This slide discusses conversion efficiency. In the equation PIN equals the power delivered to the system from the input, PLOSS is the power dissipated in the regulator (and external components) during the conversion, and PO is the output power which is the easiest to calculate because the Vout and Iout are constant in a Vreg. Efficiency is defined as the ratio between the output and input power. Substituting the input power with the sum of output power and the power lost in the conversion the equation can be solved for the power loss. This is useful in the thermal design. A higher efficiency means lower power losses and as a result easier thermal design, smaller package, and longer battery life. Thermal resistance is the ability of the package to dissipate the heat generated inside the device: the lower the Rth, the better the ability to dissipate power. Be careful that if there is a diode (as in non-synchronous conversion) part of the power is dissipated there, so the Ploss inside the regulator is different from the Ploss calculated in the previous formula. ST’s on-line simulation tool is able to provide the breakdown of the power lost in the various circuit elements.