Altera Power Delivery Network - Manual (Page 21)

Chapter 1: Power Delivery Network (PDN) Tool User Guide 1–17
Setting Up the PDN Tool
© March 2009 Altera Corporation Power Delivery Network (PDN) Tool User Guide
Spreading Parasitics
Based on the design, you can select either a Low, Medium, High, or Custom value for
the effective spreading R, L values that the decoupling capacitors see with respect to
the FPGA. You can ignore the spreading inductance. Ignoring the spreading
inductance leads to an optimistic result and is not an accurate representation of the
impedance profile that the FPGA encounters.
The Ignore option helps you understand that the spreading inductance in
combination with the BGA via inductance is the limiting factor from a PCB
perspective to decouple the FPGA at high frequencies. Be careful when choosing the
Ignore
option while estimating a final capacitor count.
BGA Via
Based on the design, you can either Ignore the BGA via component or Calculate the
effective via inductance based on the layout. If you are in the middle of layout, you
can directly enter the effective loop R, L via parasitics in the Library tab and choose
the Custom setting under BGA Via to include the via parasitics.
Plane Capacitance
Based on the design, you can either Ignore the interplanar capacitance between the
power and ground plane, or Calculate the plane capacitance based on the layout. If
you are in the middle of layout, you can directly enter the plane capacitance in the
Library
tab and choose the Custom setting under Plane Cap to include the plane
capacitance parasitics.
The next section in the Decap Selection tab deals with target impedance calculation
that was described earlier in the user guide.
The final section in the Decap Selection tab provides the ability to select the various
high/mid frequency decoupling capacitors based on footprint, layer, and orientation
to meet the target impedance you can choose X2Y type of capacitors in the Footprint
column besides two-terminal capacitors. The capacitance value for the X2Y capacitor
may be different from that of the two-terminal capacitor. A warning message of
"Wrong Footprint" is displayed if you choose a wrong combination of capacitance and
footprint. You can define custom capacitor values (such as User1, ..., User4) needed
for high/mid frequency decoupling specific to the design. However, you cannot
change the capacitor parasitics (ESR and ESL) in this tab. This can only be done in the
Library
tab.
You can change the parasitics of the bulk decoupling capacitors in the Library tab and
define the mounting inductance specific to the design. You also can define custom
capacitor values (such as User5, User6) for low/mid frequency decoupling specific to
the design.
As provided in other tabs, you can save and restore the final capacitor count and other
settings for a specific set of assumptions. You can also revert back to default settings.