In a bowl, combine pretzels, butter and 1/2 cup sugar. Press into a 13-in.x9-in.x2-in.baking pan. Bake at 400 degrees F for 7 minutes. Cool.Meanwhile, in a mixing bowl, beat cream cheese and remaining sugar until creamy. Fold in pineapple and whipped topping;chill until serving. Break pretzel mixture into small pieces; stir into pineapple mixture.