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Compiler: C2000

vikas saini
Prodigy 30 points

Tool/software: TI C/C++ Compiler

Hi,

I am working on 28379D DSP.  I want to start my time base counter, exactly when my ADC I/P signal (Sinusoidal) cross zero. This synchronization between the time base and zero crossing must be maintained. The purpose is to have synchronized pulse pattern for power converters. How can I achieve this. Is any solution exist with out hardware zero cross signal.

Regards

Vikas

  • 0
    TI__Guru 60865 points

    Hi Vikas,

    What latency is acceptable for this zero-crossing pulse?

    The ADC PPB has limit compares and zero crossing detect, so you could setup the ADC to continuously sample and then have the PPB event sync the ePWM when zero-crossing is detected.  This will be subject to latency/jitter based on the ADC max sample rate...about 300ns.  

    If you need a lower latency/lower jitter sync, then you can use the analog comparators.  These will be somewhat less accurate than the ADC, however.

  • 0 in reply to Devin Cottier
    Prodigy 30 points

    Hi Devin,

    Thanks for the reply. My ADC sampling rate is 1.1 kHz, and switching frequency is 550 Hz. I want to run my converter in 11 pulse mode with sampling at zero and maximum value of time base counter. To maintain the synchronization, do I need to use sync pulse every cycle. How I decide that sync event  generated by PPB at zero crossing and waveform is in +ve half.

    Regards

    Vikas

  • 0 in reply to vikas saini
    TI__Guru 60865 points

    Hi Vikas,

    I'm not sure I exactly follow all the application-specific details of what needs to be synchronized and when, but if you only want the ePWM sync. pulse from the PPB for the positive zero crossing, I think you can just use the upper PPB limit compare and set the limit to 0.  Then use the lower limit compare to generate an ISR to reset the upper compare when the signal crosses back to something like -5% of signal amplitude ormaybe a fixed value like -50 LSBs.