SLUSEX2A September   2025  – September 2025 UCC27734 , UCC27735

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 Enable Function (UCC277x5 Only)
      3. 6.3.3 Undervoltage Lockout (UVLO)
      4. 6.3.4 Level Shifter
      5. 6.3.5 Output Stage
      6. 6.3.6 Low Propagation Delays and Tightly Matched Outputs
      7. 6.3.7 HS Node dV/dt
      8. 6.3.8 Split Grounds (COM and VSS)
      9. 6.3.9 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 RHO/RLO
        6. 7.2.2.6 Selecting Bootstrap Diode
        7. 7.2.2.7 Estimate the UCC2773x Power Losses
        8. 7.2.2.8 Application Example Schematic Note
      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. 8.1.2 Development Support
    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

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7.2.2.4 Selecting Bootstrap Resistor (RBOOT)

The optional resistor RBOOT is selected to limit the current in DBOOT and limit the ramp up slew rate of voltage of VHB–HS.  For this design, we selected a current limiting resistor of 2.2Ω.  The bootstrap diode current (IBOOT(pk)) was limited to roughly 6.5A.

Equation 10. R B O O T = 2.2   Ω
Equation 11. I B O O T p k =   V D D - V B O O T R B O O T =   15   V - 0.6   V 2.2   Ω   ≈ 6.5   A

The power dissipation capability of the bootstrap resistor is important. The bootstrap resistor must be able to withstand the short period of high power dissipation during the initial charging sequence of the bootstrap capacitor. This energy is equivalent to 1/2 × CBOOT × V2. This energy is dissipated during the charging time of the bootstrap capacitor (~3 × RBOOT × CBOOT). Special attention must be paid to use a larger size RBOOT when a larger value of CBOOT is chosen.