• TI Thinks Resolved

SN6505A: Spread Spectrum Range & Cycle/Maximum Turns Ratio/Dead Time

Part Number: SN6505A

Hi team,

I'm an FAE supporting some industrial companies in Japan.

My customer considers employing SN6505A and he asked me following questions.

  1. What is frequency fluctuation range of spread spectrum?
    Also, how long is its change period?
  2. Although the calculation example of the minimum turns ratio is described at equation (10),
    is there a limit on the maximum turns ratio?

  3. Is the dead time tbbm=115ns?
  4. Is it necessary to put a gap in the core of transformer to use?

I would appreciate your cooperation in advance.

Best regards,

Shota Mago

  • Hi Mago-san,

    Thanks for posting this on E2E.

    1) Let me do a follow-up with you on this separately.
    2) Directly no, but indirectly the limit is placed by the 1A maximum output current of the 6505 at the primary side. This, along with the output load current desired, will limit how high a turns ratio we can go up to.
    3) Yes.
    4) We leave this to the transformer vendors to implement their core design the best way they deem fit. It depends on the specs needed, such as ET product (V-us spec) which in turn depends on voltage swing at primary and secondary, and switching frequency, primary inductance desired, output current desired, budget for DC resistance losses and so on. So we feel it is best to give them the desired specs and check with them directly on how they wish to implement. The 6505 device does not place any restriction as such on this.

    I hope this helps! I will follow-up on #1 - please don't hesitate to ask us any additional questions.
    Best regards,

  • In reply to Abhi Aarey:

    Hi Abhi-san,

    Thanks for your quick reply and detail answer!

    I will be waiting for following up in terms of spread spectrum.
    Within 2 days reply would be very helpful for me.

    Again, I appreciate your support.

    Best regards,
    Shota Mago
  • In reply to Shota Mago:

    Hi Mago-san,

    Thank you for your patience :)

    I checked with my colleagues (thanks Anant K), and we have the following details to share:
    1) The typical spread is +/- 4% of the average switching frequency (fsw)
    2) The typical modulation frequency ( for the change period) is fsw/16.

    I hope this helps!
    Please don't hesitate to ask us any further questions.

    Best regards,