SLVSDY5E January   2018  – February 2024 TPS61322

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and Functions
    1.     Pin Functions
  7. 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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Soft Start
      2. 7.3.2 Boost Controller Circuit
      3. 7.3.3 21
      4. 7.3.4 Undervoltage Lockout
      5. 7.3.5 Current Limit Operation
      6. 7.3.6 Overtemperature Protection
      7. 7.3.7 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Boost without Schottky Diode
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Maximum Output Current
          3. 8.2.1.2.3 Inductor Selection
          4. 8.2.1.2.4 35
          5. 8.2.1.2.5 Capacitor Selection
          6. 8.2.1.2.6 37
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Boost with Schottky Diode
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Inductor Selection
          2. 8.2.2.2.2 Schottky Diode Selection
          3. 8.2.2.2.3 Capacitor Selection
        3. 8.2.2.3 Application Curves
    3. 8.3 System Examples
      1. 8.3.1 Detail Design Schematics
  10. 9 Power Supply Recommendations
  11. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  12. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    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
  13. 12Revision History
  14. 13Mechanical, Packaging, and Orderable Information

Package Options

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

Because the inductor affects steady state operation, transient behavior, and loop stability, the inductor is the most important component in power regulator design. There are three important inductor specifications, inductor value, saturation current, and dc resistance (DCR).

The TPS61322xx is optimized to work with inductor values between 0.7 µH and 13 µH. The inductor values affect the switching frequency. The estimated switching frequency in continuous conduction mode(CCM) can be calculated by Equation 2. The switching frequency ƒSW is not a constant value, which is determined by the inductance, the inductor current ripple, the input voltage and the output voltage. The current ripple ILH is fixed to 200 mA typically, but it can be affected by the inductor value indirectly. Normally when a smaller inductor value is applied, the inductor current ramps up and down more quickly. The current ripple becomes bigger because the internal current comparator has delay to respond. If a smaller inductor peak current is required in applications, a higher inductor value can be used. However, The inductor and output capacitor must be considered together for the loop stability. The output capacitor and the inductance will influence the bandwidth and phase margin of the converter. Consequently, with a larger inductor, a bigger capacitor normally must be used to ensure the same L/C ratio for a stable loop. For best stability consideration, a 4.7-µH inductor is recommended for 2.2-V output voltage application.

Equation 2. GUID-60775ABC-13DF-401A-9091-BB11B5C3E539-low.gif

where

  • fSW is the switching frequency of the converter
  • ILH is the inductor current ripple
  • η is the boost converter power convert efficiency

Having selected the inductance value, follow Equation 3 to Equation 5 to calculate the inductor's peak current for the application. Depending on different load conditions, the TPS61322xx works in continuous current mode or discontinuous conduction mode(DCM). In different modes, the peak currents of the inductor are also different. Equation 3 provides an easy way to estimate whether the device works in CCM or DCM. Equation 4 shows the peak current when the device works in CCM and Equation 5 shows the peak current when the device works in DCM.

Equation 3. GUID-20F051EB-4B3D-455F-A989-8AC30636F9A4-low.gif

where

  • ILH is the inductor current ripple
  • η is the boost converter power convert efficiency
Equation 4. GUID-ADD22769-5931-4249-969B-1E6CEAB79462-low.gif

where

  • IL,peak is the peak current of the inductor
  • ILH is the inductor current ripple
  • η is the boost converter power convert efficiency
Equation 5. GUID-1BEFD189-0A90-42D6-A652-919CB6CA29FB-low.gif

where

  • IL,peak is the peak inductor.
  • ILH is the inductor current ripple

The saturation current of the inductor must be higher than the calculated peak inductor current, otherwise the excessive peak current in the inductor harms the device and reduces the system reliability.