Rohidas,
For detailed calculations, check out the below app note.
http://www.ti.com/lit/an/slyt286/slyt286.pdf
Luckily we have a reference design exactly for this application, check out PMP7330.
https://www.ti.com/tool/PMP7330
Hope this helps,
-Orlan…
Meng,
Can you share the link to the reference circuit? I cannot find it.
I believe you are referring an inverting buck-boost topology, please see following appnotes for guidance
http://www.ti.com/lit/an/slyt286/slyt286.pdf
http://www.ti.com/lit/an/snva856…