SN74LVT244B: About tolerance of input voltage in datasheet

Negative voltages below −0.5 V are allowed as long as the current through the clamp diode is limited to less than 50 mA.

Positive voltages above 7 V are not allowed, for any practical length of time. For a different logic family, the AHC/AHCT Designer’s Guide (SCLA013) describes the consequences as follows:

Input voltages greater than 7 V must be avoided to preclude damage to the gate oxide of the input stage. This damage is not necessarily permanent, but will adversely affect the expected lifetime of the circuit. The gate oxide of AHC devices is only 200 Å thick. An input voltage of 7 V corresponds to a field strength over the gate oxide of 350 kV/cm. Although breakdown of the oxide is expected only at input voltages above 10 V, electrons tunnel increasingly into the gate oxide at field strengths greater than 350 kV/cm, influencing characteristics of the transistors and causing failure.