Influence of temperature control limits on passively cooled computing system performance
Passively-cooled electronic systems such as tablet computers and cell phones commonly are thermally limited by the allowable touch temperature of their surfaces. These systems typically cannot cool maximum processor power in steady state and simultaneously meet surface temperature restrictions. The primary surface temperature control method for thin mobile devices is to limit power, typically resulting in lower computing performance. Improved thermal designs allow higher power dissipation and therefore increased computing performance. Thermal and mechanical design engineers typically operate in terms of temperature for a given power, and this is not usually translated to computing performance. It can be difficult to justify a better thermal design if it is not quantified in its utility to the user. This paper quantifies the tradeoffs between thermal solution performance/temperature control limits and computing performance for two tablet computers and one cell phone that all use the same type of SoC processor.
A study of the maximum theoretical power dissipation of tablets under natural convection conditions
This study determines the limits of natural convection cooling for ideal handheld devices of various sizes based on simulations. Four popular tables were tested to determine the surface temperature rise under heavy computational and graphics loads. The thermal performance of each tablet based on hot spot temperature is measured against the performance of an ideal tablet of the same size and a figure of merit for the efficiency of heat dissipation is calculated to see how well they perform against the ideal tablet. The factors affecting the maximum possible power dissipation are the available surface area and surface finishes, selection of the outer shell materials, thermal interface materials, heat spreaders and air gaps. In most cases, the limiting factor in the thermal design of these devices is not the temperatures of the internal components but the temperature of the external surfaces since these are in direct contact with the skin of the user. This study presents a method for analyzing the efficiency of the thermal design of these devices.
Future direction of power management in mobile devices
Mobile devices such as smartphones have two major restrictions from the standpoint of design: thermal dissipation and the supply of battery power. Thermal dissipation restricts power consumption of AP (Application Processor), which additionally limits computational performance. Battery usage time is also determined by power consumption of the mobile device. Due to these reasons, power management to improve efficiency of electric power usage becomes a very crucial part of mobile product design. In this paper, we look into power management from two different hierarchical aspects: power management techniques at the processor design level and PMIC (Power Management IC) at the power analog circuit level. Particularly, PMIC in the smartphone is expanding its role to a multi-function solution chip from the traditional function of power conversion and distribution. Future direction of PMIC and engineering challenges will be also discussed.