JAJSG01D June   2012  – August 2018 LMZ20502

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      概略回路図
      2.      VOUT = 1.8V、自動モードでの標準的な効率
  4. 4 改訂履歴
  5. 5 Pin Configuration and Functions
    1.     Pin 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 System Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Nano Scale Package
      2. 7.3.2 Internal Synchronous Rectifier
      3. 7.3.3 Current Limit Protection
      4. 7.3.4 Start-Up
      5. 7.3.5 Dropout Behavior
      6. 7.3.6 Power Good Flag Function
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 PWM Operation
      2. 7.4.2 PFM Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Detailed Design Procedure
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
        2. 8.2.1.2 Setting The Output Voltage
        3. 8.2.1.3 Output and Feed-Forward Capacitors
        4. 8.2.1.4 Input Capacitors
        5. 8.2.1.5 Maximum Ambient Temperature
        6. 8.2.1.6 Options
      2. 8.2.2 Application Curves
    3. 8.3 Do's and Don'ts
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Soldering Information
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 デバイス・サポート
      1. 11.1.1 デベロッパー・ネットワークの製品に関する免責事項
      2. 11.1.2 開発サポート
        1. 11.1.2.1 WEBENCH®ツールによるカスタム設計
      3. 11.1.3 ドキュメントのサポート
        1. 11.1.3.1 関連資料
    2. 11.2 ドキュメントの更新通知を受け取る方法
    3. 11.3 コミュニティ・リソース
    4. 11.4 商標
    5. 11.5 静電気放電に関する注意事項
    6. 11.6 Glossary
  12. 12メカニカル、パッケージ、および注文情報
    1. 12.1 Tape and Reel Information

パッケージ・オプション

デバイスごとのパッケージ図は、PDF版データシートをご参照ください。

メカニカル・データ（パッケージ｜ピン）
  • SIL|8
サーマルパッド・メカニカル・データ
発注情報

7.4.2 PFM Operation

When in AUTO mode, and at light loads, the device enters PFM. The regulator estimates the load current by measuring both the high side and low side switch currents. This estimate is only approximate, and the exact load current threshold, to trigger PFM, can vary greatly with input and output voltage. The Application Curves show mode change thresholds for several typical operating points. When the regulator detects this threshold, the reference voltage is increased by approximately 10 mV. This causes the output voltage to rise to meet the new regulation point. When this point is reached, the converter stops switching and much of the internal circuitry is shut off, while the reference is returned to the PWM value. This saves supply current while the output voltage naturally starts to fall under the influence of the load current. When the output voltage reaches the PWM regulation point, switching is again started and the reference voltage is again increased by about 10 mV; thus starting the next cycle. Typical waveforms are shown in Figure 14:

LMZ20502 fig_24.gifFigure 14. Typical PFM Mode Waveforms: VIN = 3.6 V,
VOUT = 1.8 V, IOUT = 10 mA
LMZ20502 D007_input_current_SNVS852.gifFigure 15. Typical No Load Input Supply Current

The actual output voltage ripple will depend on the feedback divider ratio and on the delay in the PFM comparator. The frequency of the PFM "bursts" will depend on the input voltage, output voltage, load and output capacitor. Within each "burst" the device switches at 3 MHz (typ.). If the load current increases above the threshold, normal PWM operation is resumed. This mode provides high light load efficiency by reducing the amount of supply current required to regulate the output at small load currents. This mode trades off very good light load efficiency for larger output voltage ripple and variable switching frequency. An example of the typical input supply current, while regulating with no load, is shown in Figure 15.

Because of normal part-to-part variation, the LMZ20502 may not switch into PFM mode at high input voltages. This may be seen with output voltages of about 1.2 V and below, at input voltages of about 4.2 V and above.