SNOSD98A May   2020  – December 2020 LM7481-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 Charge Pump
      2. 8.3.2 Dual Gate Control (DGATE, HGATE)
        1. 8.3.2.1 Reverse Battery Protection (A, C, DGATE)
        2. 8.3.2.2 Load Disconnect Switch Control (HGATE, OUT)
      3. 8.3.3 Over Voltage Protection and Battery Voltage sensing (VSNS, SW, OV)
      4. 8.3.4 Low Iq Shutdown and Under Voltage Lockout (EN/UVLO)
    4. 8.4 Device Functional Modes
    5. 8.5 Application Examples
      1. 8.5.1 Redundant Supply OR-ing with Inrush Current Limiting, Over Voltage Protection and ON/OFF Control
  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
      3. 9.2.3  Input Transient Protection: ISO 7637-2 Pulse 1
      4. 9.2.4  AC Super Imposed Input Rectification: ISO 16750-2 and LV124 E-06
      5. 9.2.5  Input Micro-Short Protection: LV124 E-10
      6. 9.2.6  Detailed Design Procedure
        1. 9.2.6.1 Design Considerations
        2. 9.2.6.2 Charge Pump Capacitance VCAP
        3. 9.2.6.3 Input and Output Capacitance
        4. 9.2.6.4 Hold-up Capacitance
        5. 9.2.6.5 Over Voltage Protection and Battery Monitor
      7. 9.2.7  MOSFET Selection: Blocking MOSFET Q1
      8. 9.2.8  MOSFET Selection: Hot-Swap MOSFET Q2
      9. 9.2.9  TVS selection
      10. 9.2.10 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 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

9.2.6.5 Over Voltage Protection and Battery Monitor

Resistors R1, R2 and R3 connected in series are used to program the over voltage threshold and battery monitor ratio. The resistor values required for setting the over voltage threshold VOV to 37.0 V and battery monitor ratio VBATT_MON : VBATT to 1:8 are calculated by solving Equation 4 and Equation 5.

Equation 4. GUID-18F46F9E-F9EB-4661-B929-E9DC42EBB577-low.gif
Equation 5. GUID-F0C00C2A-6435-4951-9B77-93F956A27999-low.png

For minimizing the input current drawn from the battery through resistors R1, R2 and R3, it recommended to use higher value of resistance. Using high value resistors will add error in the calculations because the current through the resistors at higher value will 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 4 gives R3 = 3.45 kΩ. Solving Equation 5 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.