JAJSCB0E June   2016  – December 2021 UCC21520


  1. 特長
  2. アプリケーション
  3. 概要
  4. Revision History
  5. 概要 (続き)
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Power Ratings
    6. 7.6  Insulation Specifications
    7. 7.7  Safety-Related Certifications
    8. 7.8  Safety-Limiting Values
    9. 7.9  Electrical Characteristics
    10. 7.10 Switching Characteristics
    11. 7.11 Insulation Characteristics Curves
    12. 7.12 Typical Characteristics
  8. Parameter Measurement Information
    1. 8.1 Propagation Delay and Pulse Width Distortion
    2. 8.2 Rising and Falling Time
    3. 8.3 Input and Disable Response Time
    4. 8.4 Programable Dead Time
    5. 8.5 Power-up UVLO Delay to OUTPUT
    6. 8.6 CMTI Testing
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 VDD, VCCI, and Undervoltage Lock Out (UVLO)
      2. 9.3.2 Input and Output Logic Table
      3. 9.3.3 Input Stage
      4. 9.3.4 Output Stage
      5. 9.3.5 Diode Structure in the UCC21520 and the UCC21520A
    4. 9.4 Device Functional Modes
      1. 9.4.1 Disable Pin
      2. 9.4.2 Programmable Dead-Time (DT) Pin
        1. Tying the DT Pin to VCC
        2. DT Pin Connected to a Programming Resistor between DT and GND Pins
        3. 41
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. Designing INA/INB Input Filter
        2. Select External Bootstrap Diode and its Series Resistor
        3. Gate Driver Output Resistor
        4. Gate to Source Resistor Selection
        5. Estimate Gate Driver Power Loss
        6. Estimating Junction Temperature
        7. Selecting VCCI, VDDA/B Capacitor
          1. Selecting a VCCI Capacitor
          2. Selecting a VDDA (Bootstrap) Capacitor
          3. Select a VDDB Capacitor
        8. Dead Time Setting Guidelines
        9. Application Circuits with Output Stage Negative Bias
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Third-Party Products Disclaimer
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Certifications
    4. 13.4 Receiving Notification of Documentation Updates
    5. 13.5 サポート・リソース
    6. 13.6 Trademarks
    7. 13.7 Electrostatic Discharge Caution
    8. 13.8 Glossary
  14. 14Mechanical, Packaging, and Orderable Information



Select External Bootstrap Diode and its Series Resistor

The bootstrap capacitor is charged by VDD through an external bootstrap diode every cycle when the low side transistor turns on. Charging the capacitor involves high-peak currents, and therefore transient power dissipation in the bootstrap diode may be significant. Conduction loss also depends on the diode’s forward voltage drop. Both the diode conduction losses and reverse recovery losses contribute to the total losses in the gate driver circuit.

When selecting external bootstrap diodes, it is recommended that one chose high voltage, fast recovery diodes or SiC Schottky diodes with a low forward voltage drop and low junction capacitance in order to minimize the loss introduced by reverse recovery and related grounding noise bouncing. In the example, the DC-link voltage is 800 VDC. The voltage rating of the bootstrap diode should be higher than the DC-link voltage with a good margin. Therefore, a 1200-V SiC diode, C4D02120E, is chosen in this example.

When designing a bootstrap supply, it is recommended to use a bootstrap resistor, RBOOT. A bootstrap resistor, is also used to reduce the inrush current in DBOOT and limit the ramp up slew rate of voltage of VDDA-VSSA during each switching cycle.

Failure to limit the voltage to VDDx-VSSx to less than the Absolute Maximum Ratings of the FET and UCC21520 may result in permanent damage to the device in certain cases.

The recommended value for RBOOT is between 1 Ω and 20 Ω depending on the diode used. In the example, a current limiting resistor of 2.2 Ω is selected to limit the inrush current of bootstrap diode. The estimated worst case peak current through DBoot is,

Equation 2. GUID-917CD78A-21D8-47DE-B51B-24E4A2C05F49-low.gif


  • VBDF is the estimated bootstrap diode forward voltage drop at 8 A.