For the topping:
Preheat oven to 400 degrees.
Mix melted butter and sugar together.
Stir in pretzels.
Spread in a 9 x 13 pan and bake for 7 minutes.
Stir to break it up and cool completely.
For the salad:
Cream together the cream cheese and sugar until well mixed.
Stir the Cool-Whip and pineapple tidbits into the cream cheese mixture.
Chill 2-3 hours.
Add pretzel mixture right before serving.