JAJSO66A December   2023  – January 2024 TPS61289

PRODUCTION DATA  

  1.   1
  2. 1 特長
  3. 2 アプリケーション
  4. 3 概要
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 Bidirectional Operation Configuration
      2. 6.3.2 VCC Power Supply
      3. 6.3.3 VHIGH and VCC Undervoltage Lockout (UVLO)
      4. 6.3.4 Enable and Programmable EN/UVLO
      5. 6.3.5 Switching Frequency
      6. 6.3.6 Programmable Switching Peak and Valley Current Limit
      7. 6.3.7 External Clock Synchronization
      8. 6.3.8 VHIGH Overvoltage Protection
      9. 6.3.9 Thermal Shutdown
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1 Bootstrap Capacitor Selection
        2. 7.2.2.2 Inductor Selection
        3. 7.2.2.3 MOSFET Selection
        4. 7.2.2.4 VLOW/VHIGH Output Capacitor Selection
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
        1. 7.4.2.1 Thermal Considerations
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 サポート・リソース
    4. 8.4 Trademarks
    5. 8.5 静電気放電に関する注意事項
    6. 8.6 用語集
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7.2.2.2 Inductor Selection

Since the selection of the inductor affects the steady state of the power supply operation, transient behavior, loop stability, and buck/boost converter efficiency, the inductor is the most important component in switching power regulator design. The three most important specifications to the performance of the inductor are the inductance value, DC resistance, and saturation current.

The TPS61289 is designed to work with inductor values between 2.2µH and 10µH. A 2.2µH inductor is typically available in a smaller or lower-profile package, while a 10µH inductor produces lower inductor current ripple.

Inductor values can have ±20% or even ±30% tolerance with no current bias. When the inductor current approaches saturation level, the inductance can decrease 20% to 35% from the value at 0A current, depending on how the inductor vendor defines saturation. When selecting an inductor, verify that the rated current of the inductor, especially the saturation current, is larger than the peak current during the operation.

Follow Equation 5 to Equation 7 to calculate the peak current of the inductor. To calculate the current in the worst case, use the minimum input voltage, maximum output voltage, and maximum load current of the application. To leave enough design margin, TI recommends using the minimum switching frequency, the inductor value with –30% tolerance, and a low-power conversion efficiency for the calculation.

Calculate the inductor DC current as in Equation 5.

Equation 5. I D C = V O U T × I O U T V I N × η

where

  • VOUT is the voltage of VHIGH in boost mode or VLOW in buck mode.
  • IOUT is the output current of the converter.
  • VIN is the voltage of VHIGH in buck mode or VLOW in boost mode.
  • η is the power conversion efficiency.

Calculate the inductor current peak-to-peak ripple as in Equation 6.

Equation 6. I P P = 1 L × 1 V O U T × V I N + 1 V I N × f S W

where

  • IPP is the inductor peak-to-peak ripple.
  • L is the inductor value.
  • ƒSW is the switching frequency.
  • VOUT is the voltage of VHIGH in boost mode or VLOW in buck mode.
  • VIN is the voltage of VHIGH in buck mode or VLOW in boost mode.

Therefore, the peak current, ILpeak, seen by the inductor is calculated with Equation 7.

Equation 7. I L p e a k = I D C + I P P 2

Set the current limit of the TPS61289 higher than the peak current, ILpeak. Then select the inductor with saturation current higher than the setting current limit.

Buck or boost converter efficiency is dependent on the resistance of the current path, the switching loss associated with the switching MOSFETs, and the core loss of the inductor. The TPS61289 has optimized the internal low side switch resistance. However, the overall efficiency is affected significantly by the DC resistance (DCR) of the inductor, equivalent series resistance (ESR) at the switching frequency, and the core loss. Core loss is related to the core material and different inductors have different core loss. For a certain inductor, larger current ripple generates higher DCR and ESR conduction losses and higher core loss. Usually, a data sheet of an inductor does not provide the ESR and core loss information. If needed, consult the inductor vendor for detailed information. Generally, TI recommends an inductor with lower DCR and ESR. However, there is a tradeoff among the inductance of the inductor, DCR and ESR resistance, and the footprint. Furthermore, shielded inductors typically have higher DCR than unshielded inductors. Table 7-2 lists recommended inductors for the TPS61289. Verify whether the recommended inductor can support the user target application with the previous calculations and bench evaluation.

Table 7-2 Recommended Inductors
PART NUMBER L (µH) DCR MAX (mΩ) SATURATION CURRENT(A) SIZE (L × W × H mm) VENDOR
XGL1060-332ME 3.3 5.7 26.0 10.0 x 11.3 x 6.0 Coilcraft
XAL1060-222ME 2.2 4.95 32.0 10.0 x 11.3 x 6.0 Coilcraft
CMLE105T-2R2MS-99 2.2 4.5 26.0 10.3 x 11.5 x 4.8 Cyntec