• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 873 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

On-time calculation

Tomoaki Yoshida91
Genius 5255 points
Part Number: LM25011

Hi team,

Our customer is designing now.

They calculate based on the data sheet for constant setting.

Questions are raised about On time and Rt setting.

There are several formula on the On time in the datasheet.

The minimum on-time calculation result of the last row is 152 ns, but in equation (9) it is 139 ns.

By substituting Vin = 36 V and Rt = 118 kΩ into equation (5), it becomes 135 ns.

What is the difference between each formula?

Also, why does the calculation result differ from the last row?

Best regards,

Tomoaki Yoshida

  • 0
    TI__Prodigy 480 points

    Hi Tomoaki,

    Equation 9 is a sanity check to verify that you can meet Ton(min) with your desired frequency. However, the other Ton is based on your Rt, and it is the actual on-time of the device.

    I believe that equation 5 does produce an answer close to 152ns. (I calculated it out to be 151ns.) I have attached those calculations.

  • 0 in reply to Eric Sato31
    Genius 5255 points

    Hi Eric-san,

    Thank you for your support.

    I understand it, but I calculated Ton_max using equation 5.

    The calculation result is 622.31ns.

    It does not meet 672ns written in datasheet.

    Please tell me this reason?

    Best regards,

    Tomoaki Yoshida

  • 0 in reply to Tomoaki Yoshida91
    TI__Prodigy 480 points
    Hello Tomoaki,

    When the formulae are evaluated as per "last row", there does appear to be some errors in the results. We have noted and we will plan to have this rectified in the next revision of the datasheet. Hope this helps.