LM5155: tr, tf

Kuramochi Tadahiko

Guru 28715 points

Part Number: LM5155
Other Parts Discussed in Thread: LM5115

Hi,

How are tr and tf calculated on the following calculator?

We would like to know to check equation(33).

Best Regards,

Kuramochi

over 4 years ago

0 Garrett Roecker over 4 years ago

TI__Mastermind 21720 points

Hi Kuramochi,

Thanks for reaching out with your question and for considering the LM5115 in your design.

The rise and fall time are just calculated based on the drive current and the gate charges of the selected MOSFET and the gate driver strength. It follows this application note

https://www.ti.com/lit/ml/slua618a/slua618a.pdf

Thanks

Garrett

0 Kuramochi Tadahiko over 4 years ago in reply to Garrett Roecker

Guru 28715 points

Garrett-san,

Thank you for your help.

I have an additional question.

Rise/Fall time is calculated by the following equation according to the document you showed.

However, CISS, CRS, and VDS,off do not exist in the calculator.

How are they calculated?

And, calculating "VGS,Miller", should Isupply be applied to ID?

Best Regards,

Kuramochi

0 Garrett Roecker over 3 years ago in reply to Kuramochi Tadahiko

TI__Mastermind 21720 points

Kuramochi,

The calculator uses the gate charges of the MOSFET as these a common values in the datasheet and the gate drive voltage of the MOSFET is know. VDS is know by the calculator as the efficiency is calculated for one input voltage.

Yes, I SUPPLY should b used for ID should be the input supply current.

Please let me know if you have any questions.

Thanks,

Garrett

0 Kuramochi Tadahiko over 3 years ago in reply to Garrett Roecker

Guru 28715 points

Garrett-san,

Thank you for your reply.

>The calculator uses the gate charges of the MOSFET as these a common values in the datasheet

Could you tell me their values?

CISS:

CRSS

VDS, OFF

I would like to verify the calculation.

Best Regards,

Kuramochi

0 Kuramochi Tadahiko over 3 years ago in reply to Kuramochi Tadahiko

Guru 28715 points

Garrett -san,

How is this situation?

Best Regards,

Kuramochi

0 Brigitte over 3 years ago in reply to Kuramochi Tadahiko

TI__Guru 61535 points

Hello Kuramochi,

You can find them at the lower end of the Excel sheet next to the efficiency and losses curves.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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LM5155: tr, tf