SLUAAY2 December   2024 ISO5451 , ISO5451-Q1 , ISO5452 , ISO5452-Q1 , ISO5851 , ISO5851-Q1 , ISO5852S , ISO5852S-EP , ISO5852S-Q1 , UCC21710 , UCC21710-Q1 , UCC21717-Q1 , UCC21732 , UCC21732-Q1 , UCC21736-Q1 , UCC21737-Q1 , UCC21738-Q1 , UCC21739-Q1 , UCC21750 , UCC21750-Q1 , UCC21755-Q1 , UCC21756-Q1 , UCC21759-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
  5. 2 SiC and IGBT Characteristics
  6. 3 Failure Modes
  7. 4 Short-Circuit Protection Approaches
    1. 4.1 Short-Circuit Current-Based Protection Implementation
    2. 4.2 Short Circuit Voltage-Based Protection Implementation
  8. 5 DESAT Circuitry Design
    1. 5.1 DESAT Circuit Component Selection
    2. 5.2 Effect of Parasitic Elements
    3. 5.3 Effect of Rlim on DESAT Noise
  9. 6 Safe Shutdown
    1. 6.1 Safe Shutdown Mechanisms
    2. 6.2 Safe Shutdown Considerations
  10. 7 Short-Circuit Test Setup and Data
    1. 7.1 Short-Circuit Bench Measurement Setup
    2. 7.2 SC Board Setup for Data Collection
    3. 7.3 Different Circuit Configurations for SC Testing
    4. 7.4 Bench Measurement Results
    5. 7.5 Overall Summary of SiC vs IGBT Power Module SC Observation
  11. 8 Key Consideration in Designing SC Protection Circuit
  12. 9 Summary
  13. 10References

5.2 Effect of Parasitic Elements

Besides the values of DESAT external circuitry (capacitance, resistance, forward voltage drop, and so forth), it is also important to pay attention to the parasitics introduced by the external circuitry and the effects. Two parasitic elements that can affect DESAT detection time are discussed here: the junction capacitance of the high-voltage diode and the parasitic capacitance on the DESAT node.

The junction capacitance of the high-voltage diode can affect DESAT detection time, because it can couple dV/dt from the drain/collector and causing current flow. When there is a negative dV/dt on the drain/collector, current is pulled from the DESAT pin; when there is a positive dV/dt on the drain/collector, current is injected into the DESAT pin. The delta current can either increase or decrease DESAT detection time.Figure 5-3 shows how larger high-voltage diode junction capacitance can result in larger DESAT pin voltage dip, resulting in longer blanking capacitor charging time.

UCC21750Q1 Junction Capacitance Simulation Result Figure 5-3 Junction Capacitance Simulation Result

Additional parasitic capacitance on the DESAT node can also affect DESAT detection time. These parasitic capacitance can come from either the clamping diodes on DESAT (Schottky diode and/or Zener diode) or the PCB trace capacitance. The clamping diode's junction capacitance is usually around 5pF, while the PCB trace parasitic capacitance varies by the system, usually in the 5pF-20pF range. Take the extra capacitance value into consideration when calculating DESAT blanking capacitor charge time.