PBKDF2 when dkLen and hLen have the same size
The output length of the F step of PBKDF, i.e. the T_i each are of the size of your hash function's (or actually: your PRF's) output.

So yes, when the desired output size is as large (or smaller) as the hash function output, we have l = 1 and thus only one call to F(P, S, c, 1).

I suppose this is also the most common way to use PBKDF-2, the extension to longer generated key sizes is only included to make the scheme more generally usable.