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LAUNCHXL-F280025C: Offset calibration in the Universal Motor Control Lab

Part Number: LAUNCHXL-F280025C

I'm looking for reference material, etc. that describes the procedure used for ADC offset calibration in the Universal Motor Control Lab.

Why is it done in this way?

At a high level:

  • PWM for all three phases is set to 50%
  • The ADC offset value is initialized to a hardware-specific value, which seems to be near mid-scale.
  • For 32000 cycles, take ADC readings
  • Ignore the first 2000 readings
  • For the remaining 30000 cycles, the offset value is set to 

0.998001 * current_offset value + 0.001999f * the read ADC value

I understand what is done, mostly, and I am looking more for "why" it is done this way.  Why 30000 iterations?  Where does the adjustment equation come from?

Thanks!