results available for push pull converters which helps in meeting EMI/EMC compliance.

Thanks & Regards,

Chethan K S

  • Hi Chethan,

    Thank you for sharing the details of application and the emissions requirements. SN6501 operates at about 360kHz (for 3.3V VCC) and hence we do not expect it being an issue for meeting EN 55011 Radiated Emissions Class B. For EN 55011 Conducted Emissions Class B, if this test will be run on AC lines and if you already have EMI chokes on those lines then conducted emissions shouldn't be an issue either.

    In general having HV Y-capacitor of about 100pF across the transformer is good for minimizing radiated emissions. If possible, do leave a footprint and decide whether to populate it or not based on your emissions testing. This should be sufficient to meet your emissions requirements.

    Please follow the PCB layout guidelines given in SN6501 datasheet Section 11 on Page 26. Let me know if you have any other questions related to this post, thanks.


    Regards,
    Koteshwar Rao