There are several details that can easily be overlooked when designing with digital power monitors and overlooking these details can lead to errors and possibly late design changes. This document provides a structured design method that incorporates the key design specifications to be observed. In conjunction with this paper is a design tool that is built upon the method discussed in this paper. The method described in this paper follows the progression illustrated in the Figure 1-1.

The first and most crucial step for designing with a digital power monitor is to define your system constraints for the device. These include the common mode voltage expected at the sense pins, the supply voltage you would like to use, the maximum current you want to measure, and the minimum current you want to measure. Common mode voltage and supply voltage are two specifications that can easily be extracted from the data sheet and used to narrow down your options. These specifications must be adhered to insure the device operates correctly and is not damaged. As for the current range the device can measure, the data sheet does not provide any bounds that can be simply looked up. The bounds are not only dependent on device specifications, but on design goals that include shunt power dissipation and resolution. The ensuing steps will provide details on how to assess a given device's current measurement bounds and determine if it will be adequate for your needs.

The shunt value ultimately determines the current measurement bounds. For a given current range, there may be a range of shunt resistance values that can be used allowing flexibility in your design. The maximum and minimum shunt values need to be calculated, to ensure you choose a shunt that will work for your application. To calculate the max shunt value, you need to look up the shunt voltage input range max listed in the electrical characteristics section of the data sheet. Some devices may have a fixed shunt voltage range as found in the Table 3-1, while others may have ranges that change according to certain register settings such as can be seen in the Table 3-2. One thing to note, is that some devices may have a different name for the shunt voltage input specification. Table 3-3 lists this specification as V_DIFF.

To find the R_{SHUNT MAX} divide the max shunt input voltage value by your max expected current value.