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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?

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  • \$\begingroup\$ Generally, your minimum on-time has very little to do with if you operate in DCM or CCM. Your load current, inductor value, input voltage and switching frequency is what determines your operating point. But you are correct, 250 ns would be the approximate on-time for CCM operation. You can still design for CCM if you inductance is high enough and the Viper is happy in skip-mode operation. What's your reasoning for wanting CCM? \$\endgroup\$ – winny Jun 1 '18 at 8:36
  • \$\begingroup\$ @winny i have no specific reaon to operate in CCM.I need maximum 300ma and nominal 150ma output current.if i operate in DCM the current ripples woulld increase .How VIPER skip mode works? \$\endgroup\$ – Rohan Jun 1 '18 at 9:30
  • \$\begingroup\$ Have you thoroughly read the data sheet to understand how it works? \$\endgroup\$ – Andy aka Jun 1 '18 at 9:33
  • \$\begingroup\$ ”i have no specific reaon to operate in CCM” Good, then you are free to choose topology as long as the performance criteria is met. \$\endgroup\$ – winny Jun 1 '18 at 9:38
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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.

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