TIDUF39 March   2025

 

  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 DAC70502: Dual-Channel, 1-LSB INL, 14-Bit, SPI Voltage-Output Digital-to-Analog Converter (DAC)
      2. 2.3.2 INA818: 35μV Offset, 8nV/√Hz Noise, Low-Power, Precision Instrumentation Amplifier
      3. 2.3.3 OPA192: High-Voltage, Rail-to-Rail Input/Output, 5µV, 0.2µV/°C, Precision Operational Amplifier
      4. 2.3.4 LM5146: 100V Synchronous Buck DC/DC Controller With Wide Duty Cycle Range
  9. 3System Design Theory
    1. 3.1 Constant Current Control Design
    2. 3.2 Constant Current and Voltage Simulation
  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 Constant Current Test Setup
      2. 4.3.2 Constant Voltage Test Setup
    4. 4.4 Test Results
      1. 4.4.1 Current Control Accuracy
      2. 4.4.2 Voltage Control Accuracy
      3. 4.4.3 CC, CV Transformation
      4. 4.4.4 Constant Current Transient Response
      5. 4.4.5 Constant Voltage Transient Response
      6. 4.4.6 Voltage Ripple at Short Circuit
      7. 4.4.7 Tracking DC-DC output
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

4.3.1 Constant Current Test Setup

Figure 4-3 shows the hardware setup to test the constant current charging performance.

TIDA-010089 Constant Current Charging Figure 4-3 Constant Current Charging

Given the capability of the design to source up to 120W of power, the input power supply needs to provide sufficient power to support the charge mode. The output electronic load (e-load) simulates the battery charging process. Set the e-load to CV mode and make sure the voltage value is lower than the output voltage set by DAC. At start-up, VSET is at 2.5V which makes the output voltage 10V at open load. Without modifying the VSET, set the e-load to less than 10V.

Connect a multimeter across the current shunt resistor on the board by placing the positive probe on TP9 and the negative probe on TP10 to measure the voltage across the sense resistor. This voltage can be utilized to calculate the output current. Using a 6.5-digits multimeter is recommended for precise measurements in the microvolt range. Due to offset in the sense resistor and the gain resistor for INA818, the calculated current across the shunt can exhibit a slight variation of 1mA to 2mA.

After completing the hardware setup, turn on the input power supply only, and observe the e-load voltage reading. At this point the e-load is acting as a multimeter measuring the open load voltage. The reading can drop to zero volts from some voltage, due to the current loop being active initially, driven by offsets in the cascading op amps and feedback resistors. At this point, the Constant Current (CC) loop has a lower voltage level and takes control of the system. Increase the IREF by applying any code of ISET which is greater than mid-voltage can pull the voltage control signal across D3, enabling the Constant Voltage (CV) loop to take control of the system.

Figure 4-4 shows the hardware setup used to test the CC discharging performance.

TIDA-010089 Constant Current Discharging Figure 4-4 Constant Current Discharging

Similar to the CC loop setup at positive current, the only difference lies in replacing the output e-load with a power supply. When the fan is off, configure the power supply within the 8W limit. When the fan is active, the output supply can be set within the 20W limit to align with the maximum heat dissipation of the design. Make sure that at full negative current range, the voltage of the power supply does not exceed 2.5V to prevent power dissipation of more than 20W.