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

9.2.2.4 Hold-Up Capacitance

Usually, bulk capacitors are placed on the output due to various reasons, such as uninterrupted operation during power interruption or micro-short at the input, holdup requirements for doing a memory dump before turning of the module, and filtering requirements as well. This design considers minimum bulk capacitors requirements for meeting functional status A during LV124 E10 test case 2 100-µs input interruption. To achieve functional pass status A, acceptable voltage drop in the output of LM74722-Q1 is based on the UVLO settings of downstream DC/DC converters. For this design, 2.5-V drop in output voltage for 100 µs is considered and the minimum holdup capacitance required is calculated by

Equation 3.

Minimum holdup capacitance required for 1-V drop in 100 µs is 470 µF.