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WEBENCH® Tools/TPS54228: Duty cycle exceeds limit??

Olli Mannisto
Expert 1750 points
Part Number: TPS54228

Tool/software: WEBENCH® Design Tools

I'm trying to design a very basic SMPS - 4.5 to 5.5 VDC in, 3.3V out, 1A max

From the feature spec it seems like TPS54228 would be a fine match, inexpensive, relatively robust SO8 powerpad etc. But webench insists it's a no go because of duty cycle?! Several other devices from the same family are excluded for the same reason.

The device has a 90% duty cycle limit and on quick calculation that should work out to <75%. So what's wrong? This happens with both the new and the classic webench

  • 0
    TI__Mastermind 26780 points
    Hi Olli,

    TPS54228 has a duty cycle limitation close to 65-70% The datasheet suggests on page 14 to use atleast an input voltage of Vo/0.65. In the WEBENCH tool, a duty cycle limit of 70% is being used. To be on safe side, the datasheet recommendation will lead to around ~5.1V VinMin. If that is something that can be adjusted on your input requirement side, you can update Vin range and use TPS54228. Otherwise, please check out other recommended solutions from the tool with your inputs and you can dial into some other solution that could also meet your requirement.

    Regards,

    Amod
  • 0 in reply to Amod Vaze
    Expert 1750 points

    I see. Well, then please do update the controller family web page which says 90%!  You really have to dig into that datasheet to find the bit where they say: The maximum recommended operating duty cycle is 65%. It'd be nice if it was up-front about that limitation.

    That's the page which says 90% front and centre: www.ti.com/.../TPS54228

  • 0 in reply to Olli Mannisto
    TI__Mastermind 26780 points
    Sure Olli, sorry about the confusion caused due to a different max limit on the family web page as compared to the datasheet. I will report this issue so it can be fixed.

    Regards,
    Amod