Battery Charger Circuit

Hi,

Please find the application circuit of BQ24401. The IC controls the switch of a buck converter (current control mode).

In this i am not able to understand the buck stage. To be precise , i am not able to understand the role of transistor Q2 , diode D5 and capacitor C9. Also , they have put a hysteretic controller to add hysteresis to the current sense signal (Capacitor C7). Please help me. Thanks in advance

The circuit is there to speed up the turn off of the main transistor by shorting the base to emmiter for a brief period.

Thanks ronv