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TPS25921L: Current limit during powering up with soft start

Takahiro Saito
Expert 5315 points
Part Number: TPS25921L

Hello team,

I want to know the current limit when the device is powering up with soft start.

In the beggining of powering up with SS, (Vin - Vout) is bigger than 1V.  In that condition, the current limit value is not defined in the datasheet.

Does the current limit work when the (Vin - Vout) is bigger than 1V? If so, does the current value is lower than the set value?

Regards,

Taka Saito

  • 0
    TI__Guru* 95911 points
    Hi Taka Saito,

    During soft start, the right value of C(ss) limits the input current to less than set current limit value.
    please refer equation 2, 3 and the application example in the datasheet and let me know if any clarification is needed.

    Best Regards
    Rakesh
  • 0 in reply to Rakesh
    TI__Expert 5315 points
    Thanks, Rakesh. I have looked at the application example you mentioned in the datasheet. I understood that the current limit protection can be worked at start-up. I also should care about the Css value to avoid the thermal issue at start-up.

    I have one more question with regard to the current limit value in the condition of (Vin - Vout)>1.0V. Compareing between I_LIMIT and I_OS at 95.3kΩ, it looks like the typical current limit value at 95.3kΩ is located between 0.9A and 1.0A when the (Vin-Vout)>1V. Is that correct?

    Regards,
    Taka Saito
  • 0 in reply to Takahiro Saito
    TI__Guru* 95911 points
    Hi Taka Saito,

    Please use the design calculator tool available at www.ti.com/.../toolssoftware for Css value calculation.

    During over current event, the device fold back the current limit from I_LIMIT to I_OS. So, the typical current limit value at 95.3kΩ changes from 1.0A to 0.9A.

    Best Regards
    Rakesh