Altera Stratix IV GX Manual page 25

Chapter 1: Power Delivery Network (PDN) Tool User Guide for Stratix IV Devices
Design PCB Decoupling Using the PDN Tool
In Step 4, you must adjust the number and value of the PCB capacitors in the
Decoupling Capacitor (Mid/High Frequency) and Decoupling Capacitor (Bulk)
fields to keep the plotted Z
capacitor combination that meets your design goal, you can try to change the
parameters at Step 2; for example, reducing the BGA via inductance used in the
Calculate option by reducing the BGA via length in the BGA_VIA tab and using the
low option for plane spreading. These changes reduce parasitic inductance and make
it easier to achieve your decoupling goal. To achieve the low spreading setting, you
must place the mid to high frequency PCB capacitors close to the FPGA device. You
also must minimize the dielectric thickness between the power and ground plane.
If you are not able to meet the Z
your design may have reached its physical limitation under the parameters entered in
Step 3. You need to go back to Step 3 and re-examine these parameters to check if they
are over pessimistic.
The design shown in
power rail. Assume that the minimum voltage supply is 0.9 V, I
current is 50% of I
V
CC
The PDN tool calculated that Z
Figure 1–16
design goal.
Z
EFF
solution is to minimize the quantity and the type of capacitors needed to achieve a flat
impedance profile below the Z
Figure 1–16. Enlarged Plot of Zeff Using the Figure 1-16 Design
© March 2009 Altera Corporation
EFF
Figure 1–16
, and the maximum allowable ripple is 3% of supply voltage. The
MAX
rail has 50 power BGA vias. The length of BGA via is assumed to be 60 mil.
shows one of the capacitor combinations that you can select to meet the
Figure 1–16 is the enlarged view of the Z
remains under Z up to F
TARGET
below Z until F
TARGET EFFECTIVE
requirement with the above changes, the PDN in
TARGET
is a decoupling example for S4GX230KF40 VCC
is 0.0077 Ω and F
TARGET
EFF
. There are many combinations, but the ideal
EFFECTIVE
.
TARGET
Power Delivery Network (PDN) Tool for Stratix IV Devices User Guide
. If you are not able to find a
is 7 A, transient
MAX
is 24.91 MHz.
EFFECTIVE
plot. As shown in the plot,
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