Honored Contributor
Honored ContributorStratix® III Device Family Pin Connection Guidelines PCG-01004-1.2
http://www.altera.com/literature/dp/stx3/pcg-01004.pdf Pin Name VCCA_PLL[L[1:4],R[1:4],T[1:2],B[1:2]] Pin Description Analog power for PLLs[L[1:4],R[1:4],T[1:2],B[1:2]]. You must connect these pins to 2.5 V, even if the PLL is not used. Altera recommends that you keep these pins isolated from other VCC for better jitter performance. Connection Guidelines Connect these pins to 2.5 V, even if the PLL is not used. Use an isolated linear supply. Power on the PLLs operating at the same frequency should be decoupled. Decoupling depends on the design decoupling requirements of the specific board. See Note 2.
