SLVS821E May   2008  – May 2019 TPS61087

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 Soft-Start
      2. 7.3.2 Frequency Select Pin (FREQ)
      3. 7.3.3 Undervoltage Lockout (UVLO)
      4. 7.3.4 Thermal Shutdown
      5. 7.3.5 Overvoltage Prevention
    4. 7.4 Device Functional Modes
  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 Inductor Selection
        2. 8.2.2.2 Rectifier Diode Selection
        3. 8.2.2.3 Setting the Output Voltage
        4. 8.2.2.4 Compensation (COMP)
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Output Capacitor Selection
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
      1. 8.3.1 General Boost Application Circuits
      2. 8.3.2 TFT LCD Application
      3. 8.3.3 White LED Applications
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Third-Party Products Disclaimer
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.1 Inductor Selection

The TPS61087 is designed to work with a wide range of inductors. The main parameter for the inductor selection is the saturation current of the inductor which should be higher than the peak switch current as calculated in the Detailed Design Procedure section with additional margin to cover for heavy load transients. An alternative, more conservative, is to choose an inductor with a saturation current at least as high as the maximum switch current limit of 4.8 A. The other important parameter is the inductor DC resistance. Usually the lower the DC resistance the higher the efficiency. It is important to note that the inductor DC resistance is not the only parameter determining the efficiency. Especially for a boost converter where the inductor is the energy storage element, the type and core material of the inductor influences the efficiency as well. At high switching frequencies of 1.2 MHz inductor core losses, proximity effects and skin effects become more important. Usually an inductor with a larger form factor gives higher efficiency. The efficiency difference between different inductors can vary between 2% to 10%. For the TPS61087, inductor values between 3 μH and 6 μH are a good choice with a switching frequency of 1.2 MHz, typically 3.3 μH. At 650 kHz TI recommends inductors between 6 μH and 13 μH, typically 6.8 μH. Possible inductors are shown in Table 3.

Typically, TI recommends an inductor current ripple below 35% of the average inductor current. Therefore, the following equation can be used to calculate the inductor value, L:

Equation 5. TPS61087 q1_1_lvs821.gif

with

VIN Minimum input voltage
VS Output voltage
Iout Maximum output current in the application
fS Converter switching frequency (typically 1.2 MHz or 650 kHz)
η Estimated converter efficiency (use the number from the efficiency plots or 90% as an estimation)

Table 3. Inductor Selection

L
(μH)		 SUPPLIER COMPONENT CODE SIZE
(L×W×H mm)		 DCR TYP
(mΩ)		 Isat (A)
1.2 MHz
4.2 Sumida CDRH5D28 5.7 × 5.7 × 3 23 2.2
4.7 Wurth Elektronik 7447785004 5.9 × 6.2 × 3.3 60 2.5
5 Coilcraft MSS7341 7.3 × 7.3 × 4.1 24 2.9
5 Sumida CDRH6D28 7 × 7 × 3 23 2.4
4.6 Sumida CDR7D28 7.6 × 7.6 × 3 38 3.15
4.7 Wurth Elektronik 7447789004 7.3 × 7.3 × 3.2 33 3.9
3.3 Wurth Elektronik 7447789003 7.3 × 7.3 × 3.2 30 4.2
650 kHz
10 Wurth Elektronik 744778910 7.3 × 7.3 × 3.2 51 2.2
10 Sumida CDRH8D28 8.3 × 8.3 × 3 36 2.7
6.8 Sumida CDRH6D26HPNP 7 × 7 × 2.8 52 2.9
6.2 Sumida CDRH8D58 8.3 × 8.3 × 6 25 3.3
10 Coilcraft DS3316P 12.95 × 9.40 × 5.08 80 3.5
10 Sumida CDRH8D43 8.3 × 8.3 × 4.5 29 4
6.8 Wurth Elektronik 74454068 12.7 × 10 × 4.9 55 4.1