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TPS73801-SEP: Output equation with line and load regulation

Part Number: TPS73801-SEP

Dear,
I know there is the accuracy equation §10 in the document "Technical Review of Low Dropout Voltage Regulator Operation and Performance" SLVA072.
But I need to have the output voltage equation in regard with the line regulation and the load regulation.
The typical output equation is :
Vout = Vfb * (1 + R2/R1) + Ifb * R2.
How shall I integrate the line and load regulation to this equation?
Proposal 1 : Vout = Vfb * (1 + R2/R1) + Ifb * R2 + Vl + Vld
Proposal 2 : Vout = (Vfb + Vl + Vld) * (1 + R2/R1) + Ifb * R2
Vl : Line regulation
Vld : Load regulation

Best regards

Mickaël Brice

  • Mickael,

    I missed seeing your post from Wednesday.   I apologize for delay.

    The VFB specification includes results across line and load as can be seen from the test conditions.

    For overall accuracy, line and load are included in VFB.  You would need to add contributions of divider error and leakage on IFB.

    If this answers your question, please click "This Resolved My Issue"
    Regards,
    Wade

  • Hi Wade,

    Thanks for your reply

    I'm agreed with you.

    I want to use this component in space application

    I need to segregate this parameters in the output voltage equation to justify the design with a worst case analysis?

    I must optimize the design by taking into account the input voltage variation and the output current variation of my application.

    How have I to take into account this parameters (Load and line regulation) in the output voltage equation Vout= Vfb*(1/R2/R1)+Ifb*R2?

    To illustrate my need for precision, for Vfb, I use the values at 25°C to determine the typical value, the initial variations and I use the curve figure 4 "Output Voltage vs Temperature", to determine by extrapolation the variations at the temperature of my application -25°C to +50°C.

    Thanks

    Regards

    Mickaël

  • Mickaël,

    The approach that I have seen for WCA analysis would be to use the full tolerance range of VFB, and add on the errors introduced from the resistor divider and feedback leakage.

    Additionally, the temperature range can be limited to reduce overall error.  This can be done by calculating a temperature coefficient (tempco), and then applying this to the mission temperature profile.

    For example, the VFB range is 1.174 to 1.246 with typical of 1.21.   This results in 1.21V +/- 3%.

    Since the bandgap voltage across temp is linear, the range can be divided down from the full -55 to 125c range.

    (1.246-1.174)/(125 +55) = 0.072/180 = 0.0004 V/degree C.

    Now this can be applied to your operating range.  Using your mission temperature profile Tj = -25 to 50.   Using this range of 75 degrees, centered about typical 25c you get 1.21 +/- 0.03 V = 1.21 +/- 2.5 %

    You can then add in the errors from resistor divider and feedback leakage contributions to have a very good approximation of worst case Vout accuracy.

    Regards,

    Wade