Let's use LTspice - Let's change the parameters with ".step"

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Design Analog Power SupplyAnalog Devices

Let's use LTspice in the previous article -In the method of checking the maximum and minimum voltage values with ".meas", introduce the ".masure" command that reads the minimum and maximum values of the output voltage when the load of the power supply IC changes. I was allowed to.

This time, we will introduce a parametric analysis method that uses the ".step" command to step-by-step change the constants in the schematic and perform a simulation.

If you are just starting LTspice, we recommend that you look at the "basics" from the list below.

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Also, if you would like to see a video on how to write a basic circuit and how to execute it, there is an on-demand seminar that does not require you to enter personal information, so please take a look if you are interested. Detailed information about the seminar is also provided to those who fill in the questionnaire.

LTspice On-Demand Seminar - Function check with RC circuit -

Let's simulate the charging time to the capacitor!

Let's check the waveform on the time axis using the ".step" command for the capacitor charging time when the resistance value is changed to 10Ω, 100Ω, and 1kΩ in the RC circuit.

Article header library 127389 pic01 1 — CR circuit

Using the .step command

To define the parameters of the resistor component with variables, right-click on the resistor and enter {X} as the Resistance value.

Article header library 127389 pic02 1 — Enter "{X}" in the [Value] field of the resistor

Select [SPICE directive] from Edit on the toolbar. Edit Text on the schematics will open, so add the .step command here.

This command either linearly or logarithmically changes the value of the variable specified by the parameter (here X), or specifies the value of the parameter by a list. This time we set three values as a list. Therefore, the description is ".step param X list 10 100 1k", and it is executed while changing the parameter X to each value in the list.

Article header library 127389 pic03 1 — Entering the .step command

Run the simulation

When I ran the transient analysis, there were three types of waveforms as shown below. The waveform is red when the resistance is 10Ω, blue when it is 100Ω, and green when it is 1kΩ. In this way, the results of changing parameters can be obtained in a single simulation, so circuit verification can be performed efficiently.

Article header library 127389 pic04 1 — Charge time waveform result

Let's apply the ".step" command to the evaluation of power supply ICs!

Let's use LTspice in the previous article -In the method of checking the maximum and minimum voltage values with ".meas", the maximum and minimum voltage values (Peak to Peak) of the output voltage during load fluctuations of the μModule series LTM8065 of the step-down regulator I read.

In addition, use the ".step" command to change the load current parameter and read the maximum and minimum voltage values (Peak to Peak) with the ".masure" command.

Article header library 127389 pic05 1 — LTM8065 simulation circuit

Open the previous download file and set the load current source settings to {X} with the maximum value as follows:

PULSE(0.5 {X} 600u 100u 100u 300u)

Also, write the ".step" command as follows.

.step param x 1 2.5 0.5

Finally, when we ran the simulation, we were able to confirm the results of the output voltage fluctuation in 0.5A steps (4 steps) from 1 to 2.5A as shown in the figure below.

Article header library 127389 pic06 1 — Load response when the maximum value of load current is changed step by step

If you open the Log file with "Ctrl" + "L" on the circuit diagram, you can read the maximum and minimum voltage values (Peak to Peak) when the step parameters are changed as shown in the figure below.

Article header library 127389 pic07 1 — Reading result of maximum/minimum value at step change

By combining ".step" and ".meas" in this way, it is possible to efficiently simulate a power supply IC.

LTspice demo file verified this time

After extracting the zip file to the same folder on a computer with LTspice installed, run LTspice to automatically start waveform display.

RC_step_test__1.zip

.step (RC circuit) simulation file

8065_step_test__1.zip

.step (LTM8065 circuit) simulation file

At the end

This time, the content was about ".step", but there are a wide variety of other commands available. We will continue to introduce various functions in the future, so please continue to support us.

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