SLUSF22 November   2024 TPS54538

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Fixed Frequency Peak Current Mode
      2. 6.3.2  Mode Selection
      3. 6.3.3  Voltage Reference
      4. 6.3.4  Output Voltage Setting
      5. 6.3.5  Switching Frequency Selection / Synchronization
      6. 6.3.6  Phase Shift
      7. 6.3.7  Enable and Adjusting Undervoltage Lockout
      8. 6.3.8  External Soft Start and Prebiased Soft Start
      9. 6.3.9  Power Good
      10. 6.3.10 Minimum On Time, Minimum Off Time, and Frequency Foldback
      11. 6.3.11 Frequency Spread Spectrum
      12. 6.3.12 Overvoltage Protection
      13. 6.3.13 Overcurrent and Undervoltage Protection
      14. 6.3.14 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Modes Overview
      2. 6.4.2 Heavy Load Operation
      3. 6.4.3 Pulse Frequency Modulation
      4. 6.4.4 Forced Continuous Conduction Modulation
      5. 6.4.5 Dropout Operation
      6. 6.4.6 Minimum On-Time Operation
      7. 6.4.7 Shutdown Mode
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Custom Design With WEBENCH® Tools
        2. 7.2.2.2 Output Voltage Resistors Selection
        3. 7.2.2.3 Choosing Switching Frequency
        4. 7.2.2.4 Soft-Start Capacitor Selection
        5. 7.2.2.5 Output Inductor Selection
        6. 7.2.2.6 Output Capacitor Selection
        7. 7.2.2.7 Input Capacitor Selection
        8. 7.2.2.8 Feedforward Capacitor CFF Selection
        9. 7.2.2.9 Maximum Ambient Temperature
      3. 7.2.3 Application Curves
    3. 7.3 Best Design Practices
    4. 7.4 Power Supply Recommendations
    5. 7.5 Layout
      1. 7.5.1 Layout Guidelines
      2. 7.5.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, 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

6.3.7 Enable and Adjusting Undervoltage Lockout

The EN pin provides electrical ON and OFF control of the device. When the EN pin voltage exceeds the enable threshold voltage, VEN_RISE, the TPS54538 begins operation. If the EN pin voltage is pulled below the disable threshold voltage, VEN_FALL, the converter stops switching and enters shutdown mode.

The EN pin has an internal pullup current source, which allows the user to float the EN pin to enable the device. If an application requires control of the EN pin, use an open-drain or open-collector or GPIO output logic to interface with the pin.

The TPS54538 implements internal undervoltage lockout (UVLO) circuitry on the VIN pin. The device is disabled when the VIN pin voltage falls below the internal VIN_UVLO threshold. The internal VIN_UVLO threshold has a hysteresis of typical 200mV. If an application requires a higher UVLO threshold on the VIN pin, the EN pin can be configured as shown in Figure 6-6. When using the external UVLO function, TI recommends setting the hysteresis at a value greater than 500mV.

The EN pin has a small pullup current, Ip, which sets the default state of the EN pin to enable when no external components are connected. The pullup hysteresis current, Ih, is used to control the hysteresis voltage for the UVLO function when the EN pin voltage crosses the enable threshold. Use Equation 4 and Equation 5 to calculate the values of R1 and R2 for a specified UVLO threshold. After R1 and R2 are settled down, VEN can be calculated by Equation 6, which must be lower than 5.5V with the maximum VIN.

TPS54538 Adjustable VIN Undervoltage LockoutFigure 6-6 Adjustable VIN Undervoltage Lockout
Equation 4. R 1 = V S T A R T × V E N _ F A L L V E N _ R I S E - V S T O P I p × ( 1 - V E N _ F A L L V E N _ R I S E ) + I h
Equation 5. R 2 = R 1 × V E N _ F A L L V S T O P - V E N _ F A L L + R 1 × ( I p + I h )
Equation 6. V E N = R 2 × V I N + R 1 × R 2 × ( I p + I h ) R 1 + R 2

where

  • Ip is 0.7µA.
  • Ih is 1.76µA.
  • VEN_FALL is 1V.
  • VEN_RISE is 1.15V.
  • VSTART is the input voltage enabling the device.
  • VSTOP is the input voltage disabling the device.