Tenn. Code Ann. § 48-58-107: Resignation of directors

(a) A director may resign at any time by delivering written notice to the board of directors, its chair or president, or to the corporation.

(b) A resignation is effective when the notice is effective unless the notice specifies a later effective date. If a resignation is made effective at a later date, the board may fill the pending vacancy before the effective date if the board provides that the successor does not take office until the effective date.