SLUS593J December   2003  – June 2022 TPS40054 , TPS40055 , TPS40057

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Recommended Operating Conditions
    3. 6.3 Thermal Information
    4. 6.4 Electrical Characteristics
    5. 6.5 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 Setting the Switching Frequency (Programming the Clock Oscillator)
      2. 7.3.2 Programming The Ramp Generator Circuit
      3. 7.3.3 UVLO Operation
      4. 7.3.4 BP5 and BP10 Internal Voltage Regulators
      5. 7.3.5 Programming Soft Start
      6. 7.3.6 Programming Current Limit
      7. 7.3.7 Synchronizing to an External Supply
      8. 7.3.8 Loop Compensation
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Selecting the Inductor Value
      2. 8.1.2 Calculating the Output Capacitance
      3. 8.1.3 Calculating the Boost and BP10 Bypass Capacitor
      4. 8.1.4 DV-DT Induced Turn-On
      5. 8.1.5 High-Side MOSFET Power Dissipation
      6. 8.1.6 Synchronous Rectifier MOSFET Power Dissipation
      7. 8.1.7 TPS4005x Power Dissipation
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Calculate Maximum and Minimum Duty Cycles
        2. 8.2.2.2  Select Switching Frequency
        3. 8.2.2.3  Select ΔI
        4. 8.2.2.4  Calculate the High-Side MOSFET Power Losses
        5. 8.2.2.5  Calculate Synchronous Rectifier Losses
        6. 8.2.2.6  Calculate the Inductor Value
        7. 8.2.2.7  Set the Switching Frequency
        8. 8.2.2.8  Program the Ramp Generator Circuit
        9. 8.2.2.9  Calculate the Output Capacitance (CO)
        10. 8.2.2.10 Calculate the Soft-Start Capacitor (CSS/SD)
        11. 8.2.2.11 Calculate the Current Limit Resistor (RILIM)
        12. 8.2.2.12 Calculate Loop Compensation Values
        13. 8.2.2.13 Calculate the Boost and BP10V Bypass Capacitance
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 MOSFET Packaging
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.1.7 TPS4005x Power Dissipation

The power dissipation in the TPS4005x is largely dependent on the MOSFET driver currents and the input voltage. The driver current is proportional to the total gate charge, Qg, of the external MOSFETs. Driver power (neglecting external gate resistance (refer to the PowerPAD Thermally Enhanced Package application note) can be calculated from Equation 41.

Equation 41. GUID-213EE9B6-F35C-49E8-9CCA-DF27E6222346-low.gif

And the total power dissipation in the TPS4005x, assuming the same MOSFET is selected for both the high-side and synchronous rectifier, is described in Equation 42.

Equation 42. GUID-D0D5D61C-20AF-4626-A875-66A64BBA008E-low.gif

or

Equation 43. GUID-60F82C53-121F-4D74-8309-85FDCED6C1B6-low.gif

where

  • IQ is the quiescent operating current (neglecting drivers).

The maximum power capability of the PowerPAD package is dependent on the layout as well as air flow. The thermal impedance from junction to air, assuming 2-oz. copper trace and thermal pad with solder and no air flow:

Equation 44. GUID-12CB3E68-0E6C-4925-906A-BD10A0D924DC-low.gif

The maximum allowable package power dissipation is related to ambient temperature by Equation 45.

Equation 45. GUID-20AC7721-B130-4410-A70A-BA470795221C-low.gif

Substituting Equation 38 into Equation 43 and solving for fSW yields the maximum operating frequency for the TPS4005x. The result is described in Equation 46.

Equation 46. GUID-EFC1C165-D4C5-4EFD-8D22-6285DEC0D5CA-low.gif