Thermal design of the TW-150 passive optical network access unit. I

This paper discusses the thermal analysis that was conducted on the TW-150 unit. The TW-150 unit is a thermally hardened product designed to operate under harsh ambient conditions ranging from -40 to 75°C and altitudes of up to 13,000 ft above sea level. The unit is designed so that the case and junction temperatures of any component should not exceed 85 and 90°C, respectively. Further, the case temperature of the optical module is to be limited to 76°C under all operating conditions. Extensive thermal analysis was conducted so that the box operates reliably under these conditions with an acceptable mean time between failure. We present a brief description of the unit and the results obtained from preliminary thermal analysis. This will be followed by discussion on mesh refinement issues and the effect of baffles inside the box. We then discuss optimization of baffles, modeling of individual chips,and selection and optimization of heat sinks.