Hello Freddy,
In previous cases, which offer similar observations, the system supplies were not able to manage the elevated peak current demand in the ADIS16375 (1.5A, ~200us) during the start-up process. In these particular cases, the resulting voltage drop violated the operating conditions and causes a "failure to start." In comparison, the ADIS16485 only has a peak current of 650mA, but it does last longer (~1.75ms).
For more details on the transient current demand from the ADIS16375, during initial start-up, please check this post out: http://ez.analog.com/docs/DOC-10800
For more detail on how to manage a power system for the ADIS16375, we offered a summary at the end of this discussion (may need to go to the second page): http://ez.analog.com/thread/39655
For more details on the transient current demand from the ADIS16485, during initial start-up, please check out page 28 in the ADIS16485 datasheet (rev B):
http://www.analog.com/static/imported-files/data_sheets/ADIS16485.pdf#Page=28
I hope that helps. Let us know what you find out.
Best,
NevadaMark