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UCC2897A: Sync two UCC2897A

Ryan.Bishop
Expert 3900 points
Part Number: UCC2897A

Hello,

We are attempting to synchronize two UCC2897A so that they operate out of phase.

The datasheet states that if you directly connect the SYNC pin from one UCC2897A to another, then they will operate in phase.

A simple solution seems to simply delay the pulse so that the received pulse is 180 degrees output of phase with the original pulse.

  1. Page 14 of the datasheet says any synchronizing frequency applied to the SYNC pin must be greater than the internal oscillator. However, Page 14 also says when SYNC is outputting pulses they are driven from the internal oscillator. How can one UCC2897A send synchronizing pulses to another UCC2897A if the pulses cannot satisfy the 'greater than the oscillator frequency' requirement?

  2. Page 14 states that the SYNC pin is bi-directional. How is the SYNC pin configured as an input or an output? How do we keep two UCC2897A from clashing with each other if they both are trying to send pulses on SYNC?

Thank you,
Ryan B.

  • 0
    TI__Mastermind 31580 points
    Hi Ryan,

    For number 1, you could setup one of the UCC2897a to run at a faster frequency so that its always the source of the sync frequency.

    For number 2, I will have to consult the IC design team to get an explanation of internal circuit of the IC, that will take a numbers of days before we will have an answer. I will also ask some of the other apps engineers if they know this off hand.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Expert 3900 points
    Hi Peter,
    Have you gotten any advice from the apps team or designers?
    Thank you,
    Ryan B.
  • 0 in reply to Ryan.Bishop
    TI__Mastermind 31580 points
    Hi Ryan

    Yes the answer I got back is

    "The sync circuit is bidirectional because as long as the Rt and Ct combination gives a frequency that is lower than the SYNC pulse, then the sync pulse will discharge the CT cap, not the internal oscillator. There should only be one High frequency Rt, Ct combination that will cause this UCC2897 to sync all of the devices. Or an external clock that is the highest frequency and all of the other UCC1987’s will take that as an input.

    If the SYNC pin is used as an input then RON and ROFF values need to be set up such that the SYNC frequency is higher than the frequency set up by the RON and ROFF pins. The SYNC used as an output you would just set up one UCC2897 to be the highest frequency and the others would be much lower frequency so they are synced by the highest frequency UCC2897"

    Regards

    Peter