TPS54561: second stage filter

Hello,

When you say second stage filter, are you referring to the input EMI filter? 

If so, please refer to this app note for more details (https://www.ti.com/lit/an/snva489c/snva489c.pdf)

Depending on your level of attenuation, the Lf and Cf will need to be appropriately tuned.

Regards,

Jimmy

Hello Anoop,

for a simple rule of thumb approach, I suggest the following.  Where Lbuck is the buck inductor, Lf is the filter inductor, Cout is the output capacitor for the buck power stage and Cf is the filter capacitor.  Make Lf<<Lbuck and Make Cout <<Cf.  Suggest Lf and Cout are an order of magnitude leass than Lbuck and Cf respectively.

Also note that the ESR of Cf will need to be equal to approximately Sqrt(Lf/Cf).

Therefore suggest the following with the example shown above.  Make Lf = 100nH, make Cf = 470uF, ESR~15mR.

Also suggest recompensating to the following:

Rcomp = 28.7k

Ccomp = 10nF

Ccomp2 = 1nF

Hope this helps?

David.

Hello Anoop,

I ran some calculations/simulations and approximate with the design above you will be below 1mV of output ripple.  

Hope this helps.

David.