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Determine LM5025B tolerance range given a particular frequency and overlap time

Akeem Whitehead
Mastermind 27940 points
Other Parts Discussed in Thread: LM5025B

On behalf of a customer:

"I'm using the LM5025B PWM controller with Overlap and I'm trying to determine the worse case minimum Output A on time.

On page 12 of the data sheet the last equation in Maximum Duty Cycle shows Max Duty Cycle = 75% - 100ns * 400 KHz = 71%.

I then go to the Electrical Characteristics Table under PWM Comparator where it shows a Max Duty Cycle of 71 percent.

Is this 71 percent directly related to the 71% in the Max Duty Cycle paragraph?

If so, does that mean if I go to a different frequency and overlap time, my actual minimum Output A on time would be (66% + 100 ns * 400 kHz) - (my overlap time * my new switching frequency).

If this isn't the case, how do I go about determining the tolerance range giving my particular frequency and overlap time?

Thank you."

  • 0
    TI__Intellectual 1390 points

    Dear customer,

    Please see my reply as below

    1)Is this 71 percent directly related to the 71% in the Max Duty Cycle paragraph?

    Yes. the test condition of this 71% result are that switcing frequency is equal to 400KHz (or RT=13.3Kohm) and the overlap time on the rising edge is equal to 100ns.

    2) If so, does that mean if I go to a different frequency and overlap time, my actual minimum Output A on time would be (66% + 100 ns * 400 kHz) - (my overlap time * my new switching frequency).

    I guess you are asking for how to calculate the maximum OUTA on time. If so, please refer to below equation

    Ouput A maximum on time= (75%-overlap time*switching frequency)/ switching frequency

    Best Regards

    Farnk

  • 0 in reply to Frank TANG
    Prodigy 10 points

    Frank,

    Thanks for the response.  What I'm trying to determine is the range of OUTA maximum on time given a different switching frequency and overlap time than what the datasheet shows.  For the conditions in the datasheet, the Electrical Characteristics Table has a range of OUTA maximum on time from 66% to 75%, but what happens to the range if the switching frequency and overlap time change to a different condition?

    Customer