UC2827-1: Issue in the Ramp pin and Duty of buck get changed

Tool/software:

Hi team,
In our sch we are  using UC2827DW-1 PWM controller.

We are facing some issue in the "RAMP" pin.We have seen that Ramp pin has a linearly increasing ramp signal,

At the sudden the ramp get cutoff in the lower voltage as per the attached 1st Image.

While the ramp cutoff the duty cycle of the buck get increased as per the attached  2nd image and it creates some noise .

Kindly give one solution for this issue