SLVSGP3A May   2023  – February 2024 TPS54KB20

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1  Internal VCC LDO and Using External Bias On the VCC Pin
      2. 6.3.2  Enable
      3. 6.3.3  Adjustable Soft Start
      4. 6.3.4  Power Good
      5. 6.3.5  Output Voltage Setting
      6. 6.3.6  Remote Sense
      7. 6.3.7  D-CAP4 Control
      8. 6.3.8  Multifunction Select (MSEL) Pin
      9. 6.3.9  Low-side MOSFET Zero-Crossing
      10. 6.3.10 Current Sense and Positive Overcurrent Protection
      11. 6.3.11 Low-side MOSFET Negative Current Limit
      12. 6.3.12 Overvoltage and Undervoltage Protection
      13. 6.3.13 Output Voltage Discharge
      14. 6.3.14 UVLO Protection
      15. 6.3.15 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Auto-Skip Eco-mode Light Load Operation
      2. 6.4.2 Forced Continuous-Conduction Mode
      3. 6.4.3 Powering the Device From a Single Bus
      4. 6.4.4 Powering the Device From a Split-rail Configuration
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Output Voltage Setting Point
        2. 7.2.2.2  Choose the Switching Frequency and the Operation Mode
        3. 7.2.2.3  Choose the Inductor
        4. 7.2.2.4  Set the Current Limit (ILIM)
        5. 7.2.2.5  Choose the Output Capacitor
        6. 7.2.2.6  RAMP Selection
        7. 7.2.2.7  Choose the Input Capacitors (CIN)
        8. 7.2.2.8  Soft-Start Capacitor (SS Pin)
        9. 7.2.2.9  EN Pin Resistor Divider
        10. 7.2.2.10 VCC Bypass Capacitor
        11. 7.2.2.11 BOOT Capacitor
        12. 7.2.2.12 RC Snubber
        13. 7.2.2.13 PG Pullup Resistor
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

7.2.2.4 Set the Current Limit (ILIM)

The RILIM resistor sets the valley current limit. Equation 16 and Equation 17 calculate the recommended current limit target. This includes the tolerance of the inductor and a factor of 0.9 for the tolerance of the current limit threshold. This example uses an estimation of 10% tolerance. Refer to the specification table for tolerance across different RILIM values. Equation 19 calculates the RILIM resistor to set the current limit. The typical valley current limit target is 27.5A and the closest standard value for RILIM is 4.32kΩ.

Equation 16. I LIM_VALLEY = I O U T - 1 2 × V I N m i n - V O U T × V O U T L × 1 + L T O L × V I N m i n × f S W × 1 0.9
Equation 17. I LIM_VALLEY = 25   A - 1 2 × 4.5   V - 3.3   V × 3.3   V 0.47   μ H × 1 + 0.2 × 4.5   V × 800   k H z × 1 0.9 = 26.7   A
Equation 18. R I L I M = 120000 I LIM_VALLEY
Equation 19. R I L I M = 120000 27.5   A = 4.36   k Ω

With the current limit set, Equation 20 calculates the typical maximum output current at current limit. Equation 21 calculates the typical peak current at current limit. As mentioned in Choose the Inductor, the saturation behavior of the inductor at the peak current during current limit must be considered. For worst case calculations, the tolerance of the inductance and the current limit must be included.

Equation 20. I O U T _ L I M m i n = I LIM_VALLEY + 1 2 × V I N m i n - V O U T × V O U T L × V I N m i n × f S W = 27.5   A + 1 2 × 4.5   V - 3.3   V × 3.3   V 0.47   μ H × 4.5   V × 800   k H z = 28.7   A
Equation 21. I L ( P E A K ) = I LIM_VALLEY + V I N m a x - V O U T × V O U T L × V I N m a x × f S W = 27.5   A + 16   V - 3.3   V × 3.3   V 0.47   μ H × 16   V × 800   k H z = 34.5   A