2013 Volume 8 Issue 2 Pages 239-253
Semiconductor scaling makes the individual part can no longer share the same supply voltage, and some chips even require multiple different supply voltage levels. Different input and output voltage standard specification of each device make use of multiple supply voltage levels. Various devices such as display, RF, USB, SD card, etc. increase the number of supply voltage levels. Moreover, analog devices often do not allow sharing power supply due to coupling noise. However, those components are commonly powered by a single power source such as a battery. Consequently, power converters such as on- and off-chip switching-mode DC-DC converters, low-dropout linear regulators and charge pumps are largely populated even on a single circuit board. Efficiency of the power converters is known to be high enough and often ignored during power management policy development. However, their actual conversion efficiency varies significantly according to device activity and power mode, which sometimes results in substantially lower efficiency than the value provided in datasheets. Moreover, hardware designers generally optimize the power converters for the maximum power supply current of the device and even perform over-design while the actual device power consumption during runtime could be largely offset from the energy-optimal operating point. This tutorial paper covers a wide range of topics on power converter-aware design and introduces several design practices; i) power converter basics and the conversion efficiency, ii) power converter voltage transition overhead, iii) power converter-aware design of embedded systems, and iv) maximum energy transfer of energy harvesting devices.