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LM25061-1 Fault Timer time

K.Hamamoto
Guru 12155 points

Hi

The fault timer time seemed longer than calculated time when customer tested the output short test.

Please see the waveform below.

Fault Timer Time at CT=0.22uF is 4.7ms. But it was 20ms.

What does the time depends on. Can you give some advice for this issue.

Regards,

K

  • 0
    TI__Mastermind 42795 points

    Hi,

    Can you show your calculations for the fault timer? Also, what was the O-scope probe impedance (you need a 10 Meg probe on TIMER).

  • 0 in reply to Eric Wright
    Guru 12155 points

    Hi

    Thank you for your reply.

    Tfault = (CT*1.72)/80uA = (0.22uF*1.72)/80uA = 4.7ms

    I am confirming to customer for O-probe impedance.I will let you know if I get the impedance.

    Regards,

    K

  • 0 in reply to K.Hamamoto
    TI__Mastermind 42795 points

    The oscillation in the current waveform is interesting. It could be that the TIMER is starting-stopping-starting due to the rise-fall of the current with an overall lengthening of the perceived fault time. Have the customer check the sourcing capability of the input supply (make sure the supply can keep the input voltage stable during the short circuit condition).

    Also check how the short is applied (electronic load or passive type load?). Electronic loads can cause issues with active hot-swap circuits.

  • 0 in reply to Eric Wright
    Guru 12155 points

    Hi 

    1.For your questions.

    The customer checked the sourcing capability.The current limit of the source was 160A.

    Also the customer applied the short by FET switch.

    2.Additional information

    They tried the start test by CC mode and CR mode.

    (CC mode , CT=0.47uF, Rpwr=75kohm,Cout=28000uF)

    (CR mode,CT=0.47uF, Rpwr=75kohm, Cout=28000uF,RL=0.26ohm)

    Then the fault timer time was different from CC mode and CR mode.

    In CR mode, it looks normal.( The rising of TIMER pin in Fault time looks glacis.)

    Regards,

    K