[amasad]

That happens in angel/pre-seed/seed rounds. They're usually much smaller contributions and are much easier to do because you're not giving out equity, you're technically taking debt which will convert to equity on the next equity financing round (usually series A).

Also after an equity round, investors typically have pro-rata rights so you can't take any money without getting their permission and ask them if they'd like to contribute more to maintain their share.