SLVSEQ0A May   2019  – March 2020 TPS54A24

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
    1.     Simplified Schematic
  3. 3 Description
    1.     Efficiency (VIN = 12 V, fSW = 500 kHz)
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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 Timing Requirements
    7. 6.7 Switching Characteristics
    8. 6.8 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  Fixed Frequency PWM Control
      2. 7.3.2  Continuous Conduction Mode Operation (CCM)
      3. 7.3.3  VIN Pins and VIN UVLO
      4. 7.3.4  Voltage Reference and Adjusting the Output Voltage
      5. 7.3.5  Error Amplifier
      6. 7.3.6  Enable and Adjustable UVLO
      7. 7.3.7  Soft Start and Tracking
      8. 7.3.8  Safe Start-Up Into Prebiased Outputs
      9. 7.3.9  Power Good
      10. 7.3.10 Sequencing (SS/TRK)
      11. 7.3.11 Adjustable Switching Frequency (RT Mode)
      12. 7.3.12 Synchronization (CLK Mode)
      13. 7.3.13 Bootstrap Voltage and 100% Duty Cycle Operation (BOOT)
      14. 7.3.14 Output Overvoltage Protection (OVP)
      15. 7.3.15 Overcurrent Protection
        1. 7.3.15.1 High-Side MOSFET Overcurrent Protection
        2. 7.3.15.2 Low-Side MOSFET Overcurrent Protection
    4. 7.4 Device Functional Modes
  8. 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  Custom Design With WEBENCH® Tools
        2. 8.2.2.2  Switching Frequency
        3. 8.2.2.3  Output Inductor Selection
        4. 8.2.2.4  Output Capacitor
        5. 8.2.2.5  Input Capacitor
        6. 8.2.2.6  Output Voltage Resistors Selection
        7. 8.2.2.7  Soft-Start Capacitor Selection
        8. 8.2.2.8  Undervoltage Lockout Setpoint
        9. 8.2.2.9  Bootstrap Capacitor Selection
        10. 8.2.2.10 PGOOD Pullup Resistor
        11. 8.2.2.11 Compensation
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
        1. 11.1.1.1 Custom Design With WEBENCH® Tools
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.13 Bootstrap Voltage and 100% Duty Cycle Operation (BOOT)

The device provides an integrated bootstrap-voltage regulator. A small capacitor between the BOOT and SW pins provides the gate-drive voltage for the high-side MOSFET. The BOOT capacitor is refreshed when the low-side MOSFET is on. The recommended value of the BOOT capacitor is 0.1 μF. A ceramic capacitor with an X7R or X5R grade dielectric with a voltage rating of 10 V or higher is recommended for stable performance over temperature and voltage.

When operating with a low voltage difference from input to output, the high-side MOSFET of the device operate at 100% duty cycle as long as the BOOT to SW pin voltage is greater than 2.2 V. The device begins to transition to 100% duty cycle operation when the high-side MOSFET off-time is less than 200 ns typical. Equation 12 can be used to estimate the input voltage the switching frequency begins to decrease. When the switching frequency decreases the BOOT to SW capacitor is not recharged as often so the BOOT to SW voltage will start to decrease. If the voltage from BOOT to SW drops below 2.2 V, the high-side MOSFET is turned off due to BOOT UVLO and the low-side MOSFET pulls SW low to recharge the BOOT capacitor. When operating at 100% duty cycle the high-side MOSFET can remain on for many switching cycles before the MOSFET is turned off to refresh the capacitor because the gate drive current sourced by the BOOT capacitor is small. The effective switching frequency reduced and the effective maximum duty cycle of the switching regulator is near 100%. The output voltage of the converter during dropout is mainly influenced by the voltage drops across the power MOSFET, the inductor resistance, and the printed circuit board resistance.

Equation 12. TPS54A24 eq_minvin_100p_dutycycle_slvseq0-tps54A24.gif

where

  • RDS(LS) = low-side MOSFET RDS(on)
  • RDS(HS) = high-side MOSFET RDS(on)
  • RDCR = DC resistance of inductor
  • tOFF = off-time that 100% duty cycle operation begins