Dear Team,
The excel tool only for MLCC output mode, could you provide electrolytic mode?
Or what can we deal with it?
BR
Kevin
Hi Kevin,
When only using electrolytic capacitors on the output, there is no ripple injection circuit needed. The design tool can still be used for figuring out the IL ripple, R8 value, R2 value, mode and Fsw settings, but without the need for the ripple injection circuit, the design is much simpler.
Please use the ESR calculations from the "Typical Applications" section in the datasheet to select output caps with enough ESR. I included Equation 10 below as an example.
NOTE: If the design is using electrolytic ONLY there should be no need for the RCC ripple injection circuit, just using the calculation above for ESR. If however, there are ceramic caps in addition to electrolytic caps, the ESR is much more difficult to calculate and you most likely will need the RCC ripple injection circuit, so please still use the design tool.
Dear Alec,
Thanks for the help.
So R7, C1 C2 should be ok for NC right?
I will ask engineer put it as place holder.
BTW, I think IIND(ripple)'s equation is very complicate.
Do you have better suggestion to calculate IIND(ripple)?
Hi Kevin,
Yes, R7, C1, C2 can be set as NC. And I agree that leaving placeholders for them is best.
For IIND(ripple) the design tool can still be used, but the equation is not actually that complex.
IIND(ripple) = ((Vin-Vout)*Vout) / (L*Fsw*Vin)
You can actually derive it from equation 2 in the datasheet:
