SNOSDE8A July   2023  – September 2023 LM74912-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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
  8. 7 Parameter Measurement Information
  9. 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 Short Circuit Protection (CS+, CS-, ISCP)
      4. 8.3.4 Overvoltage Protection and Battery Voltage Sensing (SW, OV, UVLO)
      5. 8.3.5 Low IQ SLEEP Mode (SLEEP, SLEEP_OV)
    4. 8.4 Device Functional Modes
  10. 9 Applications 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 Charge Pump Capacitance VCAP
        3. 9.2.3.3 Input , Supply 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 Selecting Short Circuit Current Threshold
          1. 9.2.3.6.1 Selection of Scaling Resistor RSET and RISCP for Short Circuit Protection
      4. 9.2.4 MOSFET Selection: Blocking MOSFET Q1
      5. 9.2.5 MOSFET Selection: Hot-Swap MOSFET Q2
      6. 9.2.6 TVS Selection
      7. 9.2.7 Application Curves
    3. 9.3 Best Design Practices
    4. 9.4 Power Supply Recommendations
      1. 9.4.1 Transient Protection
      2. 9.4.2 TVS Selection for 12-V Battery Systems
      3. 9.4.3 TVS Selection for 24-V Battery Systems
    5. 9.5 Layout
      1. 9.5.1 Layout Guidelines
      2. 9.5.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.3.5 Overvoltage Protection and Battery Monitor

Resistors R1, R2 and R3, R4 connected from SW pin to ground is used to program the undervoltage and overvoltage threshold. The resistor values required for setting the undervoltage threshold (VUVLO to 5.5 V) and overvoltage threshold (VOV to 37.0 V) a are calculated by solving Equation 6 and Equation 6.

Equation 6. GUID-20230630-SS0I-7RH0-CTVH-ZPFWSMWNR5SK-low.svg
Equation 7. GUID-20230630-SS0I-DKPL-WPZ4-CCZCQZF5T2CQ-low.svg

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, VUVLOF is 0.55 V. Select R1 = 100 kΩ. Solving Equation 14 gives R2 = 11.5 kΩ. Solving Equation 15 with R3 selected as 100 kΩ and VOVR = 0.6V gives R4 = 1.65 kΩ as standard 1% resistor values closest to the calculated resistor values.

An optional capacitor CUV can be placed in parallel with R2 on UVLO resistor ladder in order to filter out any fast undervoltage transients on battery lines to avoid false UVLO trigger.

For this application example separate resistor ladder is selected to program overvoltage and undervoltage threshold. However common resistor ladder from SW pin to ground can also be used as shown in Section 8.3.4