Using the LOS to Select a Clock Input, Si533xx series

by <a href=""><font color="#000000"><font size="2">Hero Employee</font></font> </a> FranBoudreau on ‎12-14-2015 07:17 AM

The Si53301 and Si53302 series buffers include a LOS feature which is used to detect a loss of input clock. The LOS is set to a logic 0 with an active input and transitions to a logic 1 when there is no input. Note there is a 15 us loss of signal detect time.

The Si533xx which have a LOS feature also includes two inputs, CLK0 and CLK1, which are switched between by using the CLK_SEL input. CLK0 is selected when CLK_SEL is a logic 0, and CLK1 is selected when CLK_SEL is a logic 1.


If the LOS0 is connected to CLK_SEL then the CLK0 input is selected provided an active input between 1MHz and 750MHz. When CLK0 becomes inactive the LOS then transitions to a logic 1 and the CLK1 is now selected after a 15 us delay to detect a LOS. Also, glitchless switching only applies when switching between two active inputs, there could be an output glitch since the CLK0 is now inactive. This “auto select” mode is considered autorevertive as CLK0 will automatically be selected once there is a CLK0 input.

In summary, LOS can be used to control the input selection, in an “autoselect revertive mode”. Keep in mind there is a 15 usec typical delay to detect a LOS, the output could produce a glitch and the inputs should be between 1 MHz and 725 MHz.