SLVSDQ8B October   2016  – June 2021 TPS54388C-Q1

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 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
    4. 7.4 Device Functional Modes
      1. 7.4.1  Adjusting the Output Voltage
      2. 7.4.2  Enable Functionality and Adjusting Undervoltage Lockout
      3. 7.4.3  Slow-Start or Tracking Pin
      4. 7.4.4  Sequencing
      5. 7.4.5  Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
      6. 7.4.6  Overcurrent Protection
      7. 7.4.7  Frequency Shift
      8. 7.4.8  Reverse Overcurrent Protection
      9. 7.4.9  Synchronize Using the RT/CLK Pin
      10. 7.4.10 Power Good (PWRGD Pin)
      11. 7.4.11 Overvoltage Transient Protection
      12. 7.4.12 Thermal Shutdown
      13. 7.4.13 Small-Signal Model for Loop Response
      14. 7.4.14 Simple Small-Signal Model for Peak-Current-Mode Control
      15. 7.4.15 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 Selecting the Switching Frequency
        2. 8.2.2.2 Output Inductor Selection
        3. 8.2.2.3 Output Capacitor
        4. 8.2.2.4 Input Capacitor
        5. 8.2.2.5 Slow-Start Capacitor
        6. 8.2.2.6 Bootstrap Capacitor Selection
        7. 8.2.2.7 Output-Voltage and Feedback-Resistor Selection
        8. 8.2.2.8 Compensation
        9. 8.2.2.9 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 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.7 Output-Voltage and Feedback-Resistor Selection

For the example design, the R6 selection is 100 kΩ. Using Equation 33, calculate R7 as 80 kΩ. The nearest standard 1% resistor is 80.5 kΩ.

Equation 33. GUID-F8ECB5A0-3862-4ED6-8369-14C9760F845A-low.gif

Because of the internal design of the TPS54388C-Q1 device, there is a minimum output-voltage limit for any given input voltage. The output voltage can never be lower than the internal voltage reference of 0.8 V. Above 0.8 V, an output voltage limit may exist due to the minimum controllable on-time. In this case, Equation 34 gives the minimum output voltage:

Equation 34. GUID-1DA7EFE2-4719-41BC-B746-C31454F620FA-low.gif

where

  • VO(min) = minimum achievable output voltage
  • t(ONmin) = minimum controllable on-time (65 ns typical, 120 ns with no load)
  • f(SWmax) = maximum switching frequency, including tolerance
  • VI(max) = maximum input voltage
  • IO(min) = minimum load current
  • rDS(on) = minimum high-side MOSFET on-resistance (15 mΩ–19 mΩ)
  • R(L) = series resistance of output inductor

There is also a maximum achievable output voltage, which is limited by the minimum off-time. Equation 35 gives the maximum output voltage.

Equation 35. GUID-ADAA45B6-841C-412B-B012-9D4798308F6F-low.gif

where

  • VO(max) = maximum achievable output voltage
  • t(OFFmax) = maximum off-time (60 ns, typical)
  • f(SWmax) = maximum switching frequency, including tolerance
  • VI(min) = minimum input voltage
  • IO(max) = maximum load current
  • rDS(on) = maximum high-side MOSFET on-resistance (19 mΩ–30 mΩ)
  • R(L) = series resistance of output inductor