Dynamic Voltage Support

Topaz HVIO I/O banks support dynamic voltage shifting. This feature lets you change the voltage to the I/O bank during user mode. There are two methods for changing the voltage:

  • If you are not using 1.8 V at all, you can simply change the voltage at any time. For example, you can change from 3.3 V to 2.5 V and then back to 3.3 V.
  • If you are changing the voltage to 1.8 V, you must enable an option in the Interface Designer (which creates a mode select pin <bank name>_MODE_SEL) and follow the timing requirements for the voltage change as described below. The value of the mode select pin chooses the voltage:
    • High—Changes the voltage to 1.8 V
    • Low—Changes the voltage back to 2.5, 3.0, or 3.3 V

To enable the option in the Interface Designer:

  1. Choose Device Setting > I/O Banks.
  2. Turn on Enable Dynamic Voltage.
  3. Save.
  4. Add the mode select pin (<bank>_MODE_SEL) to your RTL design.
  5. Recompile.
Note: Some HVIO I/O banks may not support the <bank name>_MODE_SEL pin. For example, if the I/O bank has dedicated I/O pins such as JTAG pins, then you cannot change the voltage.

When switching the voltage, pull down the voltage to 1.8 V for at least 1 ms before pulling the mode select signal high. Similarly, wait for at least 1 ms after releasing the mode select signal before changing the voltage back to the higher level.

Figure 1. VCCIO Switching Waveform (2.5, 3.0, or 3.3 V to 1.8 V )