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LMX2492EVM: PLLatinum Sim

AY
Prodigy 180 points

Part Number: LMX2492EVM
Other Parts Discussed in Thread: LMX2492

Hi,

I am using the PLLatinum Sim to design the active loop filter for LMX2492. When I try to get a suggestion for a third order Active Type A loop filter(as the VCO tune needs higher than 5V for our design), the result of PLLatinum Sim is always 'filter not stable'.

I also noticed that the polarity of the op-amp connection for Active Type A topology is strange as the Vbias is connected to Vin-. I am expecting the Vbias is at the Vin+. Is there a bug in the software?

Thanks.

  • 0
    TI__Mastermind 28031 points
    AY,

    This looks like a bug in the software. It seems like the 2nd and 4th order works, but the 3rd order gives R1=0. If you go to the design screen, you can force a value of R1 and this will allow you to design.

    For now, the workaround is to set to 4th order and set the T4/T3 ratio to something low, or even to 0%. I'll chase down this bug, but it might take some time to release to the web.

    Regards,
    Dean