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Honored Contributor
Honored ContributorCan Cyclone IV JTAG VCC use separate 2.5V instead of VCCA?
The Cyclone IV handbook in section 8-47 says: --- Quote Start --- For device using VCCIO of 2.5, 3.0, and 3.3 V, refer to Figure 8–23. All I/O inputs must maintain a maximum AC volt...
Altera_ForumHonored Contributor
Honored Contributor --- Quote Start --- However, as the current layout stands it is inconvenient to send the VCCA plane to the jtag connector. It is far more convenient to have a small local 2.5V linear regulator instead (I have a nice little spot for it). I understand that the reason for the 2.5V instead of VCCIO (which is 3.3V in this case) it to get farther away from the 4.1V overshoot (not sure why not just install the clamping diodes to VCCIO instead of using the VCCA PLL supply). --- Quote End --- I completely agree with your analysis. You MUST observe the FPGA maximum ratings. If you achieve it e.g. by JTAG clamp diodes, it's O.K. as well. Up to now, I'm using 3.3V JTAG for all Cyclone I to IV devices, with respective protection means.
