You can use two Healing Infusion powers per encounter, but only once per round. At 16th level you can use three Healing Infusion powers per encounter, but only one per round.
The target gains a +1 power bonus to AC until the end of the encounter, and you expend an infusion crafted with your Healing Infusion class feature. The target can end the bonus as a free action to gain temporary hit points equal to its healing surge value + your Constitution modifier.
Level 21: Temporary hit points equal to the target's healing surge value + three times your Constitution modifier.
Level 11: Temporary hit points equal to the target's healing surge value + twice your Constitution modifier.