SNOSDF7A May   2023  – December 2023 LM74703-Q1 , LM74704-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  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 Input Voltage
      2. 8.3.2 Charge Pump
      3. 8.3.3 Gate Driver
      4. 8.3.4 Enable
      5. 8.3.5 FET Status Indication (FETGOOD)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Conduction Mode
        1. 8.4.2.1 Regulated Conduction Mode
        2. 8.4.2.2 Full Conduction Mode
        3. 8.4.2.3 Reverse Current Protection Mode
  10. 9 Application and Implementation
    1. 9.1 Application Information
    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 Charge Pump VCAP, Input and Output Capacitance
        4. 9.2.2.4 Selection of TVS Diodes for 12-V Battery Protection Applications
        5. 9.2.2.5 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications
      3. 9.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Documentation Support
      1. 10.1.1 Related Documentation
    2. 10.2 Receiving Notification of Documentation Updates
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  12. 11Revision History
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

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

9.2.2.5 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications

A typical 24-V battery protection application circuit shown in Figure 9-3. This circuit uses two unidirectional TVS diodes to protect from positive and negative transient voltages.

GUID-20231127-SS0I-JMDG-2XGV-BJ5SPLJHD92H-low.svg Figure 9-3 Typical 24-V Battery Protection With Two Unidirectional TVS

The breakdown voltage of the TVS+ must be higher than the 48-V jump start voltage, less than the absolute maximum ratings of the anode and enable pin of the LM74703-Q1 and LM74704-Q1 (65 V) and must withstand 65-V suppressed load dump. The breakdown voltage of TVS- must be lower than the maximum reverse battery voltage –32 V, so that the TVS- is not damaged due to long time exposure to reverse connected battery.

During ISO 7637-2 pulse 1, the input voltage goes up to –600 V with a generator impedance of 50 Ω. This behavior translates to 12 A flowing through the TVS-. The clamping voltage of the TVS- can not be the same as that of the 12-V battery protection circuit because during the ISO 7637-2 pulse, the ANODE to CATHODE pin voltage seen is equal to (-TVS Clamping voltage + Output capacitor voltage). For a 24-V battery application, the maximum battery voltage is 32 V, which indicates that the clamping voltage of the TVS- must not exceed, 75 V – 32 V = 43 V.

Single bidirectional TVS can not be used for 24-V battery protection because breakdown voltage for TVS+ ≥ 65 V, maximum clamping voltage is ≤ 43 V and the clamping voltage can not be less than the breakdown voltage. Two unidirectional TVS that are connected back-to-back need to be used at the input. For the positive side TVS+, the SMBJ58A with the breakdown voltage of 64.4 V (minimum), 67.8 (typical) is recommended. For the negative side TVS-, the SMBJ26A with breakdown voltage close to 32 V (to withstand maximum reverse battery voltage of –32 V) and maximum clamping voltage of 42.1 V is recommended.

For 24-V battery protection, a 75-V rated MOSFET is recommended to be used along with the SMBJ26A and SMBJ58A connected back-to-back at the input.