SNOSD87A July   2021  – February 2022 LM74501-Q1

PRODUCTION DATA  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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. Parameter Measurement Information
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Input Voltage
      2. 8.3.2 Charge Pump
      3. 8.3.3 Enable
      4. 8.3.4 Gate Driver
      5. 8.3.5 SW (Battery Voltage Monitoring)
      6. 8.3.6 Gate Discharge Timer
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Full Conduction Mode
      3. 8.4.3 VDS Clamp
  9. Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Reverse Battery Protection
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Design Considerations
        2. 9.2.2.2 MOSFET Selection
        3. 9.2.2.3 Gate Discharge Timer Capacitor Selection (CT)
        4. 9.2.2.4 Charge Pump VCAP, Input and Output Capacitance
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 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

Package Options

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

MOSFET Selection

The important MOSFET electrical parameters are the maximum continuous drain current, ID, the maximum drain-to-source voltage, VDS(MAX), the maximum source current through body diode, and the drain-to-source on resistance, RDSON.

The maximum continuous drain current, ID, rating must exceed the maximum continuous load current. The maximum drain-to-source voltage, VDS(MAX), must be high enough to withstand the highest differential voltage seen in the application. This would include any anticipated fault conditions. As the LM74501-Q1 has an integrated VDS clamp control with threshold of 20 V (typical), MOSFETs with voltage rating of 40 V can be used with the LM74501-Q1. The maximum GATE pin voltage of the LM74501-Q1 can drive is 13.9 V, so a MOSFET with 15-V minimum VGS must be selected. If a MOSFET with < 15-V VGS rating is selected, a Zener diode can be used to clamp VGS to safe level. During start-up, inrush current flows through the body diode to charge the bulk holdup capacitors at the output. The maximum source current through the body diode must be higher than the inrush current that can be seen in the application.

To reduce the MOSFET conduction losses, the lowest possible RDS(ON) is preferred. Selecting a MOSFET with forward voltage drop of < 50 mV is a good starting point and gives good trade off between power dissipation and cost.

The BUK7Y3R0-40H MOSFET is selected to meet this 12-V reverse battery protection design requirements and it is rated at:

  • 40-V VDS(MAX) and ±20-V VGS(MAX)
  • RDS(ON) 2.55 mΩ (typical) and 3-mΩ maximum rated at 10-V VGS

Thermal resistance of the MOSFET must be considered against the expected maximum power dissipation in the MOSFET to ensure that the junction temperature (TJ) is well controlled.