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TPS5430: Please Help Review this Design with a Second Stage Filter

Yuanchen Zhu
Intellectual 425 points

Part Number: TPS5430

Tool/software:

Dear TI experts and gurus,

  Could you help me review this circuit, which i designed and followed the methodology in "sszt824" doc of "Design a Second-stage Filter for Sensitive Applications"?  For my senario which is for RF power supply, I would also like to further reduce the 500kHz ripple of TPS5430as much as possible as shown below circuit. (My requirement is output of 5V, Imax<1A).  

       

Here I choose L1 to be 22uH, which gives XL1≈ 69.12ohm (fsw = 500kHz). And I plan to have first stage filter of 60dB and second stage of 40dB, thus XC1 ≈ 0.07ohm. That leads to C1 ≈ 4.55uF, so I choose C1 to be 4.7uF.

Follow the rule of C2 = 10*C1 = 47uF (XC2= 6.77mohm) . And 40dB attenuation gives me XL2 = 0.67ohm, which means L1 ≈ 210nH. And to make enough margin, i finally choose L1 to be 470nH.

I wonder how do we decide on the value of damping resisor of 250mohm, and also its rated power.

Please help me review this design process and don't hesitate to give any advice. Thanks.

Regards,

Yuanchen

  • +1
    TI__Mastermind 21672 points

    Hello Yuanchen

    Your overall filter design looks good to me. 

    For value of Rdamp, I would recommend keeping it 10x of DCR of your inductor. Additionally, check frequency response of 2nd stage filter for selected values and see what is the minimum value of Rdamp required to keep Q below 1. You can start with Rdamp = 1 ohm, then progressively reduce it to bringQ lower. Recommeded range for Q is 0.6 to 1.

    Hope this helps 

    Thank you

    Regards

    Onkar Bhakare