Traditional and Non-Invasive Stability Measurement

Sometimes you have no access to the feedback loop of a voltage regulator. This application note shows how you can measure the stability in such cases non-invasively.

The stability of voltage regulators is a very important parameter in electronic systems. Unexpected ringing due to load changes can affect the whole system performance. Measuring the phase margin of the feedback system helps to evaluate the stability and uncovers critical resonances. 

In some cases the feedback loop of the voltage regulator is not accessible from outside. The Bode 100 in combination with the Picotest J2111A current injector enables you to measure the output impedance of the system and to determine the phase margin of the system without breaking the feedback loop. As a result you are able to perform a Non-Invasive Stability Measurement (NISM).

We have performed the measurements on the Picotest VRTS 1.5 and the VRTS 2 board. The VRTS 1.5 board contains a floating regulator whereas the VRTS 2 board features a ground-based regulator circuit.

Please download the corresponding application note describing first the traditional loop gain measurement and second an output impedance measurement where we apply NISM: