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LM61480: Equation (2)

Koji Ikeda
Expert 5565 points
Part Number: LM61480

Hello Support team,

Customer ask if Equation (2) is really correct. They think V_ON - V_OFF =V_EN-HYST, could you review?

Thanks,

Koji Ikeda

  • 0
    TI__Guru 50120 points

    Hi Ikeda-san,

    I have confirmed that existing Equation 2 in the datasheet is not incorrect. 

    It should have been the following 

    Since there is a voltage divider on enable, the ratio of (Voff / Von) = (Ven_rising - Ven_hyst) / (Ven_rising)

    Solving for Voff, you get Voff = Von * (Ven_rising - Ven_hyst) / (Ven_rising). Now the units add up and end result is a calculation in terms of voltage.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 5565 points

    Jimmy-san,

    Thank you for your support.

    V_EN_H and VEN_rising are not in datasheet electrical characteristic. I think V_EN_H = VEN_rising = V_EN (Enable input-threshold voltage – rising). Is this correct? If you can update the equation, it's helpful.

    Thanks,

    Koji Ikeda

  • +1 in reply to Koji Ikeda
    TI__Guru 50120 points

    Hello Ikeda-san,

    Please use the below corrected equation for Voff 

    Ven = enable input-threshold voltage -rising

    Ven_hyst = enable threshold hysteresis 

    There is no typical value for the hysteresis parameter. Customer would need to account for this tolerance for worse case calculation.

    Regards,

    Jimmy

  • 0 in reply to Jimmy Hua
    TI__Expert 5565 points

    Jimmy-san,

    Customer pointed out, if they calculate V_EN=1.263V and VEN_HYST=0.4V(as TYP), 1 - VEN / VEN_HYST =  -2.1575.... Is this equation true?

    Thanks,

    Koji Ikeda

  • +1 in reply to Koji Ikeda
    TI__Guru 50120 points

    Hi Ikeda-san,

    The enable ratio was accidentally flipped.

    New equation should be :

    • V_OFF = V_ON* ( 1 – VEN_HYST / V_EN).

    Apologies for the confusion here. 

    Regards,

    Jimmy