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LMZ31506: About slow start of LMZ31506

hisashi yoda
Intellectual 640 points
Part Number: LMZ31506
Other Parts Discussed in Thread: TPS84621, TPS84620, TPS82130

LMZ31506のスロースタートについて教えてください。

LMZ31506のデータシートの9.16 Slow Start (SS/TR)にて、時間とコンデンサの定数の関係についてTable6に記載されていますが、計算方法はどこに記載されていますか？

データシートは下記リンクを参照しております。www.ti.com/.../lmz31506.pdf

  • 0
    Intellectual 640 points

    Please tell me about the slow start of LMZ31506.

    In 9.16 Slow Start (SS / TR) of the LMZ31506 data sheet, the relationship between time and capacitor constants is described in Table 6. Where is the calculation method described?

    Please refer to the link below for the data sheet. www.ti.com/.../lmz31506.pdf

  • 0 in reply to hisashi yoda
    TI__Mastermind 18370 points

    Hi Hisashi Yoda,

    We often describe this relationship in such a table and not via an equation.
    You can see this in many TI converters data-sheet such as TPS84620, TPS84621, ...

    If you need a SS timing that is not in table, I suggest that you use linear interpolation between two closest points in the table.
    As we currently have no other published information in this regards.

    If you need the calculation for other reasons, please let me know.

    Regards,

    Yitzhak Bolurian

  • 0 in reply to Yitzhak Bolurian
    Intellectual 640 points

    Hi Yitzhak Bolurian

    Thank you for your answer.

    I asked a question because it was described in 8.2.1.2.4 Soft Start-Up Capacitor Selection in the data sheet of TPS82130.

    The reason we need the information is to calculate the change in time (tss / tr) due to the variation of the capacitor (Css / tr).

    If you have any information, please provide it.

    Regards,

    Yoda

  • 0 in reply to hisashi yoda
    TI__Mastermind 18370 points

    Hi Yoda,

    I am trying to find the relationship between Css and Tss in a different format for you.

    But, what you ask for (or need) is actually easy to figure out using the table.

    For example, let's assume that your Tss is set to be 3.5 mS, which is in between the two points 2.8 mS and 4.6 mS mentioned in the table.

    Therefore the the change in time (tss / tr) due to the variation of the capacitor (Css / tr) can be calculated by  (4.6 - 2.8)/(10000 - 4700)= 1.8/ 5300 =

    0.00034 mS/pF = 0.34 mS/nF

    Hope this makes sense,

    Regards,

    Yitzhak Bolurian

  • 0 in reply to hisashi yoda
    TI__Mastermind 18370 points

    Hi Yoda,

    Here is the equation as promised.
    But please note that the device already has a 3.3 nF capacitance inside.
    So you have to add 3.3nF (in parallel) to the value of the capacitor that you are using externally.

    Hope this addresses your inquiry.

    Regards,

    Yitzhak

  • 0 in reply to Yitzhak Bolurian
    Intellectual 640 points

    Hi Yitzhak Bolurian

    Thank you for your answer.

    The information in the attached file (7.3.11 Slow Start (SS / TR)), is it included in the data sheet of LMZ31506?

    Regards,

    Yoda

  • 0 in reply to hisashi yoda
    TI__Mastermind 18370 points

    Hi Yoda,

    The provided information (Cut and paste) is not available in the LMZ31506 datasheet.
    But you can verify yourself that the equation + my comment about the 3.3 nF will provide the exact same results as in the table in the LMZ31506 data sheet.

    In case the above addressed your questions, please set the status of this post to resolved.

    Regards,

    Yitzhak