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TMS320F28055: I have a problem to anderstanding ADC

Kiselev Dmitry
Expert 1400 points
Part Number: TMS320F28055

I don't  anderstand what is Overlap mode adn NonOverlap mode? Data sheet have a table, when is some data fo defferent mode. Table I'm attached. I have a problem with ADC conversion. When I insert to ACQPS different data from table, I have a differents result of signal. Some signal have noise, when I insert another data to ACQPS, noise reduce. How can I anderstand what data need to ACQPS? And What mode working my ADC, overlap or not?

  • 0
    TI__Guru 62975 points

    The OVERLAP vs NONOVERLAP mode is described in more detail in the ADC chapter of the technical reference manual.

    In summary, the ADC works in two logical steps:

    1. Expose the internal ADC S/H cap to sample the ADC pin over a period of ACQPS+1 ADC clock cycles
    2. Store and convert the S/H cap voltage to a digital value

    In overlap mode, a new SOC is allowed to start Step 1 sampling of the pin while an older, active conversion is still processing Step 2.  In theory, this allows for faster MSPS throughput, but the concurrent activity may introduce errors to the system.

    The non-overlap mode will not allow a new SOC to start Step 1 sampling until the active conversion completes Step 2.

    The overlap mode is enabled by default and can be disabled through the ADCCTL2[ADCNONOVERLAP] bit.

    There is also an ADC first-sample issue which may introduce random noise.  It is described in the errata.