SLVSE22B September   2017  – June 2018 TPS560430

UNLESS OTHERWISE NOTED, this document contains PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency vs Output Current VOUT = 5 V, 1100 kHz, PFM
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
    7. 7.7 Switching Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Fixed Frequency Peak Current Mode Control
      2. 8.3.2 Adjustable Output Voltage
      3. 8.3.3 Enable
      4. 8.3.4 Minimum ON-Time, Minimum OFF-Time and Frequency Foldback
      5. 8.3.5 Bootstrap Voltage
      6. 8.3.6 Over Current and Short Circuit Protection
      7. 8.3.7 Soft Start
      8. 8.3.8 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Shutdown Mode
      2. 8.4.2 Active Mode
      3. 8.4.3 CCM Mode
      4. 8.4.4 Light-Load Operation (PFM Version)
      5. 8.4.5 Light-Load Operation (FPWM Version)
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Custom Design With WEBENCH® Tools
        2. 9.2.2.2 Output Voltage Set-Point
        3. 9.2.2.3 Switching Frequency
        4. 9.2.2.4 Inductor Selection
        5. 9.2.2.5 Output Capacitor Selection
        6. 9.2.2.6 Input Capacitor Selection
        7. 9.2.2.7 Bootstrap Capacitor
        8. 9.2.2.8 Under Voltage Lockout Set-Point
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 Compact Layout for EMI Reduction
      2. 11.1.2 Feedback Resistors
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Development Support
        1. 12.1.1.1 Custom Design With WEBENCH® Tools
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DBV|6
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.2.5 Output Capacitor Selection

The device is designed to be used with a wide variety of LC filters. It is generally desired to use as little output capacitance as possible to keep cost and size down. The output capacitor (s), COUT, should be chosen with care since it directly affects the steady state output voltage ripple, loop stability, output voltage overshoot and undershoot during load current transient. The output voltage ripple is essentially composed of two parts. One is caused by the inductor current ripple going through the Equivalent Series Resistance (ESR) of the output capacitors:

Equation 10. TPS560430 slvse22-equation-10.gif

The other is caused by the inductor current ripple charging and discharging the output capacitors:

Equation 11. TPS560430 slvse22-equation-11.gif

The two components in the voltage ripple are not in phase, so the actual peak-to-peak ripple is smaller than the sum of the two peaks.

Output capacitance is usually limited by transient performance specifications if the system requires tight voltage regulation with presence of large current steps and fast slew rate. When a large load step happens, output capacitors provide the required charge before the inductor current can slew up to the appropriate level. The regulator’s control loop usually needs 8 or more clock cycles to regulate the inductor current equal to the new load level. The output capacitance must be large enough to supply the current difference for 8 clock cycles to maintain the output voltage within the specified range. Equation 12 shows the minimum output capacitance needed for specified VOUT overshoot and undershoot.

Equation 12. TPS560430 slvse22-equation-12.gif

where

  • KIND = Ripple ratio of the inductor current (ΔiL / IOUT)
  • IOL = Low level output current during load transient
  • IOH = High level output current during load transient
  • VOUT_SHOOT = Target output voltage overshoot or undershoot

For this design example, the target output ripple is 30 mV. Presuppose ΔVOUT_ESR = ΔVOUT_C = 30 mV, and chose KIND = 0.4. Equation 10 yields ESR no larger than 125 mΩ and Equation 11 yields COUT no smaller than 0.91 µF. For the target overshoot and undershoot limitation of this design, ΔVOUT_SHOOT = 5% × VOUT = 250 mV. The COUT can be calculated to be no smaller than 8.3 µF by Equation 12. In summary, the most stringent criteria for the output capacitor is 8.3 µF. Consider of derating, one 22-µF, 10-V, X7R ceramic capacitor with 10-mΩ ESR is used.