In what sequence should I turn on and off the power and input signals of a general purpose logic IC?

In general, power and input should be applied in the following order to satisfy the absolute maximum ratings.

Fig. 1 Input/Output Equivalent Circuit of TC74HC/HCT
Fig. 1 Input/Output Equivalent Circuit of TC74HC/HCT

If the power supply and input signals of the general-purpose logic IC are in the wrong order, it may cause malfunction, destruction, or damage to the IC or equipment, so be careful.

(1)Connect GND
(2)Connect VCC (on)
(3)Connecting Input Signals (Turning On)

Turn off the power supply in the reverse order of turning on the power supply.

ICs without an input tolerant function (such as the TC74HC/HCT series) have a protection diode on the input side as shown in Fig. 1. If the order is incorrect, an unnecessary current will flow through this diode to the input and output, damaging the IC and equipment.

Products with an input tolerant function such as TC74VHC/VHCT, TC74LCX, TC74VCX (no input protective diode for forward direction from input to power supply) can apply an input signal even when power is not applied. Therefore, the loading sequence of (2) and (3) is not required.

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