An apparatus (200) for tuning a feedback loop that is arranged to regulate an output voltage (Vout) of a switched mode power supply, SMPS (100), in accordance with a control law defined by control law parameters. The apparatus includes a natural frequency estimator (210) arranged to determine a respective estimate of a natural frequency of each of two zeros in a transfer function that corresponds to a model of the feedback loop. The natural frequency estimator (210) comprises: an output voltage deviation determining module (212) arranged to determine, for each of a plurality of points in a search space, wherein the coordinates of each of the points correspond to candidate values of the natural frequencies of the zeros, a deviation of the output voltage of the SMPS that occurs in response to a variation in a load current of the SMPS; and a goal function evaluation module (214) arranged to evaluate a goal function using the determined deviation of the output voltage of the SMPS at each of the plurality of points to obtain a measure of at least one of a size and a recovery time of the respective output voltage deviation. The natural frequency estimator (210) is arranged to estimate a location of a minimum of the goal function in the search space based on the evaluated values of the goal function, the location of the minimum corresponding to the natural frequencies of the zeros. The apparatus further comprises a control law parameter calculator (220) arranged to calculate, based on the determined estimates of the natural frequencies of the zeros, the control law parameters for tuning the feedback loop, and a feedback loop tuner (230) to tune the feedback loop in accordance with the calculated control law parameters.