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TPS53355: Ripple Injection circuit components value calculation

Madhu Sharma
Expert 2915 points
Part Number: TPS53355

Hi,

In the datasheet of TPS53355, it is mentioned that equation 11, 12 and 13 to be used for ceramic output capacitors.

But, these equations satisfy for different values of C2 and R7.

So is there any other methods or rule of thumbs to select C2 and R7 values?

Also from webench, I observed that, C2 and R7 are selected such that Left hand side of equation 11 is slightly greater than right hand side( considering Vin=12 V , Vout=0.8V at 28A, webench gives C2 and R7 such that Left hand side is 2.7 E-7 and right hand side is 2.6 E-7). I would also like to know will there be any performance issues if this difference is large ?

Thanks & Regards,

madhu

  • 0
    TI__Mastermind 23845 points
    Hi,

    Normally webench is taking your design input (VIN,VOUT,etc) as consideration when calculating these values. Therefore i would start my design following those values. You can check in the webench simulation whether if the design is stable. The key for this converter is to create an injection ripple at the FB pin in order the design to be stable and one of the method of creating that injection ripple is using R7 and C2 network through AC coupling capacitor to FB.

    Thanks
    -Arief