SLUSCV2B June   2017  – August 2026 TPS54308

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 Timing Requirements
    7. 5.7 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 PWM Control
      2. 6.3.2  Force Continuous Conduction Mode (FCCM)
      3. 6.3.3  Error Amplifier
      4. 6.3.4  Slope Compensation and Output Current
      5. 6.3.5  Enable and Adjusting Undervoltage Lockout
      6. 6.3.6  Safe Start-Up into Prebiased Outputs
      7. 6.3.7  Voltage Reference
      8. 6.3.8  Adjusting Output Voltage
      9. 6.3.9  Internal Soft Start
      10. 6.3.10 Bootstrap Voltage (BOOT)
      11. 6.3.11 Overcurrent Protection
        1. 6.3.11.1 High-Side MOSFET Overcurrent Protection
        2. 6.3.11.2 Low-Side MOSFET Overcurrent Protection
      12. 6.3.12 Output Overvoltage Protection (OVP)
      13. 6.3.13 Thermal Shutdown
    4. 6.4 Device Functional Modes
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 TPS54308 8V to 28V Input, 5V Output Converter
      2. 7.2.2 Design Requirements
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1 Custom Design With WEBENCH® Tools
        2. 7.2.3.2 Input Capacitor Selection
        3. 7.2.3.3 Bootstrap Capacitor Selection
        4. 7.2.3.4 Output Voltage Set Point
        5. 7.2.3.5 Undervoltage Lockout Set Point
        6. 7.2.3.6 Output Filter Components
          1. 7.2.3.6.1 Inductor Selection
          2. 7.2.3.6.2 Output Capacitor Selection
          3. 7.2.3.6.3 Feedforward Capacitor
      4. 7.2.4 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 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 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
7.2.3.6.3 Feedforward Capacitor

The TPS54308 is internally compensated. The internal compensation network is composed of two capacitors and one resister shown on the block diagram. Depending on the VOUT, if the output capacitor COUT is dominated by low ESR (ceramic types) capacitors, it can result in low phase margin. To improve the phase boost, an external feedforward capacitor C6 can be added in parallel with R2. C6 is chosen such that phase margin is boosted at the crossover frequency.

Equation 16 for C6 is tested:

Equation 16. TPS54308

For this design, feedforward capacitor C6 is not needed because load transient performance looks good and meets design requirement. If further boosting phase margin for low-ESR (ceramic types) capacitors is desired, use Table 7-2 as a starting point for the feedforward capacitor choosing. TI also recommends in series with one 2kΩ resistor (R6) with this feedforward capacitor to get better steady-state performance under high VIN with a heavy load.

Table 7-2 Recommended Component Values
VOUT (V)L (µH)COUT (µF)R2 (kΩ)R3 (kΩ)C6 (µF)R6 (kΩ)
1.85.66610049.9472
2.56.86610031.6472
3.3104410022.1752
5154410013.3752
1222441005.231002