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Frequently Asked Question

The loop filter was working great until I changed the divide ratio in PLL. What happened?

A PLL is a closed loop feedback system and is stable under a limited set of conditions. The selection of the loop filter must take into consideration the PLL divider and charge pump settings. Frequently the loop will appear stable over small changes in the dividers and the charge pump setting, however actual stability should be verified using a tool such as ADIsimCLK. Even though the loop may remain stable with these changes, the loop bandwidth and phase margin will most likely change.