MEMORY DATABOOK - Al Kossow's Bitsavers

_APPLICATIONS __ -------------________ _5. NOTES ON MOUNTING 1 MBMEMORY ON A BOARDThe advent of a 64K bit dynamic RAM such as theMSM3764 has made it extremely easy to mount 1 M8memory on a board from the viewpoint of mountingspace. In this case, however, note the following pointssince the number of memory elements mounted is solarge as 128 - 176 (when redundant bits are provided).Point to be noted Consideration Practical exampleMounting ofmemoryelementsMemory elements may be integrated ordivided.(Design the memory array(s) to makethe drive lines shortest.)81 I I I I I I II MemoryarrayEmEBrEmEMemory array Memory arrayMemory Take care about the delay time and Drive elementelementundershoot noise of the drive element.drivi ng method (If the condition VILmin =IS::-lV recom·Delaymended for the MOS dynamic RAMtimeoperation is satisfied, the memory elements Elementwill display the full reliability.)7404 Mediumspeed(mA)NoiseIOL16 074S04Highspeed20 XMeasuresagainst noiseo Two layers are enough for a board.(Pay attention to the power line pattern.)o High frequency noise Mount a 0.1 - 1 "F capacitor for every twomemory elements.o Low frequency noise Mount a tantalum capacitor etc. of 50 "For more near the power input pin of thememory package.Timing design o Prevent skew between each timing in order Use ICs of the same tipe for racing timingto enhance the system access speed.(for example, RAS or CAS).o Make a sufficient margin in timing design.Skew and mounting delayThermal design Thermal design under the worst condition Operation at a case temperature of 70°Cis required.must be guaranteed.m448