SLUUDN8 July   2026 TMS320F28P550SJ , TMS320F28P650DK

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Library Notice
  6. 3Library Architecture
    1. 3.1 Background Processing
    2. 3.2 Foreground Processing
    3. 3.3 Data Transfer Mechanism
  7. 4Metrology Calculations
  8. 5Configuration and Data Structures
  9. 6Calibration Module
  10. 7User Specific Configurations
    1. 7.1 Debug Mode
      1. 7.1.1 The Function of Debug Mode
      2. 7.1.2 How to Configure DEBUG Mode Parameters
    2. 7.2 ADC Mode
      1. 7.2.1 Using the On-Chip ADC
      2. 7.2.2 Two Point Calibration
        1. 7.2.2.1 Step 1 – Offset Calibration (Zero-Input Point)
        2. 7.2.2.2 Step 2 – Gain Calibration (Full-Scale Point)
      3. 7.2.3 Using an External ADC
    3. 7.3 Switching Between Modes
    4. 7.4 THD Algorithm Selection
      1. 7.4.1 Method 1 – Based on PLL (Default When the HARMONICS_SUPPORT Macro is Not Defined)
      2. 7.4.2 Method 2 – Goertzel DFT (When the HARMONICS_SUPPORT and USE_GOERTZEL_THD Macros are Both Defined)
      3. 7.4.3 Method 3 – 2048-Point Real FFT (When the HARMONICS_SUPPORT Macro is Defined But the USE_GOERTZEL_THD Macro is Not)
    5. 7.5 Topology Selection
    6. 7.6 Enable Features
    7. 7.7 System Parameters
    8. 7.8 Scaling Factors Per Phase
  11. 8Running the Example
    1. 8.1 Accessing the Parameters Per Phase
    2. 8.2 Accessing the Total System Measurements
    3. 8.3 Accessing the Phase Status Flags

7.2.2.1 Step 1 – Offset Calibration (Zero-Input Point)

With no AC signal applied to the ADC inputs:

  1. Call the ADC_calibrateOffsets() function once at start-up before the App_startDataCollection() function.
  2. This function averages 1000 consecutive ADC readings on the voltage and current channels to find the DC midpoint:
    • ADC_calibrateOffsets(); // call with no AC input connected
  3. The function stores the measured averages in the internal variables g_voltageOffset and g_currentOffset. These averages are then subtracted from every subsequent ADC reading in the ADC_readNormalized() function. The theoretical midpoint for a 12-bit ADC with a bipolar signal centered at Vref/2 (1.65V) is 2048, but component tolerances shift this midpoint in practice.

  4. If the ADC_calibrateOffsets() function is not called, the default values of ADC_VOLTAGE_DC_OFFSET and ADC_CURRENT_DC_OFFSET are used, as defined in the adc_config.h file (both default to 2048.0).