JAJSEJ4C January   2018  – July 2018 TPSM84209

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      アプリケーション概略図
      2.      効率と出力電流との関係
  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 Typical Characteristics (VIN = 5 V)
    7. 6.7 Typical Characteristics (VIN = 12 V)
    8. 6.8 Typical Characteristics (VIN = 24 V)
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Adjusting the Output Voltage
      2. 7.3.2  Input Capacitor Selection
      3. 7.3.3  Undervoltage Lockout (UVLO)
      4. 7.3.4  Output Capacitor Selection
      5. 7.3.5  Feed-Forward Capacitor
      6. 7.3.6  Operating Range
      7. 7.3.7  Output Current Rating
      8. 7.3.8  Enable (EN)
      9. 7.3.9  Internal Soft Start
      10. 7.3.10 Safe Start-Up Into Prebiased Outputs
      11. 7.3.11 Light Load Efficiency / Eco-Mode
      12. 7.3.12 Voltage Dropout
      13. 7.3.13 Overcurrent Protection
      14. 7.3.14 Output Overvoltage Protection (OVP)
      15. 7.3.15 Thermal Performance
      16. 7.3.16 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Active Mode
      2. 7.4.2 Eco-Mode Operation
      3. 7.4.3 Shutdown Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Setpoint
        3. 8.2.2.3 Input Capacitors
        4. 8.2.2.4 Output Capacitors
        5. 8.2.2.5 Enable Control
      3. 8.2.3 Application Waveforms
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
    3. 10.3 EMI
      1. 10.3.1 EMI Plots
    4. 10.4 Package Specifications
  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. 11.2 WEBENCH®ツールによるカスタム設計
    3. 11.3 ドキュメントの更新通知を受け取る方法
    4. 11.4 コミュニティ・リソース
    5. 11.5 商標
    6. 11.6 静電気放電に関する注意事項
    7. 11.7 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

7.3.5 Feed-Forward Capacitor

The TPSM84209 is internally compensated to be stable over the operating range of the device. However, depending on the output voltage and amount of output capacitance, an additional feed-forward capacitor, CFF, may be added for optimum performance. Adding additional output capacitance above the minimum reduces the output voltage ripple of the device. However, adding additional output capacitance also reduces the cross-over frequency of the device, slowing the response to load transients. Adding a feed-forward capacitor when adding more output capacitance helps to restore cross-over frequency of the device, restoring the transient response.

The external feed-forward capacitor must be placed in parallel with the top resistor divider, RFBT. The placement of CFF is shown in Figure 19. Table 6 lists the required CFF values for different amounts of output capacitance. For output voltages < 2.5 V, it is not recommended to add a CFF capacitor.

TPSM84209 FBresistorDiv2.gifFigure 19. Feed-Forward Capacitor

Table 6. CFF Values(1)

VOUT RANGE (V) Amount of COUT
MIN MAX 47 µF (1 x 47 µF) 94 µF (2 x 47 µF) 141 µF (3 x 47 µF) ≥ 188 µF (4 x 47 µF)
2.5 < 3.3 Not applicable CFF = 100 pF CFF = 220 pF CFF = 330 pF
3.3 < 5 Not applicable CFF = 100 pF CFF = 330 pF CFF = 330 pF
5 6 CFF = 100 pF CFF = 330 pF CFF = 330 pF CFF = 330 pF
(1) The CFF values listed in this table apply when RFBT = 10 kΩ. To calculate the value of CFF when using another RFBT value, multiply the CFF value listed in the table by 10 kΩ / RFBT.