What is your definition of "low"? Some people think it's a 700, some people think it's a 600, some think it's a 500, etc. It's probably all relative to what the person's score was before they had the bumps on their credit.
FHA mortgages require a 500 credit score, and most FHA lenders minimum score requirements tend to be 600, 620, or 640 - with FHA anything less than a 580 score requires a 10% down payment, otherwise just 3.5% down is required.
VA mortgages have no score requirement, but VA lenders score requirements are similar to FHA's. VA is 100% financing for Veteran's.
USDA Rural Development mortgages have no score requirement - however if you go through a lender most will have 620 or 640 minimum scores, but if you go Direct to USDA they do not have any minimum score requirements, but it takes a little bit longer - this would not be an option for you unless you purchased past Chadds Ford.
Fannie Mae & Freddie Mac mortgage programs require a 620 score, however with less than 20% down you will likely need at least 660-680 scores.
Credit score isn't the only item considered though, what is on your credit report is equally as important. If there are late payments or delinquent accounts in the last 12 months when you apply then that can curtail your chances of qualifying. If it's free of those items for the past 12 months then your credit is likely good enough as it is. If there is good reason for negatives, such as an accident at work that prevents you from making money, a medical situation keeping you from working, or a death of a family member who was a wage-earner (among other situations) then that is taken into consideration.