ZHCU578 October   2018

 

  1.    说明
  2.    资源
  3.    特性
  4.    应用
  5.    设计图像
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 TPS92692-Q1
    3. 2.3 LM74700
    4. 2.4 System Design Theory
      1. 2.4.1 Design Procedure
        1. 2.4.1.1  Operating Parameters, Duty Cycle
        2. 2.4.1.2  Setting the Switching Frequency
        3. 2.4.1.3  Inductor Value Calculation
        4. 2.4.1.4  Peak Inductor Current
        5. 2.4.1.5  Calculating RIS (R9)
        6. 2.4.1.6  Minimum Output Capacitance
        7. 2.4.1.7  Setting the LED Current
        8. 2.4.1.8  Soft-Start Capacitor
        9. 2.4.1.9  Overvoltage Protection (OVP)
        10. 2.4.1.10 Main N-Channel MOSFET Selection
        11. 2.4.1.11 Rectifier Diode Selection
        12. 2.4.1.12 Thermal Protection
      2. 2.4.2 Designing for Low EMI
        1. 2.4.2.1 EMI Performance
        2. 2.4.2.2 EMI Filter Design
          1. 2.4.2.2.1 Additional EMI Considerations
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Nominal Operation Waveforms
          1. 3.2.2.1.1 Loop Stability Measurements Block Diagram
        2. 3.2.2.2 Efficiency and Line Regulation: Done for different power level for Boost (Hi Beam and Lo Beam) or Boost to Battery for Lo Beam only
        3. 3.2.2.3 Thermal Scan
  9. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  10. 5Related Documentation
    1. 5.1 商标

2.4.2.2 EMI Filter Design

The input EMI filter consists of a differential mode PI filter formed by the input capacitors (C2 through C3, C4, C5, and C6) and the input inductor (L1). The primary purpose of the filter is to minimize EMI conducted from the circuit to prevent it from interfering with the electrical network supplying power to the LED driver. Frequencies in and around the switching frequency of the LED driver (fundamental and harmonics) are primarily addressed with this filter, and the filter cutoff frequency is determined by the inductor and capacitor resonance. An input common-mode filter (L5) is also included to reduce high-frequency common-mode noise at 30 MHz and above.

Sufficient differential mode noise filtering on the output is generally provided by the output capacitor assuming low equivalent-series-resistance (ESR) ceramics are used as in this reference design for CISPR-25 class 5 conducted limits. A common-mode filter has also been added to the output (L4) to account for high frequencies with unknown loads. This filtering may not be required in an end application depending on the load. This LED driver has been designed with the assumption that a connection to chassis ground is not available.

For more information on EMI filter design, see the application notes AN-2162 Simple Success With Conducted EMI From DC-DC Converters and Input Filter Design for Switching Power Supplies.