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

10.2 OR-ing Application Configuration

Basic redundant power architecture comprises of two or more voltage or power supply sources driving a single load. In its simplest form, the OR-ing solution for redundant power supplies consists of Schottky OR-ing diodes that protect the system against an input power supply fault condition. A diode OR-ing device provides effective and low cost solution with few components. However, the diodes forward voltage drops affects the efficiency of the system permanently, since each diode in an OR-ing application spends most of its time in forward conduction mode. These power losses increase the requirements for thermal management and allocated board space.

The LM74700-Q1 ICs combined with external N-Channel MOSFETs can be used in OR-ing Solution as shown in Figure 10-18. The forward diode drop is reduced as the external N-Channel MOSFET is turned ON during normal operation. LM74700-Q1 quickly detects the reverse current, pulls down the MOSFET gate fast, leaving the body diode of the MOSFET to block the reverse current flow. An effective OR-ing solution needs to be extremely fast to limit the reverse current amount and duration. The LM74700-Q1 devices in OR-ing configuration constantly sense the voltage difference between Anode and Cathode pins, which are the voltage levels at the power sources (VIN1, VIN2) and the common load point respectively. The source to drain voltage VDS for each MOSFET is monitored by the Anode and Cathode pins of the LM74700-Q1. A fast comparator shuts down the Gate Drive through a fast Pull-Down within 0.45 μs (typical) as soon as V(IN) – V(OUT) falls below –11 mV. It turns on the Gate with 11-mA gate charge current once the differential forward voltage V(IN) – V(OUT) exceeds 50 mV.

GUID-64244F95-3F47-4999-ABFC-1D86E80C803B-low.gifFigure 10-18 Typical OR-ing Application

Figure 10-12 to Figure 10-15 show the smooth switch over between two power supply rails VIN1 at 12 V and VIN2 at 15 V. Figure 10-16 and Figure 10-17 illustrate the performance when VIN2 fails. LM74700-Q1 controlling VIN2 power rail turns off quickly, so that the output remains uninterrupted and VIN1 is protected from VIN2 failure.