Filter
Top Products
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 todrive 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 dependson DRAM load SeeAN-305
‘‘Precautions to TakeWhen Driving Memories’’
TLF5012–5
FIGURE 5The DP84244 Usedas a Bufferin a LargeMemory Array (greaterthan 88 DRAMs)Controlled bythe DP8409A
TLF5012–6
FIGURE 6at
PLH
Measured to27V on Outputvs C
L
TLF5012–7
FIGURE 6bt
PHL
Measured to08V on Outputvs C
L
5