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

5.1 Effective Number of Bits

For the noise test details, see Section 4.4.1.1. For DC ENOB, the equivalent input current noise under 0A input is tested and ENOB is calculated. By recording the conversion results of the ADC, SNR and ENOB can be calculated. The test results are shown in Table 5-1.

Table 5-1 Noise and DC/AC ENOB Comparison
DEVICETMCS1123B3COMPETITOR’S DEVICE
Bandwidth250kHz120kHz
Full-Scale Range±22A±18A
ADCADS7043AMC1035
Sinc3 64OSR		ADS7043AMC1035
Sinc3 64OSR
DC PerformanceRMS /mA91648966
SNR/dB48514649
ENOB /bits7.68.17.37.8

The linear measurement range of the TMCS1123B3 is ±20.7A and the full-scale range is ±22A. The linear range takes up to 94.1% of the full-scale range, the linear measurement range of the competitor's device is ±15A and the full-scale range is ±18A. The linear range takes up to 83.3% of the full-scale range.

Even the bandwidth of the TMCS1123 (250kHz) is higher than competitor’s device (120kHz), the input current noise is almost the same which means TMCS1123 has lower noise density than competitor’s device. Adding an extra filter circuit can further improve the accuracy of the TMCS1123.