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20 MHz Output Clock - F28377S EPWM

DavidG
Intellectual 290 points

Other Parts Discussed in Thread: CONTROLSUITE

Hello again,

After poking around several examples and the datasheets I have been unable to locate physical limitations or nominal operation ranges for the ePWM modules in terms of frequency on the F28377S.  I'm looking to generate a 20 MHz signal if it's possible.  The issue that I'm running into is that the most I can get out of it before the waveform becomes unacceptably noisy or unreadable is around 5 MHz (and that's pushing it.)  My impression of the HRPWM modules was that they might be capable of higher speed operation, but the controlSUITE examples have not proved this.  Is the chipset capable of providing a 20 MHz signal (whether PWM or otherwise)?  I do have the SYSCLK maxed at 200 MHz and related peripheral clocks as high as possible.

Is there tuning I might be able to do to fix this signal up?  A coworker mentioned that he could not find a slew rate for the pwm modules, is there support for this?

The waveform I'm getting from the hrpwm_prdupdown_sfo_cpu01 controlSUITE project is below (excuse the quality, I did not have a drive on hand to get a better capture with):

  • 0
    TI__Guru 57255 points

    Hi David,

    The PWM peripheral (and any other outputting peripheral ) utilizes the GPIO output buffers to drive the line high or low.  Therefore, the specifications for the GPIO output timing is what you should be looking for with regards to slew rates, etc - and these can be found in the device datasheet.

    The load on the pin AND your method of measuring the signal are both things to consider here.

    Note that the HRPWM won't help with high speed vs the ePWM, it helps more with the precision placement of edges.  I might recommend that you use the simpler ePWM for trying to generate your high-frequency signal first - and then add in the HRPWM functionality if you require more precision/accuracy.


    Thank you,
    Brett