cyclone 3 fpga current rating

I wonder, how webbench power architect can answer the question of your design's core current consumption? It can't know about. The device manual tells:

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Altera offers two ways to estimate power for a design: the Excel-based Early Power Estimator and the Quartus II PowerPlay Power Analyzer feature.

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Except for a small idle current, the core current is only dependant on logic activity: number of switching logic cells times core frequency. Most designs have a moderate core current consumption, because only a small number of logic cells is permanently switching.