SLUS720F February   2007  – June 2019 TPS40195

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Application Diagram
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Electrical Characteristics
    5. 7.5 Dissipation Ratings
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Enable Functionality
      2. 8.3.2  Voltage Reference
      3. 8.3.3  Oscillator and Synchronization
      4. 8.3.4  Undervoltage Lockout (UVLO)
      5. 8.3.5  Soft Start
      6. 8.3.6  Selecting the Short Circuit Threshold
      7. 8.3.7  5-V Regulator
      8. 8.3.8  Prebias Start-up
      9. 8.3.9  Drivers
      10. 8.3.10 Power Good
      11. 8.3.11 Thermal Shutdown
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Typical Application 1
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Output Inductor, LOUT
          2. 9.2.1.2.2 Output Capacitor, COUT
          3. 9.2.1.2.3 Input Capacitor, CIN
          4. 9.2.1.2.4 Switching MOSFET, QSW
          5. 9.2.1.2.5 Rectifier MOSFET, QSR
          6. 9.2.1.2.6 Component Selection for the TPS40195
            1. 9.2.1.2.6.1 Timing Resistor, RT
            2. 9.2.1.2.6.2 Setting UVLO
            3. 9.2.1.2.6.3 Setting the Soft-Start Time
            4. 9.2.1.2.6.4 Short-Circuit Protection, RILIM
            5. 9.2.1.2.6.5 Voltage Decoupling Capacitors, CBP, and CVDD
            6. 9.2.1.2.6.6 Boost Voltage, CBOOST and DBOOST (optional)
            7. 9.2.1.2.6.7 Closing the Feedback Loop RZ1, RP1, RPZ2, RSET1, RSET2, CZ2, CP2 AND CPZ1
          7. 9.2.1.2.7 Application Curve
      2. 9.2.2 Typical Application 2
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
      3. 9.2.3 Typical Application 3
        1. 9.2.3.1 Design Requirements
        2. 9.2.3.2 Detailed Design Procedure
        3. 9.2.3.3 Application Curves
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Device Support
      1. 11.2.1 Related Parts
    3. 11.3 Documentation Support
      1. 11.3.1 Related Documentation
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Community Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

9.2.1.2.6.6 Boost Voltage, CBOOST and DBOOST (optional)

Selection of the boost capacitor is based on the total gate charge of the switching MOSFET and the allowable ripple on the boost voltage, VBOOST. A ripple of 0.2 V is assumed for this design. Using these two parameter and equation (26) the minimum value for CBOOST can be calculated.

Equation 36. TPS40195 q_cboost_lus720.gif

The total gate charge of the switching MOSFET is 13.3 nC. A minimum CBOOST of 0.066-μF is required. A 0.1-μF capacitor was chosen. This capacitor must be able to withstand the maximum input voltage plus the maximum voltage on BP. This is 16 V plus 5.4 V which is 21.4 V. A 50-V capacitor is used.

To reduce losses in the TPS40195 and to increase the available gate voltage for the switching MOSFET an external diode can be added between the BP pin and the BOOST pin of the device. A small signal schottky should be used here, such as the BAT54.