(a) This section applies to an open-end account agreement that provides for credit card transactions:
(1) in which the creditor relies on one of the ceilings authorized by Chapter 303 for the rate of interest; and
(2) in connection with which the creditor does not impose or receive a merchant discount.
(b) Interest or time price differential may not be charged for a billing cycle of an open-end account credit agreement if:
(1) the total amount of the obligor's payments during the cycle equal or exceed the balance owed under the agreement at the end of the preceding billing cycle; or
(2) an amount is not owed under the agreement at the end of the preceding billing cycle.