Apple Inc.
In-system power usage measurement

Abstract:

Systems and methods are provided for performing an in-system measurement of power consumption without exclusive use of an in-line current-sense resistor. Indeed, these systems and methods may take advantage of existing parasitic resistances in an electronic device--such as resistances that might vary over time and under different operating conditions. To perform an in-system measurement, a digital value of a first voltage caused by an unknown amount of current flowing into a power-consuming component over an unknown resistance may be measured. Before or afterward, a current source may be activated to add or subtract a known amount of current to the unknown amount of current, resulting in a second voltage over the unknown resistance, and a digital value of the second voltage over the unknown resistance may be measured. The power consumption by the power-consuming component can then be calculated from these values.