LM3405: more detail equation than Equation (12) to calculate duty cycle

Takao Yamamoto5

Expert 1690 points

Part Number: LM3405

Dear all,

Could you teach me more detail equation than Equation (12)?

I think that we should add DCR and impedance of inductor to Equation (12). Is this idea wrong?

Best regards,

over 7 years ago

0 Clinton Jensen over 7 years ago

TI__Mastermind 25500 points

Hello Takao,

Equation 12 is a good approximation, but yes, you can add in the voltage drop due to inductor DCR to the numerator if you want to get even closer. This app note has some more information:

Regards,

Clint

0 Takao Yamamoto5 over 7 years ago in reply to Clinton Jensen

Expert 1690 points

Dear Clinton,

Thank you for your answer.
And your answer is very helpful for me.

I would like to check one thing.
Should I need to add the impedance of inductor to Equation 12?

Best regards,

0 Clinton Jensen over 7 years ago in reply to Takao Yamamoto5

TI__Mastermind 25500 points

Hello Takao,

No, you do not need to add the impedance. It is not a loss that will affect the duty cycle. Only the inductor DCR needs to be added for better accuracy.

Regards,

Clint

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LM3405: more detail equation than Equation (12) to calculate duty cycle