LTM4668A output current at burst mode

Hello

LTM4668A datasheet rev.A P.11 says below.

"During Burst Mode operation, the peak current of the inductor is set to approximately 400mA in normal operation
even though the output of the error amplifier (COMP) indicates a lower value."

My understanding is below.

Is it correct ? 

" If LTM4668A is set to burst mode, output curent limit  becomes from TYP 2.0A to 400mA .

 If the load requirement is greater thean 400mA ,  we should select the other mode . "

Maybe,  myunderstanding is incorrect but  I don't understanding  above datsheet description.

Please let me know your advice.

Regards,

Teli 

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  • 0
    •  Analog Employees 
    on Jun 24, 2021 7:35 AM

    Hello,

    Burst mode is entered and left automatically by the part itself. You have the chance with the configuration to allow Burst mode in general, but the decision about (and when) entering or leaving Burst Mode is not yours.

    If  you want to operate as efficient as possible in low load condition select BurstMode. if your low load efficiency is not important or your load is always high you might 'defeat' BurstMode.

    You can check the difference in efficiency between BurstMode or PulseSkip in the diagrams on page 5

  • Hello

    Thank you for your reply.

    My specification is 6V input -> 0.9V output 1.2A.   ( the other outputs are 0.95V 0.2A, 1.8V 0.3) 

    Minimum on time of LTM4668A is 60ns TYP and that of above condition is 68ns.

    So I thought that  it might be difficult to use LTM4668A in this specification.

    ( Lead time of LTM4668  is long and I can not use t it now. I have the stock of  LTM4668A )

    Then I found below description of datasheet P.10.

    "In the cases where the minimum duty cycle is surpassed, pulse-skipping mode (MODE/SYNC = GND) or Burst Mode (MODE/SYNC = INTVCC) has to be implemented"

    So I wanted to select burst mode or pulse skipping mode.

    Then I found below description of  LTM4668A datasheet rev.A P.11 .

    "During Burst Mode operation, the peak current of the inductor is set to approximately 400mA in normal operation
    even though the output of the error amplifier (COMP) indicates a lower value."

    If above means that output current limit is set to 400mA at MODE/SYNC= INTVCC(burst mode),

    I'm going to select pulse skipping mode.

    Please let me know your advice what does above 400mA mean.

    Regards,

    Teli

  • +1
    •  Analog Employees 
    on Jun 24, 2021 9:26 AM in reply to teli

    Hello,

    in this scenario I would go with pulse skip mode to achieve good regulation for the 0,9V rail.

    BurstMode should work as well, but I have not tried this operation close to the minimum on-time.

    BustMode and the 400mA limit means that the delivered bursts have a maximum peak of 400mA, which is normally fully sufficient for low power operation with currents below 200mA.

Reply
  • +1
    •  Analog Employees 
    on Jun 24, 2021 9:26 AM in reply to teli

    Hello,

    in this scenario I would go with pulse skip mode to achieve good regulation for the 0,9V rail.

    BurstMode should work as well, but I have not tried this operation close to the minimum on-time.

    BustMode and the 400mA limit means that the delivered bursts have a maximum peak of 400mA, which is normally fully sufficient for low power operation with currents below 200mA.

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