DP8418 datasheet(20/28 Pages) NSC

20 / 28 page

Switching Characteristics

All AC parameters are specified with the equivalent load

capacitances including traces of 88 DRAMs organized as 4

banks of 22 DRAMs each Maximums are based on worst-

case conditions including all outputs switching simulta-

neously This in many cases results in the AC values

shown in the DP84XX DRAM controller data sheet being

much looser than true worst case (maximum) AC delays

The system designer should estimate the DP8419 load in

hisher application and modify the appropriate AC parame-

ters using the graph in

Figure 10 Two example calculations

are provided below

TLF8396 – 22

FIGURE 10 Change in Propagation Delay

Relative to ‘‘True’’ (Application) Load Minus

AC Specified Data Sheet Load

2 Examples

1) A mode 4 user driving 2 16-bit banks of DRAM has the

following approximate ‘‘true’’ loading conditions

CAS

- 300 pF

Q0-Q8

- 250 pF

RAS

- 150 pF

max tRPDL e 20 ns b 0ns e 20 ns (since RAS load-

ing is the same as that which is spec’ed)

max tCPDL e 32 ns b 7ns e 25 ns

max tCCAS e 46 ns b 7ns e 39 ns

max tRCC e 41 ns b 6ns e 35 ns

min tRHA is not significantly effected since it does not

involve an output transition

Other parameters are adjusted in a similar manner

2) A mode 5 user driving one 16-bit bank of DRAM has

the following approximate ‘‘true’’ loading conditions

CAS - 120 pF

Q0-Q8 - 100 pF

RAS - 120 pF

A C parameters should be adjusted as follows

with RAHS e ‘‘1’’

max tRICL e 70 ns b 11 ns e 59 ns

max tRCDL e 55 ns a 1ns b 11 ns e 45 ns

(the a 1 ns is due to lighter RAS loading the b 11 ns

is due to lighter CAS loading)

min tRAH e 15 ns a 1ns e 16 ns

The additional 1 ns is due to the fact that the RAS line

is driving less (switching faster) than the load to which

the 15 ns spec applies The row address will remain

valid for about the same time irregardless of address

loading since it is considered to be not valid at the

beginning of its transition

TLF8396 – 23

FIGURE 11a Output Load Circuit

TLF8396 – 34

FIGURE 11b DP8417 TRI-STATE Waveforms

Absolute Maximum Ratings (Note 1)

If MilitaryAerospace specified devices are required

please contact the National Semiconductor Sales

OfficeDistributors for availability and specifications

Supply voltage VCC

70V

Storage Temperature Range

65 Cto a150 C

Input Voltage

55V

Output Current

150 mA

Lead Temp (Soldering 10 seconds)

300 C

Operating Conditions

Min

Max

Units

VCC

Supply Voltage

450

550

Ambient

Temperature

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