TIDUF65 March   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Consideration
    3. 2.3 Highlighted Products
      1. 2.3.1 TMCS1123
      2. 2.3.2 ADS7043
      3. 2.3.3 AMC1035
      4. 2.3.4 REF2033
  9. 3System Design Theory
    1. 3.1 Hall-Effect Current Sensor Schematic Design
    2. 3.2 Analog-to-Digital Converter
      1. 3.2.1 Delta-Sigma Modulator
        1. 3.2.1.1 Common-Mode Voltage Limit
        2. 3.2.1.2 Input Filter
        3. 3.2.1.3 Interface to MCU
      2. 3.2.2 12-bit SAR ADC
        1. 3.2.2.1 Common-Mode Voltage Limit
        2. 3.2.2.2 Input Filter
        3. 3.2.2.3 Interface to MCU
    3. 3.3 Power Supply and Reference Voltage
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
    2. 4.2 Software Requirements
    3. 4.3 Test Setup
      1. 4.3.1 Precautions
    4. 4.4 Test Results
      1. 4.4.1 DC Performance
        1. 4.4.1.1 Output Voltage Noise and ENOB After A/D Conversion
        2. 4.4.1.2 Linearity and Temperature Drift
      2. 4.4.2 AC Performance
        1. 4.4.2.1 SNR Measurement
        2. 4.4.2.2 Latency Test
      3. 4.4.3 PWM Rejection
      4. 4.4.4 Overcurrent Response
      5. 4.4.5 Adjacent Current Rejection
      6. 4.4.6 Power Supply Rejection Ratio
      7. 4.4.7 Digital Interface
  11. 5Performance Comparison with Competitor’s Device
    1. 5.1 Effective Number of Bits
    2. 5.2 Latency
    3. 5.3 PWM Rejection
  12. 6Design and Documentation Support
    1. 6.1 Design Files
      1. 6.1.1 Schematics
      2. 6.1.2 BOM
      3. 6.1.3 PCB Layout Recommendations
        1. 6.1.3.1 Layout Prints
    2. 6.2 Tools and Software
    3. 6.3 Documentation Support
    4. 6.4 Support Resources
    5. 6.5 Trademarks
  13. 7About the Author

4.4.3 PWM Rejection

During PWM switching, the phase current suffers large common-mode voltage transients of up to 10kV/μs with an IGBT based 3-phase inverter, which can affect the accuracy of current sensor. Therefore the PWM rejection, also called common-mode transient immunity (CMTI) is an important parameter to provide accurate current measurement. To test the PWM rejection of the TMCS1123, a 3-phase inverter with 320VDC bus (TIDA-010025) and an AC motor were used. The TMCS1123 on the TIDA-010937 was connected to the phase U of the 3-phase inverter and the software on the C200 MCU was configured to sample the phase current with the ADS7043 data converter over 1200 PWM periods, while continuously changing the start of conversion time of the ADC from the beginning of the PWM cycle to the end of the PWM cycle increasing the system-on-chip (SoC) in 60ns steps every new PWM cycle. This results in an equivalent 16MHz sampled current measurement over one PWM period. To make sure the current does not change over the 1200 PWM periods (10kHz PWM period), the current was impressed to 3A DC. The test setup is shown in Figure 4-13.

GUID-20240201-SS0I-TW6L-1RB4-RG6NL4GLWJCQ-low.svg Figure 4-13 TMCS1123 PWM Rejection Test Setup

In Figure 4-14, the blue curve is the oscilloscope waveform of the output voltage and the red curve is the input current of the TMCS1123 measured with a current probe. The TIDA-010025 outputs a 3A average DC current. The small transient noise spikes are due to the oscilloscope being sensitive to the IGBT inverter PWM switching.

GUID-20240201-SS0I-MQ3Z-3ZPD-2NTCGC07JJTT-low.png Figure 4-14 Oscilloscope Measurement of Output Voltage and Input Current of TMCS1123

Figure 4-15 shows the phase-current measurement (blue using the ADS7043 SAR ADC as explained earlier). The blue curve is the waveform of the U phase current measured with the time triggered ADS7043, as described earlier (16MHz equivalent sample rate) and the red curve is U phase voltage waveform. There is no ringing during PWM switching on the TMCS1123 output; therefore, the TMCS1123 also retains high accuracy during the PWM switching.

GUID-20240201-SS0I-PS6J-JW26-FN7TMWDRZFCL-low.png Figure 4-15 TMCS1123 Current Over One PWM Cycle Samples With Time Triggered ADS7043 ADC