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

4.4.6 Power Supply Rejection Ratio

Power supply noise usually adds extra noise on the output voltage of the Hall sensor, which reduces the accuracy of the sensor. Power supply rejection ration (PSRR) is an important parameter for Hall sensors. In PSRR tests, a 300mV, 100kHz peak-to-peak ripple is injected to the TMCS1123 supply voltage. The output voltage ripple of the TMCS1123 shows the ability to reject the power supply ripple. In this test, a DC power supply and signal generator are used to generate this ripple. The block diagram is shown as Figure 4-24.

GUID-20240201-SS0I-HHH5-FKHH-6ZBQQHLWLVWB-low.svg Figure 4-24 PSRR Test Setup

In Figure 4-25, the purple curve is the injected voltage ripple with a 320mV peak-to-peak value and 100kHz frequency. The scope plot shows the both the reference voltage VREF and output voltage VOUT of TMCS1123 have the same frequency ripple. Record the VREF and VOUT in 100ms, measure the peak-to-peak value of the waveform in 100ms and compare the value with the results under no power-supply ripple.

GUID-20240201-SS0I-JDPG-HZC6-SSXDB5HKFHBB-low.png Figure 4-25 Power Supply Ripple, Reference Voltage, Output Voltage Waveform

The results are shown in Figure 4-26 and Figure 4-27.

GUID-20240201-SS0I-VX95-MJBV-M9H8QSDB0RPR-low.pngFigure 4-26 TMCS1123 Output Voltage vs GND at High Supply Voltage Ripple
GUID-20240201-SS0I-TNK5-XXJC-KFWH2QFJ1NVJ-low.pngFigure 4-27 TMCS1123 Output Voltage vs VREF High-Supply Voltage Ripple

When the power supply ripple is added, the ripple of VOUT is 94mVPP and differential output voltage ripple of VOUT – VREF is 80mV, the differential output helps TMCS1123 to reduce output noise brought by power supply ripple and improve the measurement accuracy.

Plot the sampling data of the ADS7043 and AMC1035, which is shown in Figure 4-28 to Figure 4-31.

GUID-20240201-SS0I-LNBT-NW8F-Q46BJ1GRFGMS-low.pngFigure 4-28 Output Noise With Supply Voltage Ripple (Sampled With ADS7043 at 10kHz)
GUID-20240201-SS0I-M8N4-TTZM-HLVM1SB95DLD-low.pngFigure 4-29 Output Noise no Supply Voltage Ripple (Sampled With ADS7043 at 10kHz)
GUID-20240201-SS0I-BJWS-P4KW-QKPDLGTKXXKR-low.pngFigure 4-30 Output Noise With Supply Voltage Ripple (Sampled With AMC1035 at 10kHz)
GUID-20240201-SS0I-FPX7-XKKF-7W3BSQDPBVRB-low.pngFigure 4-31 Output Noise With no Supply Voltage Ripple (Sampled With AMC1035 at 10kHz)

For ADS7043, the peak-to-peak noise is around 600mA and for AMC1035, the value is around 450mA. These results are consistent with DC noise test results in Section 4.4.1.1. Using Delta-Sigma modulators can further reduce the influence from the power supply ripple.

The results show spectral aliasing due to higher signal frequency (100kHz) than sampling frequency (10kHz).