TIDUF97 September   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 Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 TMAG6180-Q1
      2. 2.3.2 MSPM0G3507
      3. 2.3.3 THVD1454
  9. 3System Design Theory
    1. 3.1 Hardware Design
      1. 3.1.1 Angle Sensor Schematic Design
      2. 3.1.2 MSPM0G3507 Schematic Design
      3. 3.1.3 RS485 Transceiver Schematic Design
      4. 3.1.4 Power Supply and Reference Voltage
    2. 3.2 Software Design
      1. 3.2.1 Angle Calculation Timing
      2. 3.2.2 Rotary Angle Calculation
      3. 3.2.3 Rotary Angle Error Sources and Compensation
      4. 3.2.4 Encoder Communication Interface
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 PCB Overview
      2. 4.1.2 Encoder and JTAG Interface
      3. 4.1.3 Software Requirements
    2. 4.2 Test Setup
    3. 4.3 Test Results
      1. 4.3.1 AMR Sensor Sin and Cos Outputs Measurement
      2. 4.3.2 Static Angle Noise Measurement
      3. 4.3.3 Rotary Angle Accuracy Measurement
        1. 4.3.3.1 Impact of Airgap on Noise, Harmonics, and Total Angle Accuracy
      4. 4.3.4 RS485 Interface and Signal Integrity
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout
      4. 5.1.4 Altium Project Files
      5. 5.1.5 Gerber Files
      6. 5.1.6 Assembly Drawings
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Authors

4.3.1 AMR Sensor Sin and Cos Outputs Measurement

Figure 4-4 and Figure 4-5 show the AMR sensor sine and cosine signals converted to single-ended at the input of the MSPM0G3507 ADCs over half a mechanical revolution from 0 to 180 degree mechanically. The signals are biased to 1.65V and the peak to peak amplitude is around 2V. The maximum voltage is around 2.65V, the minimum voltage is around 0.65V. The full-scale input range of the MSPM0 internal ADC is 3.3V using external REF3533 reference. That means the AMR sensors use 62% of the full-scale range giving enough headroom for signal chain gain and offset changes.

TIDA-010947 Single-Ended AMR Sensor Sine Waveform at the MSPM0 ADC1 InputFigure 4-4 Single-Ended AMR Sensor Sine Waveform at the MSPM0 ADC1 Input
TIDA-010947 Single-Ended AMR Sensor Cosine Waveform at the MSPM0 ADC0 InputFigure 4-5 Single-Ended AMR Sensor Cosine Waveform at the MSPM0 ADC0 Input

To measure the signal to noise ratio and effective number of bits, 2000 consecutive of the sine and cosine signals where measured at a 32kHz sample rare and a fixed angle.

The following two figures show the offset corrected sine and cosine signals in the time domain over 62.5ms. The 1.65V bias voltage was subtracted from the corresponding A/D converted sine and cosine input signal. The peak to peak noise is within 0.6mV. Figure 4-6 and Figure 4-7 show the corresponding histogram of the sine and cosine signal.

TIDA-010947 Sine Voltage Signal of AMR Sensor at Mechanical Angle of 67.48 deg With Bias Voltage CorrectionFigure 4-6 Sine Voltage Signal of AMR Sensor at Mechanical Angle of 67.48 deg With Bias Voltage Correction
TIDA-010947 Cosine Voltage Signal of AMR Sensor at Mechanical Angle of 67.48 deg With Bias Voltage CorrectionFigure 4-7 Cosine Voltage Signal of AMR Sensor at Mechanical Angle of 67.48 deg With Bias Voltage Correction
TIDA-010947 Histogram Sin Signal, 2000 SamplesFigure 4-8 Histogram Sin Signal, 2000 Samples
TIDA-010947 Histogram Cos Signal, 2000 SamplesFigure 4-9 Histogram Cos Signal, 2000 Samples

The standard deviation, signal-to-noise ratio (SNR) and effective number of bits (ENOB) versus full-scale range are shown in Table 4-4. With the ADC in 64-times averaging mode the SIN signal’s ENOB is 13.3 bit, the COS is 13 bit.

Table 4-4 Standard Deviation, SNR and ENOB versus TMAG6180 Full Scale Range
Parameter X-axis Y-axis Comment
Standard deviation [mV] 0.082 0.101 RMS
Sin/Cos amplitude [V] 1 1 peak
SNR [dB] 81.7 80 dB
ENOB [bit] 13.3 13 Bit