How should I turn on/off the power and inputs?
The following figure shows the input/output equivalent circuit of the TC74HC/HCT series.
[Figure: input/output equivalent circuit of TC74HC/HCT]
In general, to meet the absolute maximum ratings, turn on the power and input in the following order: (1) connect GND，(2) connect VCC，(3) connect input signals. To turn off, do it in the reverse order of power-on.
Products that have the input tolerant function (products that do not have an input diode in the direction from the input to the power source) such as TC74VHC/VHCT，TC74LCX，and TC74VCX can apply input signals when no power is supplied. Therefore，(2) and (3) are not required. However, the input diode current (IIK) of absolute maximum ratings cannot be exceeded.