Altera Device-Specific Power Delivery Network - Manual (Page 22)

design. You can choose a Low value of effective spreading inductance if you have optimally designed your
PDN Network. Optimum PDN design involves implementing the following design rules:
• PCB stackup that provides a wide solid power/ground sandwich for a given supply with a thin
dielectric between the planes. This minimizes the current loop, which reduces the spreading
inductance. The thickness of the dielectric material between the power/ground pair directly influences
the amount of spreading/loop inductance that a decoupling cap can see with respect to the FPGA.
• Placing the capacitors closer to the FPGA from an electrical standpoint.
• Minimizing via perforations in the power/ground sandwich in the current path from the decoupling
caps to the FPGA device.
Due to layout and design constraints, the PDN design may not be optimal. In this case, you can choose
either a Medium or High value of spreading R and L. You can also change the default values or use the
Custom field listed in the library specific to the design.
Dielectric Material Library
This library lists the dielectric constant values for the various commonly used dielectric materials. These
values are used in the plane capacitance calculations listed under the Plane_Cap tab. You can change the
values listed in this section.
If you change the default values listed in the various sections in the Library tab, you can save the changes
by clicking Save Custom. You can restore the default library by clicking Restore Default located at the
top right-hand corner of the Library page. You can also restore the saved custom library by clicking
Restore Custom.
User Set F
EFFECTIVE
You must decouple to a F
EFFECTIVE
higher than what is calculated for the power rails of some Altera
device families. In this case, you must set the F
EFFECTIVE
option to Override in the System_Decap tab.
The PDN tool 2.0 then uses the F
EFFECTIVE
value entered here.
Enlarged_Graph
In the Enlarged_Graph tab, you can view the enlarged Z-profile plot. The PDN tool 2.0 switches to this
tab when you click on the Z-profile plot in the System_Decap tab. You can go back to the System_Decap
tab when you click the Return button.
22 Dielectric Material Library
UG-01157
2015.03.06
Altera Corporation Device-Specific Power Delivery Network (PDN) Tool 2.0 User Guide
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