Many engineers seem to have trouble with the stability of linear regulators. Given how little stability information is published by the manufacturers of these devices, this is not surprising. In most linear regulators, the output capacitor ESR provides the control loop zero, stabilizing the regulator. The datasheet generally offers little information regarding the stability of the regulator as a function of the load current, output capacitance and output capacitor ESR, which are the external parameters which impact the stability of the regulator.
This article will provide a method for the determination of capacitor ESR required to achieve a particular phase margin for any output capacitance value, based on a single output impedance measurement.