SNOSDC2B September   2021  – July 2022 LM74721-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 Reverse Battery Protection (A, C, GATE)
        1. 8.3.1.1 Input TVS Less Operation: VDS Clamp
      2. 8.3.2 Load Disconnect Switch Control (PD)
      3. 8.3.3 Overvoltage Protection and Battery Voltage Sensing (VSNS, SW, OV)
      4. 8.3.4 Boost Regulator
    4. 8.4 Shutdown Mode
  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 Detailed Design Procedure
        1. 9.2.2.1 Boost Converter Components (C2, C3, L1)
        2. 9.2.2.2 Input and Output Capacitance
        3. 9.2.2.3 Hold-Up Capacitance
        4. 9.2.2.4 MOSFET Selection: Q1
      3. 9.2.3 Application Curves
    3. 9.3 What to Do and What Not to Do
  10. 10Power Supply Recommendations
    1. 10.1 Transient Protection
  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

8.3.1.1 Input TVS Less Operation: VDS Clamp

The LM74721-Q1 features an integrated VDS clamp that operates the external MOSFET as an active clamp to dissipate the automotive ISO7637 pulse 1 transient.

When the ISO7637 pulse 1 is applied at the input:

  • The GATE goes low and turns OFF the MOSFET after the voltage drop across A and C reaches V(AC_REV) threshold.
  • After the voltage across Drain and Source of the MOSFET reaches VCLAMP level (34-V minimum), it is turned ON back in saturation, operating as an active clamp and dissipates the ISO7637 pulse 1 energy.

Figure 8-2 shows circuit operation during ISO7637 pulse 1.

Note that the reverse current flows from VOUT back to input during the ISO7637 pulse 1 test dropping the VOUT. The output filter must be designed to ensure that VOUT does not go negative during ISO7637 pulse 1 test. For all the other ISO7637 pulses that is pulse 2a, 2b, 3a, 3b, the input and output filter components suppress these pulses.

Figure 8-2 LM74721-Q1 Ideal Diode Circuit Operation During ISO7637 Pulse 1