TMZ spoke with Brown's manager Reno Rankin ... who tells us the 23-year-old actor admits he drank 3 glasses of wine in his home on August 12 ... when a female friend drove over to listen to his new CD.

Brown says he was so excited to play the album for his friend ... he waited for her outside his L.A. home and when she rolled up, he got into the driver's seat to pop his CD into the player.

As TMZ previously reported, cops claim the car didn't have a license plate -- and they stopped to check out the situation. That's when they found Brown behind the wheel and arrested him for DUI.

But Brown's rep tells us, "He never intended to drive anywhere at all" -- insisting he was ONLY in the car to play the CD for his friend.