LP2996LQ National Semiconductor, LP2996LQ Datasheet - Page 15

• Manufacturer Part Number: LP2996LQ
• Description: DDR Termination Regulator
• Manufacturer: National Semiconductor

Typical Application Circuits
HSTL APPLICATIONS
The LP2996 can be easily adapted for HSTL applications by
connecting V
V
resistors. AVIN and PVIN should be connected to a 2.5V rail
for optimal performance.
QDR APPLICATIONS
Quad data rate (QDR) applications utilize multiple channels
for improved memory performance. However, this increase
in bus lines has the effect of increasing the current levels
required for termination. The recommended approach in
terminating multiple channels is to use a dedicated LP2996
for each channel. This simplifies layout and reduces the
internal power dissipation for each regulator. Separate V
signals can be used for each DIMM bank from the corre-
sponding regulator with the chipset reference provided by a
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
plane it is advisable to use multiple bulk capacitors and
REF
voltage of approximately 0.75V for the termination
DDQ
to the 1.5V rail. This will produce a V
TT
is distributed across a long
FIGURE 13. Typical SSTL-2 Application Circuit
FIGURE 12. HSTL Application
(Continued)
TT
and
REF
15
local resistor divider or one of the LP2996 signals. Because
V
variations are minor, there should be little difference between
the reference signals of each LP2996.
OUTPUT CAPACITOR SELECTION
For applications utilizing the LP2996 to terminate SSTL-2 I/O
signals the typical application circuit shown in Figure 11 can
be implemented.
addition to high frequency decoupling. Figure 12 shown
below depicts an example circuit where 2 bulk output capaci-
tors could be situated at both ends of the V
optimal placement. Large aluminum electrolytic capacitors
are used for their low ESR and low cost.
REF
and V
TT
are expected to track and the part to part
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TT
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plane for