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Altera_Forum
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14 years ago

Can VREF be other than VCCIO/2?

Must VREF be equal to 1/2*VCCIO, or can it be, say, 2/3*VCCIO? BTW, I'm using a Cyclone III M164 package. (very small physical board constraints) I'm trying to interface to a chip that has...
Altera_Forum's avatar
Altera_Forum
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14 years ago

What about memory VREF? I am having issues using DDR memory. I've connected fpga memory banks to 2.5V power supply and their VREF pins to 1.25V using two 1K resistors as divider (yes, my bad, I've saved money and didn't place special DDR memory power supply driver). Now when I power up my board, the 2.5V is OK, but I see 2.0V on VREF pin instead of 1.25V. Maybe I don't need to power VREF pin at all?

P.S. This happens when FPGA is not configured, I didn't test it configured to use memory.

P.P.S. all other banks where memory is not connected use 3.3V. Core voltage is OK.