JAJSM65A march   2023  – may 2023 LMR36501 , LMR36502

PRODUCTION DATA  

  1.   1
  2. 特長
  3. アプリケーション
  4. 概要
  5. Revision History
  6. Device Comparison Table
  7. Pin Configuration and Functions
  8. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD (Commercial) Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 System Characteristics
    7. 7.7 Typical Characteristics
  9. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Enable, Shutdown, and Start-up
      2. 8.3.2  Adjustable Switching Frequency (with RT)
      3. 8.3.3  Power-Good Output Operation
      4. 8.3.4  Internal LDO, VCC UVLO, and VOUT/FB Input
      5. 8.3.5  Bootstrap Voltage and VBOOT-UVLO (BOOT Terminal)
      6. 8.3.6  Output Voltage Selection
      7. 8.3.7  Soft Start and Recovery from Dropout
        1. 8.3.7.1 Soft Start
        2. 8.3.7.2 Recovery from Dropout
      8. 8.3.8  Current Limit and Short Circuit
      9. 8.3.9  Thermal Shutdown
      10. 8.3.10 Input Supply Current
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Standby Mode
      3. 8.4.3 Active Mode
        1. 8.4.3.1 CCM Mode
        2. 8.4.3.2 AUTO Mode - Light Load Operation
          1. 8.4.3.2.1 Diode Emulation
          2. 8.4.3.2.2 Frequency Reduction
        3. 8.4.3.3 FPWM Mode - Light Load Operation
        4. 8.4.3.4 Minimum On-time Operation
        5. 8.4.3.5 Dropout
  10. 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  Choosing the Switching Frequency
        2. 9.2.2.2  Setting the Output Voltage
          1. 9.2.2.2.1 VOUT / FB for Adjustable Output
        3. 9.2.2.3  Inductor Selection
        4. 9.2.2.4  Output Capacitor Selection
        5. 9.2.2.5  Input Capacitor Selection
        6. 9.2.2.6  CBOOT
        7. 9.2.2.7  VCC
        8. 9.2.2.8  CFF Selection
        9. 9.2.2.9  External UVLO
        10. 9.2.2.10 Maximum Ambient Temperature
      3. 9.2.3 Application Curves
    3. 9.3 Best Design Practices
    4. 9.4 Power Supply Recommendations
    5. 9.5 Layout
      1. 9.5.1 Layout Guidelines
        1. 9.5.1.1 Ground and Thermal Considerations
      2. 9.5.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Device Nomenclature
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 ドキュメントの更新通知を受け取る方法
    4. 10.4 サポート・リソース
    5. 10.5 Trademarks
    6. 10.6 静電気放電に関する注意事項
    7. 10.7 用語集
  12. 11Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ(パッケージ|ピン)
サーマルパッド・メカニカル・データ
発注情報

Layout Guidelines

The PCB layout of any DC/DC converter is critical to the optimal performance of the design. Poor PCB layout can disrupt the operation of an otherwise good schematic design. Even if the converter regulates correctly, bad PCB layout can mean the difference between a robust design and one that cannot be mass produced. Furthermore, to a great extent, the EMI performance of the regulator is dependent on the PCB layout. In a buck converter, the most critical PCB feature is the loop formed by the input capacitor or capacitors and power ground, as shown in Figure 9-15. This loop carries large transient currents that can cause large transient voltages when reacting with the trace inductance. These unwanted transient voltages disrupt the proper operation of the converter. Because of this, the traces in this loop must be wide and short, and the loop area as small as possible to reduce the parasitic inductance. Figure 9-16 shows a recommended layout for the critical components of the LMR3650x.

  1. Place the input capacitors as close as possible to the VIN and GND terminals.
  2. Place bypass capacitor for VCC close to the VCC pin. This capacitor must be placed close to the device and routed with short, wide traces to the VCC and GND pins.
  3. Use wide traces for the CBOOT capacitor. Place CBOOT close to the device with short/wide traces to the BOOT and SW pins. Route the SW pin to the N/C pin and used to connect the BOOT capacitor to SW.
  4. Place the feedback divider as close as possible to the FB pin of the device. Place RFBB, RFBT, and CFF, if used, physically close to the device. The connections to FB and GND must be short and close to those pins on the device. The connection to VOUT can be somewhat longer. However, the latter trace must not be routed near any noise source (such as the SW node) that can capacitively couple into the feedback path of the regulator.
  5. Use at least one ground plane in one of the middle layers. This plane acts as a noise shield and as a heat dissipation path.
  6. Provide wide paths for VIN, VOUT, and GND. Making these paths as wide and direct as possible reduces any voltage drops on the input or output paths of the converter and maximizes efficiency.
  7. Provide enough PCB area for proper heat-sinking. As stated in Section 9.2.2.10, enough copper area must be used to ensure a low RθJA, commensurate with the maximum load current and ambient temperature. The top and bottom PCB layers must be made with two ounce copper and no less than one ounce. If the PCB design uses multiple copper layers (recommended), these thermal vias can also be connected to the inner layer heat-spreading ground planes.
  8. Keep switch area small. Keep the copper area connecting the SW pin to the inductor as short and wide as possible. At the same time, the total area of this node must be minimized to help reduce radiated EMI.

See the following PCB layout resources for additional important guidelines:

GUID-20230113-SS0I-D8SZ-RJ88-K4JS6VNZX5BP-low.svg Figure 9-15 Current Loops with Fast Edges