Practical difference between drive and topspin

I've noticed that during the game, if I receive a fast ball on backhand, due to having less time to do the topspin, my backhand stroke is shorter, and essentially looks like a drive. How is it possible to impart top-spin even when there's no time to do the full stroke?

Hi Ali,

The key here is the contact.  Try to turn your bat over the ball more so that you get a brushing contact over the top of the ball even if the stroke isn't big.  The contact will generate the topspin on the ball with limited length of stroke and time available.