I am operating the buck converter with STmicroelectronics VIPER01 IC to step down the input voltage of 200 volts to 6 volts in continous current mode 300 mA load current. The operating frequency is 120 kHz for VIPER01. My minimum turn on time comes about to be 250 ns for 200 volts input voltage. The minimum turn on time is listed 270 ns in the Viper01 datasheet. Would the Viper01 switch to discontinous mode of operation instead of continous mode due to not able to produce the minimum turn ontime? Or would it still produce the 270 ns at the output?
If it's not able to generate a short enough pulse, my guess is it will skip the next pulse every few periods to maintain the right voltage. Maybe you will need to use a larger inductor.