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

8.3.2 Charge Pump

The charge pump supplies the voltage necessary to drive the external N-channel MOSFET. An external charge pump capacitor is placed between VCAP+ and VCAP– pins to provide energy to turn on the external MOSFET. For the charge pump to supply current to the external capacitor, the EN pin voltage must be above the specified input high threshold, V(EN_IH). When enabled, the charge pump sources a charging current of 300-µA typical. If EN pins is pulled low, then the charge pump remains disabled. To make sure that the external MOSFET can be driven above the specified threshold voltage of the MOSFET, the VCAP+ to VCAP–voltage must be above the undervoltage lockout threshold, which is typically 6.6 V, before the internal gate driver is enabled. Use Equation 1 to calculate the initial gate driver enable delay.

Equation 1. TDRV_EN=75  μs+CVCAP×VVCAP_UVLOR300 μA

where

  • C(VCAP) is the charge pump capacitance connected across ANODE and VCAP pins
  • V(VCAP_UVLOR) = 6.6 V (typical)

To remove any chatter on the gate drive, approximately 900 mV of hysteresis is added to the VCAP undervoltage lockout. The charge pump remains enabled until the VCAP+ to VCAP–voltage reaches the typical 13 V, typically, at which point the charge pump is disabled, decreasing the current drawn on the ANODE pin. The charge pump remains disabled until the VCAP+ to VCAP– voltage is below the typical 12.1 V, enabling the charge pump. The voltage between VCAP+ to VCAP– continue to charge and discharge between 12.1 V and 13 V as shown in Figure 8-1. By enabling and disabling the charge pump, the operating quiescent current of the LM74703-Q1 is reduced. When the charge pump is disabled, the charge pump typically sinks 5 µA.

GUID-20231127-SS0I-9QLQ-D5MN-4Q8R1DSL6G33-low.svgFigure 8-1 Charge Pump Operation