LOS (Loss Of input Signal) detects whether the clock input is valid or not. When input clock is valid, LOS# register bit = 1 and LOS# pin = high. When input clock is invalid, LOS register bit = 0 and LOS# pin = low.

At power-up, the LOS# pin is kept low until input is detected valid. Therefore, the LOS# pin can be used for the timing of OE# insertion and other operations.

The LOS# signal is only effective if PWRGD/PWRDN# pin is high. If this pin is low, then LOS# is low regardless of input validness