LTC3891 PLLIN

Sorry, repeat question that I asked in the wrong forum.

Has anyone used the PLLIN/MODE for external synchronization?

I've tried all the options shown on the evaluation board schematic and had no luck.

Other circuits that I've designed recently using the LTC3895 and LTC3858-1, have both worked as described, locking on from a wide range of frequencies.

I just can't get this feature to work in the LTC3891.

  • 0
    •  Analog Employees 
    on May 10, 2021 2:24 AM

    Hi Wsurfdoug,

    hope you are doing well.

    Are you testing it on the actual demo board or did you build a prototype and referenced the design on the demo board? If you are working on the demo board, try to remove the JP2 that selects the mode of operation since the PLL already locks the frequency with respect to the external source that can be set between 75kHz and 750kHz.

    Regards,

    Siglo

  • Hi Siglo,

    Thanks for the information. I'm working on my own design that uses the same layout as the demo board. It's hard to get the PLLIN bit wrong.

    Unfortunately, it's been a few weeks since I looked at this design as I'm working on another project using the LT8705.

    Once I've refreshed myself regarding this issue I'll re-post my findings. I've a sneaky feeling it may be my the test set up that was at fault and I won't know until I repeat the test. 

    Kind regards,

    Doug