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

8.3.1 Charge Pump

The charge pump supplies the voltage necessary to drive the external N-channel MOSFET. An external charge pump capacitor is placed between CAP and VS pins to provide energy to turn on the external MOSFET. In order for the charge pump to supply current to the external capacitor, the EN and SLEEP pin voltage must be above the specified input high threshold. When enabled the charge pump sources a charging current of 4-mA typical. If EN or SLEEP pin is pulled low, then the charge pump remains disabled. To ensure that the external MOSFET can be driven above its specified threshold voltage, the CAP to VS voltage must be above the undervoltage lockout threshold, typically 6.6 V, before the internal gate driver is enabled. Use Equation 3 to calculate the initial gate driver enable delay.

Equation 1. GUID-20230630-SS0I-FZMW-SPJC-9XKP70WZ6VQW-low.svg

where

  • C(CAP) is the charge pump capacitance connected across VS and CAP pins
  • V(CAP_UVLOR) = 6.6 V (typical)

To remove any chatter on the gate drive approximately 1 V of hysteresis is added to the VCAP undervoltage lockout. The charge pump remains enabled until the CAP to VS voltage reaches 13.2 V, typically, at which point the charge pump is disabled decreasing the current draw on the VS pin. The charge pump remains disabled until the CAP to VS voltage is below to 12.2 V typically at which point the charge pump is enabled. The voltage between CAP and VS continue to charge and discharge between 12.2 V and 13.2 V as shown in Figure 8-1. By enabling and disabling the charge pump, the operating quiescent current of the LM74912-Q1 is reduced. When the charge pump is disabled it sinks 15 µA.

GUID-20230630-SS0I-QS99-1ZB9-PQMWRFXSBRFN-low.svgFigure 8-1 Charge Pump Operation