SLUSEE1C may   2020  – april 2023 TPS543320

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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  VIN Pins and VIN UVLO
      2. 7.3.2  Enable and Adjustable UVLO
      3. 7.3.3  Adjusting the Output Voltage
      4. 7.3.4  Switching Frequency Selection
      5. 7.3.5  Switching Frequency Synchronization to an External Clock
        1. 7.3.5.1 Internal PWM Oscillator Frequency
        2. 7.3.5.2 Loss of Synchronization
        3. 7.3.5.3 Interfacing the SYNC/FSEL Pin
      6. 7.3.6  Ramp Amplitude Selection
      7. 7.3.7  Soft Start and Prebiased Output Start-Up
      8. 7.3.8  Mode Pin
      9. 7.3.9  Power Good (PGOOD)
      10. 7.3.10 Current Protection
        1. 7.3.10.1 Positive Inductor Current Protection
        2. 7.3.10.2 Negative Inductor Current Protection
      11. 7.3.11 Output Overvoltage and Undervoltage Protection
      12. 7.3.12 Overtemperature Protection
      13. 7.3.13 Output Voltage Discharge
    4. 7.4 Device Functional Modes
      1. 7.4.1 Forced Continuous-Conduction Mode
      2. 7.4.2 Discontinuous Conduction Mode During Soft Start
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 3.3-V Output, 1.0-MHz Application
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Switching Frequency
          2. 8.2.1.2.2  Output Inductor Selection
          3. 8.2.1.2.3  Output Capacitor
          4. 8.2.1.2.4  Input Capacitor
          5. 8.2.1.2.5  Adjustable Undervoltage Lockout
          6. 8.2.1.2.6  Output Voltage Resistors Selection
          7. 8.2.1.2.7  Bootstrap Capacitor Selection
          8. 8.2.1.2.8  BP5 Capacitor Selection
          9. 8.2.1.2.9  PGOOD Pullup Resistor
          10. 8.2.1.2.10 Current Limit Selection
          11. 8.2.1.2.11 Soft-Start Time Selection
          12. 8.2.1.2.12 Ramp Selection and Control Loop Stability
          13. 8.2.1.2.13 MODE Pin
        3. 8.2.1.3 Application Curves
      2. 8.2.2 1.8-V Output, 1.5-MHz Application
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  9. 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
  10. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
8.2.1.2.2 Output Inductor Selection

To calculate the value of the output inductor, use Equation 6. KIND is a ratio that represents the amount of inductor ripple current relative to the maximum output current. The inductor ripple current is filtered by the output capacitor. Therefore, choosing high inductor ripple currents impacts the selection of the output capacitor because the output capacitor must have a ripple current rating equal to or greater than the inductor ripple current. Choosing small inductor ripple currents can degrade the transient response performance. The inductor ripple, KIND, is normally from 0.1 to 0.4 for the majority of applications giving a peak-to-peak ripple current range of 0.3 A to 1.2 A. The recommended minimum target IRIPPLE is 0.2 A or larger.

For this design example, KIND = 0.3 is used and the inductor value is calculated to be 3.0 µH. An inductor with an inductance of 3.3 µH is selected. The RMS (Root Mean Square) current and saturation current ratings of the inductor must not be exceeded. The RMS and peak inductor current can be found from Equation 8 and Equation 9. For this design, the RMS inductor current is 3 A, and the peak inductor current is 3.4 A. The chosen inductor is a XEL5050-332MEB. The inductor has a saturation current rating of 8.4 A, an RMS current rating of 10.6 A, and a typical DC series resistance of 13.3 mΩ.

The peak current through the inductor is the inductor ripple current plus the output current. During power up, faults, or transient load conditions, the inductor current can increase above the calculated peak inductor current level calculated in Equation 9. In transient conditions, the inductor current can increase up to the switch current limit of the device. For this reason, the most conservative approach is to specify the current ratings of the inductor based on the switch current limit rather than the steady-state peak inductor current.

Equation 6. GUID-81F0380E-C1A0-4404-B291-64A6E15D1A01-low.gif
Equation 7. GUID-976190FB-7AC1-4014-B511-E8E0930EB7C3-low.gif
Equation 8. GUID-345EBC09-F268-4149-8F7E-4042378B2792-low.gif
Equation 9. GUID-B46D00C0-298F-4B16-A4A0-3A19AF2C9428-low.gif

Table 8-2 shows recommended E6 standard inductor values for other common output voltages with a 1-MHz fSW. Using an inductance outside this recommended range typically works but the performance can be affected and must be evaluated. The recommended value is calculated for a nominal input voltage of 12 V. The minimum values are calculated with the maximum input voltage of 18 V. The maximum values are calculated with an input voltage of 5 V for all but the 5-V output. For the 5-V output, an 8-V input is used.

Table 8-2 Recommended Inductor Values
OUTPUT VOLTAGE (V) SWITCHING FREQUENCY (kHz) MINIMUM INDUCTANCE (µH) RECOMMENDED INDUCTANCE FOR 3 A (µH) RECOMMENDED INDUCTANCE FOR 2 A (µH) MAXIMUM INDUCTANCE (µH)
1 1000 0.68 1 1.5 3.3
1.8 1.5 2.2 3.3 4.7
3.3 2.2 2.2 4.7 4.7
5 3.3 3.3 4.7 6.8