Two new devices are now available for this application. The
DP84240
is
pin
and
function
compatible
with
the
DM74S240. The DP84244 is likewise compatible with the
DM74S244. However, this is where the similarity between
the devices ends. Both the DP84240 and the DP84244
have been designed specifically to drive DRAM arrays.
Fig-
ure 5 shows a typical application of the DP84244, used in
conjunction with the DP8409A, to drive a very large memory
array.
Figures 6a, 6b show some typical performance curves for
these circuits. Note that, at over 500 pF, the propagation
delay through these drivers is on the order of 15 ns. This
delay includes propagation delay and rise or fall time. Even
with this high speed, chip power dissipation is still main-
tained at a reasonable level as demonstrated by the graphs
shown in
Figures 7a, 7b of power versus frequency.
The DP84240 and the DP84244 are fabricated on a high
performance oxide-isolated Schottky bipolar process. Spe-
cial circuit techiques have been used to minimize internal
delays and skews. Additionally, both rise and fall time char-
acteristics track closely as a function of load capacitance.
This has been accomplished through impedance matching
of the upper and lower output stages. The result of these
characteristics is a substantial reduction of skew in both the
address and control lines to the DRAM array.
*
Resistor required depends on DRAM load. See AN-305
‘‘Precautions to Take When Driving Memories.’’
TL/F/5012 – 5
FIGURE 5. The DP84244 Used as a Buffer in a Large Memory Array (greater than 88 DRAMs) Controlled by the DP8409A
TL/F/5012 – 6
FIGURE 6a. t
PLH
Measured to 2.7V on Output vs. C
L
TL/F/5012 – 7
FIGURE 6b. t
PHL
Measured to 0.8V on Output vs. C
L
5
Summary of Contents for DP8400
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