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TMS320F28379D: High Resolution PWM Signal

Sinan KAMILCELEBI
Intellectual 520 points
Part Number: TMS320F28379D

Hi,

Is it possible to produce a floating point PWM signal below 1 Hz with DSP? (for example 0.575 Hz)

Thanks,

Sinan,

Best regards.

  • 0
    TI__Mastermind 23410 points

    Hi Sinan,

    Typically low frequency PWM operation (below 250 kHz) does not require HRPWM; the normal capabilities of EPWM are enough. Is this a requirement in your system?

    Best Regards,

    Marlyn

  • 0 in reply to Marlyn Rosales Castaneda20
    TI__Guru 52020 points

    I dont think HRPWM is needed. Standard EPWM will do the trick!

  • 0 in reply to Marlyn Rosales Castaneda20
    Intellectual 520 points

    Hi, Marlyn:

    Yes, it's a requirement on my system. When I looked at the EPWM section in TRM, I could not create the low frequency (for example 0.575 Hz) I wanted with the formulas. Probably, DSP doesn't support low frequency.

    Thanks,

    Sinan.

  • 0 in reply to Sinan KAMILCELEBI
    TI__Mastermind 23410 points

    Hi Sinan,

    You could try the below as an example:

    In up-down count mode,

    TPWM = 2(TBPRD)(TTBCLK)

    TTBCLK = 1/ (EPWMCLK/(HSPCLKDIV * CLKDIV))

    EPWMCLK can be configured to SYSCLKOUT/2 through the EPWMCLKDIV bit. If your SYSCLKOUT is 200Mz, then EPWMCLK will be 100MHz.

    The max value HSPCLKDIV can be is 14, and for CLKDIV its 128. 

    HSPCLKDIV * CLKDIV = 1792

    TBCLK = EPWMCLK / (HSPCLKDIV * CLKDIV) = 100M / 1792 = 55803.6

    TTBCLK = 1/TBCLK = 1/55803.6 = .000018

    Your desired frequency is .575 Hz so TPWM = 1/.575 = 1.73913

    We can use the first equation [TPWM = 2(TBPRD)(TTBCLK)] to solve for TBPRD now

    TBPRD = TPWM / (2*TTBCLK) = 1.73913 / (2*.000018) = 48309

    This is the above in code:

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    // Set EPWMCLK to SYSCLKOUT/2. If SYSCLKOUT is 200MHz, EPWMCLK will be 100MHz
    SysCtl_setEPWMClockDivider(SYSCTL_EPWMCLK_DIV_2);
    // Within EPWM Initialization: Setup HSPCLKDIV and CLKDIV
    EPWM_setClockPrescaler(myEPWM1_BASE,
    EPWM_CLOCK_DIVIDER_128,
    EPWM_HSCLOCK_DIVIDER_14);
    // Within EPWM Initialization: Setup Count mode and TBPRD
    EPWM_setTimeBaseCounterMode(myEPWM1_BASE, EPWM_COUNTER_MODE_UP_DOWN);
    EPWM_setTimeBasePeriod(myEPWM1_BASE, 48309);
    XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    Best Regards,

    Marlyn