SLVAG18 April   2025 TPSI3100 , TPSI3100-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Why DESAT Protection Is Needed
    1. 1.1 Key Considerations for DESAT Protection
  5. 2Key DESAT Circuit Components
    1. 2.1 Circuit Startup Behavior
  6. 3Design Example
    1. 3.1 Design Requirements
    2. 3.2 Threshold Equations
    3. 3.3 Given Parameters
    4. 3.4 Inserting Given Parameters into Equations
    5. 3.5 Solving Equations for Unknowns
    6. 3.6 Selecting Resistances to Satisfy Equations
    7. 3.7 Determining Blanking Capacitance
    8. 3.8 Final Component Values
    9. 3.9 Lab Testing
  7. 4Closing

3.2 Threshold Equations

Selecting appropriate resistance values ensures that the blocking diode becomes forward biased while the IGBT is on, allowing proper voltage sensing.

  1. Condition for sensing voltage, allows the blocking diode to become forward biased when IGBT is on:
    Equation 1. V C E D E S A T + V F D I O D E < R D I V 1 + R D I V 2 R D I V 2 + R D I V 1 + R L I M × V D D H
  2. Overcurrent threshold equation, select the desired voltage threshold (VCE (DESAT)) to trip the comparator (VREF+):
Equation 2. V R E F + < R D I V 2 R D I V 2 + R D I V 1 × V C E ( D E S A T ) + V F ( D I O D E )

Using the example IGBT I-V curve from earlier, it looks like IC = 10 A at VCE = 7.5V. With this overcurrent threshold value, solve for the resistances. Please keep in mind that I-V curves are typical and devices may individually have variation.

DESAT Selection VCE Threshold Figure 3-1 DESAT Selection VCE Threshold