TIDUF88 October   2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Accuracy of Bus Voltage Measuring
      2. 2.2.2 Shunt Current Measuring
      3. 2.2.3 Insulation Impedance Monitor
    3. 2.3 Highlighted Products
      1. 2.3.1 BQ79731-Q1
      2. 2.3.2 TPSI2140-Q1
      3. 2.3.3 ISO7841
      4. 2.3.4 SN6507
      5. 2.3.5 TPS7B6950
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Bus Voltage Accuracy
      2. 3.3.2 Current Sensing Accuracy
      3. 3.3.3 Insulation Impedance Accuracy
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author

2.1 Block Diagram

Figure 2-1 shows the high-voltage BMS block diagram. BMS is divided into three individual reference designs: TIDA-010271 for the battery monitor unit (BMU) in pack, TIDA-010253 for the battery control unit (BCU), and TIDA-010272 for the high-voltage monitor unit (HMU).

TIDA-010272 BMS Block Diagram Figure 2-1 BMS Block Diagram

Figure 2-2 shows the TIDA-010272 block diagram. BQ79731 uses four channels of general purpose input/output (GPIO) and VF analog-to-digital converter (ADC) inputs to measure the test point of BAT+, RACK+, RACK–, and VN. VN is voltage between PE and BAT–. The resistor ladders are designed with 1500V bus voltage and the input range of ADC reference.

TIDA-010272 TIDA-010272 Block Diagram Figure 2-2 TIDA-010272 Block Diagram

The BQ79731 device provides two separate channels of current sense ADC (CSADC) to measure the shunt current. The shunt is not mounted on the board, requiring a real shunt or shunt simulator to give out the differential cross voltage to CSADC input. The BQ79731 also provides two thermistor inputs to enable the calibration of temperature shift either for shunt or CSADC.

The BQ79731, TPSI2140, and switch (SW) together, and form an asymmetric insulation impedance detection circuit. The high-side TPSI2140 is used to change the resistance between BAT+ and PE by adding or not adding the RH resistor, which can create two equations between RisoP, RisoN, VN, and VBAT. VBAT is the rack voltage. VN and VBAT can be measured in a switching duty cycle of TPSI2140. This can enable the calculation of RisoP and RisoN.