Analysis and modeling of passive device degradation for a long-term electromagnetic emission study of a DC–DC converter
Introduction
The consideration of the electromagnetic robustness (EMR) of integrated circuits (IC) appeared in these last years, i.e. the evolution of parasitic emission and susceptibility to electromagnetic interferences with time for electronic devices working in harsh environments. Publications such as [1] have demonstrated that the electromagnetic emission (EME) of digital circuits and I/O buffers changes with time because of the activation of intrinsic degradation mechanisms. As presented in a few works, the simulation can be utilized to predict the long-term EMC behavior. For example, in [2], the simulation results confirmed the evolution of the electromagnetic susceptibility of a phase-locked loop before and after aging stress.
A switch-mode power supply (SMPS) is selected as the device under test in this study. Because of their high power efficiency, switch-mode power supplies are widely used in electronic applications [3]. However, one main drawback of SMPS is the noise delivered by the switching activity, responsible for conducted and radiated electromagnetic emission. In this way, the management of the parasitic emission of SMPS is a frequent topic in the literature on electromagnetic compatibility (EMC) [4], [5]. Several recent studies presented the long-term behavior of SMPS. Due to the degradation of the electrolytic capacitor which is used to filter the output voltage of SMPS, an increase of the ripple of the output voltage of SMPS was illustrated in [6], [7]. Another consequence is the increase of electromagnetic emission, as shown in [8], where the increase of the EME of a DC–DC converter after thermal stress is associated with the degradation of output filtering passive devices, not only the capacitor but also the inductor in the output side. As a following study of [8], this paper focuses on the construction of passive component degradation models, and the application of these degradation models in the long-term EME study of a buck DC–DC converter.
Section snippets
DC–DC converter
The studied SMPS is based on the NCP3163 switching regulator from On Semiconductor. It is configured in step-down operation, in order to convert the voltage 12 V provided by a battery into a regulated voltage 3.3 V for a constant resistive load equal to 3.4 Ω. The switching frequency is set to 237 kHz. A simplified schematic of the converter is presented in Fig. 1. The test board has been designed to characterize conducted emissions. The output conducted EME of the converter is measured through a
Aging impact on different capacitors
Two kinds of output filtering capacitors: aluminum capacitors and tantalum capacitors suffer from the thermal stress. As illustrated in Fig. 2, the comparison of impedance before and after aging shows that a significant degradation is observed only with aluminum electrolytic capacitors. Besides, a gradual increase of ESR of electrolytic capacitors is shown in Fig. 3. The figures illustrate only one sample of each type, but the plotted data are representative of all the tested components of the
Degradation models of passive devices
Electrical models of the aluminum capacitor and the powder iron inductor have already been proposed in [8]. In this study, the modeling of passive devices focuses on the degradation evolution over aging time.
Modeling of the evolution of conducted emission
Fig. 14 details the preliminary model of the output side of converter. The converter is modeled by an ideal switch which is controlled by a rectangular voltage source. Besides, the models of passive devices are added to the output side of the switch. The transient simulations are performed with Agilent's Advanced Designed System (ADS), and the emission level in frequency domain is obtained by the Fast Fourier transform (FFT) of the output voltage. To model the long term behavior of the
Conclusion
This paper aims at modeling the thermal aging impact on passive devices and its application for the long-term EME study of a buck DC–DC converter. The experimental results demonstrate that the aluminum capacitor and the powder iron inductor have a gradual evolution over the aging time. The degradation models of aluminum electrolytic capacitor and powder iron inductor are constructed. Finally, an electrical model of the converter output side is built, where the degradation models of passive
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