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Non conventional PWMs

Francesco Musolino
Prodigy 160 points
Other Parts Discussed in Thread: TMS320F28035

Hi,

I'm using the TMS320F28035 microcontroller in order to set up the digital control of a DC-DC converter. To this purpose, I'm wondering if this device could supports spread spectrum clocking and/or if there are some techniques to generate non conventional modulations other then the classical PWM (better if documented).

Thank you very much

  • 0
    TI__Guru 60865 points

    Hi Francesco,

    One clocking option you have on this device is internal oscillator.  We provide a method to compensate the oscillator for temperature drift with the following flow:

    sample temp sensor -> calculate new oscillator trim based on interpolation of factory temp sensor/oscillator calibration data -> apply oscillator trim

    The second two steps of this are bundled as a function in the header files.  

    You can try the following to get frequency spreading:

    sample temp sensor -> add frequency modulation offset to sensor reading -> call function that does last two steps

    Note that we have not qualified this approach. 

  • 0 in reply to Devin Cottier
    TI__Guru 57255 points

    Francesco,

    Another method to get spread spectrum PWM waveforms might be to vary the PWM's period from cycle-to-cycle.  To do this the period register should be configured to load from its shadow register (see PRDLD register bit in the documentation).

    You'd then modify the duty cycle (the %age will likely be your controlled variable) and period accordingly from cycle-to-cycle or as you desire.


    Thank you,
    Brett