MHV12-1.0K2000P output voltage limited to 300V

I am unable to increase the output voltage of MHV12-1.0K2000P beyond 300V with MCU that creates the control voltage. I have created the control voltage through PWM and then sending through a low pass filter, I have also used a opamp buffer.

Hello Dr. Manivanan, Thank you for your question, please check the Datasheet Pg 3 . I thinking you are having an issue with it having a over current. This has a over protection current protection. Can you please check to see if this is the issue.