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Original question:

Question of LM3526

LM3526: Inrush Current Limit

Shota Mago
Expert 8110 points
Part Number: LM3526

Hi team,

My customer has been using LM3526MX-L/NOPB and provided some questions as follows.

  • They has been using this device over 10 years but it failed at output short test for a few months.
    Is there any design/process change for this device recently?

  • At CURRENT LIMIT section, it describes that “~ limits the output current to approximately 1.0A typical”.
    On the other hand, SOFT START section describes that “the maximum in-rush current is internally limited to 1.5A”
    Is those difference just from Typ and Max value of Isc?

  • Although datasheet describes that “the maximum in-rush current is internally limited to 1.5A”, figure.15 shows that about 2Apk inrush current before current is limited to 1A.
    A similar phenomenon(4Apk inrush current was observed before current limit) was observed on the customer's board.
    Is this correct behavior for this device?
  • What is difference between ISC(Short Circuit Output Current) and OCTHRESH(Over-current Threshold)?

I'm looking forward to hearing back from you.

Best regards,

Shota Mago

  • 0
    TI__Mastermind 18031 points

    Hi,

    1. For short test failure, how many units fail? Is the IC broken? What's the value of the input and output cap?

    2. Soft-start  technology is used to reduce the irush current as start-up.

        As start up, charger will charge output and input cap which will form big current. Soft-start means the internal MOS working from cut-off region to saturation region to limit the current.

    3. Current limit and short circuit have same current limit block or function. But they start from the variable resistance region to saturation region. Output cap already fully charging at first. Hot short meaning output voltage suddenly fall to zero which will lead to very high current. It needs response time to current limit. So it will have a period when the current is very high.

    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.