• State
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 575 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.

TPS54425: About current limit

Tsukui Yusuke
Guru 21930 points
Part Number: TPS54425

Hi,

Could you tell me about IOCL calculation formula?
Customer wants to know how to calculate the IOCL to determine the rated current of the inductor.
TPS54425 ocp.pdf

Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Expert 4875 points

    Hi Yusuke-san,

    The overcurrent protection for TPS54425 is implemented using a cycle by cycle current limit. The IOCL in the datasheet is the valley current limit level from ATE test. It is a low side current limit level not related to the working condition. It is not necessary to calculate the IOCL from OCP threshold. What you could do is to calculate the ripple current for inductor and add up the IOCL in the datasheet to get the estimate peak inductor current during OC. 

    For example, if the ripple current for inductor is 2A. Typical IOCL for TPS54425 is 5.4A. The estimated peak inductor current will be 7.4A under OC.

    Best,

    Anthony

  • 0 in reply to Anthony Lang
    Guru 21930 points

    Anthony-san,

    Thank you for your support.
    Let me ask you one more thing.

    I found the following post.
    https://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/539133/1968070#1968070

    And I found the following formula from your post.
    ・OCL threshold = IL/Rdson
    ・Valley current level = Iocl-1/2*inductor ripple
    Customers want to calculate the exact OCL value in accordance with the inductor.
    Could you give me your advice?

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Expert 4875 points
    Hi Yusuke-san,

    For the pre post, I think the datasheet is misleading. And I double checked with designer for this family part and also checked the ATE test result after that. I found that the Iocl in the datasheet is indicating the valley current level that will be limited no matter what inductor will be selected. It is an open loop test without inductor. In this case, this Iocl is the real valley inductor current limit.

    Valley current limit=Iocl, average inductor current@OC=Iocl+1/2inductor ripple, peak inductor current@OC=Iocl+inductor ripple.

    Sorry for the confusion here.

    Best,
    Anthony