Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

Cyclone III 3.3V LVTTL output only at 2.5V

Hey all,

I'm using the Cyclone III (EP3C120F780C7) DSP development kit and would like to use 3.3V LVTTL outputs on the right HSMC header using the provided breakout board. The I/Os I'm using are connected to I/O bank 5 and 6. So far everything is working as expected, but instead of 3.3V I only get 2.5V on the HSMC breakout board outputs.

The schematic doesn't show anything that would limit the voltage and according to the datasheet the I/O banks are capable of 3.3V as well. Clamping diodes, which are required for 3.3V operation should be automatically enabled by Quartus II when I choose the 3.3V LVTTL option in Pin Planner. So, frankly I don't really know what else to do. Again, all other settings work, but not the 3.3V.

Did anyone else have a similar issue (output voltage less than what the user specified)?

Thanks!

1 Reply

  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    13 years ago

    If the supply voltage, or VCC, to those banks is 2.5V then that is what you are going to get on the output. Even if you change it in Quartus.

    I have the Cyclone III development kit and I believe banks 5 and 6 are at 2.5V. You can check the schematic for yourself.