Looking at the TLC2272 datasheet - it's noted the recommended operating condition is to VDD - 1.5V (so I can only expect an input of 3.5 at the output in voltage follower mode)?
I'm looking for it to have a high input impedance (no interference on circuit being monitored).
Stated more accurately, the d/s refers to that as the "Input voltage range", and yes, it will
only track voltages up to Vdd-1.5V. So, the outputs are "rail-to-rail" [or pretty close], but
the input range is only rail-to-(rail-1.5V). However, the TLV2371 is rail-to-rail on both inputs
and outputs, so that's what you want.
And Mark makes a good point. You will only get close to rail-to-rail output if the opAmp
output is not loaded down. CMOS opAmps have typical output impedances somewheres
around 100 ohms or so, so a 1K load would drag the output down by 10%.
CMOS opAmps are not the fastest in general, but with 3 Mhz gain-bandwidth product, the
TLV2371 is fast enough for most microcontroller apps. Especially as a follower amp with
unity-gain, the bandwidth BW = GBW/Gain = 3Mhz/1 = 3 Mhz.