Binding to min-tags and max-tags

[X3Technology]

When I set these to an actual number, it works fine.
"min-tags='1'" --> works
"max-tags='3'" --> works

But, when I bind these to a variable in the $scope, they dont work.
$scope.min_limit=1;
$scope.max_limit=3;

"min-tags='min-limit'" -> does not work
"max-tags='max-limit'" -> does not work

This always results in the validation error for minTags/maxTags being true.