The power consumption of an FPGA depends on a number of different factors and is highly dependent on the design. Accurate power estimation methods must be used to ensure that the power supply system meets the FPGA requirements. Manufacturers of FPGAs provide web tools for power calculation. These calculators consider design resource usage, toggle rates, operating clock frequencies, I/O usage and many other factors to generate the FPGA power estimation. The FPGA has three major configurable elements: configurable logic blocks (CLBs), I/O blocks (IOBs), and interconnects. The CLBs provide the functional logic elements while the IOBs provide the interface between the package pins and internal signal lines with the programmable interconnect resources providing routing paths to connect the inputs and outputs of the CLBs and IOBs onto the appropriate networks. The voltages applied to the FPGA are designated as VCCINT for the CLBs (or core) and VCCO for the voltage supplied to the IOBs. Some FPGAs have an additional voltage input designated as VCCAUX.