When doing a loan against a deposit account is it always necessary to check the Deposit Account box in the TIL disclosure?

Do you mean the "required deposit" box?

Reg. Z 226.18(r) states: Required deposit. If the creditor requires the consumer to maintain a deposit as a condition of the specific transaction, a statement that the annual percentage rate does not reflect the effect of the required deposit.

Footnote 45A says a required deposit need not include, for example: (1) an escrow account for items such as taxes, insurance or repairs; (2) a deposit that earns not less than 5 percent per year, or (3) payments under a Morris Plan.

So, if the deposit account is earning less than 5%, it is my understanding the box needs to be checked. However, our bank always checks the box when a deposit account is required, no matter what rate we are paying.