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TMS320F280040C-Q1：What are the application scenarios or cases for "PPB Error Calculation" ?

chao yang
Expert 1620 points
Part Number: TMS320F280040C-Q1

Hello all

When I looked at the ADC section of F28004x manual, I found "PPB Error Calculation" feature in the ADC post-processing module.As follow

I have a few questions to communicate：

  1. Why artificially add an error to a result that has already been corrected for offset? What are the scenarios where this feature is used?（In terms of system architecture, it seems that two consecutive subtractions have been made for the result of the ADC conversion.）
  2. "a bipolar signal is necessary or convenient for control calculations."----Why is this feature good for bipolar signal processing?
  3. I mainly use DSP for digital power applications,so how can this feature be incorporated into digital power design？

I look forward to your reply and would appreciate it very much.

  • +1
    TI__Guru 60865 points

    Hi Chao,

    These two offsets are slightly different in that the first stage (OFFCAL) will saturate while the second stage (OFFREF) will produce a signed result.  Depending on the use case, the user can use one or the other (or possibly both).  

    Generally the bipolar signal is used to detect zero crossing, or for integrating absolute error.  Note that "Zero-crossing" can be in the literal sense (e.g. a sensed 60Hz AC waveform crosses 0V or the voltage in one phase of the motor switches from positive to negative or vice-versa) or with respect to a setpoint (e.g. the bus voltage that is to be controlled to 400V crossed from below the 400V setpoint to above the 400V setpoint).   On the zero-crossing side, there is actually HW further downstream in the PPB that can detect the zero crossing and send a trip to the ePWM- or generate an ISR.  This can allow for triggering an ISR only when action needs to be taken or can allow for bang-bang control or just very quick actuation of the ePWM without CPU intervention.