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PWM comparators

Victor Azevedo
Intellectual 725 points

Greetings, i'm trying to use PWM module from TM4C123GH6PMI launchpad. I have been loking the datasheet and found that there is a comparator in Count/Down mode with saw teeth to compare and generate a PWM exist, but from the ROM datasheet i can't find a way to use it.

Is it supose to use an internal signal to compare with a external signal like from ADC or other way.

I need to generate a PWM exit with a value given by my system function that comes from a PI or PID controller.

What commands should i use if possible? Is there any example i could guide on? Also want to achieve a 10kHz pwm frequency.

  • 0
    TI__Guru**** 244440 points

    Hello Victor,

    The API

        PWMGenConfigure(PWM0_BASE, PWM_GEN_0,
                        PWM_GEN_MODE_DOWN | PWM_GEN_MODE_NO_SYNC);

    in the code at the following TIVAWare example

    C:\ti\TivaWare_C_Series-2.1.0.12573\examples\peripherals\pwm\reload_interrupt.c

    can be modified for UP-DOWN counter instead of DOWN Counter.

    The PWM Generator compares the up-down count value with the comparator value in the PWMCMPA or PWMCMPB based on which pin will be used to generate the final output.

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Intellectual 725 points

    And what is the variable that is used to compare in that example?

    All i see in these examples are interruptions and updates of fixed numbers.

    The number in with i can set the PID value to change the duty cycle.

  • 0 in reply to Victor Azevedo
    TI__Guru**** 244440 points

    Hello Victor,

    I don't get the question here.

    The functions PWMPulseWidthSet is used to set the comparator to get the Duty Cycle.

    If you would post a pseudo code, it would be helpful.

    Regards

    Amit

  • 0 in reply to Amit Ashara
    Intellectual 725 points

    Amit, this is my problem:

    Wref-Wreal=error;

    Erro -> PI/PID -> Iref

    Iref-Ireal=error2

    by histeresis, its easy and done.

    But to use PWM i need a new PI/PID, so i get:

    error2 -> PI/PID -> Vref

    I suppose this Vref is my PWMPulseWidthSet, but in that comand you know the maximum frequência you want to use, and Vref you dont know what are the values. How to i know that my Vref is going to change between the range i have choosen for the PWMPulseWidthSet?

     

    I hope i made my point this time. The compare function of PWM, how it works and how its implemented for this case.

  • 0 in reply to Victor Azevedo
    TI__Guru**** 244440 points

    Hello Victor,

    Yes, I do understand it better now. One way is to calibrate the error with a schmoo of duty cycle so that a reference table can be built before the application is run, which will help gauge the new duty cycle based on how much error is there

    Regards

    Amit