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A detailed transient thermal study for a Remote Keyless Entry System with dynamic heat sources is performed using numerical simulations. The device is packaged in a 54 lead SOIC (small outline IC) package with an exposed copper slug, attached to a 4-layer PCB with thermal vias embedded in the board. The challenge resides in the transient thermal interaction between the several dynamic heat sources (channels), activated in a sequential fashion following different powering profiles and patterns. The main purpose of the device is to wirelessly provide a communication path between the remote key and the receiver placed in the car, so the distance and the signal strength between the two are paramount for an optimal operation. The signal strength is directly associated with the voltage (and associated powering) levels. Several operating scenarios are evaluated while modifying the system design (with/without thermal via pattern) and varying power dissipation and duration levels. The study starts first with all channels dissipating steady state power, followed by activating the entire dynamic system comprised of six channels dissipating power reaching over 17 W at different time intervals. The transient thermal behavior of each source is analyzed during the process, and indicates that the targeted design at 14 V exceeds the thermal budget (150C) after only 3 powering cycles. Based on the analysis of the complex temperature fields for the multiple dynamic source system, alternative power profiles are identified to improve the thermal performance of the overall wireless system, by splitting the power in selective channels. Several additional cases are further investigated, and the optimized power profiles indicate that they satisfy the thermal budget under various operating conditions and several multiple cycles, while still maintaining the device voltage at 14 V levels.
Date of Conference: 28-31 May 2008