The voltage supply minimum and maximum values in the PDN tool specified as ripple percentage are different when compared to the minimum and maximum voltage specifcation in the Altera® device Datasheet recommended operating conditions. Voltage supply ripple and Datasheet voltages for recommended operating conditions are reflected in different forms in the power delivery system.
The voltage specifications in the device Datasheet are considered DC values. The ripple of the voltage regulator module (VRM) is shown as the change in the power supply voltage level. Altera® devices are designed to operate within a specific voltage range which is considered the DC specification, which is in turn translated to the requirement for the voltage regulator module (VRM) ripple specification.
The ripple values in the PDN tool are for AC conditions. The ripple due to device switching activity is shown as noise added to the voltage from the power supply. Altera provides recommendations for allowable power rail noise, which is shown as the maximum power rail ripple in the PDN tool.
The two types of voltage specifications have different considerations and require different design methodologies (VRM model vs. decoupling). It is a general practice in power delivery system design to consider the two voltage specifications separately and to ensure the two specifications are met.
For example, if the VCCIO typical specification is 3.0V in the Datasheet, the VRM must be set to send out 3.0V, not 3.15V (where 3.15V is the maximum recommended voltage). The VRM is not ideal and the output voltage will fluctuate slowly. This fluctuation must be controlled within a range so normal device operation is not affected by the fluctuation. That range is the DC specification from the device Datasheet.
Device switching activity leads to transient noise (high frequency spikes) seen on the power supply rails. This noise can cause functionality issues if they are too high. The noise needs to be dampened within a range and the range is defined as a % of power supply voltage. This range is listed in PDN tool as a guideline. Different rails have different specifications because of their sensitivity to the transient voltage noise as well as how much current is used by the power rail. These factors affect how the power rails must be decoupled.
In summary, the Datasheet DC voltage minimum and maximum voltages need to be met by the power supply design. The PDN ripple guideline needs to be met with the power delivery network design which includes decoupling capacitors, plane capacitance, as well as package and on die capacitance if available for the device.