SLAAEE6 October   2023 MSPM0L1306 , MSPM0L1306

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Hardware Introduction
  6. 3Software Introduction
  7. 4Gauge GUI Introduction
  8. 5Current Detection and Calibration Method
    1. 5.1 MSPM0 OPA Introduction
      1. 5.1.1 OPA input and output limitation
      2. 5.1.2 OPA Accuracy Influence
    2. 5.2 Current Detection Method
    3. 5.3 Current Calibration Method
      1. 5.3.1 (R1+R2)/R2 calibration
      2. 5.3.2 OPA1 Voffset calibration
      3. 5.3.3 R3/(R4+R3) calibration
      4. 5.3.4 Vref calibration
  9. 6Solution Evaluation Steps
    1. 6.1 Step1: Hardware Preparation
    2. 6.2 Step2: Evaluation
  10. 7MSPM0 Gauge Solution Test Results
    1. 7.1 Calibration Test Result
    2. 7.2 Current Detection Result
      1. 7.2.1 Test Under 25°C
      2. 7.2.2 Test Under 0°C
      3. 7.2.3 Test Under 50°C
      4. 7.2.4 Conclusion
    3. 7.3 Current Consumption Test
  11. 8Solution Summery and Improvement Direction
    1. 8.1 Shunter Resistor
    2. 8.2 ADC and its Reference
    3. 8.3 Runtime Calibration

5.3.2 OPA1 Voffset calibration

The reason to do Voffset calibration is that you want to reduce its influence when calibrating R3/(R4+R3). For more information, see structure 2 in Figure 5-4. You will change the signal connection on the OPA1 input, from GND(MSEL) and PA18(PSEL) to OPA0 output (MSEL and PSEL). By comparing the voltage at OPA0 and OPA1 output, you know the OPA1 output offset. In this demo, two different GAIN settings are used, you need to do two offset calibrations as well. Equation 7 shows the equation based on ADC detected numbers.

Equation 7. NVoffset=NA13- NA12

Although this adds some gain error as the R3 value will be a little different with difference structures, the key reason why we change the structure is that the Voffset error is acceptable as the output voltage offset is small after choopering, and a DAC offset is needed as the voltage offset can be bidirectional.