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Deconstructing the Step Load Response Reveals a Wealth of Information

What can be learned from the Step Load response and why we should care?

When analyzing power circuits, engineers routinely evaluate the stability using gain?phase measurements also known as bode plots. Many manufacturers of voltage and low-dropout regulators are now doing away with the bode assessment in favor of only the step load response. The two tests are related, however, an incorrect assessment can lead to incorrect performance conclusions and poor resulting system performance. This article will show what can be learned from the step load response and why we should care.

In many cases it can be difficult or impossible to measure the Bode response of a system, since this is an invasive measurement, and the control loop may be inaccessible. In many monolithic devices, the necessary connections many not be available. In these cases it is often possible to perform a “small?signal step load response” or an output impedance test. A specially designed, transconductance signal injector can support the measurement of both the small?signal step load response and the output impedance of a voltage regulator. One such injector is the Picotest J2111A solid state current injector.

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