SLUSE20B March   2020  – April 2022 UCC27284

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History B
  5. 5 Pin Configuration and 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 Switching Characteristics
    7. 6.7 Timing Diagrams
    8. 6.8 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 Enable
      2. 7.3.2 Start-Up and UVLO
      3. 7.3.3 Input Stage
      4. 7.3.4 Level Shifter
      5. 7.3.5 Output Stage
      6. 7.3.6 Negative Voltage Transients
    4. 7.4 Device Functional Modes
  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 Select Bootstrap and VDD Capacitor
        2. 8.2.2.2 Estimate Driver Power Losses
        3. 8.2.2.3 Selecting External Gate Resistor
        4. 8.2.2.4 Delays and Pulse Width
        5. 8.2.2.5 External Bootstrap Diode
        6. 8.2.2.6 VDD and Input Filter
        7. 8.2.2.7 Transient Protection
      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 Third-Party Products Disclaimer
    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

8.2.2.5 External Bootstrap Diode

The UCC27284 incorporates the bootstrap diode necessary to generate the high-side bias for HO to work satisfactorily. The characteristics of this diode are important to achieve efficient, reliable operation. The characteristics to consider are forward voltage drop and dynamic resistance. Generally, low forward voltage drop diodes are preferred for low power loss during charging of the bootstrap capacitor. The device has a boot diode forward voltage drop rated at 0.85 V and dynamic resistance of 1.5 Ω for reliable charge transfer to the bootstrap capacitor. The dynamic characteristics to consider are diode recovery time and stored charge. Diode recovery times that are specified without operating conditions, can be misleading. Diode recovery times at no forward current (IF) can be noticeably less than with forward current applied. The UCC27284 boot diode recovery is specified as 50 ns at IF = 20 mA, IREV = 0.5 A. Dynamic impedance of UCC27284 bootstrap diode naturally limits the peak forward current and prevents any damage if repetitive peak forward current pulses exist in the system for most applications.

In applications where switching frequencies are very high, for example in excess of 1 MHz, and the low-side minimum pulse widths are very small, the diode peak forward current could be very high and peak reverse current could also be very high, specifically if high bootstrap capacitor value has been chosen. In such applications it might be advisable to use external Schottkey diode as bootstrap diode. It is safe to at least make a provision for such diode on the board if possible.