SLVSFH8B September   2021  – March 2022 LM74720-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)
      2. 8.3.2 Overvoltage Protection and Battery Voltage Sensing (VSNS, SW, OV)
      3. 8.3.3 Boost Regulator
    4. 8.4 Device Functional Mode (Shutdown Mode)
  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
      2. 9.2.2 Automotive Reverse Battery Protection
        1. 9.2.2.1 Input Transient Protection: ISO 7637-2 Pulse 1
        2. 9.2.2.2 AC Super Imposed Input Rectification: ISO 16750-2 and LV124 E-06
        3. 9.2.2.3 Input Micro-Short Protection: LV124 E-10
      3. 9.2.3 Detailed Design Procedure
        1. 9.2.3.1 Design Considerations
        2. 9.2.3.2 Boost Converter Components (C2, C3, L1)
        3. 9.2.3.3 Input and Output Capacitance
        4. 9.2.3.4 Hold-Up Capacitance
        5. 9.2.3.5 Overvoltage Protection and Battery Monitor
        6. 9.2.3.6 MOSFET Selection: Blocking MOSFET Q1
        7. 9.2.3.7 MOSFET Selection: Load Disconnect MOSFET Q2
        8. 9.2.3.8 TVS Selection
      4. 9.2.4 Application Curves
    3. 9.3 Do's and Don'ts
  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 Third-Party Products Disclaimer
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.3.3 Boost Regulator

The LM74720-Q1 integrates a boost converter to provide voltage necessary to drive the external N-channel MOSFETs for the ideal diode and the load disconnect stages. The boost converter uses hysteretic mode control scheme for the output voltage (VCAP–VVS) regulation along with the constant peak inductor current limit (ILX). When the CAP–VS voltage is below its nominal value of typically 11.9 V, the low side switch of the boost is turned on and the inductor current rises with the slope of VS/L approximately. After the current hits the limit of ILX, that is,140 mA (typical), then the low side switch is turned off and the inductor current discharges to the output till it reaches zero. The low side switch is turned on again and the switching cycle repeats until the CAP–VS voltage has risen above the boost rising threshold of 13 V (typical). After this threshold level is reached, the boost converter switching is turned OFF to reduce the quiescent current.

For the boost converter to be enabled, the EN pin voltage must be above the specified input high threshold, V(ENR). The boost converter has a maximum output load capacity of 29-mA typical. If EN pin is pulled low, then the boost converter remains disabled.