Do I need two input capacitors? (parallel DC-DC design)

[blapcb]

I am planning to use two identical (almost) DC-DC circuits using L5970, both running off the same source. Both circuits call for an input capacitor (10uF). My question is, can I make due with just one capacitor for both circuits or do I have to have one for each? (which essentially would simply mean that they are in parallel). Thanks.

 

[FvM]

Buck converters have the pulsating current on the input side. Low ESR input capacitors are required to reduce the amount of interfering currents spread all over the circuit. Although the input capacitor selection (and possible usage of additional filters) depends on your noise level requirements: You should follow the suggestion first.

 

[dick_freebird]

You can "make do" if you want more instability and less efficiency.
Having the input bounce while you're connecting it to the load
helps not one bit. Maybe the dime you save is worth it, but not
to me. We see several percent efficiency loss in input decoupling
(albeit on 10A integrated bucks).