TIDUF91 December   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 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 DRV3901-Q1
  9. 3System Design Theory
  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 Hardware Setup
      2. 4.3.2 USB2ANY Explorer Setup
    4. 4.4 Test Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
    2. 5.2 Tools and Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5. 5.5 Trademarks
  12. 6About the Author

1 System Description

The battery junction box of hybrid (FHEV, PHEV) and full-electric vehicles (BEV) integrates the core function of disconnecting fuses to protect the battery pack from excessive currents, permanent damage, or thermal runaway. Key requirements are fast response time, reliable deployment when requested while avoiding false triggering, and high diagnostic coverage. Compared to blow or melting fuses, pyro-fuses excel in deployment time and flexibility in defining current profiles to trigger. Also pyro-fuses can be actively triggered not only in the event of excessive pack currents but in the event of a collision.

This reference design demonstrates how to build an automotive-grade, functional safety-compliant single- or dual-squib driver design.

This design showcases a single- or dual pyro-fuse driver for automotive applications in hybrid or full-electric vehicles running from a typical 12V supply rail. The TIDA-020075 features the DRV3901 device, a single-channel, highly integrated squib driver intended for automotive EV pyro-fuse applications. The device includes the power supplies, current sensing and regulation, and diagnostics and protection functions needed to drive a squib load. The design also incorporates several key functions unique to the device that are different from traditional squib drivers. These functions include a hardware pin trigger interface, an energy reservoir capacitor diagnostic, an addressable SPI, and optimized driver stage with integrated charge pump, and additional deployment current options.

To support a diagnostic for the system energy reservoir capacitor, the DRV3901-Q1 integrates a switch and monitor circuit to be able to bias and monitor the discharge voltage of the reservoir capacitor. This enables the device and the external MCU to detect a loss or failure of the reservoir capacitor or the approximate value in normal operation.

The power stage utilizes a protected high-side and low-side switch to provide robustness against unintended driving due to a variety of fault conditions. An integrated charge pump provides minimal drop-out voltage across the switches during deployment to enable operation down to low supply voltages. A wide variety of deployment options are available to optimize for different types of squib loads or for specific application requirements.

The pyro-fuse driver can be configured, safety-monitored, and employed through an addressable SPI bus. This reduces MCU resource requirements, and when sharing the SPI bus with TI's contactor drivers (DRV3946), the design reduces further wiring. Additionally, TI’s battery pack monitors (BQ79731) are equipped with an SPI hub to further reduce wiring effort and tunnel communication through the isolated vertical interface (VIF).

The SPI incorporates multiple robustness functions including a CRC, address readback capability, and various bus fault detection mechanisms.

As an alternative trigger method, the hardware pin trigger (TRGx) interface allows for a deployment command to be issued directly in hardware to the DRV3901-Q1. This allows the flexibility to either trigger the deployment with MCU hardware pins, directly with the overcurrent function of the pack monitor (BQ79731), or through other external hardware such as the airbag collision detection. The hardware trigger pins support a 2-pin interface with both threshold or PWM-based options to provide robustness against miss deployment while still providing flexibility to support a variety of interface options.

TIDA-020075 Typical Pyro-Fuse Driver SystemFigure 1-1 Typical Pyro-Fuse Driver System