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LMR33620: LMR33620 Question about Short - Circuit Output Current?

Bob Lee62837
Mastermind 7230 points
Part Number: LMR33620

Dear support member,

My customer used LMR33620.

I have a question.


Question
It is described as 500A - 600A in the Short - Circuit Output Current graph of Fig. 3 of the data sheet.

Can the current flow from 500A to 600A when this device is short-circuited?

Best regard.

Bob Lee.

LMR33620 Question.pdf

  • 0
    TI__Genius 11040 points

    Hi Bob,

    This will be the average output current.  This should not be used as a current supply since the device will be in hiccup operation. 

    Best Regards,

    Katelyn

  • 0 in reply to Katelyn Wiggenhorn
    Mastermind 7230 points

    Dear Katelyn,

    Thank you very much for reply.

    May I ask add a question?

    Question
    From the graphs of Fig11 and Fig12, the inductor current is 3A,
    In Fig 3, it ranges from 500A to 600A.

    The range is different, which of Fig3 and Fig11, Fig12 is correct?


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Genius 11040 points
    Hi Bob,

    All three figures are correct. Figure 3 shows the average DC output current, while Figure 11 and Figure 12 show the inductor current. The hiccup performance seen in Figure 11 and Figure 12 lowers the average output current (Figure 3), and consequently improves the thermal dissipation during short circuit.

    Please let me know if you have any additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Mastermind 7230 points

    Dear Katelyn,

    Thank you very much for reply.

    May I ask a add question?


    Q1
    What is dc avarage output curretnt of Fig3?
    The title of Fig3 is "Short-Circuit Output Current".


    Q2
    Could you teach how to obtain output current at short circuit?


    Output current at short circuit is not describe.
    Datasheet 15 page "8.3.3 Current limit and short circuit" is only Isc.


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Genius 11040 points

    Hello Bob,

    Q1:

    The output current will vary depending on the inductor current.  The output current is the average of the inductor current.  The below image shows the inductor current will vary from 0A (0A output current) and 3A (hiccup event).  If you measure the output current with a DMM over a large enough time range, you will measure the average output current of both the 'off time' (0A inductor current) and the 'hiccup time' (3A inductor current). 

    Q2:

    You can measure the output current during short circuit, by shorting the output and measuring the current with a DMM.

    Please let me know if anything remains unclear or if you have any additional questions.

    Best Regards,

    Katelyn Wiggenhorn

  • 0 in reply to Katelyn Wiggenhorn
    Mastermind 7230 points

    Dear Katelyn,

    Thank you very much for reply.


    I understood "The output current is the average of the inductor current ".

    May I ask a add question?


    Q3
    What is the inductor current when the output current in Fig.3 is 500A to 600A?
    Is there a circuit diagram at that time?


    Q4
    If the inductor current is 0 A and 3A as shown in Figure 12,do you think that the output current of the average current of the inductor will be 500A to 600A as shown in Fig. 3?


    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    Mastermind 7230 points

    Dear Katelyn,

    I thought about average of the output current.

    The LMR33620 is equipped with Hiccup mode.
    This current value is limited by overcurrent Operation of 3.5 A (typ).
    Hiccup mode operation Duty is (on 20 msec typ, off 94 msec typ) .


    When it calculate the average value current from this operation,
    The average of the output current is Isc = 3.5 A / (20 ms + 94 ms) = 0.614 A

    Is the might be unit in Fig 3 not A but mA?

    Best regard.
    Bob Lee.

  • 0 in reply to Bob Lee62837
    TI__Genius 11040 points
    Hi Bob,

    Yes, this should be in mA. Thank you for pointing out this discrepancy. I believe this is the reason for the confusion between us.

    I apologize for this mistake, and I will share this with the author.

    Please let me know if anything is still unclear, or if you have additional questions.

    Best Regards,
    Katelyn
  • 0 in reply to Katelyn Wiggenhorn
    Mastermind 7230 points

    Dear Dear Katelyn,

    Thank you for checking the contents.
    I heartily thank you.

    I appreciate your continued support.

    Best regard.
    Bob Lee.