Simple RAW 3

[Arkhios]

Q343: The Paladin's Sacred Weapon Channel Divinity power, it let's you add your charisma bonus to your attack when attacking with a weapon. Is this in addition to or instead of your normal ability bonus (strength or dexterity) for that attack?

A343. In addition. Remember it lasts only 1 minute (10 rounds) and depending on how frequently you get a short rest, it might take a long time before you get to use it again, so use it wisely.