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TPS62913: How to get good Vout rms noise on WeBench?

Kazuhiko Hirano
Genius 15098 points
Part Number: TPS62913
Other Parts Discussed in Thread: TPS62912

Hello,

My customer is asking the following buck converter spec.

Vin=12V
Vout=1.8V,
Iout(max)=2A
Vout rms noise <50uV

I am thinking around TPS62912 or 3 to recommend and ran WeBench steady state simulation with Spread Spectrum=Random, Second Stage Filter=Enabled and Cff Enable.
However, Vout ripple is 1.14mVpp, it looks much larger than 50uV rms. I do not know what's wrong.
Though Oslo presentation slides show ~10uV rms noise at Vout, how can I get such good number on the WeBench?
WBDesign788_Steady State-1.pdf

Best regards,

K.Hirano

  • 0
    TI__Expert 4645 points

    Hirano-san,

    Thank you for your question.  First, the schematic shown is not using the recommended LC filter, as the COUT is much less than recommended.  Please follow the recommendations in the datasheet in Table 8-2. 

    This is not the cause of WEBENCH showing higher output ripple though. It seems that the ripple shown is at the output of the first LC filter, not after the ferrite bead filter.  The ferrite bead filter will reduce the ripple by ~30dB.  This can be seen in the datasheet in Figures 6-7 through 6-10. I will check with the WEBENCH team about this.

  • 0
    TI__Genius 9540 points

    Hi ,

    Our Webench team is following up on adding the post-ferrite bead ripple to the report.

    So i will close this post first , please let us know if you have any further question .

    BRs,

    Young