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

1 System Description

Single or multi-turn absolute rotary angle encoders are used in many applications such as servo drives and robotics, where an absolute mechanical angle position is required. Absolute encoders typically offer a serial unidirectional or bidirectional half-duplex or full-duplex RS485 interface with vendor specific or open encoder protocols.

This reference design demonstrates a small form-factor absolute single-turn magnetic rotary angle encoder circuit design using on-axis sensing, as shown in Figure 1-1. A circular disc magnet is mounted to the end of the rotating shaft of the encoder. A static PCB with the TMAG6180-Q1 high-precision analog AMR 360° angle sensor is mounted on-axis with configurable air gap from the top of the AMR sensor package to the circular disc magnet. The effective air gap includes the location of the AMR and Hall sensor inside the IC package. The integrated two independent Hall sensor outputs at X and Y axes are used to extend the angle range of the sensor to 360° mechanically.

TIDA-010947 On-Axis Magnetic Angle Sensing Principle Figure 1-1 On-Axis Magnetic Angle Sensing Principle

The TMAG6180-Q1 features integrated signal conditioning amplifiers and provides differential sine and cosine analog outputs related to the direction of the applied in-plane magnetic field.

A Cortex M0 MCU MSPM0G3507 with 4MSPS dual sampling 12-bit ADC with up to 128-times hardware integrated averaging enables low noise and low latency absolute angle calculation and a 4-Mbaud UART for high-speed rotary angle data transmission. The absolute encoder circuit design offers a bidirectional interface using a half-duplex RS-485 transceiver with integrated 120Ω switchable termination in a small 10-VSON package. A 5V supply with ±10% tolerance is required to power the absolute encoder circuit.