Part Number: SN74AHC00
Hello Team,
Customer recently observed a potential abnormal behavior when using the ON Semiconductor CMOS NAND gate MC74HC00ADR2G in their UPS system. The issue appears when the input driving capability is relatively weak.
In the test setup shown in Figure 1, when the resistor R1 is increased to 3 kOhm, the input impedance of the NAND gate seems to change unexpectedly. As a result, the voltage at node VA drops abnormally to approximately 2.8 V, even though the 5 V supply rail remains stable with no observable voltage drop.
From the measurement waveform Figure 2, it appears that the NAND gate input may be drawing more current than expected when the driving source impedance becomes higher. This behavior suggests a possible abnormal input impedance characteristic under low input drive current conditions.
