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Tiva 129 VCO Frequencies

Aaron Geier
Intellectual 600 points

I've noticed that the VCO frequency for the 129 processor can be changed between 320MHz and 480MHz.  The 123 processor, the VCO is fixed at 400MHz.

Other than being able to achieve different effective clock frequencies, would there be a reason to choose 320MHz over 480MHz or vice versa?  Would you expect less power consumption when running a 320MHz VCO over a 480MHz VCO?

  • 0
    Guru 47900 points

    Aaron Geier said:
    Would you expect less power consumption when running a 320MHz VCO over a 480MHz VCO?

    Would that not yield to, "Quick/easy" experimental derivation?    And - as each application is unique - your (real) needs will be best met via this means...

    Using another vendor's ARM - w/similar VCO choices - we noted (slight) changes in consumption.    (this may/may not overflow here - thus experimentation suggested)    The final (derived) system clock choice dominated power consumption - thus the VCO choice played a far reduced role.   (again - that noted @ 2 other ARM vendors)

    EMI was impacted (i.e. agency test/approvals) - and was influenced by the external xtal frequency - as well.    The VCO flexibility provided here may enable a reduction in EMI - all things being equal.

  • 0
    TI__Guru**** 244400 points
    Hello Aaron,

    The USB operation from PLL requires 60MHz which can only be derived from 480MHz. I USB is not critical to the application then the VCO can be lowered down to 320MHz which will give the effective maximum usable frequency of 80MHz that would be on par with TM4C123 applications that can work at 80MHz maximum.

    The same result can be achieved with 480MHz but then reduced VCO shall incur slightly less current consumption.

    Regards
    Amit