In many electronic systems, it is desirable to be able to measure the current drawn by one or more components or subsystems. Current drawn is related to the overall energy consumption of the system. If the current drawn by all devices of interest is accurately sensed, an accurate computation of energy being consumed by the system may be performed. If current measurements are not accurate, the accuracy of the overall energy calculation is reduced. Most motorized vehicles (for example, cars, buses and the like) include electronic systems that are subject to adverse conditions that may impact the accuracy of current measurements because of the location of the electronic systems in or on the vehicle. A significant factor that may affect current measurement accuracy is that automotive batteries are typically subject to wide swings in output voltage. Battery voltage swings result from many factors, including loading and state of battery charge. Another factor that is likely to affect measurement accuracy is a wide variation in temperature at the location where current is being measured. For example, an automotive engine compartment is subject to wide temperature variation depending on such factors as operating conditions and seasonal temperature change.
In addition, it may be desirable to provide short circuit protection for a load while the current flow to the load is measured. Another complicating factor is the desire to obtain an accurate current measurement in a manner that utilizes as little battery voltage as possible. In systems in which it is desirable to provide a digital value corresponding current drawn by a load, still another factor complicating current measurement is the desirability of protecting an analog-to-digital converter adapted to produce the digital value from being damaged by an over-voltage condition. For these reasons, it is a challenging problem to obtain accurate current draw measurements for devices and electronic systems that are powered by a battery in a motor vehicle.