SLVSFR9B September   2021  – August 2022 LM74722-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Dual Gate Control (GATE, PD)
        1. 8.3.1.1 Reverse Battery Protection (A, C, GATE)
        2. 8.3.1.2 Load Disconnect Switch Control (PD)
        3. 8.3.1.3 Overvoltage Protection and Battery Voltage Sensing (VSNS, SW, OV)
      2. 8.3.2 Boost Regulator
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical 12-V Reverse Battery Protection Application
      1. 9.2.1 Design Requirements for 12-V Battery Protection
        1. 9.2.1.1 Automotive Reverse Battery Protection
          1. 9.2.1.1.1 Input Transient Protection: ISO 7637-2 Pulse 1
          2. 9.2.1.1.2 AC Super Imposed Input Rectification: ISO 16750-2 and LV124 E-06
          3. 9.2.1.1.3 Input Micro-Short Protection: LV124 E-10
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Design Considerations
        2. 9.2.2.2 Boost Converter Components (C2, C3, L1)
        3. 9.2.2.3 Input and Output Capacitance
        4. 9.2.2.4 Hold-Up Capacitance
        5. 9.2.2.5 Overvoltage Protection and Battery Monitor
        6. 9.2.2.6 MOSFET Selection: Blocking MOSFET Q1
        7. 9.2.2.7 MOSFET Selection: Load Disconnect MOSFET Q2
        8. 9.2.2.8 TVS Selection
      3. 9.2.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
    1. 10.1 Transient Protection
    2. 10.2 TVS Selection for 12-V Battery Systems
    3. 10.3 TVS Selection for 24-V Battery Systems
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Receiving Notification of Documentation Updates
    2. 12.2 Support Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.2.6 MOSFET Selection: Blocking MOSFET Q1

For selecting the blocking MOSFET Q1, important electrical parameters are the maximum continuous drain current ID, the maximum drain-to-source voltage VDS(MAX), the maximum drain-to-source voltage VGS(MAX), and the maximum source current through body diode and the drain-to-source ON resistance RDSON.

The maximum continuous drain current, ID, rating must exceed the maximum continuous load current.

The maximum drain-to-source voltage, VDS(MAX), must be high enough to withstand the highest differential voltage seen in the application. This includes all the automotive transient events and any anticipated fault conditions. TI recommends to use MOSFETs with VDS voltage rating of 60 V along with a single bidirectional TVS or a VDS rating 40-V maximum rating along with two unidirectional TVS connected back-to-back at the input.

The maximum VGS LM74722-Q1 can drive is 14 V, so a MOSFET with 15-V minimum VGS rating must be selected. If a MOSFET with < 15-V VGS rating is selected, a Zener diode can be used to clamp VGS to safe level, but this results in increased IQ current.

To reduce the MOSFET conduction losses, lowest possible RDS(ON) is preferred, but selecting a MOSFET based on low RDS(ON) cannot always be beneficial. Higher RDS(ON) provides increased voltage information to the LM74722-Q1 reverse comparator at a lower reverse current. Reverse current detection is better with increased RDS(ON). Choosing a MOSFET with < 50-mV forward voltage drop at maximum current is a good starting point. Based on the design requirements, BUK7Y4R8-60E MOSFET is selected