LTC3866 and LTC3851A, Question about external clock signal for synchronization

Hi,

I have some questions about the external clock signal for synchronization to MODE/PLLIN pin.

I'm considering designing an external clock signal with frequency of 400kHz to 700kHz and ON time of 75ns to 500ns.

- Is there any problem with the ON time period? 

- Please let me know the specifications of the ON time.

Regards,

Kazu