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Trying Out the ROHM Solution Simulator (1)

2021.11.10

Points of this article

・There are essentially two types of simulations available for switching regulators, "Frequency Domain" and "Time Domain".

・In the ROHM Solution Simulator, component values in a simulation circuit can easily be modified when performing simulations.

Operation of the ROHM Solution Simulator is extremely simple. Why not try it out once, just to get a sense of how to use it. As examples, we’ll describe two simulations you can try: first, the frequency characteristics of a step-down switching regulator, and second, the transient response characteristic waveform of the device. Try actually running the simulations according to the examples. For a faster introduction to the ROHM Solution Simulator, please refer to the “Hands-On User’s Manual（PDF）“.

Trying Out the ROHM Solution Simulator
（1）： Simulation of the Frequency Characteristics of a Step-down Switching Regulator

Go to the ROHM Solution Simulator web page, and click on “Switching Regulators” in the “ICs Solution Circuit” category (Fig. 1); a list like that in Fig. 2 appears (the screen layout may change without advance notice).

Fig. 1. “ROHM Solution Simulator” web page, “Switching Regulators” in “ICs Solution Circuit” Category

Fig. 2. List of Switching Regulators in “ICs Solution Circuit”

From this list, select the “BD90640EFJ” step-down switching regulator IC. Here, the frequency characteristics of a power supply circuit that uses this IC is simulated, so click on “Simulation” in the “Frequency Domain” column. There are two types of simulations, “Frequency Domain” and “Time Domain”; we will perform the time domain simulation in part (2).

When accessing the simulator from the product page, search on “BD90640EFJ” and scroll down to the “Tools” section. In the list of simulations are displayed the two types, frequency domain and time domain, and a simulation guide (PDF) for the IC. Upon clicking on “Frequency Domain”, the simulation starts as shown above. The simulation guide presents various other simulation methods in addition to that of this example, and should be consulted.

When the simulation starts, the simulation circuit is displayed, as shown in Fig. 3. Upon clicking the Run symbol (▶) in the center of the circuit diagram, the screen switches to that shown in Fig. 4, and the simulation and component values can be modified.

Fig. 3. “SCHEMATIC INFORMATION” screen for the BD90640EFJ Solution Circuit

Fig. 4. Simulation start screen appearing when the Run symbol （▶） in Fig. 3 is clicked

At this time, simulation results for the frequency characteristics (Bode plot) under the default conditions are already displayed.

In this circuit, one component that adjusts the frequency characteristics is the phase compensation resistor R3, in the red circle. Try changing R3 and run a simulation to see how the Bode plot changes.

Upon double-clicking on R3, the Property Editor for R3 opens, as in Fig. 5; change RESISTANCE_VALUE from the default value of 20k to 3k and execute the simulation. The simulation begins upon clicking the ▶ symbol, in the red circle at the top of the screen in Fig. 4; the result is output within a few seconds.

Fig. 5. Property Editor to change the value of R3

The Bode plot resulting when R3 is changed to 3 kΩ should have gain and phase characteristics different from those for the default value of 20 kΩ.

In the forthcoming part (2), a time domain simulation example is presented.

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