The maximum amount of the credit is $500 - if you take a look at the form and follow the calculations you can see that $5,000 is the maximum amount of the original loan that can be used for the calculation to not exceed the hard cap of $500.
https://www.revenue.state.mn.us/Forms_and_Instructions/m1slc_18.pdf
Note: The 2018 form also specifically mentions this cap of $5,000 - see form line 11
[Edited: 1.22.19 to updated form for 2018]
