You're right, that was the hole here. The reply by Tuna-Fish gives the correct reason for this setup (different voltages). The actual power converter usually ne

You're right, that was the hole here. The reply by Tuna-Fish gives the correct reason for this setup (different voltages). The actual power converter usually needs at least an off-chip capacitor, even if the logic is integrated, because that's too large to be cost-efficient in silicon; so there might be an opening even if as much as possible was integrated - haven't thought that through though.