Obsolescence in EMC Risk Assessment: A Case Study on EFT Immunity of Microcontrollers

This paper investigates the obsolescence in EMC risk assessment by conducting an experimental case study on two commercially available Atmel microcontrollers (μCs), i.e. SAM3 and SAM7, the former being more recent but still pin-to-pin compatible. To this end, electrical fast transient (EFT) testing was performed according to the IEC 61000-4-4 standard to identify and clarify the failure occurring in the μCs individual voltage supply pins. The μC crash was considered as the immunity criterion to monitor the failure due to the EFT bursts. Results demonstrate, in a reproducible manner, that SAM3 was more immune to transient disturbances compared to SAM7 on all the considered supply pins, excluding the phase-locked loop. Moreover, regardless of the μC version, the core supply pin was found to be the most susceptible to EFT injection. These results show that replacing a SAM7 μC by a SAM3 μC calls for a detailed EMC analysis, particularly when dealing with obsolescence, since a more modern, compatible IC does not necessarily provide a higher immunity.