use lt6237 as a Voltage follower，fail to track when voltage under 1.2V

The common mode voltage range (Vcm on page 3 of the data sheet) has a

minimum of 1.5V and a maximum of 4V (for Vsupply = 5V), which is in

keeping with your simulation result.

Thanks,  in my PCB, the threshold is 1.44V. Could you recommend me another IC without any change in PCB,  can work from 1V to 3V in 5V supply.

Which package option are you using?

Assuming you're using the S6 or MS8 package:

https://www.analog.com/media/en/technical-documentation/data-sheets/18067fc.pdf

Has rail-to-rail inputs and outputs, a higher gain/bandwidth product,

and is targeted to "low-noise, low-distortion" applications. Some

of the specifications are inferior to the LT6237, but in an absolute

sense are still quite good. The pinouts for S6/MS8 are compatible,

from a quick check (check yourself just to be sure).

Thanks for your help again. I need to replace it with LT1807IMS8#PBF for MS8.

in lt6237`s datasheet, recommend it rail to rail output, in lt1807`s datasheet, recommend it rail to rail input and output. however, in features of both datasheets,  introduce them output swing rail to rail. could you show me the difference?

There are ways of designing op-amps that have rail-to-rail inputs,

and there are ways of designing op-amps that have rail-to-rail outputs,

and these are separate features -- designers can choose to do one,

or both, or neither of these features.  I annotated the simplified

schematics for the two op-amps below, showing the different choices

that were made.

There are ways of designing op-amps that have rail-to-rail inputs,

and there are ways of designing op-amps that have rail-to-rail outputs,

and these are separate features -- designers can choose to do one,

or both, or neither of these features.  I annotated the simplified

schematics for the two op-amps below, showing the different choices

that were made.