Can I bring a backpack as a personal carry on along with my small suitcase on the plane?

I have a small suitcase which meets the carry one dimensions requirements but I was wondering If I could bring a backpack that would fit under my seat. Does its dimensions add on to my carry on suitcase dimensions which would put it over the maximum dimensions? Im going to put the suitcase in the overhead bin. Im flying delta and expedia. Thank You!