SLVS642F April   2006  – January 2024 TPS5420

PRODUCTION DATA  

  1.   1
  2. 1Features
  3. 2Applications
  4. 3Description
  5. 4Electrostatic Discharge Caution
  6. 5Ordering Information
  7. 6Pin Assignments
    1. 6.1 Terminal Functions
  8. 7Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information 
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  9. 8Application Information
    1. 8.1 Functional Block Diagram
    2. 8.2 Detailed Description
      1. 8.2.1  Oscillator Frequency
      2. 8.2.2  Voltage Reference
      3. 8.2.3  Enable (ENA) and Internal Slow Start
      4. 8.2.4  Undervoltage Lockout (UVLO)
      5. 8.2.5  Boost Capacitor (BOOT)
      6. 8.2.6  Output Feedback (VSENSE)
      7. 8.2.7  Internal Compensation
      8. 8.2.8  Voltage Feed Forward
      9. 8.2.9  Pulse-Width-Modulation (PWM) Control
      10. 8.2.10 Overcurrent Limiting
      11. 8.2.11 Overvoltage Protection
      12. 8.2.12 Thermal Shutdown
      13. 8.2.13 PCB Layout
      14. 8.2.14 Application Circuits
      15. 8.2.15 Design Procedure
        1. 8.2.15.1  Design Parameters
        2. 8.2.15.2  Switching Frequency
        3. 8.2.15.3  Input Capacitors
        4. 8.2.15.4  Output Filter Components
          1. 8.2.15.4.1 Inductor Selection
          2. 8.2.15.4.2 Capacitor Selection
          3.        40
          4.        41
        5. 8.2.15.5  Output Voltage Setpoint
        6. 8.2.15.6  Boot Capacitor
        7. 8.2.15.7  Catch Diode
        8. 8.2.15.8  Additional Circuits
        9. 8.2.15.9  Circuit Using Ceramic Output Filter Capacitors
        10. 8.2.15.10 Output Filter Component Selection
        11. 8.2.15.11 External Compensation Network
    3. 8.3 Advanced Information
      1. 8.3.1 Output Voltage Limitations
      2. 8.3.2 Internal Compensation Network
      3. 8.3.3 Thermal Calculations
    4. 8.4 Performance Graphs
  10. 9Revision History

Package Options

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

To calculate the minimum value of the output inductor, use Equation 4:

Equation 4. GUID-6CCF7229-25D7-4B29-86C3-7A051FC71C31-low.gif

KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current. Three things need to be considered when determining the amount of ripple current in the inductor: the peak to peak ripple current affects the output ripple voltage amplitude, the ripple current affects the peak switch current, and the amount of ripple current determines at what point the circuit becomes discontinuous. For designs using the TPS5420, KIND of 0.2 to 0.3 yields good results. Low output ripple voltages is obtained when paired with the proper output capacitor, the peak switch current is below the current limit set point, and low load currents can be sourced before discontinuous operation.

For this design example, use KIND = 0.2, and the minimum inductor value is 27 μH. The standard value used in this design is 33 μH.

For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded. The RMS inductor current can be found from Equation 5:

Equation 5. GUID-B6B9A193-4405-42DA-B094-E94256CF5FD3-low.gif

and the peak inductor current can be determined using Equation 6:

Equation 6. GUID-EAAF707A-1ACB-483A-8C70-649005E3CCAD-low.gif

For this design, the RMS inductor current is 2.002 A, and the peak inductor current is 2.16 A. The chosen inductor is a Coilcraft MSS1260-333 type. The nominal inductance is 33 μH. It has a saturation current rating of 2.2 A and a RMS current rating of 2.7 A, which meets the requirements. Inductor values for use with the TPS5420 are in the range of 10 μH to 100 μH.