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TPS62913: Inductor value

Pjs
Intellectual 890 points
Part Number: TPS62913

Hi, 

I'm looking at using the TPS62913 in a design that requires 11-13V input to 3.3V output @ 3A. 

I read in the datasheet that it suggests that for best efficiency a 2.2uH inductor can be used so long as Dmax is under 45%. However, when I create a custom inductor in Webench of 2.2uH, it warns me that the recommended minimum value is 3.3uH.

Where does webench generate its minimum recommended value from and should I be concerned about this?

Also, can you clarify what the issue is, if the inductor is too small - e.g. 1uH for instance?

Many thanks

  • +1
    TI__Expert 4645 points

    Thank you for your question.  I am tracking down WEBENCH implementation for the 3.3V default values chosen as the 4.7uH inductor only.  This doesn't match the recommendations in the datasheet, as both 4.7uH and 2.2uH are supported.  I would suggest using the datasheet application section recommendation of 2.2uH and 2.2MHz settings for this, along with the capacitance recommended.  The XGL4030 series inductors are also recommended with good performance.  If using a smaller inductor, there are a few complications:

    1. The ripple increases by 2x from a 2.2uH inductor.

    2. The internal compensation is not set up for the LC pole using that low of an inductance while keeping the capacitance low.

  • 0 in reply to Steve Schnier
    Intellectual 890 points

    Hi Steve, 

    Thanks for the quick + helpful response :). 

    If it's to do with internal compensation, is there enough headroom on the 2.2uH to account for 20% tolerance on the inductance value plus any value derating caused by heating / saturation? I assume this has been taken into account with the datasheet recommendation of the XGL4030/XGL4020 series.

    Many thanks

  • +1 in reply to Pjs
    TI__Expert 4645 points

    Yes, the tolerance of the inductance has been taken into consideration.  Unfortunately the WEBENCH model is not matching the recommendations in the datasheet at the moment, which is being addressed.