• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 20 subscribers
  • Views 346 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LMX2594: Can't get lock when VCO_PHASE_SYNC is enabled

LMX2594: VCO_PHASE_SYNC question

David Caruth
Prodigy 60 points
Part Number: LMX2594

Hello,

I'm trying to use the LMX2594 with VCO_PHASE_SYNC and wanted to check the correct sequence of writing register R0.  With VCO_PHASE_SYNC enabled, TICS shows the last register write to R0 as 0x641C.  But is it necessary to first run the VCO calibration (FCAL) before setting the VCO_PHASE_SYNC from low to high?  i.e. should we write 0x241C first, wait for the VCO cal to finish, then write 0x641C to enable VCO_PHASE_SYNC?  Or should we write 0x241C, wait for the cal to finish, and then write 0x6414 (don't re-run the FCAL)?

Also, is the VCO_PHASE_SYNC bit self-clearing?  Or does it need to be de-asserted with another register write to R0?

Thanks!

  • 0
    TI__Mastermind 28011 points

    Hi,

    VCO_PHASE_SYNC and FCAL_EN are both in the same register.  So whenver R0 is written with FCAL_EN=VCO_PHASE_SYNC=1, it should both re-calibrate the VCO and also apply the SYNC.  However, this will be a category 2 phase sync (good if the output frequency is a mulitple if the input frequency).  If the output frequency is NOT a multiple of the input frequency, then it is necessary to toggle the SYNC pin after this.

    The VCO_PHASE_SYNC bit is NOT self-clearing, nor should it be.  By setting this bit to 1, it also engages the IncludedDivide as well.  So if you do the phase sync, and then program VCO_PHASE_SYNC=0, you will lose the phase sync.

    Regards,

    Dean