SLVS839F July   2008  – October 2014 TPS54331

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Simplified Schematic
    1.     TPS54331 (D Package) Efficiency
  5. Revision History
  6. Pin Configuration and Functions
    1.     Pin Functions
  7. Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Switching Characteristics
    7. 7.7 Typical Characteristics
  8. Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Fixed-Frequency PWM Control
      2. 8.3.2  Voltage Reference (Vref)
      3. 8.3.3  Bootstrap Voltage (BOOT)
      4. 8.3.4  Enable and Adjustable Input Undervoltage Lockout (VIN UVLO)
      5. 8.3.5  Programmable Slow Start Using SS Pin
      6. 8.3.6  Error Amplifier
      7. 8.3.7  Slope Compensation
      8. 8.3.8  Current-Mode Compensation Design
      9. 8.3.9  Overcurrent Protection and Frequency Shift
      10. 8.3.10 Overvoltage Transient Protection
      11. 8.3.11 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Eco-mode™
      2. 8.4.2 Operation With VIN < 3.5 V
      3. 8.4.3 Operation With EN Control
  9. Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1  Custom Design with WEBENCH Tools
        2. 9.2.2.2  Switching Frequency
        3. 9.2.2.3  Output Voltage Set Point
        4. 9.2.2.4  Input Capacitors
        5. 9.2.2.5  Output Filter Components
          1. 9.2.2.5.1 Inductor Selection
        6. 9.2.2.6  Capacitor Selection
        7. 9.2.2.7  Compensation Components
        8. 9.2.2.8  Bootstrap Capacitor
        9. 9.2.2.9  Catch Diode
        10. 9.2.2.10 Output Voltage Limitations
        11. 9.2.2.11 Power Dissipation Estimate
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Electromagnetic Interference (EMI) Considerations
  12. 12Device and Documentation Support
    1. 12.1 Custom Design with WEBENCH Tools
    2. 12.2 Device Support
      1. 12.2.1 Development Support
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Input Capacitors

The TPS54331 device requires an input decoupling capacitor and, depending on the application, a bulk input capacitor. The typical recommended value for the decoupling capacitor is 10 μF. A high-quality ceramic type X5R or X7R is recommended. The voltage rating should be greater than the maximum input voltage. A smaller value can be used as long as all other requirements are met; however a value of 10 μF has been shown to work well in a wide variety of circuits. Additionally, some bulk capacitance may be required, especially if the TPS54331 circuit is not located within about 2 inches from the input voltage source. The value for this capacitor is not critical but should be rated to handle the maximum input voltage including ripple voltage, and should filter the output so that input ripple voltage is acceptable. For this design two 4.7-μF capacitors are used for the input decoupling capacitor. The capacitors are X7R dielectric rated for 50 V. The equivalent series resistance (ESR) is approximately 2 mΩ and the current rating is 3 A. Additionally, a small 0.01-μF capacitor is included for high frequency filtering.

Use Equation 6 to calculate the input ripple voltage.

Equation 6. TPS54331 new_eq4_lvs839.gif

where

  • IOUT(MAX) is the maximum load current
  • ƒSW is the switching frequency
  • CBULK is the bulk capacitor value
  • ESRMAX is the maximum series resistance of the bulk capacitor

The maximum RMS ripple current must also be checked. For worst case conditions, use Equation 7 to calculate the maximum-RMS input ripple current, ICIN(RMS).

Equation 7. TPS54331 new_eq5_lvs839.gif

In this case, the input ripple voltage is 143 mV and the RMS ripple current is 1.5 A.

NOTE

The actual input voltage ripple is greatly affected by parasitics associated with the layout and the output impedance of the voltage source.

The actual input voltage ripple for this circuit is listed in Table 3 and is larger than the calculated value. This measured value is still below the specified input limit of 300 mV. The maximum voltage across the input capacitors would be VIN(MAX) + ΔVIN / 2. The selected bulk and bypass capacitors are each rated for 50 V and the ripple current capacity is greater than 3 A, both providing ample margin. The maximum ratings for voltage and current must not be exceeded under any circumstance.