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Maximum switching frequency of C2000 MCUs

Panos
Prodigy 160 points

Hi to everyone,

Just a small and maybe silly question for most of you. I have used some TI C2000 MCUs and I have seen that for an MCU there is no a maximum switching frequency specification of PWM  modules. Actually a PWM module may operate at  frequencies below 1/2 system clock frequency, but practically the applied switching frequency depends on the bandwidth of the MCU. In case it is low, the MCU decreases the switching frequency.

Summarizing, I would like to ask if there is a specification for an MCU that says "Maximum switching frequency = XXX kHz"?

Thank you

ps1 I want to choose a MCU for a project and I have been asked what is the maximum switching frequency. I answered the above, and told that because it  depends on the code and etc, the final answer will be given for sure after downloading the code into the MCU.
ps2 If this question has been already answered please tell me where...

  • 0
    Guru 192875 points

    Hi panos,

    Here's the formula to calculate PWM Frequency:

    Here, TBCLK can be at the max equal to SYSCLK.

    Hence, if you consider TBPRD as 50 then here's the table:

    TBPRD 50
    TBCLK 1.67E-08
    Tpwm 8.50E-07
    Fpwm 1.18E+06

    I hope this gives you a clear picture.


    Regards,

    Gautam

  • 0 in reply to Gautam Iyer
    Prodigy 160 points
    Hi Gautam,

    Thank you for the immediate response. I tried to describe this formula in my post. As I understand there is no actual hardware limitation other than the TBCLK. The value of TBPRD can be any (?) number. Considering 60 MHz cpu frequency then your example applies. However, sometimes the MCU decreases the clock rate if there is not enough bandwidth.

    Summarizing there is not a specification other than the system clock frequency. My project is around 200 kHz and the clock frequency of most C2000 MCUs is above 60 MHz.

    Thank you
  • 0 in reply to Panos
    Guru 192875 points
    The value of TBPRD can be any (?) number.

    Yes, but this should be decided according to the required step (duty) resolution.

    Summarizing there is not a specification other than the system clock frequency. My project is around 200 kHz and the clock frequency of most C2000 MCUs is above 60 MHz.

    Very true!

    Regards,
    Gautam
  • 0 in reply to Gautam Iyer
    TI__Guru 57255 points

    Hi,

    To add a bit more detail:

    Physically, the max PWM speed will have two dependencies. 
    (1) the system clock frequency as you've suggested
    (2) the GPIO specifications found in the individual device's datasheet.  This is necessary because the PWM will connect to the GPIO driver before leaving the chip and it will have a certain drive strength.  For example on the F28027, the datasheet gives 15MHz as the maximum toggling frequency.

    Realistically, you are also correct, the maximum switching frequency will often have some dependency on the software controlling it as well. 


    Thank you,
    Brett