I am using the LTM4668 in a multi-channel parallel configuration. From the picture below, channel 1 and 2 are tied together and are programmed to output 1V. The regulator is outputting 0.95V, but PGOOD won't go high. Am I doing anything wrong?
They are compatible, the only difference between LTM4668 and LTM4668A is the switching frequency (1MHz, 2.25MHz), hence the version are optimised for different voltage output ranges, please see datasheet page 1 of each part.
So your initial PGood problem has nothing to do with LTM4668 or LTM4668A. It's just the parallel connection of PG1 and PG2 which is not correct as stated in my original post. (For your setup with parallel channels).