CY2305 Behavior on Removal of Input Reference - KBA82621

Version: **

 

Question:

What is the effect on the CY2305 output when the input reference clock is removed?

 

Answer:

The output usually holds the original frequency for only a few cycles. Generally, you cannot expect more than two or three cycles at the normal frequency. It then drops toward a lower frequency. 

For example,

100 MHz drops towards 80 MHz, stops after ~120 cycles
80 MHz drops towards 70 MHz, stops after ~120 cycles
60 MHz drops towards 50 MHz, stops after ~90 cycles
40 MHz drops towards 30 MHz, stops after ~50 cycles
20 MHz drops towards 14 MHz, stops after ~25 cycles
10 MHz goes very quickly towards 5 MHz, stops after ~10 cycles

In all cases for the frequencies above, the output clock stops about 1.5 to 2 microseconds.