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[F28M36P63] Concerto : PWM Modulation @100kHz and 16Bit

Eduard Bart54
Prodigy 40 points
Other Parts Discussed in Thread: CONTROLSUITE

Hello,

I'm using the Concerto F28M36P63 Controller ( http://www.ti.com/tool/tmdscncd28m36 ).

The DSP is running with 150MHz ( 6,67ns /step).

For an application I want to configure one PWM module (e.g. ePWM1 with high resolution) to work with 16-Bit Resolution.

In normal ePWM mode that leads to a frequency of about 2,288 kHz.

-> (  150Mhz / 65536 ) = 2,288kHz    ( 65536 = 16-Bit Resolution for the PWM timer -> TBPRD Register )

The frequency should be higher for the needed application. ( best would be 100kHz)

In the manual it says that in high Resolution mode (pwmHR) a step size of about 150ps is possible.

With 150ps it should be possible to reach 16-Bit resolution @ 100kHz but I'm not sure how to configure the Registers.

So I've got two questions:

1. Is it possible with the 16-Bit resolution and the 100kHz ( I think it is) ?

2. How do I have to configure the registers?

-> I don't see a possiblity to run the PWM timer with 150ps, only with SYSCLKOUT = 6,67ns

-> Is it enough to configure the compare Register (CMPA / CMPB) in high resolution?

 My thought is that the timer must also have high resolution to match the CMPA / CMPB value.

Thanks very much for your answers !!!

Regards

Jens

  • 0
    TI__Guru 57255 points

    Hi Jens,

    1) Typically yes.  According to the datasheet, the specification for the typical HRPWM resolution is 150ps whereas the worst case performance is 300ps.  A minimum is not given in the datasheet, but <120ps is possible.  The resolution from the HRPWM changes with temperature and other parameters.

    2) The standard PWM (ePWM) works as you have described - the the minimum step for the ePWM is given by the chip's SYSCLK.  The HRPWM enhancement uses special IP to add more resolution to the ePWM module and is mostly independent of SYSCLK.  

    • Once you configure the peripheral correctly (and assuming you turn autoconvert/AUTOCONV mode on), you should be able to write a 32-bit value to EPwm1Regs.CMPA.all.  The most-significant 16bits will go to the standard resolution ePWM output, bits 8-15 will go to the HRPWM unit and bits 0-7 are ignored. 
      • The HRPWM will only be able to give about 150ps of resolution.  As a result, each bit increment to bits 8-15 will not always result in an increased CMPA output with AUTOCONV on.
    • A good example to refer to may be the following:
      \controlSUITE\device_support\f28m35x\v202\F28M35x_examples_Control\hrpwm_slider\


    The HRPWM section of the F28M35x TRM should provide you with more details.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Prodigy 40 points
    Hi Brett,

    thanks very much for your reply. I got it working.

    I am Aware that there might be voltage and temperature issues with such high frequencies.
    We will see how high the resolution and how fast the PWM has to be in the end.

    But in principal it works now.

    Thank you very much for your fast reply.

    Regards,
    Jens