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

1 System Description

High voltage interlock loop (HVIL) is a safety feature within hybrid or electric vehicles (HEV, EVs) that protects people that come in contact with the connectors to the high voltage battery during normal operation, maintenance, or repair. The HVIL system monitors the integrity of the physical connection of the cables between the high voltage battery and various subsystems throughout the vehicle. The HVIL system indicates which of the following states the high voltage connectors are in: closed connection (normal operation), open connection (an intentional battery disconnect during maintenance or unintentional disconnect due to a faulty connection), short to battery, or short to ground states.

HVIL connectors are designed in a way that keeps the HVIL signal circuit independent of the high voltage power delivery circuit. As the connector is unplugged, the HVIL signal circuit opens before the high voltage power delivery. The HVIL circuitry alerts the battery management system (BMS) of an open connection and allows the BMS to immediately shut off the high voltage power to prevent arcing during disconnect. This also protects against a floating high voltage for a loose wire.

This working principle of an HVIL system consists of a low voltage, constant current signal that independently runs through the cable between the high voltage battery and subsystem. The HVIL design consists of a constant current generator, a current sensing block, the load connectors and clamps, a modified window comparator, and digital logic gates. The design and implementation of each of these blocks is detailed throughout this reference design.

In addition to automotive systems, HVIL is also implemented in various industrial applications that operate with high voltages, such as heavy machinery factory installations, high-voltage smart grids, and relevant applications where there are heavy electrical installations or setups. HVIL is used to avoid damage to a person and equipment when the system is under use.

As Figure 1-1 shows, multiple subsystems can be connected in to the HVIL circuitry in series. In the example image, the traction inverter, DC-DC converters, and onboard charger all operate at a high voltage and need to have an interlock loop. Alternatively, these subsystems can each have a unique HVIL circuitry that is only connected to one subsystem at a time.

TIDA-020069 Typical Interlock System Figure 1-1 Typical Interlock System