Digital Electronics: Principles, Devices and Applications

Logic Families 1795.11 Guidelines to Handling and Using CMOS DevicesThe following guidelines should be adhered to while using CMOS family devices:1. Proper handling of CMOS ICs before they are used and also after they have been mounted on the PCboards is very important as these ICs are highly prone to damage by electrostatic discharge. Althoughall CMOS ICs have inbuilt protection networks to guard them against electrostatic discharge,precautions should be taken to avoid such an eventuality. While handling unmounted chips, potentialdifferences should be avoided. It is good practice to cover the chips with a conductive foil. Oncethe chips have been mounted on the PC board, it is good practice again to put conductive clips orconductive tape on the PC board terminals. Remember that PC board is nothing but an extensionof the leads of the ICs mounted on it unless it is integrated with the overall system and propervoltages are present.2. All unused inputs must always be connected to either V SS or V DD depending upon the logic involved.A floating input can result in a faulty logic operation. In the case of high-current device typessuch as buffers, it can also lead to the maximum power dissipation of the chip being exceeded,thus causing device damage. A resistor (typically 220 k to 1 M should preferably be connectedbetween input and the V SS or V DD if there is a possibility of device terminals becoming temporarilyunconnected or open.3. The recommended operating supply voltage ranges are 3–12 V for A-series (3–15 V being themaximum rating) and 3–15 V for B-series and UB-series (3–18 V being the maximum). For CMOSIC application circuits that are operated in a linear mode over a portion of the voltage range, suchas RC or crystal oscillators, a minimum V DD of 4 V is recommended.4. Input signals should be maintained within the power supply voltage range V SS