ZHCST56 September   2023 LM74700D-Q1

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  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
  8. 7 Typical Characteristics
  9. 8 Parameter Measurement Information
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 功能方框图
    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
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Design Considerations
        2. 10.2.2.2 MOSFET Selection
        3. 10.2.2.3 Charge Pump VCAP, Input and Output Capacitance
      3. 10.2.3 Selection of TVS Diodes for 12-V Battery Protection Applications
      4. 10.2.4 Selection of TVS Diodes and MOSFET for 24-V Battery Protection Applications
      5. 10.2.5 Application Curves
      6. 10.2.6 OR-ing Application Configuration
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
      2. 10.4.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 接收文档更新通知
    2. 11.2 支持资源
    3. 11.3 Trademarks
    4. 11.4 静电放电警告
    5. 11.5 术语表
  13. 12Mechanical, Packaging, and Orderable Information

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10.2.6 OR-ing Application Configuration

Basic redundant power architecture comprises of two or more voltage or power supply sources driving a single load. In 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, because each diode in an OR-ing application spends most of the time in forward conduction mode. These power losses increase the requirements for thermal management and allocated board space.

The LM74700D-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. LM74700D-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 must be extremely fast to limit the reverse current amount and duration. The LM74700D-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 LM74700D-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. A fast comparator turns on the Gate with 11-mA gate charge current once the differential forward voltage V(IN) – V(OUT) exceeds 50 mV.

GUID-20230809-SS0I-NQNH-HL4K-PZ2R7FB5LQHM-low.svgFigure 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 48 V and VIN2 at 50 V. Figure 10-16 and Figure 10-17 illustrate the performance when VIN2 fails. LM74700D-Q1 controlling VIN2 power rail turns off quickly, so that the output remains uninterrupted and VIN1 is protected from VIN2 failure.