JAJU732C June   2019  – July 2022

 

  1.   概要
  2.   Resources
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1. 1.1 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1  UCC21530
      2. 2.2.2  AMC1311
      3. 2.2.3  AMC3302
      4. 2.2.4  AMC3306M05
      5. 2.2.5  LM76003
      6. 2.2.6  LMZ31707
      7. 2.2.7  OPA320
      8. 2.2.8  ISO7721
      9. 2.2.9  SN6501
      10. 2.2.10 SN6505B
      11. 2.2.11 TMP235
      12. 2.2.12 LMT87
      13. 2.2.13 TL431
      14. 2.2.14 LMV762
      15. 2.2.15 TMS320F280049 C2000 MCU
      16. 2.2.16 TMDSCNCD280049C
    3. 2.3 System Design Theory
      1. 2.3.1 Dual Active Bridge Analogy With Power Systems
      2. 2.3.2 Dual-Active Bridge - Switching Sequence
      3. 2.3.3 Dual-Active Bridge - Zero Voltage Switching (ZVS)
      4. 2.3.4 Dual-Active Bridge - Design Considerations
        1. 2.3.4.1 Leakage Inductor
        2. 2.3.4.2 Effect of Inductance on Current
        3. 2.3.4.3 Phase Shift
        4. 2.3.4.4 Capacitor Selection
        5. 2.3.4.5 Soft Switching Range
        6. 2.3.4.6 Switching Frequency
        7. 2.3.4.7 Transformer Selection
        8. 2.3.4.8 SiC MOSFET Selection
      5. 2.3.5 Loss Analysis
        1. 2.3.5.1 Design Equations
        2. 2.3.5.2 SiC MOSFET and Diode Losses
        3. 2.3.5.3 Transformer Losses
        4. 2.3.5.4 Inductor Losses
        5. 2.3.5.5 Gate Driver Losses
        6. 2.3.5.6 Efficiency
        7. 2.3.5.7 Thermal Considerations
  8. 3Circuit Description
    1. 3.1 Power Stage
    2. 3.2 DC Voltage Sensing
      1. 3.2.1 Primary DC Voltage Sensing
      2. 3.2.2 Secondary DC Voltage Sensing
    3. 3.3 Current Sensing
    4. 3.4 Power Architecture
      1. 3.4.1 Auxiliary Power Supply
      2. 3.4.2 Isolated Power Supply for Sense Circuits
    5. 3.5 Gate Driver
      1. 3.5.1 Gate Driver Circuit
      2. 3.5.2 Gate Driver Bias Power Supply
      3. 3.5.3 Gate Driver Discrete Circuits - Short-Circuit Detection and Two Level Turn Off
  9. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Required Hardware and Software
      1. 4.1.1 Hardware
      2. 4.1.2 Software
        1. 4.1.2.1 Getting Started With Software
        2. 4.1.2.2 Pin Configuration
        3. 4.1.2.3 PWM Configuration
        4. 4.1.2.4 High-Resolution Phase Shift Configuration
        5. 4.1.2.5 ADC Configuration
        6. 4.1.2.6 ISR Structure
    2. 4.2 Test Setup
    3. 4.3 PowerSUITE GUI
    4. 4.4 LABs
      1. 4.4.1 Lab 1
      2. 4.4.2 Lab 2
      3. 4.4.3 Lab 3
      4. 4.4.4 Lab 4
      5. 4.4.5 Lab 5
    5. 4.5 Test Results
      1. 4.5.1 Open-Loop Performance
      2. 4.5.2 Closed-Loop Performance
  10. 5Design Files
    1. 5.1 Schematics
    2. 5.2 Bill of Materials
    3. 5.3 PCB Layout Recommendations
      1. 5.3.1 Layout Prints
    4. 5.4 Altium Project
    5. 5.5 Gerber Files
    6. 5.6 Assembly Drawings
  11. 6Related Documentation
    1. 6.1 Trademarks
  12. 7Terminology
  13. 8About the Author
  14. 9Revision History

3.5.3 Gate Driver Discrete Circuits - Short-Circuit Detection and Two Level Turn Off

SiC MOSFETs work in the linear region during normal operation. Unlike IGBTs, which have a sharp transition from saturation to active region, SiC MOSFETs have a large linear region and do not have a sharp saturation behavior under conditions with excessive currents. The transition to saturation region happens at significantly high drain source voltage (Vds) and the drain current (Id) reaches significantly high value, which can be as high as 15 times the normal current and can blow out the device. A DESAT detection circuit is necessary to detect this condition and protect the SiC MOSFET.

Figure 3-16 shows the circuitry for detecting short circuits. The diode, D11, interacts with the high-voltage drain pin of the MOSFET. At the start of the short circuit, the current flowing in the MOSFET channel increases dramatically until saturation, and the voltage from drain-to-source also increases and can reach up to the DC bus voltage. The voltage built up across C48 is compared with a voltage reference (3 V) set by the shunt regulator TL431 using the LMV762, which triggers the protection stage to shut down gate driver IC. See the Automotive Dual Channel SiC MOSFET Gate Driver Reference Design with Two Level Turn-off Protection for details on working with this circuit.

GUID-0E805E6D-7DB5-4581-8D9E-1FD77DD9C00F-low.gifFigure 3-16 Short-Circuit Detection of SiC

In the event the SiC experiences a short circuit, it is detected and turned off. During the turn off process, the voltage overshoot can exceed the breakdown down voltage of the device and can destroy the switch completely. To avoid this, a two-level turn off process is initiated where the SiC MOSFET, instead of completely turning off in one shot, is made to turn off at two levels. This helps in preventing overshoot across the switch and keeps it within the safe operating area. Figure 3-16 shows the circuit for the two-level turn off process where a dual comparator, LMV762 (U12A and U12B), is used to initiate turn off by discharging the capacitors of the gate at two voltage levels. The capacitor C41 and R36 form an RC circuit which discharges the gate to a lower voltage level during turn off. The resistor R46 and C46 are used to set the delay time between the turn off transitions.