SLVS892F December   2008  – April 2019 TPS61175

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Switching Frequency
      2. 7.3.2 Soft Start
      3. 7.3.3 Overcurrent Protection
      4. 7.3.4 Enable and Thermal Shutdown
      5. 7.3.5 Undervoltage Lockout (UVLO)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Minimum ON Time and Pulse Skipping
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Custom Design with WEBENCH Tools
        2. 8.2.2.2  Determining the Duty Cycle
        3. 8.2.2.3  Selecting the Inductor
        4. 8.2.2.4  Computing the Maximum Output Current
        5. 8.2.2.5  Setting Output Voltage
        6. 8.2.2.6  Setting the Switching Frequency
        7. 8.2.2.7  Setting the Soft-Start Time
        8. 8.2.2.8  Selecting the Schottky Diode
        9. 8.2.2.9  Selecting the Input and Output Capacitors
        10. 8.2.2.10 Compensating the Small Signal Control Loop
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Development Support
      1. 11.2.1 Custom Design with WEBENCH Tools
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.3 Selecting the Inductor

The selection of the inductor affects steady state operation as well as transient behavior and loop stability. These factors make it the most important component in power regulator design. There are three important inductor specifications, inductor value, DC resistance and saturation current. Considering inductor value alone is not enough.

Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation level, its inductance can fall to some percentage of its 0-A value depending on how the inductor vendor defines saturation current. For CCM operation, the rule of thumb is to choose the inductor so that its inductor ripple current (ΔIL) is no more than a certain percentage (RPL% = 20–40%) of its average DC value (IIN(AVG) = IL(AVG)).

Equation 6. TPS61175 eq_il_lvs892.gif

Rearranging and solving for L gives:

Equation 7. TPS61175 eq_L_SLVS892.gif

Choosing the inductor ripple current to closer to 20% of the average inductor current results in a larger inductance value, maximizes the converter’s potential output current and minimizes EMI. Choosing the inductor ripple current closer to 40% of IL(AVG) results in a smaller inductance value, and a physically smaller inductor, improves transient response but results in potentially higher EMI and lower efficiency if the DCR of the smaller packaged inductor is significantly higher. Using an inductor with a smaller inductance value than computed above may result in the converter operating in DCM. This reduces the maximum output current of the boost converter, causes larger input voltage and output ripple, and typically reduces efficiency. Table 5 lists the recommended inductor for the TPS61175.

Table 5. Recommended Inductors for TPS61175

PART NUMBER L
(μH)		 DCR MAX
(mΩ)		 SATURATION CURRENT
(A)		 SIZE
(L × W × H mm)		 VENDOR
D104C2 10 44 3.6 10.4 × 10.4 × 4.8 TOKO
VLF10040 15 42 3.1 10 × 9.7 × 4 TDK
CDRH105RNP 22 61 2.9 10.5 × 10.3 × 5.1 Sumida
MSS1038 15 50 3.8 10 × 10.2 × 3.8 Coilcraft

The device has built-in slope compensation to avoid subharmonic oscillation associated with current mode control. If the inductor value is lower than 4.7 μH, the slope compensation may not be adequate, and the loop can be unstable. Applications requiring inductors above 47 μH have not been evaluated. Therefore, the user is responsible for verifying operation if they select an inductor that is outside the 4.7-μH to 47-μH recommended range.