Hello!
Is it safe to configure a FPGA with 1.8 VCCIO standard set (i.e. LVCMOS18) and supply the VCCIO pads by 3V3? I am going to switch a power supply from 3V3 to1V8 several seconds after the configuration. Vref pads are not used.
Best regards, krzysiek
krzysiek,
Since the IO driver is selected by choosing the number of transistors to drive in parallel (drive strength) a driver configured for 1.8V LVCMOS will be much stronger when operated at 3.3V.
I believe you will have to choose you IO standard carefully so as to not have too many signal integrity problems.
If you download the encrypted hspice models, and can simulate, you could actually see just how much stronger the 1.8V driver is when operated at
3.3V.Conversely, you could choose a 3.3V driver that you want for later operation, and then see just how weak it gets when operating from 1.8 volts. I believe this is a better choice.
Aust> Hello!
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