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I am trying to achieve this plot in LTspice from the datasheet of LT1762. (I am a beginner trying to understand how this works) enter image description here

My schematic is as follows: enter image description here

The output I get is this. enter image description here

What am I doing wrong?

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  • \$\begingroup\$ My main goal is to try to plot Dropout Voltage vs. Output Current . I cannot figure out what I am doing wrong. \$\endgroup\$ Commented Aug 11, 2023 at 5:45
  • \$\begingroup\$ What is the Y-axis in your simulation result? \$\endgroup\$
    – sai
    Commented Aug 11, 2023 at 10:05
  • \$\begingroup\$ it was V(in,out) i.e the difference in the input and output voltages. \$\endgroup\$ Commented Aug 11, 2023 at 10:11
  • \$\begingroup\$ I am getting similar error while plotting the quiescent current vs input voltage graph. \$\endgroup\$ Commented Aug 11, 2023 at 10:23

2 Answers 2

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The problem is with the .step temp -50 125 50 command. What this command will do is run a series of plots from -50\$^\circ\$C to 125\$^\circ\$C in 50\$^\circ\$C steps. Each value in a .step command is discrete and will run the simulation over again plotting another trace in a new color with just that parameter changed, it is not a continuous sweep like a DC sweep. While the .step command editor will let you set a 'sweep' with temp as the parameter it will not give you a continuous variable to plot against. If you change the Y axis to plot temp it will show you the initial value \$\pm\$0.1 as you can see on your graph.

In order to recreate the original chart you would need to sweep the temperature and plot with that as the Y axis, I'm not aware of a way to do this in LTspice, there may not be a way. I believe the temperature parameter has to be set at the beginning of a simulation sweep and can not be changed mid sweep, you can only step it over multiple sweeps.

Also in your other .step command I think you can leave out dec, that's for doing a logarithmic step by decade and requires a lower limit, upper limit, and the number of steps per decade as parameters whereas you have a list of values.

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I tried the same circuit at my end and I get 2.5V output. I did the DC sweep analysis instead. You can see the output below:

enter image description here

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