Can someone explain to me how to do an uncircumcised man (blow job)

Okay so I can't make my husband finish during a blow job: I'm not really experienced he's my first in everything. He tells me that I'm doing it right and that it feels good but he stops me every time and finishes during sex instead. 
Am I doing something wrong? Is an uncircumcised penis different? He always tells me it's getting too rubby or too sensitive and that's he's unable to finish from only a blow job. 
Any tips?