Experimental Identification Method for Small-Signal Analysis of Smart Power ICs

Smart power integrated circuits (ICs), as the combination of control and power functions on a single chip, enable the production of more miniaturized systems. This paper presents an experimental method for the small-signal frequency-response analysis of smart power ICs in switch-mode power supplies. In this method, the switching-duty-cycle output of a power IC is converted into a digital signal by using two high-speed counters during each switching period, and the power IC's control input signal is simultaneously converted into a digital signal by an analog-to-digital converter. After processing the data of the duty-cycle output and the control input, not only the transient response but also the frequency response of the power IC can be obtained. Using least square identification, the smart power IC's transfer function is finally synthesized from the measurement data. This analysis method, referred to as sampling the transient responses and frequency responses of power ICs, can efficiently provide reliable and accurate transfer functions whether the switching frequency of a power IC is jittered or frequency modulated. The experiments using different power ICs were presented herein to validate the analysis method. The results were discussed, and the effectiveness and practicality of the method were verified.