T.I. grabbed the mic at his daughter's birthday bash, but instead of dropping lines ... he got sentimental talking about the "apple of my eye."

Tip threw the huge party for his 16-year-old daughter Deyjah at Bianco Ultra Lounge in Atlanta Thursday night ... which included appearances by rappers Joe Gifted, Dada, Young Dro and Silento.

We're told Tip dropped $50k on the event and hired MusicBusinessPolitics to plan it.

And yes, it was a full family affair -- Tiny was there for her daughter's bday too.