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Compiler/TMS320F28035: pwm1.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2;

user5220604
Prodigy 250 points
Part Number: TMS320F28035
Other Parts Discussed in Thread: CONTROLSUITE

Tool/software: TI C/C++ Compiler

C:\ti\controlSUITE\development_kits\HVMotorCtrl+PfcKit_v2.1\HVPM_Sensored

What does the formula for "marked red" mean? Why do we do this calculation?

// Initialize PWM module
pwm1.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2; // Prescaler X1 (T1), ISR period = T x 1
pwm1.HalfPerMax=pwm1.PeriodMax/2;
pwm1.Deadband = 2.0*SYSTEM_FREQUENCY; // 120 counts -> 2.0 usec for TBCLK = SYSCLK/1
PWM_INIT_MACRO(1,2,3,pwm1)

// Initialize PWMDAC module
pwmdac1.PeriodMax=500; // @60Mhz, 1500->20kHz, 1000-> 30kHz, 500->60kHz
pwmdac1.HalfPerMax=pwmdac1.PeriodMax/2;
PWMDAC_INIT_MACRO(6,pwmdac1) // PWM 6A,6B
PWMDAC_INIT_MACRO(7,pwmdac1) // PWM 7A,7B

  • 0
    TI__Guru** 115500 points

    The code calculates the value of PWM period register based on the PWM frequency (T) and CPU frequency ( SYSTEM_FREQUENCY), and the count mode of PWM for motor drive is up/down mode, so it needs to be divided by 2.
    pwm1.PeriodMax = SYSTEM_FREQUENCY*1000000*T/2; // Prescaler X1 (T1), ISR period = T x 1

    PWMDAC is an option function for motor control, just used for debugging, to converts any s/w variables to an analog signal using PWM signals through the external low-pass filters. Below code will be used to set the period register value of PWM for PWMDAC function, the PWM frequency must be greater than the cut off frequency of LPF.
    pwmdac1.PeriodMax=500; // @60Mhz, 1500->20kHz, 1000-> 30kHz, 500->60kHz

    Please refer to PWM_INIT_MACRO() and PWMDAC_INIT_MACRO(), both calculated value will be set to related PWM period registers.

  • 0 in reply to Yanming Luo
    Expert 1185 points

    Hi 

    what does exactly "T" means in the code? why it is referred as sampling frequency instead of PWM frequency :

    float32 T = 0.001/ISR_FREQUENCY;    // Samping period (sec),  see parameter.h 

    and what is ISR_FREQUENCY ?

    // Define the ISR frequency (kHz)
    #define ISR_FREQUENCY 10

    regards

  • 0 in reply to lio messi
    TI__Guru** 115500 points
    As the comments for the code, ISR_FREQUENCY is the frequency of interrupt subroutine, often, it equals to PWM frequency, and PWM frequency equals to sample frequency for ADC by default. T is the period with sec unit of ISR/PWM.
  • 0 in reply to Yanming Luo
    Expert 1185 points
    Hello dear Luo
    Thank you so much.
    I have got it.
    regards