The Time-Base (TB) submodule is used to setup the ePWM modules with a frequency of 400 kHz. Each ePWM module has a time-base counter (TBCTR). There are three modes of the time-base counter: UP, DOWN, and UP-DOWN. The frequency of the PWM events (${\mathrm{F}}_{\mathrm{P}\mathrm{W}\mathrm{M}}$ ) is controlled by the time-base period (TBPRD) register and the mode of the time-base counter.

For up and down count modes:

For up-down count mode:

Where, ${\mathrm{T}}_{\mathrm{P}\mathrm{W}\mathrm{M}}$ is the period of the PWM events and ${\mathrm{T}}_{\mathrm{T}\mathrm{B}\mathrm{C}\mathrm{L}\mathrm{K}}$ is the period of the time-base clock. The time-base clock (TBCLK) is a prescaled version of the ePWM clock (EPWMCLK). This clock determines the rate at which the time-base counter increments and decrements.

For the use-case discussed in this application report, the up-down count mode is utilized as it provides more configurability options due to the symmetry of the count mode. Start by finding ${\mathrm{T}}_{\mathrm{P}\mathrm{W}\mathrm{M}}$:

Now that you know what ${\mathrm{T}}_{\mathrm{P}\mathrm{W}\mathrm{M}}$ is, you can start calculating the value for TBPRD:

The time-base clock is defined through the following formula:

The maximum EPWMCLK is defined in the device-specific data sheet. EPWMCLK is usually the same as SYSCLK but some devices may have a clock divider, EPWMCLKDIV, which reduces the frequency of the ePWM clock. The high-speed clock divider (HSPCLKDIV) and the clock divider (CLKDIV) are programmable dividers used to help achieve a desired ePWM time-base clock. For this use-case, both clock dividers are set to divide by 1 and EPWMCLK is 100 MHz.

Now that you have all of the needed parameters, you can calculate the TBPRD value:

What this means is that the time-base counter counts from zero to 125 and then back to zero. This counts as one period of the ePWM output, resulting in a 400 kHz output frequency for EPWM1, EPWM2, and EPWM3.

The following code is generated from SysConfig:

// EPWM1 (the code is the same for EPWM2 and EPWM3, except for the base address)
EPWM_setClockPrescaler(myEPWM1_BASE, EPWM_CLOCK_DIVIDER_1, EPWM_HSCLOCK_DIVIDER_1); 
EPWM_setTimeBasePeriod(myEPWM1_BASE, 125); 
EPWM_setTimeBaseCounterMode(myEPWM1_BASE, EPWM_COUNTER_MODE_UP_DOWN);