Do You Know Your Onboard Temperature Sensing IC?

It is a common practice in electronic packaging to deploy onboard temperature sensing ICs for thermal health monitoring and control. The IT equipment industry has seen exponential increase in power and power density growth on devices and PCBs. In turn, more and more IC temperature sensors are used in highly complex algorithms and are expected to be highly accurate in predicting the local thermal conditions. In many cases they are even used to correlate to air temperature. However, care must be taken in understanding the different factors that influence the temperature readings of these devices. Some of the factors that have direct impact on the quality of the temperature reading include parasitic heating due to adjacent components and placement location, airflow condition, circuit design in connecting these devices to the board, accuracy and tolerance of these devices. In addition, because of the increase in component power density, the temperature difference between the device temperature, for example junction temperature, and board sensor temperature can be very different and the range can vary a lot as well. In this paper, thermal numerical modeling, as well as empirical work at the system and board levels, was performed to understand the implications of the temperature readings from these devices. Several of the commercially available onboard temperature sensing ICs are compared as well. It is the intention of this work to point out these areas in order for thermal and system design practitioners to intelligently use these devices appropriately. Also, a high-level environmental monitoring and control system (EMCS) policy is illustrated for highly configurable multi-board equipment.