I would like to design a fail safe backup DC/DC converter. My input is 28V and I have to use one main source and one backup source. If main source is failed, then backup will turn on immediately. Is there any power monitor for this application ? I found a LTC4420 for this kind of application but I'm not sure.
12V, 2.5A output needs.
LTC4420 can only operate up to 18V input supply. 28V is above its abs max rating. You should use LTC4418 + external MOSFETs for this application.