This design does not reflect the device's typical use and does not take into consideration the current necessary to drive loads off-chip, which is a large percentage of the total supply current. Using device-usage data that compiler output files provide, as well as estimated toggle rates that the designer provides, these equations can provide realistic power estimates. When dealing with large devices and complex designs, however, these equations involve a tedious manual process that often requires you to create complex spreadsheets or other software programs. The software tools now available incorporate the necessary equations and allow you to easily make important power-consumption estimates. The results help you to answer important questions early in the design process concerning how to reduce power or improve heat dissipation with thermally enhanced packages, heat sinks, or fans.
Models differ slightly among architectures but typically resemble the following example.
In nonvolatile PLDs, the product-term sense amplifiers usually draw most of this current. This current increases as the number of product terms increases. Additional contributors to standby current include current that internal pullup or pulldown resistors draw and leakage current of the device transistors. Internal ac current refers to the internally consumed current, which is proportional to the clock frequency. The more clocks that a design uses, the more current necessary to drive the clock tree.