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TPS563212: UVLO calculations

James VDC
Prodigy 240 points
Part Number: TPS563212

Hello,

I am trying to setup the UVLO and am following the formulas in the datasheet.  Is there a MIN difference between VSTART and VSTOP?  I do not see a specification for this, but am finding that my calculations for R1 always end up with a negative result.  I was beginning with a desired VSTART of 12VDC and VSTOP of 11VDC.  

Thank you for your assistance.

James

  • 0
    TI__Expert 8100 points

    Hi James,

    I will check the calculation process and give you reply later!

    BRs

    Zixu

  • 0
    TI__Expert 8100 points

    Hi James,

    Although there is no specific description for illustrating Min difference, the range of VSTART/VSTOP could be limited from the formula listed in datasheet.

       

    The value of VSTART/VSTOP should be greater than value of VEN_FALL/VEN_RISE from above formula. Otherwise the calculated result of R1 could be negative.

    BRs

    Zixu

  • 0 in reply to Zixu Wang
    Prodigy 240 points

    Zixu,

    Forgive me if I am mistaken, but that doesn't seem to work out either.

    Vstart = 12
    Vstop = 11

    12/11 = 1.09
    1.01/1.15 = 0.878

    1.09 > 0.878

    However, Vstart * (VEN_FALL/VEN_RISE)-Vstop
                    12 * (0.878) - 11 = 
                     10.536 - 11 = -.464

    Am I doing something wrong?

    Thanks

  • 0 in reply to James VDC
    Prodigy 240 points

    I am wondering if it isn't something like:
    VStop/.877 = MIN VStart ?

    And, if that is the case, what is the minimum value permissible for R1?

  • 0 in reply to James VDC
    TI__Expert 8100 points

    Hi James,

    Sorry for the typo. The value of VSTART/VSTOP should be greater than value of VEN_RISE/VEN_FALL.

    May I check what odes "VStop/.877 = MIN VStart" mean? Where do you get such formula?

    At present, we may do not have such formula to regulate the value of MIN Vstart.

    BRs

    Zixu

  • 0 in reply to Zixu Wang
    Prodigy 240 points

    Zixu,

    That makes more sense.  Thank you.

    Sure, what I did was simply work the calculation to result in a positive number for the numerator

    (VStart * (VEnFALL/VEnRISE) - VStop)

    VStart * 0.878 - VStop

    So, VStart * 0.878 needs to be greater than Vstop

    Therefore a simple way of getting without a lot of difference between: Vstop/0.877 

  • 0 in reply to James VDC
    TI__Expert 8100 points

    Hi James,

    Yes, the formula you used is right.

    There may be no permissible minimum value for R1. The value of R1 could be calculated from formulas in datasheet and please make sure the VEN is within the range of recommended operating condition.

    BRs

    Zixu