Hi Jeffrey.
Based on the description you have provided, I get the understanding that you want to use the PWM/DAC functionality on ePWM7 and ePWM8, available on pins GPIO157-GPIO160. At first, only ePWM1 is HRPWM configurable, as provided in the documentation below:
So, it is not possible to use the PWM-DAC functionality using HRPWM configuration for any ePWM module, except ePWM1.
Up to 250kHz, HRPWM is typically not required as per TI documentation, so the ePWM modules can be used for PWM-DAC functionality, however, to have good DAC resolution, the PWM frequency will have to be low, i.e., TBPRD needs to be high. This will surely affect the DAC bandwidth, as it depends on the cutoff frequency of the on-board RC filter, leading to harmonic ripple in DAC output. The R-C filter values can be found in page 13 of the following documentation:
So, a trade-off needs to be done between DAC resolution and DAC bandwidth when using the ePWM module for PWM-DAC functionality, and TBPRD needs to be chosen appropriately.
Currently, there is no documentation available from TI, for implementing the PWM-DAC functionality, specifically in F28379D, following this discussion on the TI C2000 forum:
However, some clarity can be gained from the documentation provided below, that implements this functionality on a similar TI controller, following from the discussion in the above forum:
I hope this helps with the issue.
