This driver doesn't support nvarchar fields (or nvarchar(max) only, doesn't matter for me - I can't change database schema just because of using PHP).
After 2 hours of googling I found solution. It's hack, but it works fine with nvarchar, decimal, varchar, int and others.
To readI found it accidentally in this blog and I'm very thankful to David Walsh:
CAST CAST field table
It's from StackOverflow: