Current chopping with an h-bridge and PWM
In the datasheet of the L298 see section "3. APPLICATIONS".  In that section there are a few schemes described and schematically shown for current limiting by chopping.  

The voltage drop of 1.8v min is the Vce(sat) of the internal transistors which will vary with current not necessarily with the voltage. This is the voltage you lose due to the less than perfect transistor switching.  

The delay times listed on page 4 are switching delays of the internal circuitry.  They are just the electrical characteristics of the device.