• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 63 subscribers
  • Views 337 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.

LM5009; Ton minimum

Ricardo Medina
Prodigy 185 points
Other Parts Discussed in Thread: LM5009

I am designing DC/DC circuit with LM5009 and I have a question with ton (min).

I have seen an information conflict between datsheet (November 2011) and LM5009QuickStartCalculator.xls, the fist one indicates ton(min): 250ns and the other one ton(min): 400ns.

Fmax=Vout/(Vinmax*250ns)  or Fmax=Vout/(Vinmax*400ns) 

Anyway Vin max is incorrect, you will have fmax when Vin was min.

¿Which is the correct value?

  • 0
    TI__Genius 11490 points

    Hello Ricardo,

     

    Fmax formulae calculates the maximum frequency at which converter can operate over the input voltage range. You are correct in saying that the maximum frequency can be achieved at minimum input voltage. But if you target that frequency the converter will not satisfy the min TON requirment at higher input voltages.

    That is why VINmax in the equation is correct.

    Regards,

    Vijay

  • 0 in reply to Vijay86929
    TI__Genius 11490 points

    Between 250ns or 400ns, it depends on how conservative a design you are doing. If you really want the current limit to work right with minimum overcurrent (400ns is with 0.1A overcurrent) you should use 400ns. The application information section assumes the user can tolerate more overcurrent and that inductor is sized appropriately. The current limit response will be faster with higher overcurrent.