Altera Device-Specific Power Delivery Network User Manual
Page 27
Chapter 1: User Guide for the Device-Specific Power Delivery Network (PDN) Tool
1–23
Design PCB Decoupling Using the PDN Tool
September 2012
Altera Corporation
Device-Specific Power Delivery Network (PDN) Tool User Guide
Step 2: Determine the Device/Power Rail to Work With
Choose the power rail with the highest F
EFFECTIVE
as the rail to work with in this
power-sharing scenario. F
EFFECTIVE
is power-rail related and can be different for power
rails that connect to the same PCB power supply. You must review all power rails that
share the PCB power rail and find the one with the highest F
EFFECTIVE
.
Step 3: Select the Parameter Setting for PDN Components
In this power-sharing scenario, considerations for selecting the PDN parameter
settings for BGA via, VRM, plane spreading, and plane capacitance are the same as
the single-rail scenario (refer to
“Derive Decoupling in a Single-Rail Scenario” on
). You must ensure the number and length of the BGA power via pairs
entered in BGA Via tab correspond to the power rail selected in Step 2.
Step 4: Derive the PCB Decoupling Scheme
The considerations and procedure for deriving the desired PCB decoupling scheme
are the same as those in Step 4 of the single-rail scenario (refer to
in a Single-Rail Scenario” on page 1–19
In this PCB power plane sharing design example, three I/O banks, V
CCIO
7A/7B/7C
of a S4GX230KF40 device are used in a DDR2 interface. They share the PCB power
plane. The power supply voltage is 1.8 V. The maximum allowable voltage ripple is
3%. The total current draw from the three banks adds up to 0.7 A. The percentage of
transient current is set at 50% for all three rails. Z
TARGET
is calculated to be 0.154
with these parameters.
After examining the F
EFFECTIVE
of three power rails. V
CCIO
7A is identified as the
power rail with the highest F
EFFECTIVE
. VCCIO 7A has four power via. The length of
BGA via is assumed to be 25 mil. The PDN tool calculates that the F
EFFECTIVE
is
approximately 70 MHz.