Tool/software:
Hi,
I think the product with the input tolerant function is an internal circuit that does not have a positive clamp diode as shown on the right side of the diagram below.
If it does not have a positive clamp diode, does it lose resistance to overvoltage and ESD? Or is there another circuit added to replace the protective diode?
Best Regards,
Nishie
Section 2.3.1 of the AHC/AHCT Designer's Guide says:
Figure 12 shows protective circuits used for advanced high-speed CMOS devices. To meet the requirements outlined previously, the protective circuit is constructed in two stages. The input is first protected by a thyristor consisting of transistors Q2 and Q3. This provides coarse protection. If the input voltage rises above about 15 V, transistor Q1 breaks down and fires the thyristor. The latter then short circuits the high currents. Resistors R1 and R2 have values of only a few ohms. Therefore, the holding current of the thyristor is several tens of mA. When the current is reduced again at the end of the discharge, the thyristor is extinguished. Transistors Q4, Q5, and Q6 operate as fine protection and are intended principally to protect the input from excessive voltages. When there are overvoltages at the input, these transistors are driven into breakdown and limit the voltage, while resistor R3 limits the current.
