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SN6505B-Q1: Radiated a and conducted emission test results

Part Number: SN6505B-Q1
Other Parts Discussed in Thread: BQ79631-Q1, SN6505B, SN6505BEVM, SN6505A-Q1


My plan is to use the SN6505B-Q1 in my reference design in order to provide 12V isolated supply from a 5V input.

The circuit I am going to use is the same of the BQ79631-Q1 Evaluation Board.

Are there reports on radiated and conducted emission tests made on this scheme configuration? (or similar configuration)

Thank you very much for your support


  • Hi Fabio,

    Thanks for reaching out and for showing interest in SN6505B-Q1.
    I see that you are looking at the automotive qualified device, could you please confirm the radiated and conducted emissions standard that your product needs to comply to?

    SN6505B operates at a frequency that helps keep the radiations from device to minimal and comply to most industrial and automotive emissions standards. Spread spectrum clocking in SN6505B also makes sure the radiations are spread out over a small band of frequencies than being at a single tone thereby reducing the peak emissions significantly. The device also has in-built slew rate control of the output voltage switch that helps further reduce emissions. Hence, we expect the device to meet most radiated emissions standards.

    Conducted emissions is usually conducted at end equipment level and the results largely depend on overall system design and input supply EMI filters. I believe we do not have conducted emissions data but we haven't had any customer report any issues with SN6505B meeting their conducted emissions requirements.

    Please do help us with the information related to your radiated and conducted emissions standard and limits. I will ask one of our colleagues to respond to it accordingly, thanks.

    Koteshwar Rao

  • Hello,

    Thank you for the answer.

    For conducted emission I agree with you, it is something difficult to measure since this is also affected by other factors. The fact that other customer did not have issue is good.
    For radiated and conducted standards our reference is based on CISPR 25.
    Since the project is focused for European market, you could consider limits coming from FCA/PSA standards.
    If you performed some radiated emission test based on CISPR 25 it would be great, preferably on the architecture shown in BQ79631 Evaluation Board.
    The purpose of my request is to have a proof of the robustness of the solution based on SN6505B-Q1 IC, at least in terms of radiated emission.

    Thank you very much for your support


  • Hi Fabio,

    I looked for the schematic of the BQ79631-Q1 Evaluation Board, but it is not included in the EVM User's Guide. Regardless of configuration, we do not have radiated or conducted emissions data of SN6505 to share against CISPR 25. My apologies. Attached below is data we have per CISPR 22/32 in the typical configuration shown in the SN6505BEVM:

    As Koteshwar mentioned, we have not had issues with customers meeting conducted emissions requirements and SN6505 devices have emissions-reducing features like spread spectrum clocking and symmetric drives, which will be effective regardless of the output circuit topology. For tightest emissions constraints, our SN6505A-Q1 is recommended since it features a lower switching frequency and switching slew rate, resulting in lower radiated and conducted emissions overall.

    As mentioned above, emissions will vary with each system based on factors like PCB layout and external component selection; for example, the isolation transformer part number can impact emissions significantly and if there is a wide manufacturing tolerance, even transformers of the same part number can have distinct emissions performance.

    Please let us know if you have additional questions.

    Thank you, and have a great weekend!
    Manuel Chavez