Hello,
Can you let us know the know the conditions which will trigger limphome mode?
One example condition that could trigger limphome mode in BCMs is MCU failure. In this case, a watchdog is used to detect the MCU failure and then watchdog output + some logic can then be used to drive the load. See below block diagram that illustrates this concept.
See this note (http://www.ti.com/lit/an/snva837/snva837.pdfabout how watchdog output can be latched in order to drive the load.
Arun