Interaction between tectonic slam of cataclysm and Endurance charge on melee stun

tectonic slam of cataclysm uses all endurance charges to boost damage/aoe - endurance charge on melee stun also gives more damage% for each endurance charge.

In what order do these 2 interact, is the damage on an attack (and the endurance charge on melee stun gem) calculated before or after consuming all charges?

Thanks if anyone knows this for sure

i want to know this to. And also... how it interact with "minimum charges"