• Locked Locked
  • Replies 1 reply
  • Subscribers 47 subscribers
  • Views 272 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

TPS40055-EP - Question On Selecting The Inductor Value

Brian Gosselin
Expert 4595 points
Other Parts Discussed in Thread: TPS40055-EP, TPS40055, TPS40054

Hi Team,

The customer is using the TPS40055-EP in a buck boost topology to generate -15V from 15V with 25W output power.

The datasheet states, "a good compromise is to select the inductance value such that the converter does not enter DCM until the load approximated somewhere between 10% and 30% of the rated output."

Does he need to insure that the inductor value is such that the current is greater than 0 at minimum load? i.e. CCM?

Is this necessary since the PWM has a sync MOSFET?  Thanks for your help!

Regards,
Brian Gosselin

  • TI__Genius 17240 points

    Hi Brian,

    I think the comment for DCM operation was initially given for TPS40054, which supports DCM operation. For TPS40055, the IC always runs at CCM mode, so the inductor current can go negative and the efficiency is lower than DCM operation. The requirement for inductor selection is similar though. Too large an inductance results in physically larger size and not good load transient. Too small an inductance results in larger ripple current. A good compromise is to select the inductance value such that the inductor current peak-peak ripple is somewhere between 20% to 40% full load current. For example, if the inductor peak-peak ripple is 20% of full load current, then as long as the load current higher than 10%, the inductor valley current will not go to negative and the efficiency will not suffer.

    Regards,

    Na