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Original question:

LM25149-Q1: I would like to know Enable voltage falling threshold of LM25149-Q1.

LM25149-Q1: Current balance of each phase during single-output two-phase operation

yuka Ouchida
Prodigy 120 points
Part Number: LM25149-Q1
Other Parts Discussed in Thread: LM25149

Hi Team,

I have a question about LM25149-Q1 dual phase operation.

Q. We use 2 units of LM25149-Q1 as single-output two-phase operation.
Can I ask how much IOUT difference of each phase(CH1,CH2)?

(for example, if 10A total output, the phase may shift up to 6A+4A, or 7A+3A...)

What factors determine the balance of the current?
Please tell me how it comes to balancing the current of each phase.

Thanks,

  • 0
    TI__Mastermind 31110 points

    Hello Yuka,

     

    You can expect a current balancing of +/- 10% typically.  Factors that determine accurate current sharing is as follows.

     

    1. Rsense tolerance

    2. Internal Slope compensation variation between the devices 

    3. Inductor tolerances.

     

    Hope this helps.

     

    David.

  • 0 in reply to David Baba
    Prodigy 120 points

    Hi David,

    Thanks for the reply.
    I have more question.

    With the current balance is ±10% (typical), is this value guaranteed by the IC?
    Is it correct to understand that there are cases where a difference of 5% is a balance, and there are cases where a difference of 10% is a balance?

    Is it possible to theoretically calculate the difference in balance?
    Is it impossible?


    Does it gradually become equilibrium after the power supply starts?

    regards,

  • 0 in reply to yuka Ouchida
    TI__Mastermind 31110 points

    Hello Yuka,

    Yes the current imbalances can be calculated.  If you need +/-5% worse case over temp and from part to part, You will need to ensure that the inductor values are matching and the Rsense are matching to ensure that you get better than +/-10% guaranteed over temp.  The device current balancing is not guaranteed, and it does not self-balance.  You may need additional circuitry to balance current in each phase which increases complexity.  Perhaps another option is to use average current mode control as this ensures the average current is sharing and not the peak current.

    Hope this helps.

    David.

  • 0 in reply to David Baba
    Prodigy 120 points

    Hi David,

    Thanks for the reply.
    I have more question.

    If we make sure that the inductor values and resistance match so that they are guaranteed to be at least +/- 10% over temperature,
    does that mean that the current imbalance is a worst-case case of +/- 5% between temperature and components?

    Is there a formula to calculate the degree of imbalance?

    Does IC(LM25149)s not have the ability to balance itself, and will it be a stable movement where it is natural?

    regards,

  • 0 in reply to yuka Ouchida
    TI__Mastermind 31110 points

    Hello Yuka,

    No, the device cannot balance itself, infect, its positive feedback, in that if imbalance exists, it will settle to a slightly worse point because the temperature causes changes in the RSENSE resistor that is not in your favor.  However, taking out the inductor tolerances will remove a significant error component in your design, but you still have slight differences in tolerances between the current sense circuits.  to calculate you have to add up all the error in the current sense, the slope comp, calculating what the differences are in the peak and then equate to the Average current.  Typically, 5% would be possible.

    Hope this helps.

    David.