Well, I plan to power it with 1 li-ion battery.As for the v, I out, I hope that it will be adjustable to more than 3A and voltage output up to 6VSUre but you cannot design anything with this spec. (primitive limited requirements)
YOu must consider and spec. V, I in and V,I out, (thus power load/source and impedance ratio) pulse load range and load switch rate. and supply ESR source to Load ESR ratio for example.
Then consider all the possibilities such as AC source DC source Battery source and what loads are intended.
Then the solution is easy. Otherwise vague and problematic.