JAJSHB8A May   2019  – October 2019 LMR34206-Q1

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1. 3.1 概略回路図
  4. 4 改訂履歴
  5. 5 概要（続き）
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
    1.     Pin Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 System Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Power-Good Flag Output
      2. 9.3.2 Enable and Start-up
      3. 9.3.3 Current Limit and Short Circuit
      4. 9.3.4 Undervoltage Lockout and Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Auto Mode
      2. 9.4.2 Forced PWM Operation
      3. 9.4.3 Dropout
      4. 9.4.4 Minimum Switch On-Time
      5. 9.4.5 Spread Spectrum Operation
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
        1. 10.2.1.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Choosing the Switching Frequency
        2. 10.2.2.2 Setting the Output Voltage
        3. 10.2.2.3 Inductor Selection
        4. 10.2.2.4 Output Capacitor Selection
        5. 10.2.2.5 Input Capacitor Selection
        6. 10.2.2.6 CBOOT
        7. 10.2.2.7 VCC
        8. 10.2.2.8 External UVLO
        9. 10.2.2.9 Maximum Ambient Temperature
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Ground and Thermal Considerations
    2. 12.2 Layout Example
  13. 13デバイスおよびドキュメントのサポート
    1. 13.1 デバイス・サポート
      1. 13.1.1 開発サポート
    2. 13.2 ドキュメントのサポート
      1. 13.2.1 関連資料
    3. 13.3 ドキュメントの更新通知を受け取る方法
    4. 13.4 サポート・リソース
    5. 13.5 商標
    6. 13.6 静電気放電に関する注意事項
    7. 13.7 Glossary
  14. 14メカニカル、パッケージ、および注文情報

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

9.4.5 Spread Spectrum Operation

The spread spectrum is a factory option in the select variants.

Table 2. LMR34206-Q1 Device Variant(s) with Spread Spectrum Operation

ORDERABLE PART NUMBER OUTPUT VOLTAGE SPREAD SPECTRUM FPWM fSW
LMR34206FSC3RNXTQ1 3.3-V Fixed Yes Yes 2.1 MHz
LMR34206FSC3RNXRQ1 3.3-V Fixed Yes Yes 2.1 MHz
LMR34206SC3QRNXTQ1 3.3-V Fixed Yes No 2.1 MHz
LMR34206SC3QRNXRQ1 3.3-V Fixed Yes No 2.1 MHz
LMR34206FSC5RNXTQ1 5-V Fixed Yes Yes 2.1 MHz
LMR34206FSC5RNXRQ1 5-V Fixed Yes Yes 2.1 MHz
LMR34206SC5QRNXTQ1 5-V Fixed Yes No 2.1 MHz
LMR34206SC5QRNXRQ1 5-V Fixed Yes No 2.1 MHz

The purpose of the spread spectrum is to eliminate peak emissions at specific frequencies by spreading emissions across a wider range of frequencies than a part with fixed frequency operation. In most systems containing the LMR34206-Q1 low frequency conducted emissions from the first few harmonics of the switching frequency can be easily filtered. A more difficult design criterion is reduction of emissions at higher harmonics which fall in the FM band. These harmonics often couple to the environment through electric fields around the switch node. The LMR34206-Q1 devices with a triangular spread spectrum use typically a ±4% spreading rate with the modulation rate set at 16 kHz (typical). The spread spectrum is only available while the internal clock is free running at its natural frequency. Any of the following conditions overrides spread spectrum, turning it off:

  • At high input voltages/low output voltage ratio when the device operates at minimum on time the internal clock is slowed disabling spread spectrum.
  • The clock is slowed during dropout.
  • The internal clock is slowed at light load in the PFM variant (LMR34206SC3QRNXTQ1, LMR34206SC5QRNXRQ1). In FPWM mode, spread spectrum is active even if there is no load.