Multiple Outputs from a General-Purpose CMOS Logic IC Come Into Conflict (Short-Circuiting)

Unlike diodes, the outputs of typical CMOS logic ICs cannot be wired-ORed together, except those with three-state outputs. Even in the case of CMOS logic ICs with three-state outputs, unintended current might flow, causing IC degradation, if they are enabled simultaneously. When creating a circuit design, ensure that multiple outputs will not be enabled at any given time. Also, the outputs of CMOS logic ICs without bushold become unstable if all of them are disabled (i.e., assume the High-Z state) without being pulled up to VCC or down to GND.

Only the gates in the same package may be wired-ANDed to increase the drive capability (i.e., output current). However, it is recommended to use high-drive ICs (with an IO of ±24 mA) instead.

Do not use multiple wired-OR gates.
Do not use multiple wired-OR gates.
Example of a parallel connection to increase drive capability (Only gates in the same package may be paralleled.)
Example of a parallel connection to increase drive capability (Only gates in the same package may be paralleled.)
Conflict of three-state outputs
Conflict of three-state outputs

CMOS邏輯IC的使用注意事項

Handling of Unused Input Pins
Input Rise and Fall Time Specifications
Connecting a Load Capacitance to a CMOS Output Pin
Calculating the Operating Supply Current and Power Dissipation
Level Shifting Using an Input-Tolerant Function
Example of Application of the Power-Down Protection Function (Partial Power-Down)
Input-Tolerant and Output Power-Down Protection Functions Available with Each Series
Types of Noise to be Noted
Countermeasures for Reducing Switching Noise
Countermeasures for Signal Reflection
Countermeasures for Crosstalk
Countermeasures for Hazards
Countermeasures for Metastability
Countermeasures for Latch-Up
Countermeasures for ESD Protection

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