1 - Al Kossow's Bitsavers

Applications BriefTMS4164A AND TMS4416INPUT DIODE PROTECTIONThe 64K DRAM family from Texas Instruments has departed from conventional input schemes for DRAMs toprovide the user with improved ESD protection and input clamping diodes for negative undershoot. Bothenhancements of device capability are possible due to the use by TI of a grounded epitaxial substrate in themanufacture of its 64K DRAMs. While the input circuit technique has provided the user with additional protectionand ease of use, it may cause anomalous testing results for the unwary test engineer who tires to drive theinputs to large negative voltages.Shown below is an equivalent circuit for the input circuitry of the TMS4164A and the TMS4416.FIGURE 1 -IIII- I..: __ JEQUIVALENT INPUT CIRCUITRYThe diode and transistor clamping circuit is the essential element in protecting the device from electrostaticdischarge (ESDI damage. Figure 2 shows the physical layout of this circuit.c:o'';:COE-o"l-.Eenc:o'';:;CO,~C.•Q.cd:9-7