elementalDamageDV * ((intelligenceDV / 500) + 1)
This means, for every 50 points in Intelligence, Frostburn Damage is increased by +10%. 500 points in intelligence would add +100%.
Frostburn Damage is rarely used in the game. The Storm Mastery's Ice Shards have a synergy skill (Torrent) that adds some Frostburn Damage to the shards. Frostburn Damage is also one of the default types of damage dealt by Sarcophagus traps.