LMX2492: The LMX2492 cannot be locked

I connected LMX2492 to an external VCO, and loop filtering adopted the fourth-order passive form. The simulation control adopted the TiPLLatinum and TICS Pro provided by Ti, in which the phase margin was set at 49.7° and the loop bandwidth was 437KHz. However, the output frequency could not be locked all the time, may I ask what caused it?Another question is what is the role of Kpd regulation, is the larger the setting, the better its phase noise performance?When I set the Kpd at 3.1mA, the remote phase noise (5MHz) got worse.The above Settings Fpd=40MHz, R_divider=1,FVco=1.5GHz, Kpd=0.4mA, Kvco=36MHz/V

Looking forwards to your suggestions!

Thanks!

Kailyn Chen：

Hello, in order to better answer your questions, I have posted this question to the E2E forum, please pay attention to their reply.

Any questions, you could either follow up directly on E2E or here that  I help to follow.

https://e2e.ti.com/support/clock-timing-group/clock-and-timing/f/clock-timing-forum/1232248/lmx2492-the-lmx2492-cannot-be-locked