JAJSMX1B September   2021  – March 2022 LM74720-Q1

PRODUCTION DATA  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
  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 サポート・リソース
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.3.5 Overvoltage Protection and Battery Monitor

Resistors R1, R2 and R3 connected in series are used to program the overvoltage threshold and battery monitor ratio. The resistor values required for setting the overvoltage threshold VOV to 37 V and battery monitor ratio VBATT_MON : VBATT to 1:8 are calculated by solving Equation 3 and Equation 4.

Equation 4. GUID-20210913-SS0I-TMMX-RN8Z-PJW0Q4QDRS31-low.gif
Equation 5. GUID-20210913-SS0I-BC3L-2CB9-M1WBKT66NPZR-low.gif

For minimizing the input current drawn from the battery through resistors R1, R2 and R3, TI recommends to use higher value of resistance. Using high value resistors adds error in the calculations because the current through the resistors at higher value become comparable to the leakage current into the OV pin. Maximum leakage current into the OV pin is 1 µA and choosing (R1 + R2 + R3) < 120 kΩ ensures current through resistors is 100 times greater than leakage through OV pin.

Based on the device electrical characteristics, VOVR is 1.23 V and battery monitor ratio (VBATT_MON / VBATT) is designed for a ratio of 1:8. To limit (R1 + R2 + R3) < 120 kΩ, select (R1 + R2) = 100 kΩ. Solving Equation 3 gives R3 = 3.45 kΩ. Solving Equation 4 for R2 using (R1 + R2) = 100 kΩ and R3 = 3.45 kΩ, gives R2 = 9.48 kΩ and R1 = 90.52 kΩ.

Standard 1% resistor values closest to the calculated resistor values are R1 = 90.9 kΩ, R2 = 9.09 kΩ, and R3 = 3.48 kΩ.