Guideline: Use Internal PCI Clamp Diode on the Pin
By default, if the assigned input, bidirectional, or tristated output pins use 3.3 V, 3.0 V, or 2.5 V LVTTL or LVCMOS I/O standards, the Intel® Quartus® Prime software enables the PCI clamp diode on the pin.
The PCI clamp diode can sufficiently clamp voltage overshoot to within the DC and AC input voltage specifications when the bank supply voltage (VCCIO) is 2.5 V or 3.0 V. You can clamp the voltage for a 3.3 V VCCIO to a level that exceeds the DC and AC input voltage specifications with ± 5% supply voltage tolerance. The clamped voltage is expressed as the sum of the supply voltage (VCCIO) and the diode forward voltage.
The PCI clamp diode in the supported Intel® devices can support a maximum of 10 mA DC current. The diode sinks the DC current when driven by a voltage level that exceeds the bank VCCIO plus the diode forward voltage. You must take the DC sink current into consideration when you interface a 2.5 V VCCIO receiver on the supported Intel® device with 3.0 V and 3.3 V LVTTL or LVCMOS I/O systems.
If you disable the diode in the Intel® Quartus® Prime software, ensure that the interface meets the DC and AC specifications.
If your system has the flexibility to accommodate a selection of driver strengths, you can also use the driver selection guideline to select the appropriate driver without using termination.
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