LMX2572: How does the LMX2572 work at -55 °C, what effect does it have on the chip?

Zhao,

My casual opinion is that in general, the phase noise performance actually improves at colder temperatures.  The biggest concern is that the LDOs might need more headroom, so you would want operate at the higher end of the voltage range.  i.e. try to stay above Vcc>=3.3V.

My official response is that this is outside the operating range of the part and this performance is not guaranteed or tested in production.  So if you run into any issues operating below -40C, these will be your issues and TI will have no obligation to support you. 

Regards,

Dean