Robinson was sent off for a dangerous tackle as he was involved in a head-to-head collision with Saints fly-half Dan Biggar.
It meant Newcastle had to play the final 20 minutes with 14 men as they suffered a 65-26 defeat at cinch Stadium at Franklin's Gardens on June 4.
Robinson's case was heard by an independent disciplinary panel on Monday.
He accepted the charge and received a three-week ban, which will be reduced to two weeks if the player completes the World Rugby Coaching Intervention Programme.
The games he will miss will be updated once fixtures are confirmed.