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SN6505B-Q1: About spread spectrum function

Kaji@PAN
Mastermind 7890 points

Part Number: SN6505B-Q1
Other Parts Discussed in Thread: LM5141, LM5141-Q1, SN6505B

Hi,

I'm a FAE for TI products.
I have received a question from a customer regarding the spread spectrum function of the SN6505B-Q1 product.

The first question is how much modulation is applied to the set frequency.
Is it possible to provide me with information about what percentage of modulation is performed on the set frequency?

The second question is about how the modulation is done and how it is controlled.
For example, the LM5141 device has low frequency modulation.
Is the SN6505B-Q1 also a modulation method with low frequency?
Or are you performing irregular (random) modulation?
Best regards,
  • 0
    TI__Genius 17100 points

    Hi Kajii-san,

    Thank you for your post! The SN6505's spread spectrum range is +/-4%. Please allow me 1 - 2 days to follow up on the second question.


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Mastermind 7890 points
    Thanks for answering the first question.
    Could you answer the second question soon?
  • 0 in reply to Kaji@PAN
    TI__Genius 17100 points

    Hi Kaji-san,

    I apologize for this delay. What is our customer's end application? Does our customer need to know the modulation method in SN6505 to pass a certain standard or requirement?


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Mastermind 7890 points
    The customer's application is a control circuit used in an automotive battery pack.
    In that circuit, the LM5141-Q1 is used with another power supply, but a low frequency modulation cycle of spread spectrum is superimposed on the power supply line. Because of this behavior, my customers want to know what the SN6505B modulation control looks like.
    Best regards,
  • 0 in reply to Kaji@PAN
    TI__Genius 17100 points

    Hi Kaji-san,

    Thank you for this information. SN6505 spread spectrum is achieved through triangular modulation that has a modulation frequency of ~1/16th the CLK switching frequency (~27kHz for SN6505B and SN6505B-Q1).

    Since SN6505 is a push-pull converter, current ripple drawn from the input supply will be small compared to other DC/DC topologies. If there is concern about ripple on the power supply line from the SN6505 circuit, an LDO supplying the SN6505 will isolate ripple by the SN6505 from the power supply line.

    Is our customer concerned about these spread spectrum modulations interfering with each other? I will await your response.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi Kaji-san, all,

    To provide context on why push-pull converters have low ripple, SN6505's D1 or D2 pins conduct current during the entirely of the switching cycle with the exception of break-before-make time, so continuous current consumption is relatively constant making current ripple drawn from the input supply small compared to other DC/DC topologies


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Mastermind 7890 points
    Thank you very much for your reply.
    Now, the customer will arrange samples of the SN6505B-Q1 and perform actual device verification, in which we will check the modulation of the LM5141-Q1 and how it affects.
    If customer verification has any problem, we will consult again.
    Best regards,