used clothing maximum charitable tax deduction

There is no maximum donation, but the paperwork changes.

For an individual non-cash donations less than $250, you need a contemporaneous written acknowledge from the charity (a receipt or some kind of letter).  You also need your own accurate records to determine the value of the items, including when purchased, the price, the date donated, the value you are claiming, and what source or proof  you used to determine the value.  You don;t send this to the IRS, but keep your proof in case of audit.

For any individual non-cash donation more than $250, you need more details and a more detailed letter from the charity.

If the combined total of all non-cash donations is more than $500 (regardless of the value of individual donations), you must include form 8283 with your tax return that describes the donations in detail, in addition to the specific receipts and documents needed for each individual donation.  Turbotax will prepare and include this form automatically. 

If your total non-cash donations for a single item or "group of similar items" is more than $5000, then you need a signed appraisal and a signature from a responsible official at the charity.  You must print and mail your return (you can't e-file) and you must include the signed forms.

I have not had any problem with making (for example) 6 or 7 separate donations to Goodwill, with a value of around $100 each and a combined value over $500.  Turbotax prepare the forms for you.