ZHCU759 July   2021

 

  1.   说明
  2.   资源
  3.   特性
  4.   应用
  5.   5
  6. 1System Description
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1  System Control and Processing
      2. 2.2.2  Analog Front End
      3. 2.2.3  Input Voltage Monitoring: 5 V, 20 V, 40 V, and ±5 V
      4. 2.2.4  Bidirectional Current Sense: ±2 A
      5. 2.2.5  Unipolar Current Sense: 0.25 A to 1 A
      6. 2.2.6  TMP461-SP: Local and Remote Temperature Sensing
      7. 2.2.7  NTC Thermistor Temperature Sensing
      8. 2.2.8  Adjustable Voltage Source
      9. 2.2.9  Fixed Output Current Source
      10. 2.2.10 Adjustable 4-mA Current Source
      11. 2.2.11 Power Tree and Power Sequencing
    3. 2.3 Highlighted Products
      1. 2.3.1  MSP430FR5969-SP
      2. 2.3.2  ADC128S102QML-SP
      3. 2.3.3  DAC121S101QML-SP
      4. 2.3.4  LMP7704-SP
      5. 2.3.5  INA901-SP
      6. 2.3.6  LM4050QML-SP
      7. 2.3.7  LM158QML-SP
      8. 2.3.8  LM139QML-SP
      9. 2.3.9  TMP461-SP
      10. 2.3.10 TPS7A4501-SP
      11. 2.3.11 TPS7H2201-SP
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Software
    2. 3.2 Test Setup
      1. 3.2.1 Voltage Monitor Test Setup
      2. 3.2.2 Current Monitor Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Voltage Measurement - Noise Floor Results
      2. 3.3.2 Voltage Measurement - Linearity Results
      3. 3.3.3 Current Measurement - Noise Floor Results
      4. 3.3.4 Current Measurement - Linearity Results
      5. 3.3.5 Analog Outputs
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 支持资源
    4. 4.4 Trademarks
  10. 5About the Author

2.2.10 Adjustable 4-mA Current Source

The adjustable current source provides up to 4 mA with a full scale accuracy of 1.5%. The circuit is adjusted by utilizing the MSP430FR5969-SP PWM output going into a passive low-pass filter that converts the PWM into a DC voltage. The DC voltage is the input to the LMP7704-SP that is configured as a voltage follower op amp that changes the gain until the voltage on the source of the transistor is equal to the DC voltage created by the low-pass filter.

Figure 2-10 shows the adjustable current source circuit.

GUID-F0E1AD63-F9FF-4717-8BFC-F6E432D7D9FE-low.gifFigure 2-10 Adjustable Current Source Circuit