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TMS320F28069: 28069: OSC fine and coarse step size and ratio

Mitja Nemec
Genius 5885 points

Part Number: TMS320F28069

Is there a min and max value for the oscillator coarse and fine step size (SPRS698F, page 33, Table 5-7)?

Is the ratio between coarse and fine step always 55/14 = 3.9285714... or is there also a min and max value for the ratio?

  • 0
    TI__Guru* 95315 points

    The oscillator trim registers are only meant to be used in conjunction with the factory-programmed oscillator temperature compensation and Device_cal() functions in OTP.  MIN and MAX values are not provided because the trim registers are not intended to be used by customers for open-loop trimming.

     

    This ratio is not constant, since the step size could shift on either direction.

  • 0 in reply to Hareesh Janakiraman
    Genius 5885 points

    Thanks for the response, I've figured as much.

    I am going to give you a bit of background anyway. I'd like to synchronize multiple MCUs on a system clock level, but I don't want to route 10 MHz signal. So I've figured, I can phase lock them to a lower frequency signal using the trim feature. This works using fine trim, but even the fine resolution is a not enough for this setup, as there is quite a lot of jitter. Since coarse trim is not an integer multiple of fine trim (at least in datasheet) I've figured I can get more resolution with linear combination of the two. Obviously this is not a viable option. Thanks for clarification.

    Is the fine trim step size smaller in new Delfino and Piccolo devices?

  • 0 in reply to Mitja Nemec
    TI__Guru 62975 points
    Mitja,

    The newer devices have moved away from the software-based oscillator trim approach. Instead there is now a hardware-based continuous analog trimming circuit. Here was a recent discussion: e2e.ti.com/.../2382745

    -Tommy