JAJS177F November   2003  – February 2020 TPS2490 , TPS2491

PRODUCTION DATA.  

  1. 1 特長
  2. 2 アプリケーション
  3. 3 概要
    1.     Device Images
      1.      代表的なアプリケーション
  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 Switching 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  VCC
      2. 7.3.2  SENSE
      3. 7.3.3  GATE
      4. 7.3.4  OUT
      5. 7.3.5  EN
      6. 7.3.6  VREF
      7. 7.3.7  PROG
      8. 7.3.8  TIMER
      9. 7.3.9  PG
      10. 7.3.10 GND
    4. 7.4 Device Functional Modes
      1. 7.4.1 Board Plug-In ()
      2. 7.4.2 TIMER and PG Operation ()
      3. 7.4.3 Action of the Constant Power Engine ()
      4. 7.4.4 Response to a Hard Output Short ( and )
      5. 7.4.5 Automatic Restart ()
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Alternative Inrush Designs
        1. 8.1.1.1 Gate Capacitor (dV/dt) Control
        2. 8.1.1.2 PROG Inrush Control
      2. 8.1.2 Additional Design Considerations
        1. 8.1.2.1 Use of PG
        2. 8.1.2.2 Faults and Backplane Voltage Droop
        3. 8.1.2.3 Output Clamp Diode
        4. 8.1.2.4 Gate Clamp Diode
        5. 8.1.2.5 High Gate Capacitance Applications
        6. 8.1.2.6 Input Bypass
        7. 8.1.2.7 Output Short Circuit Measurements
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Select RSNS and CL setting
        2. 8.2.2.2 Selecting the Hot Swap FET(s)
        3. 8.2.2.3 Select Power Limit
        4. 8.2.2.4 Set Fault Timer
        5. 8.2.2.5 Check MOSFET SOA
        6. 8.2.2.6 Set Under-Voltage Threshold
        7. 8.2.2.7 Choose R5, and CIN
        8. 8.2.2.8 Input and Output Protection
        9. 8.2.2.9 Final Schematic and Component Values
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 PC Board Guidelines
      2. 10.1.2 System Considerations
    2. 10.2 Layout Example
  11. 11デバイスおよびドキュメントのサポート
    1. 11.1 開発サポート
    2. 11.2 ドキュメントのサポート
      1. 11.2.1 関連資料
    3. 11.3 関連リンク
    4. 11.4 ドキュメントの更新通知を受け取る方法
    5. 11.5 コミュニティ・リソース
    6. 11.6 商標
    7. 11.7 静電気放電に関する注意事項
    8. 11.8 Glossary
  12. 12メカニカル、パッケージ、および注文情報

8.2.2.3 Select Power Limit

In general, a lower power limit setting is preferred to reduce the stress on the MOSFET. However, when the TPS2490 is set to a very low power limit setting, it has to regulate the FET current and hence the voltage across the sense resistor (VSNS) to a very low value. VSNS can be computed as shown in Equation 12:

Equation 12. TPS2490 TPS2491 tps2490_equation7.gif

To avoid significant degradation of the power limiting accuracy, a VSNS of less than 5 mV is not recommended. Based on this requirement the minimum allowed power limit can be computed as follows:

Equation 13. TPS2490 TPS2491 tps2490_equation8.gif

Because the VPROG pin, which programs the power limit of the device, has a minimum voltage of 0.4 V, the set PLIM must also result in the voltage at VPROG being greater than 0.4 V. Based on this requirement the minimum allowed power limit can be computed as follows:

Equation 14. TPS2490 TPS2491 tps2490_equation9.gif

Because the power limit has to satisfy both the VSNS and VPROG, the greater PLIM,MIN value is used as the basis for sizing the resistive divider. In this design example it is 50 W. The maximum ratio of the resistive divider can be computed as follows:

Equation 15. TPS2490 TPS2491 tps2490_equation10.gif

In Equation 16 R3 is picked as 41.2 kΩ. R3 must be greater than 4 kΩ, but TI recommends that 10 kΩ or greater be used. The resistive divider ratio is used to calculate R4, and next largest available resistor is chosen.

Equation 16. TPS2490 TPS2491 tps2490_equation11.gif

We choose 4.64 kΩ for our final value of R4.