SLVSAF7C September   2010  – April 2019 TPS61251

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Device Options
  7. 7 Pin Configuration and Functions
    1.     Pin 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 Current Limit Operation
      2. 9.3.2 Soft Start
      3. 9.3.3 Enable
      4. 9.3.4 Undervoltage Lockout (UVLO)
      5. 9.3.5 Power Good
      6. 9.3.6 Input Overvoltage Protection
      7. 9.3.7 Load Disconnect and Reverse Current Protection
      8. 9.3.8 Thermal Regulation
      9. 9.3.9 Thermal Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Power-Save Mode
      2. 9.4.2 Snooze Mode
      3. 9.4.3 100% Duty-Cycle Mode
  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 Output Voltage Setting
        3. 10.2.2.3 Average Input Current Limit
        4. 10.2.2.4 Maximum Output Current
        5. 10.2.2.5 Inductor Selection
        6. 10.2.2.6 Output Capacitor
        7. 10.2.2.7 Input Capacitor
        8. 10.2.2.8 Checking Loop Stability
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
    3. 12.3 Thermal Consideration
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
    2. 13.2 Development Support
      1. 13.2.1 Custom Design With WEBENCH® Tools
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resource
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.2.2.5 Inductor Selection

As for all switch mode power supplies two main passive components are required for storing the energy during operation. This is done by an inductor and an output capacitor. The inductor must be connected between VIN and SW pin to make sure that the TPS61251 device operates. To select the right inductor current rating the programmed input current limit as well as the current ripple through the inductor is necessary. Estimation of the maximum peak inductor current can be done using Equation 7.

Equation 7. TPS61251 eq_ILmax_DD_lvsaf7.gif

Regarding the example from above the current ripple (ΔIL) will be 290 mA and therefore an inductor with a rated current of about 800 mA should be used.

The TPS61251 device is designed to work with inductor values between 1 µH and 2.2 µH. TI recommends a 1.5 µH inductor for typical applications. In space constrained applications, it might be possible to consider smaller inductor values depending on the targeted inductor ripple current. Therefore, the inductor value can be reduced down to 1 µH without degrading the stability.

In regular boost converter designs the current through the inductor is defined by the switch current limit of the converters switches and therefore bigger inductors have to be chosen. The TPS61251 device allows the design engineer to reduce the current limit to the needs of the application regardless the maximum switch current limit of the converter. Programming a lower current value allows the use of smaller inductors without the danger to get into saturation.