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Original question:

UCC28951: Maximum frequency at SYNC in follower mode

UCC28951: Maximum frequency at SYNC in follower mode

AhmadBashar Taji
Prodigy 40 points
Part Number: UCC28951

Tool/software:

Hello and thank you for your support,

I guess my question was not clear.

The minimum limit is 1.8 times the switching frequency, and the maximum is x times the switching frequency, what is the value of x?

For example, for a fixed RT (say 57.5k ohm which corresponds to a switching frequency of 100kHz), the minimum SYNC frequency is equal to 1.8 times the converter frequency (in this case = 180kHz), but what is the maximum SYNC frequency in such a case.

In other words, how high can the SYNC frequency goes relative to the converter frequency?

With best regards

  • 0
    TI__Guru* 76135 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru* 76135 points

    Hello,

    When you are synchronizing a clock,  you need to sync a slower programed clock to a faster sync signal.  You can't synchronize a faster programed clock a slower sync signal.  

     

    The internal clock is 2X the internal frequency.  This clock is what you are trying to synchronized.  Having a sink signal that 1.8*100/2 = 90% of the sync signal will not work.  The sync signal needs to be faster than the internal clock.

    In your exampled the programed internal clock frequency is 200 kHz.  To sync this you would need a signal greater than 200 kHz.  In general the sink signal is 1.25 times or greater than the programed clock frequency.

    I think you might be worried about tolerance.  The oscillator which has a tolerance of +/- 8%.  In this case the programed frequency would be 92 to 108 kHz in your example.  In this case the internal clocks maximum programed frequency would be 108 kHz*2 = 216 kHz.  The sync frequency of the master clock the input to the sync pin should be 216 kHz*1.25 = 270 kHz.

    I believe the 1.8 term in the data sheet is in error.  This does not make sense because the master clock is 2X the programmed frequency.

    Thank you for interest in Texas Instruments (TI) products.  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.

    Regards,