LTC3891 PLLIN

Question

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.

ADIApproved · Accepted Answer

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)

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LTC3891 PLLIN