SNVSAZ4A February   2021  – March 2021 TPS541620

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, Internally Compensated Advanced-Current-Mode Control
      2. 7.3.2  Enable and UVLO
      3. 7.3.3  Internal LDO
      4. 7.3.4  Pre-biased Output Start-up
      5. 7.3.5  Current Sharing
      6. 7.3.6  Frequency Selection and Minimum On-Time and Off-Time
      7. 7.3.7  Ramp Compensation Selection
      8. 7.3.8  Soft Start
      9. 7.3.9  Remote Sense Function
      10. 7.3.10 Adjustable Output Voltage
      11. 7.3.11 Power Good
      12. 7.3.12 Overcurrent Protection
      13. 7.3.13 Overvoltage and Undervoltage Protection
      14. 7.3.14 Overtemperature Protection
      15. 7.3.15 Frequency Synchronization
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application - Dual Independent Outputs
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  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  Output Voltage Resistors Selection
        6. 8.2.2.6  Adjustable Undervoltage Lockout
        7. 8.2.2.7  Bootstrap Capacitor Selection
        8. 8.2.2.8  BP5 Capacitor Selection
        9. 8.2.2.9  PGOOD Pullup Resistor
        10. 8.2.2.10 Current Limit
        11. 8.2.2.11 Soft-Start Time Selection
        12. 8.2.2.12 MODE1 and MODE2 Pins
      3. 8.2.3 Application Curves
      4. 8.2.4 Typical Application - 2-Phase Operation
        1. 8.2.4.1 Design Requirements
        2. 8.2.4.2 Detailed Design Procedure
          1. 8.2.4.2.1  Switching Frequency
          2. 8.2.4.2.2  Output Inductor Selection
          3. 8.2.4.2.3  Output Capacitor
          4. 8.2.4.2.4  Input Capacitor
          5. 8.2.4.2.5  Output Voltage Resistors Selection
          6. 8.2.4.2.6  Adjustable Undervoltage Lockout
          7. 8.2.4.2.7  Bootstrap Capacitor Selection
          8. 8.2.4.2.8  BP5 Capacitor Selection
          9. 8.2.4.2.9  PGOOD Pullup Resistor
          10. 8.2.4.2.10 Current Limit
          11. 8.2.4.2.11 Soft-Start Time Selection
          12. 8.2.4.2.12 MODE1 Pin
        3. 8.2.4.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
      1. 10.2.1 Thermal Performance
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    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

8.2.2.2 Output Inductor Selection

To calculate the effective value of the output inductor, use Equation 24. K is a ratio that represents the amount of inductor ripple current relative to the maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing high inductor ripple currents impacts the selection of the output capacitor since the output capacitor must have a ripple current rating equal to or greater than the inductor ripple current. Choosing small inductor ripple currents (through a large inductor) can degrade the transient response performance. The inductor ripple, K, is normally 0.1 to 0.4 for the majority of applications, giving a peak-to-peak ripple current range of 0.6 A to 2.4 A. The target Iripple must be 0.3 A or larger.

For this design example, K = 0.3 is used and the inductor values Lo1 and Lo2 are calculated to be 0.506 µH and 1.329 µH, respectively. An inductor with an inductance of 0.56 μH is selected for VOUT1 and 1.2 μH for VOUT2. It is important that the RMS (Root Mean Square) current and saturation current ratings of the inductor not be exceeded. The RMS and peak inductor current can be found in Equation 26 and Equation 27, respectively. For VOUT1 in this design, the RMS inductor current is 6.019 A and the peak inductor current is 6.833 A. The chosen inductor is a Coilcraft XAL6030-561. For VOUT2 in this design, the RMS inductor current is 6.032 A and the peak inductor current is 7.073 A. The chosen inductor for VOUT2 is a Coilcraft XAL6030-122. XAL6030-561 has a saturation current rating of 29 A, an RMS current rating of 17 A, and a typical DC series resistance of 3.01 mΩ. The XAL6030-122 has a saturation current rating of 22 A, an RMS current rating of 13 A, and a typical DC series resistance of 6.8 mΩ.

The peak current through the inductor is the inductor ripple current plus the DC output current. During power up, faults, or transient load conditions, the inductor current can increase above the calculated peak inductor current level calculated in Equation 27. 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 the current ratings of the inductor based on the switch current limit rather than the steady-state peak inductor current.

Equation 24. GUID-20200915-CA0I-VF3X-KFZS-TF8P7VGQXCLH-low.gif

Equation 25. GUID-20200915-CA0I-VGRP-GCMF-6SZJMH9WDN9M-low.gif

Equation 26. GUID-20200915-CA0I-RG3T-XFVR-TJQQDLB6HSCC-low.gif

Equation 27. GUID-20200915-CA0I-WHQJ-GKZ7-RZVHDP1V6CNS-low.gif