SLVS975C September   2009  – April 2018 TPS54318

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency vs Output Current
  4. 4 Revision History
  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
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed Frequency PWM Control
      2. 7.3.2  Slope Compensation and Output Current
      3. 7.3.3  Bootstrap Voltage (Boot) and Low Dropout Operation
      4. 7.3.4  Error Amplifier
      5. 7.3.5  Voltage Reference
      6. 7.3.6  Adjusting the Output Voltage
      7. 7.3.7  Enable and Adjusting Undervoltage Lockout
      8. 7.3.8  Soft-Start Pin
      9. 7.3.9  Sequencing
      10. 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
      11. 7.3.11 Overcurrent Protection
      12. 7.3.12 Frequency Shift
      13. 7.3.13 Reverse Overcurrent Protection
      14. 7.3.14 Synchronize Using the RT/CLK Pin
      15. 7.3.15 Power Good (PWRGD Pin)
      16. 7.3.16 Overvoltage Transient Protection
      17. 7.3.17 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Small Signal Model for Loop Response
      2. 7.4.2 Simple Small Signal Model for Peak Current Mode Control
      3. 7.4.3 Small Signal Model for Frequency Compensation
  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  Step One: Select the Switching Frequency
        2. 8.2.2.2  Step Two: Select the Output Inductor
        3. 8.2.2.3  Step Three: Choose the Output Capacitor
        4. 8.2.2.4  Step Four: Select the Input Capacitor
        5. 8.2.2.5  Step Five: Minimum Load DC COMP Voltage
        6. 8.2.2.6  Step Six: Choose the Soft-Start Capacitor
        7. 8.2.2.7  Step Seven: Select the Bootstrap Capacitor
        8. 8.2.2.8  Step Eight: Undervoltage Lockout Threshold
        9. 8.2.2.9  Step Nine: Select Output Voltage and Feedback Resistors
          1. 8.2.2.9.1 Output Voltage Limitations
        10. 8.2.2.10 Step 10: Select Loop Compensation Components
        11. 8.2.2.11 Power Dissipation Estimate
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Custom Design With WEBENCH® Tools
      2. 11.1.2 Development Support
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.11 Power Dissipation Estimate

Use Equation 43 through Equation 52 to help estimate the device power dissipation under continuous conduction mode (CCM) operation. The power dissipation of the device (PTOT) includes conduction loss (PCOND), dead time loss (PD), switching loss (PSW), gate drive loss (PGD) and supply current loss (PQ).

Equation 43. PCOND= (IOUT)2 × RDS(on)
Equation 44. PD = ƒSW × IOUT × 0.7 × 60 × (10)–9
Equation 45. PD = ƒSW × IOUT × 0.7 × 60 × (10)–9
Equation 46. PSW = 2 × (VIN)2 × ƒSW × IOUT × 0.25 × (10)–9
Equation 47. PSW = 2 × (VIN)2 × ƒSW × IOUT × 0.25 × (10)–9
Equation 48. PGD = 2 × VIN × 3 × (10)–9 × ƒSW
Equation 49. PQ = 350 × (10)–6 × VIN

where

  • IOUT is the output current (A)
  • RDS(on) is the on-resistance of the high-side MOSFET (Ω)
  • VOUT is the output voltage (V)
  • VIN is the input voltage (V)
  • ƒSW is the switching frequency (Hz)
Equation 50. PTOT = PCOND + PD + PSW + PGD + PQ

For a given ambient temperature,

Equation 51. TJ = TA + RTH × PTOT

For maximum junction temperature (TJ(max) = 150°C)

Equation 52. TA(max) = TJ(max) – RTH × PTOT

where

  • PTOT is the total device power dissipation (W)
  • TA is the ambient temperature (°C)
  • TJ is the junction temperature (°C)
  • RTH is the thermal resistance of the package (°C/W)
  • TJ(max) is maximum junction temperature (°C)
  • TA(max) is maximum ambient temperature (°C)

Additional power can be lost in the regulator circuit due to the inductor ac and dc losses and trace resistance that impact the overall regulator efficiency. Figure 36 and Figure 37 show power dissipation for the EVM.

TPS54318 tj_vs_pd_slvs946.gif
TA = 25°C No air flow
Figure 36. Power Dissipation vs Junction Temperature
TPS54318 tamax_vs_pd_slvs946.gif
TJ(max) = 150°C No air flow
Figure 37. Power Dissipation vs Ambient Temperature