SLVSHN0 September   2024 TPS548B23

ADVANCE INFORMATION  

  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
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  D-CAP4 Control
      2. 7.3.2  Internal VCC LDO and Using External Bias On the VCC Pin
        1. 7.3.2.1 Powering the Device From a Single Bus
        2. 7.3.2.2 Powering the Device From a Split-Rail Configuration
      3. 7.3.3  Multifunction Configuration (CFG1-5) Pins
        1. 7.3.3.1 Multifunction Configuration (CFG1-2) Pins (Internal Feedback)
        2. 7.3.3.2 Multifunction Configuration (CFG1-2) Pins (External Feedback)
        3. 7.3.3.3 Multifunction Configuration (CFG3-5) Pins
      4. 7.3.4  Enable
      5. 7.3.5  Soft Start
      6. 7.3.6  Power Good
      7. 7.3.7  Overvoltage and Undervoltage Protection
      8. 7.3.8  Remote Sense
      9. 7.3.9  Low-side MOSFET Zero-Crossing
      10. 7.3.10 Current Sense and Positive Overcurrent Protection
      11. 7.3.11 Low-side MOSFET Negative Current Limit
      12. 7.3.12 Output Voltage Discharge
      13. 7.3.13 UVLO Protection
      14. 7.3.14 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Auto-Skip (PFM) Eco-mode Light Load Operation
      2. 7.4.2 Forced Continuous-Conduction 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 Output Voltage Setting Point
        2. 8.2.2.2 Choose the Switching Frequency
        3. 8.2.2.3 Choose the Inductor
        4. 8.2.2.4 Choose the Output Capacitor
        5. 8.2.2.5 Choose the Input Capacitors (CIN)
        6. 8.2.2.6 VCC Bypass Capacitor
        7. 8.2.2.7 BOOT Capacitor
        8. 8.2.2.8 PG Pullup Resistor
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    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)
  • VAN|19
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.3 Choose the Inductor

To calculate the value of the output inductor (LOUT), use Equation 9. The output capacitor filters the inductor-ripple current (IIND(ripple)). Therefore, selecting a high inductor-ripple current 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. On the other hand, larger ripple current increases output ripple voltage, but improves signal-to-noise ratio and helps to stabilize operation. Generally speaking, the inductance value must set the ripple current at approximately 15% to 40% of the maximum output current for a balanced performance.

For this design, the inductor-ripple current is set to 30% of 20A output current. With a 800klHz switching frequency, 16V as maximum VIN, and 3.3V as the output voltage, Based on these parmaters, Equation 9 calculates an inductance of 0.546μH . A nearest standard value of 0.55µH is chosen.

Equation 9. L = V I N m a x - V O U T × V O U T I R I P P L E × V I N m a x × f S W = 16   V - 3.3   V × 3.3   V 0.3 × 20 A × 16   V × 800   k H z = 0.546   μ H

The inductor requires a low DCR to achieve good efficiency. The inductor also requires enough room above peak inductor current before saturation. The inductor current ripple is estimated using Equation 10. For this design, by tying the CFG1 pin to VCC, IOC(valley) is set to 21A, thus peak inductor current under maximum VIN is calculated as 22.98A with Equation 11.

Equation 10. I R I P P L E = V I N m a x - V O U T × V O U T L × V I N m a x × f S W = 16   V - 3.3   V × 3.3   V 0.55 μ H × 16   V × 800   k H z = 5.95   A
Equation 11. I L ( P E A K ) = I O U T + I R I P P L E 2 = 20   A + 5.95   A 2 = 22.98   A
Equation 12. I L R M S = I O U T 2 + I R I P P L E 2 12 = 20   A 2 + 5.95   A 2 12 = 20.07   A

The selected inductance is a Coilcraft XAL7070-551MEB. This has a saturation current rating of 43 A , RMS current rating of 29-A and a DCR of 1.6 mΩ max. This inductor was selected for its low DCR to get high efficiency.