Practical aspects of thermal transient testing in live digital circuits

Thermal Transient Testing is a method practically used to determine the thermal model of an integrated circuit´s case and cooling facilities. The traditional measurement setup of this diagnostic examination does not allow in-circuit testing in case of fully digital semi-custom devices, such as complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs) and programmable system on a chip devices (PSoCs) because it demands an accessible on-chip p-n junction for temperature rise initiation and temperature monitoring. The article presents a proposed novel measurement setup of the thermal transient testing developed for programmable logic devices that implements the required measurement means exploiting the general purpose programmable logic fabric. The main objective of the research is to determine the effects of the interaction between a live digital circuit and the thermal transient testing environment in order to ascertain the feasibility of an on-chip thermal testing facility making possible in-circuit measurements. A simple test environment and the obtained measurement results are presented in order to prove the applicability of the proposed measurement method. The article also presents an application of the logi-thermal simulation method enabling designers to optimize the relative placement of the measurement elements and the user logic. Simulation results showing the application of the method are included in this paper as well.