I want to know IC control method

Hi everyone.
I’m reviewing multi-phase controller+ DrMOS for efficiency increase and to cover heavy load current.
Now I’m reviewing datasheet about MPQ2977 and MPQ86940 for automotive driving system.
SO, i have few question.
Control method is defferent with another PWM methode.
How to control with IDROOP+output of differential amp. and Vramp+Vref.
I didn’t understand PWM Gen. through Comp. Output.
Please let me know.