TIDUF61 May   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 Highlighted Products
      1. 2.2.1 TLV9002-Q1
      2. 2.2.2 TLV9034-Q1
      3. 2.2.3 TPS7B69-Q1
      4. 2.2.4 SN74HCS08-Q1
      5. 2.2.5 SN74HCS86-Q1
    3. 2.3 System Design Theory
      1. 2.3.1 TIDA-0020069 Operation
        1. 2.3.1.1 Constant Current Source
          1. 2.3.1.1.1 Design Goals
          2. 2.3.1.1.2 Design Description
          3. 2.3.1.1.3 Design Notes
          4. 2.3.1.1.4 Design Steps
        2. 2.3.1.2 Current Sensing
          1. 2.3.1.2.1 Design Goals
          2. 2.3.1.2.2 Design Description
          3. 2.3.1.2.3 Design Steps
        3. 2.3.1.3 Load Connections and Clamps
        4. 2.3.1.4 Modified Window Comparator
        5. 2.3.1.5 Digital Logic Gates
      2. 2.3.2 Status Indication
        1. 2.3.2.1 Normal Operation (Closed Connection) State
        2. 2.3.2.2 Open Connection State
        3. 2.3.2.3 Short-to-Battery State
        4. 2.3.2.4 Short-to-Ground State
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Normal Operation (Closed Connection) Test Results
      2. 3.3.2 Open Connection Test Results
      3. 3.3.3 Short-to-Battery Test Results
      4. 3.3.4 Short-to-Ground Test Results
      5. 3.3.5 Disable (Shutdown) Test Results
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  11. 5Tools and Software
  12. 6Documentation Support
  13. 7Support Resources
  14. 8Trademarks
  15. 9About the Author

2.3.1.2 Current Sensing

Current sensing is a critical element for automotive HVIL designs. In the past, current sensing was the primary mode of detecting a closed connection in the HVIL loop compared to an open connection. Measuring current across a shunt resistor indicates a closed connection where current is flowing. Conversely, a lack of current indicates an open connection during a battery disconnect scenario. However, a design that only relies on current sensing does not account for fault conditions when a short occurs throughout the load. For example, when the HVIL-Send and HVIL-Return pins are shorted together, current flows across the current sensing shunt resistor regardless of whether the load is closed (normal operation) or open (battery disconnect). This is why it is important to account for the voltage values of HVIL-Send and HVIL-Return by measuring these voltages and comparing against predetermined thresholds. For this reference design, the current sensing circuitry provides redundancy to improve the overall safety of the system. The output voltage of the current sensing circuitry can also be used as feedback to the constant current generation for precision designs that require accurate, regulated HVIL currents.

This design features a high-side current sensing circuit with respect to the constant current sink generator. The shunt resistor is placed between the HVIL-Return signal and collector of the BJT in the constant current generator circuit. One channel of the TLV9002-Q1 is configured as a difference amplifier across the shunt resistor.

The schematic Figure 2-10 features the TLV9002-Q1, using one channel to measure the HVIL current. The circuit design is based on the Analog Engineer's Circuit: High-Side Current-Sensing Circuit Design. Reference this analog circuit design for more details about the circuit, including downloadable simulation models.

TIDA-020069 High-Side Current Sensing Circuit Figure 2-10 High-Side Current Sensing Circuit