SN74AVC1T45: Input Impedance

Hi Brad,
It's not explicitly stated in the datasheet, but you can use the datasheet specs to calculate a worst-case input impedance:

The input leakage current is listed as 5uA (max) for the A and B ports, and the max voltage they were tested at is 3.6V.

R_in = V_in/I_in = 3.6V / 5uA = 720 kohm

I would expect the input impedance to typically be higher than that, but that's a good minimum value to work with for system design. I usually just use 1 Mohm since that's pretty close to most CMOS inputs.