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LM25141: About Hiccup mode behavior at start up

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Guru 21045 points
Part Number: LM25141
Other Parts Discussed in Thread: LM5141

Hi Team,

 

We simulated LM25114 at the following conditions.

At the result, LM25141 can start up but VOUT is around 3.15V (less than 3.8V(target voltage)) and IOUT is around 8.3A(current limit value).

After that, this device enter the Hiccup mode.

Is this behavior correct?

 

I guess that LM25141 enter the Hiccup mode even if start up so a simulation is wrong.

Is my understanding correct?

 

[Conditions]

VIN=20V

VOUT=3.8V

IOUT=5A

Current limit = around 8.3A

Fsw=440kHz

L=6.8uH

Cout=22uF x 2

Load capacity is 500mF (ESR is around 35mohm)

 

[Sim circuit]

Please refer to the attached file.

 

Regards,

Kanemaru

LM25141 ver2.tsc

  • 0
    TI__Mastermind 40040 points
    Hello Hideto,

    I think the issue with your bench unit is due to the large output capacitance and short start up time? have you tried increasing the soft start time?

    Hope this helps?

    David.
  • 0 in reply to David Baba
    Guru 21045 points

    Hi David-san,

     

    Thank you for your prompt reply.

    I will try simulation with long soft start.

     

    And, I have one more question.

    Does LM25141 have the upper limit level of Soft Start time?

    (by the way, Max soft start time is 10ms in WEBENCH.)


     

     

    Regards,

    Kanemaru

  • 0 in reply to Hide
    TI__Mastermind 40040 points
    Hello Kanemaru san,

    The Soft-Start is fully programmable, there is no limit.

    Hope this helps?

    David.
  • 0 in reply to David Baba
    Guru 21045 points

    Hi David-san,

     

    I changed from 2ms (Css is 39nF) to 20ms (Css is 390nF) and Reset time is around 1ms(CRES is 18nF).

    However, LM25141 don’t enter the hiccup mode even if the inductor current reached the current limit.

    Is this behavior correct?


     

    Regards,

    Kanemaru

  • 0 in reply to Hide
    TI__Mastermind 40040 points
    Hello Kanemaru san,

    I think the issue you was experiencing previously with a small Css, is that you were hitting current limit on start up initiating hiccup, which will reset soft start and the current limit events will continue to repeat every time you tried restarting into a large Cout. The part would never get out of a restart to current limit event because Css was so small. Now you have increased Css, your start up time has significantly increased and the inrush currents charging up Cout has decreased below the current limit level. If you increase your load current beyond the current limit level, you should hit current limit and the part will then begin to hiccup again?

    Hope this helps?

    David.
  • 0 in reply to David Baba
    Guru 21045 points

    Hi David-san,

     

    LM25141 enter Hiccup mode when Soft Start pin voltage reaches 1.2V.

    So, I understand that LM25141 can't enter Hiccup mode until Soft Start pin reaches 1.2V

    Is my understanding correct?


     

    Regards,

    Kanemaru

  • 0 in reply to Hide
    TI__Mastermind 40040 points
    Hello Kanemaru san,

    The LM5141 will enter into hiccup if 512 consecutive cycles of current limit occur, even during start up.

    I hope this helps?

    David.
  • 0 in reply to David Baba
    Guru 21045 points

    Hi David-san,

     

    I understand that LM25141 enter Hiccup mode if around 1.16ms ((1/fsw) * 512 cycles) of current limit occur.

    However, LM25141 are switching (don’t enter Hiccup mode) for around 180ms at start up.

    Is this behavior correct?


     

    Regards,

    Kanemaru

  • 0 in reply to Hide
    TI__Mastermind 40040 points

    Hello,

    It will depend if you hit current limit within the long 180ms start up.  If you hit current limit you will enter into hiccup.

    Hope this helps,

    David.

  • 0 in reply to David Baba
    Guru 21045 points

    Hi David-san,

     

    Thank you for your comment.

    So, I understand that this behavior is correct.

     

    Regards,

    Kanemaru