SLVSH38 November   2023 TPS61377

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison Table
  6. 5 Pin Configuration and 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 VCC Power Supply
      2. 7.3.2 Enable and Programmable UVLO
      3. 7.3.3 Soft Start
      4. 7.3.4 Switching Frequency
      5. 7.3.5 Programmable Inductor Peak Current Limit
      6. 7.3.6 Shut Down
      7. 7.3.7 Overvoltage Protection
      8. 7.3.8 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation
      2. 7.4.2 Forced PWM Mode
      3. 7.4.3 Auto PFM Mode
  9. 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 Setting Output Voltage
        2. 8.2.2.2 Inductor Selection
        3. 8.2.2.3 Bootstrap Capacitor Selection
        4. 8.2.2.4 Input Capacitor Selection
        5. 8.2.2.5 Output Capacitor Selection
        6. 8.2.2.6 Loop Stability
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
        1. 8.4.2.1 Thermal Considerations
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

8.2.2.5 Output Capacitor Selection

The output capacitor is mainly selected to meet the requirements at load transient or steady state. The loop is compensated for the output capacitor selected. The output ripple voltage is related to the equivalent series resistance (ESR) of the capacitor and its capacitance. Assuming a capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated by Equation 8:

Equation 8. GUID-02C13409-FA91-43D7-A1A1-AA0D05B0F98F-low.gif

where

  • COUT is the output capacitor
  • IOUT is the output current
  • VOUT is the output voltage
  • VIN is the input voltage
  • ΔV is the output voltage ripple required
  • ƒSW is the switching frequency

The additional output ripple component caused by ESR is calculated by Equation 9:

Equation 9. ΔVESR=ILpeak×RESR

where

  • ΔVESR is the output voltage ripple caused by ESR
  • RESR is the resistor in series with the output capacitor

For the ceramic capacitor, the ESR ripple can be neglected. However, for the tantalum or electrolytic capacitors, it must be considered if used.

The minimum ceramic output capacitance needed to meet a load transient requirement can be estimated using Equation 10:

Equation 10. GUID-6BE71636-E837-4C3E-ADB7-3EF40D2830DF-low.gif

where

  • ΔISTEP is the transient load current step
  • ΔVTRAN is the allowed voltage dip for the load current step
  • ƒBW is the control loop bandwidth (that is, the frequency where the control loop gain crosses zero)

Take care when evaluating the derating of a ceramic capacitor under the DC bias. Ceramic capacitors can derate by as much as 70% of the capacitance at the respective rated voltage. Therefore, enough margins on the voltage rating must be considered to ensure adequate capacitance at the required output voltage.