SNOSDB7 December   2020 LM74500-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. Typical Characteristics
  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 Gate Driver
      4. 8.3.4 Enable
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Conduction Mode
  9. Application and Implementation
    1. 9.1 Reverse Battery Protection for Automotive Body Control Module Applications
    2. 9.2 Reverse Polarity Protection
    3. 9.3 Application Information
      1. 9.3.1 Typical Application
        1. 9.3.1.1 Design Requirements
        2. 9.3.1.2 Detailed Design Procedure
          1. 9.3.1.2.1 Design Considerations
          2. 9.3.1.2.2 MOSFET Selection
          3. 9.3.1.2.3 Charge Pump VCAP, Input and Output Capacitance
        3. 9.3.1.3 Selection of TVS Diodes for 12-V Battery Protection Applications
        4. 9.3.1.4 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications
        5. 9.3.1.5 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 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

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. It is recommended to use MOSFETs with voltage rating up to 60-V maximum with the LM74500-Q1 because SOURCE pin maximum voltage rating is 65-V. The maximum VGS LM74500-Q1 can drive is 13 V, so a MOSFET with 15-V minimum VGS rating should be selected. If a MOSFET with VGS rating < 15 V is selected, a zener diode can be used to clamp VGS to safe level. During startup, inrush current flows through the body diode to charge the bulk hold-up 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, lowest possible RDS(ON) is preferred.

Based on the design requirements, preferred MOSFET ratings are:

  • 60-V VDS(MAX) and ±20-V VGS(MAX)

DMT6007LFG MOSFET from Diodes Inc. is selected to meet this 12-V reverse battery protection design requirements and it is rated at:

  • 60-V VDS(MAX) and ±20-V VGS(MAX)
  • RDS(ON) 6.5-mΩ typical and 8.5-mΩ maximum rated at 4.5-V VGS to ensure lower power dissipationa cross the FET

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