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

4.4.1.1 Output Voltage Noise and ENOB After A/D Conversion

The DC noise measurement was conducted at 0A current, using ADS7043 and AMC1035 to sample the output voltage of the TMCS1123 at 10kHz, and then scale the sampled voltage to the effective input current. Figure 4-4 to Figure 4-7 show the effective output noise with TMCS1123 after A/D conversion. The effective output noise with the delta-sigma modulator AMC1035 is lower since the Sinc3 OSR 64 filter has a 80kHz cut-off frequency and hence reduce the noise floor versus the SAR ADC.

GUID-20240201-SS0I-DW3R-WDW5-FJ2FSXBK2C5J-low.pngFigure 4-4 TMCS1123B3 Effective Noise at 0A Input After A/D Conversion (ADS7043)
GUID-20240201-SS0I-1DLW-L0SC-BM30WZHPZTTX-low.pngFigure 4-5 TMCS1123B3 Effective Noise at 0A Input After A/D Conversion
(AMC1035, Sinc3 OSR64)
GUID-20240201-SS0I-2QMT-DXNP-F3HGGDJMWLLX-low.pngFigure 4-6 TMCS1123B1 Effective Noise at 0A Input After A/D Conversion (ADS7043)
GUID-20240201-SS0I-DRDP-FQDJ-RZSQZ2MDXHXN-low.pngFigure 4-7 TMCS1123B1 Effective Noise at 0A Input After A/D Conversion
(AMC1035, Sinc3 OSR64)

Calculate the ENOB according to the noise root mean square (RMS) value, the results are listed in Table 4-4.

Compare the noise results of the TMCS1123B3 and TMCS1123B1 devices, when ADS7043 is used. The input noise RMS for the B1 version is 110.13mA, 20% larger than the B3 version, but the full-scale range of the B1 version is 3 times larger, so ENOB for B1 is 8.93 bits, 1.4 bits higher than the B3 version.

Compare the results of the ADS7043 and AMC1035 devices. Using the Sinc filter can significantly help to reduce the noise for both the B1 and B3 versions. When using TMCS1123B1 and AMC1035, 64 times OSR Sinc3 filter helps reduce 38% noise and gains 0.7 bits ENOB compared with the results of the ADS7043.

Table 4-4 ENOB Test Results
DEVICE TMCS1123B3 (±22A) TMCS1123B1 (±66A)
ADC ADS7043 AMC1035
Sinc3 OSR = 64		 ADS7043 AMC1035
Sinc3 OSR = 64
Output noise

RMS/mA		 91 64 105 68
SNR /dB 48 51 56 60
ENOB (DC)/bit 7.6 8.1 9.0 9.7