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

2.3.2.2 Open Connection State

The TIDA-020069 is in an open connection state when one of the high-voltage connectors was disconnected or there is an open connection throughout the interlock loop. During this state, the onboard LED marked Open Connection is turned on, as shown in the test results image. An open load condition can happen due to a service disconnect switch, disconnecting the high-voltage connectors, or due to a loose connection in the wiring harness. An unintentional open load, which can result from collision or fault connectors, can be difficult to locate because the behavior is the same regardless of where in the loop the open occurs. During this state, the high-voltage battery of the HEV/EV is disabled, as the TIDA-020069 is indicating an improper connection of high-voltage connectors.

Figure 2-16 illustrates the expected behavior of HVIL-Send and HVIL-Return during an open load state. The high-voltage connectors are modeled as resistors that have an open between them. This open can occur at any point within the interlock loop: before the load, between load resistors, or after the load. In this state, no current flows through the interlock loop, as shown by a change in the CS-Output current sensing test point.

TIDA-020069 Interlock Line Open Load Figure 2-16 Interlock Line Open Load

In an open connection state, HVIL-Send is expected to be greater than the Upper Threshold voltage level set by the Section 2.3.1.4 circuit stage, while HVIL-Return is expected to be less than the Lower Threshold voltage level. The differential voltage between HVIL-Send and HVIL-Return increases during this state, as HVIL-Send is pulled closer to the 5V VCC supply voltage coming from the TPS7B69-Q1 and HVIL-Return is pulled closer towards ground. HVIL-Return is not pulled entirely to ground in this case because HVIL-Return is connected to ground through the collector of the BJT transistor in the Section 2.3.1.1 circuit. The input voltage, VIN, to the non-inverting input terminal of the TLV9002-Q1 used in the Section 2.3.1.1 circuit was set to 1V. This voltage is reflected onto the input of the inverting terminal, via the concept of virtual short in a closed feedback system, and is connected to the emitter of the BJT. Therefore, the value of HVIL-Return, which is connected to the collector of the BJT, is:

Equation 10. VHVIL-Return=VIN-+VCE-SAT=VIN++VCE-SAT=Vi×R2R1+R2+VCE-SAT

The TIDA-020069 is designed to allow for flexibility to accommodate various OEM requirements for HVIL systems. Many variables can be adjusted to meet the requirements for each system, including: loop current (ILOAD), loop resistance (RLOAD), and supply voltage. However, the TIDA-020069 requires that the Lower Threshold voltage set in the Modified Window Comparator stage is greater than this HVIL-Return voltage calculated during the open condition. The resistor divider that sets Lower Threshold must yield a higher voltage than the resistor divider that sets VIN+ to the TLV9002-Q1.