SLVS974F September   2009  – May 2020 TPS54218

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency versus Output Current
  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 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  Slope Compensation and Output Current
      3. 7.3.3  Bootstrap Voltage (Boot) and Low Dropout Operation
      4. 7.3.4  Error Amplifier
      5. 7.3.5  Voltage Reference
      6. 7.3.6  Adjusting the Output Voltage
      7. 7.3.7  Enable and Adjusting Undervoltage Lockout
      8. 7.3.8  Soft-Start Pin
      9. 7.3.9  Sequencing
      10. 7.3.10 Constant Switching Frequency and Timing Resistor (RT/CLK Pin)
      11. 7.3.11 Overcurrent Protection
      12. 7.3.12 Frequency Shift
      13. 7.3.13 Reverse Overcurrent Protection
      14. 7.3.14 Synchronize Using the RT/CLK Pin
      15. 7.3.15 Power Good (PWRGD Pin)
      16. 7.3.16 Overvoltage Transient Protection
      17. 7.3.17 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Small Signal Model for Loop Response
      2. 7.4.2 Simple Small Signal Model for Peak Current Mode Control
      3. 7.4.3 Small Signal Model for Frequency Compensation
  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  Step One: Select the Switching Frequency
        2. 8.2.2.2  Step Two: Select the Output Inductor
        3. 8.2.2.3  Step Three: Choose the Output Capacitor
        4. 8.2.2.4  Step Four: Select the Input Capacitor
        5. 8.2.2.5  Step Five: Minimum Load DC COMP Voltage
        6. 8.2.2.6  Step Six: Choose the Soft-Start Capacitor
        7. 8.2.2.7  Step Seven: Select the Bootstrap Capacitor
        8. 8.2.2.8  Step Eight: Undervoltage Lockout Threshold
        9. 8.2.2.9  Step Nine: Select Output Voltage and Feedback Resistors
          1. 8.2.2.9.1 Output Voltage Limitations
        10. 8.2.2.10 Step 10: Select Loop Compensation Components
        11. 8.2.2.11 Power Dissipation Estimate
      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 Support 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

8.2.2.8 Step Eight: Undervoltage Lockout Threshold

The undervoltage lockout (UVLO) can be adjusted using an external voltage divider on the EN pin of the TPS54218. The UVLO has two thresholds, one for power up when the input voltage is rising, and one for power down or brown outs when the input voltage is falling. For the example design, the supply must turn on and start switching once the input voltage increases above 3.1 V (VSTART). Switching continues until the input voltage falls below 2.8 V (VSTOP).

The programmable UVLO and enable voltages are set using a resistor divider between the VIN pin and GND to the EN pin. Equation 32 and Equation 33 can be used to calculate the resistance values necessary. From Equation 32 and Equation 33, a 48.7-kΩ resistor between the VIN pin and the EN pin and a 32.4-kΩ resistor between the EN pin and GND are required to produce the 3.1-V start voltage and the 2.8-V stop voltage.

Equation 32. TPS54218 eq3a_r1_lvs946.gif
Equation 33. TPS54218 eq4a_r2_lvs946.gif