SLVSB14B October  2011  – February 2016 TPS54821


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1Absolute Maximum Ratings
    2. 6.2ESD Ratings
    3. 6.3Recommended Operating Conditions
    4. 6.4Thermal Information
    5. 6.5Electrical Characteristics
    6. 6.6Typical Characteristics
  7. Detailed Description
    1. 7.1Overview
    2. 7.2Functional Block Diagram
    3. 7.3Feature Description
      1. 7.3.1Fixed Frequency PWM Control
      2. 7.3.2Continuous Current Mode Operation (CCM)
      3. 7.3.3VIN and Power VIN Pins (VIN and PVIN)
      4. 7.3.4Voltage Reference
      5. 7.3.5Adjusting the Output Voltage
      6. 7.3.6Safe Start-up into Pre-Biased Outputs
      7. 7.3.7Error Amplifier
      8. 7.3.8Slope Compensation
    4. 7.4Device Functional Modes
      1. 7.4.1 Enable and Adjusting Undervoltage Lockout
      2. 7.4.2 Adjustable Switching Frequency and Synchronization (RT/CLK)
      3. 7.4.3 Adjustable Switching Frequency (RT Mode)
      4. 7.4.4 Synchronization (CLK mode)
      5. 7.4.5 Slow Start (SS/TR)
      6. 7.4.6 Power Good (PWRGD)
      7. 7.4.7 Bootstrap Voltage (BOOT) and Low Dropout Operation
      8. 7.4.8 Sequencing (SS/TR)
      9. 7.4.9 Output Overvoltage Protection (OVP)
      10. 7.4.10Overcurrent Protection
      11. 7.4.11Thermal Shutdown
      12. 7.4.12Small Signal Model for Loop Response
      13. 7.4.13Simple Small Signal Model for Peak Current Mode Control
      14. 7.4.14Small Signal Model for Frequency Compensation
  8. Application and Implementation
    1. 8.1Application Information
    2. 8.2Typical Application
      1. 8.2.1Design Parameters
      2. 8.2.2Design Guide - Step-By-Step Design Procedure
        1. Typical Application Schematic
        2. Operating Frequency
        3. Output Inductor Selection
        4. Output Capacitor Selection
        5. Input Capacitor Selection
        6. Slow Start Capacitor Selection
        7. Bootstrap Capacitor Selection
        8. Under Voltage Lockout Set Point
        9. Output Voltage Feedback Resistor Selection
          1. Output Voltage
        10. Component Selection
        11. Transient Considerations
      3. 8.2.3Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1PCB Layout Guidelines
    2. 10.2Layout Example
      1. 10.2.1Estimated Circuit Area
  11. 11Device and Documentation Support
    1. 11.1Trademarks
    2. 11.2Electrostatic Discharge Caution
    3. 11.3Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Orderable Information

1 Features

  • Integrated 26 mΩ / 19 mΩ MOSFETs
  • Split Power Rail: 1.6 V to 17 V on PVIN
  • 200 kHz to 1.6 MHz Switching Frequency
  • Synchronizes to External Clock
  • 0.6V ±1% Voltage Reference Over Temperature
  • Low 2 µA Shutdown Quiescent Current
  • Monotonic Start-Up into Pre-biased Outputs
  • Adjustable Slow Start/Power Sequencing
  • Power Good Output Monitor for Undervoltage and Overvoltage
  • Adjustable Input Undervoltage Lockout
  • Software Tools Available

2 Applications

  • Digital TV Power Supplies
  • Set Top Boxes
  • Blu-ray DVDs
  • Home Terminals
  • High Performance Point of Load Regulation

3 Description

The TPS54821 in thermally enhanced 3.5 mm x 3.5 mm QFN package is a full featured 17 V, 8 A synchronous step down converter which is optimized for small designs through high efficiency and integrating the high-side and low-side MOSFETs. Further space savings are achieved through current mode control, which reduces component count, and by selecting a high switching frequency, reducing the inductor's footprint.

The output voltage startup ramp is controlled by the SS/TR pin which allows operation as either a stand alone power supply or in tracking situations. Power sequencing is also possible by correctly configuring the enable and the open drain power good pins.

Cycle by cycle current limiting on the high-side FET protects the device in overload situations and is enhanced by a low-side sourcing current limit which prevents current runaway. There is also a low-side sinking current limit which turns off the low-side MOSFET to prevent excessive reverse current. Hiccup protection will be triggered if the overcurrent condition has persisted for longer than the preset time. Thermal hiccup protection disables the device when the die temperature exceeds the thermal shutdown temperature and enables the part again after the built-in thermal shutdown hiccup time.

Device Information(1)

TPS54821VQFN (14)3.50 mm x 3.50 mm
  1. For all available packages, see the orderable addendum at the end of the datasheet.

Simplified Schematic

TPS54821 sim_sch_fp_lvsb14.gif

Efficiency, VOUT = 3.3 V, FSW = 480 kHz

TPS54821 eff1_slvsb14.png