How many uses of channel divinity should be expended in the following example?
- A character is using that a weapon that deals 2d6 thunder damage on a hit.
- They cast Thunderous Smite, using a bonus action.
- Then cast Booming Blade (at 5th level), making a melee attack as an action.
- On a hit, the weapon does a total of 2d6 + 1d8 + 2d6 thunder damage.
The first time you hit with a melee weapon attack during this spell's duration, your weapon rings with thunder that is audible within 300 feet of you, and the attack deals an extra 2d6 thunder damage to the target.
At 5th level, the melee attack deals an extra 1d8 thunder damage to the target, and the damage the target takes for moving increases to 2d8.
When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling.
I'm interpreting this as three separate rolls for thunder damage, each requiring a use of Channel Divinity to maximize. Instead of one use of Channel Divinity to maximize all of them at once.
One of the main reasons I'm thinking this, is because another use of Channel Divinity needs to be expended to maximize the secondary damage from Booming Blade, as it's a completely separate roll.