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Original question:

LM3526: Inrush Current Limit

LM3526: inrush current

user6370547
Prodigy 60 points
Part Number: LM3526

I am currently designing a circuit using the LM3526.
Therefore, can you answer the following questions?

What is the "Over-current Threshold"?
The DC Electrical characteristics table in the data sheet states that the "over-current thereshold is 2.2A(typ).
I don't know the difference from the current limit.

From Figure14, I can read that the flag is pulled low  when the inrush current reaches 2.2A.
So, if the flag is pulled low by applying the limited current, it is considered that the flag is pulled low even when 1A current is flowing after the inrush current flows in Fig. 14.
But in Figure 14, the flag is pulled low only for the inrush of 2.2A.

  • 0
    TI__Mastermind 18031 points

    Hi Sir,

    See below description from datasheet of section 'Transient Over-current Delay'.

    Hope this information will answer your question.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Prodigy 60 points

    I have a additional question.

    According to the table of DC Electrical charcteristics of data sheet, "over-current threshold" is 2.2A(Typ).
    On the other hand, current limit is 1.0A  from the datasheet of section "CURRENT LIMIT".
    And, the maximum in-rush current is 1.5A from the datasheet of section "SOFT START".

    I confirmed the section of "Transient Over -current Delay" you have presented.
    Although the current limit status is described, what is the above current limit at this section?

    If 1.2A in-rush current flows for 2ms, will the flag be pulled low?
    (1.2A< "over-current threshold" is 2.2A(Typ).)
    (1.2A >  1.0A  from the datasheet of section "CURRENT LIMIT".)
  • 0 in reply to user6370547
    TI__Mastermind 18031 points

    1.As the 'Transient Over-current Delay' section described, the deglitch time is 1ms. If the inrush current is above 1ms, the fault flag will be asserted.

    2. You can also set the delay time by external RC circuit.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Prodigy 60 points

     You described that "If the inrush current is above 1ms, the fault flag will be asserted".
    Then, please tell me the limit value of in-rush current.
    2.2A (Over current threshold)? or 1.0A(current limit ) ?

  • 0 in reply to user6370547
    TI__Mastermind 18031 points

    No matter OC or current limit, if exist above 1ms, will assert fault flag.

  • 0 in reply to Ziv Zhang
    Prodigy 60 points

    Thank you for reply.

    1. Then, if inrush current of 0.5A flows for 3ms, will flag be pulled down?

    2. I have a additional question.
    What is the difference betweeen "OC" and "current limit"?

  • 0 in reply to user6370547
    TI__Mastermind 18031 points

    1. Inrush current means very high transient current. 0.5A is below current limit value.

        It will not pull down fault flag.

    2. OC current is a current platform higher than current limit. Used to suppress the transient high current.

       Current limit is to limit the stable current which is above the current limit threshold.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Prodigy 60 points
    I'm sorry many times

    I'm still not sure.

    If inrush current of 1.2A flows for 2ms, will flag be pulled down?
    (In this situation, inrush current(2ms) is longer than  'Transient Over-current Delay'(1ms).
    Howevwe, Inrush current is  less than OC(2.2A).)

    Current linit  is to limit the "stable current".
    Therefore, I thinlk that it is not necessary to consider the inrush current.

    Is the above my understanding correct?
    I'm sorry many times, but please answer.
  • 0 in reply to user6370547
    TI__Mastermind 18031 points

    If the current is constant 1.2A for above 2ms, fault will assert.

    If current is 2.2A 0.5ms and then 1A constant, fault will assert.

    If current 2.2A 0.5ms and then <1A constant, fault will not assert.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click 'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Prodigy 60 points

    Thank you.
    I resolved my issue.