SLVSDS9E July   2018  – August 2021 TPS63805 , TPS63806 , TPS63807

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Typical Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Control Loop Description
      2. 9.3.2  Precise Device Enable: Threshold- or Delayed Enable
      3. 9.3.3  Mode Selection (PFM/PWM)
      4. 9.3.4  Undervoltage Lockout (UVLO)
      5. 9.3.5  Soft Start
      6. 9.3.6  Adjustable Output Voltage
      7. 9.3.7  Overtemperature Protection - Thermal Shutdown
      8. 9.3.8  Input Overvoltage - Reverse-Boost Protection (IVP)
      9. 9.3.9  Output Overvoltage Protection (OVP)
      10. 9.3.10 Power-Good Indicator
    4. 9.4 Device Functional Modes
      1. 9.4.1 Peak-Current Mode Architecture
        1. 9.4.1.1 Reverse Current Operation, Negative Current
        2. 9.4.1.2 Boost Operation
        3. 9.4.1.3 Buck-Boost Operation
        4. 9.4.1.4 Buck Operation
      2. 9.4.2 Power Save Mode Operation
        1. 9.4.2.1 Current Limit Operation
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Custom Design With WEBENCH® Tools
        2. 10.2.2.2 Inductor Selection
        3. 10.2.2.3 Output Capacitor Selection
        4. 10.2.2.4 Input Capacitor Selection
        5. 10.2.2.5 Setting The Output Voltage
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
      2. 13.1.2 Development Support
        1. 13.1.2.1 Custom Design With WEBENCH® Tools
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.2.2.2 Inductor Selection

The inductor selection is affected by several parameters such as the following:

  • Inductor ripple current
  • Output voltage ripple
  • Transition point into power save mode
  • Efficiency

See Table 10-3 for typical inductors.

For high efficiencies, the inductor must have a low DC resistance to minimize conduction losses. Especially at high-switching frequencies, the core material has a high impact on efficiency. When using small chip inductors, the efficiency is reduced, mainly due to higher inductor core losses. This needs to be considered when selecting the appropriate inductor. The inductor value determines the inductor ripple current. The larger the inductor value, the smaller the inductor ripple current and the lower the conduction losses of the converter. Conversely, larger inductor values cause a slower load transient response. To avoid saturation of the inductor, the peak current for the inductor in steady-state operation is calculated using Equation 2. Only the equation which defines the switch current in boost mode is shown because this provides the highest value of current and represents the critical current value for selecting the right inductor.

Equation 1. GUID-6E308DC0-5977-4CD0-8346-4B720D8F54B7-low.gif
Equation 2. GUID-9B45BC90-8FFC-4DDA-A9F2-150C5CD96B1D-low.gif

where

  • D = Duty Cycle in Boost mode
  • f = Converter switching frequency
  • L = Inductor value
  • η = Estimated converter efficiency (use the number from the efficiency curves or 0.9 as an assumption)
Note:

The calculation must be done for the minimum input voltage in boost mode.

Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. It is recommended to choose an inductor with a saturation current 20% higher than the value calculated using Equation 2. Table 10-3 lists the possible inductors.

Table 10-3 List of Recommended Inductors
INDUCTOR VALUE [µH] SATURATION CURRENT [A] DCR [mΩ] PART NUMBER MANUFACTURER(1) SIZE (LxWxH mm)
0.47 5.4 7.6 XFL4015-471ME Coilcraft 4 x 4 x 2
0.47 5.5 26 DFE201612E Toko 2.0 x 1.6 x 1.2