LP2994M National Semiconductor, LP2994M Datasheet - Page 12

• Manufacturer Part Number: LP2994M
• Description: DDR Termination Regulator
• Manufacturer: National Semiconductor

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Typical Application Circuits
how to use two resistors to level shift V
reference voltage of V
at V
Conversely, the R2 resistor can be placed between V
and V
reference voltage of V
the resistors can be seen below:
Reference Voltage
DDR-SDRAM and the motherboard chipsets usually require
a reference voltage which tracks V
feature in most applications it is advisable to use two equal
resistors as a resistor divider. This prevents long V
from running across the motherboard picking up noise which
can interfere with performance. However, in a few applica-
tions it may be desirable to use the V
(Continued)
TT
DDQ
the following equation can be used.
to shift the V
DDQ
DDQ
TT
/2. The equations relating V
/2. To calculate the exact voltage
output lower than the internal
TT
TT
FIGURE 10. Decreasing V
. To implement this
FIGURE 9. Increasing V
above the internal
TT
output on the
REF
TT
traces
SENSE
and
12
TT
TT
V
LP2994 to generate the V
plished by using an RC filter on the output of V
V
chipsets and memory is well under 1µA combined, therefore,
a fairly large resistor such as 1k
recommended capacitor would be a 1uF X7R ceramic
capacitor.
by Level Shifting
TT
REF
by Level Shifting
= (V
signal. Typically, the reference voltage required by
DDQ
/2) x ( 1 - R1/R2)
V
TT
= (V
20045910
20045909
DDQ
/2) x ( 1 + R1/R2)
REF
signal. The can be accom-
or larger can be used. A
TT
to create a