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

7.2.2.2 Choose the Switching Frequency and the Operation Mode

The switching frequency and operation mode are configured by the resistor on MSEL pin. Select one of three switching frequencies: 800kHz, 1.1MHz, or 1.4MHz. Refer to Table 6-4 for the relationship between the switching frequency, operation mode, ramp, and RMSEL.

Switching frequency selection is a tradeoff between higher efficiency and smaller system design size. Lower switching frequency yields higher overall efficiency but relatively bigger external components. Higher switching frequencies cause additional switching losses which impact efficiency and thermal performance. For this design, set the switching frequency to 800kHz, and set the light load operating mode as Skip-mode (DCM).

When selecting the switching frequency of a buck converter, the minimum on-time and minimum off-time must be considered. Equation 9 calculates the maximum fSW before being limited by the minimum on-time. When hitting the minimum on-time limits of a converter with D-CAP4 control, the effective switching frequency changes to keep the output voltage regulated. This calculation ignores resistive drops in the converter to give a worst case estimation.

Equation 9. f S W m a x = V O U T V I N m a x × 1 t O N _ M I N = 3.3   V 16   V × 1 30   n s = 6875   k H z
Equation 10 calculates the maximum fSW before being limited by the minimum off-time. When hitting the minimum off-time limits of a converter with D-CAP4 control, the operating duty cycle maxes out and the output voltage begins to drop with the input voltage. This equation requires the DC resistance of the inductor, RDCR, selected in the following step so this preliminary calculation assumes a resistance of 2.2mΩ. If operating near the maximum fSW limited by the minimum off-time, the variation in resistance across temperature must be considered when using Equation 10. The selected fSW of 800kHz is below the two calculated maximum values.
Equation 10. f S W m a x = V I N m i n - V O U T - I O U T m a x × R D C R + R D S O N _ H S t O F F _ M I N m a x × V I N m i n - I O U T m a x × R D S O N _ H S - R D S O N _ L S
Equation 11. f S W m a x = 4.5   V - 3.3   V - 25   A × 2.2   m Ω + 5.8   m Ω 150   n s × 4.5   V - 25   A × 5.8   m Ω - 2.3   m Ω = 1510   k H z