Altera Power Delivery Network User Manual
Page 10
1–6
Chapter 1: Power Delivery Network (PDN) Tool User Guide
Setting Up the PDN Tool
Power Delivery Network (PDN) Tool User Guide
© March 2009
Altera Corporation
The upper limit of the frequency target for a given supply can be determined from the
plot where the series combination of the plane spreading inductance and the BGA via
inductance (Z
SPREAD
+ Z
VIA
) profile crosses the Z
TARGET
profile.
shows the
upper limit of frequency target calculation.
Decoupling using PCB capacitors becomes ineffective at high frequency. There is a
cut-off frequency that you must decouple the power supply up to. This frequency
ranges from tens of MHz to higher depending on the parameters, such as parasitic
inductance, OPD capacitors, and ODC, of selected power rail. Altera has new
family-specific PDN tools released that provide a suggested cut-off frequency,
F
EFFECTIVE
, as the guide line for PCB decoupling.
f
For information regarding the availability of the PDN tool that targets your device,
refer to the Altera website at
.
You must determine the proper F
TARGET
in case the information regarding the PCB
decoupling cut-off frequency is not available. You must decouple the power supply
up to this frequency and expect the package and die parasitics to take over the
decoupling for higher frequencies. For most supplies, this frequency is around
80 MHz for any power supply with reasonable Z
TARGET
. Expect this frequency to be
even lower, in the range of 50 MHz for the core power supply. Expect the device to
take over at a frequency lower than the maximum frequency target that can be
achieved on an optimally designed board (specifically for the Stratix
®
II GX, Stratix III,
and Stratix IV device families).
After all this information is available, Z
TARGET
can be calculated as:
Figure 1–5. Frequency Target Calculation
Equation 1–1.
Z
TARGET
VoltageRail
%Ripple
100
----------------------
•
MaxTransientCurrent
----------------------------------------------------------
=