SLVSDU5A April   2018  – November 2019 TPS57112C-Q1

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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 Typical Characteristics Curves
  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
        1. 7.3.3.1 Error Amplifier
      4. 7.3.4 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 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
    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

Package Options

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

8.2.2.2 Output Inductor Selection

The inductor selected works for the entire TPS57112C-Q1 input-voltage range. To calculate the value of the output inductor, use Equation 21. The k(IND) coefficient represents the amount of ripple current in the inductor relative to the maximum output current. The output capacitor filters the inductor ripple current. Therefore, choosing high inductor ripple currents impacts the selection of the output capacitor, because the output capacitor must have a ripple-current rating equal to or greater than the inductor ripple current. In general, the inductor ripple value is at the discretion of the designer; however, k(IND) is normally from 0.1 to 0.3 for the majority of applications.

For this design example, use k(IND) = 0.3; the calculated value of the inductor is 2.2 µH. For this design, the choice is a nearest standard value of 1.5 μH. For the output-filter inductor, it is important not to exceed the rms current and saturation current ratings. Use Equation 23 and Equation 24 to find the rms and peak inductor currents.

For this design, the rms inductor current is 2 A and the peak inductor current is 2.42 A. The chosen inductor is a Coilcraft XLA4020-152ME_. It has a saturation current rating of 9.6 A and an rms current rating of 7.5 A.

The current flowing through the inductor is the inductor ripple current plus the output current. During power up, faults, or transient load conditions, the inductor current can increase above the calculated peak inductor current level calculated previously. In transient conditions, the inductor current can increase up to the switch-current limit of the device. For this reason, the most conservative approach is to specify an inductor with a saturation current rating equal to or greater than the switch-current limit rather than the peak inductor current.

Equation 21. TPS57112C-Q1 eq12_L1_SLVSAH5.gif
Equation 22. TPS57112C-Q1 eq13_iripp_SLVSAH5.gif
Equation 23. TPS57112C-Q1 eq14_ilrms_SLVSAH5.gif
Equation 24. TPS57112C-Q1 eq15_ilpeak_SLVSAH5.gif