Yup , 3.3v.
I use a cheap and tiny 5v to 3.3v .
Or :(presuming you are using a satellite direct,)
Some cc3d boards have an extra pair of flexi / main ports with 3,3v. , but I don't think I've seen a cc3d atom with these .
Or : the Hyperion satellite is rated 4.5 to 9.5v. Certainly happy on 5v and work good for me.