Is it safe to use 1.22V for C3 Vccint?

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Although a C3 FPGA device doesn't draw more than 1A on Vccint after power-up, it is probably a good idea to design the Vccint rail up to 2-3A for in-rush current.

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There's no inrush current with C III devices. Since CII, VCCINT power-up current is guaranteed to be below the static idle current of the device. You can achieve VCCINT considerably above 1 A with designs that have very high system clocks and and a high register toogle rate. But this is unlikely to happen in typical designs.