LP2994 Datasheet, PDF (13/15 Pages) National Semiconductor (TI) – DDR Termination Regulator

Typical Application Circuits (Continued)
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FIGURE 11. Creating a Reference Voltage for Memory and Chipsets
Output Capacitor Selection
For applications utilizing the LP2994 to terminate SSTL-2 I/O
signals the typical application circuit shown in Figure 12 can
be implemented.
FIGURE 12. Typical SSTL-2 Application Circuit
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This circuit permits termination in a minimum amount of
board space and component count. Capacitor selection can
be varied depending on the number of lines terminated and
the maximum load transient. However, with motherboards
and other applications where V_TT is distributed across a long
plane it is advisable to use multiple bulk capacitors and
addition to high frequency decoupling. Figure 13 shown
below depicts an example circuit where 2 bulk output capaci-
tors could be situated at both ends of the V_TT plane for
optimal placement. Large aluminum electrolytic capacitors
are used for their low ESR and low cost.
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FIGURE 13. Typical SSTL-2 Application Circuit for Motherboards
In most PC applications an extensive amount of decoupling
is required because of the long interconnects encountered
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