SNOSD17G October   2017  – December 2020 LM74700-Q1

PRODMIX  

  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. 7 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Input Voltage
      2. 9.3.2 Charge Pump
      3. 9.3.3 Gate Driver
      4. 9.3.4 Enable
    4. 9.4 Device Functional Modes
      1. 9.4.1 Shutdown Mode
      2. 9.4.2 Conduction Mode
        1. 9.4.2.1 Regulated Conduction Mode
        2. 9.4.2.2 Full Conduction Mode
        3. 9.4.2.3 Reverse Current Protection Mode
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Typical Application
        1. 10.1.1.1 Design Requirements
        2. 10.1.1.2 Detailed Design Procedure
          1. 10.1.1.2.1 Design Considerations
          2. 10.1.1.2.2 MOSFET Selection
          3. 10.1.1.2.3 Charge Pump VCAP, input and output capacitance
        3. 10.1.1.3 Selection of TVS Diodes for 12-V Battery Protection Applications
        4. 10.1.1.4 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications
        5. 10.1.1.5 Application Curves
    2. 10.2 OR-ing Application Configuration
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Receiving Notification of Documentation Updates
    2. 13.2 Support Resources
    3. 13.3 Trademarks
    4. 13.4 Electrostatic Discharge Caution
    5. 13.5 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

9.3.2 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 ANODE 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 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 ensure that the external MOSFET can be driven above its specified threshold voltage, the VCAP to ANODE voltage must be above the undervoltage lockout threshold, typically 6.6 V, before the internal gate driver is enabled. Use Equation 1 to calculate the initial gate driver enable delay.

Equation 1. GUID-F07D8A6C-7C92-46AB-B243-5D983DED01D3-low.gif

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 ANODE voltage reaches 13 V, typically, at which point the charge pump is disabled decreasing the current draw on the ANODE pin. The charge pump remains disabled until the VCAP to ANODE voltage is below to 12.1 V typically at which point the charge pump is enabled. The voltage between VCAP and ANODE continue to charge and discharge between 12.1 V and 13 V as shown in Figure 9-1. By enabling and disabling the charge pump, the operating quiescent current of the LM74700-Q1 is reduced. When the charge pump is disabled it sinks 5-µA typical.

GUID-DB9EEC25-7367-4623-BD74-3A945149BBF9-low.gifFigure 9-1 Charge Pump Operation