SLUSF25A September   2025  – November 2025 UCC27834 , UCC27884

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 Dynamic Electrical Characteristics
    7. 5.7 Timing Diagrams
    8. 5.8 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 Input Stages and Interlock
      2. 6.3.2 Undervoltage Lockout (UVLO)
      3. 6.3.3 Level Shifter
      4. 6.3.4 Output Stage
      5. 6.3.5 Low Propagation Delays and Tightly Matched Outputs
      6. 6.3.6 HS Node dV/dt
      7. 6.3.7 Operation Under Negative HS Voltage Condition
    4. 6.4 Device Functional Modes
      1. 6.4.1 Input and Output Logic Table
      2. 6.4.2 Operation Under 100% Duty Cycle Condition
  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 Selecting HI and LI Low Pass Filter Components (RHI, RLI, CHI, CLI)
        2. 7.2.2.2 Selecting Bootstrap Capacitor (CBOOT)
        3. 7.2.2.3 Selecting VDD Bypass Capacitor (CVDD)
        4. 7.2.2.4 Selecting Bootstrap Resistor (RBOOT)
        5. 7.2.2.5 Selecting Gate Resistor RON/ROFF
        6. 7.2.2.6 Selecting Bootstrap Diode
        7. 7.2.2.7 Estimate the UCC278X4 Power Losses
      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 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

7.2.2.2 Selecting Bootstrap Capacitor (CBOOT)

The bootstrap capacitor should be sized to have more than enough charge to drive the gate of FET Q1 high, without depleting the bootstrap capacitor more than 10%. A general rule is to size CBOOT to be at least 10 times; as large as the equivalent FET gate capacitance (Cgs).

Cg is calculated based on the voltage driving the high side FET gate (VQ1g) and the FET gate charge (Qg).  VQ1g is approximately the bias voltage supplied to VDD subtracted by the forward voltage drop of the bootstrap diode (VBOOT). In this design example, the estimated VQ1g was approximately 14.4V

Equation 1. V Q 1 g ≅   V D D   - V B O O T = 14.4   V

The FET used in this example had a specified Qg of 33nC. Based on Qg and VQ1g the calculated Cg was 2.3nF.

Equation 2. C g =   Q g V Q 1 g =   33   n C 14.4   V   ≅ 2.3   n F

Once Cg is estimated, CBOOT should be sized to be at least 10 times larger than Cg.

Equation 3. C B O O T ≥ 10   ×   C g ≥ 23   n F

For this design example a 100nF capacitor was chosen for the bootstrap capacitor.

Equation 4. C B O O T = 100   n F